Influence of electrical parameters of electrodischarge machining of state of aluminium matrix surface
Maria Trzaska*, Jan Perończyk**, Dionizy Biało*** *Politechnika Warszawska, Wydział Inżynierii Materiałowej, ul. Wołoska 141, 02-507 Warszawa **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. 3, 2005 pages 51-56
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abstract The paper deals with problems of high efficiency electrodischarge machining (EDM) of aluminium composites with using a transistor generator. The composite with Al+20%Si+3%Cu+1%Mg matrix and with SiC particle reinforcements were mnufactured by a powder metallurgy method using hot extrusion. The reinforcing phase exhibited an average granularity of 7 μm and volume fraction of 5% in the composite. The influence of the following electrical parameters during the machining course and state of the surface after machining were estimated: amplitude of the current in pulse I in the range of 4÷16A, duration time of the pulse ti in the range of 32÷500 μs and filling pulse coeffcient η in the range of 0.4÷0.8. It was stated, that productivity of EDM is higher if higher is value of current I and pulse filling coefficient η (Fig. 2). The influence of the pulse duration ti on the productivity, occures only for higher current value I - productivity Vw grows for small ti (Fig. 3). The roughness of the surface was investigated as a function of EDM electrical parameters. Roughness parameters Ra and Rz are highest for the higher current values I (Fig. 4) and growths for higher pulse filling coefficient η (Fig. 5). Moreover a roughness growth for longer time ti was observed (Fig. 5). State of the composite surface after EDM machining was estimated as a result of scaning microscope images investigatious - Figures 6 and 7 and of microanalyse probes for selected areas of surface. It has been noticed that small solid remelted areas of material and small craters after eroded material occurred on the composite surface after machining. Their dimensions also depend on electrical parameters of EDM machining. Composite surface is enrichod in carbon from the decomposed kerosone used as a dielectric during machining (Tab. 1). Comparative reseach of the composite material and matrix material shows that productivity of electrodischarge machining of the matrix is higher than productivity of composite machining by about 6÷10%. Key words: electrodischarge machining, aluminium matrix composite, surface microgeometry