High Frequency Weld Roll Forming Machine,Surveying suitability of welding processes for roll formed parts

Of the many weld processes used, resistance and fusion welding are the most likely to be integrated with roll forming. This article takes a look at two resistance welding processes: high frequency welding and rotary spot welding.

 
A high-frequency welder does its work after material moves through an induction coil.

Resistance welding differs from fusion welding in that pressure is applied to the weld until the molten area coalesces, cools, and solidifies. Two resistance welding processes commonly integrated with roll forming are high-frequency welding and rotary spot welding.

High-frequency Welding
From hair dryers to clothes dryers, electrical devices we use every day require different electrical amperages or voltages, but the electrical frequency, be it the 60-hertz (60 cycles per second) frequency used in the U.S. or the 50-Hz (50 cycles per second) used in Europe, usually is left as is.

However, when the incoming line frequency is increased to a level of 100,000 to 800,000 Hz, some interesting phenomena occur. At these high frequency levels, current flows only at or near the surface of a conductive material, rather than through the entire thickness. The higher the frequency, the less "skin depth," or penetration, the current has.

When two high-frequency, current-carrying surfaces are brought together, the current concentrates on the two adjacent edges, allowing the direction and location of the current flow to be controlled precisely. If the current is controlled by the location of ground-return conductors so that it follows a V pattern, a weld between the two adjacent edges is formed at the intersection of the V. If the two edges are forged together with enough pressure, the impurities are squeezed out of the weld joint as slag, producing a strong weld with a good appearance and narrow heat-affected zone (HAZ).

The high-frequency welding process can fuse any material that can be welded, including steel, copper, brass, aluminum, stainless steel, titanium, and gold. Even unusual material applications, such as joining copper and steel together, are feasible. Material thickness is not a restriction, as the process can weld materials from 0.004-in.-thick foils up to 1⁄2-in.-thick, heavy-wall tube.

Two distinct types of high-frequency welding are:

Induction welding, which uses an energized copper coil that is wrapped around the part without contacting it. As the material flows through the electromagnetic field created by the coil, current is induced into the material. The need to adjust, maintain, and replace contacts is eliminated.
Contact welding, which sends current flowing into the material through copper alloy, tungsten, or silver-tungsten contacts that touch and ride on the material.
The high-frequency weld process allows very high line speeds, depending on the material and thickness, and is an efficient process for the production of relatively simple round, square, and rectangular tube and pipe commodities. For instance, a tube forming line producing 1-in.-diameter, 0.090-in.-thick-wall conduit can operate routinely at speeds up to 1,000 feet per minute (FPM).