High Current Transformers for Resistance Welding
UK-born engineer Elihu Thomson discovered in 1876 that copper could be fused together, but it wasn’t until 1885 that a resistance welding process was proposed. Direct energy spot welding is a resistance welding process that joins metals by applying pressure while simultaneously supplying electrical current to the weld area.
Resistance spot welding has evolved into a fast and cost-effective welding method widely used in sheet metal fabrication. The automotive sector has benefited from this technique through the use of spot welding robots, enabling higher production and assembly speeds. Although this technique is primarily used for welding steel, there is an increasing trend to substitute steel with aluminum to achieve mass optimization over time. The market is estimated to reach nearly $500 million by 2031.
Power Supply in Welding
Spot welding machines typically operate with AC voltage. The specific power for a given welding application is determined by process development and optimization based on material properties, desired weld quality, material thickness, and speed requirements. The heart of the welding machine’s power supply is a high-current transformer, designed for the maximum power and load that can be expected for the application. REO’s RFT-HS toroidal transformers use multiple toroidal cores to achieve the required power. The units have a standard wired input and use a copper busbar as the secondary side.
The toroidal design can be up to 40% more efficient than conventional EI transformers, which is crucial in price-sensitive applications. REO’s toroidal transformers offer further advantages: they can be encapsulated to achieve an ingress protection (IP) rating of up to IP20, and the REO design allows for quick assembly in devices or control cabinets, saving time and thus money. They have been specifically developed to outperform standard EI transformers and offer lower losses.
Applications of Spot Welding
Automotive Industry
As mentioned, spot welding is a key component of the automotive industry due to its cost-effectiveness, reliability, and speed. Manufacturing companies can easily automate assembly lines by using spot welding robots. A sheet metal or pressed panel made of steel or aluminum can be transformed into a functional part in seconds.
Electronics
Since this welding process prevents overheating of electronic components, many components such as switches, potentiometers, relays, circuit boards, and batteries are well-suited for spot welding.
Nail Manufacturing
This is a continuous high-speed spot welding process that converts carbon steel coils into thousands of nails per minute.
Kitchen Appliances
Spot welding is commonly used to manufacture door and cabinet handles, spatulas, and certain kitchen utensils like cookie cutters.
Medical Industry
The medical industry also benefits from the welding quality and speed of this process. In orthodontics, for example, spot welding is used for the secure attachment of dental implants.
Advantages of Spot Welding
- Spot welding is considered one of the fastest and cleanest welding methods.
- The process is easy to understand.
- Unlike other methods such as arc or TIG welding, there is no open flame.
- The process is easily automated.
- Multiple workpieces can be joined simultaneously.
- No use of filler materials required.
- There is no need for the use of shielding gases.
Disadvantages of Spot Welding
- Workpiece alignment and pressure are critical.
- Spot welding can cause deformation in some areas of the base metal.
- It is generally not possible to weld material thicknesses greater than 3 mm.
- The joints produced can be weaker than with some other welding methods.
- The welding current can be diverted (shunted) from the electrodes to other welds on the workpiece, leading to poor welding performance.
As the optimization of production techniques continues, especially with the increasing use of aluminum in automotive and aircraft production, making products lighter and more fuel-efficient, resistance welding is likely to remain an important manufacturing process for many years to come.
