| With the rapid development of science and technology,the preparation technology of high density alloy is more mature.Tungsten alloy has the characteristics of high density,high melting point,high strength,high hardness,high temperature resistance,wear resistance and corrosion resistance,so it is widely used in aerospace,military,space nuclear power system,radiation shielding,die casting mold,counterweight block,armor piercing projectile core,instrumentation and medical equipment and other industries.The chemical properties of tungsten are active,and the affinity with other atoms is strong.It is easy to produce bonding and chip formation during cutting process,which aggravates tool wear and affects cutting accuracy.Tungsten is a brittle material at room temperature.At the same time,due to its high wear resistance and high hardness,it is easy to cause tool wear and chipping,thereby reducing production efficiency,processing surface quality and parts qualified rate,and ultimately leading to higher processing costs.At present,rotary ultrasonic machining has been proved to have unique advantages in the processing of hard and brittle materials : small cutting force,good surface quality and low subsurface damage depth.Therefore,in this thesis,the tungsten alloy is processed by rotary ultrasonic machining,but the hard and brittle characteristics of tungsten alloy will inevitably lead to surface and subsurface damage.At present,the removal mechanism of tungsten alloy material by rotary ultrasonic grinding is not clear,and the influence of processing parameters on the surface and subsurface damage depth is not explored.In view of this,this thesis will carry out the research on surface and subsurface damage of tungsten alloy rotary ultrasonic grinding,provide theoretical guidance for rotary ultrasonic grinding of tungsten alloy,and provide reference for the preparation of higher quality tungsten alloy parts.The main work of this thesis includes the following aspects :(1)A single diamond tool was designed and the variable cutting depth scratch test was completed to study the scratch force,surface morphology and subsurface damage under the condition of ultrasonic excitation.The results show that the scratch trajectory will change under ultrasonic excitation,and the change of scratch trajectory has a positive effect on the reduction of scratch force and subsurface damage depth.At the same time,through the observation and analysis of scratch surface morphology,the continuous evolution process of tungsten alloy workpiece material from plastic removal behavior to brittle removal behavior in the process of variable cutting depth scratch is obtained.(2)The effects of ultrasonic grinding conditions on grinding force,surface morphology,surface roughness and subsurface damage depth were studied by rotating ultrasonic grinding test and corresponding ordinary grinding test.The test results show that under the parameters used in the test,the grinding force,surface roughness and subsurface damage depth obtained by ultrasonic grinding are all smaller than those obtained by non-ultrasonic grinding.At the same time,based on the abrasive particle trajectory equation and the indentation fracture mechanics model,the obtained test results are theoretically analyzed,and the influence of ultrasound on the results is further explored.(3)Based on ABAQUS simulation software,the effects of spindle speed,feed speed,grinding depth,ultrasonic frequency and ultrasonic amplitude on grinding force and subsurface damage depth were studied in depth through the five-factor and three-level rotary ultrasonic grinding simulation of orthogonal tungsten alloy.The results show that grinding depth has the greatest influence on grinding force and subsurface damage depth,and ultrasonic amplitude has the least influence on grinding force and subsurface damage depth.Grinding force and subsurface damage depth are negatively correlated with spindle speed,and positively correlated with feed speed,grinding depth and ultrasonic frequency,and decrease first and then increase with the increase of ultrasonic amplitude.At the same time,the test was designed to verify the simulation results,and the prediction model of subsurface damage depth was established based on the test results. |
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