Papers by Author: Yan Chen

Abstract: AFRP(Aramid Fiber Reinforced Plastics) is widely used in the aerospace and automotive while there are many problems in machining AFRP such as furry, delamination, burns and so on. Milling experiments of AFRP have been conducted to study the influence of different helix angle (0°, 30°, 60°) and cutting tools (traditional end mill, multiple flute end mill and compression end mill) on cutting force and machined surface quality. The results indicated that the cutting force has been reduced and the surface quality has been improved with the increase of helix angle. The cutting tool structure can make greater influence on machined surface quality than the cutting parameters. A cutting tool with the structure of multiple flute or herringbone cutting edge could reduce the axial cutting force. However the cutting force is too small to cut off fibers when using a multiple flute end mill. A good processing surface can be achieved while cutting with a compression end mill or a tool with big helix angle.

Abstract: An experiment of face milling of Invar36 was conducted by using coated carbide insert, the microhardness was tested and the metallographic structure was observed to figure out the principles of work-hardening. The results showed that the depth of work-hardening ranges from 80μm to 160μm among the parameters selected in the experiments. The degree and the depth of work-hardening were significantly affected by the axial depth of cut and feed per tooth. The degree and the depth of work-hardening showed a tendency to increase with the increase of the axial depth of cut and feed per tooth. Compared with the axial depth of cut and feed per tooth, cutting speed had less influence on the degree and depth of work-hardening. The degree and depth of work- hardening decreased slowly with the increase of cutting speed. Metallographic observation showed that work-hardening layer consisted of the thermal force influenced layer and the force influenced layer, while the amorphous metallographic structure was observed in the thermal force influenced layer, and lattice distortion was observed in the force influenced layer.

Abstract: End milling is conducted on carbon fiber reinforced plastics (CFRP) by using a diamond coated cemented carbide tool. Taguchi design method is employed to investigate the influence of cutting speed, feed rate and depth of cut on surface roughness. In Taguchi method, a three level orthogonal array has been used to determine the S/N ratio. Analysis of variance (ANOVA) and pareto diagram are used to determine the most significant milling parameters affecting the surface roughness. The results indicate that only the depth of cut has great statistical significance on the surface roughness, while the influences of cutting speed and feed are negligible. SEM micrographs shows that with the increase of depth of cut, a great deal epoxy resin will adhere to the finished surface. The greatest S/N ratio (1.46dB) is obtained during the validation experiment with optimum milling parameters.

Abstract: An experimental study on milling of Invar36 was conducted by using coated carbide insert to characterize the cutting force. The Taugchi's design of experiment was used for experimentation and the cutting force regression equation was established based on the principles of probability statistics and regression analysis. The results showed that the cutting force was significantly affected by the axial depth of cut and the feed per tooth, and with the increase of the axial depth of cut, the cutting force increased very quickly. Compared with the axial depth of cut, radial depth of cut and cutting speed had less influence on the cutting force. The established regression equation was highly reliable.

Abstract: Carbon fiber reinforced plastics (CFRP) use in many industries applications has seen a dramatic increase over the last decade. Milling is the most practical machining operation for removing excess material. The work presented details the effect of different cutting parameters on the surface roughness and integrity of machined multidirectional CFRP laminates. The results indicate that the surface morphology mainly relates to the fiber orientation. Increasing cutting speed leads to severe softening, degradation and burning of the matrix material that binds fibers together. The feed speed has little effect on the surface morphology. And the roughness value Ra increases with the feed rate, and decreases with the cutting speed.

Abstract: This article focuses on the drilling of carbon fiber reinforced plastics (CFRP) laminate with brazed diamond core drill under no cooling condition. The effect of grit size, wall thickness of core drill and feed speed on machining quality at the hole exit is studied. The experimental results indicate that the grit size has a significant influence on the diameter of the hole exit. The expanding factor of diameter at hole exit increases with the decrease of grit size. Both large wall thickness and high feed speed lead to serious drilling-induced defects of the hole exit. The drilling-induced defects at hole exit are transformed from broken-edge and burr to local tear.

Abstract: Cu-Sn-Ti brazing alloys are gaining importance as active brazing alloys for brazing diamond tools. The microstructure at the interface between diamond or Ti-coated diamond grits and Cu-Sn-Ti brazing alloy and bonding strength have been investigated in this paper. The results show that TiC layer forms between diamond and alloy matrix during the brazing process and Sn- and Ti-based intermetallic phase forms between TiC and the bonding matrix. And compound SnTi₃ forms between the Ti-coated diamond grits and Cu-Sn-Ti brazing alloy. Furthermore, the bonding strength between Ti-coated diamond grits and brazing alloy is higher than that between diamond grits and brazing alloy.

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.