Papers by Author: Jiu Hua Xu

Abstract: High speed milling tests were performed on the SiCp/2009Al composites to investigate the cutting forces by using PCD tools in the speed range of 600-1200m/min. The results showed that the peak value of the cutting force Fy (in the tool radial direction) was in the range of 700-1450N under the present cutting condition. The maximum amplitude of cutting force vibration in the tool radial direction can reach 700N. Cutting forces increased with increasing feed rate or radial depth of cut and decreased with increasing cutting speed. Negative rake angle and relatively large tool nose radius were recommended as far as cutting forces was concerned. Materials with higher volume fraction or smaller reinforcement particle size had the bigger cutting forces. T6 heat treatment can increase the cutting forces significantly but the using of coolant can decrease the cutting forces evidently.

Abstract: The grinding experiments on titanium alloy Ti-6Al-4V are conducted with monolayer brazed CBN wheels which are manufactured with rare earth Lanthanum modified Ag-Cu-Ti filler. Grinding force and temperature are measured as well as the topography of wheel surface. Brazed CBN wheels fabricated with Ag-Cu-Ti filler are used for comparison. The results indicate that Lanthanum restrains spread of filler, and keeps the integrity of cutting edges, which increased the sharpness, reduced the grinding force and temperature. Meanwhile, the compounds on the surface of CBN grits are finer and compacter with the addition of Lanthanum, which improves the bonding strength of joint between filler and CBN grits. Lanthanum improves the performance of the brazed CBN wheels while grinding Ti-6Al-4V.

Abstract: An investigation was undertaken to explore the grinding energy and removal mechanisms in grinding zirconia by using brazed diamond wheels. The grinding forces were measured and the morphological features of ground workpiece surfaces were examined. The results indicate that material removal mechanisms are dominated by the combined removal modes of brittle and ductile. The prevailing removal mechanism for the ground surface of zirconia changes from brittle to ductile when the maximum chip thickness change from large to small.

Abstract: A new technology kind of brazed monolayer cup diamond grinding wheel was developed via laser in an argon atmosphere. Grinding performances of this kind of brazed wheel in the surface grinding of the granites were studied. The experiment results show that the normal grinding forces and wear of diamond grits become higher with the increasing of the accumulated removal volume during grinding granites process. When continuous dry grinding was employed, the grits of the brazed diamond grinding wheel fail mainly in attired wear mode other than pull-out ones in conventional electroplated and sintered diamond tools, which indicates that the strong retention of brazing alloy to the diamond grits and longer service life of this kind of wheel.

Abstract: The purpose of this paper is used Ansys to simulate the temperature field of laser brazing by FEM. The 3-D solid elements are used in FEM model, and nonlinear factors of temperature-dependent material properties are considered. The surface temperature grades have been attained, and the brazing experiment have been conducted, the results show that the wetting of Ni-Cr alloy to diamond is good. This study is useful for selecting reasonable processing parameters on laser brazing.

Abstract: Tool life and tool wear, cutting forces and cutting temperature, surface finish, chip formation and surface generation were investigated when milling SiC_p/2009Al composites at the cutting speed of 1200m/min using PCD tools. The results showed that PCD tool life was 150min when the 0.1mm tool wear criterion was chosen. PCD tool mainly suffered from tool grain breaking-off, chipping, abrasive wear, micro cracks and adhesive wear due to he very high-frequency impact and scrape of SiC particles. The peak value of the cutting force Fy (the radial direction) was over 1300N and the cutting vibration was very severe. The cutting temperature was 523.7°C. Pits, voids, matrix tearing and scratch were the main defects on the machined surface. The deformation layer thickness was about 20-35μm. The chip for the vol.20%SiC_p/2009Al composite took the form of flow type and the mechanisms of the chip formation were the combination of dynamic behavior of voids/micro-cracks and adiabatic shear. For the vol.35%SiC_p/2009Al composite, the chip was non-continuous and had the tendency of saw-toothed type. Material swelling and side flow, tool-workpiece relative vibration, feed rate and tool nose radius, removal mode of SiC particles were the main mechanisms of surface generation.

Abstract: Multilayer brazed CBN wheel segments based on graphite self-lubricating has been fabricated. The bending strength of wheel segments was measured and the fracture morphology of tested segments was detected. The results show that the bending strength of segments with CBN grains decrease to a small extent from 116MPa to 97MPa with the linear increase of graphite content from 5 wt.% to 15 wt.%. Due to the poor strength and certain stress concentration by the added graphite, the fracture interface transfers from the whole CBN grains to the bonding matrix with the increasing of the graphite. In addition, the pore sizes are decreased obviously.

Abstract: Despite the facts that carbon fiber reinforced plastics (CFRP) components are mostly produced near net shape, machining, especially drilling is often required in order to bring the component into dimensional requirements and prepare it for assembly. Rapid drill wear and serious machining defects are the key problems in CFRP drilling, and employing proper drill is an effective way to solve these problems. In this paper, tests of the brazed diamond core drill are presented and the related issues, such as the thrust force, the drilling quality and the drill wear are studied.

Abstract: During the brazing process, the high brazing temperature, the chemical and physical reaction between diamond and alloy, and the residual stress would result in the thermal damage of diamond. The morphology and mechanism of thermal damage is studied when the brazed diamond grits is brazed using Ni-Cr alloy in this paper. The results show that the manifestations of the thermal damage mainly include surface graphitization, erosion pits, microcrack and breaking. The graphitization only occurs on the surface of diamond grits. And the microcrack of diamond grits appears near interface.

Abstract: Polycrystalline diamond (PCD) tools were used in high speed machining of SiCp/2009Al and TiCp/TC4 composites. The results showed that milling forces decreased with the increasing cutting speed, and that the force value of vol.20%SiCp/2009Al was less than that of the matrix. The machined surface roughness Ra is less than 0.8μm for all the milling experiments until cutting time was 180 minutes. The machined surface included some defects such as scratches, craters, micro cracks and so on. Surface finish can be improved through increasing cutting speed. When milling, gradual flank wear and slight edge chipping took place on the PCD tool flank. But no obvious abrasive wear was observed. However, the PCD tool suffered from significant abrasive wear in the flank when turning. A flow type chip was formed either for milling or turning when vol.20%SiCp/2009Al was used. Some voids and micro cracks were found in the chip. For TiCp/TC4 composite, the chip took the form of interrupted saw-toothed due to the dynamic behavior of micro crack. Although PCD tool was very suitable for high speed machining of SiCp/2009Al, its geometry parameters must be rightly chosen for TiCp/TC composite, or else sever edge chipping would take place in a few minutes.