Study of tool engagement and tool path strategy in high speed end milling

Abstract

This thesis presents an investigation of the relationship between tool engagement, tool path strategy (TPS) and the machining output during pocketing operation to form a mould. For pocketing, the cutting tool is required to travel along a straight path and corner path by following the predefined tool path strategy. Variation of tool engagement occurs during the pocketing that leads to fluctuation of cutting force and cutting temperature that give a bad impact on surface quality. Although previous studies have demonstrated a relation between cutting force and tool engagement, the relation with cutting temperature has not given much attention. The aim of this study is to improve surface quality of mould through end milling process by considering tool engagement, tool path strategy, cutting force and cutting temperature. Firstly, the tool engagement models for slot and peripheral cutting for different case of corner cutting were developed. From the model, relation between tool engagement and three different types of tool path strategy were analysed. The significant changes of tool engagement were observed during the corner when the tool changes direction for each tool path strategy. Then, experimental work was conducted to investigate the effect of variation engagement for the tool path strategies on cutting force and cutting temperature. The highest cutting force and cutting temperature were found in pocketing operation by using inclination tool path strategy compared to contour and zig zag tool path strategy. The variation of tool engagement is one of the attributed to high cutting force and cutting temperature. Further investigation was conducted to evaluate the effect of cutting parameters on cutting force, cutting temperature and surface finish. The three key parameters are cutting speed, feed per tooth and depth of cut. Taguchi L9 design of experiment and analysis of variance (ANOVA) was used to determine the significant factors that influence the result. Within the range of cutting parameters that have been selected, cutting speed and feed rate were the most significant parameters that influence cutting force, cutting temperature and surface finish. Meanwhile, it was found that the increasing of cutting speed and feed per tooth have shown increasing of surface roughness. Finally, the relationship between cutting parameters (controllable factors) and machining output (uncontrollable factors) with surface roughness for different tool engagement angles were established. Pearson correlation analysis was used to explore the correlation between the controllable and uncontrollable factors. It was found that, most of the factors have positive relationship between each other. Then, multiple regression analysis was used to establish the correlation models. From the analysis, the model showed acceptable accuracy and are significant. The main achievement of this study is improving surface quality of a mould, which the surface roughness obtained is in the range of surface quality of mould. In addition, it was found that cutting temperature is also closely related to cutting forces and tool engagement that affected surface quality