African Fusion November 2015

Low stress no distortion welding

next to each other. In Figure 16 the part to the top of the im- age being a LSND part and the one in the lower half being a conventionally welded part. The levels of distortion seen in the part are apparent to the naked eye, and therefore it is straightforward to do a quick visual assessment of the parts to compare the differences in distortion. Bending of the part occurs along the length of the com- ponent when moving towards the centre from the stiffer outside sections. In addition there was some twist occurring in the parts. It could be seen that the GMAW-welded part exhibits a significantly higher level of bow and twist than the LSND part. The difference in twist was hard to accurately quantify using simple measurements; however the reduc- tion in bowing could be estimated to be reduced by around 3.0 mm, with a peak bow on the conventional part being in the region of 10 mm. The majority of the distortion occurred while the part cooled after it was removed from the fixture. It should also be remembered that the level of distortion occurring in the con- ventional part, before removal fromthe fixtureandduringweld- ing, was such that some of the welds were produced off-seam. This was not the case when welding using the LSND process. Discussion and conclusions A prototype robot mounted DC-LSND GMAW system with a cooling head andwelding torchon the same side of thewelded joint has been integrated and demonstrated successfully in an industrial facility. Welds have been produced with acceptable weld quality withnosignificantmetallurgical discrepancieswhencompared to standard samples. Distortion has been reduced by up to 40%-50%on simple components. The systemhas been shown to successfully overcome any disruption of the welding arc and GMAW process when the cooling is applied to the same side of the weld joint with the cooling delivery system close behind thewelding torch. Although further work is required to optimise the configuration anddesign to suitmore generalised complex 3D weld profiles. Repeatability of the welding results on butt welds and simple profile joints and sections has been demonstrated. The process has been successfully applied and demonstrated on a number of real component example geometries, although further refinement and development of the system would be required for full production and acceptability in a general industrial manufacturing environment. Acknowledgements The author acknowledges the support of all project partners involved in “Creating Opportunities for the Manufacture of Lightweight Components” MALCO (TSB Project No. TP/TP/ DSM/6/1/16131); TWI; Gestamp Tallent; BOC Gases (Linde); Isotek Electronics; Dytel Technologies; Comau Estill (UK); Bent- ley Motors; Komatsu (UK); and the University of Strathclyde. The author andall project partners alsogratefully acknowl- edge the financial support and assistance in the part funding of the MALCO project received from The Technology Strategy Board/Innovate UK. Copyright © 2015 International Institute of Welding: Originally published in the proceedings of the IIW International Conference of 2015, Helsinki, Finland: High-Strength Materials – Challenges and Applications.

Figure 15: A comparison of the effect of distortion on repeatability and weld quality on typical LSND (top) and conventional GMAW welded (bottom) beam parts manufactured in the trial. It can be seen that the induced distortion in the conventionally welded part causes the weld path to drift off the seam.

the joint to prevent disruption of the arc. The orientation of the torch and cooling head is shown in Figure 14, illustrating the part being welded using the robotic LSNDwelding system developed. The second image in this figure clearly shows that the seal is working effectively to contain the CO 2 and to allow through head extraction of the gas after sublimation of the CO 2 snow cooling to the hot surface of the weld bead. Visual inspection of the trial parts after welding fromboth the LSND process and the standard GMAW process revealed significant differences in the distortion patterns. This exami- nation, as shown in Figure 15, reveals that the distortion oc- curring in the standard weld part has caused the assembly to move relative to the pre-programmed robotic weld path, and effectively the weld is off seam. This effect begins to appear fromabout half way along this weld and gradually moves further off toward the end of the weld (the point closest to the camera). This is not the casewith the LSND weld, which results in a stronger, more consistent and better quality weld It should be noted that the holding fixture did have a small lateral clearance to allow the parts to be assembled, which made movement possible. It was designed with some clear- ance to ensure that any distortion would not cause the part to become stuck in the fixture. The differing effects of the two welding processes were also evident in the magnitude of the heat-affected zones be- ing displayed on the surface of the parts. It was clear to see the material phase-change regions (HAZ) due to the effects of the welding on the part and these were considerably smaller on the LSND part than the standard GMAW welded part. This can be seen in Figure 16, where the two parts are compared Figure 16: A comparison of the visible HAZ on typical LSND (top) and conventional MAG welded (bottom) beam parts manufactured in the trial.

November 2015

AFRICAN FUSION