Papers by Author: Hang Gao

Abstract: Abrasive flow machining is a suitable technique for surface polishing due to its rheological characteristics, however, it's difficult to achieve uniform roughness for polished surfaces as the material removal mechanism is still ambiguous. In this paper the viscoelastic properties of abrasive flow media are incorporated to explore the phenomena of inconsistent material removal in the AFM polishing process, where the material removal near the edges is obviously higher than that in the middle along the flow direction. The rheological parameters of the viscoelastic constitutive model adopted are varied to study the polishing effectiveness under different process conditions. The results of numerical analysis reveal that there exist distinct differences of viscoelastic stress fields between the edges and the middle regions, which leads to the material removal near the edges is higher than that in the middle. It could be concluded that the viscoelastic properties of abrasive media play the dominant role for the inconsistent material removal in abrasive flow machining process.

Abstract: The cutting heat, during the process of drilling fiber reinforced resin matrix composites, has a significant effect on the quality and the tool wear. In this paper, based on the homogenization hypothesis of the material and the finite difference method, a temperature field model for drilling unidirectional Kevlar composites was developed. During the drilling process, the heat source formed by cutting edge and chisel edge can be seen as a conical heat source. The results show that the temperature field distribution is ellipse away from the drilling zone with the longer axis paralleling to the fiber direction and changes close to the drilling zone.

Abstract: Aiming at the difficulty of 65% volume fraction SiCp/Al composites micro-hole machining and the problem of exit defects, the ultrasonic vibration-assisted grinding (UVAG) method for micro-hole machining was experimental studied taking Φ2-3mm hole for example. Results indicated that the thrust force was reduced by 79.8% through UVAG with lower fluctuation and the tool wear was much less than conventional drilling (CD). Lower thrust force and better exit quality were obtained with the increasing of the ultrasonic amplitude.

Abstract: Aiming at the quality problems of ‘over polishing’ and ‘insufficient polishing’ in the process of traditional extrusion abrasive flow machining,An abrasive flow polishing method at the constantly small pressure difference is developed, the hydraulic proportional control system is designed, and the mathematical modeling of the hydraulic proportional control system for small pressure difference constant extrusion polishing abrasive flow machining is set up. The simulation results show that the polishing pressure can be well controlled and the stability of polishing velocity is improved, which will improve the extrusion abrasive flow polishing quality.

Abstract: Quartz fiber reinforced ceramic matrix composites have poor thermal conductivity yet high fiber hardness that make them difficult for machining. Especially for drilling of blind hole, the cutting heat can not be conducted away from the semi-enclosed hole quickly, which may result in serious tool abrasion and poor machined quality. Experimental research on helical milling process was carried out, specifically on the machining of Φ8mm blind hole. Exploiting grinding mechanism, self-developed electroplated diamond trepanning tool was used. The experimental results show that the helical milling method exhibit advantages e.g. reducing cutting force, improving cutting heat dissipation and achieving good hole quality.

Abstract: Scratch tests on (001) face, doubler face and tripler face of KDP crystals are carried out at room temperature. It shows that the friction ceoffcients of different crystal faces are affected seriously by the crystal oritations, their variation periods of (001) face, doubler face and tripler face are 90^o, 180^o and 180^o, their attitudes of relative anisotropy are 50%, 43.8% and 43.8%, and all of them are less than 0.4. The scratch mechanism of KDP crystal consists of four types: elastic and plastic deformation, ploughing, microchip, and surface damage. Differences between elastic and plastic deformation and ploughing are not obvious due to the soft-brittle nature of KDP crystal.

Abstract: ts difficult to guarantee the surface quality when processing the carbon/silicon carbide (C/SiC) composites, and also easy to produce burr defect. So firstly the law of the burrs generated on different direction of fiber was analyzed theoretically. And then we milled the C/SiC composites by electroplating diamond cutting tool with different cutting parameters and fiber directions. The cutting force and the burr area size of the milling surface were also tested. After analyzing the results, the milling burr evaluation method was proposed. Then the burr area size of different fiber directions was analyzed, and the effect on the surface quality of fiber direction during milling process was studied. The result shows that the angle between surface laid carbon fiber direction and cutting direction has a significant influence on the processing quality. Milling surface quality was declined in order as 0°, 45°, 90° and 135°. So in order to improve the quality of the milling surface, the angle between surface laid fabric fiber direction and cutting direction should be less than 45°.

Abstract: KDP crystal (Potassium dihydrogen phosphate single crystal) is extremely difficult to obtain flawless surface because of its soft, brittle, and hygroscopic. And a large amount of time has been spend on obtaining flawless surface with ultra-precision machining methods. In order to quickly reduce surface roughness on KDP crystal, a new micro-deliquescence polishing method with fine water mist was proposed, the polishing tool with fine water mist was designed, and the polishing experiment was carried out. The micro-deliquescence polishing with fine water mist can improve the surface quality of KDP crystal quickly, so it is an effective preprocessing before ultra-precision machining.

Abstract: Abrasive medium plays an important role in the application of abrasive flow machining (AFM), a process that finishes complex internal and external geometries. A new abrasive medium needs to be fabricated due to a lack of literature on it. In this work, a new abrasive medium was fabricated by using styrene butadiene rubber (SBR) as carrier and DF-101S was used to study its characterization. Results showed that new abrasive medium with good fluidity and temperature stability was obtained. Processing experiments have also been carried out by using new abrasive medium and MLLD60, and ZYGO was used to study the surface characteristics of the work-piece. Experimental results indicate that the new abrasive medium is applicable to AFM process.

Abstract: Aiming at the problem of poor machinability in conventional drilling of aramid/epoxy composites, the formation reason for fuzzing damage was analyzed. In order to obtain better machining quality, a combined machining technology based on sawing and grinding mechanism was proposed and the corresponding drilling tools were developed. Drilling experiments were conducted to explain the machining performance of the drilling tools. The results show that the sawing drilling tool with negative rake angle can effectively restrain fuzzing damage and the sawing-grinding drilling tool decreases the thrust force about 20%~55% with electroplated diamond abrasives. The combined machining technology of sawing and grinding achieves damage-free machining quality in drilling of aramid/epoxy composites.