Visualization of the Abrasive.Waterjet Cutting Process by Mohamed Hashish ABSTRACT--Cutting with abrasive waterjets was visualized in three types of materials: Lexan, Lucite and glass. Movie cameras were used at speeds of 64 and 1000 frames/s to record sequences of the jet penetration in these materials. It was found that the cutting process consists of two basic modes of erosion, The first, known as the cutting-wear mode, occurs at relatively shallow angles of impact. This mode results in a steady-state jet-solid interface. The other mode, the deformation-wear mode, occurs at large angles of impact and results in an unsteady penetration zone. The relative contribution of each of these two modes or mechanisms to material removal depends on the process parameters. The cutting process is cyclic in nature when the deformation- wear mechanism is partially or totally contributing to cutting. Qualitative and quantitative results of these visualization experiments suggest a mechanistic model for the penetration process. The results of this work may also be expanded to explain other 'stream-like' cutting-tool processes, such as laser and flame cutting. List of Symbols dj = jet diameter d m d.= f= h= h c = ha = fn= N= hi= P= Pc t= bl = Xo= Oc = Oe = Oo = mixing-tube diameter waterjet-orifice diameter camera speed in frames per second depth of cut penetration rate depth of cut due to cutting wear depth of cut due to deformation wear depth of uncut portion due to jet deflection at the exit particle-mass-flow rate number of passes number of frames over which depth h is achieved waterjet pressure critical threshold pressure time traverse rate entry length after which jet reaches maximum depth angle between jet-velocity vector and traverse- velocity vector jet-deflection angle at entry edge interface angle at depth hI initial angle of jet-solid interface Mohamed Hashish is Senior Research Scientist, Flow Research, Inc., 21414 68th Avenue South, Kent, WA 98032. Original manuscript submitted." April 6, 1987. Final manuscript received: August 5, 1987. Introduction High-velocity abrasive waterjets are new tools for cutting and machining hard materials? In this new technology, the cutting action is performed by abrasive particles that are accelerated and contained in high-velocity waterjets. The waterjets are formed by water at very high pressures (up to 400 MPa) being forced through small sapphire orifices (from 0.25 to 1.5 mm in diameter). The flow of a waterjet in a mixing tube up to 2 mm in diameter will create enough suction to entrain up to 50 g/s of abrasives. Figure 1 shows a schematic of an abrasive-waterjet nozzle. Considerable research is still needed to develop a basic understanding of the cutting process. This paper describes one such research effort that studied the actual penetra- tion of abrasive waterjets in solids. Visualizations of the penetration process were conducted on three different types of transparent materials using different parameters. The important abrasive-waterjet parameters include: waterjet pressure, waterjet diameter, mixing-tube diameter, mixing-tube length, abrasive material, abrasive flow rate, abrasive particle size, traverse speed, angle of cutting, and number of passes. Some of these parameters were varied during the visualization experiments to differentiate among their effects. In this paper, the experimental setup is described first, followed by a description of the target materials and test parameters. Qualitative and quantitative visualization observations are then presented and discussed. Finally, HIGH-PRESSURE WATER TUBE ABRASIVE PORT ORIFICE WATER JET MIXING TUBE ABRASIVE-WATER JET Fig. 1--Abrasive-waterjet nozzle Experimental Mechanics 9 159