Research On Failure Analysis And Design Theory For Micro End Mill

Micro cutting technology is a kind of micro machining technology on the basis of traditional cutting technology, andfacing up to the demand of machiningmicro-structure parts. It has most of the traditional cutting technology advantages, and is one of the most main method of the micro-structure processing at present and has broad market prospects. As the execution unitof micro-machining, micro cutting tool is a very important part of the micro cutting system. Due to micro tool failure problem is more serious than traditional cutting tools, it has become the bottleneck which restricted the development of micro cutting technology.Based on scientific theories and methods includingtribology, fracture damage mechanics, mechanical dynamics, differential geometry,geometrykinematics theory and numerical calculation, the design theory of micro end mill was systematically researched according to failure phenomenonof micro milling cutter in the present work, mainly including the following aspects:1. The failure mechanism of carbide micro end mill when milling the stainless steel was clarified. The failure experiment of micro tool under static and dynamic was designed and the type and mechanism of micro miller failure were also studied. The wave-like wear shape on flank face and abrasive, adhesive and diffusive wear were appeared when milling stainless steel with carbide micro miller. The types of failure were that tip break at the beginning of cutting and early fracture over large bending stress. The fail mechanism was that ductile tearing of CO phase along the grain boundary of WC. The early fracture was from juncture of tool neck and cutting edge where the core was the smallest and the crack was extended radioactively. The micro mill fracture was bending fracture after comparing the morphology of fracture under the static and dynamic loading. The relation of tool wear and the frequency spectrum magnitude change of cutting force was revealed by analyzing frequency spectrum magnitude change. The Taguchi method was applied to study the effect of manufacturing parameters on tool wear and surface roughness when milling stainless steel, which gave the suggestion that the lower feed rate resulted in better wear resistance and surface roughness.2. The geometry modeling and strength analysis of micro end mill was researched.The uniform model of helix and plain of cutting edge curve with considering the continuity of cutting edge curve on different revolution surface was built. The accurate envelope model of axial direction section was built by using non-instantaneous enveloping method and combing the character of grinding end mill. A design method of axial cross-section based on non-instantaneous enveloping theory which was precise, simple, suitable for complex envelope groove design and avoiding the situation that it can not be solved because of singularities and sleek shape of the grinding wheel section was proposed. Based on the strength analysis, the influence of geometry structure on stress distribution in different stress concentration area of micro end mill was studied, which could guide the geometry design of micro end mill.3. The integral structural design theory of micro end mill under high speed machining was proposed. The uniform dynamic model of variable cross-section pre-twisted beam was built with considering shear effect and gyroscopic effect when variable cross-section of micro end mill was spinning. The impact of micro end mill’s geometry structure on its dynamic performance under different rotation speed was analyzed by applying this model, which could be the guidance of integral structural design and process optimization of micro end mill. The method of determining the initial critical speed was present based on the change of inherent frequency.4. The grinding and failureverification experiment on micro end mill was carried out. The main axis movement equation of the grinder was derived and the grinding process was designed based on the motion planning of CNS7 D grinder. At last, some micro end mill with different character was manufactured. The design theory of micro end mill in this thesis was valid by comparing the failure character and machining performance of experiment under different geometrical parameters.