An
e-mail question addressed to this site.
Ed, the tier one automotive parts company I work for,
has been told by the Chrysler corporate weld engineer responsible for welding
that we have to use "self shielding (SS) flux cored wires" when welding
on galvaneald parts. The SS wires we have tried have caused us numerous weld issues.
Our weld rework rates so far have been in the sixty to a hundred percent range.
The workers who operate the robots and clean the welded parts frequently complain
about the self shielded dust and weld fumes. Also the paint shop is appalled at
having to paint over a weld slag that is very difficult to remove. Ed. What is
the logical, justification for using these wires?
Ed's Answer:
I feel your pain and this classic auto weld process nonsense
which by the way has been going on for more than a decade. Let me tell you one
application story about this same "engineer" (a weld engineer would
never recommend these wires) and how his ridiculous welding recommendations has
cost his company Chrysler millions during the last decade. click
here.
An
automotive management solution to the engineering problems generated by the self
shielded flux cored wires. Joe, ship that bloody robot line
and those self shielded flux cored weld wires down to Mexico.
[]
The SS weld wire recommendation may result in excess burn through and welds that
require the weld shop to place a second weld repair pass. The high part heat generated
from electrode negative and poor quality consumables can result in uncontrolled
weld chemistry, unknown HAZ mechanical and weld properties that can lead to premature
weld or part failures.
[] The excess weld heat also vaporized the galvanealed
surfaces along side the HAZ reducing the part's corrosion resistance potential.
GALVANEALED
WELD POROSITY. When
you read in a weld spec "that no external weld porosity is allowed on glavanealed
or galvanized welds" you know that spec has been written by a person with
minimal weld process expertise.
When
welding galvanealed parts you can expect a low level of "internal" random
small pore porosity dispersed throughout the welds with any of the commom weld
transfer modes utilized. With MIG welding as the weld energy content increases
there should be less porosity.
Expect more weld porosity from the low energy
short circuit mode and much less weld porosity from the higher energy pulsed and
spray transfer modes. Spray transfer should provide less weld porosity than pulsed
MIG welds. When the spray and pulsed modes are used, most of the galvanealed coating
surface is vaporized at the leading edge of the weld puddle.
When welding galvanealed with the self shielded flux cored wires, you will always
get more weld porosity that that attained from the cleaner MIG spray or the pulsed
process. The self shielded weld slag does a poor and inconsistent job of protecting
the weld from the atmosphere and part of the SS slag is actually responsible for
the porosity. Most of the self shielded weld porosity results from atmospheric
nitrogen that gets into the welds and produces pores that contain N2.
There
is no such thing as an optimum quality weld on a "galvanized part",
therefore when welding galvanized with any weld process, compensation is required
in both the weld quality specifications applied and in the weld procedures utilized.
As soon as a weld is made on that coated part, the zinc coating in the
weld area is destroyed and therefore the weld influenced area will rust at the
same rate as an uncoated steel. If the auto industry was really interested in
the weld quality it produced, it would require that the galvanize coatings be
applied after the welds are made.
If
you have spent more than 10 minutes reading the information at this web site,
please remember your weld career is based on your weld management or weld process
control expertise, if you have a moment check out Ed's books and unique weld training
resources.
GALVANIZED
PARTS AND WELD POROSITY.
The
reality for galvanized MIG and flux cored welds is that most welds will contain
much more internal weld porosity than external weld porosity, yet most auto weld
quality specifications will typically only half heartily address the external
weld surface weld porosity.
It takes only a few minutes to cut and section
robot weld samples to determine both the internal weld fusion and weld porosity
content. However
if the auto industry demanded internal weld qualification evaluations on it's
galvanized welded parts that industry would then have to make the logical engineering
decision to stop welding on galvanized parts.
That weld porosity you may
find on those stamped parts may be formed by lubricants on the part surface or
the alloy reactions from the zinc surface coating or a combination of both.
As long as welds are going to be made on galvanized parts, engineers should be
careful of the applications selected and should provide tight controls of the
zinc surface content and coating thickness allowed.
External
Weld Evaluation. Rather than arguing with a weld inspector about the size
of an individual, external weld pore in a galvanized weld, its more logical that
weld specifications should require to measure the weld length and size of the
acceptable part of the weld to see if it meets the minimum design weld size criteria.
Why be concerned with a 1.5 mm diameter surface weld pore if you have
made the weld length 2 mm longer than it needs to be. Why be concerned about a
1.5 mm surface weld pore on a two mm part when you measure that lap or fillet
weld on the part and find out your fillet or lap weld is actually 4 mm, or twice
the size it needs to be.
I
recently viewed some self shielded welds on galvanized parts and a quality manager
was arguing about the acceptable size of an individual weld pore when at the same
time he missed the fact that on the 3 mm fillet welds which were required to be
25 mm in length, half the weld was nothing more than a shallow concave crater
offering a weld with unacceptable weld strength.
WHEN
THE AUTO INDUSTRY WELD SPEC STATES A WELD IS NOT ACCEPTABLE AS IT HAS A WELD SURFACE
PORE, THIS INDUSTRY FORGETS THAT THE WORLDS MOST STINGENT PRESSURE VESSEL AND
PIPE CODES PROVIDE A GENEROUS ALLOWANCE FOR WELD POROSITY.
As
MIG spray transfer provides high weld energy and a protective argon mix protects
the minimum alloy content MIG weld, its logical that the MIG process should always
produce superior weld quality in contrast to self shieded flux cored wires on
the same parts. When using MIG on galvanized parts use a low silicon wire like
the E70S-3 and a high energy low oxidizing MIG gas like argon 25 CO2. On parts
< 1.8 mm straight CO2 is beneficial. Use the highest weld settings, "less"
fore hand or push technique, avoid weld weaves, use crater fill data and ensure
the weld surface is always convex.
ED.
WHY WOULD ANY WELD CONSUMABLE MANUFACTURER WANT TO SELL WELD CONSUMABLES THAT
ARE NOT WELL RECEIVED BY THE INDUSTRY IT SERVES?
Many
weld consumable manufacturers like to recommend a weld consumable that their competitors
do not sell. Typically this may not be the best weld consumable for the intended
application, however in the auto industry once a weld consumable is selected for
a specific part, thanks to the common weld engineering and management weld process
apathy the weld wire selected is typically cast in stone. Selling a so called
unique good or a bad weld consumable like the self shielded flux cored wires or
that so called special three part MIG gas has become a traditional weld sales
tactic directed at gullible and ignorant industries as it ensures once the so
called unique consumable are purchased no one else can bid on on that weld consumable
business.
Weld
Reality. From a weld
mechanical, weld chemistry, weld quality and weld productivity perspective, in
contrast to MIG wires, the self shielded flux cored wires offer no weld benefits,
they do however offer;
[a]
excess weld spatter,
[b] excess weld porosity,
[c] tenacious difficult
to remove weld slag,
[d] poor and inconsistent weld fusion,
[e] two to
three hundred percent higher weld consumable costs,
[f] weld fumes and dust
that would be considered a chemical
weapon of mass destruction if found in
Iraq.
[g]
more weld heat in the parts, increased burn through and distortion potential.
[h]
lower weld deposition rates increasing weld cycle times and lowering weld speeds
again adding more heat to the parts,
[i]
excess part heat that can lower both the part mechanical properties and reduce
the corrosion resistance in the weld HAZ area..
SELF SHIELD WELD FACTS:
[a]
SS WIRES AND WELD HEAT:
In contrast to MIG short circuit transfer, in which typically 70% of the heat
is applied to the weld wire tip and the arc goes on and off approx. 100 times
per-second, the SS wires "straight polarity", open arc weld transfer
mode can dramatically increase the part heat and dramatically increase the weld
burn-through potential of thin gage applications, especially as most wires used
are oversize for the intended application. Keep in mind also that in contrast
to SS wires, MIG typically provides welds with greater weld deposition rates providing
faster weld speeds which also provide less part heat. The high heat from SS wire
applications typically will lower the parts mechanical properties and can reduce
the surface coating along side the welds lowering the corrosion resistance.
A fundamental weld fact: The smallest self
shielded flux cored wires available today " 0.035" (1mm) cannot weld
fillet or butt welds longer than 30 mm in length on steels < 1.7 mm without
great potential for weld burn through.
[b] SS WIRES. WELD FUMES AND DUST: In
contrast to MIG welds, the weld fumes and dust from weld cleaning operations produced
from the self shielded wires are typically hazardous and may actually contain
carcinogenic components that few people want to inhale consume or discuss. How
much barium / strontium compounds, high iron content, manganese, and unique alloy
combination mixtures do you want your workers to absorb from that high volume
weld smoke? Recently while test welding these products for approximately one hour,
I felt sick and bilious for the next twenty four hours.
When
using the self shielded weld wires, weld shops have to invest in costly, large
ventilation equipment that would not be required with MIG wires. Of special concern
is the secondary smoke, grinding particles and dust that can get out of the robot
cells. Also consideration must be given for the long term health of the manual
welders that have will have to use these wires to carry out the weld repairs which
will be necessary on most gage galvanealed welded parts.
[c]
SS WIRES AND WELD SPATTER: With MIG welding, the
weld spatter is controllable. With the self shielded products additional man power
is typically required for weld spatter clean up. Also the weld cell equipment,
sensors and weld part fixtures will typically be heavily contaminated with the
unnecessar weld spatter. The
excessive weld spatter is also a reason for the frequent contact tip changes that
this process requires with robot welds.
[d]
SS WIRES, WELD SLAG & PAINT:
MIG produces a minuscule amount
of weld surface slag. In contrast, the self shielded flux cored wire weld slag
is extensive and difficult to remove. If E Coat or paint over the welds is required
this requires consideration.
[e]
SS WIRES AND WELD SPECS. The
ludicrous weld standards applied with these self shielded products is enough to
make one feel ashamed to be part of the weld profession. Some of the self shielded
wires approved have an AWS E71T- GS designation. The GS simply means the electrode
supplier conforms to no specification but his own. The big three corporate weld
specs that allow the use of these wires will often show an indifference for the
weld quality attained.
A
corporate weld spec may be concerned about having no more than 20 percent of the
weld metal having weld undercut. Yet few weld specs will address the fast freeze
self shielded welds which can create suck back craters on the underside (no slag
protection) of thin parts <1.6mm. The suck back craters in the gage metals
can be as deep as the gage metal being welded.
The
corporate weld spec may not allow a single pore in the coated weld suface, yet
the spes will allow an SS weld to be full of porosity, have large concave weld
craters or provide inferior inconsistent mechanical weld properties.
[f]
SS WIRES AND PROMOTIONAL BS. Lincoln describes one of it's
self shielded wires as "an operator favorite" On another one of these
products Lincoln states "it's an extremely popular wire with excellent operator
appeal, low spatter and good weld appearance".
When
you read the descriptions of the SS wires you have to ask yourself what planet
are these people from Lincoln from.
[e]
SS WIRES, WELD HEAT AND WELD POLARITY.
MIG uses reverse polarity (RP). With RP the majority of the weld heat is absorbed
by the electrode wire, (negative electrons drawn to positive wire tip). The self
shielded (SS) wires uses straight polarity (SP) in which most of the weld heat
is absorbed by the weld part. The wire size and weld current used and ability
of the part to absorb the heat will determine how much heat is produced and what
the weld burn through potential.
In the weld wire literature the user
is informed that SP puts less heat into a weld. The SP weld heat distribution
does allow the use of larger SS weld wires. However with SS wires typically larger
wires than MIG wires are utilized so the SS weld current requirements are often
higher. Also on thin gage parts < 2 mm the RP. MIG process allows short circuit
transfer in which the arc is on - off many times per-second. The SC. RP process
is much more suited to gage applications and gaps than any SS product.
Irrespective
of the weld polarity utilized, the self shielded wires are an "open arc weld
transfer mode" in which the arc energy generated is nearly constant.
In
contrast to SS wires, the MIG process offers the unique short circuit mode of
weld transfer in which the arc goes on - off many times per-second.
The
low weld parameter, short circuit transfer weld mode, the small much lower cost
MIG wire diameters, the weld gas coverage which provides low voltages and arc
stability are the reasons that short circuit transfer is the world's most beneficial
weld process for 1 to 2 mm gage metals.
[f]
SS WIRE DUCTILITY. The SS weld
wires have less wire ductility and strength than the MIG wires. As small 0.035
- 0.045, SS wires are now being selected for metals less than 2 mm, extensive
robot wire feed issues may be generated.
[g]
SS WIRES AND WELD REPAIRS: The SS wires are today
responsible for the greatest amount of weld repairs in the North American auto
/ truck industry. Although its a common practice in automotive / truck plants,
to place a self shielded wire repair weld on top of a SS weld with slag. This
is usually against the advice of the AWS wire specifications, and its often an
invitation to a future weld product liability law suit.
When
repairing self shielded welds with the weld slag left in place, both the repair
weld fusion and weld quality potential will suffer greatly. Due
to the tenacious weld slag which forms on the self shielded wire welds, this process
does not allow for quality weld repairs. When repairing welds with burn holes
the manual welder will typically extend the SS wire stick out to avoid weld burn
through. Using the term "welds" for these repair welds is a real stretch.The
repair welds will have poor fusion and be saturated with both weld slag and porosity.
The welds on top of welds may produce excess alloy dilution producing extra high
strength welds with poor ductility.
[h]
SS WIRES AND WELD MECHANICAL PROPERTIES: The
fact that the welded part is galvanealed or galvanized is irrelevant. I have had
mechanical weld tests performed on the SS wires and also on MIG wires. The weld
test results indicate that MIG provides the best internal and external weld quality
and meets all the mechanical needs. Its also notable that with a MIG short circuit
weld that the weld throat depth will be much deeper than the self shielded wire
weld. The SS welds penetration is often shallow and the welds tend to be concave
with often more slag depth than weld depth.
LINCOLN
ELECTRIC STATES THAT THE SS WIRES ARE SUITED TO COATED APPLICATIONS YET LINCOLN
PROVIDE NOT ONE PIECE OF PRACTICAL WELD EVIDENCE TO SUPPORT THEIR CLAIMS.
Weld
fusion and weld throat depth are the two things that add up to the weld strength
and integrity. When tensile tests are taken of the SS wire welds or of the MIG
welds, if the weld quality is sound with both processes the welds will pull apart
in the area's weak link, the heat affected zone, HAZ. As the SS wires put more
weld heat into the part's HAZ , the SS wires HAZ is usuall larger and therefore
weaker than that of the short circuit HAZ.
[i]
SS WIRES AND WELD COSTS.
It amazes me that in an industry that looks for so many ways to shave a $1 of
the cost of a vehicle that some one in engineering would recommend the self shielded
wires with out examining the weld cost consequences.
The price of the
small diameter <1.6 mm, self shielded wires can be two to four times per-pound
the cost of a small diameter MIG wires. The weld deposition efficiency of the
self shielded wires also dramatically increases the weld consumable costs. With
a MIG weld set correctly, the weld deposition efficiency should be at least 99%,
in contrast the SS weld could be one third weld, one third weld slag and one third
weld spatter.
Example.
Lets say a foot long MIG weld requires 0.1 lbs. The MIG wire cost $1 a pound so
the MIG weld wire cost per foot of weld is 0.10 cents. In this proportion the
weld gas for the 0.1. lbs would be approx. 0.05 to 0.10 cents so the MIG consumables
cost for the foot of weld would be 0.15 to 0.20 cents.
The small diameter
0.035 or 0.045 self shielded wires cost approx. $3 lb. Due to poor weld deposition
efficiency it takes 0.15 lbs of wire for the foot of weld. The self shielded wire
will cost 0.45 cents per foot of weld. 15 to 20 cents for the MIG / gas combo,
versus 45 cents for the self shielded wire weld now multiply that by numerous
welds on millions of vehicle parts.
MIG
wire weld transfer is much more stable than the self shielded welds. On many thin
gage applications <1.6 mm, in contrast to self shielded the lower arc energy
MIG process will allow for higher wire feed rates, (higher weld deposition rates).
Typically MIG will allow for a twenty to forty percent increase in weld deposition.
This means when using MIG in contrast to self shielded wires, there may be a potential
of 15 to 30 percent reduction in weld labor costs or a 15 to 30% increase in robot
weld speeds.
A
great impact on weld costs is robot weld efficiency and weld rework costs. Thanks
to Chrysler's weld spec requirement, robots are today using the worlds most inefficient
and costly weld process and often generating weld rework that's typically greater
than 60 percent.
PARTS
LESS THAN 0.035 OR 1 MM.
The
welded gage thickness used on cars and trucks seems to decrease each year which
should not be a surprize as few designers in the auto industry are aware of weld
process and gage limitations. One part I worked on in 2005 had a galvanized 0.8
mm part welded to an 8 mm galvanized part. Today many coated products are being
designed that are less than 1.2 mm and the the SS process is still recommended.
I
hope the auto industry hears this message loud and clear.
The SS welds in
contrast to MIG welds will always be inferior.
The SS welds are poorly suited
for thin gage hydro formed parts, especially on parts < 1.6mm, and thin parts
that require butt welds, fillet welds, weld gaps, and weld lengths on thin gage
that are over 50 mm in length.
I have tier one suppliers E Mail
me and tell me they are using the SS wires and with the lowest possible wire feed
settings and they are still cutting through the parts like a plasma cutter.
It
would be beneficial to the big three management if they recognized the health
and cost consequences of this self induced SS process situation. This big three
company should take note of the weld processes used on galvanealed and galvanized
parts by it's global partners and competitors.
Its time to correct this
costly weld process recommendation, an engineering recommendation that should
makes this corporation bury it's head in the sand.
DESIGN CONSIDERATION THAT ALLOWS WELD
PROCESS QUALITY
/ PRODUCTIVITY OPTIMIZATION
Managers may want to consider providing their designers, engineers and manufacturing
supervision with robot weld process training. Automotive companies will benefit
by hiring managers, engineers and technicians that actually understand the weld
processes they work with. My robot process control training program is unique
in that the training places focus on design and weld compatibility with the weld
process utilized, along with the management, engineers, technician requirements
for robot weld best practices and robot weld process controls.
I
hope this is not your weld management mentality. When you use a
crappy weld
process you send the parts to Mexico as there
you won't find unions that will
object.
In
Jan. 2005 I visited a plant in Mexico making car door parts. The parts varied
in thickness from 0.8 to 2 mm. The parts were galvanized and the weld consumables
used were 045 1.2 mm Lincoln NR 152 SS wires. The SS wires in Mexico cost $2.40
lb while 035 MIG wire was available for $0.060 lb. The weld rework from the SS
welds was mostly caused by weld burn through. The weld rework average was typically
50%. As over 350,000 parts a year were required the high weld rework was a great
concern.
The weld lengths on the galvanized gage parts were typically
15 to 24 mm long. The robots used were Fanuc and the latest 355 Lincoln power
sources were utilized. Fifty percent of the small SS weld lengths on the parts
that were considered acceptable were nothing more
than a concave crater and this
weld situation was impossible to rectify with the voltage sensitive weld consumables
or the new Lincoln power source.
The SS welds as usual looked awful and
the parts were full of weld spatter. Two workers were required for the weld clean
up and weld rework. As there were no corporate weld engineers imposing their welding
will on this Mexican plant, I was allowed to make unhindered weld process changes.
It took me less than three hours to change over to 035 (1 mm) MIG wires with argon
10 CO2 and set the new weld data. With the lower cost MIG wires we produced zero
weld rework and increased productivity by 10%.
I
wonder when the year 2010 arrives will some car or truck plant be reporting on
the problems its having with it's self shielded flux cored welds. Like the Iraq
army an industry will get the personnel and technology it deserves.
Thanks
to the Chrysler corporate weld engineer, thanks to hundreds of apathetic auto
/ truck manufacturing managers and engineers and thanks to companies like Lincoln
Electric and Hobart who's management tout their weld process technology capability
and yet offer a process ignorant industry their poor self shielded consumables,
in 2005 we are getting some of the worst welds the world has ever seen on some
of the highest tech cars and trucks ever built.
Question
on E71T-8.
Ed
Which is the most common, all position, self shielded flux core wire used for
out door structural projects and could you provide some best practice info?
Answer:
The AWS E71T-8. 5/64
wire. This obnoxious wire belongs in a 1920 ship yard, its hard to imagine why
the worlds largest weld consumable manufacturers cannot put a little R&D.
time and money into these wires and develop something wwith a little welder appeal.
This wire is common for structural welds on construction projects, however these
wires are also difficult to use.
E71T-8
Weld Tips:
[]
The E71T-8 wire operates best in a very narrow voltage range.
[] The common
5/64 woeld best at 19 to 22 volts. If the operator changes the wire stickout the
voltage can be out side the narrow operating range. The operator should try to
maintain a 3/4 (18 mm) wire stick out from the contact tip to weld..
[]
Too little voltge causes excess spatter, arc instability and convex cold weld.
[]
Too high voltage causes porosity and excess weld fluidity.
[] Minimum weld
spatter is an indication of correct weld voltage.
[] Long cable lengths
and poor cable lug and ground connections will influence the weld voltage and
current.
[] The best power source for the E71T-8 wire, use a regular CV
power source or a generator with a CV adaptor.
[]
Use back hand or drag. Direct the weld wire into molten pool and angle gun approx.
10 degrees.
[] For good starts, clip the wire stick out to 1/2 (12mm) and
start with a short stick out. Hold the puddle for a second.
If
you really want to see the affects of self shieded
flux cored wires, you may
want to visit here
Thanks
to management and weld engineering process ignorance and thanks to salesmanship
based on weld process ignorance and greed, the self shielded products are too
frequently utilized in auto and truck plants. I would not doubt that these products
in the last decade have cost this industry more than 100 million dollars in weld
rejects and unnecessary weld rework, and god knows what their impact has been
on the health of the workers who unfortunately have to work in the plants where
they are used.
2007:
If you could see the numerous auto parts that have been built in the last decade
with self shielded (SS) flux cored wires you would be astonished at the apathetic
management acceptance of the poor weld productivity, quality, extensive weld rework,
tenacious weld slag, and the hazardous dust and fumes. The only people you will
see smiling around these products are the SS wire manufactures and weld salesmen.
