Study On Turning Process Of Silver-Impregnated Graphite

Silver impregnated graphite is a kind of composite material which takes porous graphite as the matrix and impregnates molten metal silver into graphite pores under high temperature and pressure.Compared with traditional graphite,the density and compressive strength of silver-impregnated graphite are greatly improved.And it provides extremely high temperature resistance and thermal-shock resistance while remaining its self-lubricating characteristics,thereby it replaces traditional graphite as an advanced sealing material in the aerospace and other fields.However,in the turning process of silverimpregnated graphite,quality problems such as surface pits and edge collapse occurred,besides,tool wear was also very serious.In order to solve the quality problems in actual processing and to explore the impact of silver impregnation on the cutting process and tool wear,this paper focuses on three aspects of chip formation mechanism,tool wear and processing quality control for turning processing of silver-impregnated graphite.The main work is as follows:(1)After testing and analyzing the physical and chemical properties and microstructure of silverimpregnated graphite materials,the fracture forms of the two phases of the composite and their influences on each other were studied after observing the morphology of chips and processed surfaces formed in the silver-impregnated graphite turning experiment and three-point bending experiment in the way of comparing ordinary graphite with silver-impregnated graphite.Then the chip formation mechanism of the silver-impregnated graphite turning process was revealed through the photographing and observation of the chip formation process in the two-dimensional orthogonal turning experiment.Against the cutting depth out of the cutting parameters and the tool rake angle out of the tool structure,which have a great influence on chip formation process,the influence of those parameters was studied.Finally,the process of chip formation was demonstrated through the model establishment.(2)Abrasive wear is the most Influential form of tool wear in the processing of silver-impregnated graphite.Therefore,two different tools of carbide and PCD were selected to study the influence of the changes in wear resistance and hardness of different tool materials on the tool wear mechanism.The form of tool wear was also studied and summarized respectively for the two different materials.At the same time,the influence of tool rake angle on the tool wear mechanism was studied.On this basis tool material and tool rake angle were optimized and we get that PCD tool with 0° rake angle has better wear condition in silver-impregnated graphite turning process.(3)Aiming at the surface roughness index which is capable of characterizing the surface pit size,a PCD tool with better performance in Chapter 3 was selected,and the influence of the tool rake angle on the surface roughness was found and we know that PCD tool with 0° rake angle was more suitable in processing of silver-impregnated graphite.After establishing the characterization of edge collapse defects on silver-impregnated graphite,the effect of cutting parameters on surface roughness and collapse defects was studied using a PCD tool with 0° rake angle.The conclusion is that the most suitable cutting parameters in turning process of silver-impregnated graphite are a cutting velocity of 47.1m/min,a feed rate of 0.1mm/r,and a cutting depth of 0.5mm.