Papers by Author: Ming Zhe Li

Abstract: The springback of spherical parts in both integral-gripper and discrete-gripper stretch forming processes were investigated by using explicit-implicit algorithm. The effect on springback value and shape errors of pre-stretching, thickness and materials were studied. The simulation results show that springback and shape errors in the integral-gripper stretch forming are bigger than that in the discrete-gripper stretch forming; the springback gradually decrease and shape errors reduce as pre-strecthing increases, a prior pre-stretching is 1%; the springback and shape errors are gradually reduced as sheet metal gets thicker; the greater the elastic modulus and yield strength of the material, the smaller the springback and shape errors of the formed parts.

Abstract: In this paper, a three-dimensional finite element model of power spinning 5A06 aluminum alloy cylinder with longitudinal and hoop ribs is established. It reveals the laws of the stress and strain distribution of the longitudinal and hoop ribs in the spinning process, provides a theoretical guidance for the further optimization of process parameters for manufacturing engineering. The 5A06 aluminum alloy cylinder validated testes are through three stages. The first is to study spinning forming of the ten longitudinal ribs. The second is to study spinning forming ten longitudinal ribs and a hoop combined rib. The third is to study spinning forming qualified samples with ten longitudinal ribs and four hoop combined ribs. Optimization aspect of the aluminum alloy reinforced spinning parameters are obtained through simulation analysis and experimental verification, to provide an ideal theoretical guidance for further material application and production.

Abstract: Although multi-point forming (MPF) is an advanced processing technique and has been investigated comprehensively as a metal working operation, there are few papers published to deal with MPF of polymers. The present paper reviews the features of MPF and evaluates the possibility of producing polymer components by means of MPF. The experimental research work makes use of PC sheets with a thickness of 3.82 mm. Numerical simulations were performed with the software ABAQUS, then spherical and saddle-shaped components were manufactured by MPF. The geometrical deviations between shaped components and their original CAD/CAM models were obtained to investigate the forming accuracy. The results confirm that MPF of PC sheet has potential for the manufacture of complex components.

Abstract: Multi-point holder forming (MPHF) adopts series of coupled holder punches, arranged between forming punches, to clamp the whole sheet in the forming zone. The multi-point holder forming processes of spherical parts of titanium mesh plate were simulated by finite element code, and the results were compared with those of multi-point die forming (MPDF). The influence of holder punch load on the deformation of spherical part in multi-point holder forming was investigated. The shape error analysis of titanium mesh formed by MPHF was performed in finial. The results showed that the spherical part had more excellent performance in multi-point holder forming, and the more deformation the titanium mesh was, the larger force of holder punch would be needed. In addition, there was a small shape error for titanium mesh part formed by MPHF before springback.

Abstract: In order to manufacture a three dimensional sheet metal part effectively, a continuous sheet metal forming process (CSMF) based on flexible roll bending has been proposed and developed. This paper mainly focuses on the fundamental aspects of the process, the principle of CSMF is introduced and the method to estimate the downward displacement of upper roll based on the desired curvature of the deformed sheet metal is presented. The variation of the upper rolls downward displacement with the desired bend radius is shown in graphically. The smoothness of the CSMF parts was measured and analyzed. In the results, it is shown that a three-dimensional sheet metal part can be formed without defects and the formed surfaces are in good agreement with the target shapes.

Abstract: A new type of discrete clamp stretch forming machine based on flexible holding technology was developed to improve the performance of traditional rigid clamp stretch forming machine used for double-curvature metal sheet forming, and its forming characters were illuminated simply. The FE model of flexible discrete clamp stretch forming was set up, and extensive numerical simulations of spherical parts for both the flexible holding mode and the rigid holding mode were carried out by dynamic explicit finite element analysis. The numerical results show that the distribution of stress, strain and thickness were well-proportioned in the flexible holding mode. The larger the spherical radius is, the smaller the minimum transitional length of sheet metal is. The transitional length of 60mm is suitable for flexible discrete clamp stretch forming in the case of considering the forming quality and material utilization. Then, the stretch forming experiment proves that the flexible holding technology is feasible, and the error contrast illustrates the new type of discrete clamp stretch forming machine is practicable.

Abstract: The deformation of sheet metal in the continuous flexible forming (CFF) process is complex and the formed result is affected by many factors. In this paper, the finite element model of CFF was founded and the forming processes of spherical parts were simulated with the software ABAQUS. The interaction between transversal deformation and longitudinal deformation in the CFF process is analyzed. Based on results of numerical simulation and forming tests, the process parameters of CFF is revised, and formed surface is measured by three dimensional sensing system, the measured results indicate the precision of formed parts are satisfactory.

Abstract: In reverse engineering, in order to analyze the accuracy of formed work-piece, the shape error between the formed work-piece and its CAD model need to be calculated. In this paper, a matching method on the basis of triangle mesh is proposed. This matching method includes three parts: pre-positioning, rough registration and fine registration. Firstly, the maximum projective plane of cloud data is designed to parallel to the xy plane through translation and rotation, and cloud data is translated by a vector which can be obtained with the point with the maximum z coordinate and the origin of coordinates. Secondly, cloud data is gradually rotated 360 degree around z axis confirm the angle making the error minimum. In this way, an initial value of ICP algorithm can be obtained, which can avoid the local convergence in the algorithm. Finally, ICP algorithm can be applied to calculate the surface error further. After matching, the error between work-piece and the CAD model can be calculated by interpolation based on triangle mesh. The results show that the matching method can obtain the higher matching accuracy.

Abstract: Springback compensation of Multi-point forming (MPF) was analyzed in the paper based on the ideal elastic-plasticity and linear hardening material models. The calculation formulas for adjusting radius of MPF die, both single-curvature and double-curvature, were obtained. Cylinder and spherical surfaces were formed by MPF equipment. Experimental results show that the errors between formed surface and target shape are within 5%. Moreover, when using formulas derived from linear hardening model, it is found that the formed surface is more close to target contour, and the presented formula can be used to determine the adjusting radius of MPF die in practice.