A method of measuring the arc radius of Rockwell diamond indenter

Abstract

Rockwell hardness is the most widely used hardness measurement method in industry at present. Taking superficial Rockwell primary standard machine in National Institute of Metrology(China) as an example, the uncertainty caused by the radius of the indenter arc accounts for 50% of the total uncertainty. In view of the important influence of the arc radius at the top of Rockwell diamond indenter on the evaluation of Rockwell hardness uncertainty, a profile projection system is established which is composed of lens, industrial camera and area-source of light. After pictures are obtained with camera, the next task for these pictures is to be calculated to get target parameter. The target parameter is obtained by profile extraction and radius calculation. In this paper, a new method is proposed as an algorithm criterion that sum of absolute value of data points and fitting arcs is used. Simplicity algorithm is introduced to iteratively solve the algorithm criterion. The purpose of using the algorithm is to eliminate the influence of outlier noise points. To verify the validity of the method in this paper, we conduct a series of experiments. The traceability experiment with standard sphere shows that the expanded uncertainty of the system of the instrument can achieve1.0µm,k=2.The uncertainty of measurement result with Rockwell diamond is1.5µm,k=2. The method in this paper bases on a simple-structural system, has high measurement accuracy, and can be used for rapid screening, evaluation, verification and calibration of Rockwell diamond indenters in industry.