Design And Experimental Study On Artificially Ordered Super-hard Fiber Cutters

This study is aimed at developing a new engineered cutter which combines the advantages of grinding wheels and cutting tools through replacing the abrasives in a grinding wheel or the inserts in a cutting tool with superabrasive fibers. Similar to a cutting tool with inserts, the engineered cutter has superabrasive fibers that are artificially ordered so as to have the desired geometric angles and edge space among themselves. Since superabrasive fibers are normally preferred for the engineered cutter, diamond fibers have been chosen in this study. For the purpose of achieving the desired geometric angles and sharp cutting edges, diamond fibers are first artificially aligned along the desired direction and distributed in a mold and fixed with epoxy resin. The spacially ordered diamond fibers are then lapped with diamond abrasives to get sharp cutting edges and the necessary clearance angles.It is well known that a grinding wheel is composed of abrasives, bond and pores, and due to the random nature of the abrasive geometries and their distribution in a grinding wheel, grinding is characterized by good surface finish and quality, good dimensional accuracies, but a high ratio of normal to tangential grinding forces, high specific energy, high temperature rise, and a high demand in grinding machine stiffness. The good surface finish and quality in grinding is largely due to the small depth of cut in individual abrasive grits which is usually in the submicron or even nanometer range. On the other hand, due to its favorable geometric parameters, such as positive rake angle, a milling cutter usually results in a low normal to tangential force ratio, low specific energy, and high material removal efficiency as compared to grinding. However, machined workpiece surface finish and quality in milling is inferior to that in grinding.Machining with an engineered cutter is expected to provide both good surface finish and high machining efficiency at the same time. The development of the engineered cutter, which combines the advantages of both grinding and cutting, is considered a technological breakthrough in cutting tools. The engineered cutter is therefore of technological importance. In this study, the current state-of-the-art in the grinding wheel structures is discussed. Presented in this study are also the recent advances in cutting tools through analyzing and comparing grinding against cutting processes. The concept of an enineered cutter is proposed and verified.The fabrication of diamond fibers is a key step towards the successful preparation of an engineered cutter. This is due to the fact that it is difficult to obtain diamond fibers through the conventional processes of fiber preparation because of the graphization tendency of diamond in a temperature range of 700-800℃or above. In order to prepare diamond fibers, this study deals with the cutting mechanisms of Polycrystalline Diamond Compacts (PDC) with an Nd:YAG laser and Wire Electric Discharge Machining (WEDM). Based on the observations with Scanning Electron Microscopy (SEM) and the analysis with Raman spectra, it is discovered that the samples cut by the Nd:YAG laser with pulse width in nanoseconds have better surface quality, less thermal damage, moreover, and a higher efficiency. Therefore, the diamond fibers with cross-sectional dimensions of 0.3×0.6×10 mm are prepared by the Nd:YAG laser cutting of PDC.The artificially oriented diamond fibers are fabricated into blocks of 3-5mm thickness. Each block contains spacially distributed fibers in epoxy resin. It is very important for a diamond fiber cutter to have sharp cutting edges so as to improve its cutting efficiency. In this regard, sharpening of diamond fibers is carried out in the preparation of diamond fiber cutter. In this study, the diamond fibers have been ground by fixed diamond abrasives and polished by free diamond abrasives, respectively, and then investigated through SEM observations. It is found that the quality of polished PDC cutter edges is better with the free diamond abrasives than that with the fixed diamond abrasives. Therefore, polishing with the free diamond abrasives is performed throughout the study.Aluminum metals reinforced by alumina or silicon carbide particles are now widely used in automotive and aerospace industries because of their enhanced mechanical properties, low density and high thermal conductivity. Nevertheless, the addition of hard particles poses great difficulty for the machining, because the hard particles, which intermittently come into contact with the cutting edges, act as abrasives against the cutting edges, which causes rapid tool wear and poor surface finish. So far, as to the machining of aluminum alloy reinforced by hard particles, a diamond cutter is recognized as the most appropriate cutting tools due to its hardness and wear resistance. However, it is difficult to fabricate a complicated diamond tool due to the extreme properties of diamond, which prevents the application of aluminum alloy in industry. To investigate the material removal mechanisms with the diamond fiber cutter, aluminum-silicon alloy is chosen as the sample material. Depth of cut is set in the range of 1-10μm for the diamond fiber cutter, which is smaller than that used in the conventional machining and larger than in grinding. Based on the SEM obervations and inspections with a surface profilometer, it is discovered that the diamond fiber cutter results in a surface roughness of Ra0.08μm on the aluminum-silicon alloy workpiece. Moreover, in a comparison study, the diamond fiber cutter is used to compare with conventioal milling cutters. The results are promising. At the similar material removal rates, the diamond fiber cutter provided obviously better surface quality than the conventioal milling cutters. The former generated smooth workpiece surface without observable machine damage such as microcracks, while the latter showed many microcracks which are perpendicular to the direction of cutting at increased depths of cut.For common engineering ceramics, such as tungsten carbide/coabalt and alumina, an increase in hardness is often accompanied by a decrease in toughness. However, there is no decrease in toughness for a nanostructured material with high hardness. Nanostructured WC/Co coatings are finding a wide application in many industries, such as manufacturing, machine tools, cutting tools, military and areospace. Because of their enhanced hardness and toughness, nanostructured materials are difficult to machine. Grinding with a diamond wheel is widely used in machining these materials. A comparative investigation is carried out in this study on the machining mechanisms of the nanostructured WC/Co coatings by the diamond fiber cutter and by diamond wheels, respectively. The study verifies that the diamond fiber cutter with zero rake angle results in better surface finish than the 600# diamond wheel. On the other hand, the diamond fiber cutter with -30°rake angle results in large ratio of normal to tangential forces. The resulting machined workpiece showed a surface with granular surface roughness and also obvious microcracks at an increased depth of cut.