Handbook of Advanced Ceramics Machining Episode 9 pdf

9.4.5 ELID Grinding of Ceramics on Vertical Grinding Center (Bandyopadhyay et al., 1997) The experiments were carried out on a vertical machining center. The silicon nitride workpieces were clamped to a vice firmly fixed onto the base of a strain gauge dynamometer. The dynamometer was clamped onto the machining center table and the reciprocating grinding operation was performed. A direct-current pulse generator was used as a power supply. The square- wave voltage was of 60–90 V with a peak current of 16–24 A. The pulse width was adjusted to 4 msec on-time and off-time. Different values for the depth of cut and for the width of cut were explored. Material removal rates of 250 mm 3 =min up to 8000 mm 3 =min were obtained. A comparison between the results obtained after an ordinary grinding operation and the results obtained after an ELID grinding operation was carried out. A modified ELID dressing procedure was also studied. The modified ELID dressing was performed in two stages: (a) at 90 V for 30 min; the insulating oxide layer was mechanically removed by an aluminum oxide stick of #400 grit size at 300 rpm; (b) another dressing stage at 90 V for 30 min. (Figure 9.20, Figure 9.21, Figure 9.22, and Figure 9.23) The conclu- sions of the study were as follows (see also Figure 9.24): 0.7 0.1 0.09 0.08 0.07 0.06 0.05 0.04 0.03 0.02 0.01 0 0.6 0.5 0.4 0.3 R z , R max (µm) R a (µm) 0.2 0.1 0 0 1000 2000 3000 Wheel grit size R a R z R max 4000 5000 6000 7000 8000 FIGURE 9.20 Effect of grit size on surface-roughness patterns. Ioan D. Marinescu / Handbook of Advanced Ceramics Machining 3837_C009 Final Proof page 226 6.10.2006 2:22am 226 Handbook of Advanced Ceramics Machining – ELID grinding can achieve high material removal rates. – ELID grinding is recommended for low-rigidity machine tools and low- rigidity workpieces. – The grinding force increases continuously during ordinary grinding. 100 (ρm/cm) 0.02 (ρm/cm) Material Si 2 N 4 #4000 mesh grinding wheel FIGURE 9.21 Typical surface-roughness patterns for #4000 mesh size wheel. 0.07 0.06 0.05 0.04 0.03 R a (µm) 0.02 0.01 0 10 12 14 16 #4000 #2000 #500 #325 V (m/sec) 18 20 22 FIGURE 9.22 Effect of cutting speed on surface roughness. (From Ohmori, H., Takahashi, I., and Bandyo- padhyay, B.P., J Mat Proc Technol, 57, 272, 1996. With permission.) Ioan D. Marinescu / Handbook of Advanced Ceramics Machining 3837_C009 Final Proof page 227 6.10.2006 2:22am Effectiveness of ELID Grinding and Polishing 227 R a (µm) 0.1 0.09 0.08 0.07 0.06 0.05 0.04 0.03 0.02 0.01 0 80 100 120 Feed rate (mm/min) 140 160 180 200 #4000 #2000 #500 #325 FIGURE 9.23 Effect of feed rate on surface roughness. (From Ohmori, H., Takahashi, I., and Bandyopadhyay, B.P., J Mat Proc Technol, 57, 272, 1996. With permission.) 0 0 (a) 1,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000 9,000 10,000 5 15 10 20 25 35 30 40 Normal grinding force (kgf) Volume of material removed, 3 mm 3 V = 1200 m/min f = 5000 mm/min DOC = 0.05 mm WOC = 2 mm CIFB-D wheel #170 (avg 80 µm) Material: silicon nitride FIGURE 9.24 Relationship between the volume of material removed and the grinding force for: (a) conven- tional grinding (From Bandyopadhyay, B.P., Ohmori, H., and Takahashi, I., J Mat Proc Technol, 66, 18, 1997. With permission.) Ioan D. Marinescu / Handbook of Advanced Ceramics Machining 3837_C009 Final Proof page 228 6.10.2006 2:22am 228 Handbook of Advanced Ceramics Machining 0 5 15 10 20 25 35 30 40 Normal grinding force (kgf) 0 (b) 1,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000 9,000 10,000 Volume of material removed, 3 mm 3 V = 1200 m/min f = 5000 mm/min DOC = 0.05 mm WOC = 2 mm CIFB-D wheel #170 (avg 80 µm) Material: silicon nitride 0 5 15 10 20 25 35 30 40 Normal grinding force (kgf) 0 (c) 1,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000 9,000 10,000 Volume of material removed, 3 mm 3 V = 1200 m/min f = 5000 mm/min DOC = 0.05 mm WOC = 2 mm CIFB-D wheel #170 (avg 80 µm) Material: silicon nitride FIGURE 9.24 (continued) (b) ELID grinding after ELID dressing; (c) ELID grinding after modified ELID dressing. Ioan D. Marinescu / Handbook of Advanced Ceramics Machining 3837_C009 Final Proof page 229 6.10.2006 2:22am Effectiveness of ELID Grinding and Polishing 229 – Grinding force is lesser during ELID grinding when compared with conventional grinding; this effect became more visible after 18 min of grinding. – An increase in the voltage value during ELID grinding will reduce the value of the grinding force even more; this effect became more visible after 18 min of grinding. – Full potential of ELID grinding can be achieved only after 24 min of grinding when the grinding force stabilizes at a low value. – ELID and conventional grinding produced almost the same surface finish in rough grinding. – The grinding force was constant and low after the modified ELID dressing procedure was applied to the wheel. 9.4.6 ELID Grinding of Bearing Steels (Qian et al., 2000) In this research, ELID as a superfinishing technique for steel bearing com- ponents was studied. The experiments were conducted in both traverse and plunge in feed modes. The wheels utilized were cast-iron-bonded using CBN as abrasive. The experiments were carried out on a common cylindrical grinder with a 3.7 kW motor spindle. The negative electrode was made out of stainless steel. A Noritake AFG-M grinding fluid diluted to 1:50 at a rate of 20–30 L=min was used as electrolytic fluid. A direct-current pulse generator was used as a power supply. The square-wave voltage was of 60–150 V with a peak current of 100 A. The pulse width was adjusted to 4 msec on-time and off-time. Three types of experiments were conducted: 1. Traverse and plunge ELID grinding for evaluating the effects of the grinding wheel mesh size and grinding method on surface rough- ness and waviness value. 2. Traverse grinding with different mesh size wheels to assess the influence of the mesh size of the wheel over the surface finish and material removal rate. 3. ELID grinding with #4000 mesh size wheel was compared with honing and electric finish methods. The conclusions were as follows: – ELID grinding as compared to conventional grinding offered a better surface finish (R a ¼ 0.02 mm for #4000 wheel). – Plunge ELID grinding outputted poorer surface finish than traverse ELID grinding, especially for coarser grit abrasive wheels (see Figure 9.25). – Waviness of ground surface improves with the increase in wheel mesh size (Figure 9.26). Ioan D. Marinescu / Handbook of Advanced Ceramics Machining 3837_C009 Final Proof page 230 6.10.2006 2:22am 230 Handbook of Advanced Ceramics Machining 500 ELID Traverse mode grinding V a : V w : V r : 16.5 m/sec 0.07 m/sec 1.66 mm/sec Depth of cut : 1−2 µm Spark-out : 10 Grinding time : 260 sec E o : 120 V: I p : 48 A T on/off : 4 µsec No ELID Roughness R a (nm) 450 400 350 300 200 250 150 100 50 0 #170 #600 (a) #1200 #4000 1200 ELID Plunge mode grinding V a : 16.5 m/sec V w : 0.07 m/sec V r : 1.66 mm/sec Spark-out : 30 sec Grinding time : 45 sec E o : 120 V: I p : 48 A T on/off : 4 µsec No ELID Roughness R a (nm) 1000 800 600 400 200 0 #170 #600 (b) #1200 #4000 FIGURE 9.25 Comparison of roughness: (a) traverse; (b) plunge. Ioan D. Marinescu / Handbook of Advanced Ceramics Machining 3837_C009 Final Proof page 231 6.10.2006 2:22am Effectiveness of ELID Grinding and Polishing 231 1200 ELID (M band) No ELID (M band) ELID (H band) No ELID (H band) Traverse mode grinding Waviness (µm/sec) 1000 800 600 400 200 0 #170 #600(a) #1200 #4000 ELID (M band) No ELID (M band) ELID (H band) No ELID (H band) Plunge mode grinding Waviness (µm/sec) 1000 800 600 400 200 0 #170 #600 (b) #1200 #4000 FIGURE 9.26 Comparison of waviness: (a) traverse; (b) plunge. Ioan D. Marinescu / Handbook of Advanced Ceramics Machining 3837_C009 Final Proof page 232 6.10.2006 2:22am 232 Handbook of Advanced Ceramics Machining – ELID process is stable for traverse mode grinding and not so stable for plunge mode grinding (see Figure 9.27). – Roundness of the ground surface increases with the mesh size of the used wheel. – Out-of-roundness can be negatively affected by the stiffness of the machine tool, not only as a result of the grinding operation. – ELID traverse grinding tends to offer a more promising potential than plunge mode grinding. 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 #170 #600 (a) #1200 #4000 ELID No ELID Traverse mode grinding Roundness (µm) ELID No ELID Plunge mode grinding Roundness (µm) 2.5 2.0 1.5 1.0 0.5 #170 #600 #1200 #4000 (b) FIGURE 9.27 Comparison of roundness: (a) traverse; (b) plunge. Ioan D. Marinescu / Handbook of Advanced Ceramics Machining 3837_C009 Final Proof page 233 6.10.2006 2:22am Effectiveness of ELID Grinding and Polishing 233 – A number of three to four spark-out passes will improve the precision (waviness and roundness) of the ground surface. – Effects of grinding parameters on surface roughness for ELID grinding and conventional grinding are comparable. – Increased depth of cut and increased traverse rate worsen the surface finish. – ELID grinding offers better results than both honing and electric polishing (see Figure 9.28). – Smooth ELID ground surfaces have poorer high band waviness than honed ones, explained by the tool performance because of the smaller contact zone. – ELID grinding technique induces compressive surface stress of about 150–400 MPa, with a smaller peak than that outputted by a honing process of 600–800 MPa. – The depth of the compressive layer produced by ELID operation (10 mm) is half the one produced by a honing operation (15–20 mm). – The cycle time of ELID grinding is twice as large as the one that characterizes the honing and the electric polishing operations; but better roughness and higher removal rate achieved through ELID grinding by a coarser wheel and higher traverse speed prove ELID grinding more cost-effective for small batch production situations. 9.4.7 ELID Grinding of Ceramic Coatings (Zhang et al., 2001a) Ceramic coatings include a large group of subspecies, such as CVD-SiC, plasma spray deposited aluminum oxide, and plasma spray deposited 240 210 180 150 120 Waviness (µm/sec) 90 60 30 0 L band M band H band Honing Electrofinishing ELID grinding Max FIGURE 9.28 Surface waviness with different processes. Ioan D. Marinescu / Handbook of Advanced Ceramics Machining 3837_C009 Final Proof page 234 6.10.2006 2:22am 234 Handbook of Advanced Ceramics Machining chromium oxide. The efficient machining and the required quality of these ceramic coatings have not been mastered yet. In this research, a comparative study of diamond grinding of ceramic coatings on a vertical grinder was done. Two types of dressing procedures as applied to cast-iron-bonded diamond wheel, with #4000 mesh size—alumina rotary dressing and ELID dressing and grinding—were compared. The conclusions can be synthe- sized as follows: – There is a critical current value for each electrolytic dressing system; when the current is smaller the thickness of the insulating oxide layer increases with the value of the current; otherwise, it decreases. – Thickness and depth of oxide layer largely depends on the coolant type. – A small increase in the wheel diameter or thickness after electrolytic dressing is noticed, conversely as in the rotary and other mechanical methods of dressing. – Roughness for the rotary dressing decreases sharper than ELID method in the first 3 min; after 3 min, the roughness decreased constantly for ELID grinding but showed a wavelike model for the dressing method. – The wear of abrasive grains will produce an instability of the grinding performance for dressing technique, while it remains constant for ELID technique. – Surface roughness depends on material properties in both methods. – All ceramic coatings except sintered SiC presented a better roughness after ELID dressing than after rotary dressing. – Plasma spray deposited chromium oxide is difficult to grind to an extremely fine roughness. – For both dressing methods, the micrographs prove that the material removal mechanism presents both brittle-fracture and ductile modes; for the ELID dressing, more ductile mode than the brittle-fracture mode was present, except for sintered SiC; whereas for the rotary dressing more brittle-fracture mode than the ductile mode was present. – Ductile-mode grinding can be implemented even on a common grinder, by controlling the wheel topography. – For the ELID method, the interaction between the abrasive grain and the workpiece surface is accomplished through a spring-damper system (because of the existence of the oxide layer), whereas for rotary dressing, the contact is rigid and stiff (see Figure 9.29); oxide layer absorbs vibrations and reduces the actual exposed cutting edge of the abrasive grain. 9.4.8 ELID Ultraprecision Grinding of Aspheric Mirror (Moriyasu et al., 2000; see also Figure 9.30) The quality of soft x-ray silicon carbide mirrors influences the performance of modern optical systems. To accomplish the high precision of these Ioan D. Marinescu / Handbook of Advanced Ceramics Machining 3837_C009 Final Proof page 235 6.10.2006 2:22am Effectiveness of ELID Grinding and Polishing 235 [...]... Marinescu /Handbook of Advanced Ceramics Machining 3837_C010 Final Proof page 254 18.10.2006 6:36pm Handbook of Advanced Ceramics Machining Ioan D Marinescu /Handbook of Advanced Ceramics Machining 3837_C010 Final Proof page 255 Mono- Versus Polycrystalline Diamond Lapping of Ceramics %Pass 100.0 90 .0 80.0 80.0 70.0 70.0 60.0 60.0 50.0 50.0 40.0 40.0 30.0 30.0 20.0 20.0 10.0 255 %Pass 100.0 90 .0 18.10.2006... of ELID grinding on the flexural strength of silicon nitride, International Journal of Machine Tools and Manufacturing, Vol 39, 199 9, pp 8 39 853 Bandyopadhyay, B.P., Ohmori, H., and Takahashi, I., Efficient and stable grinding of ceramics by electrolytic in-process dressing (ELID), Journal of Materials Processing Technology, Vol 66, 199 7, pp 18–24 Ioan D Marinescu / Handbook of Advanced Ceramics Machining. .. 41, 193 , 2001 With permission.) Ioan D Marinescu / Handbook of Advanced Ceramics Machining 3837_C0 09 Final Proof page 240 6.10.2006 2:22am Handbook of Advanced Ceramics Machining 240 9. 4.12 ELID Grinding of Hard Steels (Stephenson et al., 2001) Hardened bearing steels like M50 was ultraprecision ground to produce an optical quality surface (Ra < 10 nm), using a 76 mm cBN grit and 500 mm depth of cut... optical components of 150–250 mm diameter 9. 4.11 ELID Precision Internal Grinding (Qian et al., 2000, 2001) Few researches have reported on mirror-surface internal grinding because of the limitation of the abrasive grit size applicable to nonmetallic bond Ioan D Marinescu / Handbook of Advanced Ceramics Machining 3837_C0 09 Final Proof page 238 6.10.2006 2:22am Handbook of Advanced Ceramics Machining 238... Ioan D Marinescu / Handbook of Advanced Ceramics Machining 3837_C0 09 Final Proof page 2 39 6.10.2006 2:22am Effectiveness of ELID Grinding and Polishing 2 39 rapidly because of the smaller diameter of the wheel The conclusions of the study are presented briefly here: – Because of the limitation of the wheel diameter, the wheel speed can be adjusted only within a small range; the effect of speed on work...Ioan D Marinescu / Handbook of Advanced Ceramics Machining 3837_C0 09 Final Proof page 236 6.10.2006 2:22am Handbook of Advanced Ceramics Machining 236 Wheel in conventional grinding x Y0 = A sinα Wheel in conventional grinding C0 Abrasive Damper, c Spring, k 1 Yr Abrasive Work Work Yr FIGURE 9. 29 Wheel–work interface models for ELID and conventional grinding... Journal of Applied Physics, Vol 87, no 6, 2000, pp 31 59 3164 Grobsky, K and Johnson, D., ELID Grinding of Large Optical (Glass Substrates), Report of Zygo Corporation, 199 8 Inaski, I., Speed-stroke grinding of advance ceramics, Annals of the CIRP, Vol 37, no 1, 198 8, p 299 Itoh, N and Ohmori, H., Grinding characteristics of hard and brittle materials by fine grain lapping wheels with ELID, Journal of Materials... behavior of brittle materials under the action of a diamond indenter Lateral and median=radial cracks were generated during the indentation process Material removal mainly results from the propagation of lateral cracks, which commonly takes place in the unloading 247 Ioan D Marinescu /Handbook of Advanced Ceramics Machining 3837_C010 Final Proof page 248 18.10.2006 6:36pm Handbook of Advanced Ceramics Machining. .. Ioan D Marinescu /Handbook of Advanced Ceramics Machining 3837_C010 Final Proof page 2 49 Mono- Versus Polycrystalline Diamond Lapping of Ceramics 18.10.2006 6:36pm 2 49 TABLE 10.1 Workpiece Material Properties Material Physical properties Density (g=cm3) Mechanical properties Tensile strength (MPa) Modulus of elasticity (GPa) Poisson ratio Compressive strength (MPa) Al2O3 99 .8% 3 .96 310 (at 258C) 220... surface roughness was Ra ¼ 1.5 mm 10.3 Experimental Results An important component of these lapping tests is the evaluation of the performance of monocrystalline and polycrystalline diamond slurry In Ioan D Marinescu /Handbook of Advanced Ceramics Machining 3837_C010 Final Proof page 250 Handbook of Advanced Ceramics Machining 250 Grain size = 1 µm 2.4 Grain size = 3 µm 2.4 Monocrystal 1.6 Monocrystal . Technol, 66, 18, 199 7. With permission.) Ioan D. Marinescu / Handbook of Advanced Ceramics Machining 3837_C0 09 Final Proof page 228 6.10.2006 2:22am 228 Handbook of Advanced Ceramics Machining 0 5 15 10 20 25 35 30 40 Normal. 8000 FIGURE 9. 20 Effect of grit size on surface-roughness patterns. Ioan D. Marinescu / Handbook of Advanced Ceramics Machining 3837_C0 09 Final Proof page 226 6.10.2006 2:22am 226 Handbook of Advanced Ceramics. #4000 FIGURE 9. 26 Comparison of waviness: (a) traverse; (b) plunge. Ioan D. Marinescu / Handbook of Advanced Ceramics Machining 3837_C0 09 Final Proof page 232 6.10.2006 2:22am 232 Handbook of Advanced Ceramics