Understanding weld tracking technology means understanding all possible smart solutions. Depending on your welding process, materials and cycle time requirements, the right solution will usually appear over time.
But do you know all the available seam tracking solutions?
What are the advantages and disadvantages of all the different seam tracking solutions?
Based on my welding situation, which seam tracking solutions are not suitable for me?
Sensor technology offers many possibilities for your welding operations. Some are low-cost and limited capabilities, some involve heavy investment and thoughtful design-a huge advantage is cost savings. Next, let Hangao Tech (SEKO Machinery) take you to understand the different types of welding tracking system for stainless steel TIG welding tube making machinery, working principles, and their respective advantages and disadvantages.
1. Touch Sensing
Touch sensing is where the robot applies a small amount of voltage to the welding nozzle or welding wire. Their functions are the same, the only difference lies in the way each method converts data into a robot. Through the voltage, the robot will rise to the working material, touch it, a short circuit occurs, and then the robot will record the position of the recorded value and tell the position of the surface of the robot. In most cases, each joint requires at least 2 touches to find the position-vertical and horizontal surfaces. The robot will connect these search vectors and triangulate the position of the welded joint.
At the corner or outer edge joints, a third touch from the robot is usually required to get all the correct positions to allow the robot to find and "track" the joint.
Touch sensing is very useful as a low-cost joint tracking solution. This is a simple software-based solution that you can apply from the teach pendant without additional systems. Another major benefit of touch sensing is that you can enter narrow areas because there is no hardware other than the connector that the robot torch nozzle prevents contact with.
However, touch sensing does have some limitations, making it a very effective solution for joint sensing and seam tracking. The first is that touch sensing is a slow process, with each search vector increasing by 3 to 5 seconds. Therefore, if you are touch-sensing on a 2D part, you may add 6 to 10 seconds to the welding cycle, and if you touch-sensing a 3D part, the cycle time for the start of each arc increases by 15 seconds.
The number of fault points with touch sensing at the arc end is also far greater than other solutions. Bent wires or dirty and scaly materials make it difficult to perform touch sensing consistently. Touch sensing is only used to find the arc starting point or arc end, and does not contribute to the difference in the length of the weld, so it will not compensate for inconsistent fixtures or tools.
Touch sensing is also limited by the type of solder joints. Fillet and lap joints are the most common and recommended joints, but even for lap joints, the material thickness must be considered. Anything smaller than 5 mm (1/4 inch) can become a problem for performing touch sensing because the wires may miss the material thickness of the upper board-causing you to exceed the part, or you can hit the lower board and get the wrong value .
Your robotic welding gun also needs a wire brake and a wire cutter equipped in the torch package to cut the wire at a known distance away from the tip so that your readings are consistent throughout the process.
Touch sensing also requires clean edges, because poorly welded or trimmed parts can produce false readings.
2. Through Arc Seam Tracking
Through Arc Seam Tracking (TAST) is the second stage of your application of touch sensing. After touch sensing, you will find the arc starting point and arc ending point, and then apply "Through Arc Seam Tracking". TAST can track the Z-axis and Y-axis of the joint, which is very suitable for thicker materials.
TAST requires a weaving process. When the wire transitions from one side of the joint to the other, the voltage is changing. This is because the extension of the wire decreases with the change of the tip to the working distance. This allows the robot to interpret voltage changes and adjust the teaching path to maintain the proper welding position in the joint.
TAST is suitable for thicker material lap joints, which need to be 5 mm (1/4 inch) or thicker to maintain stability. It is not recommended to perform TAST at a lower thickness (in fact, I have never witnessed it using a seam tracking app during my years of work), otherwise you may risk worm tracking or meandering welding-this will reduce The integrity of the weld during the entire process.
The reason why it is not recommended to use thinner materials during the entire welding process, and tends to wash or remove the shoulder of the upper plate. This cleaning does not cause a significant voltage change, which causes the robot to search-this is where the worm risk comes into play.
Another limitation of TAST is that you have to increase the cycle time because it requires the robot to pass through the joints. Generally, TAST's travel speed is limited to 35-50 inches per minute. TAST is also limited to MIG applications-TIG or Plasma is not possible.
Finally, TAST is limited to carbon steel or stainless steel. The voltage is not consistent with aluminum, and TAST cannot be performed reliably. The condition of the material is also very important. Part cleanliness, proportions or rust have an impact on the parameter group because you set the standard required for voltage changes. Therefore, a 2% voltage change on negative Y due to oxide scale or rust on the metal will cause inconsistent characteristics of TAST.
Since the robot must be welded for tracking, TAST cannot perform dry operation either. Stickiness is also problematic, because when you pass the tack, the sticking out will change, so the robot will lose track until it comes out on the other side of the tack weld.
3. 2D Vision System
Imagine 2D vision like a camera. It takes a reference image of the ideal part before striking the arc and matches the reference image with each new subsequent part-detecting any offset and adjusting the welding path. It only provides black and white images, where the image is on its surface. 2D cannot determine height or depth, and is not considered a reliable process for seam tracking.
Joints such as V-joints and lap joints are very problematic for 2D Vision because it cannot determine the depth of these types of welded joints. Glossy materials like aluminum are also problematic for 2D systems. Generally, 2D is used to identify parts instead of tracking. It is a vision-based system, so external light interference is critical to the performance of optical components. In addition, the camera lens is very sensitive to welding spatter and arc damage.
