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High speed welding without the drawbacks

26 July 2016

There are several ways in which manufacturers seeking to improve welding productivity can boost throughput. However, unless the process is considered in detail by someone who truly understands welding, there is a risk that higher throughout could come at a cost, as ESAB explains

 

The 'cost' could be reduced joint integrity due to inadequate penetration, increased post-weld labour to correct distortion and/or remove spatter, or more gouging and rework to remove defects.

Mechanised and robotic welding offer significant productivity gains where the joint design and volumes justify the expenditure, but often the full potential is not realised because the welding process itself has not been optimised. While tandem welding offers significant benefits for some applications requiring high productivity, this welding process is more complex and does not suit all manufacturers.

ESAB offers equipment for mechanised and robotic welding, as well as tandem welding processes. For customers who want to achieve a combination of high welding speed, excellent joint integrity, minimal distortion and spatter, and process control that is simpler than that required for tandem welding, the company offers the SAT (Swift Arc Transfer) process. SAT is a development of the rotational arc welding process. SAT welding benefits from an excellent transfer rate that results in higher deposition than can be achieved by conventional spray arc or pulse arc welding.

SAT delivers 80% of the benefits of tandem welding for welding both thick and thin plate but in a simpler, more economical way. Importantly, the SAT process is able to achieve very high welding travel speeds often double that of conventional pulse welding while maintaining good penetration. This is a benefit not seen in most competitive high speed gas metal arc welding processes.

ESAB has developed SAT welding to be more manageable than previous attempts at rotational arc welding and, therefore, simpler to implement and more practical for use in a variety of production environments. The result is good penetration with a low risk of undercut, even at high travel speeds, for fillet welds and lap fillet welds in carbon steels typically 3 to 10mm thick (plates over 15mm thick can be welded); heat input is low, so distortion is reduced, and tight control over the welding process minimises spatter.

By using AristoRod non-copper-coated wires and ESAB’s True Arc Voltage technology that accurately monitors and controls the voltage at the welding tip, ESAB achieves effective arc control which, in turn, results in a more stable arc and the ability to maintain the required penetration, root fusion and steady metal transfer, even at high travel speeds. ESAB’s OK AristoRod non-copper-coated wires feature Advanced Surface Characteristics (ASC) and eliminate problems with copper flakes contaminating wire feeders, liners and torches, which contributes to smooth, trouble-free feeding and reduced maintenance even at the very high wire feed speeds used in SAT welding. AristoRod ASC wires are available in Marathon Pac bulk wire packaging (250 or 475kg) that reduces downtime because spools do not have to be changed frequently. 

Best results for SAT welding are achieved with wires of 0.9 to 1.0mm diameter and wire feed rates of up to 30m/min, with various standard shielding gases to choose from. As an example of the productivity that can be achieved, a 1.0mm wire fed at 25m/min with a welding current of 375A results in a deposition rate of 9.2kg/h for fillet welds in the PB position. With an excellent bead profile, little or no distortion, and only minimal spatter, the finished joint often needs no post-weld dressing or cleaning.

When implementing an SAT welding process, the user requires an inverter power source – for example, an Aristo Mig 5000iw – and Robofeed 3004w ELP encapsulated wire feeder, together with a U82 control unit featuring SAT synergic lines and ESAB’s SoftStart function that minimises spatter on startup. This set-up can either be applied to a new mechanised or robotic welding system, or retrofitted to existing equipment. Other factors that help to ease implementation are the use of common torch positions and a stickout length that is no different from normal.

Manufacturers considering implementing the SAT process will be interested in a set of comparative calculations prepared by ESAB, based on the welding of a car seat (see table). Compared with a standard MAG wire process, the SAT process with AristoRod wire reduces the cycle time from 121 to 90s (of which the welding times are 69 and 39s, respectively), hence the productivity increases from 30 to 40 pieces per hour. Taking into account other costs such as consumables, labour and depreciation, the unit cost reduces from €1.16 to €0.90 (a 22.4% saving) and the annual output rises from 120,285 seats to 159,975 seats, which is an increase of 33%.

Wire                                                 AristoRod SAT™             Standard MAG wire

Cycle times

Pieces/hour

Welding time

91 s

40

39 s

121 s

30

69 s

Consumed wire kg/piece

Price of wire €/kg

Cost weld material/piece €

Gas costs per piece €

Operator costs per piece €

Depreciation added piece €

0.04

1.50

0.06

0.05

0.63

0.16

0.04

1.40

0.06

0.06

0.83

0.22

Total costs/piece

0.90

1.16

Annual production pieces

159,975

120,285

 
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