Three-dimensional metrology of microturning tool edge radii

Abstract

The cutting edge radius is a significant parameter of a micromachining tool. When it is not sufficiently sharp, ploughing, which affects the whole machining process and workpiece quality, will occur. It is then essential to be able to estimate the value of the cutting edge radius accurately. In this paper, a three-dimensional strategy that can be used to measure the microturning tool edge radii is presented. The strategy is based on robust cylinder fitting that is applied to a 3D point cloud of the tool. It is implemented in C++ with Open Computer Vision and Point Cloud Library. It was validated using a virtual point cloud, resulting in errors of 0.42% and 1.11% without noise and with noise, respectively. Additionally, uncertainties of 0.045μm and 0.082μm were obtained. It was successfully applied to six microturning inserts: three unused tools and three used tools. The point clouds were obtained with two different 3D surface reconstruction techniques, focus variation with a photon microscope and a multi-view stereo with a scanning electron microscope. The obtained results were more coherent, i.e., they were less dispersed; for example, in non-used tools, the range was [3.11μm–3.90μm] and for the conventional circle fitting the range was [2.62μm–4.38μm]. The traditional method is indirect: the 3D point cloud is sliced into 2D point clouds (profiles) fitted with circles. This 3D-2D process might result in errors. The proposed method is a direct 3D approach with no slicing step.