Welder Comparisons
There is no doubt that in today's world, the square wave welder is a niche welder. Consequently, HF induction welding is by far the preferred method of welding on most mills.
Square Wave vs. AC and DC Welders
The major advantages of the square wave welder when compared to the other two conventional ERW methods (i.e., AC and DC welding) are listed in Table 1 below.
| Criteria | AC | DC | Square |
| Susceptible to Weld Spatter | Yes | No | No |
| Susceptible to Weld Stitching | Yes | No | No |
| Location of Power Supply Important | No | Yes | No |
| High Maintenance Cost | No | Yes | No |
Table 1: ERW Welder Comparison
Square Wave vs. HF Welders
The advantages of the square wave welder when compared to the HF welder are listed as follows:
More Forgiving Weld Presentation
With HF welding, the presentation of the weld seam is critical to the success of the process. Although important with square wave welding, it is not nearly as critical. In addition, because the electrode wheel is contoured to the radius of the tube being welded, it can be used to hold the form of the open tube during welding. This feature is especially useful on smaller tubes where it is difficult to control the edges.
No Impeder Required
Because square wave welders (as well as AC and DC) do not require the use of any inside impeder, the I.D. of the tube is free of any mechanical devices. This is especially important when welding tubes with very small diameters, where it is physically difficult to put enough ferrite inside the tube to efficiently and effectively HF weld. One typical application is the production of carbon-steel refrigeration or fuel line grade tubing.
Another application where the lack of an impeder is preferred is when some sort of inline I.D. coating of the tube is being performed. The presence of an impeder would make it difficult to deliver the coating substance to the inside of the tube.
Higher Welding Heat Transfer Efficiency
Because square wave welding is a contact welding process, the heat transfer efficiency of the process is much greater than HF induction welding. Although HF contact welding is also a contact method, it is generally not used on the smaller tube sizes and, therefore, does not typically compete with square wave welding.
Wider Heat Affected Zone
In situations where severe bending of the weld zone is required, a square wave welded tube may have some benefits over comparable HF induction welded tubes. With the advent of hydro-formed tubular products (i.e., tube sections that are deformed using hydraulic pressure to expand them inside a dieset), there is some speculation that the wider heat-affected zone on a square wave welded tube may be more plastic. Although further data was not available at the time this paper was written, experiments designed to support this theory will be conducted shortly.
"Retrofittable" to Existing Systems
Because the square wave power supply is essentially an AC power supply, it can used to replace aging AC power supplies. By doing so, tube manufacturers can increase the weld quality and, by doing so, increase the production yield on the mills.
In addition, the second generation of square wave power supply incorporates a solid state design that allows finer control of the output wave form. This added control allows the welder to be tuned to the specific tube being produced on the mill. The result is again better weld quality and increased production yields. Furthermore, the newer power supplies offer high reliability and increased availability of spare parts and service.
Conclusion
Although the Square Wave Welder may not be the best welder for every application, it does fill a niche in today's market. In addition, the possibilities of its use in the hydro-form tube industry make it a viable welder for today's tube producers.