Study On Control Method Of Surface Quality Of Soft Metal Lead By Ultra-precision Cutting

In the field of defense weapon system research,the samples of precision physical experiment involved in the large scientific experimental equipment require high surface quality.The surface quality of the sample has a great influence on experimental results and determines the reliability of experimental results.The soft metal of lead plays an important role in precise physics experiments because of its unique material characteristics.In this paper,ultra-precision cutting technology is used to process lead to obtain high surface quality to ensure the accuracy of precision physical experiment results.Firstly,the factors affecting surface quality of soft metal lead were studied by ultraprecision cutting technology.The results show that the main factors affecting surface quality are the damage of the machined surface,the side flow and the built-up edge.The reasons affecting surface quality are analyzed.Then the surface quality is optimized from different aspects:(1)From the perspective of materials,lead is modified by deep rolling.After the treatment,surface hardness of lead is improved.In ultra-precision cutting process,surface damage is significantly decreased and the built-up edge disappears.The minimum surface roughness is reduced to 19.02 nm.(2)From the perspective of the interaction between the diamond tool and lead,oil cutting fluid is replaced by alcohol in ultra-precision cutting process.The results show that surface damage and side flow decrease and the built-up edge disappears.The minimum surface roughness decreases to 8.83 nm.At the same time,with the increasing of the feed,the factors affecting surface quality change from ‘grain boundary step' to side flow,and then change from side flow to side flow and the built-up edge.(3)From the perspective of heat generation in the cutting process,low temperature device is adopted to create low temperature environment.It helps the heat generated by cutting to be discharged quickly.The results demonstrate low temperature environment on the role of alcohol and oily cutting fluid is different.When the feed is low and alcohol is used as cutting fluid,low temperature environment is not obvious to the improvement of surface quality.With the increasing of feed,the heat increases in the cutting process.When oil cutting fluid is used as cutting fluid,low temperature environment immediately plays a significant role in the surface quality.The friction and wear experiment were used to study the mechanism of surface quality improvement in alcohol as cutting fluid.The results show that when alcohol is used as the lubricating fluid between diamond and lead,the wear morphology is brighter.It demonstrates low oxidation degree of lead.The frictional force and friction coefficient is lower,which means less heat is produced during the cutting process.At the same time,alcohol is volatile and can quickly discharge the heat,which reduces the temperature of the interface between the diamond tool and lead,and then reduces the possibility of the formation of the built-up edge and prevents material softening caused by the temperature.The effect of grain orientation on ultra-precision cutting was studied by molecular dynamics simulation.The results show that the plastic deformation of lead is mainly carried out by Schockley partial dislocation.When the cutting direction is {100}<011> and{100}<012>,the subsurface damage is the lowest.When the cutting direction is {110}<001>,the subsurface damage is the highest.This is because the direction of {110}<001> produces twin boundary during processing.It affects the removal of lead and the formation of machining surface.In the cutting process,the grain orientation influences the separation of chip and surface material through the formation of stagnation region.At the same time,it also affect the recovery of surface material.The recovery height is the smallest(0.1nm)in the direction of{100}<001>.The recovery height is the largest(1nm)in the direction of {110}<001>.When materials are polycrystalline,the difference in the surface recovery height caused by grain orientation,which will increase the surface roughness.The formation mechanism of side flow is that the stagnation region will make the separation of chip and material.The materials will be squeezed by tool to form the machined surface.During the process of extrusion deformation,the material will undergo plastic deformation and flow toward the machined surface to form side flow.In the direction of {100}<001> and {100}<011>,the phenomenon of side flow is the most serious.The surface residual height increases significantly.The surface roughness is the lowest.However,{110}<001> is the weakest.The surface roughness is the highest.