Papers by Author: Xi Peng Xu

Abstract: Rotary ultrasonic machining (RUM) is considered as an effective machining method, which has been utilized to machine hard and brittle materials such as advanced ceramics. In order to improve the hole wall surface quality during RUM, it is important to wash away swarf in the gap between the tool and the workpiece as fast as possible. In this paper, a new machine process – intermittent rotary ultrasonic machining (IRUM) – is introduced for the first time. The cutting force, surface roughness and coolant flow rate in conventional rotary ultrasonic machining (CRUM) process and IRUM process are compared. It is found that compared with CRUM, the output coolant flow rate could be increased significantly by using the IRUM method. It is also found that the surface roughness of workpiece can be improved significantly in IRUM.

Abstract: In this paper, a newly developed ultra-fine abrasive polishing pad by gel technology was adopted to polish silicon wafer on a nano-polishing machine. In order to evaluate the machining performances of the polishing pad, the influences of abrasive sizes, abrasive concentration and polishing parameters (pressure, rotating speed and machining time) on the silicon wafer were investigated respectively. Optical microscope and ZYGO 3D surface analyzer were applied to examine the surface morphologies and surface roughness of the polished silicon wafer respectively. The experimental results showed that the surface roughness of silicon wafer decreased with the decreasing of abrasive grits and the increasing of abrasive concentration and polishing parameters (pressure, rotating speed and polishing time) when polishing silicon wafer with the polishing pad containing Al2O3 abrasive. When abrasive concentration, polishing pressure and polishing time reached certain values, few changes would happen for the silicon wafer.

Abstract: An experimental study was carried out to investigate the force in drilling of engineering ceramic with a brazed diamond tool. The drilling forces and protrusion heights of diamond grains were measured. The results showed that the variation of cutting forces, increasing with the cutting time, was divided into three phases for a drilled hole. For each phase, the variation of cutting forces was different. The drilling forces also increased with the numbers of drilled holes due to the wear of diamond grits. The distance values of the cutting force between the end of first phase and the end of second phase approximately kept constant.

Abstract: In the present study, zirconia ceramic was ground with a resin-bonded diamond wheel on a precision surface grinding machine. Grinding temperatures generated at the wheel-workpiece contact zone were measured using a sandwiched foil thermocouple, and the net consumed grinding powers were also measured. The energy partition to the diamond abrasives was estimated using measured grinding temperatures and powers. Based on the energy partition values obtained from the analyzed results, the diamond tip temperature was calculated and found to be over 1000°C if the circular grain contact of radius was less than a critical value for ductile field grinding of zirconia ceramic.

Abstract: The present study was undertaken to compare the consumed power in surface grinding of three different materials with a vitrified CBN wheel. High speed steel, stainless steel, and natural granite were used as the workpiece materials in the experiments. Two different depth of cut and workpiece velocity were combined to give different material removal rates. The spindle power was in-process monitored in each pass of grinding. The radius wear of the grinding wheel was also measured and the morphologies of CBN grains were observed during the grinding of high speed steel and granite. The power for the grinding of high speed steel was found to be the lowest under any operating parameters. For other two materials, the results became complex. At shallower depth of cut, the power for the grinding of stainless steel was higher in most cases. However, the power for the grinding of granite was higher under larger depth of cut. It was found that the grinding wheel failed much earlier in the grinding of granite as compared with the grinding of high speed steel.

Abstract: The present study was undertaken to compare the hardness and transverse rupture strength (TRS) of metal-based tooling composites containing diamonds of different grit sizes. Two kinds of bond matrix, copper-based and iron-based, were applied in the fabrication of the composites. In the copper-based matrix, rare earth was used as an additive. Diamonds of three different grit sizes were incorporated into two bond matrix, thereby forming six kinds of diamond composites. SEM and EDS were used to analyze the fractured surfaces of the composites. It was found that the diamonds of medium grit size in the copper-based bond matrix led to the highest hardness and TRS. For the iron-based bond matrix, however, the hardness and TRS of the composites containing the coarsest diamonds were found to be the highest. In same bond matrix, a close relationship between TRS and hardness was established.

Abstract: Plenty of studies on wear mechanism of diamond grains show that the specific failure form of single diamond grit has a close relationship with its load. Monolayer diamond grinding wheels and samples for shearing test are prepared by a high frequency induction brazing technique in this paper. The normal abrasion mechanism of diamond grains has been found through the comparison between the single grain tangential load during grinding and the shearing failure-load of the single grit of the test samples. The result shows that the dynamic strength of diamond grains is relative to the static strength after being brazed. Most of the grains are micro-broken during grinding, and only a few of them are pulled-out or broken-off.

Abstract: Grinding forces, protrusion and wear of diamond grit have been studied in grinding granite with a single-layer brazed diamond wheel. The experiment results indicate that the primary wear progression of diamond grits in the whole grinding process follows the mode of whole, micro-fractured, macro-fractured and pull-out when grinding granite with the brazed diamond wheel. The proportions of the whole, fractured, pull-out, break flat and the mean height protrusion of grains are more closely related to grinding forces. The grinding forces decreased with the increasing proportions of whole and break flat grains, and the tangential and normal force components increased with the gradual wear of the brazed diamond wheel during a long-time grinding process.

Abstract: In this study, rock minerals of natural stone were finely polished with loose abrasive and ELID technology to study the surface behaviours. After these rock specimens were polished to ultra smooth surfaces, the surface characteristics were observed with microscope and analyzed with surface texture analyzer. It was found that the calcite and fluorite minerals could be polished to high surface quality with fine loose aluminum oxide abrasive. But ultra smooth quartz surface must be finished with superabrasive ELID polishing technology. The weakly acidic coolant might bring chemical damage to calcite and fluorite minerals under the condition of ELID polishing process.

Abstract: The present study was undertaken to examine the effects of metal coatings at the surfaces of diamonds impregnated in metal bond matrices. Diamonds with or without coatings were incorporated into same bond matrix to form two metal-diamond composites in order to reveal the effects of coatings. Diamonds with same coatings were applied to three bond matrices to check the influences of matrix properties on the effects of coatings. The transverse rupture strength (TRS) of the composites was measured to ssess their mechanical behavior. Circular sawing was also conducted to reveal the contribution of coatings to diamond retention. SEM was used to analyze the fractured surfaces of the composites. For same bond matrix, the coatings at diamonds were found to increase the TRS of the composites. However, it is difficult to compare the effects of coatings in different bond systems.