Effect of tool quality on the machinability characteristics of Al-Cu and Al-Si cast alloys

The present work was performed on three types of alloys, viz., Al-6% Cu (coded HT200), 319 alloy, and 356 alloy using dull inserts. The results show that the shape of the dull inserts and cutting characteristics varied from one insert to another and hence it was difficult to obtain reproducible results. Due to the bad shape of the dull inserts, the cutting forces required to machine 14 m of distance were 40–50% higher than those required using new inserts to machine 120 m of cutting distance. The profile of surface roughness using dull tools was almost twice that of the profile obtained using new inserts. However, the signals were much wider in the former case with less number of peaks. Due to the severe irregularities of the edges of the dull tools, neither the alloy composition nor the heat treatment is relevant. The surface finish of all alloys was characterized by the presence of cracks and shallow holes. Residual stresses varied along the width of the machined block. All stresses were of tension type compared to compression type in the un-machined shoulders. Due to the high applied forces required when using dull inserts, the resulting residual stresses were almost twice that generated by new inserts in spite of the large difference in the machining distance. Due to the use of showers of coolant, the chips in all cases were shiny with no signs of burning. In all cases, the burrs were separated from the workpiece.