weld seam detection

I've worked on such projects myself. It seems easy, for an accurate bend you just need to position the tube's seam in the same place each time.

The most successful (automatic) method used an optical (color) sensor to see the seam. However, weld color often varies and surfaces blemishes/scratches can give false triggers.

Detecting the minute change in wall thickness at the seam may also work. But is affected by swarf.

The most reliable results came when we used a operator to insert the tube and align the seam. Best of luck. ffeJ.

If using a pinch roll to bend a slight area of flatness should be observed immediate to the weld seam.

The tube your referring to is CDW (Cold Drawn Welded) or ERW (Electrical Resistance Welded)

The CDW I have been using, the seam is difficult to detect, even by eye and a finger in the tube (Building a Off Road buggy frame)

Have you looked at X-ray, Eddy current testing.

a feeler inside the tube that touches the welded seam as the tube is rotated, then stops when the electrical contact is made, is this possible?

Cold Drawn Seamless has to be done visually or one of the above.

Oh, and the poster that said about swarf, you really don't want that in your tube, as it jams the inner mandrel as it tries to slide along the tube as you bend it.

The inner mandrel stops the tube from collapsing as the bender pulls the tube around the former.

Is it possible to put some kind of marker on the weld when it is performed.

The best way to do this is with ultrasound testing.

The ultrasound beams are penetrating the metal and reflecting back to the receiver. The deflection path is longer when the seem is directly under the scanner head so this process can be done in situ and used to drive the sheet or pipe bending machine to rotate the pipe if it wanders off a bit.

All other processes mentioned are either impossible to automate or too dangerous for normal conditions. For x-ray you need the appropriate licenses and the equipment is prohibitively expensive while your finger only works if the weld area has not yet had any treatment like grinding or paint or etching. Same for the colour detector.

It would depend on what level of automation you are looking for and the quantity of tubing that will be consumed in manufacturing. ( here is a little trade secret) Have your vendor run a marking line over the weld. Most of the labeling equipment used for pipe and tubing can be easily modified to print a line over the weld during manufacturing. You can now use optical monitoring equipment to detect the weld and interface it with the benders. If the line needs to be removed then most cleaning processes will work. Sometimes, depending on the color, it adds a cool aesthetic value depending on the part. This is a good fix "if" you are using allot of tube.

I work for United Tube in Medina OH, we are a welded mechanical tube mill. For bare tubing there is no need because the seam is darker; but for galvanized tube we mark the seam with a black injet for customer's who request it (those using optical sensoring can detect this line on the weld seam).