Ming Zhe Li

Multi-point forming technology for sheet metal

Abstract Multi-point forming (MPF) is an advanced manufacturing technology for three-dimensional sheet metal parts. In this paper, an MPF integrated system is described that can form a variety of part shapes without the need for solid dies, and given only geometry and material information about the desired part. The central component of this system is a pair of matrices of punches, and the desired discrete die surface is constructed by changing the positions of the punches though CAD and a control system. Typical examples show the applicability of the MPF technology. Wrinkles and dimples are the major forming defects in the MPF process, but numerical simulation is a feasible way to predict forming defects in MPF. In conventional stamping, the method to form sheet metal with a blankholder is an effective way to suppress wrinkling; and the same is true in MPF. An MPF press with a flexible blankholder was developed, and the forming results indicated the forming stability of this technique. Based on the flexibility of MPF, varying deformation path MPF and sectional MPF were explored that cannot be realized in conventional stamping. By controlling each punch in real-time, a sheet part can be manufactured along a specific forming path. When the path of deformation in MPF is designed properly, forming defects will be avoided completely and large deformation achieved. A workpiece can be formed section by section though the sectional MPF, and this technique makes it possible to manufacture large size parts in a small MPF press. Some critical experiments were performed that confirmed the validity of the two special MPF techniques.

Analytical Analysis of Three-Roll Bending of Thin-Plate

In this paper, an analytical solution for the three-roll bending process of thin-plate was presented. Based on the theoretical analysis on continuously loading and unloading deformation of the plate during roll-bending, the curvature equations governing the bending behavior of thin-plate were set up and then solved by integration. Combing the solutions with the geometrical relationships in three-roll bender, the deflection and bending angles occurring during the steady continuous bending period were obtained by an iterative scheme. Numerical examples were given to illustrate the application of the solutions. The variation of the top roll’s position with the intended bend radius, the curvature and deflection distributions on bent plate were shown in graphically and discussed.

Research on Continuous Multi-Point Forming technology for three-dimensional sheet metal

Continuous Multi-Point Forming (CMPF) is an advanced sheet metal forming technology. It can manufacture three-dimensional surfaces of different shapes by adjusting the curvatures of flexible rollers and displacement of upper flexible roller. CMPF experimental equipment was designed. Finite Element Analysis (FEA) model was established. To show the characteristics of CMPF, conventional roll bending was compared with it. Process of CMPF and action force between flexible rollers and sheet metal were researched by numerical simulation method; simulation results can offer assistance to optimise the design of CMPF equipment. Spherical, saddle and twisty surfaces were simulated and their experimental results were presented.

3.06 – Multipoint Forming

The double curved sheet-metal parts with large size and thin-walled have been used in the field of aviation, spaceflight, shipping, vehicle, and architecture widely. Generally, the double curved sheet-metal parts are formed by solid die, but the cost for manufacturing of solid die is very high and the manufacturing cycle of solid die is very long. In order to solve the problems of solid die, Jilin University have done lots of works about flexible sheet-metal forming technology and digital manufacturing, such as multipoint forming (MPF) and flexible stretching forming (FSF). MPF is using a group of punch elements to shape the surface of the tool in place of a solid die firstly. Then, each element can be controlled by computer so that the curved tool surface can be changed at any time. MPF have been used for the manufacture of steel structure of Birds Nest Stadium (Beijing Olympic Game). FSF can increase the rate of materials utilization and close-fitting dies sharply than conventional stretch forming, by replace integrally gripping jaws to discrete multi-gripping jaws. Flexible control of multi-gripping jaws also can be achieved in a simple way based on new principle of stretching forming. FSF have been used in the cab of high-speed train and landmark building successfully. Furthermore, flexible roll forming, spin forming, continuous rolling, and stamping with flexible bank-drawer also pioneered at Jilin University, based on lots of numerical simulation and experiments.

The Effect of Discrete Grippers on Sheet Metal Flexible-Gripper Stretch Forming

Flexible-gripper stretch forming is a new flexible manufacturing process of sheet metal. Four numerical simulation models of discrete grippers were established using finite element method, the effect of the numbers of grippers on stress distribution, thickness distribution and gripping surface shape of the spherical parts were studied. The results show that the clamped edge of the spherical parts formed by using integral grippers is straight，the tensile stress distribution is uneven and the thickness is obviously reduced. However, the stress distribution on the parts formed by using discrete grippers stretch forming is relatively uniform, with the increase in the numbers of grippers, the thickness increases, and the more gripping surface curvature of the parts is close to the curvature of die, the better forming quality of the parts is.

Development of Flexible Rolling Device for 3D Plate

To effectively form three-dimensional sheet metal parts with various curvatures produced in small quantities, flexible rolling forming, a new flexible forming method is being developed. Firstly, concept of the flexible rolling forming is introduced and its characteristics and working principle are analyzed by the combination of conventional rolling and multi-point forming. Secondly, the equipment design scheme of flexible rolling forming is put forward and the relevant device is developed. Thirdly, the feasibility and practicality of flexible rolling forming are verified by rolling several typical three-dimensional surface parts such as spherical and saddle surface parts by self-developed device. Finally, verifies the reasonableness of the device and at the same time possesses the important guiding significance to the research and development of practical flexible rolling forming equipment.

Power Spinning Study of Thin-Walled 5A06 Aluminum Alloy Cylinder with Longitudinal and Hoop Inner Ribs for Manufacturing Engineering

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.

Study of Multi-Point Flexible Floating Clamping System of Multi-Roll Stretch Forming Process

Multi-Roll Stretch forming process is a new flexible process which is used for forming hyperbolic-degree surface pieces. Using the Multi-point flexible floating clamping system, the metal sheet can be more easily formed, and the flexibility can be much higher, which the ordinary floating clamping cannot have. A series of finite element simulations and experiments have been done for the process of forming saddle-shaped parts using Multi-Point flexible floating clamping system, and ordinary floating clamping system. The results show that the quality of the part formed using flexible floating clamping system is better.

Flexible Stretch Forming Technology for Sheet Metal Based on Discrete-Gripper and Multi-Point Die

To solve the problem of low material utilization in traditional stretch forming process, a flexible stretch forming method was proposed, which can be realized by interaction of the multi-point stretch forming die with discrete-gripper stretch forming machine. The principle and characteristics of sheet metal flexible stretch forming technology was introduced, structural composition and working principle of the multi-point stretch forming die and discrete-gripper stretch forming machine were expounded, and the technology experiments was carried out with a self-designed flexible stretch forming technology equipment for sheet metal. The experimental results indicate that structure of multi-point stretch forming die and discrete-gripper stretch forming machine are reasonable, and flexible stretch forming technology can be realized by above-mentioned die and machine, stretch forming parts has a good quality and its shape error can satisfy requirements of production.

The Effect of Loading Path on Forming Results in Multi-Gripper Flexible Stretch Forming

Multi-gripper flexible stretch forming (MGFSF) is a recent technological innovation of sheet metal flexible forming process. Straight jaws in traditional stretch forming machine are replaced by a pair of opposed clamping mechanisms which can move relative to each other. Taking the case of forming a sheet metal into spherical surface by stretching the sheet in two opposite directions, the finite element models of MGFSF under various loading paths were established and the effects on stretch amount, strain and thickness of the simulated parts were analyzed comparatively. It is founded that compared to the horizontal-tilting (HT) and horizontal-vertical (HV) loading paths, the horizontal-tilting-vertical (HTV) loading path would result in more uniform stretch amount, strain and thickness distributions also with lower strain and thickness reduction, which improves the forming quality significantly. Finite element simulations also revealed that the material flow state in the transition zone can be improved effectively and the local strain concentration can be greatly suppressed with reasonable loading path, which would decrease the possibility of material failure.