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High-performance welding process for thick sheets

OTC DAIHEN EUROPE GmbH is presenting a new automated welding process called D-Arc, for the first time in the Welding and Cutting exhibition in Germany. The focus is on the machining of metal sheets of up to a maximum of 19 mm (3/4 inch) thickness, which usually go through a complex seam preparation before the welding process. In order to produce a suitable V-seam, the respective workpiece must be milled or whetted before the automated welding process, which takes some time to prepare


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Figure: OTC’s coordinated total solution for the D-Arc process, consisting of Welding machine Welbee DPS, robot FD-V20, torch type DTWH 6500 S, DF-PL and DF-PS wire-feed conveying systems and FD-11 robot control unit.


The established welding process requires several automated welding passes to fill the V-seam, starting from the root over several layers and - depending on the desired filling pattern (keyword: ‘caterpillars’). In all cases, the uniform order for robotic technology plays an important role.


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Figure: Example of conventional multi-layer welding; here CO2, 1.6 mm solid wire, 300 A, 30 V, welding speed 30 cm/min, 6 layers, and gap area: 123.5 mm2, warping: 7°


The tandem welding process is usually used for this purpose, in order to obtain the desired result via a double-wire system. This is a tedious process, which also works exclusively with straight seam sections, because for physical reasons, the narrower curves can break the rear arc and cannot keep the track.


The D-Arc welding process from OTC provides visible improvements to the result, since the seam preparation work can be reduced to a minimum. According to the manufacturer, it suffices to merely chamfer the workpieces unilaterally.


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Figure: The new D-Arc process from OTC allows single-layer welding of thick metal sheets with high efficiency. D-Arc uses the combination of a rotating and oscillating arc to produce a high material input with a controlled heat input, without the need for a large seam preparation.


The decisive difference compared to conventional welding processes is that the D-Arc process requires a single automated welding pass to fill the seam. In addition to the enormous time advantage, the operator saves significant material here because, no pronounced V-seam needs to be filled. Furthermore, the entire process time is considerably shorter.


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Figure: Example of the D-Arc welding process; CO2, 1.6 mm solid wire, 650 A, 45 V, welding speed of 30 cm / min, only 1 layer, gap area: 38.5 mm2, warping: 1 °, optimal root formation without counter-welding.


The D-Arc process is so successful because of the numerous prerequisites for the welding of thick metal sheets: while the classical arc burns above the component in order to melt the material, the arc in the D-Arc process is burned directly into the melt. This is made possible by the high-speed change of rotational and pulse arc, at a frequency of about 100 hertz.


With its own new power source, Welbee DPS, OTC has fulfilled the process-relevant requirements for thick plate welding. This equally includes corresponding OTC torch equipment which can withstand the required current of at least 600 amperes. The suitable OTC torch even withstands up to 1,000 amperes.


Since large amounts of wire are still required during the welding process of thick sheets, wire conveying speeds of up to 100 m/minute are required, in order to perfectly perform the welding task within one working cycle. From a qualitative point of view, the seam result via D-Arc is comparable to a sub-Powder seam. 



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Figure: D-Arc welding pattern