| Silicon carbide particle reinforced aluminium matrix composites(Si C/Al-MMCs)has high specific strength,specific stiffness,wear resistance and excellent resistance to damage.So SiC/Al-MMCs is becoming more and more widely used in military and civil fields such as advanced weapon systems,aerospace,automotive,sports and electronic packaging,etc.There is potential for SiC/Al-MMCs to replace many traditional materials.However,SiC/Al-MMCs’ superior physical properties as above can result in severe tool wear,vibration and complicated defects form of machined surface problems,especially the high volume fraction of SiC/Al-MMCs.Therefore,the further study on the cutting force and tool wear of the high volume fraction SiC/Al-MMCs will be of great guidance to its machining and more extensive application.Turning experiments of 50 vol.% Si C/Al-MMCs under different tools,different cooling and lubrication methods and different cutting parameters were carried out.The main conclusions of this paper are as follows:The K10 tool broke off overall in seconds and could not be used in machining high volume fraction Si C/Al-MMCs.PCD tool has better wear resistance and low material adherence properties,which make it the most suitable tool for machining high volume fraction SiC/Al-MMCs.When the volume fraction of SiC keeps the same,larger particle size may cause larger size of the single pit on the rake face,greater average wear width of the cutting edge and worse surface quality of the machined surface.The effect of different cooling and lubrication methods on flushing of the shedding SiC particles in cutting area is obviously different,and flushing ability is an important factor which influences the boundary wear.But flushing ability has little effect on the flank wear.Cutting oil and Emulsion have caused serious boundary wear because of the poor flushing ability while MQL and Liquid Nitrogen can effectively reduce the boundary wear.MQL’s lubricating ability and Liquid Nitrogen’s cooling effect can decrease friction coefficient and help tool maintain hardness,so the width of flank wear decreases.Compared with dry cutting,the cooling effect of Liquid Nitrogen speeds up tool breakage,and the severe boundary wear of Cutting oil weakens the strength of the tip of the tool and indirectly causes the tool to break down.There was no tool breakage in the whole cutting distance when machining with MQL and Emulsion due to their even tool wear.Cooling and lubrication can not prevent the production of build-up edge(BUE),and BUE is very unstable.The shedding of BUE is an important factor for the tool breakage when machining SiC/Al-MMCs.It shows that MQL has excellent flushing ability and effectively plays the role of cooling and lubricating.So MQL has a positive effect on reducing boundary wear,flank wear and avoiding tool breakage,which make it the best cooling and lubrication method in machining SiC/Al-MMCs.The main cutting force and axial force are not sensitive to the change of cutting speed,and cutting force increases with the increase of depth of cut and feed rate.Increasing cutting speed,depth of cut and feed rate will aggravate the fluctuation of cutting force.When machining Si C/Al-MMCs,it is not appropriate to use standard deviation or fractal dimension to evaluate the fluctuation of the radial force signal.The effect of cooling and lubrication on cutting force is reflected by the influence of tool wear.BUE will increase cutting force and cause a great change in cutting force at different cutting distance. |
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