Abrasive water-jet controlled depth milling of Ti6Al4V alloy – an investigation of the role of jet–workpiece traverse speed and abrasive grit size on the characteristics of the milled material

Due to difficulties in the use of traditional mechanical methods to mill of difficult-to-machine materials (especially in thin section), methods such as chemical milling or etching have commonly been employed. However, increasing legislative restriction on disposal of effluent has resulted in an increase in the environmental costs of such processes, and has prompted examination of alternative processes for milling to a controlled depth. Abrasive water-jet (AWJ) technology is used in a routine manner in manufacturing industry to cut materials that are difficult to cut by other methods. A similar process, where AWJ is used for controlled depth milling (CDM) is thus considered here. The main problem to be solved in the use of AWJ as a CDM technique is that of tolerance on depth, surface waviness and surface roughness of the milled area. In the current work, the effects of jet–workpiece traverse speed, number of passes of the jet and abrasive grit size on the material removal rate, surface waviness and surface roughness are investigated. Traverse speed is shown to govern the operative mechanism of material removal and thus the material removal rate. It is also shown that the surface waviness can be reduced as the traverse speed is increased, but it should be noted that waviness increases with number of passes of the jet over the workpiece. The surface roughness is not strongly dependent on traverse speed. Smaller sized grit leads to a reduction in material removal rate but also to a decrease in both waviness and roughness.