Machining is a collective term for various material removal processes comprising e.g. turning, milling and grinding. These are among the most common manufacturing processes for producing component and products used on a daily basis. As a matter of fact, machining is often applied as a final step in the production line in order to reach correct workpiece dimensions, surface finish and shape, with close tolerance accuracy thus accounting for approximately 15 % of the value of all mechanical components worldwide.
During a turning operation, the topic of the current thesis, a material portion called “chip” is removed from the workpiece using a cutting tool. A considerable waste of material, up to 10 % of the workpiece material might be removed in order to reach the final geometrical dimensions of the product. Desired product properties are achieved by controlling the processing parameters e.g. cutting forces, chip morphology, temperature and surface roughness which may be a difficult task.
Currently, the manufacturing industry addresses these challenges via simulation tools to increase the knowledge and optimization possibilities of the operation. Hence, in order to accurately simulate the machining processes, it is of utmost importance to accurately represent the behavior of the workpiece material, the interaction at the tool-chip interface and the local fracturing that occur during the chip formation. During this material removal process, regions of the workpiece material are subjected complex phenomena e.g. extremely large deformations, high strains and strain-rates together with elevated temperatures.
Thus, in the current thesis, a modeling framework is presented which accounts for both the material response, tool-chip interaction and fracture in the workpiece during machining. In particular main efforts have been put on the development of a model to represent the onset and evolution of damage followed by subsequent fracture. The modeling framework is implemented in a commercial software to simulate 2D machining (orthogonal cutting). The results obtained are validated against experimentally obtained chip formations, cutting forces and tool-chip contact lengths for machining of the difficult-to-cut material, Alloy 718.