In the spin welding process, precise temperature control is crucial for ensuring weld quality and preventing overheating defects. Excessive temperature can lead to coarsening of material grains, softening of the heat-affected zone, and even defects such as cracks and porosity; insufficient temperature may cause incomplete fusion and slag inclusions. Therefore, a comprehensive temperature control scheme is needed, encompassing process parameters, equipment design, operating techniques, and auxiliary measures.
Matching the rotation speed with the welding speed is fundamental to temperature control. Rotation speed directly affects the efficiency of frictional heat generation: too low a speed results in insufficient frictional heat, preventing the material from reaching a plastic flow state and easily leading to incomplete penetration defects; too high a speed causes heat to concentrate in localized areas of the weld, causing overheating or even melting of the material, damaging the solid-state bonding characteristics of friction stir welding. Welding speed determines the heat input per unit length: too slow a speed prolongs the high-temperature dwell time, exacerbating softening of the heat-affected zone; too fast a speed may result in insufficient heat input, leading to incomplete plasticization of the material and the formation of tunnel-type defects. In practice, a reasonable combination of rotation speed and welding speed needs to be determined through process experiments. For example, in aluminum alloy welding, the rotation speed range is usually set first based on the material thickness, joint type, and equipment power. Then, the welding speed is adjusted to achieve a smooth "fish scale" pattern on the weld surface, avoiding burrs or dents.
Precise control of the pressure is crucial for temperature distribution. The pressure in a spin welding machine refers to the depth to which the stirring pin penetrates the workpiece. Its magnitude directly affects the contact area and pressure distribution of the friction interface. Insufficient pressure results in poor contact between the shoulder and the workpiece surface, reduced frictional heat generation efficiency, and poor material fluidity, easily leading to burrs on the weld surface or internal voids. Excessive pressure, on the other hand, causes excessive shoulder compression, forcing material out of the weld and forming burrs, while also increasing the equipment load and potentially causing overheating. For example, in friction stir welding lap joints, the pressure needs to be adjusted according to the thickness difference of the materials being welded. Ideally, the shoulder should just press into the surface of the lower layer of material. Parameters can be optimized by observing the weld formation quality or measuring the burr height. Adjusting the stirring head angle optimizes the heat transfer path. A suitable angle reduces resistance during welding and utilizes the beveled effect of the shoulder to seal the welding material, minimizing heat loss. If the spin welding machine's angle is too small, the contact area between the shoulder and the workpiece surface increases, concentrating frictional heat generation but also accelerating heat dissipation, potentially leading to excessively high weld center temperatures and insufficient edge temperatures. Conversely, an excessively large angle reduces the contact pressure between the shoulder and the workpiece, decreasing heat generation efficiency. It is generally recommended to control the stirring head angle between 1° and 3°, with the specific angle requiring fine-tuning based on material flowability and welding speed.
Equipment heat dissipation design and environmental adaptability are crucial for preventing overheating. During operation, the motor, stirring head, and other components of the spin welding machine generate significant heat due to high-speed rotation and friction. Poor heat dissipation not only affects equipment lifespan but can also cause localized overheating of the welded workpiece through heat conduction. Therefore, the equipment must be equipped with an efficient cooling system, such as forced air cooling or liquid cooling, to ensure stable temperatures for critical components. Furthermore, when welding in high-temperature or high-humidity environments, it is necessary to compensate for the influence of ambient temperature by adjusting welding parameters or adding preheating/postheating measures. For example, in high-temperature conditions during summer, the rotation speed can be appropriately reduced or the welding speed increased to reduce heat input.
Standardized operating procedures and real-time monitoring are supplementary to temperature control. During the spin welding machine process, the welder needs to indirectly judge the temperature status by observing the weld formation quality (such as surface gloss and flash size) and listening to the operating sounds of the equipment (such as changes in motor load). Simultaneously, the weld surface temperature can be monitored in real time using non-contact infrared thermometers or thermal imagers. When the temperature approaches the material's critical value, parameters should be adjusted immediately or welding should be paused. For example, when welding thick plates, if bluing is observed at the weld edge (excessive temperature), welding can be paused and local cooling measures implemented until the temperature drops to a reasonable range before resuming work.
The application of auxiliary measures can further optimize the temperature control effect. For example, preheating the workpiece before welding can reduce the temperature gradient during the welding process and reduce thermal stress; post-weld heat treatment can eliminate residual stress and improve joint performance. In addition, adopting process sequences such as segmented welding and symmetrical welding can also avoid heat concentration and reduce the risk of overheating.
