拋光機設(shè)計,拋光機設(shè)計,拋光機,設(shè)計 Lapping and polishing process for obtaining super-smooth surfaces of quartz crystal J.L. Yuan * , P. Zhao, J. Ruan, Z.X. Cao, W.H. Zhao, T. Xing Research Center of Science, Zhejiang University of Technology, Hangzhou 310014, PR China Abstract The lapping and polishing processes to obtain the damage-free surfaces and A level surface roughness of quartz crystal is discussed and realized by adopting soft material polishers, fine abrasive powders, and suitable working environments, by taking account of the minimization of mechanical actions in polishing process. The material removal mechanism in the process of ultra-precision polishing is discussed, and the basic formation models of surface roughness are also put forward. A super-smooth surface of quartz crystal with 12 A level roughness have been obtained by adopting the SiO 2 abrasive powders and the K3 pitch polisher in the experiments. # 2003 Elsevier Science B.V. All rights reserved. Keywords: Lapping and polishing; Super-smooth surface; Quartz crystal 1. Introduction Material science and technology make remarkable pro- gress and the application of newly developed materials to various devices have increased rapidly. In particular, when fabricating a high-performance device, it is often necessary to adopt high-level lapping and polishing. Recently, the study of ultra-precision machining, which forms the van- guard of machining methods, has developed rapidly and its contributions to industry have been notable. When elevating such lapping and polishing methods to ultra-precision machining, it is essential to improve conventional polishing techniques steadily or add new working principles, thus ensuring the highest qualities and accuracy on worked surfaces. Ref. 1 shows that a soft polisher will reduce the deterioration of surface roughness, if meeting unfortu- nately with large abrasives or dusts in polishing. It is the most important to get satisfactorily a smooth working face and suitable elastic polisher. To obtain the super-smooth surface, it is also extremely important to select abrasives. The report 2 has shown that the ultra-precision polishing of quartz crystal can be realized by using SiO 2 fine powders. In this report, the processes to obtain the damage-free surfaces and A level surface roughness of quartz crystal is discussed and realized by adopting soft material polishers, fine abrasive powders, and suitable working environments, by taking account of the minimization of mechanical actions in polishing process. 2. Lapping mechanism and polishing mechanism In the process of lapping, the action effect of abrasives and the properties of lap material have the close relation. Abra- sives in the ways of rolling and micro-cutting remove the quartz crystal. The micro-cracks are produced on the quartz crystal surface due to the action of abrasives. It is the main way to remove quartz material in lapping. The crack area will burst apart because of micro-cracks extension and intersection, so quartz crystal is removed. The length dis- tribution of micro-cracks beneath the quartz surface is nearly equal. The higher is the load, the longer are the cracks. The general conclusion is that the propagation depth beneath the quartz surface is one-third of average abrasive size. The properties of polisher material and abrasive powders are the essential conditions to ensure the super-smooth surfaces. A soft polisher will reduce the deterioration of surface roughness 1, if meeting unfortunately with large abrasive or dusts in polishing. To obtain the super-smooth surface, it is extremely important both to select abrasives and get satisfactorily a smooth face and suitable elastic polisher. Hard abrasive will generate grooves, on material surface during lapping and polishing in general. However, this Journal of Materials Processing Technology 138 (2003) 116119 * Corresponding author. Tel.: 86-571-85132902. E-mail address: (J.L. Yuan). 0924-0136/03/$ see front matter # 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S0924-0136(03)00058-X mechanism does not apply to the ultra-precision polishing if the hardness of abrasive powder is equivalent to that of worked material. It has shown that the material removal process, containing both the initiation of point defects and the stochastic fracture at an atomic scale due to the bom- bardment of SiO 2 particles on the quartz crystal surface, may be considered as the essential part of the mechanism of ultra- precision polishing 2. 3. Experimental procedures 3.1. Determination of optimum lapping parameters The machining margin of quartz crystal is almost removed in lapping process, so the lapping efficiency makes great effect on the whole machining time. On the other hand, the lapped surface integrity will effect polishing time and quality. Experiment shows that the process parameters affecting surface roughness and lapping efficiency are abra- sive properties and size, concentration of lapping slurry, lapping speed and lapping pressure, etc. To ensure the surfaces machining accuracy of the quartz crystal, initial parallelism of the quartz specimens is adjusted to less than 0.5 mm. Then their roughness is improved on a conditioning ring-type lapping machine with #1000, #2000 and #4000 Al 2 O 3 powders. The lapping parameters (lapping speed and lapping pressure) effecting on the stock removal of quartz crystal are changed, and the relations between stock removal and the parameters are shown in Figs. 1 and 2. Fig. 1 shows that lapping speed is proportional to the stock removal. This is because, the bigger is the speed, the longer are the machining micro-cracks caused by abrasives cutting in unit time; as a result, the stock removal becomes larger. The experiments also show that the higher is the lapping speed, the smaller is the surface roughness. Fig. 2 shows the relation between lapping pressure and stock removal. It shows that stock removal is proportional to lapping pressure. This is because that, with the increase of lapping pressure, the single abrasive grain force exert- ing on the surface of the specimen and crack length beneath the surface of specimen relatively increase; this also causes the increase of the stock removal. But the increasing of lapping pressure is not unconstrained, as when the pressure increases too much, the quartz specimen will be broken. Fig. 3(a)(c) shows correspondingly roughness profiles of quartz crystal lapped by #1000, #2000 and #4000 Al 2 O 3 abrasives, respectively. The results show that the finer are the abrasives, the smaller are the scratches and indentation of single abrasive, and also the smaller is the micro-crack length. As a result, the smaller is the surface roughness, the smaller is the corresponding stock removal. Fig. 4 shows the relations among abrasive size, stock removal and surface roughness. In order to get higher quality and higher stock removal, the reasonable scopes of lapping parameters are as follows: concentration of lapping slurry is 2030 wt.%, lapping speed is 80170 m/min and lapping pressure is 100 150 g/cm 2 . 3.2. Ultra-precision polishing machining After lapping, the specimens are rinsed with distilled water and then wiped clean with absorbent cotton soaked with acetone. Then, put the quartz specimens together with the stainless steel jig on the conditioning ring-type polishing machine. Soft K3 pitch polisher (with 4 mm mesh groove) and SiO 2 powders were applied to polish of quartz crystal to obtain A level surface roughness. First, the quartz specimens are polished with 0.3 mm CeO 2 powders for 210 min to remove the damaged layer left by the lapping machining. Then, the specimens are polished with 500 A SiO 2 fine powders to obtain perfect surface. TheFig. 1. The relation between lapping speed and stock removal. Fig. 2. The relation between lapping pressure and stock removal. J.L. Yuan et al. / Journal of Materials Processing Technology 138 (2003) 116119 117 experimental process is carried in a clean room without dusts. The polishing conditions are as follows: polishing pressure is 18 g/cm 2 and polishing speed is 143.4 m/min. 4. Results and discussion In order to compare the polishing results, several kinds of powders are used in this study under the same polishing conditions. Fig. 5 shows the stock removals of quartz with varied abrasives. Figs. 68 show the roughness profiles relative to the abrasives of Fe 2 O 3 ,CeO 2 and SiO 2 , respec- tively. The stock removals calculated from Fig. 5 are: l.4, 7, and 8.4 A /s corresponding to Fe 2 O 3 , CeO 2 , and SiO 2 powders and the maximum roughness are 15, 25 and 12A corre- sponding to Fe 2 O 3 , CeO 2 , and SiO 2 powders. On the polished surfaces by SiO 2 powders, the maximum roughness is within 12A . This result means that the super-smooth surfaces of quartz crystal are obtained by taking account of the minimization of mechanical actions in polishing process. The material is removed at the atomic scale. Fig. 3. The roughness profiles of lapped quartz crystal. Fig. 4. The lapping relations among abrasives size, stock removal and surfaces roughness. Fig. 5. The polishing relations among abrasives size, stock removal and surfaces roughness. Fig. 6. Roughness profile polished by Fe 2 O 3 (by Talystep). 118 J.L. Yuan et al. / Journal of Materials Processing Technology 138 (2003) 116119 5. Conclusions The optimum scopes of lapping parameters of quartz crystal are determined by experiments. A conventional optical polishing method has been improved to ensure the super-smooth surfaces on quartz crystal. Soft K3 pitch polisher and SiO 2 powders were applied to polishing of quartz crystal to obtain A level surfaces roughness: (1) The mechanical action of abrasives includes rolling and micro-cutting in lapping process of quartz crystal. (2) The rolling actions of the abrasives form the indenta- tion with micro-cracks, the micro-cutting actions of the abrasives form scratches with cracks under the bottom. (3) Lapping speed and lapping pressure are proportional to lapping stock removal of quartz crystal. The finer abrasives will cause smaller surface roughness and lower stock removal. (4) The determined scopes of lapping parameters are as follows: concentration is 2030 wt.%, lapping speed is 80170 m/min and lapping pressure is 100150 g/cm 2 . (5) The properties of the polisher material and abrasive powders are essential conditions to ensure the super- smooth surfaces. (6) Under the given experimental conditions, 12A sur- face roughness of quartz crystal was obtained. (7) The stock removal polished with SiO 2 powders is 1.4 A /s, which confirms that the material removal is at the atomic scale. Acknowledgements The authors are thankful for the financial aid to this project supplied by Zhejiang Provincial Natural Science Foundation of China (501097) and Young Scientist Training Project of Zhejiang Provincial Natural Science Foundation of China (RC RC02066). References 1 T. Kasai, K. Horio, T. Karaki-Doy, Ann. CIRP 39 (1) (1990). 2 J.L. Yuan, Z.F. Tong, SME MR 91-193, 1991. Fig. 7. Roughness profile polished by CeO 2 . Fig. 8. Roughness profile polished by SiO 2 (by Talystep). J.L. Yuan et al. / Journal of Materials Processing Technology 138 (2003) 116119 119