Research On The Three Kinds Of Typical Micro-structure Defects

Currently, the demand for components which are within millimeter or even micron scale, composed by a variety of materials, and have high geometric accuracy and surface quality is increasingly urgent. Generally, micro-parts or structures are realized through the micro-machining process. Compared with the conventional machining, there is a big difference on machining mechanism, accuracy, features and so on for the micro-machining. But on the other hand, the defects such as burrs and crack which are common in the conventional machining will also arise during the machining of micro-parts.The main purpose of this thesis are to conduct investigations on the formation mechanism and control for three types of micro-defects, that are micro-burrs on the valve, crack and thermal damage in the bone drilling and milling respectively. At present, researches conducted by the foreign and domestic scholars are mainly focused on the formation and control of burrs in the turning, milling and drilling.Researches on the micro-grinding burrs are very limited. On the bone cutting, most investigations are focused on the temperature threshold of thermal damage and the influence factors of the micro-defects. But until now, there is not a consistent conclusion on the optimal parameters adopted in the bone drilling, and researches on the bone micro-machining are still very limited and not widely reported.In view of problems above, main research contents of thesis are as followed:1. Establishing the finite element model of single abrasive grain cutting,formation mechanism of micro-burrs was investigated. Combining the simulation and experiments results, influence of grinding parameters on burrs size was investigated.Finally, a prediction model of burrs size was put forward.2. Cutting force and temperature were the key factors which had a big influence on the defects of bone cutting. The effects of drilling parameters on drilling force and temperature were investigated using the single –factor test methodology, and the correlation models among spindle speed, feed rate and thrust force, temperature were built. Basing on the response surface methodology, the optimal drilling parameters were got. Then the drilling performance of coated and uncoated drill bits was compared in terms of force and temperature. Finally, predrilling was adopted to lowerthe temperature in the high speed micro-drilling.3. By using the single –factor test methodology, the effects of milling parameters on milling force and temperature were investigated. The correlation models among spindle speed, feed rate and milling force, temperature were also built. Basing on the experiment results, the optimal milling parameters were got. In addition, the anisotropy of bone on mechanical property and thermos physical property were also studied in the experiment.