Spot welding and projection welding are both common techniques in resistance welding, and they complement each other in various applications, especially in the automotive industry. Spot welding is often used for joining sheet metal parts in car bodies, while projection welding is typically employed for connecting standard components and body parts.
Spot welding is primarily used for joining thin sheets under 3mm, though in some cases, it can handle materials up to 8mm thick. However, as the thickness increases, the cost-effectiveness of spot welding decreases.
Projection welding is essentially an improved version of spot welding. It’s mainly used for welding stamped parts made of low-carbon steel and low-alloy steel. There are many types of projection welding, including sheet-to-sheet welding, nut and bolt welding, wire cross welding, and T-joint welding.
For sheet-to-sheet projection welding, the ideal thickness range is 0.5-4.0mm. When welding thinner sheets, the design of the projections becomes more challenging, and the welder’s responsiveness needs to be more precise. As a result, materials thinner than 0.3mm are usually welded using spot welding.
Compared to spot welding, projection welding has several distinct features. Bellow are the difference of spot welding and projection welding:
- Multiple Welds in One Cycle: Projection welding can join multiple points in a single cycle, boosting productivity and avoiding issues like currentshunting. This allows forwelding point placement in tight spaces without distance restrictions, whereas spot welding can only weld one point at a time, making it better suited for smaller parts or areas that don’t require extensive connections.
- Concentrated Current: In projection welding, the current is focused on the projections, creating a high current density that reliably forms smaller nuggets. In spot welding, achieving such small welding nuggets for a given thickness is much harder.
- Consistent Strength: The precise placement and uniform size of projections ensure consistentjointstrength. For a given strength requirement, the joint of projection welding can be smaller than those in spot welding.
- Reduced Surface Marks: Projection welding uses large flat electrodes, and since the projections are on one workpiece, the other workpiece’s surface shows minimal indentation. The larger welding electrodes also have lower current density and better heat dissipation, reducing wear and maintenance costs. In contrast, spot welding’s smaller electrodes create noticeable marks on the surface, affecting aesthetics.
- Tolerance to Surface Contaminants: Projection welding is less affected by oil, rust, oxide layers, or coatings on the workpiece surface compared to spot welding. However, a clean surface still ensures more stable joint quality.
- Limitations of Projection Welding: The process requires additional steps to create projections and uses larger electrodes. Welding multiple points at once demands higher electrode pressure and welding current, necessitating more powerful equipment and higher peak currents.
- Flexibility of Spot Welding: Spot welding can connect parts in various positions, even in tight spaces, using specially shaped electrodes—a capability projection welding lacks.
These are the key differences between spot welding and projection welding. If you’re interested in resistance welding, it’s worth diving deeper into these two processes. Whether you’re a current user or planning to purchase a resistance welding machine, this article should help you make informed decisions and improve your operations.
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