Compensation of geometrical errors of CAM/CNC machined parts by means of 3D workpiece model adaptation

In modern industry conditions, it is very important to develop methodologies for reducing costs and achieving the maximum quality of machined parts, especially considering the dimensional accuracy of workpieces. Geometrical and dimensional inaccuracies are due to several factors, such as workpiece and tool deformation during machining, thermal distortions, tool wear, and machine tool inaccuracy. There are two main approaches used to improve the accuracy of workpieces: mapping the tool-workpiece displacement and altering the finishing tool path or the interpolated tool position to compensate the dimensional errors. The aim of this paper is to propose a new compensation approach, based on adaptation of the geometrical 3D CAD model used to generate trajectories by CAM software. The concept is to produce a first workpiece using a CAM-generated tool path. Then, the workpiece is measured using optical methods and the displacements between the ideal workpiece model and the measured point-cloud are calculated. Eventually, the displacement vectors are applied to calculate a compensated workpiece model. Such model is then used as a reference by CAM software to calculate the compensated tool path, which is applied for production of subsequent workpieces. The mathematical background and implementation details are given together with an example of application to a benchmark workpiece purposely machined with inaccurate tools. As the results show, the new approach was able to compensate the geometrical inaccuracies of the benchmark workpiece.