Active precision design for complex machine tools: methodology and case study

Machine tool design starts with the determination of performance specifications. Precision of the NC axes is an important aspect of machine tool design. Conventionally, the precision specification of machine tools is empirically determined, resulting in poor designs with insufficient or excessive precision. To provide a cost-effective precision specification for complex machine tools, such as gear cutting machines, an active precision design approach is proposed to generate the specification of the positioning repeatability of NC axes to meet the designated working precision requirements of the machine tools. The methodology consists of error analysis and precision design in four steps: (1) workpiece surface formation modeling in terms of the motion axes and layout of the machine tool, and the generating principle of workpiece features; (2) workpiece machining error modeling based on the workpiece surface formation model by considering kinematic errors of the NC axes of the machine tool; (3) workpiece machining precision modeling via the machining error model; and (4) precision allocation according to the required workpiece precision and the machining error model. The methodology is demonstrated and validated through a case study of precision design for a six-axis CNC spiral bevel gear milling machine.