Advances in High Porductivity - High Quality Machining

Doctoral thesis, 2005

Quality, productivity and flexibility are vital factors in today’s machining industry in order to remain competitive. Nowadays, finished products not only have to be produced within specific tolerance limits, but they also have to posses high standards in terms of surface integrity, i.e. physical and chemical properties of the surface and its vicinity. On the other hand, manufacturers must adapt at higher pace to changes in product specifications such as modified geometry, new work-material, higher requirements on the surface finish, or lower environmental impact throughout the cycle life of the product. Therefore, machining processes with enhanced flexibility are needed. Last but not least, the ability of a company in being profitable is closely related to its productivity, i.e. how efficient the recourses are used to create valuable products. In prior research there has been an extensive amount of work focused on specific topics described above. Nevertheless, it is often the case that an improvement in product quality has a bad impact on productivity, or improved productivity diminishes flexibility and vice versa. In this work, the effect new cutting technologies on product quality, flexibility and productivity have been investigated. The approach has been empirical and statistical methods have been used. The work is divided in three different topic areas. Firstly, the thesis explores the possibilities of high-pressure jet-assisted machining for turning difficult to cut materials, especially for those applications where existing tool geometries are not effective such as near net shaped products, unleaded alloys and stainless steels. It is shown that ultra high pressure cooling significantly improves chip formation and breakage, and thus productivity, as well as surface finish. Secondly, the relationship between residual stress, surface topography and cutting parameters in hard turning was investigated. It was found that residual stress are significantly influenced by cutting parameters which opens the possibility of manufacturing products with Taylor made stress profiles in order to enhance the fatigue life of the component during service. Hard turning can outperform grinding not only in terms of product quality, but also in flexibility and productivity. Third and last, new coating designs were investigated for dry machining applications. Dry machining is gaining industrial and academic interest since coolant costs are on the increase due to environmental concerns. Two coating concepts were studied: titanium-aluminium-nitride (TiAlN), which is a single phase solid solution material, and titanium-silicon-nitride (TiSiN), which is a nanocomposite structured material. Optimal coating composition and adhesion treatments are described in the thesis.