African Fusion November 2015

SAIW Member profile: Hydra-Arc Low str ss no distortion welding

extraction and to minimise interference with the welding arc and weld pool. Thermocouples were attached to the underside plate material, positioned at 7.5, 15 and 20 mm from the weld centreline, and bead-on-plate tests conducted. By attaching the thermocouples to the underside of the plate they were protected from being ripped off by the cooling head or direct impingement of the CO 2 . The welding trials were carried out with and without cooling, using the cooling arrangement shown in Figure 1 and 2. Sample results from the thermocouple study can be seen in Figure 4, which shows the effect of the cooling on the temperature profiles. Further, a comparison of weld macro sections shows that thewelds fromboth conventional and LSND processes exhibit similar cross sectional shapes, beadwidths andheights, aswell as comparable levels of penetration. The two macro sections can be seen in Figure 5. Representative sampleswere thenmeasured for distortion using a Faro arm measurement system and macro sections taken to reviewweld quality. Typical sample distortion results for the bead on plate specimens are illustrated in Figure 6, which clearly show that a reduction in distortion of between 40-50% is achievable with the system in the trial. The typical results for bead on plate samples are illustrated as a simple visual side-by-side comparison as shown in Figure 7. The microstructure examination of samples from both weldmethods showed the resultingmicrostructure to be very similar. And when the micro-hardness was also checked by traverses across typical samplewelds, the results fromsimilar populations where not significantly different. Once a reliable system was established, the trials were repeated using simplified ‘real’ joint conditions using the robot mounted DC-LSND welding system. Trials were carried out on butt welds in 2.0 and 2.5 mm thicknesses in XF350 steel plates, andon a ‘tophat’ section in 2.5mmsteel, withboth 2.0mmand 2.5 mm closer plates; this condition being chosen as it is repre- sentativeofmanyoftheweldjointsusedinautomotiveproducts. Figure 4: Temperature plots for 2.5 mmmaterial welded at 650 mm/min using the robotic LSND system: (a) conventional (top graph), without cooling active; and (b) cooled (lower graph) using the DC-LSND with CO 2 snow.

Figure 5: A comparison of macro section results for conventional GMAW weld (top); and the LSND process weld (below) for typical bead on plate sample welds.

Figure 6: A comparison of the out of plane distortion measurements in typical sample welds.

Figure 7: A visual comparison of distortion in typical sample bead on plate welds. Representative sampleswere thenmeasured for distortion andmacro sections taken to reviewweldquality. It canbe seen in Figure 8 that themacro section from the LSNDweld exhibits

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November 2015

AFRICAN FUSION