| With the remarkable development of modern microelectronics, information, optical and automotive industry in recent years, unprecedented high demand of flatness and surface roughness for optoelectronics, engine piston rings and valve plate has been put forward. Lapping and polishing are effective methods to achieve maximal precision of processing, workpiece can achieve very high flatness and extremely low surface roughness after lapping and polishing. Lapping devices are prerequisite to ensure lapping and polishing process, and the demand of domestic market for high-end ultra-precison lapping equipments is increasingly strong. The overall level of design and manufacturing technologies of ultra-precision lapping and polishing equipments is not high in our country, ultra-precision lapping and polishing equipments can satisfy roughness in nanometer scale are extremely lacking.In this paper, key components of ultra-precision lapping machine are researched, and an ultra-precision lapping machine is designed by advanced modular CAD technologies. It can receive a good planeness of 0.002 mm/400 mm of lapping plate after precision turning. The stability of the process can be guaranteed by three-level pressurizing and elastic component. Adsorption system with adaptive function is designed to ensure that workpiece surface is pressed against lapping plate tightly, and material removal is evenly. Vibration monitoring system is designed for online monitoring the amount of vibration of lapping plate during machining process.Finite element analysis software ABAQUS is adopted for lapping plate structure stiffness analysis and modal analysis, and the impacts of different internal cooling grooves on lapping plate structure stiffness are researched. Gradual pressurization method is adopted to reduce the sudden height changes of deformation, and maximum deformation occurs at the largest diameter of lapping plate which close the glass workpiece. Cooling performance and lapping plate stiffness are taken into consideration to the design and select the grooves, The result shows that the structure with four ring grooves is considered in priority for spiral grooves inner cooling structure, and the structure with six fan grooves is considered in priority for fan-shaped grooves inner cooling structure, when the structure with two ring grooves is considered in priority for concentric circle grooves inner cooling structure. The stiffness of lapping plate is decreased after slotting, but still within the allowable amount of deformation. The first four natural frequencies of three kinds of inner cooling structure of lapping plate are basically in agreement, the first four modes of vibration of concentric circle grooves inner cooling structure with four ring grooves or five ring grooves is lower than other inner cooling structure significantly.Under the coupled action of friction heat and force field, the influences of rotational state of workpiece and the working pressure on transient temperature during the lapping process are researched by finite element analysis software. It’s a circular ring of temperature contour of lapping plate when workpiece is not roatation. Along with the increase times of the rotation, the temperature is increased gradually by the accumulation of warming layer. Friction heat transfers to bottom layer and both sides from the contact surface of lapping plate and glass. For the glass workpiece, the friction heat transfers to the circle direction of glass from the zone workpiece is skidding off the lapping plate, the temperature contour is shown in fan-shaped. When the workpiece rotates in the same direction with the lapping plate, the temperature contour of the glass surface is shown in the shape of concentric circles. Without the accumulation in the zone workpiece is skidding off the lapping plate, the friction heat distributed uniformly. When the workpiece rotates in the reverse direction with the lapping plate, heat is generated more due to the relative speed between workpiece and the grinding is greater than it rotates in the same direction. It generates more friction heat and improves processing efficiency when heavier working pressure is chosen.The influences of technological parameters of lapping and polishing on the surface quality and machining efficiency of circular grating glass are studied by single factor experiment and combined process experiment. For the lapping process, blunted abrasive is updated timely after lapping plate is grooved, it can achieve a higher material removal rate and smaller surface roughness. The surface roughness and the material removal rate increases with increasing abrasive size. When processing time is extended, the surface roughness reduces gradually and fails to moderate, when material removal rate decreases gradually. The removal rate decreases increases along with workpiece speed, when surface roughness first decreases and then increases slightly. The surface roughness reduces gradually and fails to moderate with increasing working pressure, when material removal rate increases gradually and fails to moderate.For the polishing process, polishing with gold velvet polishing pad, material removal rate and surface roughness are smaller compared with the polyurethane polishing pad, however, the stair slope error is more serious. The surface roughness of the workpiece and the material removal rate increases with the increasing abrasive size. After coarse lapping process, deep scratches generated on the surface of circular grating glass, the surface damage is restored to smooth gradually by combined process experiment. The optimized parameters of combined process help to reduce processing time, meanwhile, surface roughness of Ra= 3.3nm and the flatness of 0.005 mm/50 mm are obtained. |
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