Hot wire TIG welding is a high-quality, efficient and energy-saving welding process that was developed based on traditional TIG welding in 1956.
The basic principle is to heat the welding wire to a certain preheating temperature before feeding it into the weld pool, ultimately achieving the goal of efficient and high-speed welding.
Characteristics and classifications of hot wire TIG welding
Through the combined effects of several factors, such as the purification of the surface of the welding wire by residual heat, the stirring of the molten pool by residual heat current, and the effect of the magnetic field of the preheating current on the shape of the welding arc, the quality of the weld seam is improved.
From the perspective of the heat input of the welding seam, the energy for preheating the welding wire and the energy for the welding arc are controlled independently.
Therefore, the increase in welding deposition speed is not directly related to the increase in heat input, which means that the melting speed of the welding wire can be increased without increasing the heat input under the condition of maintaining the same heat input.
Under the same current, the welding speed can be increased by more than two times.
Compared with TIG welding, hot wire TIG welding significantly increases the deposition and welding speed, which is suitable for welding medium thickness welding structures, while having the characteristics of high-quality welds in welding TIG.
Compared with MIG welding, the deposition speed is not significantly different, but the wire feed speed of hot wire TIG welding is independent of the welding current, which allows better control of weld formation.
For open slot welds, sidewall fusion is much better than MIG welding.
Many specific hot wire TIG welding methods have been developed around the method of heating the welding wire, further improving its deposition efficiency and expanding its range of applicability. They are mainly classified as shown in Figure 1.
Figure 1: Main classifications of hot wire TIG welding methods.
High Frequency Induction Hot Wire TIG Welding of Aluminum Alloy
Hot wire TIG welding methods existing at home and abroad use a certain current in the welding wire to heat it by the resistance generated by the welding wire itself. However, this method has some shortcomings:
First, the temperature of the welding wire is difficult to control, which affects the welding efficiency and quality.
Secondly, there is a hot wire current circuit between the workpiece and the welding wire adjacent to the main welding circuit. The welding arc is affected by the magnetic Lorentz force of this circuit, causing magnetic strike, which has an adverse effect on the shape of the weld and the precise positioning of the arc. In severe cases, it can even prevent welding.
Third, for low-resistance welding wires such as Al and aluminum alloys, the resistance heating efficiency is low, making it difficult to reach the appropriate temperature.
Therefore, traditional hot wire TIG welding is not suitable for welding alloys such as Al and Cu.
Compared with traditional hot wire TIG welding, high frequency induction heating hot wire TIG welding has the following characteristics:
- High wire heating efficiency and fast heating speed.
- Suitable for heating various metal materials of welding wire, especially low resistance welding wire.
- There is no interference from the magnetic field of the bypass current, eliminating the phenomenon of magnetic strike.
- The temperature of the welding wire can be precisely controlled by controlling the high-frequency output current. By changing the output oscillation frequency and utilizing the high-frequency induction skin effect, the depth of induction heating can be controlled.
Study on TIG welding with hot wire arc:
- Arc hot wire preheating temperature analysis
Using the TIG arc as a heat source, the welding wire about to enter the weld pool is directly heated, as shown in Figure 2.
The main factors affecting the temperature of the welding wire are the hot wire arc current I, the wire feeding speed V, the surface heat dissipation of the welding wire Qf and the radiation heat transfer of the welding arc on welding wire Qt.
Among them, the first two are the main influencing factors. The influence of Qt still exists in the case of no hot wire welding, so it can be omitted when compared, and Qf can be attributed to the effective heating effect of the arc η.
- Influence of hot wire arc current and wire feed speed
Figure 3 shows the measurement principle, using energy storage spot welding to weld the thermocouple to the welding wire and fix it on the bench. Under the motor drive, the welding gun moves at a certain speed to simulate wire feeding.
The electrical signal generated by the thermocouple is connected to a multi-channel temperature measuring device, and the data obtained is then transmitted to a computer for storage and analysis.
As shown in Figure 4, the temperature increases sharply at a certain time and then slowly decreases. The temperature at the hottest point in the temperature field where the heat source moves (4) can be considered as the temperature when the arc passes the thermocouple.
The temperature of the welding wire as it enters the weld pool is obtained by combining the wire feed speed, the distance between the arc heating point and the weld pool and using interpolation.
As shown in Figure 5, when the wire feeding speed is constant, the temperature rise increases linearly with the current, and its slope is determined by the heating efficiency η; When the hot wire arc current is constant, the temperature rise decreases according to a hyperbolic rule with the wire feeding speed, and the shape of the hyperbola is determined by the heating efficiency η.
The heating efficiency η of different wire feed speeds can be calculated from the slope of the curve.
- Conclusion
(1) The temperature rise of the welding wire using the hot wire arc method is linearly related to the hot wire arc current and inversely proportional to the wire feeding speed.
(2) Arc hot wire TIG welding can significantly improve the efficiency of TIG welding.
