Pusat Pengajian Kejuruteraan Mekanikal - Tesis

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Browsing Pusat Pengajian Kejuruteraan Mekanikal - Tesis by Author "Ja’afar, Noor Azam"

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    Multi-stage and multi-responses optimization of punching die performance using taguchi method
    (2020-04-01)
    Ja’afar, Noor Azam
    Punching process is one of the fundamental technologies in metal forming operations. The sharpness of the die edge in the punching process is very important to ensure the quality of the produced hole. Hole punching is a multi-stage and multi-response process, beginning with the fabrication of the die, where machining parameters need to be considered, then geometries of the die, i.e. the design parameters, and finally the punching process parameters. At each stage, the responses are different but would be implicitly related between stages. From the literature review, the evaluation and optimization of these stages are usually treated separately and explicitly to avoid complexity. Thus, the new approach to investigate the effect of punching die wear was taken by considering all stages in punching die process, starting from the fabrication, design and punching process utilisation. The purposes of this study were to improve the sharp edge of punching die from wear problem in order to enhance punching tool life and product quality. The study parameters at every stage of fabrication process, design process and punching operation were considered in a series of experiments and optimization processes using the Taguchi Method. Analysis of variance (ANOVA) was used to determine the significant factors that affect the responses. As the study considers the entire punching process, the results of the experiment from the previous stage has been utilized for the next stage of experiment. In the first stage, the effects of WEDM cutting parameters of pulse on time, pulse off time, servo voltage and ignition pulse current on the surface roughness and white layer thickness (WLT) of 2379 steel were evaluated. In the second stage, the effects of two die design parameters, i.e. die clearance angles and die opening sizes, were compared on the accuracy and quality of punched holes produced on 1.4-mm thick S275 mild steel. The die was fabricated using the optimal WEDM cutting parameters identified in the earlier stage. Burr formations and die weight losses were used as an indicator for determining the best die design parameters. Subsequent experimentation was conducted to optimize the die design parameters for die opening size, angular clearance angle and die clearance on die wear. Finally, based on these optimal die design parameters, several punching dies were fabricated for the optimization of the punching process parameters such as material types, sheet thickness, and lubrication on die wear. A non-linear mathematical model was developed for predicting the response of the die wear. For the first stage, it was found that pulse on time was the most significant factor affecting the surface roughness for both types of cutting modes (main cut and multiple trim cuts). Meanwhile, the results show that pulse on time and pulse off time were the most significant factors on WLT for both main cut and multiple trim cuts. The second stage results show that the design parameters combination of Ø20 mm die opening size, 0.50° angular clearance angle and 2% die clearance would give the optimal condition for the lowest wear rate. Final results show that the combination of punching process parameter of electro-galvanized (EG) plate of 1.4 mm thickness and no lubrication gave the optimal condition for the lowest wear. The confirmation experiment showed that the predicted results by the developed mathematical model differ by only 0.0007% with the actual value. The developed model helps appropriate selections of die design geometries, WEDM machining parameter during fabrication and punching parameters during operation to improve the tool life and product quality.