Influence of reinforced particle size on electrodischarge machining of aluminium matrix composites
Jan Perończyk*, Dionizy Biało**, Marek Oleczek** *Politechnika Warszawska, Wydział Inżynierii Produkcji, Instytut Technologii Maszyn, al. Niepodległości 222, 00-663 Warszawa **Politechnika Warszawska, Wydział Mechatroniki, Instytut Inżynierii Precyzyjnej i Biomedycznej, ul. św. A. Boboli 8, 02-525 Warszawa
Quarterly No. 2, 2006 pages 65-69
DOI:
keywords: aluminium matrix composites, electrodischarge machining, reinforcement
abstract The paper deals with the problems of electrodischarge machining (EDM) of composites with Al-20%Si-5%Fe-3%Cu- 1%Mg matrix. Composites were manufacturing by the powder metallurgy route in the process of cold isostatic compaction, degassing and hot extrusion. Aluminium alloy powder with above mentioned composition were gas atomized at high cooling rate of 104÷106 K • s−1. Powder particles have characteristic irregular rounded shape shown in Figure 1. Its size changes in broad range of 5÷150 μm. As the reinforcing phase Al2O3 particles with average size of 3, 9, 23 and 53 μm were used. Samples had constant fraction of reinforcing phase - 10 by volume. Microstructure of the matrix powder and morphology of Al2O3 reinforcing phase are shown in Figures 2 and 3. After processing composites have homogenous structure with small silicon crystals, without porosity (Fig. 4). These composites are especially promising materials. This kind of light, temperature - resistant, wear - resistant, with low coefficient of thermal expansion has commercial potential for application in electrical equipment, automobile and aircraft industries. In Table 1 composite used in presented research is shown, its composition, hardness, UTS and coefficient of thermal expansion. Electrodischarge machining was performed using an EDEA-25 machine equipment with RLC generator. The generator had 6 modes of energy of single discharge. Ei in the range of 0.044 to 2.268 mJ, listed in Table 2. EDM machining was curried out in a free-system i.e. the diameter of the composite sample was the same that diameter of copper electrode. The main parameters determined after the machining was: volumetric productivity Vw (mm3/min) and roughness of the machined surface expressed as Ra (μm). It was shown that energy of single discharge influence mainly on the EDM process running (Fig. 5). The higher was Ei, the higher were value of Vw. Influence of reinforcing particle size on Vw is not as strong. It was noticed that increasing particle granularity from 3 to 53 μm caused decreasing in process productivity 14 to 18% (Fig. 6). The highest productivity was for matrix material. Figure 7 shows how the discharge energy affects the surface roughness during EDM. The value of Ra increases as this energy increases. When the size reinforcing particles is growing roughness parameters Ra is also growing. Surface profilograms determined at the discharge energy of 2.268 mJ is shown in Figure 8. We can see that the higher reinforcing particle are in composites, the more rough is the surface after EDM.