Best approach to program a weld

[Splinky]

Hi,

We have an XRC 2001 UP20 with an external axis that we need to use to overlay weld the entire inside of a tube.  We need to weld around the pipe in either a spiral or else weld around, step the robot out 3/4" and go around again.  We also need to weave the weld. 

We have been using SMOVC commands to turn the rotary axis, but there are getting to be a lot of programming points as the part is fairly big.

I was wondering if hover weaving might be of some help, or if someone has some experience in this type of job.

Thanks,

Ron

[Robodoc]

Ron,

I understand you are welding the inside of a pipe and the pipe is on an external axis (using SMOVC only comes up with external or base axis).  You should have two options turned on.  One is pause weaving.  This allows the robot to sit in one place and weave while the part turns under it.  The second thing is endless rotation.  With endless rotation, you can keep turning the external axis and not run into "pulse limits".  With these two options turned on, you would program one full pass on the inside of the tube with the weave. At the end of the pass execute the endless rotation command (to reset the pulse counts) then shift the program the amount you need for each pass (the pitch).  Knowing the pitch and the length of the tube, you can count the passes and know how many to do.

There are some things you need to know.  Endless rotation is not really endless.  The endless rotation command only resets the controller pulse count, not the pulse count in the encoder.  This means every once in a wile you will have to unwind the external axis or reset the encoder.  The other thing is there will be a slight pause at the command to reset the endless rotation.  Without knowing the thickness of the tube you are welding (I'm assuming you are doing some kind of plasma transfer to coat the inside of your tube) I don't know if the pause will cause any issues with your process.

I hope your robot is big enough to reach inside the tube from one end to the other and you have not added some long bar that holds the weld torch at one end.  This would overload the B and T axis on the robot and cause all kinds of trouble.

[Splinky]

Robodoc,

We do have a long torch attached, but it rides on a roller system so there is very little torque on B and T.  We are shopping for a UP50 right now to replace this unit as we are also concerned about damaging the machine. 

I have pause weaving turned on, but not endless rotation.  We are planning to weld one turn CW and one turn CCW to avoid the pulse limits.  We are using an IMOV to step the robot over 20mm between passes.

What I am trying to figure out now is how to shift the job using an SFTON.  I have read all of the documentation I can find but cannot seem to get it to work.  I placed -40mm in P001 and added SFTON P001 to my program, but the robot wants to shift to a -x and -z point.  I am sure it is something simple that I am not grasping. 

Thanks for your advice!

Ron

[Splinky]

So we now have a UP50 installed with endless rotation and pause weaving and are ready to start programming this again.  Having a pause while we reset the pulse count won't be good unless it is very short (less than 0.5 seconds).  In a perfect world we would weld a spiral from one end to the other.  I read through the Endless Rotation manual that came with the robot and it talks about using the MTE command to turn a specified amount of turns during a move.  The only issue IU can see there is that it apparently only works with MOVJ and I'm not sure that we can accurately control the weld travel speed with a JOINT move.

What I would really like to see is a program where we could teach one point at the start of the weld and enter parameters for step over and amount of turns.  This would make it pretty simple for the operator when new jobs come into the shop.

Any suggestions?

Thanks,

Ron