Continuous technical progress is the principle of HEXA-METAL Kft in Hungary, under the leadership of Managing Director Sándor Katona and Technical Director Imre Hüse. Since its foundation in the 1990s, the company has focussed on consistent technical development and has experienced outstanding growth.

The company will continue to follow this principle in the future, and HEXA-METAL Kft is one of the first companies to sign up for the REHM GmbH u. Co. KG welding technology partner programme. As an experienced specialist in this sector, the company is open to new technical processes and is interested in testing the innovative solutions offered by the REHM partner programme for complex welding work.

One of the many tasks is to weld seams inside parts of complex machine constructions that are difficult to access, economically and in accordance with quality requirements. This is a complex matter. The base frame of the 16 m long drilling rig in Fig. 1 presents the welders with serious difficulties due to the welding of vertical and horizontal fillet welds in the inner, semi-enclosed space and the narrow access possibilities.

The vertical, 300 mm long fillet welds shown in Fig. 2 at the joint of the inner stiffeners and the side wall were previously welded in the PF position from bottom to top in accordance with the regulations. Welding in the vertical position is necessary because the rotation of the structure is difficult to loosen in this production phase.

Due to the use of traditional welding equipment and the low current values used in the vertical position, work was carried out in the power range of the short/mixed arc. The power range used, together with the material transition and the extremely heavy welding position, led to considerable spatter. The welding speed and therefore also the productivity was very low. As a result of the strenuous, uncomfortable position and the difficult accessibility, the weld seams are not homogeneous, which is unfortunately usually the case in such instances. Removing the spatter and repairing the seam defects also requires enormous effort from the employees, as this work is difficult and very time-consuming in the narrow areas and due to the small holes.

Zur Erleichterung der Arbeit, der Verbesserung der Qualität und der Erhöhung der Produktivität haben wir das Gerät REHM MEGA.PULS® FOCUS eingesetzt. Bei der Aufgabe sind wir von folgenden Merkmalen ausgegangen:

• Durch den fokussierten Lichtbogen, gepaart mit der niedrigen Wärmezufuhr kann auch in der senkrecht nach unten gerichteten Schweißposition (PG) eine sichere Einschmelzung erreicht werden, wobei das Schweißgut nicht herunterfließt 
• Dank des extrem kurzen Lichtbogens (der Lichtbogen brennt tief in der Schmelze) kann der Vorgang hervorragend überwacht werden, der Schweißer sieht genau, was im Schmelzgut passiert
• Bei diesem Verfahren hat die Brennerhaltung keinen Einfluss auf das Ergebnis 
• Der Lichtbogen ist auch bei unsicherer Brennerführung äußerst stabil
• Das Spritzen ist auch bei unsicherer Brennerführung nur geringfügig​

After the technological tests had also convinced the experts at HEXA-METAL Kft. and the fulfilment of quality expectations was assured, the ‘wonder weapon’ was used immediately.  Thanks to the controlled droplet transfer, a considerable improvement was observed in the spattering, so that the time required for reworking was also significantly reduced. The stable arc provided by the FOCUS.PULS process and the reliable fusion have meant that the vertical fillet welds can now be welded in the PG position, i.e. from top to bottom, instead of the previous PF position.

On the one hand, this is also more convenient for the welders and, on the other, it significantly reduces the production time of the 300 mm long fillet welds. In the past, a current of 150 A and a wire feed speed of 3.2 m/min were used for the short arc in the PF position. Today, however, a current of 200 A and a wire feed speed of 8 m/min are used for the same weld seams with the FOCUS.PULS process. Measurements of the production time of fillet welds produced with both variants showed that the production time when using the conventional technology was around 140 s, whereas it could be reduced to 30-35 s with the new process and the modified welding position. This represents a time reduction of 75 % and therefore an enormous increase in productivity.

In the case of a 300 mm long fillet weld, the time saving was 10 s, but on the 16 m long construction there are 25 internal stiffeners with 2 fillet welds on each side. Therefore, the total time saving - for these vertical fillet welds alone - amounts to almost 3 hours of the main welding time. Thanks to this three-hour time saving at a volume flow rate of 16 l/min, 2880 litres less shielding gas was used for welding the stiffeners.

The time required to clean weld seams produced using the traditional method is around 10 minutes per metre of weld seam. Due to the fact that the use of the FOCUS.PULS process results in less spatter, this time is reduced to about 3 minutes per metre of weld, resulting in a saving of about 70%. The total length of the fillet welds of the stiffeners is 30 metres, so the reduced cleaning time when using the new process is around 3.5 hours.

The use of the modern FOCUS.PULS process and the change in welding position result in the following advantages when welding vertical weld seams:

• More comfortable welding position
• Reliable fusion
• More homogeneous and beautiful weld seam surface
• Significantly shorter arc times → Significant time and cost savings
• Less spatter → Significant savings in post-processing
• Less shielding gas consumption
• Less deformation of the construction

Fig. 3 and 4 shows a comparison of the fillet welds made using the traditional and FOCUS.PULS methods directly on the girder of the bridge crane. With the FOCUS.PULS method, the seam is beautiful with reliable fusion despite the constrained position. Despite the unusually high wire feed rate in the constrained position (9.8 m/min), the arc and the weld metal can be well controlled. The reinforcement plates of the beam are already produced using the FOCUS.PULS process after the successful test. 

The experience gained in connection with the REHM partner programme shows that the right choice of technology and tools adapted to the product and the welding task is extremely important for the work process.  The possibilities hidden in the FOCUS.PULS process variant can offer solutions that cannot be realised with the familiar MIG/MAG processes. It is important to familiarise yourself with new technologies because they can make the difference between ‘possible’ and ‘impossible’.