A strategy for on-machine springback measurement in rotary draw bending using digital image-based laser tracking

Rotary draw bending is a commonly used metal forming technique for profile bending. Due to the elastic recovery of the material, springback compensation to control the bent product quality is one of the critical manufacturing issues. The realized bend angle has to be measured for springback compensation before removing the profile from the machine, and the bending process can follow an iterative approach until the product quality is satisfied. However, this trial-and-error is costly for batch production in manufacturing. An on-machine measurement technique is therefore developed to measure springback in rotary draw bending with an affordable laser and a webcam. An image processing technology is integrated with the manufacturing process to track the deformation and measure springback angle in real time, eliminating the need for the workpiece to be transferred to a measurement device. In this paper, bending experiments were conducted with AA6082 rectangular hollow profiles bent at 30°, 45°, 60°, and 90° angles, and springback angles from the conventional manual measurement were compared to that from the on-machine measurement. Since the difference in springback measurement between the proposed and the conventional methods was within 0.15° on average, it is demonstrated that the laser tracking, on-machine measurement is a feasible real-time springback measurement technique for Industry 4.0.

An Enhanced Hybrid Springback Compensation Approach: Springback Path – Displacement Adjustment Method For Complex Shaped Products of Sheet Metal Forming

Springback compensation is critical in sheet metal forming. Advanced techniques have been adopted in the design stage of various sheet metal forming processes, e.g. stamping, some of which are for complex shaped products. However, the currently available numerical approaches are not always sufficiently accurate and reliable. To improve the accuracy of springback compensation, an enhanced hybrid springback compensation method named Springback Path – Displacement Adjustment (SP-DA) method has been developed in this study based on the well-known conventional displacement adjustment (DA) method. Its effectiveness is demonstrated using FEM analysis of low, medium and high strength steels adopted in automobile industry, in which a symmetrical model owning geometry complexity similar to an auto body panel was established. The results show this new enhanced SP-DA method is able to significantly improve the accuracy of springback compensation comparing to conventional displacement adjustment technique.

Springback Prediction of Dieless Forming of AZM120 Sheet Metal Based on Constitutive Model

Springback control is a key issue of the sheet-metal-forming process. In this paper, the mechanism of sheet-metal-forming along the folding trajectory of the computer numerical control (CNC) four-side automatic panel bender was studied, based on the bend-forming springback compensation theory of the power function material model. Firstly, the mechanical property of AZM120 sheet metal standard samples was tested. Then, a theoretical model of springback compensation under plane strain conditions was built, based on the constitutive relationship of the elastic or the elastic-plastic power hardening material. In addition, a sheet-metal-forming trajectory model was designed for sheet metal bending using the vector method. Finally, a laser tracker was used to acquire the folding trajectory, and then the reliability of the trajectory model was verified. On this basis, the influences of geometric and process parameters, such as sheet thickness, forming angle, and bending radius in springback control, were studied according to the theoretical formula and verified by experiments. The proposed method is generally applicable to operation conditions where the bending radius ranges between 1.5 and 6.0 mm and plate thickness ranges from 0.8 to 2.5 mm, and the achieved overall accuracy was more than 89%.

Multi-point forming springback compensation control oftwo-dimensional hull plate

Springback is always a technical problem in sheet metal forming. In this article, the rapid springback compensation control of two-dimensional hull plate is realized by theoretical calculation and numerical simulation. For the cylindrical shell, according to the bending forming theory of medium and thick plates, the total elastic-plastic bending moment is established, and the curvature change before and after springback is deduced. The curvature correction coefficient is determined by the precise numerical simulation technology. At the same time, the validity of the method is verified by cold bending experiment. For the shell with variable curvature, it is divided into several cylindrical surfaces according to the curvature gradient of its geometric section line. The compensation curvature array is obtained by the correction compensation algorithm of springback curvature of cylindrical plate, and the algorithm is verified by numerical simulation. The results show that the method is very close to the expected results. Thus, the efficiency and precision of forming will be improved, and the foundation of digitization of sheet metal forming is established.