Time and Twin welding
Last but not least, new materials and applications have opened up new performance standards and a wide range of applications for the MIG/MAG welding process, as has the increasing use of technically mature microelectronics and digital technology. Jobs with particular welding power requirements however call for a specialised variant of MIG/MAG welding: “TIME” welding. For very long weld seams with a large cross-section and a high deposition rate, the TIME process is currently the most economical solution.
In contrast to conventional MIG/MAG welding, the TIME process has a longer, free wire tip in the welding torch (referred to as greater “stick-out”), as well as a faster wire speed and modified shielding gases. By definition, high-performance welding processes have one or more solid wires with a 1.0 mm or 1.2 mm diameter, with a wire feed speed of more than 15 m/min. Processes with a greater wire diameter or with flux-cored wires also count among the high-performance welding processes if the deposition rate is more than 8 kg/h.
The TIME high-performance process can be carried out as manual, mechanised or automated. Efficient power source technology contributes to successful application of this process, as do electrodes with good conveying properties and shielding gases tailored to the particular case. The most powerful TIME variant has two wires that melt simultaneously in one weld pool. In this “TimeTwin” process, the contact tubes in the special welding torch are insulated from each other, so that the material transfer for each filler wire is selectively controlled. The result is doubled or tripled welding speed compared to MIG/MAG welding, with the best possible quality and virtually no welding spatter.
Shielding gases used include inert gases with an active gas component. This normally means a mixture of gases, the main component being argon, and also incorporating helium, carbon dioxide and oxygen. Tests have shown that for many applications, excluding one of these components brings optimum results. However, argon is always the main component. In many cases, helium contributes significantly to speeding up welding. The reason for this is the very hot TIME arc on the one hand, and the high heat conductivity of helium on the other, which also contributes to optimum joining of rising edges of the weld seam. The right amounts of carbon dioxide and oxygen to use also depend on the application.
In principle, the power source technology corresponds to the MIG/MAG application, as do the wire feed and welding torches. In design and performance, the components are specifically adapted to the requirements of TIME high-performance welding. Therefore, time manual welding torches already have an adjustable contact tube for stick-out control and a dual circuit cooling system. The latter cools the gas nozzle directly and at full power also ensures a high duty cycle, as well as making detachment of welding spatter easier.
A special feature of the TimeTwin welding process is the separate welding potential, each of the two filler wires with its own power source. A synchronisation unit on the power sources ensures that material transfer on the filler wires occurs at the same time. Wire movement and welding current curves are separate for each arc.
TIME and TimeTwin high-performance welding is primarily applied in machine construction, steel engineering, crane construction, shipbuilding, vehicle manufacture and boiler manufacturing. Materials in those applications include unalloyed steels, low-alloy steels, unalloyed structural steels, fine-grained structural steels and steels resistant to low temperatures. The process offers a whole range of benefits. The deposition rate is more than 10 kg/h. The helium component of the shielding gas produces a deep fusion penetration and provides dynamic, very strong weld seams. Indicators of good weld properties are the clean seam surfaces, flush weld toes, and the marked decrease in welding spatter. There is no need for any rework. The suitability of high-performance welding processes for all sheet thicknesses is proof of the high degree of flexibility they offer. Even difficult welding positions do not require a reduced deposition rate, and the moderate heat application keeps component distortion to a minimum.
In contrast to TIME single-wire welding, TimeTwin welding is restricted to mechanised and automated applications due to its two filler wires. Particularly with pulsed arcs, droplet detachment from the two filler wires occurs without any reciprocal influence allowing the welding of even aluminium alloys. The benefit of the two-wire process as opposed to the single-wire process is in improved control of the weld pool. This allows a substantially higher energy input, resulting in an increase in the welding speed. Equally beneficial is the delayed activity of the second arc, producing the effect of increased outgassing TIME and therefore significantly reduced pore formation.
TIMEand TimeTwin high-performance welding are exceptionally well-suited to the increased welding power and burn-off rate. Increased flexibility means that the user can weld reproducible, low-spatter weld seams at very high welding speeds. The high-performance welding processes is suitable for use mainly in steel-processing sectors with large, welding-intensive components.