We are recently having a lot of problems with touching welds up on one of our robots, we have two robots welding at the same time on the same part and we seem to be carrying out a lot of reteaching on just one of the robots. The welds seem to be moving and when we correct them a few parts later the welds need to be touched up again but we have no problems with the other robot. They both weld on the same jig which only turns twice for access and then they move over to the other jig and we have the same problem from the same robot on the other jig. Is there anything I should be checking as calibration ok and robot solid but cant think of what else to look at.
weld touch up
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hagsy -
March 17, 2017 at 8:19 PM -
Thread is marked as Resolved.
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You do not state which robot or controller or process you are using so I am shooting in the dark here.
Some common steps you could consider;
1 Release the brakes of all axis (one at the time) and check for backlash.
This means you should be able to move the axis and feel the same (constant) amount of torque (resistance) when doing this.
If you feel a low resistance at first changing into higher resistance when you rotate further you have a worn or faulty transmission.
Also you should feel a more or less constant resistance all the way, if you are not sure compare it with the other robot.(if you are not experienced with this is not a bad idea at all to check the “good” robot first so you know what to expect.
2 When you are correcting the welds try to do this with jogging axis and not Cartesian or tool coordinates. If one axis is bad you will notice that you can regain the right position by moving one (or two) the same axis, this will indicate a problem in one (or two) axis.(TW and BW are the most vulnerable axis)
3 Check motor mountings, once I had a similar problem and it turned out the bolts for fixing the BW axis motor where lose.
4 When you are correcting the same weld over and over again write down the position of that point.
View, display change display position agl (angel).
If this position changes back and forward the problem may be external, in case the position changes in one direction it may indicate a robot problem.(vague indication, depends on robot type).
5 Make some reference point(s) on your jig.
The easy-est way to do this (when MIG or MAG welding) is by welding at least 3 wire contact tips (threaded part welded) on the jig, make a program which positions the torch over the contact tips in such a way you can inch and retract the wire in an out of the welded tip without any friction.
Try to keep the torch orientation as fixed as possible to rule out the robot.(TCP / Calibration errors).
Do the same thing on a part which is not moving (torch cleaner, base of the robot).
If the first (moving) reference points are not ok but the fixed point are ok the problem is not in the robot.
If all reference points change the problem is in the robot.
6 Rule out the torch by making a reference point on a fixed position and use one of the grease nipples on the TW axis as reference on the robot. the fixed point could be as easy as the edge of the torch cleaner or somthing else stable.(depending of the adjustments you have to make to your program, if you are TIG welding this check may be too crude).
That is all I can think of right now.
Good luck and I hope to hear from you again, something like problem found / solved would be nice! -
[/img][/img]Thanks for the reply, some good things in there and I will check them all as soon as possible. I am just using basic mig welding nothing fancy and I will be back in work on Tuesday so will let you know how it goes and if I find anything.
Regards
Mark -
I have set up a tip check program and noted the axis angles down, I will do the same for the arc starts and arc ends when the cell isn't running and get our facility on to check for backlash.
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It is better to note the axis angle (AGL) value, it is then more clear to see which axis has a problem.
And you really need to add a second reference point to rule out the torch (the grease nipple on the TW axis).
then you will be able to tell for sure if the problem is in the robot or in the torch. -
Still ongoing as been very busy lately so unable to get a look at the robot as yet