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Abstract
Ti-6Al-4V alloy is one of the advanced materials broadly used in aerospace and biomedical area, especially for miniature components or devices, due to its extraordinary properties at high temperature and resistance to corrosion and light weight. However, the stability in high temperature environment and the high hardness resulting in difficult to be machined by conventional mechanical machining process now is a challenge for mass production of those components and devices. Although there are some improvements in earlier studies, there are still some limitations to implement those studies in the machining process of Ti-6Al-4V alloy, including complicated system and different tool materials used. In this thesis, a new hybrid micro-milling process – nanosecond laser cutting and consequent mechanical micro milling – has been studied to improve the machining performance. The mechanical micro milling process has been conducted on a CNC machine with two flutes AlTiN coated carbide micro mills. Comparing to other hybrid methods, this is a more concise and flexible micro milling method. Cutting force which is critical to tools’ wear and lifetime is a main experimental subject while the surface roughness and burr size are other two main subjects, as these two factors are the major problems affecting the finished surface quality. Response surface methodology (RSM) has been used to develop models to predict the resultant cutting force, surface roughness and burr size, and the models have been assessed by comparing with actual experimental values. In addition, the significance of different parameters, such as depth of cut, feed and spindle speed, have been determined by analysis of variance (ANOVA) in different micro machining processes.
Comparisons between results of pure mechanical and hybrid micro milling processes show that there has been significant improvement in all aspects by new methods. It is found that influences from different parameters present a similar performance in hybrid methods compared to the mechanical milling. In these methods, increase depth of cut increases cutting force and reduce finished surface quality while higher spindle speed and lower feed are able to improve those results.
Results of ANOVA indicate that the depth of cut is the most significant factor which mainly affects cutting force. Moreover, the significance of feed on cutting force which is clear in mechanical micro milling process has been reduced by the new methods, which is also shown in the results of ANOVA. RSM also successfully predicts adequate values compared with experimental results.