A technical note on grit embedment following abrasive water-jet milling of a titanium alloy

Abrasive water-jet (AWJ) technology is routinely used to cut materials that are difficult to cut by other methods. However, whilst the technology for through-cutting of materials is mature, the process is also being developed for controlled depth milling (CDM) of materials since other processes such as chemi-milling are under increased pressure due to legislative restrictions and costs associated with effluent disposal. Grit embedment and surface morphology is considered to be an issue for the service life of components manufactured by AWJ-CDM, especially in environments where fatigue failure is a concern. In the current work, the effects of milling parameters (namely jet-workpiece traverse speed, jet impingement angle, milling direction and grit size) on the surface morphology and degree of grit embedment are investigated for the milling of a titanium alloy (Ti6Al4V) with garnet grit. Up to 40% of the area of a milled surface has been shown to consist of embedded grit. It has been demonstrated that grit embedment can be minimized either by milling with a high jet traverse speed at low impingement angles or by low speed milling at jet impingement angles up to 45° in the backward direction only. However, even in the best cases, 5% of the area of a milled surface was composed of embedded grit. The levels of grit embedment and development of surface morphology have been observed to depend upon complex interactions of the various processing parameters, and a rationale for the observed behaviour has been proposed.