Machine Tool Performance and Precision

This chapter introduces main machine tool design, construction and testing aspects to achieve high precision on machined parts. Not only the machine tool but also the machining process itself is a source of errors on parts. Therefore, a holistic view involving machine and machining is required. The design of high precision machines involves some basic principles and methodologies which are presented in depth further on. A key factor is the identification of error sources, studying their physical causes and relevance to the final uncertainty. Thus, assembly error, thermal growth, component deformations and control inaccuracy are described. Errors in components and subassemblies are propagated along the kinematic chain of the machine, producing larger positional errors at the tool tip position and tool axis orientation. The use of homogeneous matrices is introduced as a very useful tool for estimating error propagation. Tool deflection and machine deformation caused by cutting forces is another important error source. Unfortunately deflection is impossible to avoid although some models are now provided with machining toolpath selector implying minimal cutting forces along error sensitive directions. After construction and just before the machine tool is delivered to the customer, the verification of precision and performance must be always performed. A description of the existing standards and procedures for this are described at the end of this chapter.