The optimized performance of linear vibration welded nylon 6 and nylon 66 butt joints

We have studied the influence on tensile strength of linear vibration welded polyamides across: 1. a range of glass fiber reinforcements from 0-50% by weight (0, 14, 25, 33, 50), 2. and in different glass fiber orientations (predominantly parallel, random or perpendicular) to the welding surface of the plaques. Parameters used for vibration welding included pressure, amplitude, frequency, melt down, weld cycle and hold time. Welding was performed on molded plaques of size 100 mm x 64 mm x 6.4 mm. Tensile bars were machined from the welded plaques for testing. Tensile tests were performed over a wide range of temperature conditions (-40 degrees C to 150 degrees C) on dry-as-molded specimens. For reinforced materials, the measured maximum ultimate tensile strength (at break) of welded joints ranged from 41.4 to 93.1 MPa. For nylon 6 with 0-50 wt.% glass fiber reinforcement, the tensile strength of welded joints under optimized welding conditions was found to peak between 14 wt.% to 25 wt.% glass fiber. This weld strength is 10-17% higher than the nonreinforced materials. Analysis of the welding interface by optical and scanning electron microscopy suggested that the thickness of the weld zone also displays a maximum at 14-25 wt.% glass fiber content. Results of the microscopy study showed that, in samples which achieve maximum tensile strength under optimized welding conditions, some of the fibers reorient along the tensile direction (perpendicular to the weld plane) and may even cross the interface. It is postulated that the high tensile strength measured from these weld joints is a result of increased thickness of the weld zone which may provide mobility to the fiber to reorient towards the tensile direction. For nylon 66 with 33 wt.% glass fiber content, a tensile strength of 81.9MPa was achieved under optimized welding conditions. This represents a 12 % increase over the non-reinforced material. Examination of the morphology of the welded joint showed that, in this case, the weld zone is ''diffused'' and not well defined. It is suspected that the state of the resin matrix may place a bigger role than the fiber orientation.