Elliptical Vibration-assisted Turning BK7 Optical Glass Surface Creation And Subsurface Damage Study

BK7 optical glass has the advantages of high strength,high temperature resistance,chemical stability and high optical uniformity,and is widely used in optics,electronics,thermodynamics,fluid science and other fields.However,because of its inherent shortcomings,such as high brittleness and low fracture toughness,BK7 optical glass has become one of the most difficult materials to process.It is very easy to produce subsurface damage(SSD),residual stress and other defects using traditional processing methods.Elliptical Vibration assisted Cutting(EVC)technology has the advantages of reducing average cutting force,reducing machining microcracks,and obtaining more regular chips.Therefore,it is widely used in the processing of hard and brittle materials such as ceramics and optical glass.However,at present,the mechanism of subsurface crack growth and material removal for EVC processing BK7 optical glass is not clear,For this reason,this paper carries out surface generation and SSD research of BK7 optical glass processed by EVC.The main research contents are as follows:(1)An SSD depth prediction model combining EVC processing characteristics is proposed.Firstly,the formation mechanism of subsurface cracks during EVC processing is analyzed.Then,based on the fracture mechanics theory of hard and brittle materials,the tool motion trajectory was analyzed,combined with the elastic recovery of BK7 optical glass during processing,the actual contact time calculation formula between the tool and the workpiece was proposed,and the relationship between cutting force and cutting load was obtained by considering the influence of the tangential force generated by the tool during tool passing on the cutting load,so as to derive the SSD depth prediction model of EVC machining BK7 optical glass.(2)Numerical simulation analysis of subsurface damage of EVC processing BK7 optical glass.Based on the actual processing state of EVC,the finite element software is used to establish a three-dimensional simulation model of EVC processing BK7 optical glass,and the simulation process considers the elastic recovery and chipping of the material in the actual processing.Then,by observing the simulation results,the influence of each cutting data on SSD depth was analyzed to verify the accuracy of SSD depth prediction model.(3)Establish a critical undeformed chip thickness prediction model.Combined with the four cutting modes proposed by Gu et al.,the EVC ductile machining of BK7 optical glass is defined as the SSD generated during processing that does not affect the strength of the material,and the lateral crack does not exceed the machined surface of the material,and the critical condition for the transformation of the cutting mode of EVC machining is proposed.Then,based on the geometric relationship between the tool and the workpiece during EVC machining,the critical undeformed chip thickness model of EVC processed BK7 optical glass was established,and the influence of different process parameters on the brittle-plastic transformation of BK7 optical glass was explored.(4)Carry out EVC cutting deep slicing experiment of BK7 optical glass.The target workpiece was cut in the groove,and then the micro-grooves created by different cutting speeds and vibration frequencies were detected and analyzed,the chip formation mechanism of the above variables in the EVC machining process was revealed,the feasibility of EVC ductile machining and the accuracy of the critical undeformed chip thickness model were verified,and the process parameter optimization principle of EVC processing BK7 optical glass was summarized.