Optimisation of cutting parameters and surface deformation during thin steel sheets plasma processing using Taguchi approach

Abstract

Plasma machining was investigated for suitability to cut thin sheets and the quality obtained was assessed. The aim of this research was to analyse the impact of the heat generated from plasma cutting on thin sheet surface deformation and heat affected zones. Plasma cutting was assumed to be noneffective for processing thin material, this technology was known primely for cutting medium to thick plates. Tremendous work was performed previously to improve the quality. However, there are no scientific publications assessed the effect of the plasma heat on thin material under 1 mm and optimised optimise the process to reduce the phenomena resulted to their minimal. The traditional cutting methods were found to be limited and time consuming. This research can be beneficial for vehicle convertors such as wheelchair accessible vehicles or similar industries where conventional cutting methods are still predominant. Therefore, an automated plasma cutter if properly optimised would be an effective solution. CNC Plasma cutter with an automated torch height adjustment was used for this experiment to process a 0.6 mm thick deep drawing cold rolled DCO1 steel grade material. Tests were carried out varying the plasma parameters speed, pressure and intensity, the quality obtained was assessed. Three-dimensional Triplescan Atos model was used to measure the maximum surface deformation. Samples were sectioned, mounted, polished, mirrored and etched with 5% Nital acid to expose the material grains. Results were gathered on a tables, then Taguchi method and Analysis of Variance were used to optimise and analyse the parameters. Results showed an effective cut for thin materials. The optimal values obtained were 8000 mm/min, pressure 70 psi and Intensity 25 A for sheet deformation whereas heat affected zones was cutting speed 8500 mm/min, pressure 80 psi and Intensity 30 A. Cutting speed and intensity had the highest impact on deformation however heat affected zones was influenced mainly by the cutting speed. The study suggested also that a mathematical model can be constructed to predict the response for both phenomena and assess the relationship strength, the method used was least square error, the tests showed that the models fit adequately and can be trusted to predict new values. Lastly, a vehicle chassis was used for the test, the results showed an effective cutting on painted material, no second processing was required. Sealant under the material required removal on plasma pathway to avoid excess smoke or fire generation. An estimation was made for the underbody chassis cut out processing time and it was found that automated plasma can reduce the cycle time to just above 40 min.