Investigations on the performance enhancement of cutting edges using EDM techniques

Abstract

Textured surfaces have found many important applications in a large number of advanced research fields, such as: electronics, information technology, energy, optics, tribology, biology, biomimetics, etc [1], There is also a variety of techniques to texture surfaces, such as: laser [2], turning, milling [3, 4], grinding [5], forming, and electrical discharge machining (EDM) [6], which is the being that focus of the present proposal. The performance of cutting tools used in turning and milling operations is strongly dependent on the cutting edge preparation [7]. Several edge preparation technologies have been developed [8], the most common of which are brush honing and micro- blasting. Brush honing involves material removal using a tool with synthetic bristles impregnated with abrasive grits. Micro- blasting entails the erosive effect of fine abrasive particles entrained in a pressurized air stream; alternatively, a viscous or granular media may be involved. One of the most recently proposed techniques for precision, non-contact edge preparation of cutting tools is by EDM processes [9]. EDM, can be used to generate controlled edge radii on cutting tools, by sinking the sharp cutting edge into an appropriate counterface material. This concept represents an innovative perspective that expands the application envelope and capability of EDM in the area of cutting tool manufacture. In light of the variability inherent to conventional edge finishing technologies, the general high level of precision associated with EDM processes would be advantageous in terms of generating consistent and complex hone geometries. Another very important aspect of the chip formation is the influence of lubrication on the rake face, which was first reported by Mallock about 130 years ago in one of the first papers ever published on machining [10]. Theoretical analyses and intricate experiments have shown that the high normal stresses in the vicinity of the cutting edge precludes lubricant penetration therein, and that lubricant infiltration into the tool-chip interface occurs through micro-channels in the rear of the contact away from the edge. The transport of liquid lubricants into the tool-chip interface is governed by the mechanisms of capillary action that promotes it and chip velocity-induced shear flow that restrains it. As the effectiveness of a lubricant is dependent on the time available for it to be adsorbed into and/or chemically react with the chip to reduce the interfacial shear strength, retention of the lubricant in the interface is as critical as its ingress. One avenue to promoting lubrication is surface texturing, which refers to appropriately structuring the topography of a functional surface can be the EDM process. Some coated cutting edges can also have their performance improved, by using some edge preparation prior to the coating [11,12]. The motivations towards using EDM for texturing cutting tools are several. As material removal in EDM inherently entails high frequency localized melting and vaporization at the microscale, the generated surface comprises a large number of microscopic, overlapping craters. Accordingly, EDM is one of the few processes with the capability to generate surfaces with a positive skewness [13], which means that the surface consists of peaks interspersed among relatively wide valleys that are ideally predisposed to entraining lubricant. EDM also offers the flexibility to tailor the texture for a specific application by controlling the size, shape and pattern of the craters as well as the location and extension of the whole texture on the rake face. The present proposal aims at investigating the performance of cutting edges prepared and textured by EDM processes using theoretical and experimental means. Cutting edges will be textured prior to machining experiments and also prior to coating and then tested in machining. Their performance will also be assessed by FEM simulations, as well as in experiments conducted in turning and milling. In the first set of experiments sharp edges will be prepared by EDM in specific geometries defined in the FEM simulations and then submitted to experimental trials, assessing the resulting forces and tool life. For the second [experimental set a batch of edges will be textured by EDM and then submitted to experimental trials to assess the same output parameters. A third batch will be textured on the rake face using selected shapes and EDM parameters, to test their effectiveness in reducing tangential force on rake face. The present proposal expects to expand the applications for EDM processes, enhance the performance of cutting edges in several machining applications, as well as the effectiveness of certain coatings, which can find its applications also in forming processes in the future. Above all, the present proposal will create the possibility of continuing to interacted and develop joint research work between the School of Engineering at Sao Carlos and the Department of Mechanical Engineering from at McMaster University. (AU)