Problems in the welding process of thin tube stainless steel

Welding thin tubes to reducer joints with relatively large diameter and wall thickness has the following problems in the past:

11 Leakage rate does not meet the requirements: After welding, the leakage rate index of the workpiece is 10Pam/s, which does not meet the requirements of 10am/s. 1.2 The diameter does not meet the requirements: Due to the poor thermal conductivity of stainless steel, local high temperature during the pipe welding process will cause The severe thermal expansion of the welding part, coupled with the high temperature melting of the welding part, is very easy to collapse and block the tube when the thin tube is connected, and it cannot meet the requirement of diameter greater than 50%

1.3 Welding parameters are not easy to set: the size of the two workpieces is very different, and it is difficult to achieve good fusion and connection. When setting suitable welding parameters for thin pipes, larger reducing joints will have unfused defects during the welding process; when setting the welding parameters of penetration reducing joints, thin pipes are likely to be welded through, collapse and blockage Tube problem 14 Difficulty in operation: In the process of welding thin tubes, changes in fine techniques and changes in welding parameters will obviously affect the welding quality. 1.5 Back gas protection is difficult: tungsten hydrogen arc welding is used to weld stainless steel, especially austenitic stainless steel , The back of the welded pipe should be protected by back gas, otherwise serious oxidation will occur, which will affect the weld formation and weld quality. Due to the small diameter of the pipe, back gas protection is not easy.

2 Improvement measures of welding process

In order to solve the technical problems existing in the argon arc welding of the thin-diameter thin wall stainless steel and the process door joints to meet the welding requirements, this paper optimizes the design of the welding structure and proposes the following measures: 21 Equipment requirements: due to the small diameter and thin wall thickness To use smaller welding parameters, the arc welding machine used requires high brazing performance, welding current with increasing and attenuating performance, welding current with good arc stabilization performance at low current and other basic functions 2.2 Cleaning before welding: The argon arc welding (T1G) welding process is extremely sensitive to pollution, especially the dirt in the welded pipe has a significant impact on the welding products with higher requirements. Therefore, the oil, dirt, and rust stains on the surface of the welded pipe, the internal weld area and the welding wire must be cleaned before welding.

2.3 Optimal design of welded joint structure The originally designed welded structure is shown in Figure 1, which is the joint form of butt-shaped circular fillet weld. The small tube body is

①2mmx0.5mm, the joint is ①6mmx2mm. Due to the difference in size between the two during the welding process, it is difficult to achieve good fusion and connection; the wall thickness of the small pipe is only 05mm, and it is easy to collapse and block the pipe during welding, even if it is welded It is not easy to meet the higher diameter requirements successfully; if the pipe is too thin, it is inconvenient to protect the inside of the pipe with argon gas, and the weld will be oxidized; the uneven manual filling of the welding wire will also affect the quality of the weld.