Each machining operation creates a feature which has certain geometric variations compared to its nominal geometry. Designers normally give design tolerance specifications on the nominal geometry, to specify how large these variations are allowed to be. One needs to estimate accuracy of various manufacturing processes in order to verify whether or not a given process plan will produce the desired design tolerances.
In machining, various factors such as deformation of the workpiece and tool, vibration, thermal deformation, inaccuracies of machine tool, etc., affect the machining accuracy. Some of these factors are dependent on the selection of cutting parameters. For a limited number of machining processes, deterministic models have been developed to provide quantitative mappings between the cutting parameters (such as cutting speed, feed, and depth of cut) and machining accuracy (such as surface finish and dimensional accuracy) [156,170,171,172].
Zhang et al. presented [171,172,173,174] a comprehensive method for predicting the machining accuracy of turning and boring operations. Their methodology can be extended to model all machining processes involving single-point cutting tools. In complex machining operations, developing mathematical models is a very difficult task. In such cases, empirical methods are often used. Kline et al. [175] proposed a system for predicting machining accuracy in end milling. Based on the past experiences of metal cutting industries, a significant amount of data has been published that describes the achievable machining accuracy of various machining processes [10,12,153].
A tolerance chart is a tool for assessing machining accuracy. It is a graphical representation of the process sequence which helps to visualize the influence of the proposed sequence on resulting dimensions and tolerances. For each step of the the operation sequence, machining accuracy is estimated and tolerance stack-ups are calculated. Automated tolerance charting has not been incorporated into most automated process planning systems. Recently, attempts have been made to automate tolerance charting [176,177]. Current research on computer-aided tolerance charting focuses on calculation of optimum intermediate tolerances typically using linear programming techniques.
In near net shape processes and electro-mechanical component assemblies, the process physics often determine the accuracy and quality of the parts. Balasubramaniam et al. [50] provides some methods for determining possible manufacturing defects in aluminum extrusion. Similar works are also reported in other manufacturing processes.