Papers by Author: Chang He Li

Abstract: Theoretical analysis and material experiment are employed to study the “single factor” material model. Based on the dislocation theory, an analysis shows that material model is deeply affected by temperature. By the least squares best fit to experimental data, material parameters are found. Experiment curves analysis and material parameters comparison show that the material parameters of “single factor” model of Mo-Cr cast iron are temperature dependent. Using the mathematical mapping between material parameters and temperature, the “single factor” material model of Mo-Cr cast iron is established, which is proven to be right by comparing with experimental measurements. This work provides a useful insight for understanding the material model and helps to develop further finite element simulation of high speed cutting process of Mo-Cr cast iron.

Abstract: A three-dimensional finite element model of helix double-edge cutting is developed to study the ending milling process of titanium alloy Ti6Al4V. Several mechanics models of milling process, such as material constitutive model, friction model and heat transfer model, are implemented to improve finite element simulating accuracy. A milling force experiment is carried out, and a good agreement between simulation and experimental value is achieved, which proved that the finite element model presented in this paper is correct. Using this finite element model, chip formation and cutting temperature are simulated and analyzed. This work will be a base for process parameter optimization, tool’s optimization selection and design during high speed milling of difficult-to-cut titanium alloy.

Abstract: A physics-based material processing simulation is approached to research the machining distortion for high speed milling of titanium alloy aircraft monolithic component by the finite element method (FEM). Several mechanics models, such as material constitutive model, material removal model, and cutting loads application model, have been implemented to improve the accuracy of finite element simulation. The distortion result of aircraft monolithic component resulting from FEM show a good agreement with the experiment result. The research result shows that the distortion law of titanium alloy aircraft monolithic component is bending distortion and protruding upward, and the maximum distortion dimension lies in the middle of monolithic component.

Abstract: The theoretical hydrodynamic pressure modeling were presented for flow of coolant fluid through the grinding zone in flood delivery grinding using roughness surface grinding wheel. The simulation results show that the hydrodynamic pressure was proportion to grinding wheel velocity, and inverse proportion to the minimum gap between wheel and work surface and the maximum pressure value was generated just in the minimum gap region in which higher fluid pressure gradient occuring. It can also be concluded the surface roughness of grinding wheel and workpiece makes the contact zone’s hydrodynamic pressure rough and unstable, i.e. the value curve considering roughness is not smooth, leading to the micro-elastohydrodynamic lubrication phenomenon.

Abstract: The development and manufacturing speed of products have become the focus of competition, at the same time the manufacturing not only has to meet user’s constantly changing needs, but also has to have a relatively strong flexibility of manufacturing technologies. Additive processes can be defined as rapid prototyping, which generate parts (prototyping) in a layered way, is gaining progress by rapid tools (RT) and rapid manufacturing (RM) for production of functional parts in small quantity and even one product without adding the cost becomes more and more critical. The paper describes which mechanism of stereo lithography (SLA) rapid prototyping can be applied to rapid tooling for production complex geometries for long-term consistency. Moreover, the paper demonstrates the application examples of rapid tooling fulfilling the required physical, mechanical and geometrical properties in precision deformation and casting process. The most notable advantage is the integration of production design and digital manufacturing within the product development period.

Abstract: Additive processes can be defined as layered manufacturing, based on the dispersed/accumulated principle, Layered manufacturing is directly transforming 3D CAD models to real objects, the reverse engineering of mechanism can be applied to layered manufacturing for production complex geometries for long-term consistency, and the analysis demonstrates the application of the reverse engineering fulfills the segments of design, production, inspection, test. The most notable advantage is the combination of digital technology and geometric model rebuilding technology.

Abstract: Based on hydrodynamic lubrication theory, a mathematical model of grinding fluid field in flood is sets up in this paper. Hydrodynamic pressure and velocity of grinding fluid are calculated by multigrid method. Additionally, crude model about the coarseness of grinding wheel and workpiece is built on the basis of slick model and solutions are obtained by multigrid method. Solutions of slick model and crude model are compared. Result shows that the solution of slick model is in good agreement with the crude model and verifies the experimental analysis.

Abstract: In the grinding process, conventional method of flood delivering coolant fluid by a nozzle in order to achieve high performance finishing. However, hydrodynamic fluid pressure can be generated ahead of the contact zone due to the wedge effect between wheel peripheral surface and work surface. In the paper, a theoretical hydrodynamic pressure modeling is presented for flow of coolant fluid through the grinding zone in flood delivery grinding. Moreover, coolant induced force can be calculated by integrate the hydrodynamic pressure distribution over the whole contact length. The theoretical results show that the hydrodynamic pressure was proportion to grinding wheel velocity, and inverse proportion to the minimum gap between wheel and work surface and the maximum pressure value was generated just in the minimum gap region in which higher fluid pressure gradient occuring. It can also be concluded the pressure distribution was uniform in the direction of width of wheel except at the edge of wheel because of the side-leakage. Furthermore, the hydrodynamic pressure and coolant induced force at wedge-like zone were also investigated experimentally. The experimental results show the theoretical model is agreement with experimental results and the model can well forecast hydrodynamic pressure distribution at contact zone between grinding wheel and workpiece.

Abstract: In the grinding process, conventional method of flood delivering coolant fluid by a nozzle in order to achieve chip flushing, cooling, lubrication and chemical protection of work surface. However the conventional flood supply system demands more resources for operation, maintenance, and disposal, and results in higher environmental and health problems. Therefore, there are critical needs to reduce the use of cutting fluid in grinding process, and MQCL grinding is a promising solution. MQCL grinding refers to the use of cutting fluids of only a minute amount typically of a flow rate of 10 to 100 ml/hour which is about hundreds orders of magnitude less than the amount commonly used in flood cooling condition. The evaluation of the performance of the MQCL technique in grinding consisted of analyzing the behavior of the tangential cutting force, G-ratio, Surface morphology and roughness. The results presented here are expected to lead to technological and ecological gains in the grinding process using MQCL.

Abstract: In the grinding process, grinding fluid is delivered for the purposes of chip flushing, cooling, lubrication and chemical protection of work surface. Lubrication and cooling are the most important roles provided by a grinding fluid. Hence, the conventional method of flood delivering coolant fluid by a nozzle in order to achieve high process performance purposivelly. However, hydrodynamic fluid pressure can be generated ahead of the grinding zone due to the wedge effect between wheel peripheral surface and part surface. In the paper, a theoretical hydrodynamic pressure modeling is presented for flow of coolant fluid through the grinding zone in flood delivery mode in the surface grinding using resin-bonded diamond grinding wheel, which based on Navier-Stokes equation and continuous formulae. The numerical simulation results showed that the hydrodynamic pressure was proportion to grinding wheel velocity, and inverse proportion to the minimum gap between wheel and workpiece and the maximum pressure was generated just in the minimum clearance region in which higher fluid pressure gradient occur. It can also be concluded the pressure distribution was uniform in the direction of width of wheel except at the edge of wheel because of the side-leakage.