Experimental And Theoretical Study On Micro Milling Of Copper

With the rapid development of micro and small technology in field of civil and national defense,the demand for micro products is increasing year by year.Micro machining is the key supporting technology for manufacturing micro products.Due to the obvious advantages,micro milling is an important part of micro machining technology group,and becomes the main machining method of various micro parts.In order to achieve high precision micro milling,this paper researches on the mechanism of effective negative rake angle and the minimum cutting thickness during micro milling process,the main works as following:(1)To accurately evaluate the cutting state of negative rake angle during micro milling,the calculation model of equivalent negative rake angle is proposed.It is found that when the cutting thickness is less than the cutting edge radius,the cutting process will be in the state of serious negative rake angle cutting.Then,the minimum cutting thickness is obtained based on the equivalent negative rake angle curve.In micro milling experiments,it is found that the minimum cutting thickness leads to the instability of the cutting force signal,forming periodic peak in the cutting force time-domain signal,and forming more low-frequency features in the cutting force frequency-domain signal,and generating serious size effect.(2)The calculation model of theoretical roughness in micro milling is established.In micro milling experiments,it is found that with the decrease of feed per tooth,surface roughness first decreases and then increases gradually.And when it is equal to the minimum cutting thickness,the optimal surface roughness can be obtained.Due to the instantaneous cutting thickness is changing with the tool rotating,the cross section of workpiece can be divided into two areas,the two sides ploughing area and middle shearing area.The surface roughness distribution on different positions presents the W shape.With the increase of the feed per tooth,the W shape of surface roughness distribution on different positions becomes more and more obvious.(3)The formation mechanism of Poisson burr and exit burr in micro milling is analyzed.In micro milling experiments,it is found that the top burr can be divided into five categories: feathery shape,broken shape,hairy shape,serrated shape and wall shape,and the exit burr can be divided into two categories: flaky shape and curled shape.Based on the analysis of the results of burr shape and size,three machining strategies are put forward,including the optimization of machining parameters,the selection of machining path and the auxiliary technology.