S-TRSW and Auto Collision Repair
The squeeze-type resistance spot welding (S-TRSW) was invented over 100 years ago. S-TRSW has been used by car manufacturers since 1940 as a superior technique for
welding sheet metal. Today a manufactured car takes up to 5,000 spot welds.
Lately, in the North American collision repair industry, only 10% of the body shops use this
type of welder. In contrast, 80% of body shops in Europe and Japan implement this method of electric spot welding
What are the different types of spot welders available?
There are two kinds of spot welders on the US market today. The first type is an AC
power unit with electric transformer built directly to a welding gun. The large suspended welder has an overhead boom and is liquid cooled. The second type is a DC-power unit
with 7-10 ft. welding cables. The cables are connected to the welding gun. The gun can be manual or air operated to squeeze the welding tips together. Forced air is used to cool
the welding cables and its pneumatic spot gun.
Welding gun and AC transformer in one unit.
AC power welders can perform double-sided welding and their reach can be increased by
using 10 to 24 inch extension welding u-arms. Using such an extension, a rear body panel can be, for instance, welded to the lower flange.
The large G-type pneumatic spot gun has an L-shaped tip/arm and a straight tip is held in the plunger. Due to the size and weight a larger spot gun weights 70 lbs. Due to its heavy
weight it is always operated with an overhead boom and a wire to a counter balancer. This makes it nearly impossible to weld hard-to-reach areas; ie: around a radiator support, or
in an engine compartment. 60% of all welding repairs can be performed by this unit. Thus, this unit is somewhat limited.
Other units such as smaller hand-held AC-units are very limited due to the lower power range and long extension arms can't be used.
What is the benefit of a separate spot gun on welding cables?
Compact DC power welders are more versatile due to the welding cables and use of
various light-weight welding guns. A separate welding gun only weights about 8 lbs. The cables and gun can be supported by a simple cable hanger or an overhead boom with an 18 lb. ratchet sping-loaded balancer (Ergonomic Work Station). The ergonomic work-
stations have been designed with the technician in mind. They are easy to use. All the welding accessories such as special welding arms and tips are organized and kept at arm's
reach. Every arm, tip and tool has its own place with picture and name. (Organizer for Tips and Arms.) There is no need for a separate tool board so that the technician does not
need to go back and forth.
Pneumatic G Welding Gun
The welding gun can be unhooked from the suspended wire to increase the reach; i.e.:
working from the inside of the car, welding around front and rear window. The G-type pneumatic spot gun with five different arms and tips can be used in 70% of the welding
repair, i.e.: around door openings, window, quarter panel, wheel house, roof and other areas with short flange and easy access. The various 10" - 24" extension U-Arms will
increase the reach: to weld rear panel to lower flange.
Manual C Welding Gun
The C-type manual spot gun works like a pair of pliers with two straight tips. There are
around eight different arms and tips which can be used for easy access as well as hard-to-reach areas; such as: narrow areas, inside engine compartment, open channel and
door skin. All in all, the manual spot gun can do 80% of all welding repairs.
Single-sided welding of non-structural areas.
The 7 to 10 ft. welding cables make it possible to do single-sided welding in non-structural
areas such as: roof panels, quarter panel, inner front wheel house and trunk floor. Single-sided welding will always penetrate by attaching the ground cable in the lower panel
and starting the first weld as far as three feet away from the ground on the top panel. This will fuse one weld at a time. This technique differs from using the old panel spotter with the
two probes weld where you could not tell if the electricity penetrated both the upper and lower panel or if the current only went through the top panel. With one probe welding you
will always penetrate both sides provided you see a red glow and if you weld in the correct sequence.
Intermittent stitch welding uses a rolling blade to seal edges when doing an overlap or a sleeve. This will prevent moisture from getting in between the joints, thus preventing the paint from cracking.
Other single-sided welding types applications are: Pin welding, Nut welding, Bolt welding, and Stitch welding.
Electricity used for sheet metal repair and dent pulling.
Instead of using a torch for heat shrinking or retention, a carbon rod (for larger area) or a
drawing bit can be used for high spots. Dent pulling can be done in several different ways. The Weld-pull-twist Slide Hammer with a reusable tip (up to 1,000 times) is very fast.
This tool replaces the nail gun and slide hammer with chuck. The six step job: weld nail - lock on chuck - pull - unlock chuck - cut nail - grind off nail, is replaced with a three step
job: weld - pull - twist.
Bear Claw with Wiggle Wire
Another fast tool for dent pulling is the "Bear Claw" with "wiggle wire". The wire will be
welded on with the stitch blade. The Bear Claw's fingers will be inserted in the loops and is pulled by hand. For heavy pulls you can weld on the "Pull Tabs" and use a "Pull Plate".
By welding 10 pull tabs side-by-side and attaching a pull plate, a force of 2 tons can be applied by using a hydraulic ram or tower.
Rule of 95
By including single-sided welding and a complete set-up with both spot guns and 15
welding arms and tips, 95% of all automotive welding repair can be done. The metal inert gas (MIG) unit is still needed for where the spot welder cannot reach or for butt welding.
Also, 95% of weld grinding is eliminated. Grind dust and hazardous fumes are reduced by 95%; and, you save 95% on cost of abrasives normally used.
Cosmetic Welding of Aluminum
Aluminum panels can be welded with the DC (direct current) machines. Data Welder
provides information on this aspect of welding in the training included with the purchase of a welder.
Powerful High-Tech Welders
The spot welding equipment of today is not to be confused with the old panel spotter of
yesteryear. The new welders use 3-phase electricity and can deliver much more amperage. A rectifier converts Amplified Current (AC) to the Direct Current (DC). The
most powerful welder today can generate 20,000 amps.
Aside from the higher power, there are three more functions that set aside our modern spot welders from the other makes.
Our welders have a Direct Current Circuit (DCC) that is critical for welding through
painted surfaces. This circuit indicates when the proper current passes through the welidng tips. It provides start of the main current and weld for the pre-set time. This means the
welding time will be the same for each weld despite what is will take for the hot tips to melt through the non-conductive primer.
Soft-Start and Pre-Heating Functions
The latest improvements are the "Soft Start" and "Pre-heating Function" or "Slope
Function". The welding cycle includes pre-heating multiple pulses from very low to full level current followed by regular 0.4 - 0.6 seconds regular main welding pulse. This
procedure will prevent heavy sparks and possibly burn-throughs. Also this new pulse pre-heating technique lowers the overall heating of the welded area and a smaller heat ring
will appear. It will weld with 100% penetration every time and will easily weld through primer without any grinding in between the panels. These functions are especially crucial
for collision repair shops where Electro-zinc coated replacement panels or painted surfaces are involved and high-strength steel is used..
Overheat Shut-off System
In order to prevent damage to the transformer from overheating, there is a built in shut-off
system. The most common cause for overheating is when the tip diameter becomes too large. Therefore, dressing them down to 6mm (1/4") is required.
Welding Strength S-TRWS vs. MIG and OEM
Tests of welding strength have been performed between S-TRSW, MIG and Original
Equipment Manufacturer (OEM). The diameter of factory (OEM) welds is normally 6mm (1/4"), while S-TRSW produces 5mm (13/64") welds. By welding 30% more with the
S-TRSW, the strength will be the same or better than OEM. When welding thinner sheet steeel, 1mm (20 ga.) to thicker 2mm (14 ga.); or 3 sheets of steel 2mm + 1mm + 2mm (20
ga + 14 ga + 20 ga) with S-TRSW the strength increases and will be almost as strong as OEM. S-TRSW is also stronger than MIG welding when welding 3 sheets of steel.
Do all Car Manufacturers Recommend S-TRSW?
The answer is No. Ford and General Motors in the US do not recommend S-TRSW. On
the other hand, Ford and GM in Europe to use S-TRSW for repair of their manufacturered vehicles. It is no different than for 30 years ago when MIG welding was introduced. It
took a long time to agree on the technique.
Does I-CAR approve of S-TRSW?
The answer is: It depends on what the car manufacturers write in their repair manuals.
I-CAR is giving training and recommendation based upon what the repair manuals are saying.
Recommended Techniques with S-TRSW
First, do not grind off E-coating between new panels. Use zinc rich "Weld Through
Primmer" in between new and existing old panels. Grind outside surface from non-conductive E-coating. But do not grind off the conductive zinc coating. Always warm
up the tips 3 - 5 times on scrap metal before starting any welding job. Then weld 30% more welds then OEM welds. Make shallow welds and always look for the red glow.
Black welds indicates too low temperature with no penetration. A welding cycle consists of Positioning - Squeeze - Weld - Hold; which takes about 6 seconds.
Today's systems have three key features. First, repair technicians can now spot weld
through the e-coating in between the panels, keeping the life-time corrosion protection intact. The zinc coating seals around the welding nugget in between the panels. The zinc
forms brass with the copper electrode on the outside spot surfaces, thus protecting the metal panels.
Secondly, repairers can now produce a pre-accidental factory type weld with far less hazardous fumes than MIG welding.
Finally, spot welding is four to five times faster than MIG welding. This calculation includes drilling the holes, MIG welding and after grinding. This is in contrast to fusing the sheet
metal with resistance spot welding and light after-wire brushing.
Hands-on Training and Future Education
Training is always important when introducing new technologies. As you are well aware,
the body shop owner or manager is responsible for a bad S-TRSW job as well as for a bad MIG welding job. Data Welder includes on-site, hands-on training with a purchase of
a Data Welder Ergonomic Workstation. The S-TRSW method has a simple and consistent technique and it is less complicated to learn than MIG welding. A compelte
workstation can preform 13 different tasks therefore it is highly beneficial to have all technicians trained to maximize the use of the equipment.
Inter-Industry Conference on Auto Colision Repair (I-CAR) offers insight on S-TRSW in "Collision Repair 2000" and "Uniform Procedures for Collision Repair". There is a new
student instruction book "I-CAR Professional Automotive Collision Repair" by James E. Duffy from Delmar Publishers which covers resistance spot welding (p161 to 167).
More and more Technical Colleges are purchasing these welders and will eventually begin hands-on training for S-TRSW.
Return on Investment
One area where collision repair facility owners and manager may have conern about
S-TRSW is the cost. True, these welding stations do cost about two to three times more than a MIG welder; however, can pay for themselves in as little as four months.
By using a simple calculation, you can figure your ROI. An average MIG welding time for a quarter panel, radiator support or rear panel is approximately four hours. You will
require only one hour with S-TRSW because the process is four times faster. If you replace five panels a week that means you are MIG welding 20 hours/week. With
S-TRSW you will accomplish it in five hours. According to the estimates you will generate a revenue of 20 hours and will have 15 hours for other additional jobs.
With a calculation on an investment of a $17,000 S-TRSW station (this includes three-phase electrical installation of receptacles and training) shows that using the welder
five hours per week will lead to ROI within four months. Increased profit will be $3,000 and increased productivity will be $2,000 per month, totaling $5,000 per month. This is
based upon 10 years use of the equipment and a shop rate of $35.00 per hour.
It is a win/win situation for the body shop owner, as well as the repair technician; regardless of the type of payroll plan used: hourly rate, flat rate or commission.
Productivity and profit will increase dramatically.