Research On The Size Effect Of Micro-cutting And The Modeling Technology Of Force Prediction In Micro-milling

Micro-cutting technologies have recently emerged as a result of the explosion of activities in micro electromechanical systems(MEMS).With the on-going development of science and technology,the demand of miniature parts with high precision and complex features is increasing.Micro cutting process has absolute advantages during the emergence of various micro-manufacturing processes due to the capable of producing complicated three-dimensional features with high accuracy and precision on a wide range of materials.There are a number of issues that prevail in microscale machining that are fundamentally different from macroscale machining and influence the underlying mechanisms of the process,resulting in changes in the chip-formation process,cutting force,process stability and machined surface.The objective of this paper focus on the relationship between malescale machining and micro-scale machining,and providing a fundamental understanding of the mechanisms that prevail in the world of microscale machining.Since the tool-edge radius does become comparable to or is sometimes greater than the uncut chip thickness on the micro-cutting process,the effect of tool edge radius should be taken into account,and the nominal tool rake angle no longer works.An ALE-FEM model was built for analysing the effects of tool edge radius on the material deformation,the stick-slide behavior and contact stress distributions.There exists a stagnation point in the material flow on the round tool-edge,so a new effective rake angle model was proposed based on the stagnation point.The simulation results show that the stagnation position is unchanging with the uncut chip thickness when the tool edge raduis is invariable;the stagantion point is increase with the edge radius when the uncut chip thickness is unchanging.As the uncut chip thickness is reduced to micron level,the chip load encountered in the process becomes the same order of magnitude as the grain size of most commonly used engineering materials.In order to investigate the influence of material microstructure on the size effect in micro cutting,A microstructure-level model for simulation of machining AISI1045 using the finite element method is presented.Compared to a conventional homogeneous FE model,the new model can captures the behavior of individual constituents during machining.The behavior of each phase is dependent on strain,strain rate,temperature,and amount of damage.The resulting chip morphology from the FE model is compared to the experimental results found in the literature.For a given material microstructure,the chip morphology changes from continuous to a quasi-shear-extrusion when the uncut chip thickness is decreased from hundred microns to few microns,and the uncut chip thickness is more closed the size of the smallest grainy the extrusion is more obviously;in the stress diagram,the maximum stress appears not only around the tool edge but the grain boundary,illustrate that the material microstructure effect is prominence during micro cutting.Micro-milling is not simply downsized from the conventional milling operation but has its own characteristics.As the size downscaling,it is not easy for the operator to detect tool wear or fractures.Accordingly,in micro-end-milling,cutting force analysis plays an important role in the determination of the characteristics of cutting processes like tool wear and surface texture,the establishment of cutting plans,and the setting of cutting conditions.Due to the size effect and aggressive feed per tooth,cutting force prediction in micro scale machining is complicated by a number of issues that are fundamentally different from macro scale machining and influence the underlying mechanism of the process.This paper presents a mechanistic cutting force model for the prediction in micro-end-milling which is divided into two cutting regimes,namely the shearing and the plough dominant regimes.Unlike the convention milling model,the shearing cutting force is expressed as a function of cutting area and cutting force coefficient which is avoiding the differential and integral process.Therefore,the cutting force coefficient is independent of the end-milling cutting conditions,be regard as constant.The ploughing force model takes the effect of elastic recovery and tool edge radius into account is developed based on the interference volume between the tool and the workpiece.The model was verified by means of cutting force measurements in micro milling and the results show good agreement between predicted and measured forces.