Characterization of factors interacting in CGI machining : machinability - material microstructure - material physical properties

Abstract: The Swedish truck industry is forced to find new material solutions to achieve lighter engines with increased strength. Customers and new environmental regulations demand both higher specific power and more environmentally friendly trucks, and this places a rising pressure on the manufactures. This demand could be met by increasing the peak pressure in the cylinders. Consequently, a more efficient combustion is obtained and the exhaust lowered. This however exposes the engine to higher loads and material physical properties must therefore be enhanced. Today, alloyed gray iron is the predominantly used engine material. This material cannot meet the requirements of tomorrow’s engines. Compacted Graphite Iron has good potential to be the replacement; it opens new design opportunities with its superior strength, which can lead to smaller, more efficient engines and additional power. The question is: how will manufacturing be affected? The main goal of this thesis is to identify and investigate the main factors’ effect and their individual contributions on CGI machining.  When the relationship between the fundamental features; machinability, material microstructure, and material physical properties, are revealed, then the CGI material can be optimized, both regarding the manufacturing process and design requirements. The basic understanding is developed mainly through experimental analysis. No attempt has been made to optimize the material to be used as engine material in this thesis. The thesis demonstrates the importance of having good casting process control. It also illustrates the microstructural properties’ effects on CGI machinability, and what new aspects of machining must be taken into account, compared to gray iron.