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Robotic MIG Welds. Fanuc and Power Wave

Advanced TIP TIG Welding
TIP TIG Welding is always better quality than TIG and 100 to 500% faster with superior quality than TIG - MIG - FCAW.

 
 
   




Robotic Welds Carbon Steel Lamp Posts

 

LINCOLN DID NOT SHED ANY
LIGHT ON THIS WELD APPLICATION:


One customer I assisted around 2005, manufactured carbon steel street lamps 11 to 7 gage. It’s a simple manual welding application. On the end of the lamps they weld a flange that mounts the lamp to the floor. The flanges were heavy duty approx. 13 mm thick. They also weld around an access box, (gage material) located on the post surface near the flange.


This street lamp application became unnecessarily complex the day they decided the parts should be welded with a robot. The company ordered a Fanuc ArcMate 100 robot. The robot came with the Lincoln Power Wave, a 450-amp, pulsed MIG power source.The robot system was sold by AGA who had the technical support of Lincoln / Fanuc. Almost two years after the robot was installed the robot had never come close to it’s daily weld production quota.

When the robot was installed it was placed on the lamp production line, however numerous weld issues occurred and the management moved the robot to another part of the plant. The robot was moved to a location where the highly trained plant personnel could “play around” with the settings. With the assistance of Lincoln, Fanuc and AGA, they played around for almost two years to no avail.

The robot lamp welding issues generated daily were numerous and the plant management viewed the robot as a liability, not capable of meeting the simple weld production goals. In the 24-month playing around period, AGA, Fanuc and Lincoln personnel made numerous visits to the plant without any success.


EXCESSIVE ROBOTIC GUN TOUCH SENSING.

To locate the two basic welded parts, the robot first used it's touch sense feature. The robot was programmed to use 28 touch points for one simple square flange and one rectangle part. The touch sensing took 50 seconds or approx. 20% of the 4 minutes 10 seconds robot cycle time. The amount of touch-sensing used was beyond excessive was an indication of the lack of expertise that had been used on this applcation.

SELECT THE WRONG WIRE SIZE AND THE WELDING PROBLEMS BEGIN.
Two years previously, when the first robot welds were made, someone recommended the pulsed MIG process, using an 0.045 (1.2mm) wire. The resulting pulsed welds from the PowerWave were too hot for the application. Someone on the Lincoln / Fanuc / AGA team, for some strange reason recommended an 045,
E71T-1, all position, gas shielded, flux cored wire.


I was requested to come to the plant to see if I could spread some "light on the subject". In a few hours I came to the conclusion that in the attempt to resolve the robot “weld process issues” too much focus was placed on the utilization of the robot's bells and whistles rather than on optimizing the parts and weld process.

The following daily weld issues occurred with the flux cored process, keep in mind the weld and production issues had nothing to do with the weld process used.

[a] Inconsistent weld results, requiring constant robot program changes.
[b] excessive weld burn through every shift,
[c] lack of weld fusion on the majority of parts,
[d] excessive undercut,
[e] slag entrapment.

THE WELD CHANGES AND $AVINGS BEGIN.
Variable weld gaps were an issue which were partially addressed by the robot touch sensing. The gaps were generated by the assemblers of the lamps. When these guys tacked the parts they did not evenly distribute the gaps. So I took on the role of the supervisor and provided instructions and gages to the assemblers that the gaps presented to the robot had to be 0.060 (1.6mm), which was acceptable for this application.

The next thing I checked was the reliability of the Fanuc robot touch sensing equipment. It worked fine. We reprogrammed the robot to touch the parts only six times instead of the 28 times used previously. I tested the repeatability, it was OK. The touch time cycle per part was reduced from 50 seconds to 10 seconds.

WELD PROCESS AND CONSUMABLE LOGIC
Any one who has read my Robotic MIG Welding books would be aware of the fundamental fact that with traditional MIG, the most superior wire size for parts less than 3/16 (4.8 mm) is an 0.035 or 0.040 wire. Especially when the parts have weld gaps. I replaced the 0.045 (1.2mm) flux cored wire with an 0.035 (1mm) MIG E70S-3 wireand used an argon 10% CO2. I welded the parts first using a combination of short circuit and spray transfer. I then set the Power Wave to produce pulse welds on the parts. All the welds produced were optimum from a quality and deposition rate perspective. Proponents of the costly pulsed process note. The differences between the pulsed and traditional short circuit and spray mode welds were not measurable.

MAKE SIMPLE ROBOT MOVES.
For the robot to weld all the way around the square end flange weld joint, which by the way was in a fixed position. The robot made two welds, one each side, each move wrapping halfway around the square joint. The robot moves were complex, stretching all 6 axis of the robot to it's limits. In stretching the robot reach limits, many of the welds did not have the weld gun positioned for optimum weld control. From a programmer perspective, when robot program points become complex, they eventually will require correction. In these circumstances the robot operator may find it difficult to duplicate the initial program moves.I had the flange reprogrammed and produced four simple straight welds with optimum gun angles.


AFTER 3 DAYS AT THE PLANT, THE PAY OFF.
With the new robot program in place, the 0.035 MIG wire and the new weld procedures, I reduced the lamp total cycle time by 50%. We welded 20 lamps and did not have an issue with a single weld. The bottom line, the customer now had a stable process and could now produce in two shifts what they were going to produce in three shifts.




CONCLUSION:
This application took place in early days of the Lincoln PowerWave. When the 0.045 MIG wire was recommended the optimum pulsed weld parameters delivered by the Power Wave, even after lap top program changes were made, were simply too high for the gage parts and weld gaps.


IN MY BOOKS AND CD TRAINING PROGRAM, PART OF THE RECOMMENDED ROBOTIC WELDING PROCESS CONTROL PROGRAM, IS EVALUATE THE SIZE OF THE WIRE AND THE SUITABILITY OF THE WELD CURRENT USED ON THE APPLICATION

Recommending a “deep penetrating” 0.045 all position flux cored wire for the pulsed power source made little sense, have you ever tried this flux core wire to weld an open root. (Fanuc had no clue, Lincoln and AGA should have known better). Also some of the flux-cored welds were made in the “vertical down” position, this wire is not designed for this, as slag entrapment always occurs. For the flux cored wire to function on the thin gage post, low weld setting had to be used. The low flux cored welding parameters, and vertical down weld positions ensured not only slag entrapment but lack of fusion for the thicker flange side of the weld.


In contrast to the 0.045 wires, the 0.035 MIG wire was the key due to its current range compatibility with the application. This part did not require the pulsed transfer mode, however as the company had spent thousands more than it needed to with the purchase of the PowerWave, I left the settings in the pulsed mode. I charged them approx. $3000 For the elimination of the weld problems, weld rework and 50% increase in production. I don't recall getting a Hall Mark thank you card from Lincoln, AGA or Fanuc.

Ed Craig www.weldreality.com:

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