The Key Technologies And Machining Mechanisms For Micro Milling Process

With the development of aerospace,biomedical engineering,defence-related science and technology,new electronics technology and environmental protection technology,the demand for the critical parts,which has the characteristic of complex structure and miniature size,becomes more and more pressing and useful.Currently,the micro machining processing technology used mainly contains micro electro mechanical system(MEMS),micro un-traditional machining and micro machining.As an increasingly sophisticated processing method,the micro milling technology overcomes the limitation of material requirements of machined parts,three-dimensional complex structure and production cost.The essential requirements of micro milling process are ensuring the surface accuracy of machined product,maintaining process stability of micro milling system and improving the material removal rate.Aimed at micro milling process with flat end mill,this paper further study on the modeling of uncut chip thickness,cutting forces prediction,instantaneous tool deflection of micro end mill,process stability and surface roughness of machined workpiece,the main contents are as follows:(1)The causes and classification of tool run-out,the parameter definition of radial offset and axis tilt of tool axis are discussed in detail.In accordance to the trochoidal trajectory of tooth considering tool run-out,the uncut chip thickness in micro milling process is proposed in this paper.The variable entry/exit angles caused by the tool runt-out and trochoidal trajectory of tooth are considered in the proposed model.The comparison results of the traditional uncut chip thickness model and the proposed instantaneous uncut chip thickness model validate the reasonability and correctness of the proposed model.(2)The shearing effect of tool flank edge,the ploughing effect of tool flank edge and the shearing effect of tool bottom edge are included in the shearing-dominant regime and the ploughing-dominant regime and then the corresponding cutting forces in micro end milling process can be modeled and analyzed.In addition.the cutting forces coefficients are analyzed and identified.At last,the comparison results of experimental measured cutting forces and predicted cutting forces are presented to validate and analyze the rationality and feasibility of the proposed cutting forces model.(3)The instantaneous tool deflection model is proposed in micro milling process with flat end mill,and the micro end mill is assumed as a continuous Timoshenko beam and the distributed cutting forces acting on the discrete elements in the tool cutting edge direction have displaced the total cutting forces acting on the tool tip.At the same time,the specific adapting piece are used to fasten the capacitive-type sensor in the x-direction and y-direction axis to measure the tool deflections in micro milling process with flat end mill.(4)According to the influences of the tool run-out,the trochoidal trajectory of tooth,tool deflections and process damping,the dynamic micro milling process model is established.The proposed model can be solved by the full-discretization method with the direct integral equations and then the stability lobes of the dynamic micro milling process are obtained.In addition,the process damping coefficients are identified and studied in micro milling process.The measured and predicted tool deflections can be compared and analyzed to validate the accuracy of the proposed model.(5)To obtain the effect of process factors on the surface roughness,the surface roughness model of micro milling process are presented considering tool run-out,the tool run-out,tool deflections and machining mechanisms.The microscope is used to measure the roughness,and the experiment results are compared and analyzed to study the influence of machining parameters and tool modal parameters.