The welding process

The welding process  is done by filling the gap layer by layer. Each layer has three passes. The robot has the ability to tilt the torch when approaching the walls of the gap. This allows you to increase penetration and reduce the likelihood of defects. During the filling, the gap expands, but for the robot that is not a problem because it can increase the cross sectional area of the welding pool. To ensure uniformity of heat input at the weld zone throughout the depth of the gap, robot increases the welding speed as the  value of heat input increases. If for some reason two gaps are not equally filled, the robot can also change the cross sectional area of the welding pool to align the filling of the two gaps. You can also carry out separate welds.

Welding Head

For these projects a welding head was used the welding head ASG Robotics WH-1.

The welding head has been developed by us for this task. It has a right and left-hand version. Compact and easy to maintain. It has everything you need: a sensor for collision detection, wire sensor, flux presence sensor, push-inlet valve for flux feed rate control , protection against welding wire stick, wire straightener, laser scanner system to monitor the gap. The thickness of the welding gun is just 10 mm.
In 2012, we succeeded in creating effective integrated solutions for welding large-diameter ball valves.
These fully welded by two circumferential welds ball valves are normally used in oil and gas transport systems.

Technical characteristics

• Narrow gap welding profile (28 mm)
• Nominal size, DN: DN 300-1400 mm
• Weld profile depth range, B: 25-120 mm
• Maximum diameter of welds, D: 2300 mm
• Maximum weight: 30000 kg

Since there are polymers inside a cooling system is required.
(Parameters may be changed for a specific customer)

For these projects, the ASG Robotics WH-1 Welding Head was used.

Technical requirements for equipment

Parallel and independent welding of two welds
Compensation of deformation and abnormalities of the gap
Forced cooling and temperature control in the welding area.
Automatic feeding and recycling of flux.

Two types of complexes were developed and manufactured:
– for welding steel ball valves DN300 – DN1400;
– for welding steel ball valves DN300 – DN700.

The two systems are identical, based on the ASG Robotics WH -1 FANUC R-710iC robot and a single-axis positioner.
The robot arm positions the welding torches while the positioner rotates the workpiece.

Single axis servo positioner (35,000 kg load capacity) consists of:
– Headstock;
– Tailstock;
– Torque arm;
– Ball Slewing Bearing Device.
The tailstock has the ability to move along the positioner axis by 700 mm.

Positioning and cooling

The ball valve is hermetically sealed with covers on which the half-axles with bearings are mounted.
Coolant and welding current transmission are supplied through the half-axles.

Once the valve has been placed on the positioner, the gap search process is started so the robotic system can automatically start welding the root pass and all following passes using the laser positioning system.

Temperature control with the Optris CTlaser LT.

After welding the root pass, the cooling system starts working and the temperature of the part is monitored.
To avoid overheating of the polymer seals, a cooling liquid is supplied to the valve body. The liquid circulates in a closed loop between the valve body and a 6 m³ tank.

Flux recirculation system