FastROOT - Kemppi

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” Keeps the arc 4 INNOVATION stable and the welding process easy to control. Figure 2. The current waveform of the FastROOT process when the filler drop is transmitted to the weld pool. The cycle is comprised of the arc and short circuit periods. Kemppi ProNews 2 • 2006 FastROOT – a new welding process for root pass and thin sheet welding In September 2005, Kemppi introduced a new welding process, FastROOT, in a welding fair in Essen, Germany. FastROOT is a MIG/MAG root pass and thin sheet welding process suitable for structural and stainless steels, which facilitates and speeds up the welder’s work. It allows for welding in all positions, resulting in the desired penetration and spatter-free weld. Jyri Uusitalo, Welding Engineer, M.Sc. FastROOT is a modifi ed short-arc welding process, which provides better welding speed and productivity than in TIG welding. The FastROOT feature can be used in Kemppi’s FastMig Synergic product family. Need for developing a new root pass welding process Kemppi’s customers recently have shown increasing interest for developing root pass and thin sheet welding processes. The welding industry is looking strongly for means to improve welding productivity and quality, as the current methods used in root pass welding, manual metal arc welding, TIG welding and the traditional MIG/ MAG welding, are not methods dedicated to root pass welding alone. There are welding machines that utilise modifi ed MIG/MAG processes for root pass welding, but even they have their restrictions. Kemppi developed the FastROOT process in close collaboration with the welding industry and could thus take the development work forward at a fast pace, specifi cally based on the requirements of the manufacturing industry. Welded one side Layer of capping run Layer of filling run Roor reinforcement Face side Root of the weld Back of weld Capping run Fill up run Root run Toe of the weld Figure 1. The root pass is the first in-groove welding run in multiple-run welding. The root cap of the root pass is the root-side, one-face welding cap.
The FastROOT welding process The FastROOT welding process controls the power source’s current and voltage parameters digitally. The welding process monitors the short circuit and controls the correct timing of the fi ller droplet transmission from the fi ller wire into the weld pool. The operating principle of the FastROOT process is that two mutually different shapes are formed from the welding current. These shapes can be referred to as the short circuit and arc period upslope stages (see Figure 2). The FastROOT process is a modifi ed short arc process and should not be confused with pulse welding. In the fi rst upslope stage, the fi ller material is transmitted during the short circuit to the weld pool, while the power of the arc is suddenly increased during the second upslope stage and sustained at the desired level (see Figure 2). Before the fi rst upslope stage, there is a short current peak in the welding current during which the fi ller material wire contacts the weld pool. During the fi rst upslope stage, the rapid increase of the current to the desired level accomplishes a so-called pinch force, which allows the drop to detach from the tip of the fi ller wire. The detachment is ensured by slowly decreasing the current. Once the drop has been transmitted to the weld pool, the second current-rising stage begins and initiates the arc stage. The device control monitors the drop detachment moment throughout the arc. The correct timing in current decrease and increase guarantee a spatter-free pass-over from the short circuit to the open arc. The so-called second upslope stage shapes the weld pool and ensures suffi cient penetration in the root pass. These two upslope stages follow each other, after which the current is reduced to the desired base current level (see Figure 2). The specifi ed base current level ensures that the next fi ller drop will be transmitted during the next short circuit. Rapid and correctly timed power source control combined with the correct shape of the current waveform in the process allow for non-interfered and spatter-free drop detachment and transmission into the weld pool. This keeps the arc stable and the welding process easy to control. Welding with the FastROOT process Kemppi’s FastMig Synergic welding devices allow the welder to adjust the wire feed, the level of the second upslope stage and the base current level. Figure 3 compares the effect of increasing base current level on the shape of the weld pass with stainless steel. Figure 4 compares the effect of the second upslope level on the shape of the weld pass. 25 60 Figure 3. Effect of the base current level on the shape of the weld pass. –9 0 +9 Figure 4. Effect of the shaping pulse level on the shape of the weld pass. Two techniques Starting point Starting point FastROOT FastROOT • Pulling MIG gun angle • Pulling 10°–15° MIG • Arc ”carries” weld pool gun angle • Vertical down welding • Overhead 5 to 6 technique straight angle MIG /MAG • Arc ”carries” weld pool • Vertical down welding • Straight 90° MIG gun angle technique • Vertical up welding technique • Oscillation: • Gun angle pointed to pipes – Flat / 12 Yes center – Vertical / 3 / 9 No • Oscillation: Yes – Overhead / 6 Yes • Oscillation delays on sides • In oscillation nodelays Starting point on sides Notice! For fill up and top pass use Synergic MIG with Solid or with Flux Cored Wire Figure 5. Two techniques for pipe welding. Oscillation Figure 6. Travel technique in root pass welding. Point where to focus the welding arc • In oscillation no delays on groove edges • Oscillation frequency is faster than in vertical up welding • Welding Power regulation according: – Opening (3,0–5,0 mm) – Root face (0–1,0 mm) – Travel speed / Oscillation wideness • Penetration increases when MIG gun is more in pulling angle Notice! Avoid too large oscillation, try to use max travel speed. Kemppi ProNews 2 • 2006 5
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FastROOT - Kemppi

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