In the welding process of mechanical frame steel structures and equipment steel structures, controlling deformation is the core aspect of ensuring overall accuracy. Welding deformation is mainly caused by uneven heat input leading to differences in localized material expansion and contraction. If not effectively controlled, it can result in dimensional deviations, assembly difficulties, and even reduced load-bearing capacity. Therefore, a comprehensive approach involving design optimization, process selection, operational procedures, and deformation correction is necessary to form a systematic control scheme.
The design phase is the primary stage for controlling welding deformation. Optimizing the weld layout can significantly reduce deformation risks. For example, welds should be placed as close as possible to the neutral axis of the structure, ensuring symmetrical weld distribution and avoiding localized stress concentration. Simultaneously, unnecessary weld quantities and sizes should be reduced, prioritizing the use of structural steel or stamped parts instead of welded components to decrease welding workload. For T-joints, while ensuring strength requirements, the smallest reasonable weld leg size should be used, and intermittent welds should be preferred over continuous welds to disperse heat input and reduce deformation accumulation.
The appropriate selection of welding process parameters is crucial for controlling deformation. Heat input is a key factor affecting deformation; excessive heat input leads to coarse grains in the material, exacerbating shrinkage deformation. Therefore, appropriate welding methods must be selected based on the type and thickness of the steel. For example, for steels with low yield strength, processes with lower heat input, such as CO₂ gas shielded welding, should be prioritized, and preheating and interpass temperatures should be minimized. For thick plate welding, multi-layer welding instead of single-layer welding can reduce the heat input per layer, while controlling interpass temperatures prevents excessive heat concentration. Furthermore, intermittent welding is suitable for welding longitudinal stiffeners and transverse stiffeners, reducing continuous heat input and balancing shrinkage stress through intermittent welding.
Welding sequence and operating procedures are the core of deformation control. For double-sided symmetrical structures, using double-sided beveling and a symmetrical welding sequence can cancel out shrinkage stresses. For example, in multi-layer welding, welding along a path symmetrical to the neutral axis of the component avoids bending deformation caused by unidirectional welding. For T-joints, when the plate thickness is large, beveled fillet welds can reduce the amount of deposited metal, thereby reducing shrinkage deformation. In addition, the accuracy of the bevel angle, gap, and arc direction must be ensured during operation to avoid local deformation differences due to parameter deviations.
The reverse deformation method is an effective means of preventing welding deformation. By analyzing the direction and magnitude of welding deformation in advance, reverse deformation is applied to the component during the assembly stage, so that the shrinkage stress after welding cancels out the reverse deformation, ultimately achieving the design dimensional requirements. For example, when welding the upper and lower cover plates of an I-beam, the cover plates are pre-bent in opposite directions to counteract welding angular deformation. The setting of the reverse deformation amount needs to be combined with material properties and welding process experience to ensure the accuracy of deformation compensation.
The rigid fixing method limits welding deformation through external constraints. Fixtures or special tooling are used to fix the component on a rigid platform, increasing its resistance to deformation and preventing displacement caused by shrinkage stress during welding. For example, when welding cylindrical tube components, the pre-reserved perimeter method compensates for longitudinal and transverse shrinkage deformation, that is, a certain weld perimeter is reserved according to the plate thickness to ensure that the post-weld dimensions meet the requirements. For H-beams, a certain length is reserved per meter of longitudinal weld to balance the shrinkage.
Deformation correction and post-processing are the last line of defense to ensure accuracy. For welding deformation that has already occurred, mechanical correction or flame heating correction methods can be used. Mechanical straightening applies a reverse force to deformed areas using a press or straightening machine to restore them to their original shape. Flame heating straightening utilizes the shrinkage stress generated by localized heating to counteract the original deformation; however, strict control of the heating temperature and area is necessary to avoid material degradation. After straightening, a comprehensive inspection of the components is required to ensure that dimensional accuracy and geometric tolerances meet design requirements.
Controlling welding deformation in mechanical frame steel structures and equipment steel structures must be integrated throughout the entire process, including design, manufacturing, operation, and post-processing. By optimizing weld layout, rationally selecting process parameters, standardizing welding sequence, applying anti-deformation and rigid fixing methods, and combining deformation straightening techniques, the risk of welding deformation can be systematically reduced, ensuring structural accuracy and quality. This process not only relies on technical means but also requires welders with rich practical experience and a rigorous operating attitude to achieve high-precision manufacturing of mechanical frame steel structures and equipment steel structures.
