Optimizing the layout of a CNC lathe

Abstract

A reasonable choice of machine layout is one of the ways to improve the quality of CNC machines and the result of a comprehensive analysis and consideration of many frequently conflicting requirements: accuracy, design feasibility, processability, productiveness, efficiency, safety, etc. The complexity of the choice of machine layout is associated with their diversity depending on the fact that machines with different designs of assembly units can have the same arrangement and, conversely, lathes with the same designs of main elements can have different layouts. Due to the multiple effects of layout on the accuracy characteristics of a machine, the optimal layout solution choice is the priority problem of machine building. The study covers the development of a technique for selecting a layout solution for the CNC lathes, which considers the random location of cutting zones and the existence of power factors related to the design and layout of a spindle unit. In the developed technique, as a criterion for choosing an optimal arrangement, the authors suggest using an accuracy layout criterion evaluated by the elastic deformations of a spindle in the cutting zone. The study resulted in analytical expressions for an objective function depending on two design variables: angles determining the location of a spindle pre-drive gear and a tool-holding group. The authors note that for the precision lathes when identifying spindle bearing radial stiffness, one should take into account the stiffness anisotropy of a housing bore for the spindle front support. For two specified design variables, the study shows the performance of a scanning method (complete enumeration for 322 points). Using this method and processing with Mathcad software, the authors obtained a possible variation range of values of specified angles for five standard layouts of spindle support bearings and limitations related to the minimization of elastic deformations of the tooling system.