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Dry Cutting
Keynote Papers
Keynote Papers Presented at the Opening Session Dry Cutting F. Klocke (2). G. Eisenblatter RWTH Aachen, Germany
Abstract: The vast majority of machining operations exploit the good cooling and lubricating characteristics of cooling lubricants (CL). But, as costs for waste disposal increase, companies are now being forced to implement strategies in order to reduce the amount of CL used in their production lines. The most logical measure which can be taken to eliminate all of the problems associated with the use of CL is dry machining. In most cases, however, a machining operation without lubricant finds acceptance only when it is possible to guarantee that the part quality and machining times achieved in wet machining are equalled or surpassed. The introduction of dry machining techniques may also include the use of minimal quantities of.lubricant (MQL). The following paper deals with the most recent developments in dry cutting. Keywords: Machining, dry cutting, environmental impact
0 Acknowledgements
absenteeism due to sickness, transfers). These are frequently estimated to be very low.
The authors would like to acknowledge all who have contributed to this paper with suggestions, discussions and documents of their work. Special thanks are given to: Prof. Ber. Haifa; Prof. Brinksmeier, Bremen; Prof. Elbestawi, Hamilton; Prof. Inasaki, Yokohama-Shi; Prof. Pollmann, Stuttgart; Prof. Schulz, Darmstadt: Prof. Spur, Berlin; Prof. Spath, Karlsruhe; Prof. Tbnshoff, Hannover; Prof. van Lutterveld. Delft; Prof. Vigneau, Evry; Prof. Weinert, Dortmund 1 Introduction In the metal cutting industry, cooling lubricants (CL) are one of the most frequently used agents. They help to achieve a prescribed result in' terms of tool life, surface finish and accuracy-to-size, and make chip-breaking and chip-transport easier. Their use is nonetheless characterised by problems in the immediate working environment and in waste disposal. These problems result in a large number of ecological problems and in a climate of increasingly strict work safety and environmental legislation. This in turn means more economic problems for manufacturing companies [2, 14, 18, 23, 551. The ecological and economical significance of the cooling lubricants becomes clear with a glance at the figures for the amounts of CL consumed annually. The consumption of cooling lubricants in Germany in the year 1994 was approx. 75,491 tonnes [60] Based on the factory gate price, the lubricant has a value of over DM200 million (591. Of the total quantity of cooling lubricants used in 1994, 28,415 tonnes were water-miscible products. Mixed with water at a concentration of 3 - 8%, this would make a quan. tity of emulsion in the order of 355,000 to 947,000 tonnes. It is estimated that approx. 350,000 tonnes of used emulsion and oil-water mixtures as well as an unquantifiable amount of grinding slurry, filter fleece and filter process materials [38] have to be processed and disposed of. Surveys indicate that few companies have accurate information regarding the actual costs incurred as a result of the use of CL (investment, depreciation, CL procurement, monitoring, maintenance, personnel, health precautions,
Source: Federal Office for Economic Affairs, WZL Distribution of quantity of coolants used in Ger-
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Surveys carried out in the German automotive industry show that workpiece-related manufacturing costs incurred in connection with the deployment of cooling lubricant at levels are several times higher than tool costs, of 7 - 17% which account for approx. 2 to 4% [49, 56, 581.
(m)
Wakoiece-dated manuiituring cost
58% 0% 0% PWMnndW3l 6% Process matends 5% Cooliq tubncant 14% + addhnal cost Dispasal wit 1%
Equipment cost Repair cost ,Energy cost
(m).
Annals of the ClRP Vol. 46/2/7997
many (20,601
Central facilities mlh up to 200 m' emu!aiionfor transfer lines Manufacturng mth a h9h percentage of indexable tip inserts
Source: WZL Lubricant cost exemplified by central facility [20]
W2:
The wide range within which CL costs fall is due to varying boundary conditions. The level of workpiece-related CL costs depends to a decisive degree on the manufacturing operation, part, required part quality, CL drag and vaporisa-
519
tion, the lubricating medium involved, the type of machine, the CL supply, the size of the facility, the situation regarding the building, CL processing and disposal and other factors. It also emerges that it is frequently difficult to identify all cost factors comprehensively, with the required degree of accuracy. Some of the quantitative values requested can only be estimated or even guessed. A cost-percentage of 17% is certainly an extreme value, which arose in the concrete example quoted, from specific circumstances within the company [58]. Even if the CL costs differ widely, the example shows that there is an enormous potential for savings. Increasingly, these findings are motivating companies to seek clarity about their own CL costs and to analyse possible means of achieving savings. This paper will give a review of today's dry machining technology. It was necessary to concentrate the paper only on the classical machining processes like turning, milling and drilling. It will consider the most commonly used mechanical engineering materials; i.e. steel, cast iron and also aluminium alloys as workpiece materials.
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Dry Cutting Ranges of application in industry
The two following examples of dry cutting show the wide range of possible applications in industry. The complete machining on machining centres of cast iron parts in small batch manufacturing at a German print machine producer is an impressive example of the long-term viability of dry machining The condition which had to be met prior to a switch to manufacturing in dry machining mode was that dry cutting operations should achieve at least the same cutting times, tool life times and part quality as in wet cutting operations. Cast materials in general and, more specifically in this case, grey cast iron, are particularly well-suited for dry machining, by virtue of the short chips, low cutting temperatures and forces as well as the lubricating effect of the embedded graphite. Nevertheless it quickly became apparent that, under the required boundary conditions, it was not going to be possible to switch'easily from wet to dry machining operations, even on cast materials. This applies increasingly, the more dependent the tools are on the cooling or lubricating effect of the fluid and the higher the degree to which their capacity is exploited in wet cutting operations. Tools for drilling, reaming and tapping operations must be regarded as particularly critical in this respect.
fluid. In the past, machining had been carried out on a transfer line with an indexable-insert drilling tool and a 10 percent oil-water-emulsion, which was externally supplied. Investigations have shown that purely dry machining is not possible due to the high tendency of the aluminium material to adhere to the tool. It was found that even minimum quantities of cutting fluid, which are fed towards the contact zone internally via the tool, suffice to achieve a drilling operation that meets the stipulated quality characteristics. For technical reasons, internal lubricant supply could not be realised in all cases, so there are applications where external feeding can also achieve good results. One example is a transfer line where two compressed air nozzles were affixed to the machine spindle to blow the lubricant out of the bore hole at the preceding station. While it is not possible to quantify the residual lubricant remaining in the bore hole, this may still be described as machining with a minimised lubricant supply. These newly created conditions enabled tool life to be increased by more than a factor of 4 compared to the previous mode of machining, to achieve more than 330,000 drilling operations. Fin.,for example, shows the measured values for diameter D, which is an important parameter for assessment of a production process. The ISF monitored a new precision tool using MQL from the first up to approx. 180,000 drilling operations. This examination was interrupted by a period in which the diameter was measured by statistical process control (SPC) carried out by the automobile manufacturer.
(m).
Source: Heidelberger Druckrnaschinen, WZL Complete machining of bearing plates in machining centres.studiedfor dry machining [20]
m:
Wherever 100% dry machining cannot be realised for technological reasons, minimal quantities of lubricant (MQL) may provide an alternative to wet cutting. The Department of Machining Technology, University of Dortmund (ISF), investigated the optimisation of drilling tools for machining with MQL in the automotive industry [57]. Investigations were carried out at the plant of a manufacturer of automobile gearboxes of die-cast aluminium (GDAISi9Cu3) to determine the extent to which it is possible to machine a dowel pin hole ( 0 1 1.9 H8) without using cutting 520
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Source: ISF Diameter values when drilling dowel pin holes with minimised lubricant supply
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Developments in dry cutting
3.1 Fundamentals of dry cutting Before reviewing developments in dry cutting, an examination of the fundamentals of the technological aspects should be made. The main functions of CL are to reduce heat generation by reducing friction and to eliminate the exertion of unacceptable influences on the structure of the subsurface layer of the workpiece by absorbing and removing heat from the cutting area. In cutting operations, CL also have an important transport function for the chips which have to be removed. Thus efficient lubrication systems enable to high performance operations in practice. CL functions are not available in dry machining operations. This means that there is more friction and adhesion between tool and workpiece. Tools and workpieces are subjected to greater thermal load (Fin.). This may result in higher levels of tool wear, e.g. in increased crater formation when steel materials are machined using uncoated carbides. However, dry cutting may also show positive effects such as a reduction in thermal shock and thus in the formation of comb-cracks when parts are machined in interrupted mode with carbides or cermets [26]. Higher machining temperatures influence chip formation. This may result in both ribbon chips and snarl chips. When reliable control over chip formation is required, it may be necessary to use cutting inserts with especially adapted chip shaping grooves towards dry cutting. In drilling operations, high chip temperatures can hamper chip removal from
Keynote Papers the bore-hole and, in extreme cases, result in blockage of the flute and ultimately in tool failure. Higher part temperatures in dry cutting may affect form and dimensional accuracy and subsurface structure (19, 351.
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- Tool: HC-P TiN-cDaM W 11.8mrn f = 0.2 mm
Source: WZL Temperatures in wet and dry drilling
Fin.:
It is a well known fact that the cutting speed is directly related to the temperature in the cutting zone [3, 4, 441. shows experimental results of flank wear versus cutting speed. Four tool grades were tested in dry cutting of steel AlSl 1045 (3, 41. Cutting time was 4 minutes and the range of cutting speed was from 6mlmin to 6lOm/min.'The curve shape of the flank wear with the increase of the cutting speed is shown in Fig. 6. Investigations [31] suggest that the dominant mechanism of flank wear at low speeds is of the abrasive type, and when speed increases this is replaced by adhesion. At higher speeds diffusion becomes the dominant wear mechanism. Based on the results described there, it can be assumed that a decrease in temperature at higher speeds will give lower flank wear.
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3
6
10
20 30
60 100
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2 M ) x M Wmin 1WO
this creates a cold junction and a hot junction at opposite ends of each of these elements. Based upon the above it may be concluded that dry cutting, associated with indirect cooling at relatively high speeds, reduces wear and extends tool life, if cooling is applied at cutting speeds where the diffusion wear mechanism IS dominant. To suit the specific requirements of a dry machining process, different influencing variables have to be taken into account. The tool has to be optimised with respect to substrate, geometry and coating. Suitable cutting materials are an essential must in order to implement dry machining operations. The high temperature hardness and wear resistance of cemented carbides, cermets, ceramics, CBN and PCD based cutting materials make these materials eminently suitable for use in dry cutting operations. There is general consensus that, in addition to the geometrical modifications required, it is necessary to use tool coatings in the development of tools for dry machining. The coating reduces friction and adhesion by virtue of the effect as a "solid lubricant", and thermal load on the substrate is diminished by the lower heat penetration capacity [16]. The reduced level of heat dissipation via the tool changes the heat flow between the tool and the chip. Since the substrate absorbs less heat more heat must be dissipated via the chip. In order to reduce thermal stresses in dry machining operations, by lowering the friction in the contact zones of the tool, it is also worth considering the approach from the material development side. In free cutting of steels and cast iron, it is well established that the machinability can be improved by utilising the effect of non-metallic inclusions, smearing out at the chipltool-interface and thus protecting the tool from wear. Ca-treatment of aluminiumdeoxidised steels is a possible way of extending comparable machinability improvements to a huge variety of engineering steel grades. Ca-treatment generally leads to a conversion of highly abrasive alumina inclusions (Al2O3) into more ductile Ca-aluminates. But the main contribution of Catreated steels to improvement of machinability is attributable to the formation of lubricating, wear-reducing layers in the contact zones of the tools (1, 11, 13, 361. This decreases the friction and the corresponding temperatures generated in the contact zones. These materials are thus highly suitable for dry machining operations. FW.7 shows the improved machining characteristics of a Ca-treated, quenched and tempered steel grade 38MnSiVS5, for dry turning with Ti(C,N)/AI,O,/liN-coated cemented carbide inserts (HCP15). The formation of wear-reducing layers, whose main constituents were determined by EDX-analysis as Al, S and Ca, increased tool life in this case by more than 400%.
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Source: CMSR Flank wear vs. cutting speed in dry cutting with different tool grades
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The requirement for lower temperature in the cutting process without using direct CL gave investigators the idea of cutting dry and at the same time cooling the cutting zone. The following methods were suggested: (i) Under Cooling System [5] where the coolant flows through channels located under the insert, then out to the environment, without any direct contact with the cutting zone. (ii) Internal Cooling by Vaporization System [15] where a vaporizable liquid, such as water, is introduced inside the shank of the tool and vaporized on the underside surface of the insert. (iii) Cryogenic Systems [8] where a stream of a cryogenic coolant, such as nitrogen, is routed internally through a conduit inside the tool. (iv) Thermoelectric Cooling Systems [33], using a module of couples of thermoelectric material elements. When an electric current is passed through the thermoelectric elements,
Source: W Z L Calcium treatment of steel improves material characteristics for dry cutting
Fin.:
Where completely dry machining is not possible, the potentials of minimal quantities of lubricant (MQL) become particularly important for minimising CL. The term "minimal
521
quantities of lubricant" is used when tiny quantities of a cooling lubricant are fed to the cutting process. When the machine is adjusted to the optimum, less than 50ml of the medium is consumed per process hour. The main benefit of the MQL technique is that, if it is correctly applied, tools, workpieces and chips remain dry, thus obviating any need for processing or finishing. So this technique may justifiably be described as "dry machining". There are a number of materiallprocess combinations which are not economically viable without MQL. This currently applies particularly to drilling, reaming and tapping in cast iron, steel and aluminium alloys, and also to end-milling operations undertaken on Al-alloys and to deep-hole drilling [6, 12. 18, 30, 41, 571. Beside these applications it was found that, for turning steel, the use of MQL reduces the friction coefficient and the cutting temperature in orthogonal cutting compared with dry cutting and conventional fluid supply. MQL has always given the best surface roughness results in turning the constructional steel SNCM439. Tight dimensional and form tolerances may present a significant restriction for dry machining and call for special countermeasures.A dry cutting process must be designed to minimise the amount of heat flowing into the part. This may be achieved by minimising the cutting forces, and also by influencing the heat distribution. Cutting forces can be reduced by positive cutting edge geometries, while heat distribution towards the part may be positively influenced by using high cutting speeds. As these examples show, the introduction of dry machining necessitates measures suitable to compensate for the primary functions of the lubricant. This, in turn, calls for a very detailed analysis of the boundary conditions and for thorough understanding of the complex interrelationshipswhich link the process, tool, part and machine tool
highest thermal conductivity of all cutting materials investigated. It is 3 to 4 times higher than that of silicon nitride and alumina. When there is high thermal load in the cutting edge engagement zone, the heat created may be removed efficiently from the cutting material by the use of CBN. In summary, the conclusion that may be drawn from the characteristic quantities of the materials is that CBN is highly suitable for dry machining of cast iron with high cutting speeds. It is evident from the manufacturing tolerances and also from the surface qualities attained, that the best results are This is different for wobble f, obtained with CBN and parallelism f,; For these two explicitly mentioned tolerances, the best results were reached with silicon nitride ceramics. The specified tolerance was exceeded in the application of alumina ceramics for only one characteristic quantity, namely the wobble fb This means that the predefined manufacturing tolerances and surface qualities can be maintained in dry machining of grey cast iron at high cutting speeds, both with the non-oxide ceramic cutting material silicon nitride Si,N, and with CBN 1471. The latter gave the best results in terms of wear behaviour. These results are congruent with those obtained by SPUR [46] and KUEMMEL [25] and in the investigat.ions conducted by SCHUELLER, DREWS et al. [29, 391.
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Mean values of roughness R, and manufacturing tolerances in turning of laminar cast iron with various cutting materials [47]
3.3 Dry machining of steel
Source: W Z L Variables which influence dry machining [20]
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3.2 Dry machining of cast iron workpieces Cast iron materials can mostly be cut dry in turning and milling operations. Cast iron materials are particularly favourable in this respect, because their cutting temperatures are significantly lower than those of steel [47]. Dry machining of laminar grey cast iron at high cutting speeds using ceramic cutting materials and cubic boron nitride (CBN) has been carried out at the Institute for Machine Tools and Factory Management (IWF), Technical University Berlin 1471. Besides other widely differing properties of ceramics (AI2O3, Si,N,) and CBN, in terms of thermal characteristics, alumina has the highest expansion coefficient, followed by CBN; this can be a particular disadvantage for the maintenance of accurate part dimensions at high cutting speeds and consequently high cutting temperatures. Additionally CBN has the 522
Drilling takes a key position in the realisation of dry machining on machining centres. The main problem in dry drilling in steel is reliable removal of the chips from the drilled hole. The risk of a chip jam in the flute becomes steadily greater as the drilling depth increases and the friction paths between the chip and the hole wall or the tool become longer [17, 321. One very promising approach is to enlarge the flutes, giving the chips more spa& and helping them to escape, since there is less resistance to chip motion (Fia. '10). Another problem is the tendency of the drill to jam in the hole if its diameter expands too much as a result of high tool temperatures. One way of correcting this is more drill taper towards the shank. A TiN-coated tool with modified flute and tapering achieved a tool path of 65m in Ck45K tempering ,steel. The mean peak-to-valley height of R, < 15 20 pm was significantly below the permitted maximum of R, < 38pm. The hole diameters were some 0.02 0.03 mm larger than the nominal diameter of 11.8mm. By comparison. an H11 tolerance permits an allowance of 0.11 mm. As shown by this exam-
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Keynote Papers
ple, a dry cut can not only achieve high removal rates, but can also meet exacting part quality requirements.
Fiq. 10:
Dry drilling of tempering steel with carbide tools
Tool pretreatment is an important aspect for dry drilling [50]. In particular, coating adhesion depends on the surface structure of the substrate after the grinding operation. Increased adhesive forces in dry cutting processes as well as increased shearing loads in the substrate-coating may affect the coating. In wet machining, interface strength is sufficient, but in dry machining variations of interface strength may cause distinct differences in tool life. There is squeezing and smearing of Co-binder phase in grinding of WC-carbides, which causes a significant loss of material strength in subsurface layers of the substrate. Micro blasting of the ground WC-carbides changes the micro topography as well as the surface integrity of tools. Surface effects of micro blasting depend on blasting pressure and the grain size of the blasting material. If the grain size of the blasting material is bigger than the grain diameter of the carbide, this induces major plastic deformation of the subsurface of the tool; if the blasting material is smaller than the carbide grain size, this increases the abrasive effect of micro blasting [511. During dry drilling tests of tempered steel at the University of Hannover (IFW) with tools micro-blasted under adapted conditions, increased interface strength and superior wear behaviour of PVD-coated tools was observed. Interface failures after a few blind holes cause high wear rates of unblasted tools, because tool wear is determined by abrasive wear of the substrate. The higher interface strength of micro-blasted tools causes a distinct reduction in width of flank wear, and homogeneous tool wear of (Ti,AI)N-coated carbide.drills (Fiq. 11) [52].
Fia 11:
Investigations at the University of Bremen (IWT) included experiments which were performed as dry reaming operations, with minimum lubrication techniques and with internal cooling. This involved reaming hardened bearing steel 1OOCr6 with a tool which was equipped with guiding pads made of PCD and with cutting inserts containing CBN. Dry machining resulted in surface roughness of R, < 3pm and deviations in shape accuracy smaller than 9pm. The complete avoidance of cooling lubricants led to a transformation of the material's microstructurewithin the subsurface of the reamed bore (Fia. 12). The use of internal cooling made it possible to improve shape accuracy to within 5pm and to reduce transformation of the material [7].
Dry drilling of steel with microblastedtools
For fine machining cf bores in hardened materials, single edge reaming seems to have the potential to replace the cost-intensive operations of grinding and honing. Single edge reaming is a process which is characterised by its ability for self-guiding inside the bore. The reaming tool is designed like a boring bar equipped with a cutting insert and three guiding pads. The guiding pads support the tool inside the bore in order to avoid distortion of the tool from the workpiece [24].
Dry reaming of 1OOCr6 (GOHRC) [7] u: This investigations show that the reaming process can successfully be employed as a dry cutting operation and has the potential to be used as a substitute for grinding and honing in some fields.
3.4 HSC dry machining of superalloys and titanium Generally speaking, we consider that conventional cutting of superalloys and titanium with carbide tools requires water based coolant. High speed cutting (HSC) may be a possibility to switch from wet to dry cutting, but is more difficult to analyse: . For continuous HS-turning, any cutting tool ceramics for superalloys and carbide for titanium has to be cooled with a great flow of water-based coolant. It is advisable to use laser assistance without any coolant if possible, to achieve better results in terms of tool wear, but only fo'r machining superalloys with ceramic tools. In discontinuous HS-milling of the previous mentioned materials, a great flow of water based coolant induces thermal shocks on any cutting material. For this reason dry cutting is recommended. Even better results in terms of tool life can be achieved MQL. This effect depends on the length of the cut between two spray depositions (effect decreases when a, increases). HS-turning and milling of steel require dry cutting [22, '40, 48, 541. In conclusion, dry cutting is not efficient for conventional machining of superalloys and titanium alloys in most cases, but it may be efficient for HSC-milling, especially when no cutting assistance is available. Experiments at McMaster University, Hamilton showed that it was possible to obtain a surface finish of R, = 0.7bm in end milling of lnconel 718 at a feed of 0.2mm/tooth and cutting speeds in the range of 1,000 to 2,000 mlmin with a round insert. Chips were collected from the fly cutting tests, which were performed in dry condition on lnconel 718 material using Sic whisker reinforced ceramic tools. These exhibit the same pattern as those produced in hard turning. Chip segmentation was clearly visible for all cutting speeds ranging from 200 to 2,000 mlmin, feed rates ranging from 0.05 to 0.2 mmltooth, axial depth of cut from 0.25 to 2 mm, and immersion ratios between 0.25 and 1 [9, lo]. It is interesting
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to note that the type of chip produced was not dependent on use of dry or wet cutting [lo].
3.5 Dry machining of aluminium alloys Aluminium alloys are among the particularly critical materials with regard to dry machining. Workpieces absorb considerable heat from the machining process due to their high level of thermal conductivity. In conjunction with the high levels of thermal .expansion, this causes deformations. In view of the low melting and softening point, problems connected with chip formation are also related. Many aluminium alloys are susceptible to adhesion with the tool and to buildup in the chip space [21, 271. In order to carry out dry drilling, reaming, tapping and end-milling operations successfully on aluminium alloys, it is essential to use tools with suitable coating systems and to use MQL. The positive influence MQL on the state of the tool and on part quality is demonstrated very impressively in Fia 13.
feed force F,. The forces in turning with uncoated inserts are higher than the forces with PCD-coated inserts. Atomic-Force-Microscopy (AFM)-analysis gives information on the morphology, topography, porosity and roughness of layers. The AFM-photograph of the tool face of a PCDcoated insert shows a regular layer structure. The wear resistance of the PCD-coated insert is better than the wear resistance of the uncoated insert. The low friction coefficient of the PCD layer means that the coated inserts are suitable for dry cutting processes.
Source: lW Fig. 14: PCD-coated inserts in dry turning
Extensive experiments were made on AlZnMgCul.5 to study the influence of cutting speed, feed per tooth, cutting angle and clearance angle on flank build-up formation (37, 531 in dry milling at the Technical University of Darmstadt ( p ~[421. ) Polycrystalline diamond has only a minor tendency for flank build-up, so further studies were made into the influence of a diamond coating applied by the CVD process, and also of two diamond-like coatings (diamond-like carbon (DLC) and a metal carbon coating). The DLC coating a-C:H is an amorphous carbon layer; it substantially consists of carbon in graphitic, amorphous and crystalline form and of hydrogen. In another version, the metal hydrocarbon coat (WC/C) can also be provided with some tungsten content. This will give the coat greater toughness and lower hardness than aC:H (Hardness (Vickers) of a-C:H: 3,000-5,000, o f WCIC: 1,000). Both coatings have a low friction coefficient against steel (p = 0.1 0.2) and an anti-adhesive effect against many materials. With the uncoated tools, neither optimisation of cutting edge geometry nor variation of cutting'speed or feed per tooth can reduce the tendency for flank build-up sufficiently to allow dry machining in production. Conditions can be improved by MQL, using quantities of less than 40ml/h to lubricate the point of machining. . The influences of the various coatings and of MQL were studied for milling with a tool 16mm in diameter. Fig. 15 shows that in dry milling, both the .a-C:H coating and the diamond coating reduce flank build-up, whereas the WC/C coating gives no improvement as against the uncoated cemented carbide. In all, the coatings tested do not permit dry machining under production conditions of the material studied, as there will always be flank build-up formation. On the other hand, MQL gives a substantial reduction of flank build-up. Increasing volume flow from 10 ml/h to 40 mllh gives no further benefit, so the smaller volume flow is sufficient to suppress flank build-up almost completely [43]. Comparable investigations have been obtained at plants of an German aircraft manufacturer [34]. Different commercial coatings (onto identical HW-K10 cemented carbide substrates) were investigated for suitability to .reduce built-up edges and virtual chip formation in dry milling of the AlZnMgCu1,5 malleable alloy. A two-step test programme was performed for this purpose: an initial test with all the selected coatings and then a performance test with the best coatings from the initial test.
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Source: Daimler Benz, wbk, WZL Dry machining operations on aluminium workFig. 13: pieces require the use of MQL [20] In dry drilling operations conducted without MQL (Fig. 13, top) the tool was useless due to adhesion of material in the chip groove after only 16 drilling operations. With MQL, there was no evidence of wear or material adhesion to the tool after 128 drilling operations. The average peak-to-valley height for bore holes produced using MQL remained below R, = 20pm and thus, like the bore hole diameters, within the tolerances [18]. When grooves were end-milled dry into a wrought aluminium alloy, there was a strong tendency for material and chips to stick to tools and parts (Fig. 13, below). MQL operations, by contrast. showed no evidence of material or chip adhesion to the milled grooves. The endmilled grooves manufactured using the MQL technique. fulfilled the tolerances required in terms of dimensional accuracy, soft spot formation, surface roughness and waviness. The main field of industrial application of PCD-coated inserts is in dry cutting processes [6].Investigations were carried out at the University of Bremen (IW)to analyse the suitability of PCD-coated inserts by dry turning of the aluminium alloy AISil8CuMgNi. This work material is a hypereutectic alloy and especially the silicon has an abrasive effect on the tool flank during the turning process. Fig. 14 shows the values of the cutting force F, thrust force F, and
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A Cutting parameters:
20
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12 ig
10
$ 8
3 4 m 6 Feed path 1: uncoated. 2: &:H coated. 3: W C coated. 4: CMdiamond coated. 5: MQL (10 mVh), 6: MQL (40 mVh)
0
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Source: PTW Fiq. 15: Influence of coating and minimal lubrication in milling AlZnMgCuI .5[42. 431
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The results and the cutting conditions used for the initial tests are shown in Fiq. 16. The experiments were done in a single tooth climb-cut milling process on a horizontal machining centre. The cutting length was 420 mm. The WClC, a-C:H and diamond coatings showed practically no built-up edges at the rake face. They are classified as 'suitable coatings'. 'Unsuitable coatings' such as CrN, MoS,, TIN, (Ti,AI)N and the uncoated cemented carbide substrate yield great built-up edges at the rake face. It is probable that the transition elements (Cr, Mo, Ti) effect considerable chemical action and result in diffusion 'reactions with the elements of the machined workpiece material (Al, Zn, Mg, Cu). This causes built-up edges, which consist of these elements and ambient oxygen.
Source: Daimler Benz. wbk Fin. 16: Dry face milling ofAIZnMgCul.5 [34]
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6 8 1 0 1 2 Milling distance I,
m 1 6
Source: wbk Fin. 17: Results from dry face milling of cast aluminium alloy AISilOMg(wa) with HC-K10 A direct comparison of dry machining with the conventional CL-application (full flooding with 5% emulsion) shows that dry machining reduces the tool life distance by 35% for the uncoated cutting inserts (HW-KIO): Examinations of the cutting edge geometry have also shown that, on the uncoated tool, dry machining produces unacceptable built-up edges and there is an adverse effect on surface quality. A comparison of the variously coated tools with the uncoated tools shows'that there is a large potential scope for development in coating technology. There are two fundamental tendencies. On the one hand, in dry processing the "soft"coatings (tungsten carbidelcarbon (WCIC); chromium carbidelcarbon (CrClC)) score with distinctly less built-up edge formation, but these coatings do not achieve the low wear values of the conventional cooling lubricant application. On the other hand, in dry milling coated tools have considerable tool life advantages compared with uncoated tools with full flooding; this can be achieved by combining a hard material layer (e.g. titanium nitride (TiN)) with a "soft" top layer coating (e.g. molybdenum sulfide MoS,). The wear characteristics achieved by this multilayer coating increase tool life by up to 10% in dry processing compared with conventional CL-technology. Diamond-coated tools likewise show clear potential for dry machining. These layer .structures deposited by the CVDmethod do not produce any built-up edge, because there is little affinity between carbon and aluminium. The tool life values obtained with this coating increase the useful life of the tool for dry milling by about 30%. 4
Partly crystalline coatings (e.g. WClC) exhibit a lower tendency to form built-up edges, in spite of their metal content (e.g. tungsten). It is suggested that amorphous parts in the coating morphology have a positive influence. Diamond shows the highest chemical and thermal resistance under the chosen cutting conditions. Practically no built-up formation was detected at the cutting tip. The coatings which turned out best have been investigated in a performance test for a cutting length of 45m. Practically no built-up edges occur on these coatings even after this long cutting distance. In summary, diamond and WClC coatings in particular may be recommended for dry machining AlZnMgCuI ,5 malleable alloys. Dry milling of aluminium casting alloys (AISi1OMg-wa) has been studied [28,451 at the University of Karlsruhe (wbk). The wear study investigations were carried out in singletoothed cutter operation with synchronised flat face-milling on a horizontal machining centre. The cutting edge penetrates the material with the maximum thickness of cut, , ,h so the resulting entrance impact on the tool cutting edge is very large. This ensures in particular that meaningful conclusions can be drawn with respect to the adhesion of the various coatings [28]. Fiq. 17 shows the results of wear measurements under various lubricating conditions.
2
Summary and outlook
Cooling lubricants (CL) help to achieve a specified result in terms of tool life, surface finish and accuracy-to-size, and facilitate chip-breaking and transport. Nevertheless, they do give rise to certain problems in the immediate working environment and in waste disposal. As costs for waste disposal increase, companies are now being forced to implement strategies in order to reduce the amount of CL they . use in their production lines. In most cases, however, a machining operation without lubricant will be acceptable only if it is possible to guarantee that this equals or surpasses the part quality and machining times achieved in wet machining. The introduction of dry cutting requires suitable measures to compensate for the primary functions of the lubricant. But this, in turn, calls for a very detailed analysis of the boundary conditions and for thorough understanding of the complex interrelationships which link the process, tool, part and machine tool. This paper gives a wide range of examples of successful implementation of dry machining of cast iron, steel, aluminium and even superalloys and titanium. The introduction of dry cutting techniques may also include MQL, e.g. milling and drilling of aluminium alloys, to achieve
525
part quality and machining times comparable with wet cutting. We have come a long way in the desired direction. However, in practice dry machining is only practical when all operations can be done dry. Very often, this is not the case under present conditions. Appropriate action therefore has to be taken to further improve the technology of dry cutting. References Apple, C.A.. 1989: The Relationship between Inclusions and the Machinability of Steel. Mechanical Working and Steel Processing Proceedings (1989). Aronson. R.B.. 1995: Why Dry Machining?. Manufacturing Engineering, 1995: p.33-36. Ber. A.. 1972: Relationship between Thermal Properties and Flank Wear of Cemented Carbide Tools. ClRP Annals, Vol. 21-1. 1972. p. 21-22. Ber, A.. 1973: The Effect of Abrasion and Thermal Properties of the Cemented Carbide Cutting Tool Grade on the Flank Wear Characteristics. ASME Transaction Journal of Engineering for Industry. Vol. 956, August 1973. p. 794-79. Ber, A.; Goldblatt. M.1989: Influence of the Temperature Gradient on the Wear in Turning Tools. ClRP-Annals VoI. 3811, August 1989. p. 69-73. Brinksmeier, E.. Walter, A., 1996: EinsatzbeispieleMr Minimalmengenkuhlschmierung und Trockenbearbeitung. Vortrag. Technische Akademie Esslingen. 10th International Colloquium, 09 11 January 1996, Tribologie Solving Friction and Wear Problems, p. 23 43. Brinksmeier, E., Kroning, R.. 1997: Generation and Properties in Cutting Hardened Steel. Proceedings of 7th Inter-nationalConference on .Metrology and Propertiesof Engi-neeringSurfaces'. Gilteborg, 2ndath April 1997, p. 445-451. Dudly. G.M.. 1976: Machine Tool Having Internally Routed Cryogenic Fluid for Cooling Interface Between Cutting Tool and Workpiece. US Patent # 3.971.1 14,1976. Elbestawi. M. A.; El-Wardany, T.I.; Di Yan; Min Tan: Performanceof Whisker-Reinforced Ceramic Tools in Milling Nickel-BasedAlloy, Annals of CIRP, vol. 42/1 [lo] El-Wardany, T.I.; Elbestawi. M. A.. 1995: High Speed Machining of Nickel-Based Super Alloys with Silicon Carbide Whisker Reinforced Ceramics. 1st International Machining and Grinding Conference, Sept. 12-14, Dearborn. Michigan, MR95-160, p.1-26. [ l l ] Hamann. J. C.; Grolleau. V.; Le Maitre, F.. 1996: Machinability Improvement of Steels at High Cutting Speeds - Study of ToolMlork Material Interaction. Annals of the CIRP. Vol. 45/1/1996. [12] Heisel. U.; Lutz. M ; Spath, D.; Wassmer. R.; Walter, U.. 1994: Application of Minimum Quantity Cooling Lubrication Technology in Cutting Process. Production EngineeringVol. U/1 (1994). p. 49 54. [13] Helisto. P.; Helle. A. S.; Pietikdinen. J , 1990: Interface Phenomena between Oxide Layers and Cemented Carbide Tools: Wear, 139/90. [14] Howes, T.D., Tonshoff. H.K., Heuer. W., 1991, Environmental Aspects of Grinding Fluids, Annals of the CIRP, Vol. 40/2:623-630. [15] Jeffries. N.P.. 1969: A New Cooling Method for Metal Cutt-ing Tools. Ph.D. Dissertation, University of Cincinnati, 1969. [16] Kammermeier. D.: Charakterisierungvon binaren und ternaren Harstoffschichten anhand von Simulations- und Zerspanuntersuchungen; Dissertation RWTH Aachen. 1992. [17] Klocke. F.; Eisenbldtter. G.; Lung, D.. 1996:Trockenbohren von Stahl mit Hartmetallwerkzeugen.In: STAHL. Formen-Fugen-Fertigen 3'96. p.31-35. [ l 8 ] Klocke. F ; Lung, D.; Eisenblatter, G.. 1996: Mindermengenkiihlschmierung - Eine Alternative zur Naabearbeitung. In: VDI - Bericht 1240: Auf dem Weg zur Trockenbear-beitung. Dusseldorf: VDI Verlag. 1996, p. 159 190. [19] Klocke. F.; Eisenblatter, G., 1996: Trockenbohren und Feinbohren in Stahl. In: Trockenbearbeitung prismatischer Teile. Hrsg.: Bartl. R., Wissenschaftliche Berichte FZKA-PFT 177,1996, p. 159 - 202. [20] Klocke. F.; A. Schulz; K. Gerschwiler u.a., 1996: Saubere Fertigungstechnologien - Ein Wettbewerbsvorteilvon morgen? In: Wettbewerbsfaktor Produktionstechnik- Aachener Penpektiven. Hrsg.: AWK Aachener Werkzeugmaschinen-Kolloquium.Dusseldorf:VDIVerlag 1996. [21] Kdnig. W.. Erinski. D.. 1983, Machining and Machinabitity of Aluminium Cast Alloys, Annals of th CIRP, Vol. 32/2: 207-21 2. (221 Kdnig. W.; Klinger. M.: Machining Hard Materialswith Geometrically Defined Cutting Edges, ClRP Annals vol. 39/1/90. (231 Konig. W.; Osterhaus. G.; Genchwller, K.. u.a.. 1993: KuhlschmierStoff - Eine okologische Herausforderung an die Fertigungstechnik. In: Wettbewerbsfaktor Produktions-technik. Hrsg.: AWK Aachener Werkzeumaschinen-Kolloquium.VDI Verlag Dusseldorf. 1993. [24] Kress. D.. 1974: Reiben mit hohen Schnittgeschwindigkeiten. Dissertation Universitdt Stuttgart. 1974 [25] Kummel. D.,1990: Mechanismen beim Hochgeschwindigkeitsfrdsen von GuReisen. Munchen: Hanser. 1990, zugl. Darmstadt. Technische Hochschule. Dr.-lng. Diss.. 1990. (261 Kurimoto, T. and Barrow. G., 1982: "The Influence of Aqueous Fluids on the Wear Characteristics and Life of Carbide Cutting Tools" Annals of CIRP. Vol. 31 I1 11982.
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[27] Lahres, M.; Linden, P.; Liu. X.; Muller-Hummel. P.; Walter, J.. 1996: "Trockenbearbeitungvon Aluminium - Knetlegie-rungen", in: FrdsenWettbewerbsvorteile durch den Einsatz innovativer Technologien; wbk Karlsruher Kolloquium. Tagungsband. Universitat Karlsruhe; 5.3.1996; p.115-130. I281 Lahres. M.; Muller-Hummel. P.; Doerfel. O., 1996; "Appliciblify of different hard coatings in Dry Milling Aluminium alloys" Surface & coatings technology, 1996. [29] Lauscher. J. 1992: Drehen mit Schneidkeramik. Dissertation RWTH Aachen. 1992. [30] Lembke. D. 1995: Feinbearbeitungvon Bohrungen. Vortrag. Technische Akademie Esslingen. 12./13.10.95. [31] Lenz, E.; Katz. 2.;Ber A.: Investigation on the Flank Wear of Cemented Carbide Tools. ASME Transaction Joumal of Engineering for Industry, Vol. 98. No. 1. 1976, p. 246-250. 1321 Lung, D.; Gerschwiler. K.; Eisenblatter. G.. 1995: Technologische Grundlagen der Trockenbearbeitung.Vortrag. Technische Akademie Esslingen, 1995. [33] Meyers, P G.. 1964: Tool Cooling Apparatus. US Patent # 3,137,184. [34] Muller-Hummel. P.; Lahres. M.. 1996: Trockenfrdsen von Al-Knetlegierungen im Flugzeugbau Beispiele des Serieneinsatzes bei der DASA. In: Barthelmd. F.. Schmalkaldener Werkzeugtagung, Schmalkalden Nov. 1996, S. 174. [35] Oosterling, J.A.J.; van Luttervelt. C.A.. 1997: Droger Verspanen. TNO-rapport 97MI-O0763/00S, 1997 [36] Paju, M., 1991: EinfluR nichtmetallischer Einschlusse auf die Zerspanbarkeit der Stahle. Konferenz Einzelbericht: Werkstoffgefuge und Zerspanung, DGM und IWF Hannover. Fortbildungsseminar25.26.2.1991. [37] Pekelharing. A.J.. 1974, Build-Up Edge (BUE): Is the Mechanism Understand?,Annals of the CIRP. Vol. 23/2:207-212. [38] Pfeiffer. W. u.a.. 1995: BIA-Report Kuhlschmierstoffe6/95; Hrsg.: Hauptverband der gewerblichen Berufsgenossen-schafn, Sankt . .._ Augustin, 1995. [39] Schuller. J.; U. Drews, 1993: Bremsscheibenfertigungfur den Ford Mondeo mit Ambrazite und Amborite. IDR 27 (1993) 4, S. 241-246. I401 Schulz. H.; Kneisel T. 1994: Tum-Milling of Hardened Steels, an Alternative to Turning, ClRP Annals vol. 43/1/94. (411 Schulz. J.. 1996: Minimalmengenschmierung -Alternative zur Trockenbearbeitungoder zur ubefluteten Kuhlschmierung?Vortrag. Technische Akademie Esslingen. 10th International Collquium. 09 11 January 1996, Tribologie - Solving Friction and Wear Problems, p. 727 738. [42] Schulz. H.; Kalhbfer. E.. 1996: Aluminium-Knetlegierungentrocken bearbeiten. Werkstatt und Betrieb 129 (1996) 7-8. S. 707-710. (431 Schulz. H.; KalhOfer. E., 1996: Umweltfreundlichesproduzieren d. Trockenbearbeitung moglich? thema Forschung 2/96, S. 16-26. [44] Shaw. M. C. 1984: Metal Cutting Principles. Oxford Science Publications Clarendon Press Oxford 1984 p. 274-275. [45] Spath D.; Walter U.; Schaupp J..1996: "Development Tendecies in Milling" 2nd Karlsruhe Colloquium on Milling 1996, pp 7-29 Institute for Machine Tools and Process Engineering, University of Karlsruhe. [46] Spur, G.; Becker. K., 1993: Hochgeschwindigkeitsdrehenvon lamellarem GrauguR. ZWF 88 (1993) 10, S.447-445. (47) Spur, G.; Lachmund, U., 1995: Trockenbearbeitung von GrauguR rnit hohen Schnittgeschwindigkeiten.ZWF 90 (1995) 6, S.302-305. [48] Tonshoff, H. K.; Wobker, H. G.. 1994: Wear Characteristics of Cermet Cutting Tools, ClRP Annals vol. 43/1/94. [49] Tonshoff. H. K.; Karpuschewski. B.; Lierse, T., 1996: Potentiale und Grenzen umweltgerechter Fertigung; in: Neue Moglichkeiten umweltgerechter Fertigung. Seminar Universitat Hannover. IFW. 1996. [50] Tanshoff. H.K.; Mohlfeld, A., 1997: Cutting Performance of PVDcoated Drills in Dry Machining, 14th Int. Plansee Seminar 1997, May 12.-16.. 1997. Reute. Tyrol, Austria. [Sl] Tonshoff, H.K.; Mohlfeld. A,. 1997: Surface Treatment of Cutting Tool Substrates, 7th Int. Conf. on Metrology and Properties of Engineering Surfaces, 2nd4th April 1997, Goteborg, Sweden. [52] Tonshoff. H.K.; Mohlfeld, A. et. al.. 1997: Wear Mechanisms of (Til. x.Alx)N Coatings in Dry Drilling, April 21.-25, 1997, San Diego. USA 1531 Tomac. N.; Trannessen. K.. 1991: Formation of Flank Build-up in Cutting Magnesium Alloys, Annals of the CIRP. Vol. 40/1:79-82. [54] Vigneau. J., 1989: Cutting Material for Machining Superalloys. International ClRPNDl Conference, Dusseldorf, 19.-20.09.1989. [55] Weinert. K.;Biermann, D.; Thamke, D., 1996: Mdglichkeiten und Grenzen venchiedener Kuhlschmiermittelkonzeptebei der spanenden Bearbeitung. report at DGMconference "Reibung und Verschleis", Bad Nauheim. 21st122nd March 1996, ISBN 3-88355-220-8. Oberursel 1996. p. 97 108. [56] Weinert. K.; Adams. F.-J.. Thamke. D.. 1995: Was kostet die Kuhlschmierung?Technika. 7(1995), p. 19-23. [57] Weinert. K.; Thamke, D.. 1996. Kuhlschmierstoffkonzeptefur die Bohrungsbearbeitung. report at VDI-conference "Auf dem Weg zur Trockenbearbeitung". Dusseldorf. 13th February 1996, VDI-Bericht 1240, VDI-Verlag Dusseldorf, 1996, p. 111-124. [58] Zielasko. W.. 1996: Trockenzerspanungin der Groa-serienfertigung; in: Auf dem Weg zur Trockenbearbeitung Herausforderungan die Fertigungstechnik.VDI Berichte 1240, VDI Verlag Dusseldorf, 1996. S. 93-110. [59] N. N.. 1994: Produzierendes Gewerbe. Fachserie 4. Reihe 3.1: Produktion im Produzierenden Gewerbe; Statistisches Bundesamt. Wiesbaden, 1994. [60] N. N.. 1994: Mineraldldaten ftir die Bundesrepublik Deutschland. Jahr 1994; Bundesamt fur Wirtschaft. Eschborn. 1995.
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Keynote Papers Presented at the Opening Session Dry Cutting F. Klocke (2). G. Eisenblatter RWTH Aachen, Germany
Abstract: The vast majority of machining operations exploit the good cooling and lubricating characteristics of cooling lubricants (CL). But, as costs for waste disposal increase, companies are now being forced to implement strategies in order to reduce the amount of CL used in their production lines. The most logical measure which can be taken to eliminate all of the problems associated with the use of CL is dry machining. In most cases, however, a machining operation without lubricant finds acceptance only when it is possible to guarantee that the part quality and machining times achieved in wet machining are equalled or surpassed. The introduction of dry machining techniques may also include the use of minimal quantities of.lubricant (MQL). The following paper deals with the most recent developments in dry cutting. Keywords: Machining, dry cutting, environmental impact
0 Acknowledgements
absenteeism due to sickness, transfers). These are frequently estimated to be very low.
The authors would like to acknowledge all who have contributed to this paper with suggestions, discussions and documents of their work. Special thanks are given to: Prof. Ber. Haifa; Prof. Brinksmeier, Bremen; Prof. Elbestawi, Hamilton; Prof. Inasaki, Yokohama-Shi; Prof. Pollmann, Stuttgart; Prof. Schulz, Darmstadt: Prof. Spur, Berlin; Prof. Spath, Karlsruhe; Prof. Tbnshoff, Hannover; Prof. van Lutterveld. Delft; Prof. Vigneau, Evry; Prof. Weinert, Dortmund 1 Introduction In the metal cutting industry, cooling lubricants (CL) are one of the most frequently used agents. They help to achieve a prescribed result in' terms of tool life, surface finish and accuracy-to-size, and make chip-breaking and chip-transport easier. Their use is nonetheless characterised by problems in the immediate working environment and in waste disposal. These problems result in a large number of ecological problems and in a climate of increasingly strict work safety and environmental legislation. This in turn means more economic problems for manufacturing companies [2, 14, 18, 23, 551. The ecological and economical significance of the cooling lubricants becomes clear with a glance at the figures for the amounts of CL consumed annually. The consumption of cooling lubricants in Germany in the year 1994 was approx. 75,491 tonnes [60] Based on the factory gate price, the lubricant has a value of over DM200 million (591. Of the total quantity of cooling lubricants used in 1994, 28,415 tonnes were water-miscible products. Mixed with water at a concentration of 3 - 8%, this would make a quan. tity of emulsion in the order of 355,000 to 947,000 tonnes. It is estimated that approx. 350,000 tonnes of used emulsion and oil-water mixtures as well as an unquantifiable amount of grinding slurry, filter fleece and filter process materials [38] have to be processed and disposed of. Surveys indicate that few companies have accurate information regarding the actual costs incurred as a result of the use of CL (investment, depreciation, CL procurement, monitoring, maintenance, personnel, health precautions,
Source: Federal Office for Economic Affairs, WZL Distribution of quantity of coolants used in Ger-
w:
Surveys carried out in the German automotive industry show that workpiece-related manufacturing costs incurred in connection with the deployment of cooling lubricant at levels are several times higher than tool costs, of 7 - 17% which account for approx. 2 to 4% [49, 56, 581.
(m)
Wakoiece-dated manuiituring cost
58% 0% 0% PWMnndW3l 6% Process matends 5% Cooliq tubncant 14% + addhnal cost Dispasal wit 1%
Equipment cost Repair cost ,Energy cost
(m).
Annals of the ClRP Vol. 46/2/7997
many (20,601
Central facilities mlh up to 200 m' emu!aiionfor transfer lines Manufacturng mth a h9h percentage of indexable tip inserts
Source: WZL Lubricant cost exemplified by central facility [20]
W2:
The wide range within which CL costs fall is due to varying boundary conditions. The level of workpiece-related CL costs depends to a decisive degree on the manufacturing operation, part, required part quality, CL drag and vaporisa-
519
tion, the lubricating medium involved, the type of machine, the CL supply, the size of the facility, the situation regarding the building, CL processing and disposal and other factors. It also emerges that it is frequently difficult to identify all cost factors comprehensively, with the required degree of accuracy. Some of the quantitative values requested can only be estimated or even guessed. A cost-percentage of 17% is certainly an extreme value, which arose in the concrete example quoted, from specific circumstances within the company [58]. Even if the CL costs differ widely, the example shows that there is an enormous potential for savings. Increasingly, these findings are motivating companies to seek clarity about their own CL costs and to analyse possible means of achieving savings. This paper will give a review of today's dry machining technology. It was necessary to concentrate the paper only on the classical machining processes like turning, milling and drilling. It will consider the most commonly used mechanical engineering materials; i.e. steel, cast iron and also aluminium alloys as workpiece materials.
2
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Dry Cutting Ranges of application in industry
The two following examples of dry cutting show the wide range of possible applications in industry. The complete machining on machining centres of cast iron parts in small batch manufacturing at a German print machine producer is an impressive example of the long-term viability of dry machining The condition which had to be met prior to a switch to manufacturing in dry machining mode was that dry cutting operations should achieve at least the same cutting times, tool life times and part quality as in wet cutting operations. Cast materials in general and, more specifically in this case, grey cast iron, are particularly well-suited for dry machining, by virtue of the short chips, low cutting temperatures and forces as well as the lubricating effect of the embedded graphite. Nevertheless it quickly became apparent that, under the required boundary conditions, it was not going to be possible to switch'easily from wet to dry machining operations, even on cast materials. This applies increasingly, the more dependent the tools are on the cooling or lubricating effect of the fluid and the higher the degree to which their capacity is exploited in wet cutting operations. Tools for drilling, reaming and tapping operations must be regarded as particularly critical in this respect.
fluid. In the past, machining had been carried out on a transfer line with an indexable-insert drilling tool and a 10 percent oil-water-emulsion, which was externally supplied. Investigations have shown that purely dry machining is not possible due to the high tendency of the aluminium material to adhere to the tool. It was found that even minimum quantities of cutting fluid, which are fed towards the contact zone internally via the tool, suffice to achieve a drilling operation that meets the stipulated quality characteristics. For technical reasons, internal lubricant supply could not be realised in all cases, so there are applications where external feeding can also achieve good results. One example is a transfer line where two compressed air nozzles were affixed to the machine spindle to blow the lubricant out of the bore hole at the preceding station. While it is not possible to quantify the residual lubricant remaining in the bore hole, this may still be described as machining with a minimised lubricant supply. These newly created conditions enabled tool life to be increased by more than a factor of 4 compared to the previous mode of machining, to achieve more than 330,000 drilling operations. Fin.,for example, shows the measured values for diameter D, which is an important parameter for assessment of a production process. The ISF monitored a new precision tool using MQL from the first up to approx. 180,000 drilling operations. This examination was interrupted by a period in which the diameter was measured by statistical process control (SPC) carried out by the automobile manufacturer.
(m).
Source: Heidelberger Druckrnaschinen, WZL Complete machining of bearing plates in machining centres.studiedfor dry machining [20]
m:
Wherever 100% dry machining cannot be realised for technological reasons, minimal quantities of lubricant (MQL) may provide an alternative to wet cutting. The Department of Machining Technology, University of Dortmund (ISF), investigated the optimisation of drilling tools for machining with MQL in the automotive industry [57]. Investigations were carried out at the plant of a manufacturer of automobile gearboxes of die-cast aluminium (GDAISi9Cu3) to determine the extent to which it is possible to machine a dowel pin hole ( 0 1 1.9 H8) without using cutting 520
,.....
0
I
m
9 -dko*l
8D
BD
n.1.m
Source: ISF Diameter values when drilling dowel pin holes with minimised lubricant supply
Fb.4: 3
Developments in dry cutting
3.1 Fundamentals of dry cutting Before reviewing developments in dry cutting, an examination of the fundamentals of the technological aspects should be made. The main functions of CL are to reduce heat generation by reducing friction and to eliminate the exertion of unacceptable influences on the structure of the subsurface layer of the workpiece by absorbing and removing heat from the cutting area. In cutting operations, CL also have an important transport function for the chips which have to be removed. Thus efficient lubrication systems enable to high performance operations in practice. CL functions are not available in dry machining operations. This means that there is more friction and adhesion between tool and workpiece. Tools and workpieces are subjected to greater thermal load (Fin.). This may result in higher levels of tool wear, e.g. in increased crater formation when steel materials are machined using uncoated carbides. However, dry cutting may also show positive effects such as a reduction in thermal shock and thus in the formation of comb-cracks when parts are machined in interrupted mode with carbides or cermets [26]. Higher machining temperatures influence chip formation. This may result in both ribbon chips and snarl chips. When reliable control over chip formation is required, it may be necessary to use cutting inserts with especially adapted chip shaping grooves towards dry cutting. In drilling operations, high chip temperatures can hamper chip removal from
Keynote Papers the bore-hole and, in extreme cases, result in blockage of the flute and ultimately in tool failure. Higher part temperatures in dry cutting may affect form and dimensional accuracy and subsurface structure (19, 351.
,/+-+.-.
Tmsl dnll mlh lhermoelectnccwples
dry
Ck45 (AISI 1045)
MQL
!! F
9SMn28 (AISI 1213)
250
I
0
40
I
I
60 Wmin Cutting apeedv,
100
- Tool: HC-P TiN-cDaM W 11.8mrn f = 0.2 mm
Source: WZL Temperatures in wet and dry drilling
Fin.:
It is a well known fact that the cutting speed is directly related to the temperature in the cutting zone [3, 4, 441. shows experimental results of flank wear versus cutting speed. Four tool grades were tested in dry cutting of steel AlSl 1045 (3, 41. Cutting time was 4 minutes and the range of cutting speed was from 6mlmin to 6lOm/min.'The curve shape of the flank wear with the increase of the cutting speed is shown in Fig. 6. Investigations [31] suggest that the dominant mechanism of flank wear at low speeds is of the abrasive type, and when speed increases this is replaced by adhesion. At higher speeds diffusion becomes the dominant wear mechanism. Based on the results described there, it can be assumed that a decrease in temperature at higher speeds will give lower flank wear.
1
2
3
6
10
20 30
60 100
C&nQrpsedv.
2 M ) x M Wmin 1WO
this creates a cold junction and a hot junction at opposite ends of each of these elements. Based upon the above it may be concluded that dry cutting, associated with indirect cooling at relatively high speeds, reduces wear and extends tool life, if cooling is applied at cutting speeds where the diffusion wear mechanism IS dominant. To suit the specific requirements of a dry machining process, different influencing variables have to be taken into account. The tool has to be optimised with respect to substrate, geometry and coating. Suitable cutting materials are an essential must in order to implement dry machining operations. The high temperature hardness and wear resistance of cemented carbides, cermets, ceramics, CBN and PCD based cutting materials make these materials eminently suitable for use in dry cutting operations. There is general consensus that, in addition to the geometrical modifications required, it is necessary to use tool coatings in the development of tools for dry machining. The coating reduces friction and adhesion by virtue of the effect as a "solid lubricant", and thermal load on the substrate is diminished by the lower heat penetration capacity [16]. The reduced level of heat dissipation via the tool changes the heat flow between the tool and the chip. Since the substrate absorbs less heat more heat must be dissipated via the chip. In order to reduce thermal stresses in dry machining operations, by lowering the friction in the contact zones of the tool, it is also worth considering the approach from the material development side. In free cutting of steels and cast iron, it is well established that the machinability can be improved by utilising the effect of non-metallic inclusions, smearing out at the chipltool-interface and thus protecting the tool from wear. Ca-treatment of aluminiumdeoxidised steels is a possible way of extending comparable machinability improvements to a huge variety of engineering steel grades. Ca-treatment generally leads to a conversion of highly abrasive alumina inclusions (Al2O3) into more ductile Ca-aluminates. But the main contribution of Catreated steels to improvement of machinability is attributable to the formation of lubricating, wear-reducing layers in the contact zones of the tools (1, 11, 13, 361. This decreases the friction and the corresponding temperatures generated in the contact zones. These materials are thus highly suitable for dry machining operations. FW.7 shows the improved machining characteristics of a Ca-treated, quenched and tempered steel grade 38MnSiVS5, for dry turning with Ti(C,N)/AI,O,/liN-coated cemented carbide inserts (HCP15). The formation of wear-reducing layers, whose main constituents were determined by EDX-analysis as Al, S and Ca, increased tool life in this case by more than 400%.
*
Source: CMSR Flank wear vs. cutting speed in dry cutting with different tool grades
w:
The requirement for lower temperature in the cutting process without using direct CL gave investigators the idea of cutting dry and at the same time cooling the cutting zone. The following methods were suggested: (i) Under Cooling System [5] where the coolant flows through channels located under the insert, then out to the environment, without any direct contact with the cutting zone. (ii) Internal Cooling by Vaporization System [15] where a vaporizable liquid, such as water, is introduced inside the shank of the tool and vaporized on the underside surface of the insert. (iii) Cryogenic Systems [8] where a stream of a cryogenic coolant, such as nitrogen, is routed internally through a conduit inside the tool. (iv) Thermoelectric Cooling Systems [33], using a module of couples of thermoelectric material elements. When an electric current is passed through the thermoelectric elements,
Source: W Z L Calcium treatment of steel improves material characteristics for dry cutting
Fin.:
Where completely dry machining is not possible, the potentials of minimal quantities of lubricant (MQL) become particularly important for minimising CL. The term "minimal
521
quantities of lubricant" is used when tiny quantities of a cooling lubricant are fed to the cutting process. When the machine is adjusted to the optimum, less than 50ml of the medium is consumed per process hour. The main benefit of the MQL technique is that, if it is correctly applied, tools, workpieces and chips remain dry, thus obviating any need for processing or finishing. So this technique may justifiably be described as "dry machining". There are a number of materiallprocess combinations which are not economically viable without MQL. This currently applies particularly to drilling, reaming and tapping in cast iron, steel and aluminium alloys, and also to end-milling operations undertaken on Al-alloys and to deep-hole drilling [6, 12. 18, 30, 41, 571. Beside these applications it was found that, for turning steel, the use of MQL reduces the friction coefficient and the cutting temperature in orthogonal cutting compared with dry cutting and conventional fluid supply. MQL has always given the best surface roughness results in turning the constructional steel SNCM439. Tight dimensional and form tolerances may present a significant restriction for dry machining and call for special countermeasures.A dry cutting process must be designed to minimise the amount of heat flowing into the part. This may be achieved by minimising the cutting forces, and also by influencing the heat distribution. Cutting forces can be reduced by positive cutting edge geometries, while heat distribution towards the part may be positively influenced by using high cutting speeds. As these examples show, the introduction of dry machining necessitates measures suitable to compensate for the primary functions of the lubricant. This, in turn, calls for a very detailed analysis of the boundary conditions and for thorough understanding of the complex interrelationshipswhich link the process, tool, part and machine tool
highest thermal conductivity of all cutting materials investigated. It is 3 to 4 times higher than that of silicon nitride and alumina. When there is high thermal load in the cutting edge engagement zone, the heat created may be removed efficiently from the cutting material by the use of CBN. In summary, the conclusion that may be drawn from the characteristic quantities of the materials is that CBN is highly suitable for dry machining of cast iron with high cutting speeds. It is evident from the manufacturing tolerances and also from the surface qualities attained, that the best results are This is different for wobble f, obtained with CBN and parallelism f,; For these two explicitly mentioned tolerances, the best results were reached with silicon nitride ceramics. The specified tolerance was exceeded in the application of alumina ceramics for only one characteristic quantity, namely the wobble fb This means that the predefined manufacturing tolerances and surface qualities can be maintained in dry machining of grey cast iron at high cutting speeds, both with the non-oxide ceramic cutting material silicon nitride Si,N, and with CBN 1471. The latter gave the best results in terms of wear behaviour. These results are congruent with those obtained by SPUR [46] and KUEMMEL [25] and in the investigat.ions conducted by SCHUELLER, DREWS et al. [29, 391.
(m).
!
Cutting *doe g*om*ty:
Cutting GonditJonS:
CmW-V Feedrate' Daplh
. N O b *0.15mn.r=2(r SN;b =0,10mm.r -20"
*l~rnhn 1 -022mm
a -024m
s i l i i rim*. Si, N,
(m).
R,
..I.,
",,
R,
..I..
".I
t
1.
f.
Roylhness ndn m d m r i n g Id-
Source: IWF
Fiq.:
Mean values of roughness R, and manufacturing tolerances in turning of laminar cast iron with various cutting materials [47]
3.3 Dry machining of steel
Source: W Z L Variables which influence dry machining [20]
-8:
3.2 Dry machining of cast iron workpieces Cast iron materials can mostly be cut dry in turning and milling operations. Cast iron materials are particularly favourable in this respect, because their cutting temperatures are significantly lower than those of steel [47]. Dry machining of laminar grey cast iron at high cutting speeds using ceramic cutting materials and cubic boron nitride (CBN) has been carried out at the Institute for Machine Tools and Factory Management (IWF), Technical University Berlin 1471. Besides other widely differing properties of ceramics (AI2O3, Si,N,) and CBN, in terms of thermal characteristics, alumina has the highest expansion coefficient, followed by CBN; this can be a particular disadvantage for the maintenance of accurate part dimensions at high cutting speeds and consequently high cutting temperatures. Additionally CBN has the 522
Drilling takes a key position in the realisation of dry machining on machining centres. The main problem in dry drilling in steel is reliable removal of the chips from the drilled hole. The risk of a chip jam in the flute becomes steadily greater as the drilling depth increases and the friction paths between the chip and the hole wall or the tool become longer [17, 321. One very promising approach is to enlarge the flutes, giving the chips more spa& and helping them to escape, since there is less resistance to chip motion (Fia. '10). Another problem is the tendency of the drill to jam in the hole if its diameter expands too much as a result of high tool temperatures. One way of correcting this is more drill taper towards the shank. A TiN-coated tool with modified flute and tapering achieved a tool path of 65m in Ck45K tempering ,steel. The mean peak-to-valley height of R, < 15 20 pm was significantly below the permitted maximum of R, < 38pm. The hole diameters were some 0.02 0.03 mm larger than the nominal diameter of 11.8mm. By comparison. an H11 tolerance permits an allowance of 0.11 mm. As shown by this exam-
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Keynote Papers
ple, a dry cut can not only achieve high removal rates, but can also meet exacting part quality requirements.
Fiq. 10:
Dry drilling of tempering steel with carbide tools
Tool pretreatment is an important aspect for dry drilling [50]. In particular, coating adhesion depends on the surface structure of the substrate after the grinding operation. Increased adhesive forces in dry cutting processes as well as increased shearing loads in the substrate-coating may affect the coating. In wet machining, interface strength is sufficient, but in dry machining variations of interface strength may cause distinct differences in tool life. There is squeezing and smearing of Co-binder phase in grinding of WC-carbides, which causes a significant loss of material strength in subsurface layers of the substrate. Micro blasting of the ground WC-carbides changes the micro topography as well as the surface integrity of tools. Surface effects of micro blasting depend on blasting pressure and the grain size of the blasting material. If the grain size of the blasting material is bigger than the grain diameter of the carbide, this induces major plastic deformation of the subsurface of the tool; if the blasting material is smaller than the carbide grain size, this increases the abrasive effect of micro blasting [511. During dry drilling tests of tempered steel at the University of Hannover (IFW) with tools micro-blasted under adapted conditions, increased interface strength and superior wear behaviour of PVD-coated tools was observed. Interface failures after a few blind holes cause high wear rates of unblasted tools, because tool wear is determined by abrasive wear of the substrate. The higher interface strength of micro-blasted tools causes a distinct reduction in width of flank wear, and homogeneous tool wear of (Ti,AI)N-coated carbide.drills (Fiq. 11) [52].
Fia 11:
Investigations at the University of Bremen (IWT) included experiments which were performed as dry reaming operations, with minimum lubrication techniques and with internal cooling. This involved reaming hardened bearing steel 1OOCr6 with a tool which was equipped with guiding pads made of PCD and with cutting inserts containing CBN. Dry machining resulted in surface roughness of R, < 3pm and deviations in shape accuracy smaller than 9pm. The complete avoidance of cooling lubricants led to a transformation of the material's microstructurewithin the subsurface of the reamed bore (Fia. 12). The use of internal cooling made it possible to improve shape accuracy to within 5pm and to reduce transformation of the material [7].
Dry drilling of steel with microblastedtools
For fine machining cf bores in hardened materials, single edge reaming seems to have the potential to replace the cost-intensive operations of grinding and honing. Single edge reaming is a process which is characterised by its ability for self-guiding inside the bore. The reaming tool is designed like a boring bar equipped with a cutting insert and three guiding pads. The guiding pads support the tool inside the bore in order to avoid distortion of the tool from the workpiece [24].
Dry reaming of 1OOCr6 (GOHRC) [7] u: This investigations show that the reaming process can successfully be employed as a dry cutting operation and has the potential to be used as a substitute for grinding and honing in some fields.
3.4 HSC dry machining of superalloys and titanium Generally speaking, we consider that conventional cutting of superalloys and titanium with carbide tools requires water based coolant. High speed cutting (HSC) may be a possibility to switch from wet to dry cutting, but is more difficult to analyse: . For continuous HS-turning, any cutting tool ceramics for superalloys and carbide for titanium has to be cooled with a great flow of water-based coolant. It is advisable to use laser assistance without any coolant if possible, to achieve better results in terms of tool wear, but only fo'r machining superalloys with ceramic tools. In discontinuous HS-milling of the previous mentioned materials, a great flow of water based coolant induces thermal shocks on any cutting material. For this reason dry cutting is recommended. Even better results in terms of tool life can be achieved MQL. This effect depends on the length of the cut between two spray depositions (effect decreases when a, increases). HS-turning and milling of steel require dry cutting [22, '40, 48, 541. In conclusion, dry cutting is not efficient for conventional machining of superalloys and titanium alloys in most cases, but it may be efficient for HSC-milling, especially when no cutting assistance is available. Experiments at McMaster University, Hamilton showed that it was possible to obtain a surface finish of R, = 0.7bm in end milling of lnconel 718 at a feed of 0.2mm/tooth and cutting speeds in the range of 1,000 to 2,000 mlmin with a round insert. Chips were collected from the fly cutting tests, which were performed in dry condition on lnconel 718 material using Sic whisker reinforced ceramic tools. These exhibit the same pattern as those produced in hard turning. Chip segmentation was clearly visible for all cutting speeds ranging from 200 to 2,000 mlmin, feed rates ranging from 0.05 to 0.2 mmltooth, axial depth of cut from 0.25 to 2 mm, and immersion ratios between 0.25 and 1 [9, lo]. It is interesting
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523
to note that the type of chip produced was not dependent on use of dry or wet cutting [lo].
3.5 Dry machining of aluminium alloys Aluminium alloys are among the particularly critical materials with regard to dry machining. Workpieces absorb considerable heat from the machining process due to their high level of thermal conductivity. In conjunction with the high levels of thermal .expansion, this causes deformations. In view of the low melting and softening point, problems connected with chip formation are also related. Many aluminium alloys are susceptible to adhesion with the tool and to buildup in the chip space [21, 271. In order to carry out dry drilling, reaming, tapping and end-milling operations successfully on aluminium alloys, it is essential to use tools with suitable coating systems and to use MQL. The positive influence MQL on the state of the tool and on part quality is demonstrated very impressively in Fia 13.
feed force F,. The forces in turning with uncoated inserts are higher than the forces with PCD-coated inserts. Atomic-Force-Microscopy (AFM)-analysis gives information on the morphology, topography, porosity and roughness of layers. The AFM-photograph of the tool face of a PCDcoated insert shows a regular layer structure. The wear resistance of the PCD-coated insert is better than the wear resistance of the uncoated insert. The low friction coefficient of the PCD layer means that the coated inserts are suitable for dry cutting processes.
Source: lW Fig. 14: PCD-coated inserts in dry turning
Extensive experiments were made on AlZnMgCul.5 to study the influence of cutting speed, feed per tooth, cutting angle and clearance angle on flank build-up formation (37, 531 in dry milling at the Technical University of Darmstadt ( p ~[421. ) Polycrystalline diamond has only a minor tendency for flank build-up, so further studies were made into the influence of a diamond coating applied by the CVD process, and also of two diamond-like coatings (diamond-like carbon (DLC) and a metal carbon coating). The DLC coating a-C:H is an amorphous carbon layer; it substantially consists of carbon in graphitic, amorphous and crystalline form and of hydrogen. In another version, the metal hydrocarbon coat (WC/C) can also be provided with some tungsten content. This will give the coat greater toughness and lower hardness than aC:H (Hardness (Vickers) of a-C:H: 3,000-5,000, o f WCIC: 1,000). Both coatings have a low friction coefficient against steel (p = 0.1 0.2) and an anti-adhesive effect against many materials. With the uncoated tools, neither optimisation of cutting edge geometry nor variation of cutting'speed or feed per tooth can reduce the tendency for flank build-up sufficiently to allow dry machining in production. Conditions can be improved by MQL, using quantities of less than 40ml/h to lubricate the point of machining. . The influences of the various coatings and of MQL were studied for milling with a tool 16mm in diameter. Fig. 15 shows that in dry milling, both the .a-C:H coating and the diamond coating reduce flank build-up, whereas the WC/C coating gives no improvement as against the uncoated cemented carbide. In all, the coatings tested do not permit dry machining under production conditions of the material studied, as there will always be flank build-up formation. On the other hand, MQL gives a substantial reduction of flank build-up. Increasing volume flow from 10 ml/h to 40 mllh gives no further benefit, so the smaller volume flow is sufficient to suppress flank build-up almost completely [43]. Comparable investigations have been obtained at plants of an German aircraft manufacturer [34]. Different commercial coatings (onto identical HW-K10 cemented carbide substrates) were investigated for suitability to .reduce built-up edges and virtual chip formation in dry milling of the AlZnMgCu1,5 malleable alloy. A two-step test programme was performed for this purpose: an initial test with all the selected coatings and then a performance test with the best coatings from the initial test.
-
Source: Daimler Benz, wbk, WZL Dry machining operations on aluminium workFig. 13: pieces require the use of MQL [20] In dry drilling operations conducted without MQL (Fig. 13, top) the tool was useless due to adhesion of material in the chip groove after only 16 drilling operations. With MQL, there was no evidence of wear or material adhesion to the tool after 128 drilling operations. The average peak-to-valley height for bore holes produced using MQL remained below R, = 20pm and thus, like the bore hole diameters, within the tolerances [18]. When grooves were end-milled dry into a wrought aluminium alloy, there was a strong tendency for material and chips to stick to tools and parts (Fig. 13, below). MQL operations, by contrast. showed no evidence of material or chip adhesion to the milled grooves. The endmilled grooves manufactured using the MQL technique. fulfilled the tolerances required in terms of dimensional accuracy, soft spot formation, surface roughness and waviness. The main field of industrial application of PCD-coated inserts is in dry cutting processes [6].Investigations were carried out at the University of Bremen (IW)to analyse the suitability of PCD-coated inserts by dry turning of the aluminium alloy AISil8CuMgNi. This work material is a hypereutectic alloy and especially the silicon has an abrasive effect on the tool flank during the turning process. Fig. 14 shows the values of the cutting force F, thrust force F, and
524
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Keynote Papers 3
1
/
/
,
/
/
A Cutting parameters:
20
IJm 16
5 14 L
12 ig
10
$ 8
3 4 m 6 Feed path 1: uncoated. 2: &:H coated. 3: W C coated. 4: CMdiamond coated. 5: MQL (10 mVh), 6: MQL (40 mVh)
0
1
2
Source: PTW Fiq. 15: Influence of coating and minimal lubrication in milling AlZnMgCuI .5[42. 431
0
The results and the cutting conditions used for the initial tests are shown in Fiq. 16. The experiments were done in a single tooth climb-cut milling process on a horizontal machining centre. The cutting length was 420 mm. The WClC, a-C:H and diamond coatings showed practically no built-up edges at the rake face. They are classified as 'suitable coatings'. 'Unsuitable coatings' such as CrN, MoS,, TIN, (Ti,AI)N and the uncoated cemented carbide substrate yield great built-up edges at the rake face. It is probable that the transition elements (Cr, Mo, Ti) effect considerable chemical action and result in diffusion 'reactions with the elements of the machined workpiece material (Al, Zn, Mg, Cu). This causes built-up edges, which consist of these elements and ambient oxygen.
Source: Daimler Benz. wbk Fin. 16: Dry face milling ofAIZnMgCul.5 [34]
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-
4
6 8 1 0 1 2 Milling distance I,
m 1 6
Source: wbk Fin. 17: Results from dry face milling of cast aluminium alloy AISilOMg(wa) with HC-K10 A direct comparison of dry machining with the conventional CL-application (full flooding with 5% emulsion) shows that dry machining reduces the tool life distance by 35% for the uncoated cutting inserts (HW-KIO): Examinations of the cutting edge geometry have also shown that, on the uncoated tool, dry machining produces unacceptable built-up edges and there is an adverse effect on surface quality. A comparison of the variously coated tools with the uncoated tools shows'that there is a large potential scope for development in coating technology. There are two fundamental tendencies. On the one hand, in dry processing the "soft"coatings (tungsten carbidelcarbon (WCIC); chromium carbidelcarbon (CrClC)) score with distinctly less built-up edge formation, but these coatings do not achieve the low wear values of the conventional cooling lubricant application. On the other hand, in dry milling coated tools have considerable tool life advantages compared with uncoated tools with full flooding; this can be achieved by combining a hard material layer (e.g. titanium nitride (TiN)) with a "soft" top layer coating (e.g. molybdenum sulfide MoS,). The wear characteristics achieved by this multilayer coating increase tool life by up to 10% in dry processing compared with conventional CL-technology. Diamond-coated tools likewise show clear potential for dry machining. These layer .structures deposited by the CVDmethod do not produce any built-up edge, because there is little affinity between carbon and aluminium. The tool life values obtained with this coating increase the useful life of the tool for dry milling by about 30%. 4
Partly crystalline coatings (e.g. WClC) exhibit a lower tendency to form built-up edges, in spite of their metal content (e.g. tungsten). It is suggested that amorphous parts in the coating morphology have a positive influence. Diamond shows the highest chemical and thermal resistance under the chosen cutting conditions. Practically no built-up formation was detected at the cutting tip. The coatings which turned out best have been investigated in a performance test for a cutting length of 45m. Practically no built-up edges occur on these coatings even after this long cutting distance. In summary, diamond and WClC coatings in particular may be recommended for dry machining AlZnMgCuI ,5 malleable alloys. Dry milling of aluminium casting alloys (AISi1OMg-wa) has been studied [28,451 at the University of Karlsruhe (wbk). The wear study investigations were carried out in singletoothed cutter operation with synchronised flat face-milling on a horizontal machining centre. The cutting edge penetrates the material with the maximum thickness of cut, , ,h so the resulting entrance impact on the tool cutting edge is very large. This ensures in particular that meaningful conclusions can be drawn with respect to the adhesion of the various coatings [28]. Fiq. 17 shows the results of wear measurements under various lubricating conditions.
2
Summary and outlook
Cooling lubricants (CL) help to achieve a specified result in terms of tool life, surface finish and accuracy-to-size, and facilitate chip-breaking and transport. Nevertheless, they do give rise to certain problems in the immediate working environment and in waste disposal. As costs for waste disposal increase, companies are now being forced to implement strategies in order to reduce the amount of CL they . use in their production lines. In most cases, however, a machining operation without lubricant will be acceptable only if it is possible to guarantee that this equals or surpasses the part quality and machining times achieved in wet machining. The introduction of dry cutting requires suitable measures to compensate for the primary functions of the lubricant. But this, in turn, calls for a very detailed analysis of the boundary conditions and for thorough understanding of the complex interrelationships which link the process, tool, part and machine tool. This paper gives a wide range of examples of successful implementation of dry machining of cast iron, steel, aluminium and even superalloys and titanium. The introduction of dry cutting techniques may also include MQL, e.g. milling and drilling of aluminium alloys, to achieve
525
part quality and machining times comparable with wet cutting. We have come a long way in the desired direction. However, in practice dry machining is only practical when all operations can be done dry. Very often, this is not the case under present conditions. Appropriate action therefore has to be taken to further improve the technology of dry cutting. References Apple, C.A.. 1989: The Relationship between Inclusions and the Machinability of Steel. Mechanical Working and Steel Processing Proceedings (1989). Aronson. R.B.. 1995: Why Dry Machining?. Manufacturing Engineering, 1995: p.33-36. Ber. A.. 1972: Relationship between Thermal Properties and Flank Wear of Cemented Carbide Tools. ClRP Annals, Vol. 21-1. 1972. p. 21-22. Ber, A.. 1973: The Effect of Abrasion and Thermal Properties of the Cemented Carbide Cutting Tool Grade on the Flank Wear Characteristics. ASME Transaction Journal of Engineering for Industry. Vol. 956, August 1973. p. 794-79. Ber, A.; Goldblatt. M.1989: Influence of the Temperature Gradient on the Wear in Turning Tools. ClRP-Annals VoI. 3811, August 1989. p. 69-73. Brinksmeier, E.. Walter, A., 1996: EinsatzbeispieleMr Minimalmengenkuhlschmierung und Trockenbearbeitung. Vortrag. Technische Akademie Esslingen. 10th International Colloquium, 09 11 January 1996, Tribologie Solving Friction and Wear Problems, p. 23 43. Brinksmeier, E., Kroning, R.. 1997: Generation and Properties in Cutting Hardened Steel. Proceedings of 7th Inter-nationalConference on .Metrology and Propertiesof Engi-neeringSurfaces'. Gilteborg, 2ndath April 1997, p. 445-451. Dudly. G.M.. 1976: Machine Tool Having Internally Routed Cryogenic Fluid for Cooling Interface Between Cutting Tool and Workpiece. US Patent # 3.971.1 14,1976. Elbestawi. M. A.; El-Wardany, T.I.; Di Yan; Min Tan: Performanceof Whisker-Reinforced Ceramic Tools in Milling Nickel-BasedAlloy, Annals of CIRP, vol. 42/1 [lo] El-Wardany, T.I.; Elbestawi. M. A.. 1995: High Speed Machining of Nickel-Based Super Alloys with Silicon Carbide Whisker Reinforced Ceramics. 1st International Machining and Grinding Conference, Sept. 12-14, Dearborn. Michigan, MR95-160, p.1-26. [ l l ] Hamann. J. C.; Grolleau. V.; Le Maitre, F.. 1996: Machinability Improvement of Steels at High Cutting Speeds - Study of ToolMlork Material Interaction. Annals of the CIRP. Vol. 45/1/1996. [12] Heisel. U.; Lutz. M ; Spath, D.; Wassmer. R.; Walter, U.. 1994: Application of Minimum Quantity Cooling Lubrication Technology in Cutting Process. Production EngineeringVol. U/1 (1994). p. 49 54. [13] Helisto. P.; Helle. A. S.; Pietikdinen. J , 1990: Interface Phenomena between Oxide Layers and Cemented Carbide Tools: Wear, 139/90. [14] Howes, T.D., Tonshoff. H.K., Heuer. W., 1991, Environmental Aspects of Grinding Fluids, Annals of the CIRP, Vol. 40/2:623-630. [15] Jeffries. N.P.. 1969: A New Cooling Method for Metal Cutt-ing Tools. Ph.D. Dissertation, University of Cincinnati, 1969. [16] Kammermeier. D.: Charakterisierungvon binaren und ternaren Harstoffschichten anhand von Simulations- und Zerspanuntersuchungen; Dissertation RWTH Aachen. 1992. [17] Klocke. F.; Eisenbldtter. G.; Lung, D.. 1996:Trockenbohren von Stahl mit Hartmetallwerkzeugen.In: STAHL. Formen-Fugen-Fertigen 3'96. p.31-35. [ l 8 ] Klocke. F ; Lung, D.; Eisenblatter, G.. 1996: Mindermengenkiihlschmierung - Eine Alternative zur Naabearbeitung. In: VDI - Bericht 1240: Auf dem Weg zur Trockenbear-beitung. Dusseldorf: VDI Verlag. 1996, p. 159 190. [19] Klocke. F.; Eisenblatter, G., 1996: Trockenbohren und Feinbohren in Stahl. In: Trockenbearbeitung prismatischer Teile. Hrsg.: Bartl. R., Wissenschaftliche Berichte FZKA-PFT 177,1996, p. 159 - 202. [20] Klocke. F.; A. Schulz; K. Gerschwiler u.a., 1996: Saubere Fertigungstechnologien - Ein Wettbewerbsvorteilvon morgen? In: Wettbewerbsfaktor Produktionstechnik- Aachener Penpektiven. Hrsg.: AWK Aachener Werkzeugmaschinen-Kolloquium.Dusseldorf:VDIVerlag 1996. [21] Kdnig. W.. Erinski. D.. 1983, Machining and Machinabitity of Aluminium Cast Alloys, Annals of th CIRP, Vol. 32/2: 207-21 2. (221 Kdnig. W.; Klinger. M.: Machining Hard Materialswith Geometrically Defined Cutting Edges, ClRP Annals vol. 39/1/90. (231 Konig. W.; Osterhaus. G.; Genchwller, K.. u.a.. 1993: KuhlschmierStoff - Eine okologische Herausforderung an die Fertigungstechnik. In: Wettbewerbsfaktor Produktions-technik. Hrsg.: AWK Aachener Werkzeumaschinen-Kolloquium.VDI Verlag Dusseldorf. 1993. [24] Kress. D.. 1974: Reiben mit hohen Schnittgeschwindigkeiten. Dissertation Universitdt Stuttgart. 1974 [25] Kummel. D.,1990: Mechanismen beim Hochgeschwindigkeitsfrdsen von GuReisen. Munchen: Hanser. 1990, zugl. Darmstadt. Technische Hochschule. Dr.-lng. Diss.. 1990. (261 Kurimoto, T. and Barrow. G., 1982: "The Influence of Aqueous Fluids on the Wear Characteristics and Life of Carbide Cutting Tools" Annals of CIRP. Vol. 31 I1 11982.
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[27] Lahres, M.; Linden, P.; Liu. X.; Muller-Hummel. P.; Walter, J.. 1996: "Trockenbearbeitungvon Aluminium - Knetlegie-rungen", in: FrdsenWettbewerbsvorteile durch den Einsatz innovativer Technologien; wbk Karlsruher Kolloquium. Tagungsband. Universitat Karlsruhe; 5.3.1996; p.115-130. I281 Lahres. M.; Muller-Hummel. P.; Doerfel. O., 1996; "Appliciblify of different hard coatings in Dry Milling Aluminium alloys" Surface & coatings technology, 1996. [29] Lauscher. J. 1992: Drehen mit Schneidkeramik. Dissertation RWTH Aachen. 1992. [30] Lembke. D. 1995: Feinbearbeitungvon Bohrungen. Vortrag. Technische Akademie Esslingen. 12./13.10.95. [31] Lenz, E.; Katz. 2.;Ber A.: Investigation on the Flank Wear of Cemented Carbide Tools. ASME Transaction Joumal of Engineering for Industry, Vol. 98. No. 1. 1976, p. 246-250. 1321 Lung, D.; Gerschwiler. K.; Eisenblatter. G.. 1995: Technologische Grundlagen der Trockenbearbeitung.Vortrag. Technische Akademie Esslingen, 1995. [33] Meyers, P G.. 1964: Tool Cooling Apparatus. US Patent # 3,137,184. [34] Muller-Hummel. P.; Lahres. M.. 1996: Trockenfrdsen von Al-Knetlegierungen im Flugzeugbau Beispiele des Serieneinsatzes bei der DASA. In: Barthelmd. F.. Schmalkaldener Werkzeugtagung, Schmalkalden Nov. 1996, S. 174. [35] Oosterling, J.A.J.; van Luttervelt. C.A.. 1997: Droger Verspanen. TNO-rapport 97MI-O0763/00S, 1997 [36] Paju, M., 1991: EinfluR nichtmetallischer Einschlusse auf die Zerspanbarkeit der Stahle. Konferenz Einzelbericht: Werkstoffgefuge und Zerspanung, DGM und IWF Hannover. Fortbildungsseminar25.26.2.1991. [37] Pekelharing. A.J.. 1974, Build-Up Edge (BUE): Is the Mechanism Understand?,Annals of the CIRP. Vol. 23/2:207-212. [38] Pfeiffer. W. u.a.. 1995: BIA-Report Kuhlschmierstoffe6/95; Hrsg.: Hauptverband der gewerblichen Berufsgenossen-schafn, Sankt . .._ Augustin, 1995. [39] Schuller. J.; U. Drews, 1993: Bremsscheibenfertigungfur den Ford Mondeo mit Ambrazite und Amborite. IDR 27 (1993) 4, S. 241-246. I401 Schulz. H.; Kneisel T. 1994: Tum-Milling of Hardened Steels, an Alternative to Turning, ClRP Annals vol. 43/1/94. (411 Schulz. J.. 1996: Minimalmengenschmierung -Alternative zur Trockenbearbeitungoder zur ubefluteten Kuhlschmierung?Vortrag. Technische Akademie Esslingen. 10th International Collquium. 09 11 January 1996, Tribologie - Solving Friction and Wear Problems, p. 727 738. [42] Schulz. H.; Kalhbfer. E.. 1996: Aluminium-Knetlegierungentrocken bearbeiten. Werkstatt und Betrieb 129 (1996) 7-8. S. 707-710. (431 Schulz. H.; KalhOfer. E., 1996: Umweltfreundlichesproduzieren d. Trockenbearbeitung moglich? thema Forschung 2/96, S. 16-26. [44] Shaw. M. C. 1984: Metal Cutting Principles. Oxford Science Publications Clarendon Press Oxford 1984 p. 274-275. [45] Spath D.; Walter U.; Schaupp J..1996: "Development Tendecies in Milling" 2nd Karlsruhe Colloquium on Milling 1996, pp 7-29 Institute for Machine Tools and Process Engineering, University of Karlsruhe. [46] Spur, G.; Becker. K., 1993: Hochgeschwindigkeitsdrehenvon lamellarem GrauguR. ZWF 88 (1993) 10, S.447-445. (47) Spur, G.; Lachmund, U., 1995: Trockenbearbeitung von GrauguR rnit hohen Schnittgeschwindigkeiten.ZWF 90 (1995) 6, S.302-305. [48] Tonshoff, H. K.; Wobker, H. G.. 1994: Wear Characteristics of Cermet Cutting Tools, ClRP Annals vol. 43/1/94. [49] Tonshoff. H. K.; Karpuschewski. B.; Lierse, T., 1996: Potentiale und Grenzen umweltgerechter Fertigung; in: Neue Moglichkeiten umweltgerechter Fertigung. Seminar Universitat Hannover. IFW. 1996. [50] Tanshoff. H.K.; Mohlfeld, A., 1997: Cutting Performance of PVDcoated Drills in Dry Machining, 14th Int. Plansee Seminar 1997, May 12.-16.. 1997. Reute. Tyrol, Austria. [Sl] Tonshoff, H.K.; Mohlfeld. 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