ARC Specialties is a Houston-based welding automation and service supplier. When the firm was approached to design a plasma grooving and filling application for a fabricating a water turbine system, technicians there realized that an automated solution could potentially solve similar challenges in various other industrial applications. They set out to design, build, and test an automated system that would solve any groove and fill challenge where large amounts of material must be removed, and the space filled with anti-corrosive filler. Their primary example is detailed here, but the system itself can be applied to any groove and fill application.

Water turbines are rotary engines that harness energy from moving water. They use wicket gates, or valves that open and close to control the water flow. Carbon steel is a corrosion catalyst where the gates overlap, so a plasma grooving-and-filling process is needed to protect the integrity of the valve seal.
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Water turbines are rotary engines that take energy from moving water and harness it into a clean and renewable energy source. These turbines use wicket gates, or valves that open and close to control the water flow in the process of generating electricity. The gates are manufactured with a base material of carbon steel. These gates open and close in an overlapping fashion to direct the flow of water. Steel touches steel where the gates overlap, which is a catalyst for corrosion in a water environment. If corrosion goes unchecked it eventually will create pitting that’s so severe it will damage the integrity of the valve’s seal.

To mitigate the corrosion, it’s necessary for the overlapping areas of each gate must be grooved out and the cavity filled again with a stainless steel filler. Stainless steel is used as it doesn’t have the propensity to corrode, so that the carbon steel base metal won’t corrode either.

“Until now, manufacturing the gates required the costly and time-consuming process of cutting a groove into the gate with a mill, and then filling the groove with stainless steel using a manual welding process,” explained ARC Specialties president Dan Allford. “To address this problem we designed an automated solution using an ABB robot.”

The automated cell
The application cell consists of the ABB robot placed together with a tool-changing station that holds both an ESAB plasma torch and an ESAB Aristo MIG 5000i power supply.

“We chose the ABB robot for its ease of programming through the IRB 5 touch screen controller,” said Jim Walker, welding technician at ARC Specialties’ Research and Development Lab.

A gate is manually fixed to a robot-controlled rotary positioner. The mock parts used during testing were approximately 2X3 ft with a thickness of several inches. Postioning the product is an important part in the initial grooving process. The part, which is lying flat initially, is tiled up 25 degrees with the surface to be grooved facing down, so that during the process gravity removes the grooved material.

The application cell consists of the ABB robot and a tool-changing station with an ESAB plasma torch and a power supply. A gate is manually fixed to a robot-controlled rotary positioner. The part lies flat, initially, and is tiled up 25 degrees with the surface to be grooved facing down, so that during the process gravity removes the grooved material.
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The robot picks up the plasma torch from the tool-changing station and creates a groove along the gate’s surface, facing down. The robot makes two passes to achieve a smooth groove and achieve a depth of 3/8 to 1/2 inches. Once the groove has been made the robot turns the gate over to lay flat with the groove exposed. The robot removes the plasma torch and picks up the ESAB Aristo MiG 5000i welding head. Then, the groove is filled with the stainless steel material using through-the-arc tracking, using the arc as the tracking sensor. This method uses amperage feedback as it oscillates back and forth across the groove to determine the location of the edges. The completed piece is removed manually from the cell and a new product piece is introduced to the robot.

“Automation in general allows customers to increase efficiency and improve quality, and in this particular case the original process was very slow due to the nature of a milling process itself which slowly chips away at the material,” said Jordan Smith, welding engineer at ARC Specialties. “In this particular case the plasma grooving process removed 80 lb/hr; however, there are applications where we can remove as much as 150 lb/hr. A typical four-tooth end mill removes about 32 lb/hr.”

In ARC’s testing the plasma torch speed was 9 inches per minute. On a 12-ft wicket gate the grooving process would take a total of 32 minutes for both passes. The welding time would take approximately 3 hours.

“Water turbine companies, or any customer needing a groove-and-fill application, that invest in this automated solution will significantly increase productivity,” said Allford.

Additionally, to improve efficiency further the cell can be configured with product stationed on each side of the robot to create a cell that can work on one wicket and then switch over to the next wicket. This would increase production, cut costs and improve ROI.