An experimental study on the springback in bending of w-shaped micro sheet-metal parts

In sheet-metal bending, defects relating to the component-forms such as springback are common. This is due to the elastic deflection that occurs in the material after the bending process takes place. The objective of the research is to study on the springback behaviour in micro sheet-metal parts. This paper reports an investigation concerning the influence of the material rolling direction on springback in the case of w-shaped bending parts. Micro bending parts using 316 L annealed stainless steel strips having thickness of 50 μm, 75 μm and 100 μm respectively were formed. The tensile and bending behaviours of the parts were observed through the experiment by considering the effect of rolling direction and size-effect related errors. The results revealed that various parameters influence the springback, such as thickness of the sheet, force applied, material rolling-direction and holding time during the sheet-deformation. The scale of the springback was also observed to be random among the parts made with a same sheet material

A parametric study on the accuracy of bending in micro W-bending using Taguchi method

High dimensional accuracy of micro-bent parts, particularly the desired bent angle, is often required. In the study reported in this paper, a micro W-bending process was used for the study addressing this issue. Four main parameters affecting the bending accuracy of the micro W-bent parts were considered: foil thickness, grain size, foil orientation and punching frequency. Based on Taguchi L8 orthogonal array (OA), a micro-sheet-metal forming machine equipped with W-shaped punch and die was used to conduct the micro W-bending experiments. The experimental results were analyzed using signal-to-noise (S/N) ratio and the analysis of variance (ANOVA). It was identified that the extent of the effect by these parameters on the micro W-bending process depends on springback behaviours. The foil thickness had highest influence on the springback amount of the bent parts. However, the negative springback was influenced mostly by the grain size, closely followed by the foil thickness. Furthermore, the optimum bending conditions for different types of the springback were obtained. Confirmation experiments were then performed not only to validate the improved bending accuracy but also to verify the extent of the contribution from each parameter to the amounts of the springbacks. Finally, mathematical models for both, positive springback and negative springback, were developed using the regression analysis. It was observed that the predicted values fit well with the experimental results, indicating the adequacy of the established models

Size effect on the springback of CuZn37 brass foils in tension and micro W-bending

With the ever-increasing demands on miniaturization, the requirement on good forming quality and high dimensional accuracy of micro parts is dramatically motivated. As a decisive factor affecting the accuracy of micro-bent parts, the springback is significantly influenced by size effects. In order to explore size-effect associated springback behaviour and evaluate the forming quality of micro-bent parts, an experimentally-based investigation on the influence of foil thickness, grain size and their interactive effect on the springback behaviour of CuZn37 brass foils with different thicknesses and grain sizes was carried out. The experimental results obtained via micro tensile tests revealed that the yield strength, Young’s modulus and elongation had a close correlation with the thickness to average grain size ratio. A micro W-bending process was used to perform the bending tests. Both springback and negative springback phenomena were observed. It was found that how size effects may influence the amount of springback would depend on the springback behaviours, e.g. positive springback or negative sprinback, etc. In addition, scatter phenomenon of the springback behaviour was analyzed quantitatively. An increased scatter was observed for the 50 μm thick specimens when the thickness to average grain size decreased, whereas an inverse tendency of the decreased scatter of the negative springback was found for the 75 and 100 μm thick specimens with increase of the grain size. Finally, forming quality of the W-shaped micro-bent parts was assessed

Optimisation of micro W-bending process parameters using I-optimal design-based response surface methodology

There is an increasingly recognised requirement for high dimensional accuracy in micro-bent parts. Springback has an important influence on dimensional accuracy and it is significantly influenced by various process parameters. In order to optimise process parameters and improve dimensional accuracy, an approach to quantify the influence of these parameters is proposed in this study. Experiments were conducted on a micro W-bending process by using an I-optimal design method, breaking through the limitations of the traditional methods of design of experiment (DOE). The mathematical model was established by response surface methodology (RSM). Statistical analysis indicated that the developed model was adequate to describe the relationship between process parameters and springback. It was also revealed that the foil thickness was the most significant parameter affecting the springback. Moreover, the foil thickness and grain size not only affected the dimensional accuracy, but also had noteworthy influence on the springback behaviour in the micro W-bending process. By applying the proposed model, the optimum process parameters to minimize springback and improve the dimensional accuracy were obtained. It is evident from this study that the I-optimal design-based RSM is a promising method for parameter optimisation and dimensional accuracy improvement in the micro-bending process

Forming of micro sheet-metal components

This chapter firstly highlights challenges in micro-sheet-metal forming and explains its characteristics and tooling design considerations. An introduction is then given to the basic processes of sheet-metal forming, emphasising, from micro-forming point of view, on the size effect, material, tooling and process capabilities. These are followed by a detailed description on the tool-design for multi-stage/progressive micro-sheet-forming. Considerations for developing a press machine system are also given in detail, concurrently with description of a newly developed machine-system at the University of Strathclyde. A case study is given for further understanding on the micro-forming tool and machine design. Lastly, several issues concerning technological competitiveness and economic aspects of micro-sheet-forming are presented as a general discussion

An experimental study on the springback in bending of w-shaped micro sheet-metal parts

In sheet-metal bending, defects relating to the component-forms such as springback are common. This is due to the elastic deflection that occurs in the material after the bending process takes place. The objective of the research is to study on the springback behaviour in micro sheet-metal parts. This paper reports an investigation concerning the influence of the material rolling direction on springback in the case of w-shaped bending parts. Micro bending parts using 316 L annealed stainless steel strips having thickness of 50 μm, 75 μm and 100 μm respectively were formed. The tensile and bending behaviours of the parts were observed through the experiment by considering the effect of rolling direction and size-effect related errors. The results revealed that various parameters influence the springback, such as thickness of the sheet, force applied, material rolling-direction and holding time during the sheet-deformation. The scale of the springback was also observed to be random among the parts made with a same sheet material