Effect of Preheating on Weld Quality of High Density Polyethylene (HDPE)

  • Razi Ur Rehman

Student thesis: Master's Thesis

Abstract

Friction stir welding (FSW) is a novel and robust welding technique employed effectively for joining metals by utilizing the frictional heating produced by the welding tool. Recently, many researchers have attempted utilizing this technique to produce high quality welds for thermoplastic polymers, in particularly high-density polyethylene (HDPE). However, defect free welds in thermoplastics are uncommon. The main objective of this research is to investigate the effect of preheating on the weld quality in butt welding of commercially available HDPE sheets. In addition, the material flow patterns are investigated by welding black and white HDPE sheets. A new tool with a rotating Teflon collar having 13 mm metallic shoulder in its center was developed. Forces in axial, traverse and lateral directions; temperatures on top and bottom surface; and materials tensile strength and fracture strain were analyzed by varying rotational speed, traverse speed and bottom plate temperature. A full factorial design with three levels of each process parameter was conducted. The welded samples were assessed by destructive and non-destructive testing techniques, namely tensile testing and weld morphology imaging, respectively. It was found that preheating the bottom surface of the samples significantly improved the weld quality. All process parameters were found to have statistically significant influence on the weld quality. The welded HDPE samples exhibiting highest average tensile strength of 28.7 MPa were achieved for welding parameters of 1500 RPM, 40 mm/min and bottom surface temperature of 60oC. The optimum process parameters that result in welding efficiency of 106.5% with average tensile strength of 27.6 MPa and average fracture strain of 137.5% were obtained at 1500 RPM, 30 mm/min and bottom surface temperature of 60oC. Common root defects during FSW of polymers have been eliminated in majority of the welds with the implementation of newly developed tool and selected process parameters.
Date of AwardMay 2020
Original languageAmerican English

Keywords

  • HDPE
  • Teflon collar
  • Temperature Gradient
  • Preheating
  • Material Mixing

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