In the precision sheet metal aluminum series processing—back plate manufacturing—welding deformation is one of the key factors affecting flatness. Due to its high thermal conductivity and low melting point, aluminum is more prone to localized shrinkage, twisting, or waviness during welding due to uneven heat input or improper process parameters, thus compromising the geometric accuracy and assembly compatibility of the back plate. To effectively control this problem, multi-dimensional improvements are needed, including design optimization, process selection, equipment control, and post-processing.
The design stage is the primary step in preventing welding deformation. The aluminum back plate structure should adopt a symmetrical layout as much as possible, avoiding weld concentration on one side or in a localized area to balance welding thermal stress. For example, in box-type back plates, longitudinal and transverse welds can be alternated, or stress can be dispersed by adding reinforcing ribs. Simultaneously, the design should allow for reverse deformation. Based on material properties and welding process, the shrinkage direction should be estimated, and the back plate should be pre-bent or pre-pressed in the reverse direction before processing to offset the post-welding deformation with the allowance, thereby approaching the design flatness requirements.
The choice of welding process directly affects the degree of deformation. For welding aluminum materials, methods with high energy density and concentrated heat input, such as TIG welding (tungsten inert gas welding) or laser welding, are recommended to reduce the heat-affected zone. For thin aluminum back plates, pulsed TIG welding can be used, achieving alternating heating and cooling through periodic current adjustment to reduce overall temperature rise. If MIG welding (metal inert gas welding) is used, wire feed speed and arc voltage must be strictly controlled to avoid an excessively large molten pool leading to uneven shrinkage. Furthermore, friction stir welding, as a solid-state welding technique, achieves connection through mechanical friction heat generation, with almost no melting process, significantly reducing welding deformation of aluminum back plates, especially suitable for long straight welds or complex structures.
Welding sequence and fixture design are crucial for controlling deformation. Welding should follow the principle of "symmetrical welding and segmented back-welding," that is, alternating welding from the center of the structure to both sides, or segmented skip welding along the weld length, to avoid heat concentration causing unidirectional shrinkage. For example, when welding rectangular aluminum back plates, the shorter diagonal welds can be welded first, followed by the remaining welds, allowing stress in each direction to cancel each other out. Simultaneously, a dedicated rigid fixture must be used to fix the back plate, ensuring a tight fit between the workpiece and the mold during welding and limiting displacement caused by thermal expansion. The fixture material should be an alloy with a coefficient of thermal expansion similar to aluminum to reduce additional stress caused by temperature differences.
Precise control of welding parameters is the core means of reducing deformation. Aluminum welding requires reasonable setting of current, voltage, welding speed, and gas flow rate based on plate thickness, weld type, and equipment performance. For example, when welding thin aluminum back plates, low current and high speed parameters are preferable to shorten the heat treatment time; thicker plates require appropriately increased heat input, but preheating treatment is necessary to reduce the temperature gradient. Furthermore, the purity and flow rate of the shielding gas must be strictly controlled to avoid localized stress concentration caused by oxidation or porosity defects. For aluminum back plates with high precision requirements, a real-time monitoring system can be introduced, using infrared thermography or laser displacement sensors to provide feedback on welding temperature and deformation, dynamically adjusting process parameters.
Post-processing is crucial for eliminating residual stress and improving flatness. After welding, the aluminum backing plate requires stress-relief annealing. This involves slowly heating to a specific temperature and holding for a certain time to relax the internal stresses of the material. After annealing, mechanical or hydraulic straightening can be used to apply reverse pressure to locally deformed areas, restoring them to flatness. For backing plates with high surface quality requirements, vibration aging technology can be combined, using high-frequency vibration to promote uniform stress distribution and avoid secondary deformation that may be caused by traditional heat treatment.
Material selection and pretreatment are also crucial. Aluminum backing plates should be made of alloys with excellent weldability, such as 5052 and 6061, whose low magnesium content and uniform grain structure help reduce the tendency for hot cracking. Before welding, the material surface must be rigorously cleaned to remove oil, oxide film, and impurities to prevent porosity or inclusions during welding, which could lead to stress concentration. For thick aluminum backing plates, pre-machining or chemical etching can be performed to form bevels or transition layers, optimizing weld formation, reducing the amount of filler metal, and thus lowering the risk of shrinkage deformation.
Controlling welding deformation in precision sheet metal aluminum series processing back plates requires a comprehensive approach throughout the entire process, including design, manufacturing, equipment, and post-processing. Through structural optimization, process matching, precise parameter control, and enhanced post-processing, flatness deviations caused by welding can be effectively suppressed, meeting the high precision and high reliability requirements of aluminum back plates in fields such as communication equipment and aerospace.
