Improvement of Machinability of Lead–Free Brass Using FEM Cutting Simulation Analysis

Abstract

Lead–added free cutting brass has been widely used as a valve material for water supply, air conditioning equipment and small parts for watches, etc. because of its excellent machinability, it is called free–cutting brass. The concentration of lead in brass is regulated in several countries and regions because its lead may cause health problems in the human body. In consideration of this problem, raw material suppliers have developed several types of lead–free brass in recent years. However, since the machinability of lead–free brass is lower than that of free–cutting brass, cutting force is large and problems such as handling of long chips are pointed out. Therefore, improvement of machinability of lead–free brass is required. In previous study, it was found that the PCD tool has the remarkable effect in cutting force reduction, it is possible to process with the same cutting force as conventional leaded free–cutting brass with sintered carbide cutting tool. On the other hand, serious problem of long continuous chip generation by using PCD tool still remained. In this study, FEM analysis was applied to predict the suitable shape of chip–breaker on tool rake surface. Commercially available FEM software was adopted and the stress and strain relationship at high–temperature and high–strain rate was measured for cutting simulation. The Greeble test was used to measure stress–strain relationship at RT, 200°C and 350°C and deformation speed of 100mm/s and 0.1mm/s. We found that calculated temperature, principal cutting force, chip thickness and tool–chip contact were close to measured values. A step with 0.7mm width and 0.2mm depth formed on tool rake by laser processing as a chip breaker show the best chip–breaking effect in cutting experiment and this is also shown in cutting simulation.