Chunguo Liu

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.

Numerical simulation of multi-point forming accuracy for polycarbonate sheet

Multi-point forming is an advanced flexible manufacture technology, which has been used in many fields successfully. In order to provide a flexible method for forming a polymer, multi-point forming is applied to the manufacture of polycarbonate sheet. An optimized DSGZ constitutive model is established to describe the stress–strain relation of polycarbonate sheet, and its parameters are determined according to experimental data. The multi-point forming process of polycarbonate sheet is introduced briefly, and a simple calculating scheme of punch height is developed. Numerical simulations of spherical and saddle-shaped parts are carried out by dynamic explicit finite element analysis, and the effects of punch number and punch radius on the surface accuracy and shape accuracy are studied. The multi-point forming experiments of polycarbonate sheet are done, and the comparisons of shape error between experimental parts and objective parts are conducted, which show that the polycarbonate products have good surface accuracy and shape accuracy.

An Integrated Control System for Sheet Metal Flexible Forming on Multi-Point Die

Multi-point forming (MPF) is a flexible forming method for sheet metal parts. It uses two reconfigurable pin groups which function as the stamping dies to form sheet. The height of each adjacent arranged pin is numerical controlled. The shape contour of the pin group can be changed via computer accordingly. The paper outlines the computer integrated control system for MPF process. It mainly includes MPF CAD/CAM software, tool control subsystem, and a measurement subsystem. The CAD/CAM software is for design of the pin group shapes, shape error compute etc. The tool control subsystem is a computer distributed control system based on industrial field bus. On the control of it, the heights of several hundreds pins are set to the desired height according to the data from host computer. The self developed laser scanning measurement subsystem is to measure the shape of formed part. After the MPF system was built, forming experiments were done. To overcome spring-back during forming, a non-parametric model was obtained by online identification with input and feedback spatial shapes. With that model the shapes of the two pin groups were predicted and used in the next cycle forming. The part shape converged to the designed shape gradually