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The Difference Between Hot Upset and Welding

In the world of manufacturing, the term “Welding” is fairly common. Even people outside of the industry can picture the process: high heat, large sparks, and the traditional welder’s helmet. When manufacturers and engineers hear the term “Hot Upset Riveting” or” Hot Upset Forming”, the recognition of the process doesn’t happen as quickly. Although the two processes utilize similar technology, the result is quite different.

What is the Difference?

Welding is a process that joins or bonds materials together. High heat is applied to the materials, causing them to melt. As they cool, the materials fuse together to create a strong connection or joint.

The Hot Upset process also applies high heat, but does not fuse the materials together. Instead, it is combined with pressure applied by our powerhead to join two or more parts together to create an assembly. As the heat is applied directly to a fastener, tenon, or workpiece, it is brought to a cherry red state and becomes malleable. It then collapses under the pressure applied by the powerhead. With Hot Upset, the heat is concentrated into the workpiece (fastener/tenon). This does not fuse the parts together like welding, but instead creates an assembly.

Why Choose Hot Upset?

The most common reason manufacturers use Orbitform’s Hot Upset process is to form hardened materials that cannot be successfully cold formed. The simultaneous use of heat and pressure allows materials like tungsten, molybdenum, and other exotic metals to be successfully formed. This process is also optimal for assembly applications that require a strong joint, such as those that have a high torque or push/pull retention force requirement or need to resist high vibrational forces. When the product design geometry allows for it, this process maximizes the amount of hole fill to create an even stronger joint.

Hot Upset vs Welding – A Case Study

An equipment manufacturer turned to Orbitform for guidance when their welded joints failed to resist high vibrational forces. Their current process consisted of welding a hardened steel rod into a hexagonal shaped hole to prevent rotation in their assembly. Unfortunately, the welding process annealed the rod, thus increasing the ductility and reducing the hardness of the steel. Orbitform’s Experts believed this to be the cause of the joint failure and suggested trying the hot upset process. We assembled samples in our Solutions Lab and found that the hot upset process was successful in creating a high torque joint with 99% hole fill at a lower temperature than their current welding process.


There are several potential processes that can be used to assemble a part. Some are widely known and familiar to many, while others are more niche and application specific. If your current method is not working, it may be time to explore a new one. With multiple assembly processes to choose from and over 35 years of assembly experience, Orbitform’s experts can help determine which one best meets your application requirements. Contact us today to discuss your assembly challenges.


Hot Upset