Metal forming processes operate in conditions of uncertainty due to parameter variation and imperfect understanding. This uncertainty leads to a degradation of product properties from customer specifications, which can be reduced by the use of closed-loop control. A framework of analysis is presented for understanding closed-loop control in metal forming, allowing an assessment of current and future developments in actuators, sensors and models. This leads to a survey of current and emerging applications across a broad spectrum of metal forming processes, and a discussion of likely developments.

Closed-loop control of product properties in metal forming

Flexibility in metal forming

Closed-loop control of product properties in metal forming: A review and prospectus

Assessment of forming parameters influencing spring-back in multi-point forming process: A comprehensive experimental and numerical study

In this study, design and fabrication of a flexible forming machine are carried out for the purpose of manufacturing a prototype of curved plate block for hull structure used in shipbuilding industry. Flexible forming dies which consist of numbers of punches in an array form for upper and lower sides are designed in view of thick plate forming. A punch has formation of male and female screws to adjust its length with regard to a given surface, and all punches are supported by each other in punch housing. Software for process configuration and punch control are developed to operate the novel flexible forming machine. The software are composed of the punch height calculation part which uses an offset surface scheme. Prior to manufacturing of a prototype, numerical simulations for a saddle-typed thick plate forming process including metal forming and spring-back analyses are carried out to predict the forming performance. Experiments are also carried out to validate and confirm the feasibility of flexible forming technology in view of practical application of thick plate forming process. Curvature radii observed in the simulation and experiment are investigated and compared. Consequently, development and practical application of flexible forming technology to the thick plate forming process are described from design of the forming machine to manufacturing of the prototype. It is confirmed that the flexible forming technology suggested in this study has enough feasibility in new application of thick plate forming in shipbuilding structures which has been formed through expensive and laborious conventional line heating.

A study on thick plate forming using flexible forming process and its application to a simply curved plate

Digitized-die forming (DDF) is a flexible manufacturing technology through which a variety of three-dimensional sheet metal parts can be produced in a DDF system. It eliminates the need to design and produce the conventional die. The central component of DDF system is a pair of matrices of punches, the punches are controlled by computer and the desired shape of die is constructed by changing the heights of punches. Based on the flexibility of DDF, new forming processes are designed that cannot be realized in conventional stamping. In varying deformation path DDF, a sheet part is manufactured along an optimal forming path, and large deformation can be achieved for the material with poor formability. In sectional DDF, a sheet part is formed section by section, and this technique makes it possible to manufacture large-size parts in a small DDF press. A closed-loop forming system was built by combining DDF with rapid 3D-shape measurement system. It is used to compensate for material springback and improve dimensional accuracy of the formed part. And a DDF system with multi-point blankholder control system was developed to control the material flow, thereby to prevent sheet parts from wrinkling and tearing. The DDF integrated system is described, and the detailed forming procedures are explained in the paper. Typical examples are presented showing the applicability of the DDF technology.

Flexible manufacturing of sheet metal parts based on digitized-die

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 Bird's 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.

3.06 – Multipoint Forming

The utility relates to a multi-roller stratifying type metal plate shearing machine which belongs to the field of machinery manufacture, comprises a plurality of rigid rollers, hydraulic cylinders, transmission parts and an assistant shearing mechanism and is characterized in that the plurality of rigid rollers are parallelly arranged on a rigid support in a sliding manner with the heights decreased sequentially from left to right, the hydraulic cylinders are arranged on the rigid support in a pin shaft and hinge manner, the end parts of piston push rods are connected with the rigid rollers directly or with a roller system support, the transmission parts are connected with the rigid support and arranged on a movable beam, and the movable beam is in sliding connection with a machine frame. The multi-roller stratifying type metal plate shearing machine has the characteristics that the plurality of rigid rollers are adopted to shear a metal plate layer by layer, and the metal plate is driven to move forward by a transmission mechanism; with the structure, a greater shearing force can be decomposed to each rigid roller so as to reduce the wear of the blades; the shearing mechanism moves independently, so that the maintenance is convenient, and the cost is low; and as the rigid rollers make rolling motion, the tension force of the blades to plate materials in the length direction of the plate is reduced, and the quality of the shearing section is improved.

Multi-roller stratifying type metal plate shearing machine

The invention relates to a flexible forming method of a variable cross-section special-shaped piece with closed cavities, belonging to the field of machinery manufacturing. The method is characterized by comprising the following steps: prefabricating upper and lower dies with cavities with final shapes, putting a prefabricated workpiece with allowance after computation into the cavities and assembling and fixing the dies; and filling a mixture into the workpiece with closed cavities or with the function of closing the cavities, igniting the mixture and swelling local workpiece through thermal shock waves, thus realizing forming of the workpiece. The method has the following characteristics: the forming force is big; different mixture proportions can be selected aiming at different preformed piece materials; and the way of first preheating and then forming, forming once or forming multiple times can be selected, thus the method is beneficial to accurate forming of the formed piece.

Flexible forming method of variable cross-section special-shaped piece with closed cavities

The invention relates to a multi-roll layer cutting metal plate shearing machine, which belongs to the field of mechanical manufacture and comprises a plurality of rigid rolls, a hydraulic cylinder, a transmission part and an auxiliary shearing mechanism. The multi-roll layer cutting metal plate shearing machine is characterized in that the rigid rolls successively lowered from left to right are slidably mounted on a rigid support in parallel, the hydraulic cylinder is mounted on the rigid support by means of a pin hinge, the end of a piston push rod is directly connected with the rigid rolls or connected with a roll system support, the transmission part is connected with the rigid support and mounted on a movable beam, and the movable beam is slidably connected with a frame. The multi-roll layer cutting metal plate shearing machine has the advantages that the rigid rolls are used for shearing a metal plate layer by layer and driven to move ahead by a transmission mechanism, larger shearing force can be decomposed on each rigid roll so that wear of a blade is decreased, the shearing mechanism moving independently is convenient in maintenance and low in manufacturing cost, the drawing force of the blade for the plate in the length direction of the blade is decreased as the rigid rolls are in rolling movement, and the quality of a shearing section is improved.

Chunguo Liu

Papers

Flexible manufacturing of sheet metal parts based on digitized-die

3.06 – Multipoint Forming

Multi-roller stratifying type metal plate shearing machine

Flexible forming method of variable cross-section special-shaped piece with closed cavities

Multi-roll layer cutting metal plate shearing machine