Papers by Author: Hong Jie Pei

Abstract: The grind-hardening test of 42CrMo steel was carried out on a forming grinding machine. The macrostructure, microstructures, micro-hardness and the depth of the hardened layer were measured and analyzed by optical micro-scope, scanning electron microscope and digital micro-hardness tester. The influences of original microstructure on the grind-hardened layer of 42CrMo steel were studied. The results show that the acicular martensite and a small amount of undissolved carbide appear in the surface layer, and slightly coarse martensite and a small amount of undissolved carbide appear in the middle layer of the completely hardened zone. Microstructure of the transitional zone varies with original structure. The microstructures and micro-hardness of the completely hardened zone have no obvious change under different original organizations, and the micro-hardness is 620HV0.5-700HV0.5. However, the distance from the slightly coarse martensite and the depth of the hardened layer increase with the uniformity improvement of the original microstructure.

Abstract: The Cemented carbide cutting tool is widely used in more machining factory, the 5 types of cemented carbide materials: YT30+Ta, YTS25, YH1, 726 and 758 and Selected to make brazing and cutting test. The experiment results shown that: (a) the hardness of cemented carbide cutting tool after being brazed does not change, redoes HRA0.1~0.2; (b) YT30+Ta, YTS25 types of cemented carbide could be brazed using 105# solder, brazing quality could be very well; (c) Wear characteristic of machine-clamping and brazed cemented carbide cutting tool is normal and hardly change in T<150 minutes. The study makes theory and experiment foundation to widely use cemented carbide cutting tools.

Abstract: In this paper, the forming processes, main effect factors and change law of the cutting direction burr in orthogonal cutting have been studied and related theories are analyzed based on the cutting experiments. The result shows that the forming processes of cutting direction burr consist of normal cutting, flexure deformation of end surface of workpiece, plastic effect, continuous cutting and shear-break separating in orthogonal cutting. And a new phenomenon was found that cutting direction burr is formed with the shear-break separation of the chip and workpiece machined surfaces. In addition, the size of cutting-direction burr varies with workpiece materials, cutting parameters and geometric parameters of cutting tool. The study may be important science and practical value in order to control and reduce cutting burr in precision machining.

Abstract: In Minimum Quantity Lubrication machining, cutting fluid is provided as mist. Mist with different velocity and diameter may lead to different cooling, lubrication effect and cutting quality. Thus, cutting quality is highly influenced by spray characteristics in MQL machining. In this study, the mathematics model of mist flow was set up first. Then spray characteristics were tested by a 3-Dimensional Particle Dynamic Analyzer. In order to study the influence of spray characteristics on cutting quality, precision turning of 45 steel was performed by a CNC Super Precision Machine Tool. The results indicate that the lowest surface roughness was obtained by supplying more cutting fluid at proper position for spraying distance of 20mm.

Abstract: Based on the investigation of two traditional vibratory modes, this paper puts forward a novel vibratory mode in high speed tapping. Vibratory tapping on stainless steel with all kinds of vibratory modes is carefully studied. Experimental results show that the new vibratory mode not only preserves the machining effect of the separable vibratory tapping, but also increases the life of tap. Therefore this study provides a new solution to increase the performance of high speed vibrat- ion tapping.

Abstract: In most machining operations undersirable burr or negative burr is created at workpiece edges. The burr/negative burr formation mechanism is analyzed based on shear strain which is obtained from simulation results of the finite element model of burr/negative burr forming process. To varify the simulation results, experiments are conducted. We observered that there exists a critical value of shear strain for burr/negative burr transformation. Burr or negative burr, which to be formed at workpiece edges can be controlled by adjusting the cutting conditions or tool geometric parameters. Edge quality of workpiece can be controlled by converting burr or negative burr forming.

Abstract: Grind-hardening machining is not only a complex process coupling mechanical, dynamical and thermal effects, but a process containing distinct changes of microstructure and properties of the workpiece grinded surface layer. Under the defined experimental conditions, an empirical formula was constituted to describe the relation between hardened layer depth and grinding parameter of grind-hardening layer, and the multi-parametric optimization was conducted. A commercial FEM software package was used to simulate the grind-hardening process. The distribution and variation characteristics of the temperature and microstructure in the grinded surface layer of workpiece were obtained and the forming mechanism of the grind-hardened layer is revealed.

Abstract: A forming model of the feed-direction burr for drilling process is made in this paper. The feed-direction burr formation is studied by experiment. The related theories are analyzed. The influence factors of the feed-direction burrs are pointed out. Furthermore, a certain number of measures to prevent and decrease the burr in drilling process are advanced.

Abstract: Based on grind-hardening experiments, the two side-direction burrs were studied. Three main stages (burr generation, augmentation and formation) in the burr yielding process were clarified and the varying laws of burr morphologies and dimensions were systematically revealed. In turn raises, some new technologies, processes and methods of actively controlling burrs were put forward.

Abstract: The cutting-direction burr is one of the important factors that influence the edge quality and performance of precision parts. The cutting-direction burr formation process is simulated with DeformTH3D. The mechanism of cutting-direction burr formation is analyzed in terms of the results of the simulation. The negative shear zone and initiation negative shear angle are discussed too. Study results show that the deformation of
CDE is an important factor affect the cutting direction burrs’ size and shape.