| With the continuous development of science and technology,ultra-precision machining technology is widely used in high-tech fields such as aerospace,military,and national defense.At present,the precision requirements of ultra-precision machining technology have reached the micro-nano scale,and the processing mechanism and cutting characteristics at the micro-nano scale are significantly different from those under macroscopic processing.Therefore,in order to guide and improve ultra-precision machining technology,it is necessary to conduct in-depth research on the cutting characteristics,removal mechanism and mechanical properties of materials at the micro-nano scale.As an important infrared optical material,single crystal germanium has been widely used in microelectronics,aerospace and new energy fields in recent years.However,single crystal germanium is a typical hard and brittle material with anisotropy,and it is easy to form cracks and pits during processing,which make it difficult to obtain a high quality optical surface.In order to obtain a high-quality optical surface,it is necessary to control the amount of material removal on the micro-nano scale when processing the single crystal germanium,so that it can be processed in the plastic region.In this paper,molecular dynamics simulation,nanoindentation experiment,single-point diamond turning experiment and other methods are used to explore the cutting characteristics of single crystal germanium in micro-nano-scale plastic cutting.The effects of different cutting process parameters on the cutting characteristics of single crystal germanium are studied,which provides theoretical basis and data support for micronano scale plastic region cutting of hard and brittle materials such as single crystal germanium.Firstly,the nano-cutting simulation of single crystal germanium was carried out by molecular dynamics simulation method.The nano-cutting mechanism of single crystal germanium was studied,and the critical cutting thickness of the elastic-plastic transition of the Ge(100)at a cutting speed of 100m/s was 0.75 nm.Then the effects of different cutting process parameters on the nano-cutting characteristics of single crystal germanium were analyzed from the changes of groove morphology,surface chip accumulation,cutting force and potential energy.Furthermore,the nano-scratch experiment was carried out on the single crystal germanium by nanoindenter.The effects of different scratch speeds on the critical state and cutting characteristics of the brittle-plastic transition of different crystal planes of single crystal germanium were studied.It is found that within a certain range,as the scratch speed increases,the critical depth and critical load of the three crystal planes of the single crystal germanium appear to increase first and then decrease.The critical cutting force of the three crystal planes when generating brittle-plastic transformation shows an obvious anisotropic.The formula for calculating the critical depth of brittle-plastic transition under the constant depth experimental parameters of Ge(110)was revised.Finally,the single-crystal germanium parts were turned by a single-point diamond lathe,and the influence of the three cutting elements on the surface quality was studied.Results show that within a certain range,the surface accuracy and surface roughness of the parts increase with the improve of cutting depth and feed rate;while it decreases and then increases as the spindle speed increases.And the optimal machining scheme for cutting single-crystal germanium parts is the cutting depth a_p=5μm,the spindle speed n=2200r/min,and the feed rate f=3mm/min. |
