On the Turn-Machinability of Lo-ex

Abstract

It seems that there are many problems as to the machining of lo-ex which is an aluminium alloy develoved as a piston material, because the alloy contains eutectic silicon which is effective to make small an expansion coefficient and nickel which is added to prevent softening at high temperatures. Therefore, the machinability of lo-ex is mainly discussed here in the light of cutting resistance, tool life, roughness of finished surface, built-up edge and chip treatment in turning. The results obtained are as follows. Lo-ex shows a dispersion of small hard crystals in the structure of soft matrix and is not so hard in appearance. In turning lo-ex the wear of the tool is unusally large and becomes more distinct with increase in cutting speed. But, compared with alusil in which much harder small crystals are dispersed than in the case of lo-ex, the wear of the tool is not so large. Using a carbide tool, the cutting resistance decreases with increase in cutting speed and, beyond some cutting speed, the cutting resistance shows constant values regardless of the cutting speed as can be observed for ordinary aluminium alloys. However, in case of the high speed steel tool, the cutting resistance shows a minimum value with rise in the cutting speed and then the cutting resistance increases again with a further increase in cutting speed. In this case, in the low speed cutting of the high speed steel tool, the built-up edge adheres largely on the tool face and the growth of built-up edge decreases with increasing cutting speed, augmenting adhesions like an oxidated deposit to the tool flank. And the surface roughness in the cutting resistance condition corresponds well to the change of cutting resistance, so the surface using a carbide tool is better than the surface using a high-speed steel tool.