The Lincoln PowerWave and Axle Cracks:
If you want to make your weld manufacturing life more expensive, more complex and less meaningful than it needs to be you could always purchase the Pulsed Lincoln PowerWave.
<1999: My weld task appeared simple, a tier one, axle manufacture located in Michigan ordered two robot systems to weld truck axles. The company I worked for supplied the robots, we were also responsible for setting up the robot cells that would provide one million axles annually. When the robot cells were complete, we were required to provide 5000 welded axles as part of the robot cell run off.
The axle manufacture had previously utilized the traditional Lincoln CV 400 to 600 amp units. This equipment using spray transfer had never created any serious weld quality or productivity issues. An inexperienced weld engineer at the axle manufacturer was responsible for the selection of the Lincoln pulsed Power Wave weld equipment. The carbon steel, MIG wire size selected by the axle manufacturer was a 0.052 (1.4mm).
Two factors were critical for the axle project:
[1] The axle fillet weld sizes must never be smaller than a 1/4 (6mm).
[2] As the annual axle production was a million plus units, every second saved on the weld cycle times was considered critical.TRADITIONAL WELDING METHOD: The axle manufacture had produced axles for decades. With the regular MIG CV equipment the axles were welded with an 0.052 (1.4mm) MIG wire and an argon CO2 mix. The CV equipment used spray transfer to weld the 1/4 (6mm) fillet welds at typical robot weld travel speeds of 20 to 22 in./min. My first objective with the Lincoln PowerWave and pulsed mode and the 0.052 wire, was to try to attain the same travel (production) rates as that previously attained. PULSED AND DEPOSITION RATES: When setting the Lincoln pulsed PowerWave weld data, to attain the desired weld speeds, I had to set the 0.052 (1.4mm) pulsed wire feed rate at slightly over 400 in./min. This wire feed rate is considered the high end of traditional spray transfer for an 0.052 wire.
Using regular MIG spray transfer and traditional CV MIG equipment, a MIG wire feed rate of 400 to 450 ipm was used with the 0.052 1.4 mm carbon steel MIG wires. This procedure had been used by the axle manufacture successfully for many years.
This CV weld equipment sells for $2000 to $4000, was very successful and had hardly changed in more than four decades.
The Lincoln PowerWave DilemmaIt was evident when I was setting the Power Wave, that the pulsed equipment did not respond well to the 0.052 wire and the 420 in./min wire feed settings. The resulting high energy, pulsed arc plasma was both "narrow and intense" resulting in a weld arc plasma that caused a "deep penetrating (digging) effect" on the axle welds.
The first big news that came from the high Powe Wave pulsed settings, was with the robot weld travel rate attained. At a weld speed of 22 ipm, I ended up with an external fillet weld profile that measured only 3/16 (4.8mm). When the 3/16 fillet weld was cut and a macro evaluation of the internal weld profile provided, it revealed that the intense, narrow pulsed plasma had caused the weld to penetrate almost threes times greater than traditional MIG spray penetration.
To get the deep penetrating, undersize fillet weld to an acceptable 1/4 fillet weld size, the robot, pulsed weld travel rate would have to be reduced to a travel rate of 15 - 17 in./min. This 25% reduction in weld travel rate would have a huge impact on the axle weld cycle time, remember every second lost was multiplied by a million axles. I went through all the possible external Power Wave pulsed parameter adjustments, however I could not change the intensity or the profile of the pulsed MIG weld plasma at the 400 - 420 ipm wire feed rates we had to use.
I reluctantly contacted Lincoln. The reason I was reluctant was simple, a life time of dealing with Lincoln had provided me with thick skin and an attitude of little expectations.
Lincoln with its reputation on the line "again", flew in one of its brighter, graduate weld engineers. The engineer arrived cell phoe to ear and s laptop in tow. I demonstrated how at the required wire feed rate, the resulting pulsed plasma was "too narrow and too intense" for the thick wall steel application. The Lincoln young engineer who looked like he just graduated high school, smiled and told me not to worry, as one of the prime features of the PowerWave was that with the assistance of their unique lap top software, he could change the power source wave forms to suit any application. I smiled back at him, and said "good luck".
To perform the test welds for the Lincoln rep, I provided a long piece of 3/8 (9 mm) carbon steel plate with a ground surface and told the Lincoln engineer that when his power source could place a robot butt weld on the surface of this 3/8 plate with the 0.052 wire without providing an unacceptable digging crater effect, then his work was done. Two days later, his over worked lap top had provided every possible combination of pulsed weld parameters and wave forms. With the 0.052 wire feed rate set at 420 ipm, the high energy, digging pulsed arc plasma still remained narrow and too intense for the axle application.
The red faced Lincoln rep who had stopped smiling the day before, packed up his computer and left, promising that "his people" would look into the situation and get back to us. Over the years I have heard this "Lincoln will get back to you" canned response many times. Of course "his people" never got back to us, after all we are all aware a duck is a duck and bull is bull.
I hope while trying to set those pulsed welds, the Lincoln engineer had absorbed a weld fact that I had known while he was still in middle school.
Pulsed welding equipment may offer millions of wave forms, however like spray transfer the pulsed mode provides a limited optimum weld parameter range for a specific wire diameter. The pulsed weld parameter range has both wire feed and peak frequency / peak current limitations. For a given wire diameter the resulting weld current from the peak and back ground pulsed current cannot exceed the maximum current utilized for traditional spray transfer.
Irrespective of the potentialwave form configerations, there are only so many electrons that can be squeezed into a MIG wire and across an arc,
its fundamental arc physics.
The bottom line. With the MIG process a stable, optimum bell shaped weld plasma is desirable as the bell shaped plasma provides good coverage of the weld area and is less condensed than a narrow concentrated plasma profile that result in a digging weld.
When using pulsed and large diameter MIG wires > 0.052, and the requirement is high wire feed rates, achieving high deposition rates > 14 lb/hr, and welding fillet welds on steels > 6 mm, a typical spray weld current range of 380- 450 amps is required. With the pulsed mode, a very high peak current of > 460 amps and high pulsed frequency is required to provide sufficient energy for the high deposition weld. The resulting high peak pulsed parameters will result in a narrow, concentrated agitated pulsed plasma, a plasma which in this case had more in common with a plasma cutting arc than it does with a MIG welding arc,
THE RESULTING ARC PLASMA FROM THE LINCOLN POWER WAVE POWER SOURCE LOOKED MORE SUITABLE FOR PLASMA CUTTING THAN FOR A CONTROLLED, STABLE MIG WELD WITH A SUITABLE WELD PROFILE.
As the down cast Lincoln engineer walked towards the plant exit with his lap top and the unique Power Wave Form software cradled in his arms,
I who have little patience for the universal, sales induced, bovine fecal weld matter, and being a pragmatic thick skinned Manchurian, (means born in the industrial heart land of Manchester. UK) decided to pour a little salt on the engineers wounds.
I asked the Lincoln rep, "don't you think it's a little ridiculous that at the end of the day, your costly Power Wave pulsed equipment provides inferior weld results to your traditional DC 400 amp MIG power source? The DC 400 power source design has changed little in more than three decades, its durable and can be purchased for 20% of the price of a Power Wave"?The Lincoln rep did not reply to my question, he just shrugged his sagging shoulders and left looking like he needed to get into a new career.
SOME WELD COSTS, WELD BENEFITS: The lower cost, traditional Lincoln CV. DC. 400 amp power source, or a Miller Delta Weld power source used on this axle application would produce spray transfer welds with superior weld fusion profiles and 20% faster weld speeds.
For optimum pulsed weld results, pulsed parameter limitations should be applied to specific wire diameters and applications irrespective of the so called, unique electronic wave form promises made by inexperienced engineers and weld equipment marketing personnel who simply do not know better.
THE LINCOLN POWER WAVE SAGA CONTINUED WHEN WELD CRACKS
OCCURRED IN THE AXLE WELDS. After the Lincoln rep left we went back to using a lower pulsed setting for the 1/4 (6 mm) fillet welds. A few axles were then pulsed welded with the Power Wave at the low robot weld travel rates of 17 ipm.
Attention was now focussed on the Ford weld specification for the truck axles. The weld spec required a "macro examination" of a specific amount of axle fillet welds. A measurement of the internal fillet weld cross section was required to ensure the minimum weld throat dimensions were being attained.
In evaluating the Lincoln Power Wave weld cross sections from the axle pulsed welds. I noticed even at the lower pulsed settings the penetration was still deep and narrow and "center weld hot cracks" had occurred in more than 20 % of the axle weld samples we tested.
Due to the narrow, pulsed deep weld penetration profiles and restrained high tensile steel weld joints, we were getting classic "hot cracks" in the axle welds.
As we had minimal weld test equipment at the robot company, I had the University of Colorado metallurgy department verify that the axle weld cracks did result from the poor pulsed weld profile. They provided written confirmation.
The center weld cracks were not a surprise from the Lincoln Power Wave pulsed welds as I had previously complained to the axle company management about the poor pulsed weld depth to width ratios and predicted the weld cracking issue.
Before we produced any more axles I notified my management, who then notified the axle manufacture management of the pulsed production and weld crack issues. We informed American Aaxle that the use of the Lincoln Power Wave pulsed mode would result in deep, narrow weld fusion, and this poor weld profile combined with the high strength steels and restrained weld joints was a classic set up for potential hot center cracks. At this time I requested to call a hold on the project.
The robot project manager and I flew to Michigan where we had a meeting with the American Axle corporate management and the responsible engineers. I explained to these personnel that their choice of the Lincoln Pulsed PowerWave, and the pulsed weld parameters utilized were creating weld cracks and reducing the axle cycle times by approx. 25% . I explained that if they complained about the Power Wave weld equipment to Lincoln, I believed Lincoln would have no choice but to exchange the four Power Wave power sources for their conventional CV. MIG equipment. If the axle company would make the power source change we could get the desired weld cycle times and eliminate future potential weld crack issues and reduce future liability concerns for axle failures. The axle company management thanked us for the data and said they would consider the matter.
WITH MOST ROBOT MIG AND RESISTANCE WELD PROBLEMS, IT'S THE HUMAN ELEMENT THAT'S TYPICALLY THE CAUSE OF MOST WELD ISSUES.
The Axle company management decided to let the decision stay with their incompetant weld engineer. The engineer would not back down from his Lincoln, Power Wave equipment selection and after we left, he convinced his managers that irrespective of the technical facts and weld crack samples presented, that he had made the right weld equipment choice. The weld equipment decision was made. American Axle stuck with the PowerWaves.
Meanwhile as the axle company could not take immediate delivery of the robots. The robot company I worked for was asked to weld a great number of axles. During this manufacturing period I noted the center weld cracks continued. I left the robot company a short time later.
In 2007 I believe the axles welds to this day are still made with this equipment. American Axle switched the PowerWave pulsed mode off. Maybe the Detroit best selling trucks will die of rust before the axle weld cracks can propagate to failure. Maybe the PowerWave was eventiually used with lower pulsed settings that don't cause cracks.
No one I discussed this with seemed to want to take this issue to a higher level, however I happen to be a catholic with a conscience. I sent a registered letter to one of Ford's lawyers in Detroit. In the letter I spelt out my concerns with the axle weld cracks on their trucks. The lawyer or Ford never replied.
Could it be that Ford did not get to hear, or did not want to hear about it's axle weld issues. Is it possible that Ford would rather wait to see how many axles fail on it's trucks and how many life's are lost before it decides what action has to be taken.There is this weld reality. Many of America's best selling trucks will have axle cracks that were caused by a companies management that would not take responsibilty for its manufacturing weld problems.
WITH ALL ENGINEERING DECISIONS IT PAYS TO BE OPEN MINDED,
IT ALSO PAYS TO KNOW THE PROCESSES YOU CONTROL
ONE DAY SOON I WILL WRITE MY LAST BOOK TITLED,
"IMAGINE A MANUFACTURING WELD SHOP WITH QUALIFIED
MANAGERS AND ENGINEERS. A WELD SHOP THAT RUNS
WITHOUT THE INFLUENCE OF SALESMEN"
