Study On The Mounting Technology Of Ultra-thin Workpiece In Precision Machining

With the rapid development of technology,an ultra-thin workpiece with light-weight,well-cooling,and excellent performance is widely used in quartz crystal oscillators,space telescopes,extreme ultra-violet lithography machines,high-power lasers and so on.Due to the low stiffness of high-aspect-ratio workpiece,internal stress,thermal stress,mounting stress,and machining stress will cause significant deformation of the workpiece,which severely restricts ultra-thin workpiece production efficiency and figure accuracy.With the further demand for quantity and figure accuracy of an ultra-thin workpiece,the traditional machining process of the ultra-thin workpiece is facing great challenges.The single-sided machining process of an ultra-thin workpiece is divided into blank selection,cutting,mounting,lapping(grinding),polishing,testing and so on.Various mounting stresses will cause significant deformation on the workpiece due to the low rigidity,after lapping and polishing,the figure accuracy of the workpiece has reached the requirements,but the elastic rebound caused by the mounting stress release after demounting will cause the deterioration of workpiece figure accuracy.Workers must rely on multiple iterations to achieve accuracy requirements,which not only has low production efficiency but also poor stability.Therefore,it is necessary to improve the production efficiency,figure accuracy,and stability of the ultra-thin workpiece by carrying out researches on mounting deformation and revealing the deformation mechanism.Based on the investigation of the ultra-thin workpiece mounting technology at home and abroad,the deformation mechanism of epoxy adhesive mounting and pitch button blocking technology was studied,the various factors affecting the mounting deformation were analyzed by experiments and finite element simulation,the improved mounting technology was proposed,it can effectively reduce the mounting deformation and the deterioration of the workpiece figure accuracy of demounting.The main research work is as follows:(1)Through comparative experiments of epoxy adhesive mounting with different methods and curing sequences,combined with finite element simulation,the mechanism of mounting deformation was analyzed,as well as the factors affecting the mounting deformation.An effective cementing method was proposed and reduced the workpiece mounting deformation from 3 μm-5 μm to 0.51 μm.(2)Using the viscoelastic properties of the pitch,the effects of creep and stress relaxation on ultra-thin workpiece deformation of pitch button blocking were analyzed.The influences of different cementing areas,heating temperature,cooling rate,material properties,pitch button size uniformity,and pitch button arrangement on the workpiece mounting deformation were studied.The ultra-thin workpiece mounting deformation was further reduced to 0.36 μm.(3)Through stress relief,mounting,lapping,polishing,testing,and other processes,Φ50 mm×1 mm ultra-thin fused silica workpiece has been machined.A flatness of PV 0.15 μm of the workpiece was achieved after polishing,and the figure accuracy reached PV 0.46 μm after demounting,which effectively suppressed the deterioration of figure accuracy of the ultra-thin workpiece after demounting.