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Design for DOE: Development of a CNC platform to Evaluate Effect of Operator’s Skill in Gas Metal ARC Welding (GMAW)
Gas Metal Arc Welding (GMAW), commonly known as MIG welding, is the dominant industrial welding method. GMAW is preferred due to its ease of operation, versatility of material types to be joined, relative high speed and low cost. Though GMAW can be adapted for robotic application, semi-automatic version with a human operator is still common. This project aims to determine the effect of human operator’s skill on the joint quality. Given that important factors, such as wire feed rate, shielding gas supply rate, voltage etc., are predetermined, it was decided that the operator’s speed, zig-zag width of weld and contact tip-to-work (CTWD) distance might impact the weldment quality. A full factorial DOE with center points was designed. However, with a human operator, it is impossible to maintain or verify that the level of the factors were held constant during the experiment. This necessitates the design of a fixture which will mimic the human operator’s motion while holding the input level of the factors constant throughout the weld length. This paper describes the design and development of CNC controlled fixture to perform the welding operation along with the effects of factors on the weldment quality as obtained from the full factorial DOE. Using the fixture experiments were conducted on AISI 1018 cold rolled steel plates. The quality of the weldment was judged by the tensile strength obtained from an Instron universal testing machine. It was found that operator’s speed and CTWD had significant impact on the welded joints whereas zigzag motion does not affect the joint strength at a level of significance.