Papers by Author: Ming Chen

Abstract: Slender shaft is of high slenderness ratio and bad rigidity. The factors, for example, cutting force, cutting heat, vibration and so on, which are produced in the processing, will affect directly the size precision of workpieces. In this research, slender shaft is 304 stainless steel bar, with length of 450mm and diameter of 10mm. In order to resolve the problem of slender shaft machining with CNC slant bed lathe not configured with the follow-rest, a self-made follow-rest was developed. With both ends clamped processing mode, it is possible to use the CNC lathe turning slender shaft. Moreover, better effect of turning of slender shaft can be attained if ultrasonic vibration cutting technology is involved. After turning process is completed, size accuracy is checked to evaluate the effect of self-made follow-rest and both ends clamped processing mode. In this study, the experimental results show that quality of the slender shaft processing has been significantly improved with the use of self-made follow-rest and both ends clamped processing mode, which has definite effects on solving the practical problems of processing.

Abstract: High strength carbon fiber reinforced polymers (CFRP) with unidirectional laminate structure have gradually developed into major materials in load-bearing aerospace components, and the cutting demand of CFRP is increasing. In this work, orthogonal cutting tests were conducted on T700 high-strength CFRP laminates to get the mechanistic force model of special cutting tools. Also cutting force coefficients were obtained when cutting T700 high-strength CFRP laminates under different fiber orientations. Experimental results showed that the lowest cutting force was obtained when fiber orientation was between 120° and 150°.

Abstract: Serrated chips were a universal phenomenon and it had a significant effect on cutting process. In this paper, single tooth dry cutting of TC11 titanium alloy were conducted on a five-axis CNC machine using Stellram milling cutter with a diameter of 32 mm. Both chip macroscopic morphology and microcosmic morphology of TC11 titanium alloy were studied in-depth examining the impact of cutting speed and feed rate to the serrated chips. The results showed that: with the increase of cutting speed, the chip morphology of titanium alloy TC4 experienced a change process from the hair bar to a “C” shape and then become a long strip. The critical cutting speed of TC11 for serrated chips was found at 80 m/min and the critical feed rate to form serrated chip was defined as 0.05mm/z. With the increasing of cutting speed, the extent of chip serration was significantly enhanced. Increasing cutting speed can decrease the feed rate to form serrated chips.

Abstract: Cutting force and temperature are the two chief factors affecting bone rehabilitation during bone cutting in many orthopedic surgeries. To reveal new knowledge of thermal and force when milling cortical bone, slotting experiments were carried on high-speed milling platform. Cutting force and temperature were measured during the milling process. The effects of cutting inputs on cutting thermal and force were researched in detail. The results showed that: feed rate and spindle speed had a great impact on the milling temperature, while the milling force was mainly influenced by spindle speed. A feed rate of 1.0-1.4 mm/s is recommended to obtain preferable milling force and temperature, and a larger feed rate of 1.2-1.4 mm/s is advised to use with a lower spindle speed (8000-20000 r/min), while a smaller feed rate of 1.0-1.2 mm/s should be chosen when spindle speed was between 20000-40000 r/min. Feeding parallel to the growth direction of the cortical bone can significantly reduce the milling temperature, but there was no obvious change in milling force. The lowest cutting temperature obtained during the experiment was around 50 °C without coolant, which was acceptable for orthopedic surgeries.

Abstract: Machined surface quality is the deciding factor when evaluating the machinability of CFRP. This present work concerns the influence of fiber orientation on the machined surface quality of the machined surface in terms of surface morphology and surface roughness during milling of unidirectional T800/X850 CFRP laminates. Four group milling tests are conducted under the fiber orientation angle of 0°, 45°, 90° and 135°, respectively. For the fiber orientation angle of 0°, the machined defects are mainly fiber pull-out and fiber brittle fracture owing to interfacial debonding between the fibers and matrix resin. For the fiber orientation angle of 45°, the machined defects are mainly resin cavities and the surface morphology is rough and presents wavy fractures. For the fiber orientation angle of 90°, smooth or neat surface is observed except for the surface as the cutting tool cutting in the workpiece on which severe cracks are observed. For the fiber orientation angle of 135°, the surface is smooth with less fibers pull-out. Evaluation profile and surface roughness of the machined surfaces were measured as well. Dramatically fluctuate of the evaluation profile is observed for the fiber orientation angle of 45° with a high surface roughness Ra. Verification tests were also conducted on the multidirectional CFRP (cross-ply) laminates. It is indicated that the presence of the fiber orientation angle of 45° is the main factor leading to the decline of the machined surface quality.

Abstract: In this paper, experiment investigation is conducted on the machinability when ball milling A880 gas turbine blade profile. Cutting force spectrum acquired online is used to optimize the cutting parameters. The results indicate that cutting force signal in time domain and frequency domain can reveal the cutting stability, which provides an experimental guideline for gas turbine blades manufacturing.

Abstract: Carbon fiber reinforced polymers (CFRP) are increasingly used in aerospace and other industries, due to its high specific strength and stiffness. Machining operations are involved between forming fabrication and assembling as a fining process, during which defects like delamination, burrs and splintering are the main cause of substandard products. This is because that CFRP is a typical difficult to machine material with distinct anisotropy and heterogeneity. Thus machinability of CFRP material under different fiber orientations is a main issue. This paper intensively investigated on cutting forces and temperatures when orthogonal cutting of 0° T700/LT03A CFRP uniform laminates, with fiber orientation from 0°to 180°. Material removal mechanisms and carbon fiber fraction modes under various fiber orientations were discussed. The results showed that fiber orientation of 90°is the worst scenario of cutting, under which condition the force and temperature of the highest level, while that of 150°indicates the other. The results of cutting temperature indicated that it is mainly from the friction heat in the zone III generated by the thrust force.

Abstract: The new developed carbon fiber reinforced polymer laminates are widely used in main structural components of big commercial aircrafts. Generally drilling is the final operations in manufacturing structure, which is the most important operation during assembly. Defects such as burrs and delamination always appear in the process of drilling, which makes it hard to control the drilling quality. In this research, the drilling defects of T800 CFRP laminates are evaluated by using a brad point drill and a multifacet drill in terms of drilling forces, burr defect and delamination detection. The results show that the spindle speed is the most significant factor affecting the delamination defect followed by the feed rate. High speed drilling and low feed rate could improve the surface quality and reduce the delamination. The multifacet drill showed excellent drilling performance than the brad point drill and generated smaller defects.

Abstract: Lots of hole machining in CFRP(carbon fiber reinforced plastics) are conducted in the astronautic fields, especially a large size hole machining. The purpose of this article is to investigate the optimal cutting parameters and allowance distribution in CFRP 18/32inch hole machining by thoroughly considering the cutting forces and burr length. All tests were run without coolant using different drills, expanding drills and reamers. The damage generated and the cutting forces produced in CFRP composites cutting were observed. Therefore, the optimal allowance distribution in CFRP large size hole machining was obtained, providing compound tools design with theoretical direction.

Abstract: Drilling is frequently used in machining of carbon fiber reinforced materials. Twist drill is mostly used in drilling composite materials and some other drills with special drill bits are also needed. Drilling induced delamination is considered one of the most serious problems during machining while drilling force plays a decisive role in delamination. This paper presents the analysis of critical thrust force with special drill bit theoretically. The method of simulation to study the critical thrust force is also introduced. In addition, effect of cutting parameters on delamination by comparing experimental results and mathematical model of twist drill is studied.