Study of the design and optimization process for the Chain-die forming technology

Abstract

This thesis investigates the design process and the optimization approaches for the Chain-die forming technology based on numerical, experimental and analytical approaches.The first objective of this thesis is to develop and validate single-stand finite element simulation models for the Chain-die forming process with simple geometries such as U-channels. The results show that the single-stand model has a good agreement with the experimental work with a maximum error of 1.5° for formed flange angle. Further study utilized 2D stamping models to predict the formed geometries of single-stand simulation results. The findings concluded that using 2D numerical models in optimizing the flower pattern diagram (cross-sections of the metal strip at every forming stand) can dramatically accelerate the tooling design process. Then the study extended the research towards the free U-bending process. The results demonstrate a thinning pattern that consists of three peaks over the bending region for a large bending ratio with corresponding valleys for the local bent radius. The location and the severity of the wear on the product are also successfully predicted. The findings obtained in this objective can help in optimizing the flower pattern design.The second objective is to develop and validate multi-stand finite element simulation model for the Chain-die forming process with complex geometries such as threshold and top hat products. The new numerical model is experimentally validated through the comparison of longitudinal strain development, forming load during the forming process and the longitudinal bow on the formed product. The results show that a multi-stand simulation approach has a much higher accuracy in predicting the development of longitudinal strain in flange edge sections for complex geometries compared with single-stand models. Also, a good agreement is found between the simulation results and the experimental results for the total forming load with a maximum error of 11%. With accurate predictions, the findings can provide a deep understanding of the Chain-die forming process and assist in optimizing the flower pattern design for products requiring multiple passes.The third objective is to develop analytical formulas for evaluating the effect of the downhill flow pass, determining the minimum inter-distance required between the forming stands, calculating the characteristic load curves and optimizing the geometry of the supporting mechanism for the Chain-die former. The influence of the elevation of the forming stands is theoretically and numerically investigated and 50% of the reduction in peak longitudinal strain is achieved in Chain-die forming a threshold product. Also, a semi-analytical model for determining the minimum inter-distance for stands involving a single active bend is derived and the comparison with the simulation results showed a good agreement. Meanwhile, an analytical approach is developed to estimate the characteristic forming load at crossbars and load-bearing pillars of the supporting mechanism which can be used as guidelines for the calibration of the production line. Besides, the calculated load curves can also be used to optimize the geometrical structure of the chain-die former, aiming at balancing the load distribution over the forming device, improving the reliability of the forming process. The findings can benefit the forming process design of the Chain-die forming technology by minimizing the number of forming stands required and by optimization of the forming device.The work presented in this thesis investigates various aspects including simple and complex geometries, process parameters and optimization methods of the Chain-die forming technology through numerical, experimental and analytical approaches. The most important contribution is the discovery of the reduction of the peak longitudinal strain caused by the elevation of the forming stand in the Chain-die forming process. Optimized elevation can eliminate around half of the longitudinal strain, and significantly reduce the number of forming stands required, leading to a reduction in the cost of the production line and minimizing the production line length. Besides, the development of the multi-stand finite element simulation model for the Chain-die forming process enables the investigation of the process parameters, leading to optimization methodologies such as determination of the minimum inter-distance required between forming stands and balancing the load distribution over the forming devices. The approaches proposed have a great potential for the industrial application of the Chain-die forming technology.n