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Introduction Precision machines are essential in modern industry and directly affect machining accuracy,repeatability, productivity and efficiency. Generally, the design of a precision machine mainly includes the design of its key elements such as mechanical structure, spindles and drive system, control and inspection systems, etc. There is a lot of literature available on the design of machine elements [1-5]; while it is difficult to cover in details on design of precision machine in one chapter. In this chapter, therefore, emphasis is placed on the mechanical and structural design of precision machines, relevant design methodology and tools driven by dynamics. Furthermore, the chapter focuses on the integrated approach for modelling and simulation of the machine and machining dynamics, and thus achieving an optimal design of the machine and its performance in the dynamic machining process. 27709
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There are two basic approaches to studying the machining dynamics. One is cutting force modelling that does not contain structural parameters of machines and has been discussed in the previous chapters; the other is the dynamic modelling of the machine and structure or the machining processes. The methodology presented in this chapter falls into the latter approach, but towards an integrated approach to covering the dynamics of both the machine and the machining process. Section 10.2 discusses design principles of precision machine tools, including the machine configuration, tool-workpiece loops, and stiffness, mass and damping issues. The material presented is only a refined formulation with an emphasis on machining dynamics. Section 10.3 formulates the machine design methodology, covering a dynamics-driven design process,modelling and simulation enhancement, and design guidelines. Section 10.4 presents the implementation perspectives on the design of precision machines, and a practical design process based on finite element analysis (FEA). Section 10.5 provides three case studies on the design of a fast tool servo system, a 5-axis bench-type milling machine tool and a precision grinding machine.
10.2 Principles
Precision machine tools are highly dynamic systems in order to sustain the required accuracy, productivity and repeatability. The precision of a machine is affected by the positioning accuracy of the cutting tool with respect to the workpiece surfaces and their relative structural and dynamics loop precisions, which are fundamental and essential for the machine design
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10.2.1 Machine Tool Constitutions
A typical precision machine consists of five major sub-systems. They are mechanical structure, the spindle and drive system, the tooling and fixture system, the control and sensor system, and the measurement and inspection system. These sub-systems are essential and directly contribute to machine tool performance. Figure 10.1 highlights the machine tool constitution and key evaluation criteria for the machine tool’s performance. Because of varied machining purposes and different machine configurations, Figure 10.1 cannot be very comprehensive, but rather provides a thorough summary for understanding the machine tool constitution and its performance evaluation related to machining dynamics in particular
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10.2.1.1 Mechanical Structure
Mechanical structure is normally comprised of stationary and moving mechanical bodies. The stationary bodies include machine base, the column and spindle housing, etc. They usually carry moving bodies, such as worktables, slides and carriages. The structural design is critical since the mechanical structure not only provides the support and accommodation for all the machine’s components but also contributes to dynamics performance possessed in a machine tool. To achieve a high stiffness, and a damping and thermal stability, two major design issues are involved in mechanical structure design, i.e., the material selection and configuration.