Materials Science Forum Online: 24-12-15 ISSN: 1662-9752, Vols. 471-472, pp 77-81 doi:1.428/www.scientific.net/msf.471-472.77 Materials Science Forum Vols. *** (24) pp.77-81 24 Trans Tech Publications, Switzerland online at http://scientific.net 24 Trans Tech Publications, Switzerland Performance of Diamond Segments in Different Machining Processes X.P. Xu 1,a, Y.B. Hong 1,a and S. Chen 1,a 1 Key Research Lab for Stone Machining, HuaQiao University, Quanzhou, Fujian 36221, China a xpxu@hqu.edu.cn Keywords: Diamond, Granite, Sawing, Dressing, Grinding Abstract. An investigation is reported of the performance of diamond impregnated segments in three machining processes - circular sawing of granite with diamond segments, dressing of diamond segments with refractory bricks and surface grinding of diamond segments with an alumina wheel. Two kinds of segments were fabricated by incorporating diamonds (either coated or uncoated) into an iron-based bond matrix. Measurements were made of the horizontal and vertical force components in the machining processes. SEM was used to examine the diamond-matrix bonding states and the ground surfaces of the segments. The changes of forces and segment wear (weight loss and wear performance) were found to be basically consistent for the three machining processes. Introduction It is estimated that one of the biggest consumptions of synthetic diamond lies in the processing of natural stone materials, in which case sawing is perhaps the most important process with regard to the production cost and efficiency. The tools most widely used for sawing are segmented circular sawblades. The segments are fabricated by embedding diamonds into a metal matrix mainly using the methods of powder metallurgy. In order to optimize the compositions of a diamond segment, the performance of the segment needs to be known fast and economically. In spite of its accuracy in estimating the performance of diamond segments, sawing of stone with a real sawblade is a time-consuming process. In many previous studies, the mechanical properties of diamond segments, such as transverse rupture strength, impact strength and hardness, were widely used to investigate the behaviors of diamond segments with different compositions [1-5]. However, it was found to be difficult in establishing a relationship between the wear performance and these mechanical properties [5-6]. Some studies investigated the effects of segment compositions through one-segment sawing, but it is much different than the sawing with a whole sawblade. In order to exploit the feasibility to assess the sawing ability of a diamond segment without doing many practical sawing tests, the present study was carried out to compare the performance of diamond sawblade segments in three different machining processes - circular sawing of granite with diamond segments, dressing of diamond segments with refractory bricks and surface grinding of segments with an alumina wheel. It is hoped that the behaviors of the diamond segments in different machining processes can provide not only useful guidelines for the optimization of segment compositions but also a basis for proposing a simple method to know the sawing ability of diamond segments. Experimental Diamond Segments. Diamond of 35/4 US mesh was used at a concentration of 35 (1.54carat/cm 3 ) in fabricating diamond segments. Fe, Cu, Sn, Ni and WC were used as the bond constituents for the segments, but Fe is around 5 wt %. The segments were sintered at 78 C in graphite moulds on an automatic hot pressing machine at an applied pressure of 35Mpa. Original diamonds and coated diamonds were added into the matrix powders respectively to produce two kinds of segments. Being measured by a Rockwell B hardenss tester, the average hardness value of the two kinds of segments were found to be 98. The microstructure of matrix and the diamond-matrix bonding were examined All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of Trans Tech Publications, www.ttp.net. (ID: 13.23.136.75, Pennsylvania State University, University Park, USA-1/5/16,16:4:26)
78 Advances in Materials Manufacturing Science and Technology 78 Advances in Materials Manufacturing Science and Technology by a HITACHI S-35 scanning electron microscope (SEM). Twenty-four segments of 4 3 1mm were brazed to the periphery of a circular steel core to form a segmented diamond sawblade. Two pieces of sawblades with diameter d s =35mm were made for the two different kinds of segments. Surface Grinding. The test rig for surface grinding of the segments is illustrated in Fig.1. Grinding tests were carried out on an M7115 grinder. A vitrified Al 2 O 3 wheel was used of diameter d s =25mm and width b=24.5mm. The peripheral speed of wheel (v s ), depth of cut (a p ) and workpiece traverse speed (v w ) were fixed at 18.6m/s, 2µm and 24cm/min respectively. The Al 2 O 3 wheel was dressed using a single-point diamond dresser before grinding of each diamond segment. No coolant was used in grinding. The horizontal and vertical force components (F h and F v ) were measured in grinding with a piezoelectric platform dynamometer (Kistler 9257BA). The force signals were fed into an A/D converter and sampled by a personal computer. Before grinding, the segments were cleaned and dried for measuring their weights. After 25 passes of grinding, they were cleaned and dried again. The percentage of weight loss was obtained from their weight changes before and after grinding. The morphologies of ground segment surfaces were examine by the SEM. v s Wheel v s Sawblade Diamond segment Dynamometer v w F h F v Worktable Fig.1 Test rig for surface grinding Fig.2 Test rig for dressing and sawing Dressing. The test rig for dressing is illustrated in Fig.2. Dressing of the segments was carried out in circular sawing of synthetic refractory bricks on an experimental sawing machine. Peripheral speed of wheel (v s ), depth of cut (a p ) and workpiece traverse speed (v w ) were fixed at 28.8m/s, 2mm and 24cm/min respectively. Tap water was used as the cutting fluid in dressing. The horizontal and vertical components of sawing forces were measured with the piezoelectric dynamometer. The force signals were fed into the A/D converter and sampled by the PC. Sawing of Granite. The experimental set-up and conditions for sawing of granite are same as those for dressing. The workpiece material for sawing was gray granite consisting of approximately 25% quartz of 1.-1.5 mm grain size, 55% plagioclase, 15% alkaline feldspar, and 5% mica and other constituents. The wear of diamond segments was assessed in terms of wear performance (W), which is defined as the ratio of the area of material sawn to the radial wear of the segments. Results and Discussion a p A/D PC Granite or refractory brick F F h v Morphologies of Segment Fracture Surfaces. SEM pictures of matrix and diamonds on segment v w Dynamometer a p PC A/D (a) bond matrix (b) coated diamond (c) uncoated diamond Fig.3 SEM pictures for the fracture surfaces of the specimens
Materials Science Forum Vols. 471-472 79 Materials Science Forum Vols. *** 79 fracture surfaces are shown in Fig.3. Although the sintering quality of the matrix is good enough to hold diamonds, the contact between coated diamonds and matrix is tighter than uncoated diamonds. Grinding with Al 2 O 3 Wheel. The changes of vertical and horizontal force components are plotted in Fig.4 for the total 25 passes of grinding. It can be seen that during initial 1 passes of grinding two forces for coated diamonds are bigger than uncoated ones. The vertical force for uncoated diamonds starts to decrease after 1 passes of grinding, whereas the horizontal force starts to decrease at a earlier stage. The vertical force for coated diamonds starts to decrease after 18 passes of grinding, whereas the horizontal force decreases earlier. Fig.5 gives the SEM pictures for the ground surfaces of the two segments. Analogous to Figs.3b and 3c, the contact between the coated diamonds and matrix is tighter as compared with uncoated diamonds, indicating a stronger hold of matrix on coated diamonds in grinding. Due to the comparatively weaker hold of matrix on uncoated diamonds, pull-out holes were found on the ground segment (see Fig.5c). Vertical force, F v 8 6 4 2 5 1 15 2 25 Serial grinding number Horizontal force, F h 4 3 2 1 5 1 15 2 25 Serial grinding number Fig.4 Vertical and horizontal forces in surface grinding of the segments Pull-out (a) coated diamond (b) coated diamond (fractured) (c) uncoated diamond Fig.5 SEM pictures of ground segment surfaces Before grinding, diamonds are fully embedded in the matrix and no diamonds protrudes above the matrix. As grinding proceeds the matrix is removed progressively and diamonds emerge from the matrix. With the increasing protrusion of diamonds, it becomes more difficult to remove materials from segments owing to the resistance of diamond grits. This can account for the increasing tendency of forces during initial grinding stages. But the resistance to the cutting of Al 2 O 3 wheel is different for the two segments. The stronger hold of matrix on coated diamonds also increased the resistance to cutting because diamonds are mainly removed in fracture (see Fig.5b), whereas some uncoated diamonds were removed through pop-outs (see Fig.5c). After a period of grinding, the segment surfaces may become smooth again due to the failure of diamond grits, thereby leading to the decreasing tendency of grinding forces. Due to the difference in diamond hold, the percentage of
8 Advances in Materials Manufacturing Science and Technology 8 Advances in Materials Manufacturing Science and Technology weight loss for the segment with coated diamonds was found to be about 75% of that for the segment with uncoated diamonds. Dressing with Refractory Bricks. The changes of vertical force in sawing of refractory bricks are shown in Fig.6. It can be seen that the force decreases with the sawing distance at progressively diminishing rates and reach to stable stages, reflecting the sharpening actions of the bricks to the segments in sawing. At the beginning stages of sawing, the force for coated diamonds is higher than uncoated diamonds. However, it becomes lower after sawing 4.3m as compared with uncoated diamonds, which might be due to the better hold of matrix on the coated diamonds and hence a higher diamond protrusion. From the percentage of each diamond state on dresses segment surfaces (see Fig.7), it can be seen that the pop-outs for coated diamonds are a little lower than uncoated diamonds. Vertical force, F v 3 25 2 15 5 Percentage (%) 8 6 4 2 Whole crystal Micro fracture Macro fracture Wear flat Pop-out 2 4 6 8 1 Sawing distance, L (m) Segment type Fig.6 Vertical force in dressing Fig.7 Diamond states on dressed segments Sawing of Granite. The changes of two force components are plotted in Fig.8 versus sawing distance, in which case sawing began with newly dressed sawblades (by refractory bricks) and continued for more than 11m without redressing of the sawblades. Although the forces for the two kinds of segments are comparable at initial sawing stages, they become lower for the segments with coated diamonds as compared with those for uncoated diamonds. 16 3 Vertical force, F v 12 8 4 Horizontal force, F h 2 4 8 12 Sawing distance, L (m) 4 8 12 Sawing distance, L (m) Fig.8 Vertical force and horizontal force components versus sawing distance An example of the changes of diamond grit protrusion height during the long-time sawing process is given in Fig.9. It can be seen that diamond protrusion height decreases with increasing sawing distance which might be due to the progressive wear of diamond grits in sawing. This can account for the increasing tendency of forces with increasing sawing distance as indicated in Fig.9. Since the change of diamond protrusion is a dynamic process, the forces exhibit fluctuation behaviors.
Materials Science Forum Vols. *** 81 Although the diamond protrusion heights just after dressing are comparable for the coated diamonds and uncoated diamonds, the former can keep a higher level, thereby leading to its lower forces after a period of grinding. The increased hold of matrix on coated diamonds might also be the main contribution to the better wear performance as indicated in Fig.1. It needs to note that the results of wear performance are consistent with those of segment weight loss in surface grinding. Protrusion height, h (µm). 8. 6. 4. 2.. Materials Science Forum Vols. 471-472 81 Newly dressed 24 99 Sawing distance, L(m) h W (m 2 /mm) 1. 8. 6. 4. 2.. Type of segment Fig.9 Change of grit protrusion height Fig.1 Wear performance of two segments Conclusions During the three machining processes, the changes of forces and segment wear are closely related to the conditions of diamond protrusion. The results obtained in the three machining processes are basically consistent although it is difficult to establish a quantitative relationship at this stage. A simple method to evaluate the sawing ability of a diamond segment might be proposed provided the interconnected relationships between dressing, grinding, sawing or other simple machining processes can be found, which still deserves much future work. Acknowledgements The research was supported by Grant No. 51753 from the National Natural Science Foundation of China, and by matching Grant (F223) from the Natural Science Foundation of Fujian Province in China. References [1] Y.S. Liao and S.Y. Luo: J. Mater. Sci. Vol. 28 (1993), p. 1245 [2] Y.H. Wang, J.B. Zang and M.Z. Wang: J. Mater. Proc. Tech. Vol. 129 (22), p. 371 [3] Q.L. Dai and X.P. Xu: J. Mater. Proc. Tech. Vol. 129 (22), p. 427 [4] J. Dwan: Ind. Diamond Rev. Vol. 63 (23), p. 5 [5] S.W. Webb: Diamond Relat. Mater. Vol. 8 (1999), p. 243 [6] X.P. Xu and Y. Li: Key Eng. Mater. Vol. 259-26 (24), p. 225.
Advances in Materials Manufacturing Science and Technology 1.428/www.scientific.net/MSF.471-472 Performance of Diamond Segments in Different Machining Processes 1.428/www.scientific.net/MSF.471-472.77 DOI References [6] X.P. Xu and Y. Li: Key Eng. Mater. Vol. 259-26 (24), p. 225. 1.428/www.scientific.net/KEM.259-26.225