Innovation in Welding: The Caterpillar Inertia Welder

In 1965 inertia welders, using a new welding process developed by Caterpillar engineers, were first marketed by Caterpillar for a wide range of industrial uses. Heralded at the time as a "breakthrough in the field of welding," inertia welding was capable of fusing both similar and dissimilar materials that in many instances were not practical to weld by other methods. According to archival records, “simple, clean, efficient, economical, safe, versatile, and high quality,” were some of the words used to describe this innovation. Everything from bicycle steering forks to jet engine components were being welded by inertia welders.

Developed by Caterpillar Engineers

The experiments that resulted in the inertia welder were carried out by Caterpillar research and development teams starting in the late 1950s. After thousands of experiments and applications, the dependability and capabilities of the welder were proved at the 1965 American Welding Society Convention in Chicago.

How it Worked

How does an inertia welder work? In 1965, project engineer Ralph Yocum explained:

Welds are formed by rigidly holding one of the pieces to be welded in a stationary fixture. The other piece is held by a rotating chuck, which is coupled directly to a flywheel and power source. The rotating parts are whirled to a predetermined speed. Then the power is shut off. By now, mechanical energy for the weld has been stored in the re-spinning part, in the flywheel, and in the motor.

Next, the parts to be welded are brought together. The frictional forces heat the contacting surfaces of the two pieces of metal to forging temperatures. A constant load (pressure) is applied against the pieces. The metals of the two surfaces mix. The weld takes place in the first second. It takes place in less time than it takes to tell about it.

Why Inertia?

The name "inertia welding" comes from the fact that mechanical energy is stored in the fly-wheel for conversion to the heat needed to make the weld. The energy available for heating and forging depends upon the flywheel weight and speed.

The only limiting factor of the process was that at least one of the pieces to be welded must be cylindrical or near-cylindrical. (Hexagonal shapes have been welded.) To be welded, surface faces do not have to be smooth.

What happened to the Inertia Welder Business?

The first two machines were used in Caterpillar plants in East Peoria, Illinois, and Glasgow, Scotland. One of the first machine sales was to an automotive plant in Russia. In 1976, Caterpillar decided to sell its inertia welder patents, rights, and manufacturing knowledge to Adams Engineering Inc. (AEI). The sale to AEI made sense, as the welder fit within their primary mission in the machine tool industry.

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