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Investigation and improvement of wear nonuniformity of diamond tools in sawing granite
International Journal of Refractory Metals & Hard Materials 83 (2019) 104961
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Investigation and improvement of wear nonuniformity of diamond tools in sawing granite ⁎
T
⁎
Peiyu Donga,b, Bo Huanga,b, , Jinsheng Zhanga,b, , Heng Zhanga,b a Key Laboratory of High-Efficiency and Clean Mechanical Manufacture (Ministry of Education), School of Mechanical Engineering, Shandong University, Jinan 250061, China b Research Centre for Stone Engineering (Shandong Province), Jinan 250061, China
A R T I C LE I N FO
A B S T R A C T
Keywords: Diamond tool Wear characteristics Maximum undeformed chip thickness Diamond abnormal failure Wear uniformity
Sawing experiments were accomplished to discuss the wear characteristics at different parts of diamond tools in the process of sawing granite in this paper. Optical microscopy, scanning electron microscopy and 3D laser microscope were main detection means for the morphology of diamond tools. Synthetic investigation on the abrasion performance of segments was developed from aspects of the wear appearance of diamond particle and metal bond, the particle protrusion height and the residual height of segments. The results indicated that smaller residual height and larger proportion of macro-fractured and pull out crystal were exhibited at the front end of traditional diamond segment compared with the rear end. Morphology characteristics of diamond tools demonstrated different abrasion mechanism, flush erosion and cavitation was the main wear mechanism for the front end, while abrasive wear was the main wear mechanism for the rear end. Maximum undeformed chip thickness per diamond particle for the front end was larger than that of the rear end due to the existence of slot, the same was true for the load of single diamond particle. By reasonably matching of diamond particles and matrix bond, the abnormal failure efficiency of the diamond particles at the front of the segment was effectively reduced and the wear uniformity of the saw tooth surface was greatly improved. Suggestions on the design of diamond tools and test verification were put forward in the end.
1. Introduction Diamond circular saws have been commonly adopted in stone processing industry with extensive application of natural granite material as decoration materials and structural engineering due to its aesthetic, physical and mechanical properties [1]. Segments made of diamond crystals and metal bond are the prime sawing tools for circular saw [2]. Granite minerals are usually removed in the form of chip through the interaction of diamond particles and workpiece, therefore, it is of great significance to understand the mechanism in stone processing. A model of sawing stone with disk-like tools was proposed by Tonshoff and Warnecke [3] and it turned out that the elastoplastic deformation occurring to the workpiece caused by diamond particles and the friction between bond and particle, bond and sawdust and workpiece and particle resulted in the interaction between the tool and the workpiece. The sawing force and energy were quantitatively analyzed and the cutting mechanism of granite sawing by diamond segments for circular
saw was investigated by Xu [4], revealing that the energy consumption depended mainly on sliding friction and the removal of material was primarily govern by brittle fracture. Widespread attention has been attracted on chip morphology as an important parameter reflecting sawing process and mechanism. Jerro et al. [5] defined the theoretical chip morphology through the area and thickness of the chip in the process of sawing by circular saw, and established the connection between sawing parameters and cutting force. Turchetta [6] derived the relationship between the tool parameters and the chip geometry of a single particle, theoretically analyzed and calculated the average chip thickness per particle, and modelled the cutting force per particle as a power function of cutting thickness. Konstanty [7] proposed a model of diamond tools sawing natural rocks under different sawing forms (diamond frame and circular saw), quantified the formation and removal of sawdust and presented hm (the maximum chip thickness) as a preliminary evaluation index of matrix wear. Diamond tool wear, inevitably occurring due to the complexity and multidimensionality of sawing process, has a great influence on the cost
⁎ Corresponding authors at: Key Laboratory of High-Efficiency and Clean Mechanical Manufacture (Ministry of Education), School of Mechanical Engineering, Shandong University, Jinan 250061, China. E-mail addresses: [email protected] (B. Huang), [email protected] (J. Zhang).
https://doi.org/10.1016/j.ijrmhm.2019.05.007 Received 15 February 2019; Received in revised form 7 May 2019; Accepted 8 May 2019 Available online 10 May 2019 0263-4368/ © 2019 Elsevier Ltd. All rights reserved.
International Journal of Refractory Metals & Hard Materials 83 (2019) 104961
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sawing, and it turned out that an increase in diamond concentration and the proportion of WeCo lead to the decrease of power consumption, sawing force and specific wear of segment. The theoretical model of diamond tool wear in sawing was proposed by Ilio and Togna [18] for the wear prediction problem, and the matrix bond should wear at an appropriate rate to ensure the efficiency of stone processing according to the model. Unfortunately, most investigations on segment wear focused on the wear characteristics on the whole worn surface, without comparing and analyzing the wear morphology at different positions. From the point of intermittent grinding. Xu, Shen and Huang [19] analyzed the characteristics of load distribution on the segment surface during circular sawing, concluding that the load on the entry end was greater than that on the end. Yu, Li and Xu [20] discussed the influence of the height distribution of diamonds and the existence of slot on the actual load in the process of granite sawing. Based on the above two factors, it was entirely possible that the actual load of some diamond particles on segment worn surface may reach or even far exceed the static pressure strength value, leading to the macro-fractured crystals. Huang, Huang and Xu [21] evaluated the wear condition of beads during the whole life of diamond wire through systematic research, and the results indicated that the wear of the region contacting the stone first was much more serious than the region contacting the stone later. Zhang, Zhang and Wang [22] investigated the wear appearance of diamond segments distributing in various areas of the sawblade by experimenting in different frame sawing machines, and pointed out that different wear characteristics of segments were shown at different areas. The present research aims at the investigation of wear morphology of different part of the surface of worn diamond segment in the process of sawing granite by diamond circular saw. The undeformed chip thickness of diamond particles in different regions along the length direction of segment was analyzed, based on which force model of single particle was established and the reasons for irregular wear of segment was explained. Experiments were conducted under the combination of diamonds of different quality and matrix bond of different components in order to compare the wear mechanisms and wear morphology of different parts of segment by examining parameters such as particle protrusion height and segment residual height, which can be conducive to improving the wear nonuniformity of worn segment.
and efficiency of processing, blade life and surface quality of workpiece, therefore many academic investigations have been carried out on the wear performance and wear mechanism of diamond tools. Gant et al. [8] evaluated the erosion resistance of diamond/WC based hard metal composites by means of the widely reported ASTM B611 test, and conducted a simulated field drilling test using fine - grained quartzite in the laboratory. The results indicated that the major wear mechanisms of the WC-Co-diamond composites in the ASTM B611 test are the predominant wear of the WC-Co matrix leaving diamond grains unsupported followed by their fracturing, shearing and detachment from the wear-surface. Similarly, the diamond grains are fractured and plucked out from the worn surface as a result of high impact loads and severe fatigue during percussive drilling. Tönshoff, Hillmann-Apmann and Asche [9] analyzed the cutting mechanism, wear properties and applications of stone sawing by circular saw and simultaneously classified the wear of segment into diamond wear and matrix wear. Liao and.Luo [10] investigated the wear behaviors of impregnated diamond tools in the sawing of granite by circular saw, reaching the decision that the wear of the metal bond is caused by abrasion along the sites of the pulled-out particles or macro-fractured diamonds, flush erosion around the sides of the diamonds and cavitation erosion in front of the diamond particles. Among them, flushing abrasive erosion is developed by the flowing action of a fluid stream carrying small stone fragments or crushed diamond fragments or solid particles around the sides of the diamond grains. Meanwhile, the breakage of diamond particles could be attributed to low cycle fatigue and impact force. Luo [11] classified the worn diamond particles into whole, micro-fractured, macro-fractured crystals and pull-out hole, and pointed out that the sawing efficiency of the sawblade reduced and even finally failure with the ratio of macro-fractured and pull-out crystal over a third. Jerro et al. [5] experimentally investigated the wear characteristics of diamond tool by circular saw for sawing different varieties of stones, and came to the conclusion that abrasion was the most common wear mechanism. Experiments were carried out by Ersoy et al. [12] with circular diamond saw for cutting ten types of rocks under different sawing conditions, drawing a conclusion that abrasion was the most common wear mechanism, and impact loads and fatigue also accelerates the wear of saws. Sun et al. [13] investigated the wear characteristic of segments with a prototype of Innovative frame saw, and the results proved that diamond particles were mainly erosion wear, and the matrix was principally flushing abrasive erosion. Segment wear is the result of the combined action of influencing factors such as cooling fluid, stone properties, sawing mode, sawing parameters and matrix components, etc. Ucun et al. [14] discussed the effects of cooling liquids on sawing performance of diamond circular saw, and the results of the study showed that minimum wear occurred with boron oil while maximum wear generated with the use of water. Sun et al. [13] developed a mathematical model to predict segment wear, statistically analyzed the effects of stone properties on the wear of segment when sawing by a machine prototype of innovative frame saw, and concluded that the main stone properties affecting the wear of segment were bending strength, uniaxial compressive strength and quartz content. Buyuksagis [15] performed an experimental study to discuss the influence of sawing mode on the sawing performances by circular saw, and it conducted that it's more efficient of the up-cutting mode due to its higher specific energy values and specific wear rate than that of the down-cutting mode. Aydin, Karakurt and Aydiner [16] experimentally studied the wear characteristics of diamond sawblade during the sawing of granite by circular saw, built the predictive evaluation model for SWR (SWR stands for the specific wear rate, which is defined as the ratio of the radial wear of the segment surface to the sawn area for evaluating the segment wear performance) and the results indicated that a large SWR value resulted from the higher traverse speed and the peripheral speed, and the lower sawing depth and the coolant flow. Ucun et al. [17] focused on the influence of matrix composition and the concentration of diamond particles on granite
2. Experimental details 2.1. Experimental equipment The sawing experiment was carried out on a diamond circular saw with a sawblade made of 75Cr1with diameter of 1600 mm and thickness of 3.5 mm (Fig. 1). The sawing rate defining as the product of sawing depth and transverse feed rate was kept at 1170 cm2/min, with an sawing depth of 15 mm and a traverse feed rate of 7.8 m/min. Furthermore, the peripheral velocity of saw blade Vs was maintained at 32 m/s. The cutting fluid was water. A total of 108 impregnated segments (24 mm × 4 mm × 13 mm) were evenly distributed on the periphery of a circular blade with the segment length of B and slot length of L, as displayed in Figs. 2 and 3. 2.2. Sawing tools and workpiece Three different segments were adopted in the test, the specifications of which were listed in Table 1. The morphologies of two types of diamond particles used in experimental are shown in Fig. 4, diamond A of medium grade has a regular shape and a relatively high proportion of complete particle, while diamond B of high quality has a complete shape, higher transparency, impact strength and thermal stability. Iron sheets are embedded inside the segment and two kinds of metal bond materials were selected in the experiment, namely CoeFeeCu and WeCo. 2
International Journal of Refractory Metals & Hard Materials 83 (2019) 104961
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Fig. 1. Circular saw device.
Fig. 3. Schematic diagram of sawblade.
3. Results Investigations on segment wear were carried out by analyzing the residual height of segment, particle protrusion height and the wear appearance of worn surface. 3.1. The residual height of segment Profile morphology of worn segment is illustrated in Fig. 6, the upper surface of segments showed diagonal lines with different slope viewed from the side after processing granite. It is obvious that lower residual height was exhibited at the front part, which means that the front end of segment wore faster than the rear end. The residual heights of different parts of segments after sawing have been measured and plotted in Fig. 7. The height difference between the front and rear end in residual height reaches 0.44 mm in segment 1 with the residual height of 11.83 mm and 12.32 mm for the front end and rear end respectively. The biggest height difference in residual height of 0.62 mm occurs in segment 2 which adopted with diamonds of high quality with lower residual height of 11.66 mm and 12.28 mm for the front and rear end respectively. Segment 3 which adopted with diamonds of high quality and matrix bond of high wear resistance displays an obvious improvement in the uniformity of segment wear with the synchronous increase in residual height and the sharp decrease in height difference. The residual height of the front and rear end are 12.12 mm and 12.41 mm respectively.
Fig. 2. Sawblade with diameter of 1600 mm.
British brown granite with high hardness and high quartz content (2000 mm in length) was chosen as the test materials and main mechanical properties and mineral composition of granite were listed in Table 2.
2.3. Sawing tests Eighteen segments with equal distance around the periphery of a circular sawblade were inspected by optical microscope and SEM to obtain the wear morphology of the worn surface. The particle protrusion height on segment surface was measured by a 3D laser microscope. As shown in Fig. 5, line marks were drawn on the flat surface of the matrix and the top of the particles, and the vertical distance between above two was the particle protrusion height. A total of 360 particles were measured and the mean value was calculated. The residual height of segments was measured by a digital vernier caliper at the front end and the rear end respectively. A total of 108 measurements were completed after sawing by measuring three times at each position.
3.2. Wear behavior of worn segment surface The wear morphology of the front and rear end of segment 1 is shown in Fig. 8. Diamond particles can be generally divided into 6 varieties according to wear morphology, as represented in Fig. 9, which are respectively emerging, whole, micro-fractured, macro-fractured, polished and pull-out crystal. Emerging crystal is a fresh diamond whose cutting edge has just exposed from the bond, displaying low particle protrusion height and poor cutting ability. Whole diamond particles exhibits complete (perfect) crystal shape without significant damage and crack on the surface, performing optimum cutting capacity. Polished crystal shows a worn 3
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Table 1 Description of the diamond segments in the sawblades. Segment
Diamond
Diamond size
Diamond concentration
Matrix composition
1 2 3
A B B
45/50 45/50 45/50
25% 25% 25%
Co (6%), Fe (64%), Cu (21%), others (9%) Co (6%), Fe (64%), Cu (21%), others (9%) W (8%), Co (85%), others (7%)
74 μm for the front and rear end respectively. The particle protrusion height of segment 3 using diamonds of high quality and matrix bond of high wear resistance is relatively lower than that of segment 1 with the average value of 96 μm and 67 μm for the front and rear end respectively.
appearance of flat or smooth surface, which will result in an increase in sawing force. Micro-fractured crystal, considered being a good help to free cutting, presents crushed particles, micro-cracks or fragments produced on its surface. Previous categories of wear continue to deteriorate and form macro-fractured crystal, which is manifested as mass collapse of crystals, lower the particle protrusion height, and the serious decline or even loss of cutting ability. Pull-out crystal exhibits a hole on worn matrix surface with the particle pulling or plucking out of the bond, in which case the sawblade will wear out quickly. Generally speaking, higher cutting ability are possessed by whole and microfractured diamond crystals, while nearly without cutting capacity are possessed by macro-fractures and pull-out crystals. The proportion of different diamond particles of the front and rear end for 3 segments has been calculated and illustrated in Figs. 10 and 11. Higher proportions of failure particles (including macro-fractured and pull-out particles) at the front end are observed on segment 1 with the proportion of 26% and 33% respectively compared with the rear end of segment. Meanwhile, the front end of segment has more emerging crystals and less polished crystals compared with the rear end. Compared with segment 1, the proportion of macro-fractured crystals at the front end of segment 2 which adopted with diamonds of high quality is significantly decreased, whereas the proportions of pullout and emerging crystals are slightly increased, with the proportion of 21%, 13%, and 35%, respectively. But it also produces more particles with better cutting ability (including whole and micro fractured crystals) with proportion of 10% and 18%, respectively. The increase of proportion of Co and the introduction of W in segment 3 improve the wear resistance in addition to the adoption of high quality diamond. It is observed that the proportion of emerging and pull-out crystals in the front-end of segment 3 shows a clear downward trend with the proportion of 10% and 28%.
4. Discussion 4.1. Wear mechanism of matrix bond The morphologies of worn segment surfaces are illustrated in Fig. 13. Apparently erosion crater and erosion track are developed in front and around of the diamond particles respectively in front end of segment, which is called flush erosion and displayed in Fig. 13(a). Tönshoff, Hillmann-Apmann and Asche [9] pointed out that the wear morphology around the particles was caused by the flowing action of a fluid stream carrying solid particles of crushed diamond fragments or small stone fragments, while the pit-like appearance of the front of the diamond particles was developed by the phenomenon of cavitation under flush erosion and abrasion action of the small stone debris. Abrasive wear is the most widespread wear mechanism of matrix bond for other parts of worn segment surface, and the wear characteristics of which is represented in Fig. 13(b). Liao and Luo [10] indicated that grooves and furrows usually occurred at the position where the diamond pulled out, far away from diamond particles or on the front end of the macro-fractured diamond particles, as stone fragments without washing away in time scratch the surface of the matrix, forming abrasive tracks on the stone surface in the sawing progress. 4.2. Diamond load distribution characteristics of worn segment Granite material is removed in the form of chip during sawing process, so the morphology and size of chip could reflect the working status of diamond to a certain extent. A definition of maximum thickness of undeformed chip of single particle has been proposed as an important index to measure the force of particles [23].
3.3. The particle protrusion height Fig. 12 shows the particle protrusion height of different parts of segment. It is observed that the particle protrusion height at the front end of segment 1 is higher than that of the rear end with the average value of 116 μm and 70 μm respectively. Compared with segment1, the particle protrusion height of segment 2 adopting with diamonds of high quality has slightly increased with the average value of 123 μm and
4.2.1. The model of maximum thickness of undeformed chip of single particle in circular saw The sawing path of single diamond particle in the process of circular
Fig. 4. The morphology of diamond particle (a) diamond A (b) diamond B. 4
International Journal of Refractory Metals & Hard Materials 83 (2019) 104961
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Table 2 Main physical–mechanical properties of granite samples. Granite type
Volume ratio of major ore components/w/%
Britain's brown
Quartz
Orthoclase
Plagioclase
Biotite
16
44
27
8
2000⋅vf ⋅L π⋅D⋅nk
⋅
ap D
compressive strength/MPa
bending strength/MPa
97
122.6
17.4
It is clear that s1, s2 are removed by particles 1 and 2, 3 with maximum thickness of undeformed chip of hm1 and hm2 respectively. Obviously, chip area removed by the front particle 1 is much larger than that of subsequent particles due to an increase in particle spacing as a result of the existence of the slot, so is hm. Assuming that particles are uniformly arranged on segment surface and the particle protrusion height is equal, hm is equal for subsequent diamond particles. The ratio of hm1 (hm of first row of particles) and hm2 (hm of subsequent particles) are presented in the following formula.
sawing is shown in Fig. 14. GCD is the chip shape of single particle whose thickness is always in a changing state, and the maximum undeformed chip thickness CE is defined as hm. Malkin [23] established the model of hm through the sawing path of diamond particles:
hm =
Shore hardness
(1)
where hm(μm) is the maximum undeformed cutting thickness per particle, vf(mm/min) is the transverse feed speed, n(rpm) is the rotational speed of spindle, ap(mm) is the sawing depth, D(mm) is the diameter of saw blade and L(mm) is the particle spacing. According to Eq. (1) hm is directly proportional to the particle spacing L when all other parameters remain unchanged.
hm1/ hm2 = 1 + B / l2
(2)
where B (mm) is the width of the slot and l2 (mm) is particle spacing within the segment. According to Eq. (2), hm of the first row of particle is much larger than that of subsequent diamond particles because of the existence of slot, with the ratio of hm1 to hm2 only related to B/l2 when other processing parameters remain unchanged.
4.2.2. Distribution characteristics of hm in circular saw The diamond particles located in the front of segment along the direction of cutting arc length are defined as the first row of particles, followed by the subsequent particles as the sawblade rotating one way during the sawing process of circular saw. Particles 1′ (final particle) on the surface of upper segment and particles 1, 2, 3 (1 is the first particles, 2, 3 are the subsequent particles) on the surface of latter segment are selected with equal spacing on the surface of segment 2 (Fig. 15).
4.2.3. Load distribution model of single particle in circular saw Xu and Yu [24] built the functional relationship between the normal force per diamond particle fn and hm based on the research in rock crushing.
fn = kn⋅hmn
(3)
where kn is parameter related to face angle of diamond particle and n is
Fig. 5. The particle protrusion height measurement. 5
International Journal of Refractory Metals & Hard Materials 83 (2019) 104961
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Fig. 6. Profile morphology of worn segment (a) segment 1 (b) segment 2 (c) segment 3.
diamond, which can easily lead to more serious macro-fractured crystals at the front end of segment. Meanwhile, particle spacing further increases by diamond shedding and macro breakage at the front end, which conducts to the enlargement of chip thickness and load per diamond and finally results in continuous increase in the proportion of macro-fractured crystals. Moreover, rapid wear on the matrix bond, higher particle protrusion height and poorer retention of particle resulted from erosion wear at the front end of segment, will lead to an increase in the proportion of pull out crystals. Conversely, diamond shedding reduces the wear resistance of segment and further accelerates the wear of segment. This is a process of continuous deterioration, resulting in a higher proportion of serious abnormal failure of diamond particles (macro-fractured and pull-out particles) at the front end, and further leading to an uneven wear of the front and rear end of segment 1. Fig. 7. The residual height of different parts of segment.
4.3. Compatibility between diamond and matrix bond 4.3.1. Sawing behavior of diamond with different quality When diamond A of medium quality was employed, abrasion and breakage are easy to occur in sawing most minerals (such as feldspar, etc.) due to its medium resistance to pressure and impact, and more macro-fractured crystals appear and the sawing ability would be lost when encountering large loads or mineral components (such as quartz) that particularly difficult to cut. However, most minerals can be easily cut without obvious abrasion and micro-fractured crystals would occur only confronting with large loads or minerals particularly difficult to cut when adopting diamond B of high quality with regular crystal shape, flat surface, strong resistance of pressure and impact. As a consequence, diamond B of high quality leads to a lower proportion of macro-fractured crystals at the front end of segment 2 and 3 compared with segment 1 using diamond A of medium quality.
consist related to workpiece material. Ratios of normal force per diamond of the first row of particle to that of the rest particles can be obtained by substituting Eq. (2) into Eq. (3), which is described in the following equation.
fn1 / fn2 = (hm1/ hm2 ) n = (1 + B / l2 ) n
(4)
It can be concluded from Eq. (4), the normal force per diamond of the first row is much larger than that of subsequent particles, with the ratio of fn1 to fn2 related to B/l2 and increased by n power. The conclusion is consistent with the results of Xu, Shen and Huang [19] and Yu, Li and Xu [20] as described earlier. Therefore, the existence of the slot results in that the mechanical load of the first row of particle is much higher than that of the rest particles in sawing process, and even beyond the strength of the
Fig. 8. SEM morphology of working surface of worn segment (a) the front end (b) the rear end. 6
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Fig. 9. Worn diamond classification (a) emerging (b) whole (c) polished (d) micro-fractured (e) macro-fractured (f) pull-out.
matrix and lower residual height at the front end of segment. Diamond of high quality in segment 2 has a strong resistance to diamond breakage under large loads, which is more likely to lead to lower proportion of macro-fractured crystals. Nevertheless, the binding force of diamond decreases due to the smooth surface of advanced diamond, and the unchanged matrix bond wears faster than the diamond particles under serious erosion at the front end, which results in a slight increase in proportion of pull-out crystals, a tiny reduction in the residual height and a bit larger protrusion height compared with segment 1. The wear of matrix at the front end has been significantly weaken due to the adoption of metal bond of high wear resistance in segment 3, which leads to a decrease in the particle protrusion height and the ratio of pull-out particles and an obvious enhancement in residual height compared with segment 1 and 2. It indicates that the bond and diamond particles wear synchronously in segment 3 for their optimum compatibility, effectively reducing the ratio of abnormal failure of diamond particles at front end, improving the wear nonuniform of surface and prolonging the service life of segment. 4.4. Design proposals for diamond tools
Fig. 10. The proportion of worn diamond particles in different parts of segment 1.
Based on the difference of wear mechanism and wear inhomogeneity in different parts of segments due to the discontinuity of segments discussed above, the following suggestions are put forward for the design of follow-up diamond tools. High quality diamond would be used at the front end and ordinary quality diamond would be used at the rear end according to the load distribution of diamond particles at different areas on the segment surface. Flushing abrasive erosion is dominant at the front end of the segment and the rear end is mainly abrasive wear, resulting in further wear deterioration of matrix and lower residual height at the front end of segment. The increase of proportion of Co and the introduction of W
4.3.2. Compatibility between diamond and matrix bond Particle protrusion height is the result of the combined action of particle wear and matrix wear. Segment 1 adopting metal bond of general quality displays serious wear of matrix and larger particle protrusion height as a result of the erosion wear occurring at the front end of segment, which increases the proportion of shedding crystals in advance without undergoing normal wear processes under large loads. On the contrary, more shedding diamond particles reduces the abrasion resistance of the segment, leading to further wear deterioration of 7
International Journal of Refractory Metals & Hard Materials 83 (2019) 104961
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Fig. 11. The proportion of worn diamond particles in different part of segments (a) the front end (b) the rear end.
Fig. 12. Particle protrusion height of different part of segment.
helps to improve the wear resistance of matrix for the front end and general quality matrix composition are maintained for the rear end. It is considered that the diamond concentration of the front end is appropriately increased to make up for the abnormal failure of diamond particles due to severe erosion wear and the large mechanical load at
Fig. 14. Diagram of device motion and chip topography.
the front end in time, while the diamond concentration at the rear end is moderately reduced to improve the utilization rate of diamond
Fig. 13. SEM morphology of matrix bond of worn segment (a) flush erosion (b) abrasive wear. 8
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Acknowledgment This work is supported by Taishan industrial leading talent project (tscy20150228) of Shandong Province, China. The authors are deeply grateful to Rizhao Hein Saw Co., Ltd. and Shandong Renown Diamond Tools Co., Ltd. for supporting this research by providing the circular sawing machine and the diamond tools. References [1] N.G. Yılmaz, R.M. Goktan, Y. Kibici, An investigation of the petrographic and physico-mechanical properties of true granites influencing diamond tool wear performance, and development of a new wear index, Wear 271 (2011) 960–969. [2] S. Turchetta, L. Sorrentino, C. Bellini, A method to optimize the diamond wire cutting process, Diam. Relat. Mater. 71 (2017) 90–97. [3] H.K. Tonshoff, G. Warnecke, Research on stone sawing, Adv. Ultrahard. Mater. Appl. Technol. 1 (1982) 36–49 P. Daniel, Hornbeam, ed. England. [4] X.P. Xu, Prevailing mechanisms for circular sawing of granites with diamond impregnated segments, Mater. Manuf. Process. 15 (2000) 123–138. [5] H.D. Jerro, S.S. Pang, C. Yang, R.A. Mirshams, Kinetic Analysis of Chipping Materials Using Superabrasive Diamond Tools, ASME, 1995. [6] S. Turchetta, Cutting force on a diamond grit in stone machining, Int. J. Adv. Manuf. Technol. 44 (2009) 854–861. [7] J. Konstanty, Theoretical analysis of stone sawing with diamonds, J. Mater. Process. Technol. 123 (2002) 146–154. [8] A.J. Gant, I. Konyashin, B. Ries, A. McKie, R.W.N. Nilen, J. Pickles, Wear mechanisms of diamond-containing hardmetals in comparison with diamond-based materials, J. Refract. Met. Hard Mater. 71 (2018) 106–114. [9] H.K. Tönshoff, H. Hillmann-Apmann, J. Asche, Diamond tools in stone and civil engineering industry: cutting principles, wear and applications, Diam. Relat. Mater. 11 (2002) 736–741. [10] Y.S. Liao, S.Y. Luo, Wear characteristics of sintered diamond composite during circular sawing, Wear 157 (1992) 325–337. [11] S.Y. Luo, Characteristics of diamond sawblade wear in sawing, Int. J. Mach. Tools Manuf. 36 (1996) 661–672 (612). [12] A. Ersoy, S. Buyuksagic, U. Atici, Wear characteristics of circular diamond saws in the cutting of different hard abrasive rocks, Wear 258 (2005) 1422–1436. [13] Q. Sun, J.S. Zhang, Z. Wang, H. Zhang, J. Fang, Segment wear characteristics of diamond frame saw when cutting different granite types, Diam. Relat. Mater. 68 (2016) 143–151. [14] I. Ucun, K. Aslantas, I.S. Büyüksağiş, S. Taşgetiren, Effect of cooling liquids on cutting process using diamond segmented disc of natural stones, Proc. Inst. Mech. Eng. Part C. 227 (2013) 2315–2327. [15] I.S. Buyuksagis, Effect of cutting mode on the sawability of granites using segmented circular diamond sawblade, J. Mater. Process. Technol. 183 (2007) 399–406. [16] G. Aydin, I. Karakurt, K. Aydiner, Wear performance of saw blades in processing of granitic rocks and development of models for wear estimation, Rock Mech. Rock. Eng. 46 (2013) 1559–1575. [17] İ. Ucun, K. Aslantas, İ.S. Büyüksagis, S. Tasgetiren, An investigation on the effect of diamond concentration and matrix material composition in the circular sawing process of granites, Proc. Inst. Mech. Eng. Part C. 225 (2010) 17–27. [18] A.D. Ilio, A. Togna, A theoretical wear model for diamond tools in stone cutting, Int. J. Mach. Tools Manuf. 43 (2003) 1171–1177. [19] X.P. Xu, J.Y. Shen, H. Huang, Analysis of key factors in order to realize sawing of granites with high efficiency, Chin. J. Mech. Eng. 34 (1998) 104–110. [20] Y.Q. Yu, Y. Li, X.P. Xu, Load-bearing analysis of diamond during sawing granite, exploration engineering, Rock Soil Drill. Tunneling (2001) 59–62 (in Chinese). [21] H. Huang, G.Q. Huang, X.P. Xu, An experimental study of machining characteristics and tool wear in the diamond wire sawing of granite, Proc. Inst. Mech. Eng. Part B. 227 (2013) 943–953. [22] H. Zhang, J.S. Zhang, S. Wang, Comparison of wear performance of diamond tools in frame sawing with different trajectories, J. Refract. Met. Hard Mater. 78 (2019) 178–185. [23] B. Malkin, Grinding Thchnology Theory and Application of Machining with Abrasives, Johnwiley and Sons, 1989. [24] X.P. Xu, J. Yu, Rock Crushing, China Coal Industry Publishing House, Beijing, 1984 (in Chinese).
Fig. 15. Distribution characteristics of hm on worn segment surface.
particles. Furthermore, full consideration was taken into the compatibility between diamond and matrix bond to balance the sharpness and abrasion resistance of segments and realize the constant wear of diamond and matrix. Wear performance prediction tests for diamond tools can be conducted on a CNC machining center equipped with force sensors and data acquisition systems to establish the relationship model between tool wear of force signal. A diamond disc as the machining tool would be mounted on the mandrel of the CNC machining center，which is composed of a disk-like support and segments welded to the edge it. The kinetic energy of the mechanical shaft is transferred to the diamond particles and the segments made of diamonds and metal bond are used for cutting. Different machining conditions are simulated by adjusting different cutting parameters. 5. Conclusion In order to investigate the wear characteristics at different regions of diamond segments, the wear morphology of the front and rear end of segment by matching diamond of different quality and matrix bond of different abrasion resistance were discussed by experiments. The conclusions could be drawn as follows. 1 The surface wear morphology of conventional segment presents obvious nonuniformity, and the residual height of the front end is obvious lower than that of the rear end due to the higher abnormal failure efficiency of diamond particles. 2 The wear characteristics of diamond particles for different parts of traditional segment surface can reflect the wear mechanism of the matrix and the load characteristics of the diamond. Erosion wear is dominant at the front end of the segment and the load of the first row of particle is much large than that of the rear end due to the existence of a slot, resulting in high proportions of pull-out and macro-fractured crystal. 3 Reasonable matching of diamond particles with different quality and metal bond with different wear resistance contributed to the reduction of diamond abnormal failure(macro-fractured and pull out crystal)and the promotion of uniformity of segment wear. 4 Suggestions are put forward for the design of follow-up diamond tools from the aspects of matrix composition, diamond quality and diamond concentration and experimental verification based on the difference of wear mechanism and wear inhomogeneity in different parts of segments
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International Journal of Refractory Metals & Hard Materials journal homepage: www.elsevier.com/locate/IJRMHM
Investigation and improvement of wear nonuniformity of diamond tools in sawing granite ⁎
T
⁎
Peiyu Donga,b, Bo Huanga,b, , Jinsheng Zhanga,b, , Heng Zhanga,b a Key Laboratory of High-Efficiency and Clean Mechanical Manufacture (Ministry of Education), School of Mechanical Engineering, Shandong University, Jinan 250061, China b Research Centre for Stone Engineering (Shandong Province), Jinan 250061, China
A R T I C LE I N FO
A B S T R A C T
Keywords: Diamond tool Wear characteristics Maximum undeformed chip thickness Diamond abnormal failure Wear uniformity
Sawing experiments were accomplished to discuss the wear characteristics at different parts of diamond tools in the process of sawing granite in this paper. Optical microscopy, scanning electron microscopy and 3D laser microscope were main detection means for the morphology of diamond tools. Synthetic investigation on the abrasion performance of segments was developed from aspects of the wear appearance of diamond particle and metal bond, the particle protrusion height and the residual height of segments. The results indicated that smaller residual height and larger proportion of macro-fractured and pull out crystal were exhibited at the front end of traditional diamond segment compared with the rear end. Morphology characteristics of diamond tools demonstrated different abrasion mechanism, flush erosion and cavitation was the main wear mechanism for the front end, while abrasive wear was the main wear mechanism for the rear end. Maximum undeformed chip thickness per diamond particle for the front end was larger than that of the rear end due to the existence of slot, the same was true for the load of single diamond particle. By reasonably matching of diamond particles and matrix bond, the abnormal failure efficiency of the diamond particles at the front of the segment was effectively reduced and the wear uniformity of the saw tooth surface was greatly improved. Suggestions on the design of diamond tools and test verification were put forward in the end.
1. Introduction Diamond circular saws have been commonly adopted in stone processing industry with extensive application of natural granite material as decoration materials and structural engineering due to its aesthetic, physical and mechanical properties [1]. Segments made of diamond crystals and metal bond are the prime sawing tools for circular saw [2]. Granite minerals are usually removed in the form of chip through the interaction of diamond particles and workpiece, therefore, it is of great significance to understand the mechanism in stone processing. A model of sawing stone with disk-like tools was proposed by Tonshoff and Warnecke [3] and it turned out that the elastoplastic deformation occurring to the workpiece caused by diamond particles and the friction between bond and particle, bond and sawdust and workpiece and particle resulted in the interaction between the tool and the workpiece. The sawing force and energy were quantitatively analyzed and the cutting mechanism of granite sawing by diamond segments for circular
saw was investigated by Xu [4], revealing that the energy consumption depended mainly on sliding friction and the removal of material was primarily govern by brittle fracture. Widespread attention has been attracted on chip morphology as an important parameter reflecting sawing process and mechanism. Jerro et al. [5] defined the theoretical chip morphology through the area and thickness of the chip in the process of sawing by circular saw, and established the connection between sawing parameters and cutting force. Turchetta [6] derived the relationship between the tool parameters and the chip geometry of a single particle, theoretically analyzed and calculated the average chip thickness per particle, and modelled the cutting force per particle as a power function of cutting thickness. Konstanty [7] proposed a model of diamond tools sawing natural rocks under different sawing forms (diamond frame and circular saw), quantified the formation and removal of sawdust and presented hm (the maximum chip thickness) as a preliminary evaluation index of matrix wear. Diamond tool wear, inevitably occurring due to the complexity and multidimensionality of sawing process, has a great influence on the cost
⁎ Corresponding authors at: Key Laboratory of High-Efficiency and Clean Mechanical Manufacture (Ministry of Education), School of Mechanical Engineering, Shandong University, Jinan 250061, China. E-mail addresses: [email protected] (B. Huang), [email protected] (J. Zhang).
https://doi.org/10.1016/j.ijrmhm.2019.05.007 Received 15 February 2019; Received in revised form 7 May 2019; Accepted 8 May 2019 Available online 10 May 2019 0263-4368/ © 2019 Elsevier Ltd. All rights reserved.
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sawing, and it turned out that an increase in diamond concentration and the proportion of WeCo lead to the decrease of power consumption, sawing force and specific wear of segment. The theoretical model of diamond tool wear in sawing was proposed by Ilio and Togna [18] for the wear prediction problem, and the matrix bond should wear at an appropriate rate to ensure the efficiency of stone processing according to the model. Unfortunately, most investigations on segment wear focused on the wear characteristics on the whole worn surface, without comparing and analyzing the wear morphology at different positions. From the point of intermittent grinding. Xu, Shen and Huang [19] analyzed the characteristics of load distribution on the segment surface during circular sawing, concluding that the load on the entry end was greater than that on the end. Yu, Li and Xu [20] discussed the influence of the height distribution of diamonds and the existence of slot on the actual load in the process of granite sawing. Based on the above two factors, it was entirely possible that the actual load of some diamond particles on segment worn surface may reach or even far exceed the static pressure strength value, leading to the macro-fractured crystals. Huang, Huang and Xu [21] evaluated the wear condition of beads during the whole life of diamond wire through systematic research, and the results indicated that the wear of the region contacting the stone first was much more serious than the region contacting the stone later. Zhang, Zhang and Wang [22] investigated the wear appearance of diamond segments distributing in various areas of the sawblade by experimenting in different frame sawing machines, and pointed out that different wear characteristics of segments were shown at different areas. The present research aims at the investigation of wear morphology of different part of the surface of worn diamond segment in the process of sawing granite by diamond circular saw. The undeformed chip thickness of diamond particles in different regions along the length direction of segment was analyzed, based on which force model of single particle was established and the reasons for irregular wear of segment was explained. Experiments were conducted under the combination of diamonds of different quality and matrix bond of different components in order to compare the wear mechanisms and wear morphology of different parts of segment by examining parameters such as particle protrusion height and segment residual height, which can be conducive to improving the wear nonuniformity of worn segment.
and efficiency of processing, blade life and surface quality of workpiece, therefore many academic investigations have been carried out on the wear performance and wear mechanism of diamond tools. Gant et al. [8] evaluated the erosion resistance of diamond/WC based hard metal composites by means of the widely reported ASTM B611 test, and conducted a simulated field drilling test using fine - grained quartzite in the laboratory. The results indicated that the major wear mechanisms of the WC-Co-diamond composites in the ASTM B611 test are the predominant wear of the WC-Co matrix leaving diamond grains unsupported followed by their fracturing, shearing and detachment from the wear-surface. Similarly, the diamond grains are fractured and plucked out from the worn surface as a result of high impact loads and severe fatigue during percussive drilling. Tönshoff, Hillmann-Apmann and Asche [9] analyzed the cutting mechanism, wear properties and applications of stone sawing by circular saw and simultaneously classified the wear of segment into diamond wear and matrix wear. Liao and.Luo [10] investigated the wear behaviors of impregnated diamond tools in the sawing of granite by circular saw, reaching the decision that the wear of the metal bond is caused by abrasion along the sites of the pulled-out particles or macro-fractured diamonds, flush erosion around the sides of the diamonds and cavitation erosion in front of the diamond particles. Among them, flushing abrasive erosion is developed by the flowing action of a fluid stream carrying small stone fragments or crushed diamond fragments or solid particles around the sides of the diamond grains. Meanwhile, the breakage of diamond particles could be attributed to low cycle fatigue and impact force. Luo [11] classified the worn diamond particles into whole, micro-fractured, macro-fractured crystals and pull-out hole, and pointed out that the sawing efficiency of the sawblade reduced and even finally failure with the ratio of macro-fractured and pull-out crystal over a third. Jerro et al. [5] experimentally investigated the wear characteristics of diamond tool by circular saw for sawing different varieties of stones, and came to the conclusion that abrasion was the most common wear mechanism. Experiments were carried out by Ersoy et al. [12] with circular diamond saw for cutting ten types of rocks under different sawing conditions, drawing a conclusion that abrasion was the most common wear mechanism, and impact loads and fatigue also accelerates the wear of saws. Sun et al. [13] investigated the wear characteristic of segments with a prototype of Innovative frame saw, and the results proved that diamond particles were mainly erosion wear, and the matrix was principally flushing abrasive erosion. Segment wear is the result of the combined action of influencing factors such as cooling fluid, stone properties, sawing mode, sawing parameters and matrix components, etc. Ucun et al. [14] discussed the effects of cooling liquids on sawing performance of diamond circular saw, and the results of the study showed that minimum wear occurred with boron oil while maximum wear generated with the use of water. Sun et al. [13] developed a mathematical model to predict segment wear, statistically analyzed the effects of stone properties on the wear of segment when sawing by a machine prototype of innovative frame saw, and concluded that the main stone properties affecting the wear of segment were bending strength, uniaxial compressive strength and quartz content. Buyuksagis [15] performed an experimental study to discuss the influence of sawing mode on the sawing performances by circular saw, and it conducted that it's more efficient of the up-cutting mode due to its higher specific energy values and specific wear rate than that of the down-cutting mode. Aydin, Karakurt and Aydiner [16] experimentally studied the wear characteristics of diamond sawblade during the sawing of granite by circular saw, built the predictive evaluation model for SWR (SWR stands for the specific wear rate, which is defined as the ratio of the radial wear of the segment surface to the sawn area for evaluating the segment wear performance) and the results indicated that a large SWR value resulted from the higher traverse speed and the peripheral speed, and the lower sawing depth and the coolant flow. Ucun et al. [17] focused on the influence of matrix composition and the concentration of diamond particles on granite
2. Experimental details 2.1. Experimental equipment The sawing experiment was carried out on a diamond circular saw with a sawblade made of 75Cr1with diameter of 1600 mm and thickness of 3.5 mm (Fig. 1). The sawing rate defining as the product of sawing depth and transverse feed rate was kept at 1170 cm2/min, with an sawing depth of 15 mm and a traverse feed rate of 7.8 m/min. Furthermore, the peripheral velocity of saw blade Vs was maintained at 32 m/s. The cutting fluid was water. A total of 108 impregnated segments (24 mm × 4 mm × 13 mm) were evenly distributed on the periphery of a circular blade with the segment length of B and slot length of L, as displayed in Figs. 2 and 3. 2.2. Sawing tools and workpiece Three different segments were adopted in the test, the specifications of which were listed in Table 1. The morphologies of two types of diamond particles used in experimental are shown in Fig. 4, diamond A of medium grade has a regular shape and a relatively high proportion of complete particle, while diamond B of high quality has a complete shape, higher transparency, impact strength and thermal stability. Iron sheets are embedded inside the segment and two kinds of metal bond materials were selected in the experiment, namely CoeFeeCu and WeCo. 2
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Fig. 1. Circular saw device.
Fig. 3. Schematic diagram of sawblade.
3. Results Investigations on segment wear were carried out by analyzing the residual height of segment, particle protrusion height and the wear appearance of worn surface. 3.1. The residual height of segment Profile morphology of worn segment is illustrated in Fig. 6, the upper surface of segments showed diagonal lines with different slope viewed from the side after processing granite. It is obvious that lower residual height was exhibited at the front part, which means that the front end of segment wore faster than the rear end. The residual heights of different parts of segments after sawing have been measured and plotted in Fig. 7. The height difference between the front and rear end in residual height reaches 0.44 mm in segment 1 with the residual height of 11.83 mm and 12.32 mm for the front end and rear end respectively. The biggest height difference in residual height of 0.62 mm occurs in segment 2 which adopted with diamonds of high quality with lower residual height of 11.66 mm and 12.28 mm for the front and rear end respectively. Segment 3 which adopted with diamonds of high quality and matrix bond of high wear resistance displays an obvious improvement in the uniformity of segment wear with the synchronous increase in residual height and the sharp decrease in height difference. The residual height of the front and rear end are 12.12 mm and 12.41 mm respectively.
Fig. 2. Sawblade with diameter of 1600 mm.
British brown granite with high hardness and high quartz content (2000 mm in length) was chosen as the test materials and main mechanical properties and mineral composition of granite were listed in Table 2.
2.3. Sawing tests Eighteen segments with equal distance around the periphery of a circular sawblade were inspected by optical microscope and SEM to obtain the wear morphology of the worn surface. The particle protrusion height on segment surface was measured by a 3D laser microscope. As shown in Fig. 5, line marks were drawn on the flat surface of the matrix and the top of the particles, and the vertical distance between above two was the particle protrusion height. A total of 360 particles were measured and the mean value was calculated. The residual height of segments was measured by a digital vernier caliper at the front end and the rear end respectively. A total of 108 measurements were completed after sawing by measuring three times at each position.
3.2. Wear behavior of worn segment surface The wear morphology of the front and rear end of segment 1 is shown in Fig. 8. Diamond particles can be generally divided into 6 varieties according to wear morphology, as represented in Fig. 9, which are respectively emerging, whole, micro-fractured, macro-fractured, polished and pull-out crystal. Emerging crystal is a fresh diamond whose cutting edge has just exposed from the bond, displaying low particle protrusion height and poor cutting ability. Whole diamond particles exhibits complete (perfect) crystal shape without significant damage and crack on the surface, performing optimum cutting capacity. Polished crystal shows a worn 3
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Table 1 Description of the diamond segments in the sawblades. Segment
Diamond
Diamond size
Diamond concentration
Matrix composition
1 2 3
A B B
45/50 45/50 45/50
25% 25% 25%
Co (6%), Fe (64%), Cu (21%), others (9%) Co (6%), Fe (64%), Cu (21%), others (9%) W (8%), Co (85%), others (7%)
74 μm for the front and rear end respectively. The particle protrusion height of segment 3 using diamonds of high quality and matrix bond of high wear resistance is relatively lower than that of segment 1 with the average value of 96 μm and 67 μm for the front and rear end respectively.
appearance of flat or smooth surface, which will result in an increase in sawing force. Micro-fractured crystal, considered being a good help to free cutting, presents crushed particles, micro-cracks or fragments produced on its surface. Previous categories of wear continue to deteriorate and form macro-fractured crystal, which is manifested as mass collapse of crystals, lower the particle protrusion height, and the serious decline or even loss of cutting ability. Pull-out crystal exhibits a hole on worn matrix surface with the particle pulling or plucking out of the bond, in which case the sawblade will wear out quickly. Generally speaking, higher cutting ability are possessed by whole and microfractured diamond crystals, while nearly without cutting capacity are possessed by macro-fractures and pull-out crystals. The proportion of different diamond particles of the front and rear end for 3 segments has been calculated and illustrated in Figs. 10 and 11. Higher proportions of failure particles (including macro-fractured and pull-out particles) at the front end are observed on segment 1 with the proportion of 26% and 33% respectively compared with the rear end of segment. Meanwhile, the front end of segment has more emerging crystals and less polished crystals compared with the rear end. Compared with segment 1, the proportion of macro-fractured crystals at the front end of segment 2 which adopted with diamonds of high quality is significantly decreased, whereas the proportions of pullout and emerging crystals are slightly increased, with the proportion of 21%, 13%, and 35%, respectively. But it also produces more particles with better cutting ability (including whole and micro fractured crystals) with proportion of 10% and 18%, respectively. The increase of proportion of Co and the introduction of W in segment 3 improve the wear resistance in addition to the adoption of high quality diamond. It is observed that the proportion of emerging and pull-out crystals in the front-end of segment 3 shows a clear downward trend with the proportion of 10% and 28%.
4. Discussion 4.1. Wear mechanism of matrix bond The morphologies of worn segment surfaces are illustrated in Fig. 13. Apparently erosion crater and erosion track are developed in front and around of the diamond particles respectively in front end of segment, which is called flush erosion and displayed in Fig. 13(a). Tönshoff, Hillmann-Apmann and Asche [9] pointed out that the wear morphology around the particles was caused by the flowing action of a fluid stream carrying solid particles of crushed diamond fragments or small stone fragments, while the pit-like appearance of the front of the diamond particles was developed by the phenomenon of cavitation under flush erosion and abrasion action of the small stone debris. Abrasive wear is the most widespread wear mechanism of matrix bond for other parts of worn segment surface, and the wear characteristics of which is represented in Fig. 13(b). Liao and Luo [10] indicated that grooves and furrows usually occurred at the position where the diamond pulled out, far away from diamond particles or on the front end of the macro-fractured diamond particles, as stone fragments without washing away in time scratch the surface of the matrix, forming abrasive tracks on the stone surface in the sawing progress. 4.2. Diamond load distribution characteristics of worn segment Granite material is removed in the form of chip during sawing process, so the morphology and size of chip could reflect the working status of diamond to a certain extent. A definition of maximum thickness of undeformed chip of single particle has been proposed as an important index to measure the force of particles [23].
3.3. The particle protrusion height Fig. 12 shows the particle protrusion height of different parts of segment. It is observed that the particle protrusion height at the front end of segment 1 is higher than that of the rear end with the average value of 116 μm and 70 μm respectively. Compared with segment1, the particle protrusion height of segment 2 adopting with diamonds of high quality has slightly increased with the average value of 123 μm and
4.2.1. The model of maximum thickness of undeformed chip of single particle in circular saw The sawing path of single diamond particle in the process of circular
Fig. 4. The morphology of diamond particle (a) diamond A (b) diamond B. 4
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Table 2 Main physical–mechanical properties of granite samples. Granite type
Volume ratio of major ore components/w/%
Britain's brown
Quartz
Orthoclase
Plagioclase
Biotite
16
44
27
8
2000⋅vf ⋅L π⋅D⋅nk
⋅
ap D
compressive strength/MPa
bending strength/MPa
97
122.6
17.4
It is clear that s1, s2 are removed by particles 1 and 2, 3 with maximum thickness of undeformed chip of hm1 and hm2 respectively. Obviously, chip area removed by the front particle 1 is much larger than that of subsequent particles due to an increase in particle spacing as a result of the existence of the slot, so is hm. Assuming that particles are uniformly arranged on segment surface and the particle protrusion height is equal, hm is equal for subsequent diamond particles. The ratio of hm1 (hm of first row of particles) and hm2 (hm of subsequent particles) are presented in the following formula.
sawing is shown in Fig. 14. GCD is the chip shape of single particle whose thickness is always in a changing state, and the maximum undeformed chip thickness CE is defined as hm. Malkin [23] established the model of hm through the sawing path of diamond particles:
hm =
Shore hardness
(1)
where hm(μm) is the maximum undeformed cutting thickness per particle, vf(mm/min) is the transverse feed speed, n(rpm) is the rotational speed of spindle, ap(mm) is the sawing depth, D(mm) is the diameter of saw blade and L(mm) is the particle spacing. According to Eq. (1) hm is directly proportional to the particle spacing L when all other parameters remain unchanged.
hm1/ hm2 = 1 + B / l2
(2)
where B (mm) is the width of the slot and l2 (mm) is particle spacing within the segment. According to Eq. (2), hm of the first row of particle is much larger than that of subsequent diamond particles because of the existence of slot, with the ratio of hm1 to hm2 only related to B/l2 when other processing parameters remain unchanged.
4.2.2. Distribution characteristics of hm in circular saw The diamond particles located in the front of segment along the direction of cutting arc length are defined as the first row of particles, followed by the subsequent particles as the sawblade rotating one way during the sawing process of circular saw. Particles 1′ (final particle) on the surface of upper segment and particles 1, 2, 3 (1 is the first particles, 2, 3 are the subsequent particles) on the surface of latter segment are selected with equal spacing on the surface of segment 2 (Fig. 15).
4.2.3. Load distribution model of single particle in circular saw Xu and Yu [24] built the functional relationship between the normal force per diamond particle fn and hm based on the research in rock crushing.
fn = kn⋅hmn
(3)
where kn is parameter related to face angle of diamond particle and n is
Fig. 5. The particle protrusion height measurement. 5
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Fig. 6. Profile morphology of worn segment (a) segment 1 (b) segment 2 (c) segment 3.
diamond, which can easily lead to more serious macro-fractured crystals at the front end of segment. Meanwhile, particle spacing further increases by diamond shedding and macro breakage at the front end, which conducts to the enlargement of chip thickness and load per diamond and finally results in continuous increase in the proportion of macro-fractured crystals. Moreover, rapid wear on the matrix bond, higher particle protrusion height and poorer retention of particle resulted from erosion wear at the front end of segment, will lead to an increase in the proportion of pull out crystals. Conversely, diamond shedding reduces the wear resistance of segment and further accelerates the wear of segment. This is a process of continuous deterioration, resulting in a higher proportion of serious abnormal failure of diamond particles (macro-fractured and pull-out particles) at the front end, and further leading to an uneven wear of the front and rear end of segment 1. Fig. 7. The residual height of different parts of segment.
4.3. Compatibility between diamond and matrix bond 4.3.1. Sawing behavior of diamond with different quality When diamond A of medium quality was employed, abrasion and breakage are easy to occur in sawing most minerals (such as feldspar, etc.) due to its medium resistance to pressure and impact, and more macro-fractured crystals appear and the sawing ability would be lost when encountering large loads or mineral components (such as quartz) that particularly difficult to cut. However, most minerals can be easily cut without obvious abrasion and micro-fractured crystals would occur only confronting with large loads or minerals particularly difficult to cut when adopting diamond B of high quality with regular crystal shape, flat surface, strong resistance of pressure and impact. As a consequence, diamond B of high quality leads to a lower proportion of macro-fractured crystals at the front end of segment 2 and 3 compared with segment 1 using diamond A of medium quality.
consist related to workpiece material. Ratios of normal force per diamond of the first row of particle to that of the rest particles can be obtained by substituting Eq. (2) into Eq. (3), which is described in the following equation.
fn1 / fn2 = (hm1/ hm2 ) n = (1 + B / l2 ) n
(4)
It can be concluded from Eq. (4), the normal force per diamond of the first row is much larger than that of subsequent particles, with the ratio of fn1 to fn2 related to B/l2 and increased by n power. The conclusion is consistent with the results of Xu, Shen and Huang [19] and Yu, Li and Xu [20] as described earlier. Therefore, the existence of the slot results in that the mechanical load of the first row of particle is much higher than that of the rest particles in sawing process, and even beyond the strength of the
Fig. 8. SEM morphology of working surface of worn segment (a) the front end (b) the rear end. 6
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Fig. 9. Worn diamond classification (a) emerging (b) whole (c) polished (d) micro-fractured (e) macro-fractured (f) pull-out.
matrix and lower residual height at the front end of segment. Diamond of high quality in segment 2 has a strong resistance to diamond breakage under large loads, which is more likely to lead to lower proportion of macro-fractured crystals. Nevertheless, the binding force of diamond decreases due to the smooth surface of advanced diamond, and the unchanged matrix bond wears faster than the diamond particles under serious erosion at the front end, which results in a slight increase in proportion of pull-out crystals, a tiny reduction in the residual height and a bit larger protrusion height compared with segment 1. The wear of matrix at the front end has been significantly weaken due to the adoption of metal bond of high wear resistance in segment 3, which leads to a decrease in the particle protrusion height and the ratio of pull-out particles and an obvious enhancement in residual height compared with segment 1 and 2. It indicates that the bond and diamond particles wear synchronously in segment 3 for their optimum compatibility, effectively reducing the ratio of abnormal failure of diamond particles at front end, improving the wear nonuniform of surface and prolonging the service life of segment. 4.4. Design proposals for diamond tools
Fig. 10. The proportion of worn diamond particles in different parts of segment 1.
Based on the difference of wear mechanism and wear inhomogeneity in different parts of segments due to the discontinuity of segments discussed above, the following suggestions are put forward for the design of follow-up diamond tools. High quality diamond would be used at the front end and ordinary quality diamond would be used at the rear end according to the load distribution of diamond particles at different areas on the segment surface. Flushing abrasive erosion is dominant at the front end of the segment and the rear end is mainly abrasive wear, resulting in further wear deterioration of matrix and lower residual height at the front end of segment. The increase of proportion of Co and the introduction of W
4.3.2. Compatibility between diamond and matrix bond Particle protrusion height is the result of the combined action of particle wear and matrix wear. Segment 1 adopting metal bond of general quality displays serious wear of matrix and larger particle protrusion height as a result of the erosion wear occurring at the front end of segment, which increases the proportion of shedding crystals in advance without undergoing normal wear processes under large loads. On the contrary, more shedding diamond particles reduces the abrasion resistance of the segment, leading to further wear deterioration of 7
International Journal of Refractory Metals & Hard Materials 83 (2019) 104961
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Fig. 11. The proportion of worn diamond particles in different part of segments (a) the front end (b) the rear end.
Fig. 12. Particle protrusion height of different part of segment.
helps to improve the wear resistance of matrix for the front end and general quality matrix composition are maintained for the rear end. It is considered that the diamond concentration of the front end is appropriately increased to make up for the abnormal failure of diamond particles due to severe erosion wear and the large mechanical load at
Fig. 14. Diagram of device motion and chip topography.
the front end in time, while the diamond concentration at the rear end is moderately reduced to improve the utilization rate of diamond
Fig. 13. SEM morphology of matrix bond of worn segment (a) flush erosion (b) abrasive wear. 8
International Journal of Refractory Metals & Hard Materials 83 (2019) 104961
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Acknowledgment This work is supported by Taishan industrial leading talent project (tscy20150228) of Shandong Province, China. The authors are deeply grateful to Rizhao Hein Saw Co., Ltd. and Shandong Renown Diamond Tools Co., Ltd. for supporting this research by providing the circular sawing machine and the diamond tools. References [1] N.G. Yılmaz, R.M. Goktan, Y. Kibici, An investigation of the petrographic and physico-mechanical properties of true granites influencing diamond tool wear performance, and development of a new wear index, Wear 271 (2011) 960–969. [2] S. Turchetta, L. Sorrentino, C. Bellini, A method to optimize the diamond wire cutting process, Diam. Relat. Mater. 71 (2017) 90–97. [3] H.K. Tonshoff, G. Warnecke, Research on stone sawing, Adv. Ultrahard. Mater. Appl. Technol. 1 (1982) 36–49 P. Daniel, Hornbeam, ed. England. [4] X.P. Xu, Prevailing mechanisms for circular sawing of granites with diamond impregnated segments, Mater. Manuf. Process. 15 (2000) 123–138. [5] H.D. Jerro, S.S. Pang, C. Yang, R.A. Mirshams, Kinetic Analysis of Chipping Materials Using Superabrasive Diamond Tools, ASME, 1995. [6] S. Turchetta, Cutting force on a diamond grit in stone machining, Int. J. Adv. Manuf. Technol. 44 (2009) 854–861. [7] J. Konstanty, Theoretical analysis of stone sawing with diamonds, J. Mater. Process. Technol. 123 (2002) 146–154. [8] A.J. Gant, I. Konyashin, B. Ries, A. McKie, R.W.N. Nilen, J. Pickles, Wear mechanisms of diamond-containing hardmetals in comparison with diamond-based materials, J. Refract. Met. Hard Mater. 71 (2018) 106–114. [9] H.K. Tönshoff, H. Hillmann-Apmann, J. Asche, Diamond tools in stone and civil engineering industry: cutting principles, wear and applications, Diam. Relat. Mater. 11 (2002) 736–741. [10] Y.S. Liao, S.Y. Luo, Wear characteristics of sintered diamond composite during circular sawing, Wear 157 (1992) 325–337. [11] S.Y. Luo, Characteristics of diamond sawblade wear in sawing, Int. J. Mach. Tools Manuf. 36 (1996) 661–672 (612). [12] A. Ersoy, S. Buyuksagic, U. Atici, Wear characteristics of circular diamond saws in the cutting of different hard abrasive rocks, Wear 258 (2005) 1422–1436. [13] Q. Sun, J.S. Zhang, Z. Wang, H. Zhang, J. Fang, Segment wear characteristics of diamond frame saw when cutting different granite types, Diam. Relat. Mater. 68 (2016) 143–151. [14] I. Ucun, K. Aslantas, I.S. Büyüksağiş, S. Taşgetiren, Effect of cooling liquids on cutting process using diamond segmented disc of natural stones, Proc. Inst. Mech. Eng. Part C. 227 (2013) 2315–2327. [15] I.S. Buyuksagis, Effect of cutting mode on the sawability of granites using segmented circular diamond sawblade, J. Mater. Process. Technol. 183 (2007) 399–406. [16] G. Aydin, I. Karakurt, K. Aydiner, Wear performance of saw blades in processing of granitic rocks and development of models for wear estimation, Rock Mech. Rock. Eng. 46 (2013) 1559–1575. [17] İ. Ucun, K. Aslantas, İ.S. Büyüksagis, S. Tasgetiren, An investigation on the effect of diamond concentration and matrix material composition in the circular sawing process of granites, Proc. Inst. Mech. Eng. Part C. 225 (2010) 17–27. [18] A.D. Ilio, A. Togna, A theoretical wear model for diamond tools in stone cutting, Int. J. Mach. Tools Manuf. 43 (2003) 1171–1177. [19] X.P. Xu, J.Y. Shen, H. Huang, Analysis of key factors in order to realize sawing of granites with high efficiency, Chin. J. Mech. Eng. 34 (1998) 104–110. [20] Y.Q. Yu, Y. Li, X.P. Xu, Load-bearing analysis of diamond during sawing granite, exploration engineering, Rock Soil Drill. Tunneling (2001) 59–62 (in Chinese). [21] H. Huang, G.Q. Huang, X.P. Xu, An experimental study of machining characteristics and tool wear in the diamond wire sawing of granite, Proc. Inst. Mech. Eng. Part B. 227 (2013) 943–953. [22] H. Zhang, J.S. Zhang, S. Wang, Comparison of wear performance of diamond tools in frame sawing with different trajectories, J. Refract. Met. Hard Mater. 78 (2019) 178–185. [23] B. Malkin, Grinding Thchnology Theory and Application of Machining with Abrasives, Johnwiley and Sons, 1989. [24] X.P. Xu, J. Yu, Rock Crushing, China Coal Industry Publishing House, Beijing, 1984 (in Chinese).
Fig. 15. Distribution characteristics of hm on worn segment surface.
particles. Furthermore, full consideration was taken into the compatibility between diamond and matrix bond to balance the sharpness and abrasion resistance of segments and realize the constant wear of diamond and matrix. Wear performance prediction tests for diamond tools can be conducted on a CNC machining center equipped with force sensors and data acquisition systems to establish the relationship model between tool wear of force signal. A diamond disc as the machining tool would be mounted on the mandrel of the CNC machining center，which is composed of a disk-like support and segments welded to the edge it. The kinetic energy of the mechanical shaft is transferred to the diamond particles and the segments made of diamonds and metal bond are used for cutting. Different machining conditions are simulated by adjusting different cutting parameters. 5. Conclusion In order to investigate the wear characteristics at different regions of diamond segments, the wear morphology of the front and rear end of segment by matching diamond of different quality and matrix bond of different abrasion resistance were discussed by experiments. The conclusions could be drawn as follows. 1 The surface wear morphology of conventional segment presents obvious nonuniformity, and the residual height of the front end is obvious lower than that of the rear end due to the higher abnormal failure efficiency of diamond particles. 2 The wear characteristics of diamond particles for different parts of traditional segment surface can reflect the wear mechanism of the matrix and the load characteristics of the diamond. Erosion wear is dominant at the front end of the segment and the load of the first row of particle is much large than that of the rear end due to the existence of a slot, resulting in high proportions of pull-out and macro-fractured crystal. 3 Reasonable matching of diamond particles with different quality and metal bond with different wear resistance contributed to the reduction of diamond abnormal failure(macro-fractured and pull out crystal)and the promotion of uniformity of segment wear. 4 Suggestions are put forward for the design of follow-up diamond tools from the aspects of matrix composition, diamond quality and diamond concentration and experimental verification based on the difference of wear mechanism and wear inhomogeneity in different parts of segments
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