Papers by Author: Wei Jun Liu

Abstract: In order to development the laser shock processing equipment, the technical features and process demand are analysis. The design requirements about laser shock processing equipment are discussed in detail by the methods of use case analysis and sequence diagram. Functional framework and technology architecture are put forward for the development of laser shock processing equipment. Finally, the equipment structure concept is given which is described for the future equipment design.

Abstract: In order to study the residual stress distribution in the titanium alloy laser rapid forming parts, the incremental-step hole drilling method is improved. Choose a calibration sample which has the same material as the test sample to conduct internal residual stress measurement by incremental-step hole drilling method. Conduct stress-release heat treatment (insulation 4 hours in 750 centigrade, furnace cooling) to the calibration sample before the measurement to uniform the internal stress. Calculate calibration compensation coefficient according to the calibration sample stress measurement result, and use the compensation coefficient to compensate the stress measurement result of the laser rapid forming sample. This method improves the reliability of internal residual stress measurement by incremental-step hole drilling method. Then use this method to measure the stress of laser rapid forming sample. The result shows that both the residual stress in the X direction and the Y direction is larger when the depth ranges from 1 mm to 3 mm. When the depth is greater than 3 mm, the residual stress decreases gradually with the hole depth increasing. The maximum value in the X direction is 147.13 MPa, and the maximum value in the Y direction is 236.32 MPa.

Abstract: Laser Metal Deposition Shaping (LMDS) is a state-of-the-art technology that combines rapid prototyping and laser processing. There are many factors affecting the quality, precision, microstructure and performance of LMDS-deposited parts. Among them, dilution ratio is a significant one since it is not only an important index to judge the laser cladding quality, but directly affects the interlayer bonding strength and performance quality of as-formed metal parts. Thus, the substantial LMDS experiments were performed to conclude the influence of processing parameters on dilution ratio of laser cladding layer. The results indicate that the influence degree of scanning speed is most significant, while that of laser power is relatively slight. In order to ensure the perfect forming quality and strong metallurgical bonding, it is necessary to choose suitable dilution ratio to accomplish the LMDS process.

Abstract: Triangular mesh is one of the widely used digital representation modes in CAD and CAM. And the offset operation of planar polygon takes an important role in path planning of layer milling complicated surfaces represented by triangular mesh. A vertex classification based adjusting method is presented. It improves the performance of edge isometry based offset algorithm.

Abstract: In order to apply mathematical mechanization method during trajectory planning for NC machining, a platform framework is put forward which integrates the mathematics mechanization and trajectory planning. The essence and application of mathematical mechanization is analysis. The basic process and the correlation function of trajectory planning are discussed based on mathematical mechanization. The technology system of mathematical mechanization platform is established for the trajectory planning. And the operation flow of the mathematical mechanization platform is defined.

Abstract: Abstract The titanium alloy direct laser fabrication process, the collapse of a side issue has interference and preventing the forming quality and forming precision. This thesis mainly contain with of temperature field analysis and actual observation, by changing the scanning mode to solve this issue. The new scanning mode, dam-type, has a good property and proves that the direct laser fabrication parameters can be complete without change through the whole forming process, and puts the process of control simply.

Abstract: In this paper, a novel method is proposed for automatically matching the measured data of a rail tanker. The spindle orientation of point cloud is determined by PCA, and then any relative point pair is well matched according to the spatial topology relations as the complexity reduction point of view, finally the data is mapped to a uniform coordinate system with the Quaternion method. The experimental results demonstrated that the proposed method achieves simplicity of implementation with robustness, and especially suitable for positioning the work piece of the rail tanker and the multi-view data fusion.

Abstract: Laser Metal Deposition Shaping (LMDS) is a state-of-the-art technology that combines rapid prototyping and laser processing. There are many factors affecting the quality, precision, microstructure and performance of LMDS-deposited parts. Among them, substrate preheating is a significant one since it can change the heat history of the LMDS process. Preheating is often used to reduce the residual stresses and the risk of thermal distortion and cracking. In this work a set of substrate preheating device for LMDS system employed with dual-channel control, namely intelligent PID temperature control and realtime serial-port temperature acquisition and feedback control, is designed and developed. In addition, the heating up rule gained through the relative experiment is introduced to reduce the overshoot amplitude of substrate preheating device by cascade control method. The results show that not only can this substrate preheating device realize the dual-channel control and continuous adjustment of substrate preheating temperature, but also can realtime collect and record the substrate temperature.

Abstract: Direct laser deposition shaping is a state-of-the-art rapid prototyping technology. It can directly fabricate metal parts layer-by-layer without any die, mold, fixture and intermediate, just driven by the laminated CAD model. Accordingly, how to improve the quality of as-formed parts becomes an urgent issue in this research field. It is well known that as for the hot working, the heat history can generate enormous influence on the microstructure and mechanical properties of the parts. Due to the large quantity of heat introduced by laser fabrication process, it is necessary to build a temperature measuring platform to realtime monitor and control the temperature field in the laser fabrication process. As a result, such platform was created to communicate with computer by the temperature data collecting module and interface standard converting module, and achieved the temperature acquisition in the serial communication process through the Microsoft programming software. The experimental result proves the validity of the platform, which can provide effective boundary condition and experimental verification for the numerical simulation. In addition, the desirable temperature distribution can be obtained through the realtime process monitoring and effective parameter adjusting.

Abstract: A new cutting force model for peripheral milling is presented based-on a developed algorithm for instantaneous undeformed chip surface with NURBS. To decrease the number of the differential element, the contact cutting edges of end-milling cutter with the part and the chip thickness curve are represented by NURBS helix, and the instantaneous undeformed chip is constructed as a ruled surface with the two curves. The cutting force generated by the edge contact length and the uncut chip area. Using the cutting coefficients from Budak[1] , the cutting-force model verified by simulation. The simulation results indicate that new cutting-force model predict the cutting forces in peripheral milling accurately.