TIG Hot Wire Welding Technology-A More Efficient and Less Cost Technology for Pipe Spool Fabrication

2017-01-24 TIG Hot Wire Welding Technology-A More Efficient and Less Cost Technology for Pipe Spool Fabrication

TIG welding is Inert Gas (pure Ar) shielded welding technology, which is widely used in welding of high-end industrial sector since its stable arc and high quality welding joint. TIG welding is also widely used in NAEC pipe spool fabrication solution. However, the limited electrode current-carrying capacity of TIG welding result in the restricted arc power, the lack of weld penetration, the low welding speed and production efficiency.

Over the years, many studies have focused on how to improve TIG welding efficiency. Therefore, the hot wire TIG emerged as required in 1956, which is a new welding process with high quality, high efficiency and low energy consumption based on the traditional TIG welding. The basic principle is that the welding wire is heated to a certain temperature before into the weld pool, and then realize high speed and high efficiency welding. The study found that wire heating can not only improve the welding speed, but also improve deposition efficiency, adjust the weld heat input, accelerate the filler wire melting speed, reduce the matrix dilution ration, expand the traditional TIG welding process applicability, and has high economic value.

Japan Papua Hitachi Industrial Company and Hiroshima University professor K. Shinozaki joint research show that hot wire TIG welding wire temperature distribution has important influence on welding appearance and quality. Precise control of the wire temperature distribution is the key to ensure the hot wire TIG welding quality. There are many factors affecting the TIG welding wire temperature, which increase the research difficulties. And also at present, research in this area is rare and application research about hot wire TIG used in pipe spool fabrication is much less.

So far, there are three hot wire TIG welding methods at home and abroad, which are resistance heating mode, high frequency induction heating mode and arc heating mode. NAEC adopts new type wire heating method depending on hot wire TIG principle and our own welding machine, which is new copper coil heating device, equipped with temperature closed-loop feedback control system to maintain the wire heating device at a constant temperature and heat the wire continuously. The stable wire feed rate can ensure the constant heating temperature. Wire heating device as shown in Picture 1.

Copper Coil Heating Device

Picture 1 Wire Heating Device

Based on the above wire heating device, NAEC R&D team do experiments to research the change rule of the wire temperature out of the conductive tip under different wire feeding speed and different heating temperature. And the conclusion is that wire feeding speed and heating temperature is a linear relationship, and also the wire heating temperature can be maintained around 220℃.

On this basis, NAEC research the weld surface forming(in the same process specification) under the different conditions of hot wire and cold wire. In the whole welding process, the hot wire TIG has better fusion and the weld seam has larger width after welding. Weld forming as shown in Picture 2, Weld size as shown in Table 1.

Picture 2 Weld Forming

Table 1 Weld Size

Through a series of experiment, NAEC draw up hot wire TIG filling process specification: wire feed speed is 2500-2800mm/min, welding current is 300A, welding voltage is 13.9-14.4V, welding speed is 160mm/min, swing frequency is 160T/min (when the bevel is narrow, we can choose not to swing in order to promote weld metal fusion); hot wire TIG cap pass specification: wire feed rate is 3200-3500 mm/min, welding current is 300A, welding voltage is 14.3-14.7V, welding speed is 160mm/min, swing frequency is 160T/min.

Based on the above hot wire TIG process specification, it can obtain better sidewall fusion and weld forming (weld forming as shown in picture 3), and also can improve metal deposition efficiency. Compared with cold wire TIG, the hot wire TIG can increase the metal deposition efficiency by 56%~71%.

Picture3 High Swing Frequency Hot Wire TIG Weld Forming

Hot wire TIG welding process effectively improve the TIG welding efficiency , not only improve NAEC equipment automation rate, but also decrease our clients' production cost.