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ULTRA SMOOTHNESS GRINDING OF GLASS WITH 140 METAL BOND DIAMOND WHEEL SAWA Takekazu 1 YASUI Heiji 1 1 Dept of Mechanical Engineering Materials Science Kumamoto University 2 39 1 kurokami kumamoto Japan Abstract Glass is one of the most important materials in the optical industries The high efficiency ultra smoothness grinding technique of the glass has been strongly required To improve the productivity in our previous researches the newly devised ultra smoothness grinding method is proposed By applying the new method to the horizontal surface grinding1 2 3 the surface roughness of cemented carbide tool silicon carbide ceramic and so on is found to attain below 30nm Rz or 5nm Ra in the measuring area of 256 m x 256 m As a result the new method is ascertained to be useful for finishing near the ultra smoothness surface In this report ultra smoothness grinding of a glass is examined The specification of metal bond diamond wheel used is the grain size of 140 and the concentration of 50 respectively The 3D surface roughness of glass formed using the suitable grinding condition attains about 27nm Rz or 1 4nm Ra Key words ultra smoothness grinding glass surface roughness nanometer diamond wheel coarse grain size metal bond 1 INTRODUCTION Glass is one of the most important materials in the optical industries that act to support the precision industries The high efficiency ultra smoothness grinding technique of glass has been strongly required since the precision industry has been recently developing and the demand for glass component of high quality and low price has been increasing To improve the productivity in our previous researches 1 the newly devised ultra smoothness grinding method is proposed1 By applying the new method to the horizontal surface grinding 2 3 the surface roughness of cemented carbide tool silicon carbide ceramic and so on is found to attain below 30nm Rz or 5nm Ra in the measuring area of 256 m x 256 m As a result the new method is ascertained to be useful for finishing near the ultra smoothness surface and ascertained to be useful This is one of a series of the researches on ultra smoothness grinding of various kinds of materials In this report ultra smoothness grinding of glass is examined using a metal bond diamond wheel of coarse grain size 2 ULTRA SMOOTHNESS GRINDING METHOD In our previous research 1 the possibility of the high removal rate ultra smoothness grinding method which can finish to almost the same smoothness formed by polishing is examined using traverse grinding It is found from the results that the smoothness which can be Fig 1 Ultra smoothness grinding method attained by traverse grinding is limited roughly over the critical surface roughness because of the occurrence of rough grinding groove parallel to grinding direction formed by grinding To diminish the groove the newly devised ultra smoothness grinding method is proposed as shown in Fig 1 and ascertained to be useful for finishing near the ultra smoothness surface First of all in the new method the workpiece wheel contact width is ground by feeding the workpiece toward the direction normal to grinding direction As shown in Fig 2 in the grinding process the feed per a wheel revolution fGn is smaller than the wear width of cutting edge wn normal to grinding direction In the second step the workpiece is slightly step fed the length of fp parallel to grinding direction so that the geometrical surface roughness Hp formed by overlapping cross sections of two wheel circles before and after the step feed becomes smoother than the required surface roughness Then the workpiece wheel contact width is ground again by feeding reversely the workpiece toward the direction normal to grinding direction By repeating such a grinding procedure the whole surface of workpiece is finished 3 EXPERIMENTS The experiments are carried out with the NC surface grinder as shown photographically in Fig 3 The grinder using air spindle has the accuracy of 0 1 m for each movement of the X Y and Z direction The experimental conditions are summarized in Table 1 The grain size and concentration of the metal bond wheel used are l40 and 50 respectively The glass used is a kind of clearceram The grinding fluid used is soluble type including a plenty of anionic surfactant The observation and roughness measurement of the ground workpiece surface are done with Nomarski type of microscope and SEM and with the surface interferometer WYKO TOPO 3D and AFM NanoScope respectively 4 DUCTILE MODE PLUNGE GRINDING OF GLASS Figure 4 shows the microscope and SEM photographs of the glass surface formed by plunge grinding with the 140 diamond wheel at vwp 0 01mm s to 1mm s under the wheel speed of Vg 12m s The wheel surface is adjusted so that the ductile mode grinding becomes possible in plunge grinding of silicon carbide ceramic 4 From the figure at vwp 1mm s to 0 05mm s the smooth ductile mode surfaces with grinding cracks are observed on the whole workpiece surface The part of the smooth ductile mode surface increases with the decrease of table speed On the other hand At the lowest table speed of vwp 0 01mm s in the present experiments the smooth ductile mode surface without grinding cracks is found all over the workpiece surface However the smooth ductile mode is Fig 3 Appearance of experimental system Table1 Experimental conditions Fig 2 Mechanism of ultra smoothness grinding Fig 5 WYKO 3D image and 2D profiles of the glass surface ground by plunge grinding Vg 12m s vwp 0 01mm s t 5 m Soluble type ascertained by separate observation to be obtained over the ground whole workpiece surface of 10mm square Accordingly the grinding cracks are considered to decrease with the decrease of table speed In addition it is considered that the ductile mode grinding is possible by slowing the table speed for using 140 mesh diamond wheel of coarse grain size A WYKO 3D image and 2D profiles of 256 m x 256 m square of glass surface ground at vwp 0 01mm s in plunge grinding is shown in Fig 5 From the figure it is found that the grinding grooves parallel to grinding direction are observed clearly on the surface The height and pitch of grinding groove are about 500nm P V The surface roughness parallel to grinding direction on the other hand is about 43nm P V The 3D surface roughness of about 700nm P V is strongly influenced by the height of grooves Then the height of grinding grooves is closely related to the maximum surface roughness Considering the results it is important to develop the new grinding method that can repress or diminish the occurrence of grinding grooves 4 ULTRA SMOOTHNESS GRINDING Figure 6 shows the microscope and SEM photographs of the glass surface formed by ultra smoothness grinding As shown from the figure the smooth ductile mode ground workpiece surface without grinding cracks and grooves is obtained Especially it is important for ultra smoothness grinding that the grinding groove is ascertained to occur little on the workpiece Figure 7 shows a WYKO 3D image and 2D profiles of 256 m x 256 m square of glass surface formed by ultra smoothness grinding at fGn 10 m rev and fp 10 m It is found from the figure the 3D surface roughness is about 27nm Rz or 1 4nm Ra and the 2D surface roughnesses parallel and normal to grinding direction are about 6 5nm Rz or 1 1nm Ra and about 8 2nm Rz or 1 3nm Ra respectively Fig 6 Microscope and SEM photographs of glass surface by ultra smoothness grinding Vg 12m s fGn 10 m rev vwn 0 38mm s fp 10 m t 5 m Soluble type SEM Microscope Grinding direction Glass Vg 12m s t 5 m Plunge grinding c vwp 0 1mm s d vwp 1mm s b vwp 0 05mm s SEM Microscope a vwp 0 01mm s SEM Microscope Grinding direction Grinding directionGrinding directionGrinding direction Grinding directionGrinding directionGrinding direction Grinding direction Fig 4 Microscope and SEM photographs of glass surfaces ground at various kinds of work speed by 140 diamond Such a high smooth surface roughness is almost the same as the surface roughness formed by lapping or polishing Figure 8 shows the AFM 3D image and 2D profile of 50 m x 50 m square of glass surface formed by ultra smoothness grinding The 2D surface roughness parallel and normal to grinding direction are about 4 5nm Rz or 0 9nm Ra and about 7 3nm Rz or 1 0nm Ra respectively It is obvious that the ground workpiece surface consists of ductile mode ground surface without grinding cracks even in the measurement of AFM accuracy order 5 CONCLUSIONS The ultra smoothness grinding of glass using a 140 metal bond diamond wheel is examined The main results obtained are as follows 1 The grinding cracks in plunge grinding of a glass with the 140 metal bond diamond wheel decreases with a decrease of table speed and as a result the ductile mode grinding is possible at table speed of 0 01m s 2 In case of the plunge grinding it is found that the grinding grooves parallel to grinding direction whose height is about 500nm are observed on the workpiece surface 3 The smooth ductile mode ground workpiece surface without grinding cracks and grooves is obtained by using the newly developed ultra smoothness grinding method 4 The 3D and 2D surface roughnesses of glass formed using the newly developed ultra smoothness grinding method and the suitable grinding condition attain about 27nm Rz or 1 4nm Ra and about 8nm Rz or 1 3nm Ra respectively ACKNOWLEDGEMENTS The authors would like to thank Mr K MIYAMOTO for the assistance to experiments and Noritake Super Abrasive Industries Co Ltd Yushiro Chemical Industry Co Ltd an