5th of May ,2022

Causes and Solutions of Welding Deformation of Stainless Steel Sheets

The welding deformation of stainless steel sheet is closely related to the welding quality. This work has certain complexity and tediousness. In the welding of stainless steel sheets, the effect of different conditions such as sheet material, shape, size, etc. should be considered, and the welding process and welding parameters should be considered. In short, the deformation resistance of the stainless steel sheet itself and the critical load of the stainless steel sheet show a corresponding relationship with the parameters of the stainless steel sheet. For this reason, scientific design and appropriate manufacturing related quantities are conducive to the control and reduction of welding deformation.

Stainless steel sheet first appeared in the early part of last century. It has smooth surface, excellent plasticity, high toughness, high mechanical strength and good corrosion resistance. Its essence is alloy steel, but it is not completely rust-free. It mainly refers to a kind of steel sheet that is resistant to weak medium corrosion. Due to different uses, the corresponding steel sheet thicknesses are also different. According to industry regulations, those with a thickness in the range of 0.2-4mm are called stainless steel sheets. Regardless of the type of stainless steel sheet, there is a high possibility of deformation during welding. The root cause of this problem is poor resistance to bending, and the following factors are also included.

The main influencing factors of welding deformation

1. Cutting process

In stainless steel sheet, its welding deformation is closely related to stainless steel cutting. In specific production activities, the following cutting modes are usually used:

① Plasma cutting

At this stage, this method is the most commonly used, but this method is usually used in the related processing activities of non-standard workpieces, and has the characteristics of insignificant cutting deformation, fast cutting speed, and relatively neat edges of thin sheets.

② Electric welding and cutting

Through the stainless steel electrode, the current of the welding machine is controlled in the range of 120A, and the stainless steel is cut. This method is relatively extensive and lacks certain standardization, which may affect the welding quality, and is generally rarely used.

③ Laser cutting

In short, the cutting work is mainly carried out with the help of laser cutting technology. This kind of cutting is widely used in high-end product processing activities. It has the characteristics of relatively concentrated laser heat source, rapid cutting, and subtle heat effect. It can be seen that the application of this technology is less likely to cause deformation, which can promote subsequent welding. development of work.

2. Internal stress

From the structural level of the stainless steel sheet, it usually bears the following two loads:

① The mid-surface load, specifically the tension, compression and shear forces distributed in the mid-zone, and evenly distributed.

② The force at an angle of 90 degrees to the middle surface is called the lateral force, which is the fundamental cause of the bending of the stainless steel sheet.

3. Welding method

The welding method is the fundamental cause of welding deformation, and is closely related to the overall welding quality of the stainless steel sheet. It mainly includes the following two welding methods:

① Gas shielded welding

In the specific welding process, the shielding gas is sprayed smoothly through the spray gun to insulate the air and the welding part, so as to protect the motor end and the arc column area and other parts, so that the welding is in a stable state and provide a comprehensive guarantee for the welding quality. According to whether the electrode is dissolved or not, gas shielded welding can be divided into non-melting electrode protection and melting electrode protection, and the melting electrode protection can be further divided into inert protection and active protection. The above methods all belong to the category of argon arc welding, and have the following characteristics: the shielding gas can isolate nitrogen and oxygen, reduce the adverse interference to the arc, reduce the negative effect on the molten pool, and control the burning of alloy elements. The welding quality is significantly improved; the arc burns smoothly, accumulates a lot of heat, and the temperature of the arc column is high.

Stainless Steel Sheets

② Electrode arc welding

This type of welding is relatively common and easy to operate, mainly using various tools such as electric welding machines and electric welding tongs.

During the welding process, the electrode and the weldment are kept in contact to ignite the arc, and then the electrode is lifted to keep a certain distance from the weldment, and the welding process is carried out on top of this. This type of welding is mainly used in non-standard equipment welding activities, and belongs to manual welding. The welding current and welding operation changes involved in this link are all done manually. For the electrode, the thickness of the stainless steel sheet is usually not more than 1.5mm, the diameter of the electrode is 1.5mm, and the thickness of the stainless steel sheet is 3mm and the diameter of the electrode is 3.2mm. This welding is most commonly used, however, it can only be used in ordinary weldments.

4. Weld size

In the specific welding process, for the weldment, whether it is local high temperature heating or rapid cooling, there is the possibility of bad strain in the weld and its surroundings. Internal stress occurs in the stainless steel sheet, which causes the stainless steel sheet to deform.

5. Welding Assembly Procedure

In the specific welding process, the cumbersome assembly procedure will cause stress in the stainless steel sheet, resulting in deformation of the welded parts.

Basic Control Measures

Whether manual welding or automatic welding is used, practical experience in welding and welding process are all important. It can be seen that operators should not only pay attention to welding technology training and increase technology accumulation, but also choose scientific welding technology to continuously improve welding. quality.

1. Choose a reasonable cut

The cutting quality is related to the deformation of the weldment. Due to the high quality requirements of the company's products, manual cutting and plasma cutting should be avoided as much as possible in specific processing links. Select a laser cutting machine with small laser spot, high energy density and fast cutting speed as much as possible, which can promote the improvement of welding quality, and carry out grinding treatment for the cut stainless steel sheet to achieve normal welding after reaching the standard.

2. Select the appropriate fixture

Through long-term exploration, it is found that rigid fixed welding is more feasible. The welding fixture is used to stably fix the weldment, and then the welding process is performed on the weldment, so as to improve the rigidity of the combination, reduce the deformation tendency, and increase the rationality of the assembly size. If the thin sheet weld is too long, it can be placed on both ends of the weld independently by the pressing iron method, thereby reducing the deformation of the weld.

3. Effectively reduce welding deformation

① During welding

On the one hand, it minimizes the plastic compressive force in the heating process, which is mainly composed of pre-stretching force; on the other hand, it effectively increases the longitudinal tensile stress in the cooling process. The above requirements are usually achieved by limiting dynamic thermal stretching as well as static thermal stretching.

② After welding

The most commonly used method is to correct the concave-convex deformation formed around the stainless steel sheet by the multi-point heating method. In most cases, the diameter of the heating point needs to be controlled within 15mm, and the internal spacing of each heating point needs to refer to the deformation of the sheet. Keep it at 50-100mm. With the help of the method of eliminating residual stress after the completion of the welding operation to counteract the welding deformation, it is found that in order to fully cope with the springback deformation after the welding of the thin sheet and ensure the appropriate size of the component, the forced welding is generally carried out by means of gap samples and slats, and then facing the component. Implement heat treatment operations to prevent and control weld distortion problems.

For stainless steel sheets, the buckling deformation is not caused by a single factor, but is usually caused by a combination of multiple factors, which makes the internal stress of the weldment exceed the critical load, and eventually flexural deformation occurs, and the control of welding deformation is related to the welding quality. In the specific welding work, we should strictly control each process, at the same time, attach importance to technical training, strengthen the accumulation of practical experience, and comprehensively improve the welding quality.

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