Papers by Author: Lei Zhang

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Authors: Zhen Guo Zhang, Pei Qi Ge, Lei Zhang, Wen Bo Bi
Abstract: The hardening characteristics could be achieved by a proper selection of the grinding conditions. It is necessary to keep the heat flux above the critical limit for the film-boiling and the austenitization within the grinding zone. In this paper, a critical thermal analysis was presented to calculate the critical heat flux, following the methods for predicting thermal damages in creep grinding and high efficient grinding. The appearances of the hardening phenomena were predicted for dry grinding and wet grinding. It also can guide the selection of the grinding conditions. Theoretical analysis was verified by the experiments. Measurements are found to be in good agreement with the theoretical predictions.
Authors: Lei Zhang, Xiao Hui Xu, Chun Feng Yang
Abstract: The dissipated heat in grinding is utilized to induce martensitic phase transformation and strengthen the unhardened steel in grinding, which can be integrated into existing production lines. The orthogonal experiments were performed to analyze the main impacting factors and the rule between the parameters and hardness layer results. The surface hardness depth is varied with different surface zone. Cutting depth is the main factor of impacting the surface hardness and hardness layer depth. Hardness layer depth is higher with the cutting depth deeper and smaller with Table speed faster, but the surface hardness is higher with the Table speed faster.
Authors: Yu Zhang, Pei Qi Ge, Lei Zhang
Abstract: The invariable heat flux is always loaded in temperature simulation for grind-hardening. The heat flux is time-variant in actual process. The paper uses experiment result of grinding force to calculate out the time variation heat flux. The grinding temperature is simulated based on time variation heat flux by ANSYS software. The variation tendencies for the grinding force and the simulated surface top temperature will be discussed.
Authors: Ru Bo Zhang, Pei Qi Ge, Lei Zhang, Bin Li, Chao Zhao
Abstract: Grind-hardening is a new integrated machining technology which utilizes grinding heat to quench the non-quenched steel directly. In this paper, the technology is applied in the process of rack form grinding. A comprehensive numerical model is developed to simulate the temperature distributions of the rack under the dry grind-hardening conditions with finite element method(FEM). The temperature dependency of the thermal properties, the triangular heat distribution of the heat flux, latent heat and the air convection are taken into account. The simulated hardness penetration depth(HPD) is deduced from the local temperature distribution, time history of workpiece according to martensitic phase transformation theory. This provides a reliable method for the proper selection of process parameters in order to produce enough heat at the contact zone, enabling the treatment of the rack.
Authors: Lei Zhang, Yu Fei Gao, Wen Bo Bi
Abstract: The grinding heat is utilized to induce martensitic phase transformation and strengthen the surface layer of AISI 5140 alloy steel by raising surface temperature higher than austenitic temperature and cooling quickly. The grinding temperature field is simulated by using finite element method (FEM). Then, the hardness penetration depth (HPD) is predicted from the temperature history and martensitic phase transformation conditions in surface grinding. The experiments of different grinding parameters are performed in surface grinding lathe. The hardness and hardness penetration depth of work piece surface layer are measured to validate the simulation and prediction. This method can be used to predict the HPD and optimize the grinding parameters forwardly.
Authors: Lei Zhang
Abstract: Nanofluids are a new class of heat transfer fluids and offer an important advantage on conventional heat transfer fluids. The nanometer-sized metallic and non-metallic solid particles or tubes are dispersed in base heat transfer fluids such as water, engineering oil and emulsion. It is a interdisciplinary field between nanoscience, nanotechnology, and thermal engineering. The nanofluids study work attracts a lot of interest from the worldwide researchers because of their fascinating thermal characteristics and potential applications in microelectronics, transportation and biomedical fields. Many important theoretical and experimental study works on convective heat transfer appeared in literature. The purpose of this article is to study theoretical and experimental findings on the enhancement of the convection heat transfer with nanofluids and analyze the key factors of thermal conductivity and convective heat transfer enhancement with nanofluids.
Authors: Zhen Guo Zhang, Pei Qi Ge, Lei Zhang, Mao Cheng Tian
Abstract: Based on the method of the statistical probability, the theory forecasting model of grinding force is modified analytically. The calculated force is used as an input factor to calculate the heat flux. Then the transient grinding temperature field is simulated using the finite element analysis (FEA). An infrared imaging system for a full area temperature measurement is used to validate the numerical model. Additionally, the experimental results are synthesized with the simulation results to analyze the temperature field and the hardness penetration depth (HPD). The distribution of the temperature field and the stability of the grind-hardening process are discussed, which could provide a reliable forecasting method for optimizing the grind process and controlling the hardening effects forwardly.
Authors: Jian Hua Zhang, Pei Qi Ge, Lei Zhang, Yang Yu, Hui Li
Abstract: The grind-hardening technology utilizes the grinding heat to harden the surface of the workpiece. The friction and wear performance of the grind-hardened layer is one of the important parameters. In this paper, the friction and wear performance of the grind-hardened layer was studied by the friction and wear experiment. The wear rate and the friction coefficient of the grind-hardened steel were studied by comparing with conventional hardened steel and non-hardened steel. The surface worn morphology and the collected wear debris of the grind-hardened steel were observed during the experiment. The wear mechanism of the grind-hardened steel was analyzed under different friction conditions.
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