Thermoplastic or known as polymer is known for its light weight property which was used in varies industry and used in the industry as a substitution for metal. Thermoplastic was the only polymer that can be welded. Friction Stir Spot Welding (FSSW) is a revelation of Friction Stir Welding (FSW) where it only need to plunge the tool at one point and create the joint. So, the purpose of the this investigation was to analyze the influence of the external heat on the tensile strength and to analyze cross section of friction stir spot welding (FSSW) joints produced on high-density polyethylene (HDPE) sheets. The analysis involved the variation of the temperature of external heat and constant rotational speed, tool plunge rate, pre-heat time and dwell time. The type of joint was single lap joints of two similar material. Mechanical characterization of joints of welded joint was carried using a lap shear test. Experimental tests were conducted to determine the most influencing factors which in this case, the external heat factor to determine the mechanical behavior of FSSW joints. The result for lap shear test was sample with external heat of 50 Celsius have the highest stress compared to others external temperature. After the lap shear test, welded joints was observed by its cross section and the result was sample with external heat of 70 Celsius has highest material movement around the welded joint with the result of percentage void of 75 percent.. The conclusion for this experiment is external heat improves the strength of the welded sample at the highest with using external heat temperature of 50 Celsius. The external heat also resulting in varies of weld surface finish, lower chip formation, and material loss. This method overcomes the insufficient heat which always leads to improper fusion and lack of weld formation.
