Quality Waterjet Newsletter – 10/07/2008 Cutting Hollow Structures Many applications in waterjet cutting are involved with hollow structures. The hollow space tends to disperse the jet and affects the cut below. Louis & Von Rad(*) did an experimental study on this phenomenon. Here is a review of their findings. Their experimental setup to simulate a hollow structure is illustrated in the top figure. Cutting tests were done on aluminum (AlMgSi0,5) with a 1-mm abrasive water suspension jet at 70 MPa of pressure and 2 kg/min of 80 mesh garnet. The parameters were chosen so that the sample below the gap was not cut through in order to preserve the evidences of remaining jet potential. The gap was filled with either air or water to study the impact of medium. The results were plotted in the other two figures. The reduction of the kerf depth and the increase of the kerf width on the sample were proportional to the size of gap. Compared to air, water made the kerf shallower and narrower because the outer layer of the jet lost energy to the surrounding water. It was also found that the thickness of the upper plate had a small impact to the kerf-depth-vs- gap-size relation (i.e. a thicker upper plate resulted in a shallower kerf), but a relatively large impact to the kerf-width-vs-gap-size relation (i.e. a thicker upper plate resulted in a wider kerf). The explanation was that the upper plate acted as a “bad” nozzle. * Louis, H. & Ch Von Rad (2000) “Cutting of hollow structures with abrasive water suspension jets,” in Proceedings of the 15^th International Conference on Jetting Technology, Ronneby, Sweden, September 6-8, pp59-67.

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