Publication: A study of punch-die misalignment in square cup deep drawing process using experiment and finite element analysis
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Date
2022-09-01
Authors
Abdul Ghafar, Alimi
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Abstract
Square deep drawing is a forming process that transforms a flat sheet metal to a seamless vessel by using a set of punch and die. Any misalignment in the punch -die assembly during the process can cause thinning, which can result in the tearing of the drawn part. The onset of thinning due to punch-die misalignment is yet to be explored fully, thus understanding the thinning initiation will be useful for process optimization. In this study, a series of comprehensive methods to identify the presence of punch-die misalignment in square cup deep drawing process is implemented. These methods are deployed at the pre-drawing, during the drawing process and at the post drawing stage. In the pre-drawing stage, an image processing technique is utilized forpre-drawiing inspection. The captured images are analysed to identify the severity of misalignment between the punch and the die. At the second stage (during forming), an in-situ method is used to observe the presence of punch-die misalignment. For this purpose, a customised die rig is fabricated and installed on a universal tensile machine (UTM). A Commercial Electrolytic Zinc-Coated Steel Sheet (SECC) was used as the specimen for the deep drawing process, and the effect of misalignment severity on drawing force and wall thickness distribution are investigated. For comparison, a finite element (FE) simulation is utilized as an early prediction of the punch-die misalignment. The simulation was conducted using Abaqus/Explicit FEA software, utilitising the Hill’48 model, to determine the stress-strain diagram and forming limit
diagram (FLD) of the SECC material. Two conditions of misalignment were simulated, 1) single axis punch-die misalignment and 2) multi axes punch-die misalignment with the misalignment severity of 0.1 mm to 0.5 mm. At the post-drawing stage, the wall thickness distributions of the cup for each misalignment conditions were investigated. Variations in wall thickness distributions would indicate the severity of misalignment between the punch and die. Specifically, a novel methods are introduced for detecting the presence of punch-die misalignment in square cup deep drawing process. Both the FE and experimental results were in good agreement with regard to the drawing forces and thinning patterns due to punch-die misalignment. Greater misalignment severity was observed to increase the drawing force and thinning in the wall of the drawn cup. For both misalignment conditions, similar wall thickness distribution patterns were observed, with the maximum thinning occurring in the cup sidewall and minimal thinning at the bottom of the cup. For single axis misalignment, the maximum thickening up to 18% has occured at the lowest misalignment severity of 0.1 mm. On the other hand, for misalignment severity of 0.3 mm and above, the maximum thinning in the x-axis was higher as compared to the y-axis by average of 0.53% and 1.72% based on FE and experimental results, respectively. For multi axes
misalignment, the maximum thickening averages at 15%, while the thinning was more pronounced in the rolling direction as compared to the transverse direction. As a conclusion, this study had contribute a positive signification implication in die making, especially punch-die alignment issue in deep drawing process. Alignment punch-die is essential in square cup deep drawing process. A series of comprehensive approach for identifying punch-die misalignment issue according to this study can be referred by researcher and industrial practioner in making high quality square cup deep drawn product.