Welding deformation analysis of energy-saving large fan

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Author : JU LAI
Update time : 2023-06-24 09:00:05

With the increasing application of energy-saving large fans in China, some problems caused by fan manufacturing processes are gradually being exposed, and welding deformation is a severe condition. The welding area of large fans is generally located at the junction of structural components. If deformation occurs, it will affect the overall structural integrity of the fan, and may even lead to serious incidents such as solder joint detachment and structural component detachment.

To address the issue of welding deformation, we first need to understand the factors that cause welding deformation in the manufacturing process of energy-saving large fans. The influence of material factors:

  1. The influence of materials is determined by their chemical composition, microstructure, and mechanical properties, which all have a significant impact on their weldability. For example, aluminum and its alloys have very active chemical properties and are resistant to corrosion, but they are prone to oxidation and burnout, making them more difficult to weld compared to iron. The impact of material factors on welding deformation is usually determined by two aspects: welding materials, including welding rods, fluxes, welding wires, metal powders, and gases; and the thermal and mechanical properties of the materials. The influence of physical properties is relatively simple - the smaller the thermal conductivity coefficient, the greater the temperature gradient, and the more obvious the welding deformation. The influence of mechanical properties on welding deformation is relatively complex - as the thermal expansion coefficient increases, the welding deformation becomes more pronounced. At the same time, as the elastic modulus of the material increases, the welding deformation decreases. Higher yield strength can result in higher residual stresses, increased deformation energy stored in the welded structure, and brittle fracture. In addition, a smaller plastic strain and a smaller plastic zone range will reduce welding deformation.

  2. The influence of the position of the weld seam in the structure: The influence of the position of the weld seam in the welded structure is apparent. The degree of restraint of the workpiece itself can vary during the welding deformation process. The rigidity of a metal structure is determined by the shape and size of its cross-section. With increasing restraint, residual welding stress increases while welding deformation decreases. The structure is also affected by external restraints, ultimately influenced by positional symmetry.

  3. The influence of welding processes on welding deformation: The welding process has an impact on welding deformation, including factors such as shrinkage. The longitudinal shrinkage of the weld seam increases with the increase in weld length. Discontinuous weld seams have smaller shrinkage than continuous weld seams. Welding methods, component positioning or fixing methods, welding input current and voltage, the use of welding jigs and fixtures, and welding sequence all have effects on welding deformation. Among them, the welding sequence has the greatest impact. Changing the welding sequence can often alter the distribution of residual stress and stress state, reduce welding deformation, and occur multi-layer welding and welding process parameters also have a significant effect on welding deformation.

To avoid welding deformation in energy-saving large fans, we can take the following measures:

  1. Improve welding structural design: The size of the weld seam has a significant impact on welding deformation. Larger weld seam sizes result in more welding volume and more significant welding deformation. Therefore, while ensuring the structural load-bearing capacity, smaller weld seam sizes should be used as much as possible in the design. It is also necessary to avoid uneven distribution and concentration of weld seams. When designing the welding structure, the weld seams should be symmetrical to the neutral axis of the cross-section or close to the neutral axis, which effectively reduces bending deformation for beams, columns, and other types of structures. Furthermore, to ensure sufficient load-bearing capacity, unnecessary weld seams should be minimized. Using press-fit structures instead of auxiliary plate structures can meet the requirements for smaller weld seam sizes, effectively preventing plate structure deformation and controlling welding deformation.

  2. Improve welding process methods: In the production process of welding components, it is necessary to choose appropriate welding methods and standards. Before welding, prevention, pre-deformation, and rigid fixation assembly methods can be employed. The anti-deformation method estimates the size and direction of welding deformation in advance and causes pre-deformation of the workpiece during assembly that is equivalent in size but opposite in direction to the residual deformation after welding, thereby canceling out the residual deformation and restoring the component to the required geometric shape and size. The rigid fixation assembly method fixes the welded component as much as possible using fixtures or rigid templates, pre-fixes the welding parts, and enhances structural rigidity to limit welding deformation effectively. Pre-stressing is often used for thin plate planar components. After welding with pre-tension or pre-expansion, the pre-stress or heating is removed, and the plate returns to its initial state, effectively reducing welding residual stress and controlling welding deformation.

  3. Carry out a post-weld correction: After the components are welded, welding deformation is inevitably generated. To reduce or eliminate residual deformation, corrective measures such as mechanical correction and flame correction can be taken. Mechanical correction analysis requires a careful analysis of the direction of weld seam stress and finding the stress points, followed by appropriate correction methods. Flame correction involves a careful analysis of the deformation status and the formulation of correction methods, determining the heating positions and correction steps. It is also necessary to have a good understanding of the material properties and determine the appropriate heating temperature to ensure that materials that are sensitive to temperature can avoid changes in performance that affect the components. When correcting thin plates, the affected area by heating temperature is narrow. It is recommended to use non-hammer methods during hammering to achieve better correction results.

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