20. Rail gas pressure welding method of low upset length without the process of bulge removal by hot shearing

Gas pressure welding is a major welding method, accounting for approximately 40% of all rail welding execution in Japan. The current method sets the standard upset length during gas pressure welding at "24 mm or more." The bulge created by upset needs to be removed by hot shearing using a bulge removal device (145 kg) brought to the site.
This process of bulge removal by hot shearing requires skilled techniques, and there is a potential risk of hot cracks on the weld interface due to the shear force generated during the bulge removal by hot shearing.
With the decrease in skilled technicians in recent years, there is a growing demand for a gas pressure welding method that can eliminate the process of bulge removal by hot shearing.

Therefore, various pressure patterns were examined using numerical analysis methods. By gradually reducing the pressing force during the welding process to reduce the upset length while increasing the temperature of the weld interface, a new method (variable pressure method) was developed that achieves weld strength equivalent to conventional methods (Figure 1).
With this method, the upset length can be reduced to 6 mm, and the bulge at the weldment can be reduced by 60% (Figure 2), allowing the bulge to be removed by grinding alone.
This results in a 40% reduction in the weight of the existing gas pressure welding apparatus and a 30% reduction in execution costs. In addition, we have also prepared an execution guide that summarizes the above.

In the future, we will work to automate the rail gas pressure welding method using this technique.