Introduction to Nuts/Bolts Projection Welding

In resistance welding, projection welding is an important process, and the most common application of projection welding is in the welding of nuts and bolts. If you’re looking to understand this process, the following article will help you learn more about nut/bolt projection welding.

In resistance welding, the application of nut/bolt projection welding is second only to spot welding. It is mainly used for connecting standard parts to sheet metal components and is widely employed in industries with a high volume of stamped parts, such as automotive manufacturing and electrical cabinets. It is highly regarded for its high production efficiency, low cost, and non-polluting nature.

Types of Nut/Bolt Projection Welding

Projection welding of nuts and bolts can be categorized based on the type of projection used, including projection point, projection ring, and projection rib types. These structural differences arise from varying bonding strengths and load conditions (static or dynamic). Simply put, the size and shape of the projection or boss determine the final bonding strength. For applications with lower strength requirements, multi-point projections such as three-point or four-point types are commonly used. For higher strength demands, ring projections or elongated ribs are preferred.

How to Choose Equipment for Nut/Bolt Projection Welding

Projection welding requires stringent welding parameters—high current, high pressure, and short duration. Therefore, equipment capable of delivering high peak currents with very short discharge times is better suited for projection welding. Traditional AC spot welders are only suitable for standard projection welding of low carbon steel. Medium-frequency inverter DC spot welders, with their full-wave rectified DC output and millisecond-level adjustable welding time, are ideal for high-standard projection welding, even on high-strength steel. For ultra-high-strength and hot-formed steels, which require very high peak currents due to their high yield and tensile strengths, capacitor discharge welders are preferred. Their effective discharge time ranges from 5 to 15 milliseconds, making them ideal for challenging projection welding applications. Ring projection nuts/bolts, often used in high-load or sealing applications, also require high-quality, precisely controlled welding power supplies, and are typically welded using capacitor discharge equipment.

How to Select Electrodes for Nut/Bolt Projection Welding

Due to the short and intense nature of projection welding, electrodes are subjected to significant pressure. Therefore, in addition to conductivity, the strength of the electrode material is critical. The welding process generates high temperatures, so the softening temperature of the electrode material is also important. Besides the traditional chromium-zirconium copper, other excellent electrode material options include alumina-dispersed copper, beryllium copper, and even tungsten copper.

How to Inspect the Quality of Nut/Bolt Projection Welding

Projection welding aims to meet the connection requirements of standard parts, so the quality inspection of nut/bolt projection welding primarily involves four methods:

Torque Testing – Can be used for non-destructive testing under certain conditions;

Push-Out Testing – Primarily used for destructive testing to measure push-out force;

Go/No-Go Gauge Testing – Ensures thread integrity after welding;

Fusion Depth Testing – Low-magnification inspection of cross-sections to assess weld nugget quality, mainly used for high-standard quality control.

The above is a brief introduction to nut/bolt projection welding. This process is increasingly applied in modern industry. If you want to learn more, feel free to consult the Agera team—we will provide the answers you’re looking for.