Let the Weld Guru guide you through the world of Robotic welding
Robot welding
Robot welding is the use of mechanized programmable tools (robots), which completely automate a welding process by both performing the weld and handling the part.
Processes like gas metal arc welding, while often automated, are not necessarily equivalent to robot welding, since a human operator sometimes prepares the materials to be welded.
Robot welding is commonly used for resistance spot welding and arc welding in high production applications, such as the automotive industry.
Robot welding is a relatively new application of robotics, even though robots were first introduced in United States industry during the 1960s.
The use of robots in welding did not take off until the 1980s, when the automotive industry began using robots extensively for spot welding.
Since then, both the number of robots used in industry and the number of their appliactions has grown greatly.
Cary and Helzer suggest that, as of 2005, over 120,000 robots are used in North American industry, with about half of them pertaining to welding.
Growth is primarily limited by the high equipment cost, and the resulting necessity of using it only in high production applications.
Robot arc welding has begun growing quickly just recently, but already it commands about 20% of industrial robot applications.
The major components of arc welding robots are the manipulator or the mechanical unit and the controller, which acts as the robot's "brain".
The manipulator is what makes the robot move, and the design of these systems can be categorized into several common types, such as the SCARA robot and cartesian coordinate robot, which use different coordinate systems to direct the arms of the machine.
Robot welding
When should robots be used for welding? A welding process that contains repetitive tasks on similar pieces might be suitable for automation. The number of items of any type to be welded determines whether automating a process or not. If parts normally need adjustment to fit together correctly, or if joints to be welded are too wide or in different positions from piece to piece, automating the procedure will be difficult or impossible. Robots work well for repetitive tasks or similar pieces that involve welds in more than one axis or where access to the pieces is difficult.
Why robot welding?
The most prominent advantages of automated welding are precision and productivity. Robot welding improves weld repeatability. Once programmed correctly, robots will give precisely the same welds every time on workpieces of the same dimensions and specifications.
Automating the torch motions decreases the error potential which means decreased scrap and rework. With robot welding you can also get an increased output. Not only does a robot work faster, the fact that a fully equipped and optimized robot cell can run for 24 hours a day, 365 days a year without breaks makes it more efficient than a manual weld cell.
Another benefit of automated welding is the reduced labor costs. Robotic welding also reduces risk by moving the human welder/operator away from hazardous fumes and molten metal close to the welding arc.
What welding processes are suitable for robot welding? Most production welding processes can be used in automated applications. The most popular, used in perhaps 80 percent of applications, is the solid wire GMAW process. This process is best for most high production situations because no postweld cleanup is required
Robot arc welding
Robot welding means welding that is performed and controlled by robotic equipment. In general equipment for automatic arc welding is designed differently from that used for manual arc welding. Automatic arc welding normally involves high duty cycles, and the welding equipment must be able to operate under those conditions. In addition, the equipment components must have the necessary features and controls to interface with the main control system.
A special kind of electrical power is required to make an arc weld. The special power is provided by a welding machine, also known as a power source. All arc welding processes use an arc welding gun or torch to transmit welding current from a welding cable to the electrode. They also provide for shielding the weld area from the atmosphere.
The nozzle of the torch is close to the arc and will gradually pick up spatter. A torch cleaner (normally automatic) is often used in robot arc welding systems to remove the spatter. All of the continous electrode wire arc processes require an electrode feeder to feed the consumable electrode wire into the arc.
Welding fixtures and workpiece manipulators hold and position parts to ensure precise welding by the robot. The productivity of the robot welding cell is speeded up by having an automatically rotating or switching fixture, so that the operator can be fixing one set of parts while the robot is welding another.
To be able to guarantee that the electrode tip and the tool frame are accurately known with respect to each other, the calibration process of the TCP (Tool Center Point) is important. An automatic TCP calibration device facilitates this time consuming task
Robot spot welding
Automatic welding imposes specific demands on resistance welding equipment. Often, equipment must be specially designed and welding procedures developed to meet robot welding requirements.
The spot welding robot is the most imortant component of a robotized spotwelding installation. Welding robots are available in various sizes, rated by payload capacity and reach. Robots are also classified by the number of axes. A spot welding gun applies approriate pressure and current to the sheets to be welded. There are different types of welding guns, used for different applications, available. An automatic weld-timer initiates and times the duration of current.
During the resistance welding process the welding electrodes are exposed to severe heat and pressure. In time, these factors begin to deform (mushroom) the electrodes. To restore the shape of the electrodes, an automatic tip-dresser is used.
One problem when welding with robots is that the cables and hoses used for current and air etc. tend to limit the capacity of movement of the robot wrist. A solution to this problem is the swivel, which permits passage of compressed air, cooling water, electric current and signals within a single rotating unit.The swivel unit also enables off-line programming as all cables and hoses can be routed along defined paths of the robot arm.
