Papers by Author: Shi Jin Chen

Abstract: In order to respond to market rapidly, save design time, reduce the cost and particularly design the machine in a predictable and reliable manner, an approach based on the integration of virtual machine tool and workpiece material removal mechanism is proposed in this article for the investigation of centerless grinding process, the prediction of workpiece roundness generation and the evaluation of dynamic characteristics of grinding system. In this approach the machine structure model is firstly presented by incorporating the kinematic relationship of the feed drive system and the material dynamic parameters of the grinding system. Then the virtual machine tool model is built by the combination of the machine mechanical structure and the control loop. Finally the virtual centerless grinding is realized by integrating the virtual machine and the workpiece material removal mechanism through their coupled surface regeneration mechanism. The comparison of the experimental and theoretical results demonstrates that this virtual centerless grinding approach can investigate the workpiece roundness generation accurately.

Abstract: Due to the unfixed state of the workpiece and the dissimilarity between sections in through-feed centerless grinding, the positions and orientations of the workpiece keep changing in the grinding process, which are coupled with the workpiece roundness generation. In this paper the positions and orientations of the workpiece are described by the dynamic equations obtained from Lagrange equation. And the homogeneous coordinate transformation is applied to present the profiles of the workpiece, grinding wheel and control wheel in the reference frame. Finally the time varying profile of the workpiece is obtained for the investigation of the material removal process in 3D space. The material properties of the workpiece, the wheels and the workrest combined with the geometric relationship of their profiles are utilized to calculate the interaction between them, including the three forces along the axes and the three moments about the axes.

Abstract: In this paper, finite element thermal analysis and experimental study were performed to verify the design concept and thermal management of a smart cutting tool with internal cooling. The main idea is to build micro cooling channel within the tool and located close to the cutting tip, forming a closed-loop of the internal cooling circuitry. The cooling lubricant contamination will be avoided and the cutting temperature be reduced when cooling fluid flows through the closed channel. The cutting temperature at the tool tip can be estimated by measuring the cooling fluids temperature at the inlet and outlet of the cooling structure. Thermal modeling based on FEA-CFD is carried out by using ANSYS and FLUENT. The simulation results demonstrate that the innovative tooling design concept can effectively reduce tool temperature away from the extremely high temperature and sensing the cutting temperature at tool tip. Preliminary experiments have further proved the concept of the tool system.

Abstract: Dry or clean cutting without the hazards of cooling liquid, and the ability to monitor thermal impact on cutting tools in real time have been very appealing to the manufacturing industries. This paper presents the FEM-based design and analysis of a smart cutting tool which possess dual functions of cooling the cutting tool with the internal cooling structure and estimating temperature at the tool tip by measurement of the cooling liquid’s temperature at the inlet and outlet of the cooling structure. To evaluate the performance and feasibility of the smart cutting tool, thermal modelling is carried out by commercial software - ANSYS and FLUENT. The numerical simulation results demonstrate that the novel tooling design concept can effectively reduce tool temperature away from the tool wear critical temperature zone and sensing the cutting temperature at the cutting tip.

Abstract: Numerical optimization method is increasingly applied into the design of machine tools so as to improve their performance. This paper employs Monte Carlo optimization method to predict and reduce the errors of ultra-precision machine tools in term of motion errors between cutting tool and workpiece closely associated with machine processing of ultra-precision machine tools. Using a quite different origin position of location coordinate system from traditional in that every ideal frame on current body is coincided with the reference actual one on the adjacent body, the motion errors are expressed in homogeneous matrix defined with adjacent bodies’ residuals in multi-body system analysis. This expression clearly shows that the final position errors are decided by the motion accuracy of the guideline, and gesture errors are affected by accuracy of the spindle assembly. With geometric errors extracted from the matrix, a new optimization method of error allocation is presented to maximize the machine precision by reasonable distribution of tolerances key parts. Using variables intimately related to motion errors and under constrained by cost, optimization model is established, then it is solved with Monte Carlo simulation method to compute top ten key factors contributed to errors and obtain distribution probabilities of both position error and gesture error. Case study formulated is reported to illustrate the method proposed and to evaluate its effectiveness.

Abstract: In this paper, a 2-D vibrating platform is designed using dual flexure hinge structure and four significant structural parameters are optimized with the integrated model of Abaqus and Isight so as to improve the platform performance. The natural frequency is increased from 496.3 Hz to 2360 Hz after optimization while the distance of travel and the stress satisfy the constrains. The optimization results are confirmed with the test data. The optimized 2-D vibrating platform is applied into the micro milling and the machined surface quality is improved. Therefore, the optimized 2-D vibrating platform is a valid equipment to carry out 2-D vibration-assisted micro milling and study the cutting mechanism.

Abstract: Two dimensional vibration-assisted machining is applied into micro-milling to improve cutting accuracy and prolong tool life. In this paper, the tool tip path of two dimensional vibration-assisted micro-milling (2-D VAMM) with different vibrating parameters is simulated and analyzed. And the computation module of chip thickness in 2-D VAMM is proposed, based on which the chip thickness characteristics is investigated using two evaluating indicators: free time ratio (FTR) and amplitude ratio (AR). The effects of vibrating parameters on FTR and AR are studied with the help of Full Factorial Design and analysis of variance. It is found that FTR can be increased by increasing the ratio of amplitude in normal direction to the feed and the ratio of frequency in normal direction to spindle speed, while AR will be enlarged with increase of the ratio of amplitude in feed direction to the feed and the ratio of frequency in feed direction to spindle speed. The simulation studies are the foundation for calculating cutting force, tool wear and surface roughness in 2-D VAMM and can also guide the further experiment.

Abstract: Micro-structured optical components (MOCs) show great promise for offering an exciting new degree of freedom and flexibility to optical designers and producers. At present, these micro/miniature components are usually manufactured by large ultra-precision machine tools in tightly controlled environment and the cost of machining is thus very high. In this study, a novel machine with compact structure and flexibility was built, specially used for machining of the MOCs. The key points of the design are given. Fresnel lens, as an example of MOCs, was machined by this machine tool, and the result shows that the form accuracy of the machine tool is in the order of sub-micrometer.

Abstract: A novel fast tool servo driven by piezoelectric actuator for precision diamond turning is designed in this paper. To overcome the inherent hysteresis and drift nonlinearity effect of the piezoelectric actuator, a closed-loop control system is established using strain gauge integrated in the actuator for position feedback, which has compact structure and can avoid interference in the machining. Furthermore, a fuzzy PI control algorithm is presented. It has not only the advantages of agility and adaptability of fuzzy control, but the characteristics of high accuracy of PI arithmetic. At last, experiments are carried out and the results show that the fuzzy PI control provides significantly better tracking accuracy and robustness against hysteresis and drift effects.

Abstract: In this paper, a finite element model of a two-dimensional orthogonal metal cutting process is used to simulate the chip formation, cutting forces, stress, strain and temperature distributions. Two deformable parts are involved in this model: the workpiece and the cutting tool. To make the results of the simulation agree the orthogonal cutting test better, the separation surface between the chip and the machined surface is not predefined in this simulation. The chip-separation criterion is based on the Johnson and Cook law. This work will help as a reference to tackle more complex cutting processes such as oblique and discontinuous cutting.