Process
Seam Tracking
Seam tracking is a welding robot function that senses where the joint actually is during the weld and corrects the torch path to follow it, so the weld lands on the seam even when the part has moved or distorted.
What it is
A taught weld path assumes the part sits exactly where it did during teaching. Real parts drift: fit-up gaps vary, fixtures wear, and heat distortion moves the joint while you weld. Seam tracking measures the joint as the robot welds and shifts the torch to follow it.
It keeps correcting along the length of the weld, which is what separates it from joint-finding methods that locate the seam once before the arc starts.
How it actually works
Two sensing methods dominate. Through-arc tracking uses the arc itself: as the torch weaves across the joint, welding current changes with the distance from the contact tip to the work, and the controller compares current at each side of the weave to center the torch and hold its height. It needs no extra hardware, but it needs weaving and works best on fillet and groove joints with sidewalls. Laser seam tracking mounts a scanner ahead of the torch that measures the joint profile, so it can follow joints without weaving and see the gap before the torch gets there.
Setup is mostly about limits. The sensor is calibrated to the TCP so corrections apply at the weld point. A search and tracking window defines where the joint is expected, and correction limits cap how far the system may move the torch, so one bad sensor reading can't swing it into the fixture.
How it differs
- Touch sensing · Touch sensing finds the joint before the weld by touching the wire to the part's surfaces and shifting the taught path to match. It corrects for where the part is. Seam tracking corrects during the weld, which also catches distortion and gap changes along the seam. Many cells use both: touch sense to find the start, then track to follow it.
- Vision offset · A vision offset measures the part once, usually before the robot moves, and shifts the whole program. Seam tracking measures continuously along the seam and adjusts the path as it goes.
Where you meet it in the field
- Configuring Seam Tracking for a FANUC Welding Robot · Sensor-to-TCP calibration, the search window, and the correction limits that keep a bad reading from moving the torch far.
- Arc Welding · Through-arc tracking rides on the weave the process already uses, which makes it the usual first choice here.
- Laser Welding · A small focused beam leaves little room for joint offset, so finding and tracking the seam matter even more.
Common questions
- Do I need to weave for through-arc seam tracking?
- Yes. Through-arc tracking reads the change in welding current across the weave, so the torch has to move side to side. If the joint or the process can't tolerate weaving, a laser seam tracker is the usual alternative.
- Why did the torch wander off the joint partway through a weld?
- Look at the correction limits and the sensor data first. Through-arc tracking can lose its signal on joints without enough sidewall, over tack welds, and where the gap changes sharply. A laser tracker can be thrown by spatter, reflective surfaces, or a dirty window. Tight correction limits keep a bad reading from moving the torch far.
- Can seam tracking make up for poor fixturing?
- Only inside its window. It compensates for normal fit-up variation and distortion. It can't correct a joint that sits outside the search window or a part that's loose in the fixture.