- Email: [email protected]
Sustainable machining through increasing the cutting tool utilization
Journal of Cleaner Production 59 (2013) 298e307
Contents lists available at SciVerse ScienceDirect
Journal of Cleaner Production journal homepage: www.elsevier.com/locate/jclepro
Sustainable machining through increasing the cutting tool utilization Fredrik Schultheiss*, Jinming Zhou, Elias Gröntoft, Jan-Eric Ståhl Lund University, Division of Production and Materials Engineering, 221 00 Lund, Sweden
a r t i c l e i n f o
a b s t r a c t
Article history: Received 31 January 2013 Received in revised form 10 June 2013 Accepted 30 June 2013 Available online 11 July 2013
Several previous articles have discussed different approaches to improving sustainability during machining operations. However, more effective utilization of cutting tools is an approach that has been overlooked in previous investigations. Increasing the effectiveness of cutting tool utilization decreases the need for new tools as well as the resources and energy needed to produce new cutting tools. The aim of this study was to maximize cutting tool utilization during machining operations without adversely affecting product quality, thus decreasing the environmental impact of machining operations. This was achieved by determining to what extent it is possible to increase total tool life by using previously worn tools in a secondary machining operation. For both the milling and turning cases investigated, experimental results showed that it is possible to increase the total tool life by approximately 50%e100% compared to equivalent conventional machining operations. The increase in tool life could decrease the production cycle time by approximately 15% and reduce energy consumption by 12% as compared to conventional machining processes. Ó 2013 Elsevier Ltd. All rights reserved.
Keywords: Machining Sustainable production Tool utilization Cutting tool
1. Introduction Sustainable development has received increasing attention in recent years. In 1987 the United Nations defined it as “development that meets the needs of the present without compromising the ability of future generations to meet their own needs” (Brundtland, 1987). Such development is needed in all parts of our modern society, including the production process. The concept of sustainable production emerged at the United Nations Conference on Environment and Development (UNCED, 1992) and has been recognized as a vital component in achieving sustainable development (Jovane et al., 2008). It requires a clear link between technology and economics (Ståhl, 2011). Sustainable development must go hand in hand with technological development in order to become an integral part of the production process. Garetti and Taisch (2012) argue that standards and norms are crucial factors for enabling a faster diffusion of new technological knowledge into modern production. Smith and Ball (2012) emphasize the importance of having a holistic view of the whole manufacturing process in order to be able to identify potential strategies for improving sustainability. Despeisse et al. (2013) present a set of tactics for achieving sustainable production, all of which could be used individually or in combination to increase the sustainability of
* Corresponding author. E-mail address: [email protected] (F. Schultheiss). 0959-6526/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jclepro.2013.06.058
production processes. Another important factor for obtaining sustainable production, discussed by Duflou et al. (2012), concerns the importance of choosing an appropriate manufacturing method for the specific part being produced. Overall, manufacturers need to evaluate process sustainability in addition to the traditional economic and technical aspects of their operations. Currently, there is no universally accepted definition of sustainable machining. Often this parameter is described in terms of processes that can result in improvements with regard to such matters as (i) reducing waste, (ii) reducing power consumption, and (iii) enhancing operational safety (Jayal et al., 2010). According to Pusavec et al. (2010), there are several different approaches to improving sustainability during machining operations. For example, the use of cutting fluid is often described as one of the main environmental hazards during machining (Kuram et al., 2013). Thus significant effort has been put into minimizing the use of cutting fluid even when machining difficult-to-machine materials (Shokrani et al., 2012). Another problem that has to be addressed is the quick wear of cutting tools. By optimizing tool life, it is often possible to improve the sustainability of a machining process while reducing the manufacturing cost. However, increased tool utilization may not always result in lowered manufacturing costs. There is a balance between tool life and the cost of both the tool and the machining process to obtain an economical tool life resulting in minimal manufacturing costs (Hägglund, 2002). Moreover, Helu et al. (2012b) caution that an increase in sustainability during machining may sometimes result in a reduced
F. Schultheiss et al. / Journal of Cleaner Production 59 (2013) 298e307
Fig. 1. Processing steps for obtaining tungsten carbide.
product quality, which could lead to poor sustainability over the whole product life cycle. Traditionally, machining processes are optimized by minimizing the manufacturing cost while still complying with technological limitations (Hägglund, 2002). Thus Schultheiss et al. (2012) presented a method for improving the machining process during normal production. But while in some cases, the economic goals correspond to the goal of sustainability, this is not always the case. In order to further consider environmental concerns, Rajemi et al. (2010) proposed a new model that takes process energy consumption into consideration while selecting process parameters during turning. A similar model was developed by Bhushan (2013). Both these models are well suited to improving the sustainability of a machining process. In an earlier article, Dahmus and Gutowski (2004) stated that the direct environmental influence of tooling is limited. Yet even though the influence of cutting tools on the overall sustainability of a machining process is limited, their influence should not be overlooked. All parts of the process need to be improved as much as possible to achieve truly sustainable machining processes. 2. Manufacture and recycling of coated cemented carbide inserts Coated cemented carbide inserts are manufactured using powder-metallurgy. Tungsten, which is an important part of the inserts, can be obtained from chemical processing of either scheelite (CaWO4) or tungstenite ((Fe, Mn)WO4). After several steps of chemical processing, pure tungsten is obtained. The next step is to obtain tungsten carbide through a process known as carburization (Ståhl, 2012). Fig. 1 briefly illustrates the processing steps for obtaining tungsten carbide. The overall energy requirement during this process is approximately 12 kWh/kg tungsten carbide, if manufactured from ore concentrates (Bhosale et al., 1990). As illustrated in Fig. 2, the process of manufacturing coated cemented carbide inserts begins by weighing appropriate amounts of the different components. The components are mixed together before being compressed into a green body. This is followed by sintering of the insert, which is a process in which the green body is heated in a protective atmosphere to a temperature of approximately 1400 C. Sintering eliminates the porosity of the cemented carbide insert. The next step is edge preparation through grinding and lapping of the insert to achieve the insert’s final shape. The final step is coating the insert with any of a number of different coatings depending on the desired characteristics. 2.1. Recycling of coated cemented carbide inserts There are two main methods of recycling coated cemented carbide cutting tools (Smith, 1994). The first, which involves chemical reprocessing of the cutting tools, is currently used for approximately 35% of all cemented carbide scrap. This process starts with mechanical crushing of the inserts to a powder, which is
299
then treated chemically. The tungsten carbide particles emerge intact and may then be crushed, washed, and dried to form a powder that can be used as raw material for the production of new cemented carbide inserts (Angerer et al., 2011). The second common recycling method, the Zn-method, in which cemented carbide inserts are treated with molten zinc, is currently used for about 25% of the cemented carbide scrap. Molten zinc creates an alloy with the cobalt binder phase, resulting in an increase in the volume of the binder phase, thereby shattering the carbide structure. The remains can then be crushed to a powder, which is in turn used as raw material when producing tungsten carbide powder for new inserts (Angerer et al., 2011). Depending on the size of the scrap input, the energy consumption for the Znmethod has been reported as approximately 2 kWh/kg of product (Kieffer and Lassner (1994)). The cost of the Zn-method is approximately 20%e35% less than that for other chemical processes, depending on the type of cemented carbide grades being recycled. Research shows that between 1955 and 1991 approximately 60% of the input tungsten was lost (Kieffer and Lassner, 1994). Since tungsten is a rare and finite resource, these losses could become an increasing concern over time. If the current consumption of tungsten continues, Seco Tools estimates that resources will be depleted within 40e100 years. By recycling cemented carbide scrap it may be possible to delay the time before the resources are depleted by approximately 35%, while also reducing CO2 emissions by approximately 40% (Seco Tools, 2010). If tool utilization could be increased by 100%, a significant amount of resources and energy could be saved. Fig. 3 illustrates the savings. A possible method for achieving this increase in tool life is discussed in the next section. 3. Increasing cutting tool utilization As discussed by Helu et al. (2012a), significant improvements in sustainability during machining processes can be obtained by optimizing process parameters. Helu et al. (2012b) prove that these improvements may not necessarily decrease the quality of the machined part. Through minor alterations to the current machining process, sustainability may be improved even further. During milling and turning operations, cutting tools are commonly used in a way that causes the major cutting edge to wear out, while the wear on the minor cutting edge is comparatively small or almost nonexistent. Tool life could be substantially increased by using the same insert in a secondary machining operation. A change in the tool setup would enable the previously lightly worn minor cutting edge to be used as a “new” major cutting edge. There are already commercial products available based on this principle (Larssons i Bjärred Mekaniska Verkstad AB, 2009), but little research has been published on the effects of using this method on the cutting tool or on the machined surface. An alternative method on increasing tool life involves what is known as the rotary tool cutting process, which has proven to be applicable to both turning (Armarego et al., 1994) and milling operations (Dabade et al., 2003). A rotary cutting tool has been shown to be capable of machining hard-to-machine materials, such as Ti6Al4V (Lei and Liu, 2002) and other aerospace materials (Ezugwu, 2007). Although the rotary tool cutting process shows great potential, it is limited to the use of round inserts. This leads to the
Fig. 2. Processing steps for manufacturing coated cemented carbide inserts (Sandvik Central Service, 1982).
300
F. Schultheiss et al. / Journal of Cleaner Production 59 (2013) 298e307
proposed method could be performed under dry cutting conditions, the advantage in terms of sustainability would be much greater. During these tests only coated cemented carbide inserts were used, primarily because these are generally the preferred choice for the materials being machined. During all experiments the tool wear was measured using an optical microscope. Surface roughness was measured using a MahrSurf PS1 portable surface roughness tester. 4.1. Milling experiments
Fig. 3. Tungsten consumption while machining a specific part using a conventional process compared to the proposed new process.
need for further studies of alternative methods of improving tool life for processes requiring other tool shapes. 3.1. Proposed method for milling It is common practice to rotate the milling cutter in only one direction during conventional production. This causes the majority of the tool wear to occur on the major cutting edge, while the minor cutting edge is only slightly worn close to the nose radius. If the rotational direction of the milling cutter is reversed after the initial operation, the major and minor cutting edges will swap places and a “new”, slightly worn, major cutting edge can be used for machining. This is, of course, provided that an appropriate milling head is used for the new rotational direction. It is thus theoretically possible to significantly increase tool life. The principle of the proposed method for milling is shown in Fig. 4. 3.2. Proposed method for turning The upper part of Fig. 5 depicts a common situation during turning. Performing a facing operation followed by longitudinal turning using a single cutting tool often results in wear on both sides of the nose radius. This setup was unsuitable for experimental investigation due to the possibility of small variations between the different feed directions. Therefore the laboratory setup, illustrated in the lower part of Fig. 5, was used during this study. In this case the cutting tool is first fed in one direction during longitudinal turning. When the cutting tool is considered worn out, the feed direction is reversed. This setup, as well as that for the initial problem described, requires a suitable workpiece where the cutting tool can be engaged from both directions.
The milling experiments were performed by face milling duplex stainless steel SAF 2304. The workpieces were slabs with a width of approximately 42 mm and a length of approximately 405 mm. The limited length of the workpiece material meant that several engagements were necessary to achieve sufficient machining time. For all experiments, SEEX09T3AFTN inserts were used in an R220.53-0100-09-7A and L220.53-0100-09-7A milling head. Fig. 6 shows a view of the rake face of an insert. Note the change of the major cutting edge when varying the rotational direction of the milling cutter. The width of the wiper edge was approximately 1.5 mm during these experiments. A SAJO HMC-40 4-axis milling machine was used for the entire test. As the different inserts may have slightly different positions during milling, it was imperative that the inserts remained at the same position in the milling head throughout the test cycle. This can be difficult to achieve as the relative position of the inserts in regard to each other may change when the inserts were moved from a right- to a left-rotating milling head. During these experiments, we attempted to position the inserts in the best way possible to minimize these variations. This positional variation may influence the accuracy of the obtained results. The milling experiment began by using the right-rotating milling head with all 7 inserts. When the tool wear approached the flank wear criterion VB ¼ 300 mm on the major cutting edge, the inserts were shifted into the left-rotating milling head and the process was repeated. In both cases, the cutting parameters remained constant with the cutting speed vc ¼ 80 m/min, the depth of cut ap ¼ 2 mm and the feed per tooth fz ¼ 0.15 mm/tooth. These parameters were chosen to coincide with the appropriate range of cutting data for semi-finishing operations of SAF 2304 in industrial applications. Even though this experiment does not conclusively prove that the proposed method could be used for all cutting data combinations, it was still considered sufficient for investigating the general feasibility of the proposed method during the intended use. 4.2. Turning experiments
4. Experimental setup In order to investigate the potential of the proposed method, both milling and turning experiments were performed. All experiments were performed without using any cutting fluid as used cutting fluid is hazardous for the environment. Thus, if the
All turning experiments were performed through longitudinal turning of a bar of AISI 4340 with an initial diameter of 168 mm and a length of 960 mm. The experiments were conducted by initially turning the workpiece with feed direction towards the chuck of the lathe (referred to as “left feed direction”), as is often the case during
Fig. 4. Illustration of the principle of the proposed method for milling.
F. Schultheiss et al. / Journal of Cleaner Production 59 (2013) 298e307
301
Fig. 5. The proposed method for turning.
conventional turning. After the cutting tool had sustained sufficient wear, the feed direction was reversed (referred to as “right feed direction”). This change was achieved by machining several grooves close to the chuck in order to allow space for the cutting tool. As the workpiece was comparatively long, a center hole and tailstock were used during all turning experiments. The inserts were commercially available CNMG120412 coated cemented carbide inserts placed in a DCLNL3225P12 or DCLNR3225P12 tool holder, depending on the feed direction. During all turning experiments, a SMT Sajo Swedturn 500 lathe was used and great care was taken to minimize all possible sources of vibrations. In total, 5 turning experiments were conducted at a depth of cut ap ¼ 2.5 mm. The feed f and the cutting speed vc during these experiments varied as shown in Table 1. 5. Results and discussion The results from the milling and turning experiments are discussed separately as there were significant differences between the proposed methods and the experiments performed. However, the basic principle behind the reuse of inserts is the same for both machining cases. 5.1. Results obtained during milling It was found that tool wear on the major cutting edge was not limited to flank wear but also involved chipping of the major
cutting edge. In some cases, this chipping was severe. Significantly the wear on the wiper edge was mainly limited to flank wear, possibly in combination with some minor chipping of the cutting edge. This lack of wear implies that any negative influence on the surface roughness during face milling should be minimal. Fig. 7 shows the flank wear on the major cutting edge for each of the 7 inserts when machining using a right- and left-rotating milling cutter respectively. Note that the tool wear on the major cutting edge displays an almost identical pattern for the right- and the left-rotating milling head. At some locations the measurements seem to imply that the tool wear decreases as a function of the machining time (T). This is of course impossible, and may be attributed to measuring problems due to adhered workpiece material. This problem could possibly have been avoided by etching the inserts and thus removing the adhered workpiece material before measuring. However, this treatment would have had a significant influence on the adhesive wear of the cutting tools. Moreover, depending on the relation between the chemicals used during etching and the composition of the cutting tool, this procedure could have resulted in chemical wear of the cutting tool. It was accordingly decided that the inserts should be measured “as is” after each test cycle. This possible source of measuring errors should be remembered when analyzing the results. Furthermore, all inserts were measured in situ while still attached to the milling head in order to minimize the variation of the relative positions of the inserts in the milling cutter. Flank wear on the wiper face was also measured throughout the whole test cycle (Fig. 8). Note that this wear is significantly smaller than that on the major cutting edge. These results strengthen the feasibility of the proposed method, though they do not conclusively prove that it is generally applicable. At the beginning of these experiments, it was thought that reusing cutting tools might have a negative influence on the surface roughness of the workpiece. In order to investigate this assumption the surface roughness was measured throughout the milling Table 1 Cutting data used during the 5 turning experiments.
Fig. 6. View of the rake face of the cutting tool during milling.
Experiment
vc [m/min]
f [mm/rev]
ap [mm]
1 2 3 4 5
200 260 170 270 220
0.25 0.25 0.30 0.30 0.40
2.5 2.5 2.5 2.5 2.5
302
F. Schultheiss et al. / Journal of Cleaner Production 59 (2013) 298e307 VB 600
VB 600
[µm]
[µm]
Insert 1 Right-rotating Major cutting edge Insert 2 Insert 3 Insert 4 Insert 5 Insert 6 Insert 7
400
Insert 1 Left-rotating Major cutting edge Insert 2 Insert 3 Insert 4 Insert 5 Insert 6 Insert 7
500
400
300
200
200
100 0
0
2
4
6
8
0
10
T [min]
0
2
4
6
8
10
T [min]
Fig. 7. Flank wear VB on the major cutting edge as a function of the machining time T for each of the 7 inserts for the right- (left) and left-rotating (right) milling head.
was observed when the feed direction was switched. Fig. 11 shows examples of flank wear as seen on the flank face and tool nose for the left and the subsequent right feed directions. The main difference is that the secondary operation results in increased flank wear around the whole tool nose radius. Thus, when implementing the proposed method, the user should be vigilant in regard to tool wear on the minor cutting edge in order not to risk excessive wear. The flank wear (VB) as a function of the machining time (T) for each of the turning cases investigated is shown in Fig. 12. When the direction changed from the left to the right feed, slightly larger flank wear was obtained for most cases. As in the milling experiments, some measuring points could be interpreted as indicating negative tool wear, which of course is impossible. This effect should be regarded as a result of measuring errors due mainly to the difficulty of measuring flank wear in a repeatable fashion. Adhered workpiece material also impeded accurate measurements of the obtained tool wear. For the test at the highest cutting speed, vc ¼ 270 m/min, only one measuring point for each feed direction was obtained due to the quick wear of the cutting tool. Only minor variations in the surface roughness were observed when changing feed direction, as shown in Fig. 13. These results indicate that the proposed method does not have any major negative influence on the product quality from this perspective. The results show no major variations of the surface roughness appeared over time; such variations as did exist were minor. The results obtained may be used to model tool life as a function of different process parameters. Several different tool life equations have been developed. One of the more common equations, published by Colding (1981), and further discussed by Hägglund (2002), is shown in Equation (1).
experiment. The results in Fig. 9 demonstrate some variations in the surface roughness. The surface roughness appears to reach its highest values at the end of use of the right-rotating milling cutter and at the beginning of the test cycle using the left-rotating milling cutter. The surface roughness at the end of the left-rotating test cycle is only slightly worse than that obtained when using a new insert in a right-rotating milling cutter. Another way of illustrating the results can be found in Fig. 10. In this figure, VB is the mean flank wear on the major cutting edge, VBmax is the notch wear on the major cutting edge and VBwiper is the mean flank wear on the wiper face. The values displayed in Fig. 10 are the average value for all 7 inserts obtained at the end of each experimental series. All values are normalized to those obtained for the right-rotating milling cutter. Fig. 10 demonstrates that the flank wear on the wiper face, VBwiper, increases when proceeding from the initial right-rotating operation to the secondary left-rotating milling operation. The wiper face is the only part of the cutting edge that is engaged during both rotational directions. These results appear to support the method as plausibly sustainable. It may also be noted that the total flank wear on the major cutting edge appears to be smaller for the left-rotating milling cutter, even though the engagement time is slightly longer for this operation. The reason for this is currently unknown. We speculate that small variations between the geometry and coating of the different parts of the cutting tool and variations of the workpiece properties could be part of the explanation. Fig. 10 also illustrates the small difference between the surface roughness values obtained for the two machining cases. 5.2. Results obtained during turning For both feed directions, primarily flank wear was observed on the cutting tool. No significant change in the wear characteristics
vc ¼ e VB 160
VB 180
[µm]
[µm]
Insert 1 Right-rotating Wiper Insert 2 Insert 3 Insert 4 Insert 5 Insert 6 Insert 7
160 140 120 100
2
e ÞHÞ Kðlnðh4$M ðN0 L$lnðhe ÞÞ$lnðTÞ
120 100
Insert 1 Insert 2 Insert 3 Insert 4 Insert 5 Insert 6 Insert 7
80 60
60
40
40
20
20 0
2
4
6
(1)
Left-rotating Wiper
140
80
0
8
10
T [min]
0
0
2
4
6
8
10
T [min]
Fig. 8. Flank wear VB on the wiper face as a function of the machining time T for each of the 7 inserts for the right- (left) and left-rotating (right) milling head.
F. Schultheiss et al. / Journal of Cleaner Production 59 (2013) 298e307 Ri 12
Ri 12 [µm]
[µm]
Right-rotating
303
Left-rotating
10
10
Rmax 8
8
6
6
Rz Rmax
4
4 Rz
2
2
Ra
Ra 0
0
2
4
6
8 T [min]
0
0
2
4
6
8
10 T [min]
Fig. 9. Surface roughness as a function of the machining time T for the right- (left) and left-rotating (right) milling head.
In Equation (1), T is the tool life, vc is the cutting speed, and he is the equivalent chip thickness as defined by Woxén (1932). It has been shown that Woxén’s definition of he in Equation (2) may produce inaccurate results for small depths of cut. However, for the normal machining range, the error resulting from using Woxén’s definition is negligible (Ståhl and Schultheiss, 2012). This definition was considered appropriate for this application. K, H, M, N0, and L in Equation (1) are all model constants.
he ¼
ap $f ap rð1coskÞ þ sin k
k$r þ 2f
(2)
In Equation (2), ap is the depth of cut, f is the feed, r is the tool nose radius and k is the major cutting edge angle. If the flank wear criteria VB ¼ 300 mm is used, the following results may be obtained, assuming that the flank wear is linearly dependent on the machining time (Table 2). Table 3 shows the model constants obtained using this set of data. The model error may be calculated as the relative difference between the experimentally obtained tool life and that predicted by the model (Table 4). Even though the model error is comparatively large in some cases, it was still considered sufficiently accurate for a comparison between the left and right feed direction. As may be seen from the table, the modeling error is large for the secondary right feed direction. It could be speculated that this phenomenon is due to the proposed method of reusing cutting tools. No proof of this was obtained during this study. In general, the wear at the tool nose radius is significantly less than the flank wear on the major cutting edge for both feed
Fig. 10. Comparison of the results obtained for the right- and left-rotating milling cutter after 7.9 min and an additional 8.3 min of machining.
directions. It could be argued that if only the wear on the major cutting edge is investigated for each of the two feed directions, the two operations should have the same tool life, with some statistical variations. This is possible since the two operations could be viewed as two separate machining operations, not influencing each other. This is, however, an oversimplification of the problem investigated. Even though the tool wear is smaller at the nose of the cutting tool, tool wear at this location will result in an increased temperature during the machining process. The increase in temperature will affect the whole cutting tool, resulting in more rapid wear of the major cutting edge. Tool wear due to increased temperature will increase in significance during the secondary machining operation since the wear at the nose radius is larger for this operation. In theory, it is thus plausible that the tool life will be slightly shorter for the secondary machining operation. This notion could to some extent be corroborated by the results presented in Fig. 14. As may be seen in Fig. 14, the secondary machining operation in the right feed direction will generally result in a slightly lower tool life for an equivalent chip thickness. However, something happens when the cutting speed is increased, resulting in a longer tool life for the right feed direction. The reason for this phenomenon is currently undetermined, but we speculate that at these cutting speeds the difference in process temperature due to the wear at the nose of the cutting tool is insignificant when compared to the high process temperature generated. The modeling error shown earlier could influence these results, even though the experimental data by itself appears to indicate similar results. It is possible that the cutting data chosen for these experiments may not necessarily correspond to the optimum for this specific machining operation in terms of part cost, for example. Based on common knowledge within the machining field, it is unlikely that this deviation could result in a significantly different outcome, given that cutting parameters are varied within reasonable limits. In order to gain a better understanding of the potential of the proposed method, the following hypothetical case may be considered. Assume that the machining time is 0.75 min for each feed direction, as illustrated in Fig. 15. Also, assume that the tool life is 15 min and that 20 parts may be produced during a conventional process, using one tool for each feed direction before both tools are worn out. Based on the previous results, we estimate that by using the proposed new method 80% of the parts produced with two cutting tools in conventional turning could be produced using a single cutting tool. Further, when using two cutting tools for machining a single part during conventional machining, the cutting tools need to be indexed during the machining process, which is estimated as taking 0.33 min/part. The cutting tool also needs to be transported to the right position, which is estimated as taking
304
F. Schultheiss et al. / Journal of Cleaner Production 59 (2013) 298e307
Fig. 11. Flank wear as seen on the flank face (left) and at the tool nose (right) for the left (top) and the subsequent right feed directions (bottom).
0.15 min/part. Replacing a finished part with a new workpiece is estimated as taking 0.33 min/part. Changing the cutting tool, due to tool wear, is estimated as taking 3 min for a single cutting tool and 5 min for two cutting tools, due to the benefits of changing several
cutting tools simultaneously. A short summary of the different values used in this hypothetical case can be found in Table 5. Based on the estimated process parameters found in Table 5, the cycle time per part, t0, may be calculated according to Equation (3). VB
VB
VB
[µm] 300
[µm] 400
vc = 200 m/min f = 0.25 mm/rev ap = 2.5 mm
[µm] 300
vc = 260 m/min f = 0.25 mm/rev ap = 2.5 mm
vc = 170 m/min f = 0.30 mm/rev ap = 2.5 mm
300 200
200 200
100
100 100
0
10
20
0
30 T [min]
0
2
4
6
VB
VB
[µm] 300
Left feed direction Right feed direction
Left feed direction Right feed direction
Left feed direction Right feed direction 0
[µm] 300
vc = 270 m/min f = 0.30 mm/rev ap = 2.5 mm
200
200
100
100
0
8 T [min]
0
0.5
1
1.5
2 T [min]
5
10
vc = 220 m/min f = 0.40 mm/rev ap = 2.5 mm
Left feed direction Right feed direction
Left feed direction Right feed direction 0
0
0
0
0.5
1
1.5
Fig. 12. Flank wear VB as a function of the machining time T for different sets of process parameters.
2 T [min]
15
20 T [min]
F. Schultheiss et al. / Journal of Cleaner Production 59 (2013) 298e307 Ra [µm]
305
2
Table 4 Modeling error for the different turning cases investigated. vc f ap he Left feed direction [m/min] [mm/varv] [mm] [mm] Error Mean [%] error [%]
Right feed direction
1.5
Error [%]
Mean error [%]
200 260 170 270 220
16.35 10.49 13.23 7.84 3.00
10.18
1
0.5
0
vc = 200 m/min f = 0.25 mm/rev ap = 2.5 mm 0
0.25 0.25 0.30 0.30 0.40
2.5 2.5 2.5 2.5 2.5
0.19 0.19 0.22 0.22 0.29
1.26 7.56 5.49 9.51 7.38
6.24
Left feed direction Right feed direction 10
20
T 100
30 T [min]
[min]
Fig. 13. Example of Ra surface roughness, for both the left and subsequent right feed directions.
Table 2 Tool life for the left and right feed directions at varying cutting data if the tool wear criteria VB ¼ 300 mm is used. vc [m/min]
f [mm/varv]
ap [mm]
he [mm]
Left T [min]
T [min]
200 260 170 270 220
0.25 0.25 0.30 0.30 0.40
2.5 2.5 2.5 2.5 2.5
0.19 0.19 0.22 0.22 0.29
38.75 5.56 26.80 1.62 2.07
19.93 4.29 13.54 2.50 2.35
Red – he = 0.19 mm Blue – he = 0.22 mm Black – he = 0.29 mm
10
Right
T t0 ¼ ti þ tind þ tpos þ twch þ wch N
(3)
Based on Equation (3) the cycle time per part for both the conventional as well as the proposed new process was calculated as t0,conventional z 2.56 min and t0,new z 2.17 min. Thus, the cycle time per part is approximately 15% shorter for the proposed new process as compared to a conventional process. The new process will also result in a decrease in the amount of energy needed to produce a single part. The energy requirement E0 for a machined part is dependent on the cycle time according to Equation (4). Pm is the engine power used during the machining process and needs to be determined for each machining case. Even though the engine power may be determined for a specific machining case, this factor is not necessary to specify in this comparison as only the relative variation is sought. As discussed by Balogun and Mativenga (2013), the machine tool also requires a significant amount of energy even while not cutting, which is described by the x constant in this simplified comparison. The x constant depicts the amount of energy used by the lathe when not cutting, as compared to the value when cutting. In this hypothetical comparison, the x constant was estimated as x ¼ 0.70, based on the authors’ experience. This estimate is partially supported by Behrendt et al. (2012), who found that up to 20% of the total energy used during milling could be attributed to the cutting process. Several more advanced models for calculating energy requirements have been published. For instance, Balogun and Mativenga (2013) conducted a detailed investigation into the energy requirements
1 100
1000
vc [m/min]
Fig. 14. Taylor curves as based on the Colding equation. The solid and dashed lines correspond to the model values for the left and right feed directions. The squares and circles correspond to the experimental values for the left and right feed directions.
of different states during a machining process. Li et al. (2013) have also published an alternative model that uses a more empirical approach to model the process energy requirements. Although these more advanced models could be considered to produce more accurate results, the simplified model presented in this article is considered adequate for this simple comparison of two similar machining processes.
T E0 ¼ Pm $ ti þ x$ tind þ tpos þ twch þ wch N
When comparing the relative values of the two processes, we found that the energy consumption is reduced by approximately 12% by using the proposed new process as compared to a conventional process (Fig. 16). Even though this hypothetical case is based only on estimated values, it still illustrates how the proposed new method may
Table 3 Model constants obtained from the experimentally obtained data. Feed direction
K
H
M
N0
L
Left Right
5.9534 6.0315
2.5256 2.3855
1.0259 0.8608
0.4789 0.5554
0.2081 0.2089
(4)
Fig. 15. A hypothetical machining scenario.
306
F. Schultheiss et al. / Journal of Cleaner Production 59 (2013) 298e307
Table 5 Hypothetical process parameters used for comparing the conventional and proposed new process. Process parameter
Variable Conventional Proposed new process process
Number of parts per cutting edge Machining time per part [min/part] Tool indexing time per part [min/part] Tool transportation without cutting [min/part] Change of workpiece [min/part] Change of cutting tool due to tool wear [min]
N ti tind tpos
20 1.5 0.33 0.15
16 1.5 0 0.15
twch Ttch
0.33 5
0.33 3
Fig. 16. Relative cycle time and energy consumption of the proposed new process compared to the conventional process.
significantly reduce production time, and thus manufacturing costs, while simultaneously increasing the sustainability of the turning process through decreasing the energy requirement. 6. Conclusions This article has presented a novel approach to increasing cutting tool utilization in both turning and milling operations. This was done to significantly increase cutting tool utilization and thus increase the sustainability of the machining process. Through the use of different experimental cases, it has been proven that the proposed method is feasible for at least some machining applications. For the cases investigated, it was possible to obtain a tool life up to twice that of a conventional machining process. In addition, no significant influence on the resulting surface roughness was observed. Cutting tools are just a small part of the whole machining process that influences sustainability. However, no part of the machining process should be neglected as every part needs to be improved in order to reach the goal of sustainable production. This does not necessarily mean that increased tool utilization is the most urgent improvement during a machining process, but rather that it is one of a whole series of factors that need to be improved to achieve a sustainable process. Only a few machining cases were investigated during this study to determine whether the proposed method is a plausible option for increasing cutting tool utilization. Although no factors limiting the use of the proposed method were observed during this study, further investigations are needed in order to determine the limitations of the proposed method. Acknowledgment This research is a part of the ShortCut research project financed by the Swedish Foundation for Strategic Research SSF. It is also a part of the Sustainable Production Initiative SPI, a joint strategic
research program of Lund University and Chalmers University of Technology. The authors would also like to thank Seco Tools as well as Larssons i Bjärred Mekaniska Verkstad AB for their assistance during this study.
References Angerer, T., Luidold, S., Antrekowitsch, H., 2011. Technologien zum Recycling von Hartmetallschrotten (Teil 1). Erzmetall World of Metallurgy 64, 6e15. Armarego, E.J.A., Karri, V., Smith, A.J.R., 1994. Fundamental studies of driven and self-propelled rotary tool cutting processes e I. Theoretical investigation. International Journal of Machine Tools and Manufacture 34, 785e801. Balogun, V.A., Mativenga, P.T., 2013. Modelling of direct energy requirements in mechanical machining processes. Journal of Cleaner Production 41, 179e186. Behrendt, T., Zein, A., Min, S., 2012. Development of an energy consumption monitoring procedure for machine tools. CIRP Annals e Manufacturing Technology 61, 43e46. Bhosale, S.N., Mookherjee, S., Pardeshi, R.M., 1990. Current practices in tungsten extraction and recovery. High Temperature Materials and Processes 9, 147e162. Brundtland, G.H., 1987. Our Common Future, World Commission on Environment and Development. Oxford University Press, Oxford, UK. Bhushan, R.K., 2013. Optimization of cutting parameters for minimizing power consumption and maximizing tool life during machining of Al alloy SiC particle composites. Journal of Cleaner Production 39, 242e254. Colding, B., 1981. The machining productivity mountain and its wall of optimum productivity. In: 9th NAMRAC, pp. 37e42. Dabade, U.A., Joshi, S.S., Ramakrishnan, N., 2003. Analysis of surface roughness and chip cross-sectional area while machining with self-propelled round inserts milling cutter. Journal of Materials Processing Technology 132, 305e312. Dahmus, J.B., Gutowski, T.G., 2004. An environmental analysis of machining. In: ASME International Mechanical Engineering Congress (IMECE) and R&D Expo, Anaheim, USA, pp. 1e10. Despeisse, M., Oates, M.R., Ball, P.D., 2013. Sustainable manufacturing tactics and cross-functional factory modelling. Journal of Cleaner Production 42, 31e41. Duflou, J.R., Sutherland, J.W., Dornfeld, D., Herrmann, C., Jeswiet, J., Kara, S., Hauschild, M., Kellens, K., 2012. Towards energy and resource efficient manufacturing: a process and system approach. CIRP Annals e Manufacturing Technology 61, 587e609. Ezugwu, E.O., 2007. Improvements in the machining of aero-engine alloys using self-propelled rotary tooling technique. Journal of Materials Processing Technology 185, 60e71. Garetti, M., Taisch, M., 2012. Sustainable manufacturing: trends and research challenges. Production Planning & Control 23, 83e104. Hägglund, S., 2002. Global Optimization of Cutting Processes. Department of Product and Production Development, Chalmers University of Technology, Gothenburg, Sweden. Helu, M., Behmann, B., Meier, H., Dornfeld, D., Lanza, G., Schulze, V., 2012a. Total Cost Analysis of Process Time Reduction as a Green Machining Strategy, Leveraging Technology for a Sustainable World. Springer, Berlin Heidelberg, pp. 299e304. Helu, M., Behmann, B., Meier, H., Dornfeld, D., Lanza, G., Schulze, V., 2012b. Impact of green machining strategies on achieved surface quality. CIRP Annals e Manufacturing Technology 61, 55e58. Jayal, A.D., Badurdeen, F., Dillon, O.W., Jawahir, I.S., 2010. Sustainable manufacturing: modeling and optimization challenges at the product, process and system levels. CIRP Journal of Manufacturing Science and Technology 2, 144e152. Jovane, F., Yoshikawa, H., Alting, L., Boer, C.R., Westkamper, E., Williams, D., Tseng, M., Seliger, G., Paci, A.M., 2008. The incoming global technological and industrial revolution towards competitive sustainable manufacturing. CIRP Annals e Manufacturing Technology 57, 641e659. Kieffer, B.F., Lassner, E., 1994. Tungsten recycling in today’s environment. Berg- und Hüttenmännische Monatshefte 139, 340e345. Kuram, E., Ozcelik, B., Bayramoglu, M., Demirbas, E., Simsek, B.T., 2013. Optimization of cutting fluids and cutting parameters during end milling by using D-optimal design of experiments. Journal of Cleaner Production 42, 159e166. Larssons i Bjärred Mekaniska Verkstad AB, 2009. EcogreenmillÔ. Larssons i Bjärred Mekaniska Verkstad AB, Bjärred, Sweden. Lei, S.T., Liu, W.J., 2002. High-speed machining of titanium alloys using the driven rotary tool. International Journal of Machine Tools & Manufacture 42, 653e661. Li, L., Yan, J., Xing, Z., 2013. Energy requirements evaluation of milling machines based on thermal equilibrium and empirical modelling. Journal of Cleaner Production 52, 113e121. Pusavec, F., Krajnik, P., Kopac, J., 2010. Transitioning to sustainable production e part I: application on machining technologies. Journal of Cleaner Production 18, 174e184. Rajemi, M.F., Mativenga, P.T., Aramcharoen, A., 2010. Sustainable machining: selection of optimum turning conditions based on minimum energy considerations. Journal of Cleaner Production 18, 1059e1065. Sandvik Central Service, 1982. Vad är hårdmetall. Sandvik AB, Sandviken, Sweden. Schultheiss, F., Lundqvist, B., Ståhl, J.-E., 2012. Cost based process optimization by incrementally changing the cutting data during sustainable machining. Advanced Materials Research 576, 742e746.
F. Schultheiss et al. / Journal of Cleaner Production 59 (2013) 298e307 Seco Tools, 2010. Recycling Used Cemented Carbide Products. Seco Tools Inc., Troy, MI, USA. Shokrani, A., Dhokia, V., Newman, S.T., 2012. Environmentally conscious machining of difficult-to-cut materials with regard to cutting fluids. International Journal of Machine Tools and Manufacture 57, 83e101. Smith, G.R., 1994. Materials Flow of Tungsten in the United States, Bureau of Mines Information Circular 9388. United States Department of the Interior, USA. Smith, L., Ball, P., 2012. Steps towards sustainable manufacturing through modelling material, energy and waste flows. International Journal of Production Economics 140, 227e238. Ståhl, J.-E., 2011. The development of NEXT STEP beyond lean production: the link between technology and economics with focus on sustainable developments.
307
In: International Conference on Applied Mechanics, Materials and Manufacturing, Shenzhen, China. Ståhl, J.-E., 2012. Metal Cutting: Theories and Models. Division of Production and Materials Engineering, Lund University in Cooperation with Seco Tools AB, Lund/Fagersta, Sweden. Ståhl, J.-E., Schultheiss, F., 2012. Analytical calculation of the true equivalent chip thickness for cutting tools and its influence on the calculated tool life. Advanced Materials Research 576, 80e86. UNCED, 1992. Agenda 21: Programme of Action for Sustainable Development. United Nations, New York, USA. Woxén, R., 1932. Theory and an Equation for the Life of Lathe Tools. In: Ingenjörsvetenskapsakademin, Handling, 119. Sweden, Stockholm.
Contents lists available at SciVerse ScienceDirect
Journal of Cleaner Production journal homepage: www.elsevier.com/locate/jclepro
Sustainable machining through increasing the cutting tool utilization Fredrik Schultheiss*, Jinming Zhou, Elias Gröntoft, Jan-Eric Ståhl Lund University, Division of Production and Materials Engineering, 221 00 Lund, Sweden
a r t i c l e i n f o
a b s t r a c t
Article history: Received 31 January 2013 Received in revised form 10 June 2013 Accepted 30 June 2013 Available online 11 July 2013
Several previous articles have discussed different approaches to improving sustainability during machining operations. However, more effective utilization of cutting tools is an approach that has been overlooked in previous investigations. Increasing the effectiveness of cutting tool utilization decreases the need for new tools as well as the resources and energy needed to produce new cutting tools. The aim of this study was to maximize cutting tool utilization during machining operations without adversely affecting product quality, thus decreasing the environmental impact of machining operations. This was achieved by determining to what extent it is possible to increase total tool life by using previously worn tools in a secondary machining operation. For both the milling and turning cases investigated, experimental results showed that it is possible to increase the total tool life by approximately 50%e100% compared to equivalent conventional machining operations. The increase in tool life could decrease the production cycle time by approximately 15% and reduce energy consumption by 12% as compared to conventional machining processes. Ó 2013 Elsevier Ltd. All rights reserved.
Keywords: Machining Sustainable production Tool utilization Cutting tool
1. Introduction Sustainable development has received increasing attention in recent years. In 1987 the United Nations defined it as “development that meets the needs of the present without compromising the ability of future generations to meet their own needs” (Brundtland, 1987). Such development is needed in all parts of our modern society, including the production process. The concept of sustainable production emerged at the United Nations Conference on Environment and Development (UNCED, 1992) and has been recognized as a vital component in achieving sustainable development (Jovane et al., 2008). It requires a clear link between technology and economics (Ståhl, 2011). Sustainable development must go hand in hand with technological development in order to become an integral part of the production process. Garetti and Taisch (2012) argue that standards and norms are crucial factors for enabling a faster diffusion of new technological knowledge into modern production. Smith and Ball (2012) emphasize the importance of having a holistic view of the whole manufacturing process in order to be able to identify potential strategies for improving sustainability. Despeisse et al. (2013) present a set of tactics for achieving sustainable production, all of which could be used individually or in combination to increase the sustainability of
* Corresponding author. E-mail address: [email protected] (F. Schultheiss). 0959-6526/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jclepro.2013.06.058
production processes. Another important factor for obtaining sustainable production, discussed by Duflou et al. (2012), concerns the importance of choosing an appropriate manufacturing method for the specific part being produced. Overall, manufacturers need to evaluate process sustainability in addition to the traditional economic and technical aspects of their operations. Currently, there is no universally accepted definition of sustainable machining. Often this parameter is described in terms of processes that can result in improvements with regard to such matters as (i) reducing waste, (ii) reducing power consumption, and (iii) enhancing operational safety (Jayal et al., 2010). According to Pusavec et al. (2010), there are several different approaches to improving sustainability during machining operations. For example, the use of cutting fluid is often described as one of the main environmental hazards during machining (Kuram et al., 2013). Thus significant effort has been put into minimizing the use of cutting fluid even when machining difficult-to-machine materials (Shokrani et al., 2012). Another problem that has to be addressed is the quick wear of cutting tools. By optimizing tool life, it is often possible to improve the sustainability of a machining process while reducing the manufacturing cost. However, increased tool utilization may not always result in lowered manufacturing costs. There is a balance between tool life and the cost of both the tool and the machining process to obtain an economical tool life resulting in minimal manufacturing costs (Hägglund, 2002). Moreover, Helu et al. (2012b) caution that an increase in sustainability during machining may sometimes result in a reduced
F. Schultheiss et al. / Journal of Cleaner Production 59 (2013) 298e307
Fig. 1. Processing steps for obtaining tungsten carbide.
product quality, which could lead to poor sustainability over the whole product life cycle. Traditionally, machining processes are optimized by minimizing the manufacturing cost while still complying with technological limitations (Hägglund, 2002). Thus Schultheiss et al. (2012) presented a method for improving the machining process during normal production. But while in some cases, the economic goals correspond to the goal of sustainability, this is not always the case. In order to further consider environmental concerns, Rajemi et al. (2010) proposed a new model that takes process energy consumption into consideration while selecting process parameters during turning. A similar model was developed by Bhushan (2013). Both these models are well suited to improving the sustainability of a machining process. In an earlier article, Dahmus and Gutowski (2004) stated that the direct environmental influence of tooling is limited. Yet even though the influence of cutting tools on the overall sustainability of a machining process is limited, their influence should not be overlooked. All parts of the process need to be improved as much as possible to achieve truly sustainable machining processes. 2. Manufacture and recycling of coated cemented carbide inserts Coated cemented carbide inserts are manufactured using powder-metallurgy. Tungsten, which is an important part of the inserts, can be obtained from chemical processing of either scheelite (CaWO4) or tungstenite ((Fe, Mn)WO4). After several steps of chemical processing, pure tungsten is obtained. The next step is to obtain tungsten carbide through a process known as carburization (Ståhl, 2012). Fig. 1 briefly illustrates the processing steps for obtaining tungsten carbide. The overall energy requirement during this process is approximately 12 kWh/kg tungsten carbide, if manufactured from ore concentrates (Bhosale et al., 1990). As illustrated in Fig. 2, the process of manufacturing coated cemented carbide inserts begins by weighing appropriate amounts of the different components. The components are mixed together before being compressed into a green body. This is followed by sintering of the insert, which is a process in which the green body is heated in a protective atmosphere to a temperature of approximately 1400 C. Sintering eliminates the porosity of the cemented carbide insert. The next step is edge preparation through grinding and lapping of the insert to achieve the insert’s final shape. The final step is coating the insert with any of a number of different coatings depending on the desired characteristics. 2.1. Recycling of coated cemented carbide inserts There are two main methods of recycling coated cemented carbide cutting tools (Smith, 1994). The first, which involves chemical reprocessing of the cutting tools, is currently used for approximately 35% of all cemented carbide scrap. This process starts with mechanical crushing of the inserts to a powder, which is
299
then treated chemically. The tungsten carbide particles emerge intact and may then be crushed, washed, and dried to form a powder that can be used as raw material for the production of new cemented carbide inserts (Angerer et al., 2011). The second common recycling method, the Zn-method, in which cemented carbide inserts are treated with molten zinc, is currently used for about 25% of the cemented carbide scrap. Molten zinc creates an alloy with the cobalt binder phase, resulting in an increase in the volume of the binder phase, thereby shattering the carbide structure. The remains can then be crushed to a powder, which is in turn used as raw material when producing tungsten carbide powder for new inserts (Angerer et al., 2011). Depending on the size of the scrap input, the energy consumption for the Znmethod has been reported as approximately 2 kWh/kg of product (Kieffer and Lassner (1994)). The cost of the Zn-method is approximately 20%e35% less than that for other chemical processes, depending on the type of cemented carbide grades being recycled. Research shows that between 1955 and 1991 approximately 60% of the input tungsten was lost (Kieffer and Lassner, 1994). Since tungsten is a rare and finite resource, these losses could become an increasing concern over time. If the current consumption of tungsten continues, Seco Tools estimates that resources will be depleted within 40e100 years. By recycling cemented carbide scrap it may be possible to delay the time before the resources are depleted by approximately 35%, while also reducing CO2 emissions by approximately 40% (Seco Tools, 2010). If tool utilization could be increased by 100%, a significant amount of resources and energy could be saved. Fig. 3 illustrates the savings. A possible method for achieving this increase in tool life is discussed in the next section. 3. Increasing cutting tool utilization As discussed by Helu et al. (2012a), significant improvements in sustainability during machining processes can be obtained by optimizing process parameters. Helu et al. (2012b) prove that these improvements may not necessarily decrease the quality of the machined part. Through minor alterations to the current machining process, sustainability may be improved even further. During milling and turning operations, cutting tools are commonly used in a way that causes the major cutting edge to wear out, while the wear on the minor cutting edge is comparatively small or almost nonexistent. Tool life could be substantially increased by using the same insert in a secondary machining operation. A change in the tool setup would enable the previously lightly worn minor cutting edge to be used as a “new” major cutting edge. There are already commercial products available based on this principle (Larssons i Bjärred Mekaniska Verkstad AB, 2009), but little research has been published on the effects of using this method on the cutting tool or on the machined surface. An alternative method on increasing tool life involves what is known as the rotary tool cutting process, which has proven to be applicable to both turning (Armarego et al., 1994) and milling operations (Dabade et al., 2003). A rotary cutting tool has been shown to be capable of machining hard-to-machine materials, such as Ti6Al4V (Lei and Liu, 2002) and other aerospace materials (Ezugwu, 2007). Although the rotary tool cutting process shows great potential, it is limited to the use of round inserts. This leads to the
Fig. 2. Processing steps for manufacturing coated cemented carbide inserts (Sandvik Central Service, 1982).
300
F. Schultheiss et al. / Journal of Cleaner Production 59 (2013) 298e307
proposed method could be performed under dry cutting conditions, the advantage in terms of sustainability would be much greater. During these tests only coated cemented carbide inserts were used, primarily because these are generally the preferred choice for the materials being machined. During all experiments the tool wear was measured using an optical microscope. Surface roughness was measured using a MahrSurf PS1 portable surface roughness tester. 4.1. Milling experiments
Fig. 3. Tungsten consumption while machining a specific part using a conventional process compared to the proposed new process.
need for further studies of alternative methods of improving tool life for processes requiring other tool shapes. 3.1. Proposed method for milling It is common practice to rotate the milling cutter in only one direction during conventional production. This causes the majority of the tool wear to occur on the major cutting edge, while the minor cutting edge is only slightly worn close to the nose radius. If the rotational direction of the milling cutter is reversed after the initial operation, the major and minor cutting edges will swap places and a “new”, slightly worn, major cutting edge can be used for machining. This is, of course, provided that an appropriate milling head is used for the new rotational direction. It is thus theoretically possible to significantly increase tool life. The principle of the proposed method for milling is shown in Fig. 4. 3.2. Proposed method for turning The upper part of Fig. 5 depicts a common situation during turning. Performing a facing operation followed by longitudinal turning using a single cutting tool often results in wear on both sides of the nose radius. This setup was unsuitable for experimental investigation due to the possibility of small variations between the different feed directions. Therefore the laboratory setup, illustrated in the lower part of Fig. 5, was used during this study. In this case the cutting tool is first fed in one direction during longitudinal turning. When the cutting tool is considered worn out, the feed direction is reversed. This setup, as well as that for the initial problem described, requires a suitable workpiece where the cutting tool can be engaged from both directions.
The milling experiments were performed by face milling duplex stainless steel SAF 2304. The workpieces were slabs with a width of approximately 42 mm and a length of approximately 405 mm. The limited length of the workpiece material meant that several engagements were necessary to achieve sufficient machining time. For all experiments, SEEX09T3AFTN inserts were used in an R220.53-0100-09-7A and L220.53-0100-09-7A milling head. Fig. 6 shows a view of the rake face of an insert. Note the change of the major cutting edge when varying the rotational direction of the milling cutter. The width of the wiper edge was approximately 1.5 mm during these experiments. A SAJO HMC-40 4-axis milling machine was used for the entire test. As the different inserts may have slightly different positions during milling, it was imperative that the inserts remained at the same position in the milling head throughout the test cycle. This can be difficult to achieve as the relative position of the inserts in regard to each other may change when the inserts were moved from a right- to a left-rotating milling head. During these experiments, we attempted to position the inserts in the best way possible to minimize these variations. This positional variation may influence the accuracy of the obtained results. The milling experiment began by using the right-rotating milling head with all 7 inserts. When the tool wear approached the flank wear criterion VB ¼ 300 mm on the major cutting edge, the inserts were shifted into the left-rotating milling head and the process was repeated. In both cases, the cutting parameters remained constant with the cutting speed vc ¼ 80 m/min, the depth of cut ap ¼ 2 mm and the feed per tooth fz ¼ 0.15 mm/tooth. These parameters were chosen to coincide with the appropriate range of cutting data for semi-finishing operations of SAF 2304 in industrial applications. Even though this experiment does not conclusively prove that the proposed method could be used for all cutting data combinations, it was still considered sufficient for investigating the general feasibility of the proposed method during the intended use. 4.2. Turning experiments
4. Experimental setup In order to investigate the potential of the proposed method, both milling and turning experiments were performed. All experiments were performed without using any cutting fluid as used cutting fluid is hazardous for the environment. Thus, if the
All turning experiments were performed through longitudinal turning of a bar of AISI 4340 with an initial diameter of 168 mm and a length of 960 mm. The experiments were conducted by initially turning the workpiece with feed direction towards the chuck of the lathe (referred to as “left feed direction”), as is often the case during
Fig. 4. Illustration of the principle of the proposed method for milling.
F. Schultheiss et al. / Journal of Cleaner Production 59 (2013) 298e307
301
Fig. 5. The proposed method for turning.
conventional turning. After the cutting tool had sustained sufficient wear, the feed direction was reversed (referred to as “right feed direction”). This change was achieved by machining several grooves close to the chuck in order to allow space for the cutting tool. As the workpiece was comparatively long, a center hole and tailstock were used during all turning experiments. The inserts were commercially available CNMG120412 coated cemented carbide inserts placed in a DCLNL3225P12 or DCLNR3225P12 tool holder, depending on the feed direction. During all turning experiments, a SMT Sajo Swedturn 500 lathe was used and great care was taken to minimize all possible sources of vibrations. In total, 5 turning experiments were conducted at a depth of cut ap ¼ 2.5 mm. The feed f and the cutting speed vc during these experiments varied as shown in Table 1. 5. Results and discussion The results from the milling and turning experiments are discussed separately as there were significant differences between the proposed methods and the experiments performed. However, the basic principle behind the reuse of inserts is the same for both machining cases. 5.1. Results obtained during milling It was found that tool wear on the major cutting edge was not limited to flank wear but also involved chipping of the major
cutting edge. In some cases, this chipping was severe. Significantly the wear on the wiper edge was mainly limited to flank wear, possibly in combination with some minor chipping of the cutting edge. This lack of wear implies that any negative influence on the surface roughness during face milling should be minimal. Fig. 7 shows the flank wear on the major cutting edge for each of the 7 inserts when machining using a right- and left-rotating milling cutter respectively. Note that the tool wear on the major cutting edge displays an almost identical pattern for the right- and the left-rotating milling head. At some locations the measurements seem to imply that the tool wear decreases as a function of the machining time (T). This is of course impossible, and may be attributed to measuring problems due to adhered workpiece material. This problem could possibly have been avoided by etching the inserts and thus removing the adhered workpiece material before measuring. However, this treatment would have had a significant influence on the adhesive wear of the cutting tools. Moreover, depending on the relation between the chemicals used during etching and the composition of the cutting tool, this procedure could have resulted in chemical wear of the cutting tool. It was accordingly decided that the inserts should be measured “as is” after each test cycle. This possible source of measuring errors should be remembered when analyzing the results. Furthermore, all inserts were measured in situ while still attached to the milling head in order to minimize the variation of the relative positions of the inserts in the milling cutter. Flank wear on the wiper face was also measured throughout the whole test cycle (Fig. 8). Note that this wear is significantly smaller than that on the major cutting edge. These results strengthen the feasibility of the proposed method, though they do not conclusively prove that it is generally applicable. At the beginning of these experiments, it was thought that reusing cutting tools might have a negative influence on the surface roughness of the workpiece. In order to investigate this assumption the surface roughness was measured throughout the milling Table 1 Cutting data used during the 5 turning experiments.
Fig. 6. View of the rake face of the cutting tool during milling.
Experiment
vc [m/min]
f [mm/rev]
ap [mm]
1 2 3 4 5
200 260 170 270 220
0.25 0.25 0.30 0.30 0.40
2.5 2.5 2.5 2.5 2.5
302
F. Schultheiss et al. / Journal of Cleaner Production 59 (2013) 298e307 VB 600
VB 600
[µm]
[µm]
Insert 1 Right-rotating Major cutting edge Insert 2 Insert 3 Insert 4 Insert 5 Insert 6 Insert 7
400
Insert 1 Left-rotating Major cutting edge Insert 2 Insert 3 Insert 4 Insert 5 Insert 6 Insert 7
500
400
300
200
200
100 0
0
2
4
6
8
0
10
T [min]
0
2
4
6
8
10
T [min]
Fig. 7. Flank wear VB on the major cutting edge as a function of the machining time T for each of the 7 inserts for the right- (left) and left-rotating (right) milling head.
was observed when the feed direction was switched. Fig. 11 shows examples of flank wear as seen on the flank face and tool nose for the left and the subsequent right feed directions. The main difference is that the secondary operation results in increased flank wear around the whole tool nose radius. Thus, when implementing the proposed method, the user should be vigilant in regard to tool wear on the minor cutting edge in order not to risk excessive wear. The flank wear (VB) as a function of the machining time (T) for each of the turning cases investigated is shown in Fig. 12. When the direction changed from the left to the right feed, slightly larger flank wear was obtained for most cases. As in the milling experiments, some measuring points could be interpreted as indicating negative tool wear, which of course is impossible. This effect should be regarded as a result of measuring errors due mainly to the difficulty of measuring flank wear in a repeatable fashion. Adhered workpiece material also impeded accurate measurements of the obtained tool wear. For the test at the highest cutting speed, vc ¼ 270 m/min, only one measuring point for each feed direction was obtained due to the quick wear of the cutting tool. Only minor variations in the surface roughness were observed when changing feed direction, as shown in Fig. 13. These results indicate that the proposed method does not have any major negative influence on the product quality from this perspective. The results show no major variations of the surface roughness appeared over time; such variations as did exist were minor. The results obtained may be used to model tool life as a function of different process parameters. Several different tool life equations have been developed. One of the more common equations, published by Colding (1981), and further discussed by Hägglund (2002), is shown in Equation (1).
experiment. The results in Fig. 9 demonstrate some variations in the surface roughness. The surface roughness appears to reach its highest values at the end of use of the right-rotating milling cutter and at the beginning of the test cycle using the left-rotating milling cutter. The surface roughness at the end of the left-rotating test cycle is only slightly worse than that obtained when using a new insert in a right-rotating milling cutter. Another way of illustrating the results can be found in Fig. 10. In this figure, VB is the mean flank wear on the major cutting edge, VBmax is the notch wear on the major cutting edge and VBwiper is the mean flank wear on the wiper face. The values displayed in Fig. 10 are the average value for all 7 inserts obtained at the end of each experimental series. All values are normalized to those obtained for the right-rotating milling cutter. Fig. 10 demonstrates that the flank wear on the wiper face, VBwiper, increases when proceeding from the initial right-rotating operation to the secondary left-rotating milling operation. The wiper face is the only part of the cutting edge that is engaged during both rotational directions. These results appear to support the method as plausibly sustainable. It may also be noted that the total flank wear on the major cutting edge appears to be smaller for the left-rotating milling cutter, even though the engagement time is slightly longer for this operation. The reason for this is currently unknown. We speculate that small variations between the geometry and coating of the different parts of the cutting tool and variations of the workpiece properties could be part of the explanation. Fig. 10 also illustrates the small difference between the surface roughness values obtained for the two machining cases. 5.2. Results obtained during turning For both feed directions, primarily flank wear was observed on the cutting tool. No significant change in the wear characteristics
vc ¼ e VB 160
VB 180
[µm]
[µm]
Insert 1 Right-rotating Wiper Insert 2 Insert 3 Insert 4 Insert 5 Insert 6 Insert 7
160 140 120 100
2
e ÞHÞ Kðlnðh4$M ðN0 L$lnðhe ÞÞ$lnðTÞ
120 100
Insert 1 Insert 2 Insert 3 Insert 4 Insert 5 Insert 6 Insert 7
80 60
60
40
40
20
20 0
2
4
6
(1)
Left-rotating Wiper
140
80
0
8
10
T [min]
0
0
2
4
6
8
10
T [min]
Fig. 8. Flank wear VB on the wiper face as a function of the machining time T for each of the 7 inserts for the right- (left) and left-rotating (right) milling head.
F. Schultheiss et al. / Journal of Cleaner Production 59 (2013) 298e307 Ri 12
Ri 12 [µm]
[µm]
Right-rotating
303
Left-rotating
10
10
Rmax 8
8
6
6
Rz Rmax
4
4 Rz
2
2
Ra
Ra 0
0
2
4
6
8 T [min]
0
0
2
4
6
8
10 T [min]
Fig. 9. Surface roughness as a function of the machining time T for the right- (left) and left-rotating (right) milling head.
In Equation (1), T is the tool life, vc is the cutting speed, and he is the equivalent chip thickness as defined by Woxén (1932). It has been shown that Woxén’s definition of he in Equation (2) may produce inaccurate results for small depths of cut. However, for the normal machining range, the error resulting from using Woxén’s definition is negligible (Ståhl and Schultheiss, 2012). This definition was considered appropriate for this application. K, H, M, N0, and L in Equation (1) are all model constants.
he ¼
ap $f ap rð1coskÞ þ sin k
k$r þ 2f
(2)
In Equation (2), ap is the depth of cut, f is the feed, r is the tool nose radius and k is the major cutting edge angle. If the flank wear criteria VB ¼ 300 mm is used, the following results may be obtained, assuming that the flank wear is linearly dependent on the machining time (Table 2). Table 3 shows the model constants obtained using this set of data. The model error may be calculated as the relative difference between the experimentally obtained tool life and that predicted by the model (Table 4). Even though the model error is comparatively large in some cases, it was still considered sufficiently accurate for a comparison between the left and right feed direction. As may be seen from the table, the modeling error is large for the secondary right feed direction. It could be speculated that this phenomenon is due to the proposed method of reusing cutting tools. No proof of this was obtained during this study. In general, the wear at the tool nose radius is significantly less than the flank wear on the major cutting edge for both feed
Fig. 10. Comparison of the results obtained for the right- and left-rotating milling cutter after 7.9 min and an additional 8.3 min of machining.
directions. It could be argued that if only the wear on the major cutting edge is investigated for each of the two feed directions, the two operations should have the same tool life, with some statistical variations. This is possible since the two operations could be viewed as two separate machining operations, not influencing each other. This is, however, an oversimplification of the problem investigated. Even though the tool wear is smaller at the nose of the cutting tool, tool wear at this location will result in an increased temperature during the machining process. The increase in temperature will affect the whole cutting tool, resulting in more rapid wear of the major cutting edge. Tool wear due to increased temperature will increase in significance during the secondary machining operation since the wear at the nose radius is larger for this operation. In theory, it is thus plausible that the tool life will be slightly shorter for the secondary machining operation. This notion could to some extent be corroborated by the results presented in Fig. 14. As may be seen in Fig. 14, the secondary machining operation in the right feed direction will generally result in a slightly lower tool life for an equivalent chip thickness. However, something happens when the cutting speed is increased, resulting in a longer tool life for the right feed direction. The reason for this phenomenon is currently undetermined, but we speculate that at these cutting speeds the difference in process temperature due to the wear at the nose of the cutting tool is insignificant when compared to the high process temperature generated. The modeling error shown earlier could influence these results, even though the experimental data by itself appears to indicate similar results. It is possible that the cutting data chosen for these experiments may not necessarily correspond to the optimum for this specific machining operation in terms of part cost, for example. Based on common knowledge within the machining field, it is unlikely that this deviation could result in a significantly different outcome, given that cutting parameters are varied within reasonable limits. In order to gain a better understanding of the potential of the proposed method, the following hypothetical case may be considered. Assume that the machining time is 0.75 min for each feed direction, as illustrated in Fig. 15. Also, assume that the tool life is 15 min and that 20 parts may be produced during a conventional process, using one tool for each feed direction before both tools are worn out. Based on the previous results, we estimate that by using the proposed new method 80% of the parts produced with two cutting tools in conventional turning could be produced using a single cutting tool. Further, when using two cutting tools for machining a single part during conventional machining, the cutting tools need to be indexed during the machining process, which is estimated as taking 0.33 min/part. The cutting tool also needs to be transported to the right position, which is estimated as taking
304
F. Schultheiss et al. / Journal of Cleaner Production 59 (2013) 298e307
Fig. 11. Flank wear as seen on the flank face (left) and at the tool nose (right) for the left (top) and the subsequent right feed directions (bottom).
0.15 min/part. Replacing a finished part with a new workpiece is estimated as taking 0.33 min/part. Changing the cutting tool, due to tool wear, is estimated as taking 3 min for a single cutting tool and 5 min for two cutting tools, due to the benefits of changing several
cutting tools simultaneously. A short summary of the different values used in this hypothetical case can be found in Table 5. Based on the estimated process parameters found in Table 5, the cycle time per part, t0, may be calculated according to Equation (3). VB
VB
VB
[µm] 300
[µm] 400
vc = 200 m/min f = 0.25 mm/rev ap = 2.5 mm
[µm] 300
vc = 260 m/min f = 0.25 mm/rev ap = 2.5 mm
vc = 170 m/min f = 0.30 mm/rev ap = 2.5 mm
300 200
200 200
100
100 100
0
10
20
0
30 T [min]
0
2
4
6
VB
VB
[µm] 300
Left feed direction Right feed direction
Left feed direction Right feed direction
Left feed direction Right feed direction 0
[µm] 300
vc = 270 m/min f = 0.30 mm/rev ap = 2.5 mm
200
200
100
100
0
8 T [min]
0
0.5
1
1.5
2 T [min]
5
10
vc = 220 m/min f = 0.40 mm/rev ap = 2.5 mm
Left feed direction Right feed direction
Left feed direction Right feed direction 0
0
0
0
0.5
1
1.5
Fig. 12. Flank wear VB as a function of the machining time T for different sets of process parameters.
2 T [min]
15
20 T [min]
F. Schultheiss et al. / Journal of Cleaner Production 59 (2013) 298e307 Ra [µm]
305
2
Table 4 Modeling error for the different turning cases investigated. vc f ap he Left feed direction [m/min] [mm/varv] [mm] [mm] Error Mean [%] error [%]
Right feed direction
1.5
Error [%]
Mean error [%]
200 260 170 270 220
16.35 10.49 13.23 7.84 3.00
10.18
1
0.5
0
vc = 200 m/min f = 0.25 mm/rev ap = 2.5 mm 0
0.25 0.25 0.30 0.30 0.40
2.5 2.5 2.5 2.5 2.5
0.19 0.19 0.22 0.22 0.29
1.26 7.56 5.49 9.51 7.38
6.24
Left feed direction Right feed direction 10
20
T 100
30 T [min]
[min]
Fig. 13. Example of Ra surface roughness, for both the left and subsequent right feed directions.
Table 2 Tool life for the left and right feed directions at varying cutting data if the tool wear criteria VB ¼ 300 mm is used. vc [m/min]
f [mm/varv]
ap [mm]
he [mm]
Left T [min]
T [min]
200 260 170 270 220
0.25 0.25 0.30 0.30 0.40
2.5 2.5 2.5 2.5 2.5
0.19 0.19 0.22 0.22 0.29
38.75 5.56 26.80 1.62 2.07
19.93 4.29 13.54 2.50 2.35
Red – he = 0.19 mm Blue – he = 0.22 mm Black – he = 0.29 mm
10
Right
T t0 ¼ ti þ tind þ tpos þ twch þ wch N
(3)
Based on Equation (3) the cycle time per part for both the conventional as well as the proposed new process was calculated as t0,conventional z 2.56 min and t0,new z 2.17 min. Thus, the cycle time per part is approximately 15% shorter for the proposed new process as compared to a conventional process. The new process will also result in a decrease in the amount of energy needed to produce a single part. The energy requirement E0 for a machined part is dependent on the cycle time according to Equation (4). Pm is the engine power used during the machining process and needs to be determined for each machining case. Even though the engine power may be determined for a specific machining case, this factor is not necessary to specify in this comparison as only the relative variation is sought. As discussed by Balogun and Mativenga (2013), the machine tool also requires a significant amount of energy even while not cutting, which is described by the x constant in this simplified comparison. The x constant depicts the amount of energy used by the lathe when not cutting, as compared to the value when cutting. In this hypothetical comparison, the x constant was estimated as x ¼ 0.70, based on the authors’ experience. This estimate is partially supported by Behrendt et al. (2012), who found that up to 20% of the total energy used during milling could be attributed to the cutting process. Several more advanced models for calculating energy requirements have been published. For instance, Balogun and Mativenga (2013) conducted a detailed investigation into the energy requirements
1 100
1000
vc [m/min]
Fig. 14. Taylor curves as based on the Colding equation. The solid and dashed lines correspond to the model values for the left and right feed directions. The squares and circles correspond to the experimental values for the left and right feed directions.
of different states during a machining process. Li et al. (2013) have also published an alternative model that uses a more empirical approach to model the process energy requirements. Although these more advanced models could be considered to produce more accurate results, the simplified model presented in this article is considered adequate for this simple comparison of two similar machining processes.
T E0 ¼ Pm $ ti þ x$ tind þ tpos þ twch þ wch N
When comparing the relative values of the two processes, we found that the energy consumption is reduced by approximately 12% by using the proposed new process as compared to a conventional process (Fig. 16). Even though this hypothetical case is based only on estimated values, it still illustrates how the proposed new method may
Table 3 Model constants obtained from the experimentally obtained data. Feed direction
K
H
M
N0
L
Left Right
5.9534 6.0315
2.5256 2.3855
1.0259 0.8608
0.4789 0.5554
0.2081 0.2089
(4)
Fig. 15. A hypothetical machining scenario.
306
F. Schultheiss et al. / Journal of Cleaner Production 59 (2013) 298e307
Table 5 Hypothetical process parameters used for comparing the conventional and proposed new process. Process parameter
Variable Conventional Proposed new process process
Number of parts per cutting edge Machining time per part [min/part] Tool indexing time per part [min/part] Tool transportation without cutting [min/part] Change of workpiece [min/part] Change of cutting tool due to tool wear [min]
N ti tind tpos
20 1.5 0.33 0.15
16 1.5 0 0.15
twch Ttch
0.33 5
0.33 3
Fig. 16. Relative cycle time and energy consumption of the proposed new process compared to the conventional process.
significantly reduce production time, and thus manufacturing costs, while simultaneously increasing the sustainability of the turning process through decreasing the energy requirement. 6. Conclusions This article has presented a novel approach to increasing cutting tool utilization in both turning and milling operations. This was done to significantly increase cutting tool utilization and thus increase the sustainability of the machining process. Through the use of different experimental cases, it has been proven that the proposed method is feasible for at least some machining applications. For the cases investigated, it was possible to obtain a tool life up to twice that of a conventional machining process. In addition, no significant influence on the resulting surface roughness was observed. Cutting tools are just a small part of the whole machining process that influences sustainability. However, no part of the machining process should be neglected as every part needs to be improved in order to reach the goal of sustainable production. This does not necessarily mean that increased tool utilization is the most urgent improvement during a machining process, but rather that it is one of a whole series of factors that need to be improved to achieve a sustainable process. Only a few machining cases were investigated during this study to determine whether the proposed method is a plausible option for increasing cutting tool utilization. Although no factors limiting the use of the proposed method were observed during this study, further investigations are needed in order to determine the limitations of the proposed method. Acknowledgment This research is a part of the ShortCut research project financed by the Swedish Foundation for Strategic Research SSF. It is also a part of the Sustainable Production Initiative SPI, a joint strategic
research program of Lund University and Chalmers University of Technology. The authors would also like to thank Seco Tools as well as Larssons i Bjärred Mekaniska Verkstad AB for their assistance during this study.
References Angerer, T., Luidold, S., Antrekowitsch, H., 2011. Technologien zum Recycling von Hartmetallschrotten (Teil 1). Erzmetall World of Metallurgy 64, 6e15. Armarego, E.J.A., Karri, V., Smith, A.J.R., 1994. Fundamental studies of driven and self-propelled rotary tool cutting processes e I. Theoretical investigation. International Journal of Machine Tools and Manufacture 34, 785e801. Balogun, V.A., Mativenga, P.T., 2013. Modelling of direct energy requirements in mechanical machining processes. Journal of Cleaner Production 41, 179e186. Behrendt, T., Zein, A., Min, S., 2012. Development of an energy consumption monitoring procedure for machine tools. CIRP Annals e Manufacturing Technology 61, 43e46. Bhosale, S.N., Mookherjee, S., Pardeshi, R.M., 1990. Current practices in tungsten extraction and recovery. High Temperature Materials and Processes 9, 147e162. Brundtland, G.H., 1987. Our Common Future, World Commission on Environment and Development. Oxford University Press, Oxford, UK. Bhushan, R.K., 2013. Optimization of cutting parameters for minimizing power consumption and maximizing tool life during machining of Al alloy SiC particle composites. Journal of Cleaner Production 39, 242e254. Colding, B., 1981. The machining productivity mountain and its wall of optimum productivity. In: 9th NAMRAC, pp. 37e42. Dabade, U.A., Joshi, S.S., Ramakrishnan, N., 2003. Analysis of surface roughness and chip cross-sectional area while machining with self-propelled round inserts milling cutter. Journal of Materials Processing Technology 132, 305e312. Dahmus, J.B., Gutowski, T.G., 2004. An environmental analysis of machining. In: ASME International Mechanical Engineering Congress (IMECE) and R&D Expo, Anaheim, USA, pp. 1e10. Despeisse, M., Oates, M.R., Ball, P.D., 2013. Sustainable manufacturing tactics and cross-functional factory modelling. Journal of Cleaner Production 42, 31e41. Duflou, J.R., Sutherland, J.W., Dornfeld, D., Herrmann, C., Jeswiet, J., Kara, S., Hauschild, M., Kellens, K., 2012. Towards energy and resource efficient manufacturing: a process and system approach. CIRP Annals e Manufacturing Technology 61, 587e609. Ezugwu, E.O., 2007. Improvements in the machining of aero-engine alloys using self-propelled rotary tooling technique. Journal of Materials Processing Technology 185, 60e71. Garetti, M., Taisch, M., 2012. Sustainable manufacturing: trends and research challenges. Production Planning & Control 23, 83e104. Hägglund, S., 2002. Global Optimization of Cutting Processes. Department of Product and Production Development, Chalmers University of Technology, Gothenburg, Sweden. Helu, M., Behmann, B., Meier, H., Dornfeld, D., Lanza, G., Schulze, V., 2012a. Total Cost Analysis of Process Time Reduction as a Green Machining Strategy, Leveraging Technology for a Sustainable World. Springer, Berlin Heidelberg, pp. 299e304. Helu, M., Behmann, B., Meier, H., Dornfeld, D., Lanza, G., Schulze, V., 2012b. Impact of green machining strategies on achieved surface quality. CIRP Annals e Manufacturing Technology 61, 55e58. Jayal, A.D., Badurdeen, F., Dillon, O.W., Jawahir, I.S., 2010. Sustainable manufacturing: modeling and optimization challenges at the product, process and system levels. CIRP Journal of Manufacturing Science and Technology 2, 144e152. Jovane, F., Yoshikawa, H., Alting, L., Boer, C.R., Westkamper, E., Williams, D., Tseng, M., Seliger, G., Paci, A.M., 2008. The incoming global technological and industrial revolution towards competitive sustainable manufacturing. CIRP Annals e Manufacturing Technology 57, 641e659. Kieffer, B.F., Lassner, E., 1994. Tungsten recycling in today’s environment. Berg- und Hüttenmännische Monatshefte 139, 340e345. Kuram, E., Ozcelik, B., Bayramoglu, M., Demirbas, E., Simsek, B.T., 2013. Optimization of cutting fluids and cutting parameters during end milling by using D-optimal design of experiments. Journal of Cleaner Production 42, 159e166. Larssons i Bjärred Mekaniska Verkstad AB, 2009. EcogreenmillÔ. Larssons i Bjärred Mekaniska Verkstad AB, Bjärred, Sweden. Lei, S.T., Liu, W.J., 2002. High-speed machining of titanium alloys using the driven rotary tool. International Journal of Machine Tools & Manufacture 42, 653e661. Li, L., Yan, J., Xing, Z., 2013. Energy requirements evaluation of milling machines based on thermal equilibrium and empirical modelling. Journal of Cleaner Production 52, 113e121. Pusavec, F., Krajnik, P., Kopac, J., 2010. Transitioning to sustainable production e part I: application on machining technologies. Journal of Cleaner Production 18, 174e184. Rajemi, M.F., Mativenga, P.T., Aramcharoen, A., 2010. Sustainable machining: selection of optimum turning conditions based on minimum energy considerations. Journal of Cleaner Production 18, 1059e1065. Sandvik Central Service, 1982. Vad är hårdmetall. Sandvik AB, Sandviken, Sweden. Schultheiss, F., Lundqvist, B., Ståhl, J.-E., 2012. Cost based process optimization by incrementally changing the cutting data during sustainable machining. Advanced Materials Research 576, 742e746.
F. Schultheiss et al. / Journal of Cleaner Production 59 (2013) 298e307 Seco Tools, 2010. Recycling Used Cemented Carbide Products. Seco Tools Inc., Troy, MI, USA. Shokrani, A., Dhokia, V., Newman, S.T., 2012. Environmentally conscious machining of difficult-to-cut materials with regard to cutting fluids. International Journal of Machine Tools and Manufacture 57, 83e101. Smith, G.R., 1994. Materials Flow of Tungsten in the United States, Bureau of Mines Information Circular 9388. United States Department of the Interior, USA. Smith, L., Ball, P., 2012. Steps towards sustainable manufacturing through modelling material, energy and waste flows. International Journal of Production Economics 140, 227e238. Ståhl, J.-E., 2011. The development of NEXT STEP beyond lean production: the link between technology and economics with focus on sustainable developments.
307
In: International Conference on Applied Mechanics, Materials and Manufacturing, Shenzhen, China. Ståhl, J.-E., 2012. Metal Cutting: Theories and Models. Division of Production and Materials Engineering, Lund University in Cooperation with Seco Tools AB, Lund/Fagersta, Sweden. Ståhl, J.-E., Schultheiss, F., 2012. Analytical calculation of the true equivalent chip thickness for cutting tools and its influence on the calculated tool life. Advanced Materials Research 576, 80e86. UNCED, 1992. Agenda 21: Programme of Action for Sustainable Development. United Nations, New York, USA. Woxén, R., 1932. Theory and an Equation for the Life of Lathe Tools. In: Ingenjörsvetenskapsakademin, Handling, 119. Sweden, Stockholm.