Diamond tools wear and their applicability when ultra-precision turning of SiCp/2009Al matrix composite
Introduction
For some precision or ultra-precision applications, such as inertial guidance systems, satellite antennae/bearing, laser reflection mirror, optical benches and high speed manufacturing equipment, exceptional resistance to distortion from high thermal gradients and mechanical stresses is often required [1]. Silicon carbide particle-reinforced aluminum matrix composites (SiCp/Al) have many outstanding properties such as high specific stiffness/strength, high wear resistance, low density, high thermal conductivity and low thermal expansion, which could wonderfully meet the requirements mentioned above [1], [2]. In the last decade, great attention has been paid to the precision/ultra-precision machining of SiCp/Al composites [3], [4], [5], [6], [7]. Due to the low plasticity and fracture toughness, non-uniformity and abrasive nature of the reinforcement, machinability of this kind of material is poor which embodied in excessive tool wear and poor surface finish even cut with diamond tools [8], [9], [10], [11]. Generally speaking, in the research of ultra-precision machining of SiCp/Al composites, most of the researchers limited their studies to the influence of cutting parameters, volume fraction and mean size of reinforcement particles on surface roughness or surface quality. Few articles have been related to the single diamond tool wear when ultra-precision turning of SiCp/Al composites. A suspected diffusive-abrasive wear of SCD tool has been found by N.P. Hung when ductile-regime machining of 10 vol.% SiCp/A359 composites was performed [5]. Unfortunately, the theoretical explanation has not been provided. Moreover, the direct experimental evidence has not been reported yet. The present study intends to enhance the understanding of the machinability of SiCp/Al composites by investigating the details of the diamond tools wear mechanisms and the applicability of SCD and PCD diamond tools when ultra-precision turning of 15 vol.% SiCp/2009Al composite.
Section snippets
Materials
The machined material in the experiments was 15 vol.% SiCp/2009Al which was produced through powder metallurgy technology and the extrusion ratio was 15:1. In particular, the mean size of the reinforcement particle was 2 μm. The 2009Al alloy contains 3.8 wt.% Cu, 1.4 wt.% Mg, 0.14 wt.% Si, 0.1 wt.% Fe and balanced Al. The typical microstructure of 15 vol.% SiCp/2009Al composite is shown in Fig. 1.
Ultra-precision turning experiments
Commercial grade natural single crystal diamond (SCD) and polycrystalline diamond (PCD) tools were
Chipping, peeling and abrasive wear
Fig. 2 shows the wearing pattern of round edge SCD tool after cutting 15 vol.% SiCp/2009Al for 6.4 km, while Fig. 3 displays the wearing pattern of straight-nose SCD tool. Obviously, microwear, chipping, abrasive wear and cleavage can be found on SCD tools. During machining SiCp/Al composites, the tool cut the soft aluminum alloy matrix and the hard reinforcement particle alternately. When encountered hard SiC particles, the cutting tool suddenly released from the state as it passed into soft Al
Conclusions
Based on the above analysis, the following conclusions can be drawn:
- (1)
Microwear, chipping, cleavage, abrasive wear and chemical wear were the dominating wear patterns of SCD tools, while PCD tool mainly suffered from abrasive wear on the rake face and adhesive wear on the flank face. It was the combined effects of abrasive wear of SiC particles and catalysis of copper in the 2009Al matrix that have caused the severe graphitization of SCD tool.
- (2)
The graphitization of SCD tool when machining SiCp
Acknowledgements
This project was supported by a grant from the State Key Laboratory Foundations of Science and Technology (51464010604HK1301) and the Institutions Natural Foundations of Jiangsu Province (09KJB460004). The authors would like to thank Liu Baoyuan and Liu Yi from Beijing Precision Engineering Institute for Aircraft Industry for their help in the experiments.
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