Hydraulic Solution for Flash-Butt Welding

Flash-butt welding uses electrical resistance to heat the ends of two metal pieces that are, in turn, forged together into continuous coils, wheel rims, rods, band saw blades, and other shapes that require seamless joints at parent metal strength.

Older machines use manual cams to move pieces together at the right velocity but today's advanced high-strength steel (AHSS) products need controlled timing down to a few milliseconds and accuracy to a thousandths of an inch. Another solution is to replace the cams with electric servo drives and use multiple PLCs to control the process, but that can result in machines that are too expensive to be widely adapted especially in applications where high power density is required to join the steel pieces.

Patented Hydraulic Flash Welding

Taylor-Winfield Technologies Inc. has developed a different approach using a single motion logic controller and hydraulic drives in a package that is extremely precise and scalable. The solution moves work pieces together with precise accuracy and timing that can be adapted to various applications and is more affordable than other options for joining AHSS steel.

"There's a growing need for flash-butt welding in aerospace, automotive, appliance, and other industries requiring seamless joints in products made from high-strength metals," said Blake Rhein, vice president of sales and marketing for Taylor-Winfield. "In these applications, the ends of the metal pieces must be moved together very precisely to create a solid, homogeneous joint."

Rhein said their solution uses a motion controller to operate a proportional hydraulic servo valve in a closed-loop automation system. In combination with Taylor-Winfield's patented "forced freeze" welding process, the company believes this process will change how this type of welding is done around the world.

"Resistance welding simply means that two pieces of metal act as resistance for an electric current," Rhein said. "When current travels between the two separated pieces of metal, a short circuit occurs that heats the ends to a molten state that makes it possible to forge them together to reach parent metal strength and thickness after trimming."

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Flash-butt welding is a two-stage process. The first stage, or "flashing," phase applies electrical current to the two work pieces separated by a small gap. As the pieces are brought together, the electrical current arcs across the interface, and the temperature at the ends reaches anywhere from 600F to 900F depending on the material being joined.

At the required temperature, the second stage, or "upset" phase, begins. The two work pieces are pushed together using a moving and stationary platen with enough force to cause the ends to forge together. This action upsets the material, meaning that excess material and impurities are forced out of the top and bottom of the joint and subsequently removed by trimming to reach parent metal thickness.

Because the process removes irregularities and impurities, flash-butt welding can successfully join a wide variety of materials: narrow and thick shapes, wide and thin metal sheets, and ferrous and nonferrous materials. But to make a successful weld, the moving platen and electrical current of the two work pieces must be precisely controlled.

Previous Designs

"In early machines, the distance between the two work pieces was manually controlled," Rhein said. "The operator would dial in the proper current, and then a cam would control the speed of the moving platen and draw the pieces together to start the flashing phase. But a cam process cannot deliver the precise timing and speeds required to join today's AHSS metals. It takes automation to precisely move the pieces together at exactly the right speed and temperature to create a strong, homogeneous weld."

Taylor-Winfield uses the motion logic controller to automate the process. A welding curve that depicts the logarithmic relationship between the two pieces in terms of time and position is loaded into the controller. The overall weld schedule lasts from 2 to 30 seconds depending on the material. But during the flash phase, the position of the mobile work piece accelerates dramatically to generate forces up to 1 million pounds per square inch to forge the pieces together.

Mike Prokop, innovation leader and assistant chief electrical engineer at Taylor-Winfield, noted that the motion logic controller had a scan rate fast enough to meet the position and timing requirements. The system implements a closed control loop in which the controller gets position signals from a transducer, and then the controller initiates a position change by activating the system's hydraulic power unit. A proportional directional valve activates a linear positioning cylinder that moves the platen containing the mobile work piece toward the stationary work piece.