.AUG 'KJD Mohamed Hashish Senior Research Scientist, Flow Research, Inc., Kent, WA 98032 Mem. ASME Pressure Effects in Abrasive- Waterjet (AWJ) Machining Abrasive-waterjets (AWJs) are formed by mixing high-pressure (up to 400 MPa) waterjets (0.1 to 1 mm in diameter) with abrasive particles in mixing tubes with typical 1/d ratios of 50 to 100. The pressure of the waterjet influences the overall performance of the abrasive-waterjet cutting system through operational and phenomenological effects. Higher pressures result in lower hydraulic efficiency, more frequent maintenance, high wear rates of mixing tubes, and fragmentation of particles before they exit the nozzle. However, with high pressures, deeper cuts can be obtained and higher traverse speeds can be used. Consequently, the hydraulic power is best utilized at an optimum pressure, which is a function of all other parameters as well as the application criteria. This paper presents data and analyses on the effect of pressure on nozzle operational characteristics, i.e., jet spreading characteristics, abrasive particle fragmentation, suction capability, wear of mixing tubes, and mixing efficiency. The effect of pressure on the parameters of cutting performance is discussed with example data. These parameters are depth of cut, specific area generation, maximum cutting traverse rate, surface waviness, and cost of cutting. Optimal pressure examples presented in this study indicate that pressures over 240 MPa are required for efficient abrasive-waterjet performance in metal cutting. 1 Introduction Abrasive-waterjets (AWJs) are most commonly formed by mixing solid abrasive particles with high-velocity waterjets in mixing tubes [1]. Typical waterjet velocities are 300 to 700 m/s with sizes in the range of 0.1 to 1 mm in diameter. As a result of momentum transfer between water and abrasives in narrow mixing tubes, focused high-velocity streams of abrasives are formed with great cutting capabilities for a very wide range of metallic and nonmetallic materials [2]. The cutting process oc- curs as a result of complex erosion phenomena that may in- volve more than one mechanism of material removal [3, 4]. The cutting performance can be controlled by adjusting the parameters of associated cutting system components. These parameters include the hydraulic, abrasive, mixing, and traversing parameters, i.e., waterjet pressure and diameter, abrasive flow rate, material type and size, mixing tube diameter and length, traverse speed, jet angle, number of passes and standoff distance. Other parameters may include the method of abrasive delivery (forced or by jet suction), the condition of abrasives (dry powder or slurry), and the geometry of the nozzle assembly. Figure 1 shows a schematic of the AWJ nozzle and parameters. In this paper, the direct and indirect effects of pressure will be presented and discussed in detail, and examples of criteria for optimization will be addressed. Contributed by the Materials Division of THE AMERICAN SOCIETY OF MECHANICAL ENGINEERS and presented at the Product and Process Design Sym- posium, ASME Manufacturing International '88, April 17-20, 1988, Atlanta, Ga. Manuscript received by the Materials Division February 18, 1988. 2 Effects of Pressure on Nozzle Operation In this section, we discuss the effects of pressure on the operation of the AWJ nozzle system without regard to cutting. PARAMETERS Waterjet Pressure Waterjet Diameter Abrasive Flow Rate Abrasive Size Abrasive Material Mixing Length Mixing Diameter Traverse Speed Angle of Cut Stand Off Distance COMPONENTS High Pressure Tube Abrasive Feed Hose Waterjet Orifice Waterjet Mixing Tube Abrasive-Waterjet Fig. 1 Abrasive-waterjet nozzle concept and parameters Journal of Engineering Materials and Technology JULY 1989, Vol. 111/221 Copyright © 1989 by ASME Downloaded From: http://materialstechnology.asmedigitalcollection.asme.org/ on 09/30/2013 Terms of Use: http://asme.org/terms