During
2000, I was requested by an engineer at VAW a tier one supplier to analyze the
welding performance of their ABB robot and ESAB Arcitec welding equipment. This
plant produces extruded aluminum parts. The aluminum welded car seats were for
Ford. The car seats and parts required small welds which were made on thin gage
6061 aluminum.
Criterion Machinery was the system integrator for the
seat frame parts. Two ABB robot cells were ordered, ABB advised Criterion that
their "Swedish Arcitec" welding power source could handle the thin gage
aluminum welding requirements. The Arcitec power source claim to fame was, it
was unique in that it was one of the first MIG power sources that was truly integrated
into an ABB robot control panel.
Two
ABB robot cells containing the Arcitec power sources were shipped to Criterion
for initial fixture and weld tests. The weld tests carried out at this time were
minimal as Criterion did not have the necessary weld process expertise to evaluate
the Arcitec or any power source. The two units were then shipped to VAW the tier
one supplier.
Since
the installation of the robot cells, continuous production of optimum weld quality
parts has been impossible due to the issues documented in this report. Weld
reject rates averaged sixty percent and the robot down time per hour averaged
20 to 30 minutes.
Many issues are documented and I have not included
them all in this report, however the primary cause of the extensive weld quality
and productivity issues at VAW was the ABB Arcitec power source . This
weld equipment had extensive electronic problems. The bottom line is the weld
results were inconsistent and unsuited to the needs for the high volume, small
welds on the thin aluminum parts.
Arcitec
Power source History.The
Arcitec power source was manufactured by ESAB in Sweden in the late 1990s. The
Arcitec was an inverter pulsed GMAW power source. This power source was integrated
into the ABB S4/S4C robot controls in an attempt to improve the communication
"response time" between the robot controller and welding power source.
I have extensive knowledge of Arcitec power source issues, as I was previously
employed by ABB, the Swedish manufacturer of robots. My position with ABB was
weld manager / senior weld process engineer. Part of my responsibility was to
evaluate the application performance of new welding equipment which included the
Arcitec.
I have evaluated many power sources during the last three decades and cannot
recall any welding power source that even came close to the amount of welding
Issues generated by the Arcitec. The bottom line, this equipment was introduced
by ESAB to the market place without sufficient testing by ESAB.
The
German marketing manager at ABB Fort Collins, made the mistake of believing the
Swedish sales spiel from the marketing manager at ESAB about the capability of
the Arcitec. Over 100 units were ordered to be installed in the ABB robots for
North America. As I tested the Arcitec and found the erratic performance and many
other issues, I documented the faults and the demonstrated the issues to the ABB
marketing manager, as this manager had foolishly ordered approx one million dollars
worth of Arcitec inventory he was not happy with my reality and he ignored the
Arcitec test results and my reports.
As
a result of the never ending software / hardware issues and erratic performance
from the Arcitec, eventually ABB did reduce it's focus and promotion of the European
ESAB package and instead focused on promoting either the slightly less inconsistent
Miller Invision, and Lincoln Power Waves.
Four years after the introduction of the erratic Arcitec, I was requested by VAW
to evaluate their poor performing robot installations. I knew the installation
had an Arcitech power source, however I was under the impression that the poor
performing Arcitecs were taken out of service and I would be examining new ESAB
units that had evolved electronically from the original equipment I had evaluated
four years previously. What I saw while welding at VAW was I believe the same
Arcitech power sources which were manufactured four years earlier. The units I
tested at VAW certainly had the same unique electronic glitches causing burn backs
and other issues which I was familiar with, and the power sources still produced
an inconsistent output weld voltage and weld performance.
VAW History of Arcitec:
[] A few months after VAW accepted
the robot cells, "three Arcitec power sources were replaced" by ABB.
The typical life of a traditional MIG power source is 10 years without requiring
repairs. With the more sophisticated, inverter pulsed equipment one would anticipate
that this equipment should at least last till the warranty runs out, which is
typically two to three years.
[]
Five months after the robots were installed, the two robots with replaced Arcitech
equipment were unable to produce consistent, acceptable weld production or quality.
Weld reject rates were in the 60-70%% range and the production cycle efficiency
rarely attained 40%.
[]A
Primary Weld Issue. "Wire Burn Backs"
From a weld production
perspective the most serious issue was the numerous welding wire burn backs
which were generated during the arc starts. The wire burn-backs have also been
a dominant cause in the abnormal weld reject rate .
A MIG wire burn-back
when aluminum welding can affect the weld in the following manner. During a burn-back
the welding wire disintegrates in the arc and either cleanly breaks off or welds
itself to the contact tip. With aluminum, a poor arc generated during a faulty
arc ignition can produce a highly oxidized surface, resulting in a dirty gray
area. The arc restart location with its oxidized aluminum surface, is a poor electrical
conductor. When the robot tries to re-strike and create an arc on this contaminated
surface, either the arc will not re-ignite or the weld will be damaged with the
contamination.
A
burn back with the aluminum wire can result in the welding wire welded or trapped
in the contact tip similar to the steels wires shown on the left. The tension
that results on the soft aluminum wire as it's fed can cause the wire to spiral
and wrap tightly around the drive rolls. In a one hour production run on the 19
0ct, 2000, I witnessed on one robot four burn-backs causing a 22 minutes or 32%
per hour production loss.
It
should be noted that there are many reasons for consistent wire burn backsand
as I have written Welding books on the subject
I am very familar with the data requirements for burn back prevention. In the
start and end data, optimum data was provided to minimize the burn backs, but
it had no effect. A primary cause of wire burn-backs with aluminum is poor wire
feed tension, however on this system we had push pull wire feed systems and had
excellent wire tension as tested when the wire exited the gun tip.
Arc
Sounds and Arc Inconsistencies: During the test of both cells, each cell was
set with the same data yet there was no similarity with the welds produced or
the arc sounds attained. As was evident to anyone standing close to the ABB cells
when welding the aluminum parts, the resulting Arcitec "arc sounds"
were extremely erratic and inconsistent. I kept things simple and only utilized
two weld schedules and I ensured the wire stickout length was optimum and constant.
The abnormal weld parameter changes that occurred during the weld were noted on
voltmeters and the weld voltage variations during the small weld cycle times were
extensive.
Arc Ignition Issues: At the arc starts, the ignition
voltage would frequently flare up to excessive levels damaging the parts and
causing wire burn-backs
When
welding thin gage aluminum the degree of difficulty is increased when the welds
are small in length. With a small weld the power source must have the capability
of "responding inside the weld cycle times". In this case the weld cycle
times average two to four seconds.
With
the Arcitec the welds required;
[a] weld start data,
[b] weld data,
and
[c] weld end data.
These
units which were sold on the basis of their fast communication between the power
source and robot control, lacked the electronic sophistication necessary to handle
the weld changes in the 2 to 4 second cycle times.
Note:
I noted the exact same power source symptoms on ABB / Arcitec units installed
at a Mexican car seat plant approximately three years previous. This plant used
the short circuit and spay modes for carbon steel welds on the new VW Beetle car
seats.
After
a day of evaluation and documenting the issues with the Arcitech VAW asked that
I contact ABB about their power sources. The ABB engineers initial response to
the problems was that the people at the auto plant were not capable of handling
the sophisticated ABB technology. ABB sent one of their most experienced tech
reps. After many hours he was unable to run either unit in an acceptable weld
production mode. Frustrated the ABB rep apologized and left.
I
had arrived at the plant on Monday. It was now Wednesday. On Friday. Ford Motor
company reps were coming to witness an optimum robot run off of their aluminum
car seats. I advised we pull out the
Arcitec equipment and replace it with welding equipment I knew could handle the
application.
This was a highly complex operation as the Arcitech and robot
control were one. I brought in a very competent integrator and on Thursday evening
the installation of new OTC equipment was complete. At midnight Thursday I had
set the optimum weld data and was able to produce consistent quality welds with
minimum robot down time. Ford came in the next morning of course having no knowledge
of what had happened during the week. Ford was very pleased with the run off and
gave the green light to VAW to start full production the following week.
I
MADE THE FOLLOWING RECOMMENDATIONS TO VAW TO ENSURE
THE ROBOTS PERFORM CONSISTENTLY
EACH SHIFT:
Implement Effective Weld Process Controls,
This data should be
posted where the robot operator can view it.
Operator
before production commences.
[1] Check fixture, ensure weld spatter does
not cause issues and fixture clamps are fully functional.
[2] Check amount
of wire available, have a spare Alco Tec De-reeler with quick connections.
[3] Check wire tension at shift start and after lunch.
[4] Check
the correct part program is in use and positioner is in correct position.
[5] Run automatic TCP control at the shift start and ensure this function
is frequent during production
[6]Start shift with new tip, repeat after
lunch.
[7] Ensure nozzle is clean, and nozzle reamer and anti-spatter
is used frequently.
[8] At shift start purge gas and check gas flow.
[10] Check wire helix at shift start, adjust wire straighten if necessary.
[11] Check part tube bore for excess weld penetration.
[12] Operators
watch for repeat weld issues and immediately report them to programmer,
[13]
Operators must check that all the welds are in place and the welds are acceptable.
[14] Ensure all parameter settings for weld schedules, ensure wire feed, voltage
and amps are adhered to.
[15] The first production part should be approved
by the programmer or supervisor before production commences.
[16]
Ensure operators are aware of what they can, and cannot adjust. Operators cannot
change the pre-qualified weld data.
[17] Ensure operators use templates
for positioning gun height or angles.
[18]
The robot operators must be trained to recognize weld sounds and weld issues
Management
Responsibility:
[]Each shift will require a VAW individual capable of addressing
programming issues.
[]Provide operators and programmers with well defined
job description.
[] Recognize the importance of the programmer position, provide
bonus incentive for quality and productivity goals.
[]Consider in future the
use of PLC controls for the robot cells to help simplify the operation of the
robot.
[] Consider in future the use of positioner's that hold more than two
fixtures.
[] Tag equipment with all settings;
[] Provide lock for OTC control
panel.
[] On your next project. take a look at the meaning of management and
engineering process ownership and provide process control
welding training for your selves and employees.
Conclusion.
The problems at VAW were extensive and had gone on for more than a year. This
was not a robot issue, the ABB robots were fine, it was simply a process issue.
It took the integrator team and myself FORTY EIGHT HOURS to get this unit running
at over 85% efficiency with minimum weld rework. There are many lessons that can
be learnt from this installation. The prime lesson when it comes to welding,remember
sales talk is cheap. Before purchasing a robot welding cell have the robot supplier
prove the welding process with an extensive run off with your application. Only
deal with robot companies or integrators that recognize and show some concern
for the consequences of their recommendations. I would recommend you take legal
action against the parties involved for your costs, however I believe you probably
wont.
Remember this event took place a few years ago, I would hope after
spreading poor performing Arcitecs around North America and Europe that ESAB has
got it's act together and the ESAB management has employed people that can actually
test a welding machine so today's Arcitec are without welding problems.
I
was paid approx. $5000 for my 5 day visit VAW. I don't believe ABB or ESAB or
Criterion Machinery were sued, and I did not recieve a Hall
Mark thank you card from them, pity!
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