Determination and optimization of resistance welding parameters applied to thermoplastics

In this study, resistance welding was applied to polypropylene and high density polyethylene with different joining angles by using chrome nickel heating elements of different shapes and thicknesses. To determine the ideal parameters, welding performances were examined using mechanical tests, microstructure investigations and thermal imaging methods. A 12V AC (50W) transformer was used. The test specimens produced using the injection machine were cut at different angles (90 °, 45 ° and 30 °). The same type was welded with resistance wires of different diameters and shapes. It was determined that the appropriate temperature was 217 ° C and the welding time was 13 seconds. Different forces were applied on the parts and the parts were adhered. The appropriate force was determined to be 20N. The mechanical properties of the welded parts were examined by applying tensile test, three point bending test and impact test. According to the tensile test results applied to welded joints of polypropylene material, welds made with 0.5 mm wire were more resistant and welded with 0.3 mm wire were weak. In addition, according to the tensile test results, welded joints made with spiral wire with 30 ° cutting angle showed the best strength. Accordingly, for the tensile tests of welded joints of high density polyethylene materials, only the samples in these parameters were tested and the weld strengths of the two materials were compared and it was found that the joints of the polypropylene materials showed better tensile strength. According to the three point bending test results, all materials were not broken by showing 3.5% stretch. The best performance was observed at 30 ° angle with samples joined by zigzag wire. Compared as materials, it is seen that welded joints of high density polyethylene materials exhibit better flexural strength. Finally, the welding regions of the materials broken from the joints by using an optical microscope were visualized at a magnification of 400 fold. When the images are examined, it is seen that the melt flows are more pronounced in the samples caused by cross and spiral wire shape. However, in the form of zigzag wire, only the lines formed during melting and cutting around a certain part of the wire were observed and the non-welded regions were determined. At the end of the study, spiral wire shape with 0.5 mm wire thickness and 13N welding time and 20N compression force gave the best mechanical results.