There exists a wide number of welding processes, ranging from simple processes to newer, high-tech processes.
Choosing the suitable welding process depends on the particular job one is working on and what is being welded; base material and thickness, heat-input limits, joint type, the accuracy of plate preparation, quality and capacity requirements, welding position, working environment, and so on.
Jari Tervolin, PEMA Welding Engineer with extensive experience in the field, discusses MAG welding and LHAW welding, two nowadays commonly used welding processes in the shipbuilding industry.
MAG welding process suitable for shipyards
MAG welding, short for metal active gas welding, is a welding process where active gas is reacting with the molten metal. It’s a commonly used welding process, thanks to its versatility, speed, and ease of adapting the process to automation. MAG welding enables flexible process: welding can be done in all welding positions when the right consumable has been selected, wire feed speed is constant and there exists a wide range of adjustments for welding parameters. As an example, when solid wire can be used as consumable, there is no need for removing a slag.
MAG welding is especially suitable for stiffener welding, T-beam welding and robotic welding, enabling straight panels and T-beams. Robotic MAG welding ensures a more stable and even welding quality. Furthermore, MAG welding with robots enables higher output welding and arc-on time as robots are not exposed to heat like manual laborers, nor do they feel the physical strain.
MAG welding process is suitable for example for stiffener welding.
“MAG welding enables flexible process: welding can be done in all welding positions when the right consumable has been selected, wire feed speed is constant and there exists a wide range of adjustments for welding parameters.”
Straight T-beams and panels with induction preheating
There have been several new product developments within the past years to use induction preheating to optimize the circumstances for fillet welding. Pemamek’s induction preheating is monitored by an in-house developed control system.
According to Tervolin, induction preheating is mainly used in MAG and tandem-MAG processes for T-beam welding and stiffener welding. In stiffener welding, the panel, and in T-beam welding the flange, is being preheated from underneath to compensate for angular deformations. During the welding process of the T-beam, induction is also preheating the web on both sides to compensate for the longitudinal bending of the T-beam, allowing it to maintain straight.
“Induction preheating enables welding with high speed, smoothening the process, minimizing angular deformations, and having straight panels and T-beams. We can also lengthen the cooling time of the weld, and avoid its hardening”, Tervolin says.
“The simulation calculates the deformations based on the dimensions of flange and web, considers whether the workpiece has holes or not, and then adjusts the values suitable for induction preheating. It automatically calculates the optimal induction power depending on the variables of the workpiece”, Tervolin explains.
Induction preheating enables straight T-beams.
Pemamek’s induction preheating is monitored by an in-house developed control system.
LHAW welding combines laser and MAG welding, bringing together the benefits of each process.
LHAW welding becoming a trend in the shipbuilding industry
LHAW welding, short for laser hybrid arc welding, combines laser and MAG welding, combining the benefits of each process to support one another. LHAW welding has become more commonly used within the past decade especially among big cruise ship manufacturers: many are shifting, or have already shifted, towards using the LHAW welding process in panel manufacturing. The same trend can be seen among naval shipyards as well as the interest in the LHAW welding process is growing rapidly, and some have already started using LHAW welding processes in panel manufacturing.
According to Tervolin, there are several reasons why LHAW welding is more suitable in panel manufacturing than SAW welding, submerged-arc welding, especially in butt welding; lower heat-input together with more symmetric welds reduces the number of deformations and enables straight panels and better impact toughness. Furthermore, the high travel speed together with material handling, efficient mechanization and control system enables good productivity. Tervolin continues:
“LHAW welding is especially beneficial in shipyards, as there is no need to correct or straighten panels afterward. LHAW welding enables rapid welding of straight panels”.