Aluminum-based MMC machining with diamond-coated cutting tools

Automotive, aerospace and train companies need to replace steel and cast iron in mechanical components with lighter high-strength alloys like Al metal matrix composites (MMC). The weight savings will lead to a reduction in the fuel consumption and environment impact. Automotive producers are testing prototypes in Al-MMCs such as brake disk and drum, callipers, piston and cylinder liners. The main limit in the MMC applications at high production volumes is the difficulty and the high cost of the machining operations (turning, milling, drilling, threading) due to the extreme abrasive properties of these materials. In fact, the MMCs reinforcement particles are very hard and produce a quick increase in the tool wear rate due to the abrasion of the cutting edge. Till now the use of MMC and Al hypereutectic alloys in the automotive, railway and aerospace industries has been limited by the following aspects: the high machining costs due to the short standard tool life; the PCD toolings are not available for complex-shape cutting tools (e.g. taps, or very small diameter drills and reamers); during the MMC parts machining a SiC powder formation occurs with the coolant pollution and, moreover, with a degradation of machine tool components (hard particles), and with a drastic decrease of PCD tool cutting life (built-up edge formation). In this paper we present the results of experimental machining tests in different cutting operations with a comparison between standard tungsten carbide tools, PCD and CVD diamond-coated cutting tools with the relative problems in the high production machining of MMC and Al hypereutectic components; conclusions drawn and the possible future developments are presented.