Transformer laminations are often welded together primarily to reduce noise and vibration, particularly in transformers used in applications like microwave ovens. Welding the laminations, which are thin sheets of steel, helps to create a more solid structure, minimizing movement and the resulting humming or buzzing sounds caused by the fluctuating magnetic field.
Here's a more detailed explanation:
Minimizing Vibration: Transformer cores are made of stacked layers of thin, electrically insulated steel sheets called laminations. When an alternating current flows through the transformer's windings, it creates a fluctuating magnetic field that can cause these laminations to vibrate, producing noise. Welding the laminations together, especially in the "E" and "I" core configurations common in microwave transformers, helps to dampen these vibrations and reduce the noise.
Acoustic Noise Reduction: The welding process, along with other methods like resin coating, helps to create a more rigid core structure, minimizing the movement and vibration of the laminations that leads to acoustic noise.
Cost-Effective Assembly: In some transformer designs, welding is used as a cost-effective method for assembling the core, particularly in mass-produced transformers like those used in microwave ovens. While insulation is crucial for preventing eddy current losses, welding can be a more efficient way to hold the laminations together than other methods like using bolts and brackets.
Eddy Current Considerations: While welding can create a path for eddy currents, in some applications the reduction in vibration and noise outweighs the increase in eddy current losses. In power transformers, insulation between laminations is more critical, and welding is generally avoided in favor of other methods to maintain high efficiency.