Effect of Tool Design on the Mechanical Properties of Bobbin Friction Stir Welded High-Density Polyethylene Sheets: Experimental Study

Abstract

Welding polymers by the friction stir welding (FSW) technique is one assembly process among several known assembly techniques which consists in welding two materials without filler material. The FSW process is based on the generation of heat due to friction and material deformation under an axial force. Among the main aspects affecting material flow, the choice of welding tool geometry has become of great interest to improve the welds quality. The main objective of this work is the welding of polymers using the FSW technique. A new method of welding HDPE (high density polyethylene) plates, called BT-FSW (bobbin tool friction stir welding) was developed. Standard rectangular shape intended for the distribution of natural gas has been successfully welded by BT-FSW. Tensile tests and hardness measurements were carried out on samples cut from the welded sheets and the results were analyzed to compare the mechanical characteristics of the plates welded by the BT-FSW and conventional FSW (C-FSW) processes. The results of the comparative studies on the micro-hardness characteristics and mechanical properties of the two welding processes indicate that welding using the bobbin tool can significantly reduce hardness and improve both weld formation and mechanical properties of joints. This study showed that the design of the welding tool has a big impact on the weld strength. An improvement in the mechanical properties of the specimens welded by BT-FSW was observed to give a better welding quality for the polymers studied.

Experimental Study of the Possibility of Butt Friction Stir Welding on Polyethylene Pipes

“…Hence, an offset of 4˚ was applied, and the tool was still rotated for several seconds before withdrawing to prevent this issue. The tool rotation speed (1100 rpm) indicated in these experiments in previous papers [6] was applied to weld 11.4 mm thick HDPE sheets. It had acceptable results in terms of weld quality free from all known defects.…”

“…It is especially established in various fields that favor the use of aluminum such as aerospace, automotive, marine, nuclear, and many other fields due to better mechanical resistance and longer life in weld joint stress, however, its applications have been extended to other metals as well as thermoplastics, especially polyethylene. Researchers [2][3][4][5][6][7][8][9][10][11][12][13] have validated that FSW is a useful method for joining polymeric materials that can be used for both structural and non-structural applications. From a review of previous experiments [5], a system has been developed that has the ability to weld multiple polymeric materials into different configurations.…”

“…It was concluded that the tool plays the most important role in producing strong welds with good surface quality [2,4]. Therefore, the main goal of the researchers [6,9] was to develop a welding tool capable of producing high quality welds, especially for welding polyethylene sheets. High-density polyethylene (HDPE) behaviors and weld formation are closely related to temperature and crystallinity [6], where thermoplastics soften and melt with heat, and thus can be welded such as high-density polyethy lene.…”

“…Therefore, the main goal of the researchers [6,9] was to develop a welding tool capable of producing high quality welds, especially for welding polyethylene sheets. High-density polyethylene (HDPE) behaviors and weld formation are closely related to temperature and crystallinity [6], where thermoplastics soften and melt with heat, and thus can be welded such as high-density polyethy lene. HDPE is a semi crystalline plastic, meaning that the material shows organized and tightly packed molecular chains, and thus has a defined melting point.…”

“…The latter is more crystalline, less branched, less flexible, and denser [14]. Many kinds of research [6][7][8][9][10][11] have been done on FSW for sheets of polymers in order to improve the welding condition. A limited number of researchers [15][16][17][18] have investigated the FSW of metallic pipes while the FSW of polymeric pipes still remains challenging.…”