Machinability Testing of Materials in Metal Cutting with Focus on Compacted Graphite Iron and Cutting Fluids

Doktorsavhandling, 2012

Due to the stringent demands for lower emission from trucks require better mechanical properties of the material to be used in the engines. Better efficiency necessitates higher peak pressure in the engines and for traditionally used material, Flake Graphite Iron (FGI), the mechanical properties starts to reach the limit of what the material can withstand. Instead of using FGI, Compacted Graphite Iron (CGI) is an excellent replacement. Compared to FGI, the vermicular graphite in CGI improves the tensile strength of the material. Although the thermal conductivity and damping ability are lower in CGI, it fulfills the engineering aspects of an engine. Concerning machinability, CGI has lower machinability than FGI, especially in continuous cutting operations. Also, as the material is recently introduced into manufacturing the knowledge of its machining is inadequate and requires improvement. It is therefore necessary to obtain increased knowledge of casting and machining of CGI to implement it successfully as an engine material. To achieve this objective a large number of CGI materials have been casted and the machinability parameters have been tested and presented in this thesis. The main focus in this thesis has been on studying the correlation between materials microstructure, their mechanical properties and machinability. The thesis covers the influence of material matrix and nodularity on the machinability of CGI material. A range of materials were tested from ferritic to pearlitic matrix. Empirical relations have been used which were driven from experimental results. Relationships between chemical compositions, material microstructure and material’s physical properties have been presented. By understanding such relationships CGI materials could be optimized for design and manufacturing requirements. For machinability analysis mainly tool life and cutting forces were taken into consideration for the evaluation of machinability analysis. Due to the complexity of machining process, the focus of the research was to develop the empirical models for tool life and cutting forces for continuous cutting operation. The influence of micro-edge geometry on the machinability of CGI has also been presented in the thesis. Empirical models for tool life and cutting forces as a function of cutting edge geometry and cutting parameters have been presented for continuous cutting operations. Machinability of CGI has also been compared with other graphitic grades of cast iron and the importance of cutting fluid use in continuous cutting operation has been highlighted. The thesis also covers the performance testing of different cutting fluids. Some methods have been presented in the thesis to evaluate the performance of cutting fluids. For cutting fluids testing, drilling and tapping tests were performed into aluminium alloy (AlSi9Cu3) and alloy steel (SAE 52100), which are the materials extensively used in automotive industry. The results reveal that type and concentration of cutting fluids have effect on the torque, thrust force, tool life and surface quality. Face turning test was also performed for Build up Edge (BUE) formation and it has been seen that concentration has also an effect on BUE formation. Bimetallic material, CGI and aluminium alloy were also tested in face turning and the results have shown importance of using cutting fluid for better surface finish.