Investigation of the taper of kerfs cut in steels by AWJ

Abstract

The abrasive water jet (AWJ) taper inside the cut material is one of the characteristic phenomena of the AWJ cutting. The taper, together with a retardation of the jet inside the kerf, causes deformation of workpieces, especially in corners and curvatures. Some deviations of the side walls from the plains perpendicular to the material surface can be observed and measured even in the straight line parts of trajectories. This paper is aimed at experimental research of this phenomenon on steels because precision cutting of stainless and hard steels with thicknesses over 10 mm is a serious problem in practice, and the AWJ cutting can solve this problem quite well. The experiments were performed on three sets of steel plates with thicknesses close to 30 mm. The steels of the first and the second set were identical (1.2379, 1.3343, 1.4307, 1.4404 and 1.4845). The steels of the first set were cut in their normal states, and the steels of the second set were subjected to cooling in the liquid nitrogen prior to cutting (marked 1.abcd/N). The third set of samples consisted of steels with very different composition and brittle/ductile behaviour cut in their normal states (1.0036, 1.2767, 1.3379, 1.7225 and 1.7733). The model for calculation of the limit traverse speed from both the jet parameters and material properties has been used for determination of the proper traverse speed scale. The widths of the cuts were measured both on the top and on the bottom of the slots. The difference between these widths has been used for evaluation of the inclination angle, i.e. the wall deviation from the plane perpendicular to the material surface, referred also as the taper. This angle can be used for determination of the tilting angle for compensation of the negative influence on workpiece. The influence of brittle/ductile behaviour and the influence of cooling in liquid nitrogen have been tried to find out. The results were also compared with the theoretical relationship between traverse speed and inclination angle (the taper) on steels presented as a result of previous investigations in scientific articles. The difference between the inlet and the outlet width of kerf made by AWJ in tested steels ranges from 5.2 to 35.4 % for the traverse speed of 5 mm min−1 and from 25.5 to 44.9 % for the traverse speed of 50 mm min−1.