In the welding process, the metal undergoes heating and melting or reaches a thermoplastic state, followed by solidification and continuous cooling as a result of heat input and transmission. This is known as the thermal welding process.
The thermal welding process plays a critical role in the entire welding process, impacting both welding quality and productivity. This is achieved through the following aspects:
- The heat applied to the welded metal affects the shape and size of the molten pool, determining its size and distribution.
- The heat and duration of the weld pool have a direct impact on the metallurgical reactions that occur in the weld pool.
- Changes in heating and cooling parameters during welding can affect the solidification process and phase transformation of the molten metal, as well as the transformation of the microstructure of the heat-affected zone.
Therefore, the microstructure and properties of the weld and the heat-affected zone also depend on the effect of heat.
- Unequal heating and cooling of welded parts can lead to an uneven state of stress, causing varying degrees of stress, deformation and strain.
- The heat of welding can cause the occurrence of various forms of cracks and other metallurgical defects due to the joint influence of metallurgy, stress factors and the structure of the welded metal.
- The input heat and efficiency of the welding process determine the melting speed of the base metal and electrode (welding wire), affecting welding productivity.
Characteristics of the thermal welding process
The thermal welding process is much more complex than normal heat treatment conditions and has the following four main characteristics:
The. Localized concentration of the thermal welding process
During welding, the weldment as a whole is not heated, but only the area close to the direct heating point. This leads to extremely uneven heating and cooling.
B. Welding heat source mobility
During the welding process, the heat source moves relative to the welding, constantly changing the heated area. As the welding heat source approaches a point in the weld, the temperature increases rapidly and cools as the heat source moves away.
w. Instantaneous Nature of the Thermal Welding Process
Under the influence of the highly concentrated heat source, the heating speed is fast (more than 1,500℃/s in the case of arc welding), which means that a large amount of thermal energy is transferred to the welding in a very short time. short. The cooling rate is also high due to the location of the heating and the movement of the heat source.
d. Heat transfer process in welding
The liquid metal in the welding pool is in a state of strong movement. Inside the weld pool, heat transfer occurs mainly through fluid convection, while outside the weld pool, it is mainly solid heat conduction with additional convective heat transfer and radiative heat transfer.
As a result, the thermal welding process involves multiple heat transfer modes, making it a complex heat transfer problem.
Wrap it up
The characteristics mentioned above make the issue of heat transfer in welding incredibly complex. Despite this, it is crucial that welding workers understand its basic principles and how it is affected by various process parameters, as this has a significant impact on controlling welding quality and improving productivity.
