Simple Approach for Evaluation of Abrasive Mixing Efficiency for Abrasive Waterjet Rock Cutting

The abrasive mixing variables, such as the abrasive and water flow rates and the focus geometry parameters, determine the profitability of an abrasive waterjet system. In this study, the mixing efficiency characteristics in abrasive waterjet rock cutting were investigated. To demonstrate comprehensively the efficiency reduction due to collision during abrasive mixing, the chance of collision was expressed as the distance between the abrasive particles in the focus. The mixing efficiency was then assessed by utilizing the empirical relationship between the experimental results and the developed model. Based on the particle density and the velocity, the closer particles showed higher chances of collision, thus yielding a reduced cutting performance. Using the distance between particles model, the optimum abrasive flow rate and the cutting performance of abrasive waterjet systems can be estimated. This developed model can be used for the design selection of abrasive flow rate and systems for the cost-effective use of abrasive waterjets.

Performance Comparison of Subtractive and Additive Machine Tools for Meso-Micro Machining

Several series of experiments were conducted to compare the performance of selected sets of subtractive and additive machine tools for meso-micro machining. Under the MicroCutting Project, meso-micro machining of a reference part was conducted to compare the performance of several machine tools. A prototype flexure of the microspline of an asteroid gripper under development at NASA/JPL was selected as the reference part for the project. Several academic, research institutes, and industrial firms were among the collaborators participating in the project. Both subtractive and additive machine tools were used, including abrasive waterjets, CNC milling, lasers, 3D printing, and laser powder bed fusion. Materials included aluminum, stainless steel, and nonmetal resins. Each collaborator produced the reference part in its facility using materials most suitable for their tools. The finished parts were inspected qualitatively and quantitatively at OMAX Corporation. The performance of the participating machine tools was then compared based on the results of the inspection. Test results show that the two top performers for this test part are the CNC precision milling and micro abrasive waterjet. For machining a single flexure, the CNC precision milling had a slight edge over the micro abrasive waterjet machining in terms of part accuracy and edge quality. The advantages disappear or the trend even reverses when stack machining with taper compensation is adopted for the micro abrasive waterjet.

Boundary condition for deformation wear mode material removal in abrasive waterjet milling: Theoretical and experimental analyses

Producing quality features with abrasive waterjet milling requires the generation of shallow kerfs with low surface waviness. Typically, such kerfs are produced by deformation wear mode of material removal realized with certain combination of process parameters chosen based on an elaborate experimental analysis. Instead, these parameters can be selected through a modeling methodology developed based on deformation wear erosion theory. As a first part of this development, it is essential to identify the conditions for the prevalence of deformation wear during the generation of shallow kerfs with abrasive waterjets. To establish this condition, this article presents a theoretical analysis of kerf formation formulated based on deformation wear erosion by solid particles. In this analysis, the interaction of the abrasive particles with the material and the subsequent material removal through deformation wear is considered to define the geometry of the cutting front. The geometry of the cutting front was then used to determine the condition at which local impact angle of abrasives striking the cutting front changes to alter the mode of material removal from deformation wear to cutting wear. This analysis has brought out the boundary condition for deformation wear as the maximum depth of kerf to be equal to the average size of the abrasive particles used in the jet. The generic nature of this condition is established with kerfing experiments over three different ductile materials.