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Introduction

WCS04-STMAN1-E

®

© 2000–2007 Inter-Industry Conference On Auto Collision Repair 2

INTRODUCTION

Topic A. Obligations To The Customer And Liability

The Collision Repair Industry has an obligation to correctly repair the customer’s vehicle. Collision repairs must be performed using:

■ recommended or tested procedures from vehicle makers, I-CAR, and other research and testing organizations.

■ quality replacement parts and materials.■ repair processes and parts as written and agreed

upon in the repair order.

If items on the repair agreement are not consistent with the repair order, it can be considered fraud.

Performing proper collision repairs requires using parts and procedures that keep remaining warranties intact. Collision repairs must restore:

■ safety.■ structural integrity.■ durability.■ performance.■ fit.■ finish.

Throughout the damage analysis and repair process, the repairer and insurer must communicate with each other and the customer. They must be in agreement with each other and the customer on how repairs will be performed. The customer must be informed of any changes in the repair plan from the original repair agreement and explain the changes and why they have to be made.

To reduce liability, make sure that all repairs are performed thoroughly and correctly. Perform the repairs as listed in the damage report and have documentation of required repairs available for customers. Be sure of the proper procedures. Technicians are considered the experts and are expected be knowledgeable on how to perform a quality repair.

Liability insurance that covers the repair facility may not always cover all damages. For example, the policy may not cover faulty repairs, leaving liability responsibility completely on the facility. A shop owner may find that repair facility liability coverage may not cover the full amount awarded in a lawsuit. The shop owner would have to pay the difference.

© 2000–2007 Inter-Industry Conference On Auto Collision Repair 3

It is difficult to reduce the risk of liability exposure. The part that the repairer can control is the chance of being found at fault. Chances can be minimized by using recommended or tested procedures from the vehicle makers, I-CAR, or other research and testing organizations. It is also important to use quality replacement parts and materials that restore fit, finish, durability, and perform at least as well as the original. Lastly, keep thorough records that document the repair process.

Keeping thorough records includes more than recording the date, mileage, and pre-existing damage. Record keeping also includes:

■ making sure all notes are legible.■ verifying the repairs that were made or not

made.■ having the customer sign a waiver for repairs

that they do not want performed. Repairers must determine their liability on not repairing safety systems such as restraint and anti-lock brake systems.

■ keeping computer printouts or worksheets on file showing wheel alignment readings or vehicle dimensions before and after repairs.

■ keeping scan tool printouts and records of computer codes for airbag, anti-lock brake, emission, and powertrain control module (PCM) systems.

■ attaching the OEM procedure printout to the vehicle repair order.

■ keeping receipts for all sublet work performed.

Squeeze–Type Resistance

Spot Welding

Text

book

®

Squeeze-Type Resistance Spot Welding v.2.2© 2000–2007 Inter-Industry Conference On Auto Collision Repair

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This material provides general directions for collision damage repair using tested, effective procedures. Follow-ing them will help assure the reliability of the repair.

I-CAR cannot accept responsibility for any individual repair, nor can it warrant to the quality of such repair. Anyone who departs from the instructions in this program must first establish that neither personal safety nor the integrity of the repair of the vehicle is compromised by the choice of methods, tools, or supplies.

I-CAR does not endorse or recommend any brands or makes of vehicles, repair equipment and supplies or other products. The appearance of various makes and brand names in any I-CAR material is purely coincidental and is based on the availability of those products at the time of production.

All recommendations presented in this program are based upon research programs or upon tests conducted by laboratories, manufacturers, or selected collision repair facilities. If performed as outlined, these recom-mendations will provide the basis for a thorough, professional repair.

© 2000–2007 by the Inter-Industry Conference On Auto Collision Repair (I-CAR) All Rights Reserved

IMPORTANT NOTICE

Squeeze-Type Resistance Spot Welding v.2.2© 2000–2007 Inter-Industry Conference On Auto Collision Repair

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Module 1–Squeeze-Type Resistance Spot Welding (STRSW) Process .................................................4A. Welding Repair Processes ........................................................................................................................ 4B. STRSW Theory ............................................................................................................................................. 8C. Review .........................................................................................................................................................10Module 2–STRSW Equipment And Settings ................................................................................. 11A. Power Sources ...........................................................................................................................................11B. Arm Sets ......................................................................................................................................................14C. Electrode Tips .............................................................................................................................................16D. Control Settings .........................................................................................................................................22F. Review .........................................................................................................................................................28

Module 3–Making Resistance Spot Welds .......................................................................................... 29A. Flange Preparation And Fit-Up ...............................................................................................................29B. Weld Characteristics ................................................................................................................................31C. Test Weld Visual Inspection ....................................................................................................................34D. Test Weld Destructive Testing ................................................................................................................38F. Review .........................................................................................................................................................39

Module 4–Weld Bonding ...................................................................................................................... 40A. Weld Bonding Process ............................................................................................................................ 40B. Vehicle Maker Recommendations .........................................................................................................45C. Choosing An STRSW Machine ..............................................................................................................46

CONTENTS

Squeeze-Type Resistance Spot Welding v.2.2–Module 1© 2000–2007 Inter-Industry Conference On Auto Collision Repair

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MODULE 1–SQUEEZE-TYPE RESISTANCE SPOT WELDING (STRSW) PROCESS

Topic A. Welding Repair Processes

I-CAR RECOMMENDED TRAINING PATHSSelect the Demonstration icon found on screen A-1 of your CD-ROM for an example of the training paths.

A-2 The recommended welding process for body panels was once an oxyacetylene-fed torch and rod.

Welding processes common in collision repair facili-ties have changed over the years, partly due to the changes in vehicle construction. Processes have included:

■ oxyacetylene welding with a steel rod and a torch fed by tanks of oxygen and acetylene. The process worked well on heavy-gauge mild steel used at the time. As the steel became thinner and stronger, heat-affect became a problem with oxyacetylene welding. The difficulty in control-ling the large heat-affect zone made the process unfavorable to vehicle makers.

■ stick electrode arc welding. At about the same time as oxyacetylene was being used on body panels, stick-arc welding was being used on frames with heavier-gauge steel. Controlling the heat-affect zone is also a problem with this process.

A-3 GMA (MIG) welding is still recommended for sectioning joints.

Gas metal arc (GMA), also referred to as metal inert gas (MIG) welding, became the next recommended welding repair method, and for Chrysler, Ford, and General Motors vehicles built in North America, the only welding repair method. The GMA (MIG) process:

■ produces a more controllable arc and, therefore, has a less heat-affect zone than the oxyacetylene or stick-arc welding processes.

■ is a concern, by most vehicle makers, with some heat-sensitive advanced high-strength steels avail-able today.

■ is still recommended by most vehicle makers where STRSW cannot reach. Also, GMA (MIG) welding is recommended for seam welds at sectioning joints.


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A-4 This door skin has a MIG-brazed joint completely across a seam, though there is no warping of the sheet metal due to excessive heat.

Another welding method that is finding increased use is MIG brazing, which:

■ uses lower heat that does not melt the base metal.

■ is an adhesion process rather than a fusion pro-cess.

■ reduces the extent of the heat-affect zone and decreases the amount of corrosion protection that may be burned away.

■ requires a larger “footprint” than GMA (MIG) welding to help ensure joint strength.

MIG brazing is being used for exterior body panels and some unitized structure applications.

More information on MIG brazing can be found in the I-CAR online program MIG Brazing at www.i-caronlinetraining.com.

A-5 The early model spot welder shown in this drawing was once the norm in European and Asian collision repair facilities.

STRSW equipment with high current levels and pressure used by vehicle makers was originally not available for use in a collision repair facility. Original spot welders outside of vehicle maker factories: ■ included “panel spotters.” The first resistance spot

welding process used on body panels was a one-sided process that used two guns pushed onto the panel to complete the circuit. With single-sided spot welding, there is no guarantee of adequate electrode tip pressure. Equipment for single-sided spot welding is available on most modern spot welders, but single-sided spot welding is generally not recommended for collision repair.

■ that were two-sided, were originally small hand-held units that typically did not have the required squeeze pressures or current levels to match many of the original factory welds.

For these reasons, European and Asian vehicle makers that recommended STRSW usually recommended anchoring panels with GMA (MIG) plug welds.


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A-6 Spot welding is recommended today for several applications, includ-ing the A-pillar flange on this 2005 Ford Mustang.

Today, STRSW is recommended for collision repair welding by most vehicle makers because of:

■ improvements in equipment, allowing welds to be made as strong as the original weld. The usual recommendation is to replace original spot welds one for one.

■ the minimal heat-affect zone. This reduces the concern when welding on advanced high-strength steels that are sensitive to heat. These steels are being used more with each model year. Low heat-affect also allows preservation of most of the existing corrosion protection. Spot welders with inverter power supplies make welds with even less of a heat-affect zone.

A-7 There is a big difference in temperature readings taken just off the edge of a just completed GMA (MIG) plug weld (top) and spot weld (bottom).

Low heat-affect was once one of the main advantages of the GMA (MIG) welding process compared to other welding processes. Compared to GMA (MIG) welding, heat-affect is one of the main advantages of STRSW. Heat-affect is much less with spot welding compared to GMA (MIG) welding.

Noncontact thermometer readings of a just completed GMA (MIG) plug weld and resistance spot weld show dramatic temperature differences. The temperature reading near a just completed GMA (MIG) plug weld is 305°C (581°F). The temperature reading near a just completed spot weld with inverter technology is 23.5°C (74°F).


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A-8 Attachment of a roof panel is a common application for STRSW.

STRSW is not just recommended on exterior body panels, but also structural applications such as pillars, rocker panels, and rail flanges.

It is critical, however, that before using the machine on a vehicle:

■ test welds should be made and destructively tested using the same type and thickness material that will be welded on the vehicle.

■ there is adequate power to the facility and to the outlet where the welder will be used.

■ it is ensured that the machine is capable of pro-ducing the recommended electrode tip pressure and current required for the application.

STRSW is not recommended for aluminum during collision repair. Though aluminum has a lower melt-ing point than steel, aluminum transfers heat much faster. For that reason, spot welding aluminum would require much higher levels of current than steel. Even with the onset of inverter technology in STRSW repair equipment, these high power requirements are not met.

A-9 Spot welds made during collision repair look just like the original joining method.

Some considerations of the STRSW process include:

■ it is the main OEM welding method, performed by robots. Repair welds can be made to look just like original welds.

■ ease of learning. Making a successful spot weld requires little training. Original construction can be duplicated in the field with less chance of error.

■ minimal sparking. Though there is some sparking with some welds, there is much less sparking than with other welding processes. Vehicle and personal protection is still required.

■ no need for drilling holes in replacement panels, such as when making GMA (MIG) plug welds.

■ no filler metal required.■ no filtered lens required. A full-face shield or safety

glasses with side shields is recommended.■ not necessary to dress the weld in most applica-

tions.

Personal safety equipment that should be worn includes safety glasses with side shields or a full-face mask. Leather gloves should also be worn. All flammable materials should be

removed before welding is performed. Do not operate or place the welder near water or in wet locations. Do not place the welder on unstable or uneven ground. Unplug the welder from the wall outlet before servicing, cleaning, or maintenance. The STRSW equipment maker’s specific safety guidelines should also be followed.


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A-10 A long arm set is required to reach both sides of the flange on this bumper reinforcement.

Considerations of STRSW also include:

■ access to both sides of the panel.■ different configurations of arm sets and electrode

tips for different areas of the vehicle.■ the possibility of a maximum combined thickness

recommendation from the vehicle maker. For example, Toyota recommends not spot welding panels during repair that have a combined thick-ness over 3 mm (1/8").

■ the requirement for proper power at the wall outlet. While this is important with any welding process, it is especially important with spot weld-ing because adequate power is required to fuse the metal in the short period of time it takes to make a spot weld. Having adequate power at the outlet may require rewiring in some cases.

A seam weld is not possible, at least with the equip-ment currently available for collision repair. Where a seam weld is required, such as many sectioning joints, a GMA (MIG) welder is usually required.

Topic B. STRSW Theory

B-1 This drawing of a cutaway resistance spot weld shows a fused nugget in the middle of the workpieces.

STRSW is a pressure-welding process. A resistance spot weld is made in three stages, including:

■ squeeze time. This stage occurs when the electrode tips close against the panels to be welded.

■ current-on time or weld time. This stage occurs when the current is turned on, lasting only for a fraction of a second.

■ hold time. This stage occurs after the current is turned off, allowing the weld to solidify.

Some welding machines allow some or all of these to be fine-tuned in a manual setting. The Pro-Spot I4, for example, allows all three settings to be customized in the “Custom B” mode.


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B-2 The first stage is the two electrode tips squeezing together, applying equal force to both sides.

Squeeze time is:

■ the amount of time it takes for the electrode tips to apply equal force to both sides of the metal.

■ necessary to delay the weld current (current-on time) until the electrode force has reached the desired level.

B-3 The second stage is a brief pulse of current lasting only a fraction of a second.

During the current-on time or weld time stage:

■ the current flows easily through the electrodes, but not as easily through the sheet steel between the electrode tips. The current tries to flow from one electrode tip to the other, but meets resistance in the steel.

■ resistance to current flow causes heat.■ there is enough heat to melt the sheet metal and

fuse the pieces together.


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B-4 The third stage is the squeeze pressure holding for a few seconds so that the molten metal can solidify.

During the hold-time stage, the:

■ current stops and the sheet metal workpiece cools.

■ force is held in place for about 1–2 seconds. Too short of a hold time can cause some of the molten metal to throw out of the weld site (metal throwout), weakening the weld.

RESISTANCE SPOT WELD STAGESRefer to screen B-5v of your CD-ROM for an animated video showing the three stages of a squeeze-type resistance spot weld.

REVIEWRefer to screens C-1 and C-2 of your CD-ROM for review questions on the theory of squeeze-type resistance spot welding.

Topic C. Review


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MODULE 2–STRSW EQUIPMENT AND SETTINGS

Topic A. Power Sources

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A-2 No matter the manufacturer, the parts of an STRSW machine are basically the same.

STRSW parts include:

■ a power source. Though the primary power source is the wall outlet, the power is transformed in the machine for welding. The transformer may be located within the arm set and electrodes or in the machine housing cabinet.

■ a control panel for setting the parameters of the weld.

■ an arm set.■ electrode tips.■ connecting cables between the arm set and the

machine cabinet.

One example of a machine with the inverter and transformer located in the arm set is the Midi-Spot Elma-C-9000T distributed by Celette.

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A-3 The power that comes from the wall is transformed to a high-current secondary power to make the weld.

The power from the wall outlet is different than the power used for the weld. There is a primary and secondary circuit. The:

■ primary circuit is the supplied voltage and current at the outlet. This is a high voltage, low current power.

■ voltage and current are transformed in the machine.

■ secondary or output circuit after the transformer is a low voltage, high current power required to make the weld. The power is also changed from alternating current (AC) to direct current (DC) in the machine.

More information on the relationships between voltage, current, and resistance can be found in the I-CAR Live program Electrical Circuits And DVOM Usage (ELE01).


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A-4 A three-phase outlet requires a unique plug (top). If the spot welder has inverter technology, it is built into the machine (bottom).

Some options for STRSW power sources include:

■ single-phase power.■ three-phase power.■ inverter technology, which can be used with both

single- or three-phase power, though three-phase power is preferred by the equipment makers and vehicle makers. Of the vehicle makers that recom-mend specific equipment, most of the welders that are recommended have inverter technology.

■ storage batteries. At least one STRSW machine is powered by storage batteries instead of using the facility’s power supply. This setup provides DC power directly from the power source. The ARC Model 1250 Hybrid System is a DC battery-powered machine.

INVERTER DEVELOPMENTRefer to screen A-5v of your CD-ROM for an animated video showing why inverter technology was developed for use with spot welding.

Refer to the Inverter Technology handout for an overview on the principles included in the Inverter Development video.

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A-6 The simulated AC is transformed into low voltage, high-current power and converted to DC power for welding.

Some considerations of equipment with an inverter power source include:

■ much shorter weld times due to the high-fre-quency current. This means less heat-affect to the surrounding metal, a factor that is good for heat-sensitive steels such as boron-alloyed steel and dual-phase steel.

■ less use of the primary line power, so more power is free for other facility equipment.

■ a transformer is still required to convert the power to low voltage, high current, but the transformer is much smaller than a machine without an inverter. For this reason, machines without an inverter are sometimes called “transformer based.”

More information on inverter power sources can be found in the article “Inverter Power Sources” in the December 20, 2004 issue of the I-CAR Advantage Online.


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A-7 Have an electrician check the power going to the wall outlet while a resistance spot weld is being made.

Regardless of whether the power available to a facil-ity is single phase or three phase, make sure that the power is adequate for the machine being used. Even the best equipment will not perform correctly if the primary power source is inadequate. For the primary power source to be adequate there must be adequate power to the outlets where the welder will be plugged in.

To ensure that there is adequate power, consult with an electrician. Have the electrician test the available current at each outlet while under load. This is done using an inductive ammeter clamped around the cables to the outlet while a machine, plugged into the outlet, is being used to make a spot weld.

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A-8 Inverter-type equipment usually requires number four gauge wire, which is thicker than number six gauge wire.

Even if the supplied power to the collision facility is at specification, current flow can be inadequate to the STRSW machine due to too small a gauge of wire from the circuit breaker to the outlets. This will cause:

■ restriction in the current flow.■ poor STRSW machine performance.■ weak welds.

The minimum wire gauge allowable for a given current rating of a circuit breaker may not provide the neces-sary sustained current required to make acceptable welds consistently. Inverter-type equipment usually requires number four gauge wire.

An extension cord can be used, but must be specially made of at least number four gauge wire to avoid a voltage drop.

If an extension cord is used, it must be properly routed to ensure it does not create a tripping hazard for repair facility personnel or become

an obstacle for other vehicles. Also, make sure the exten-

sion cord does not rest in standing water.


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B-1 STRSW arm sets may be insulated (top) or bare (bottom), and are avail-able in several design configurations for reaching different locations.

Spot welding arms:

■ are available in different sizes and styles to allow access around obstructions.

■ are usually thick enough to withstand high pres-sures and have efficient current flow.

■ may be insulated to prevent accidental shorting to adjacent areas that have bare metal. Insulated elec-trodes are also available for some machines.

■ are usually made of either aluminum or the same copper alloy as the electrode tips.

Topic B. Arm Sets

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B-2 This is a basic C-clamp and piston arm set.

One type of spot welding arm is the C-clamp and piston. This type of arm uses a:

■ stationary C-clamp arm.■ piston arm that moves toward the stationary arm

until contact is made.


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B-3 An X-clamp type of arm set will reach where some C-clamps cannot, but generally require an increase in inlet pressure for proper clamping force at the tips.

The X-clamp type arm:

■ is so called because of the more central pivot location than the C-clamp arm.

■ allows easier access to some flange locations.■ may be the standard arm set or an accessory to

the normal C-clamp arm set.■ requires always using the shortest arms that will

reach the weld site to ensure proper clamping pressure.

■ may require increasing inlet pressure to maintain proper pressure with longer arms. For example, for the X-clamps on the Saitek Invertex Z-1 machine, Saitek recommends increasing the inlet pressure by 15 psi for each 100 mm (4") additional length beyond the initial 70 psi for the 229 mm (9") arms.

Car-O-Liner® calls this type of accessory arm set “A-tongs” for the CR-series of spot welding equipment.

B-4 Arm set installation varies by machine.

When installing the different arm sets:

■ the arm set may pivot into position.■ there may be a collar-type fitting that slips over

the base of the gun.■ set screws may require tightening.■ a different set of electrode tips may be

required.■ the arm sets may self-align the electrode tips due

to the design. Many C-clamp style arm sets self-align the tips.


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C-1 Electrode tips are made of a copper alloy.

Electrode tips are made of copper alloy, which:

■ has less electrical resistance than steel.■ will not stick together. Steel transferring to the

electrode tips during the weld process can cause the electrode tips to stick together or to the workpiece.

Topic C. Electrode Tips

C-2 Electrode tips are available in various shapes and diameters.

Electrode tip styles include:

■ straight.■ curved.■ combination curved and straight.■ single or double angle.■ domed.■ different lengths.■ different diameters.

Use the arm set and electrode tip that will provide the easiest access for a good contact.


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C-3 Some welders have electrode tip ends that can be removed from the main shank.

Many STRSW manufacturers use removable electrode tips, which:

■ are a separate end of the electrode tip.■ are typically press-fit rather than threaded.■ should be routinely cleaned using emery cloth

or P-120 grit sandpaper.■ can be reshaped, but are normally replaced when

worn.■ extend the time before the entire tip and shank

must be replaced.

The machine should be turned off and unplugged before maintaining or replacing the electrode tips.

C-4 The electrode tip end can be domed (left) or have a truncated shape with a flat end (right).

The end of the electrode tip:

■ diameter varies depending on the welder manu-facturer. A contact diameter of 6 mm is stan-dard, according to the International Standards Organization (ISO) standard, for sheet thicknesses between 0.5–1.25 mm.

■ may be flat or domed in shape.■ diameter increases with use. The combination

of heat and pressure causes the electrode tip to “mushroom,” which is the tip end developing a larger diameter than the rest of the tip.

The larger the electrode tip diameter, the more cur-rent required to produce a quality weld.


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C-5 Electrode tips can become misaligned, requiring adjustment.

The electrode tips:

■ are usually 90° to the workpiece. There are elec-trode tips designed to access hard-to-reach areas that will not be 90° to the workpiece.

■ must be aligned with each other so the electrode tips make flat contact with the workpiece. Tips not aligned can result in an oblong-shaped weld. Aligned tips are also necessary for proper current flow during the current-on or weld time.

C-6 When aiming the electrodes, hold the stationary tip at the spot, and press the trigger to advance the movable tip.

Aim the electrodes to the weld site by:

■ touching the workpiece against the stationary electrode.

■ triggering to make the weld without moving the arm set.

OBLONG WELDSelect the Demonstration icon found on screen C-5 of your CD-ROM for an example of an oblong weld.


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C-7 Two types of arm sets and electrode tips, illustrated here, show how different configurations allow accessing flanges.

Use different types of arm sets and electrode tips on different flange designs. For example:

■ straight electrode tips, where there is full access to the flange on both sides.

■ single or double angle, for use on areas such as a wheelhouse.

C-8 Resistance spot welders are either air-cooled (left) or liquid-cooled (right).

Repeated welds cause the electrode tips to get hot. Heat increases resistance, reducing the current avail-able to make the weld. Most STRSW machines have a coolant system for keeping machine parts cool, including the electrode tips. The system is either liquid-cooled or air-cooled.

Air-cooled systems use the same compressed air source as the inlet air for the electrode arm force.

Liquid-cooled systems use a 50/50 mixture of coolant and water. No special type of coolant is required. Coolant is used primarily to prevent corrosion in the lines. Some welders use a refrigerator to cool the water in the reservoir. Examples include the InvertaSpot ATMw® and Car-O-Liner CR510.


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C-9 The small tube opening, revealed when the electrode tip end is removed (left), is where the coolant enters the tip.

Some welder manufacturers allow the liquid coolant to flow all the way to the tips. With this type of the system, the coolant:

■ is pumped through lines inside the arm sets.■ flows into the hollow replaceable tip end.■ returns outside of the line back to the pump

reservoir.■ circulation is constant whenever the coolant

pump is turned on.

Two examples of this type of coolant system can be found on the CompuSpot 800 and the MIDIspot QSVM 9000 distributed by Celette. The system on the Car-O-Liner CR510 has two lines, one to send the coolant to the tips, the other to return the coolant back to the pump.

C-10 A spot welder should be able to make a long series of welds without overheating.

An STRSW machine must be able to make numerous welds in succession. This is sometimes called the duty cycle rating of the machine.

Making a series of welds using high-current flow causes heat. The efficiency of the cooling system will help control the heat and allow the welding process to continue and the weld quality to remain high.

Most newer machines have built-in safety features to prevent machine damage due to overheating. Some machines even have a built-in temporary shutdown feature.


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C-11 The two tips on the left are worn and have imbedded steel, requir-ing cleaning or reshaping.

Electrode tips are the only contact with the workpiece and do wear down. Some signs that electrode tips require attention include:

■ poor looking welds, such as molten metal throwing out of the weld.

■ steel buildup, which may cause the electrode tips to stick to the workpiece.

■ a darkened copper color.■ excessive current required to make the weld. As

the tips mushroom, more current is required to make a good weld.

The machine may indicate that the tips require atten-tion. One example is the MIDIspot QSVM 9000 distributed by Celette, which does a running count of the number of spot welds and lights up a red light on the gun after 50 welds have been made.

C-12 Occasional cleaning with P120-grit sandpaper helps maintain electrode tips.

Electrode tip maintenance recommendations include:

■ storing electrode tips where they will not be dam-aged. There is usually a storage compartment available with the welding machine or attached to the welding machine housing.

■ not using an adjustable wrench, pliers, or locking pliers to remove electrodes if they will be reused. These tools can easily slip and mar the soft copper alloy.

■ keeping the tips clean by occasionally cleaning them with emery cloth or P120-grit sandpaper. The frequency of the cleaning depends on usage.

■ dressing electrode tips, ideally with a tool designed for this purpose, at least for final shaping. Rough shaping can be done with a file. If the proper tool is not available, replacement of the tip or the tip end may be the most practical.

Allow the electrode tips to cool before checking for looseness or proper alignment. TIP MAINTENANCE

Refer to screen C-13v of your CD-ROM for a video on tip maintenance recommenda-tions.


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D-1 The display screen on this welder shows two of the three basic parameters for a spot weld setting: time and current.

Parameters for setting a resistance spot weld include:

■ clamping force.■ current, or the amount of secondary current for

the weld.■ weld time or current-on time.

One inverter-type welder that requires manual setting of the current and current-on time is the Compu-Spot 800HF.

D-2 Clamping force is set by adjusting the inlet pressure (top). On this welder display (bottom), inlet pressure is shown at the right, while clamp-ing force is estimated on the left.

Clamping force:

■ is set by manually adjusting the inlet pressure on the machine. Inlet pressure is typically 50–130 psi (4–9 bar). The inlet pressure on the machine may be expressed in bars. One bar equals 14.5 psi.

■ at the electrode t ips varies between 135–500 kg (300–1,100 lb). The clamping force may be expressed in decanewtons (daN). The for-mula for converting daN to pounds (lb) of force is: daN X 2.2481 = lb of force.

■ can be measured at the tips with a pressure tester. The inlet pressure reading on the machine will not indicate the amount of clamping force at the tips.

■ is not for assisting in joint fit-up. If some of the clamping force has to be used to force the sheet metal together, the remaining force may not be adequate to perform a strong weld.

The range between the minimum and maximum inlet pressure and clamping force is large. This is because different applications, such as welding on multiple thicknesses, different strengths of steel, and weld bonding, require different pressures.

The Car-O-Liner CR510 display screen shows both the inlet pressure and the estimated clamping force at the tips. The CompuSpot 800HF display screen shows the estimated clamping force in decanewtons.

Topic D. Control Settings


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D-3 The amount of current may be displayed as a percentage of the available secondary current.

The amount of current provides the heat to the weld. The amount of current used to make the weld may be:

■ shown as a percentage of the total current avail-able, the actual amount of current expressed in amps (A), or both.

■ programmed based on the thickness of the workpieces selected and the type of steel. The programmed setting may not be adjustable.

■ adjustable in a manual mode.

Current is not independently adjustable on the MIDIspot QSVM 9000 distributed by Celette.

D-4 How long the current stays on may be shown in milliseconds. On this welder, a time of “.17” refers to 170 milliseconds.

Current provides heat to the weld, but how much heat is actually used to make the weld is more of a function of time. The current-on time or weld time:

■ is the time that current passes through the joint.

■ affects weld size. A longer time makes a larger weld. If the current is on too long, however, the electrodes may heat too much. This can result in a large heat-affect zone and distortion of the tips. A large heat mark around the spot weld is a usual indicator of too much time.

■ is usually measured in milliseconds on inverter-equipped machines. On machines without an inverter, time is measured and adjusted in terms of cycles of power, the same cycles used for frequency. One cycle is 1/60 of a second in a 60 Hertz power system (North America) and 1/50 of a second in a 50 Hertz power system (Australia and New Zealand).

■ may automatically “slope” up and/or down for different applications. This reduces the heat-affect on heat-sensitive steels.


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D-5 The 170 milliseconds that each of these inverter-equipped weld displays show, is a fraction of the time that a non-inverter machine requires to make a weld.

An inverter makes it possible to use more current over a shorter time when compared to non-inverter machines.

This short time interval produces little heat, lessening the concern of heat-affect on heat-sensitive steels such as boron-alloyed steel, dual-phase steel, and martensitic steels.

Current-on time is measured in milliseconds on a machine equipped with an inverter. A time of 170 milliseconds means that the current is flowing through the electrode tips for 170-thousandths of a second. On non-inverter machines, a common cur-rent-on time was about one-half second.

D-6 These display screens are a sample of the programmed settings allowed on different machines.

Programmed settings allow a technician to make one or two selections on a keypad and let the machine calculate the other parameters. Some typical settings include:

■ steel thickness.■ heat-sensitive steel.■ zinc-coated steel.■ weld bond.■ pulsed feature.■ vehicle maker specification.


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D-7 This setting is for a weld on two thicknesses of metal, each 2 mil-limeters thick.

Steel thickness is listed in millimeters. This is a starter setting that many machines use. The thickness of one panel may be required or a combined thickness of all of the panels.

METAL GAUGE THICKNESS TOOLSelect the Activity icon on screen D-7 of your CD-ROM for an example of a tool made by I-CAR for measuring

steel thickness.

D-8 Some spot welders have a specific programmed setting for making welds on boron-alloyed steel.

The machine may have a specific setting for heat-sen-sitive steels, such as boron-alloyed steel, dual-phase steel, and martensitic steels. The setting may specifi-cally name the type of steel, or have a more generic name such as “multiphase steels.”

The setting may cause a two-step weld to be made, one step to pre-heat the steel and a second step to make the weld. The setting may also slope up the current before making the weld, and may slope down after the weld time. The intention is to reduce the concern over heat-affect.


26

D-9 This welder has a programmed setting when weld bonding that makes a two-step weld with one press of the trigger.

A weld bond setting is designed to help account for a thickness of adhesive between the mating surfaces.

The setting may cause a two-step weld, with the first step pre-heating the spot to burn through the adhesive. The setting may also slope the current up similar to other settings.

D-10 The “Zn” refers to a weld being made on zinc-coated steel.

Zinc makes up most of the galvanized or galvannealed coatings on many steels.

Zinc has a lower melting point than steel and also lower electrical resistance. These qualities can make the zinc combine with the steel during the current-on or weld-time stage, lowering the resistance of the steel.

To account for this, either more current or a pre-pulse of current may be applied with a zinc-coated setting.


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D-11 The pulse mode on this machine shows the length, in milliseconds, of each pulse.

The pulsed setting may also be called “soft-start.” The setting is designed to burn off impurities in the weld zone which might cause the welder to add more current if they were not burned off. This serves to strengthen the weld while minimizing the heat-affect of more current.

D-12 This machine is able to input vehicle maker programmed settings when the vehicle maker information is released.

The pulsed setting may also be called “soft-start.” The setting is designed to burn off impurities in the weld zone which might cause the welder to add more current if they were not burned off. This serves to strengthen the weld while minimizing the heat-affect of more current.

D-13 The “Custom B” setting on this machine allows programming for a specific weld series, so the settings can be recalled at another time.

Some machines do not have pre-set programs. On most machines that do, the programmed settings are only starting settings. Most machines allow for some adjustments after making a test weld. Adjustments may be able to be made for the amount of current, weld time, and clamping force. Hold time is usually set at the factory.

Once the test weld is successful, many machines allow the settings to be saved in a memory location for later recall when doing a similar job.

Updates to existing pre-set programs, or completely new programs, may be able to be uploaded with software from the welder manufacturer.


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D-14 The indicators on these machines are telling the operator that something is not right with the weld setup.

Some resistance spot welders have “smart” features. These smart features may:

■ indicate if a parameter is not set right to make a good weld.

■ not make a weld until the clamping force and other factors are set right.

■ not make a weld if the primary power source is not adequate.

Some examples of welders with smart features include the MIDIspot QSVM 9000 distributed by Celette, which measures the resistance of the workpieces and uses a red or green light to indicate whether the weld may be a success. The Tecna 3650 will not make a weld if the clamping force is not set right. The CompuSpot 800 also indicates if the pressure setting is too low to make an adequate weld.

SETTING ADJUSTMENTSRefer to screen D-15v of your CD-ROM for a video on how digital settings and microproces-sors have changed adjustment parameters on spot welding equipment.

Topic E. Review

REVIEWRefer to screens E-1 and E-2 of your CD-ROM for review questions on spot welding equip-ment.


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E-COATSelect the Activity icon on screen A-3 of your CD-ROM for an interactive exercise on prepar-ing a flange for making spot welds.

MODULE 3–MAKING RESISTANCE SPOT WELDS

Topic A. Flange Preparation And Fit-Up

A-2 E-coat must be removed from the exterior of each flange.

For current to flow, there must be a metal-to-metal path between the electrode tips. Zinc coatings and weld-through primer, which commonly contains zinc, will allow current to flow. E-coat, finish materials, sealers, or adhesive between the electrode tips will prevent current flow.

When preparing a replacement flange for spot weld-ing without adhesive:

■ remove the E-coat from the exterior flange, but avoid removing the zinc coating. If the specific locations for the repair spot welds are known, only remove the E-coat from those areas.

■ remove the E-coat from the inner mating flange surfaces if required by the vehicle or equipment maker. Again, avoid removing the zinc coating.

■ clean the flanges with wax and grease remover.■ some vehicle makers, such as Volvo, recommend

applying weld-through primer to mating surfaces where the E-coat has been removed. Some vehicle makers, such as the Chrysler Group, do not rec-ommend the use of weld-through primer.

A-3 Joint fit-up usually requires several clamps so that there are no gaps.

When fitting up the joint for STRSW:

■ make sure there are no gaps along the entire length to be welded. Use a hammer and dolly to straighten the flange, if necessary. Any gaps will cause excessive resistance and sparks and may even blow a hole through the flange. There is usually some sparking when spot welding, but a shower of sparks is one sign of a bad weld.

■ use clamps.


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A-4 By using shunting, a spot weld can be made even though there is a coating on the mating surfaces.

Using a clamp to complete the circuit for a weld is called shunting the current. Shunting:

■ is required when there is no metal-to-metal con-tact at the weld mating surfaces, such as when the E-coat is retained or when weld bonding with adhesive between the flanges.

■ allows a path for the current to flow, which is from one electrode tip and through the clamp before making the weld between the electrode tips. Very quickly, the E-coat or adhesive burns away between the electrode tips and the current flows between the electrodes.

■ requires the E-coat to be removed from the outer surfaces, at least where the electrode tips and shunt clamp contact the workpieces.

■ is not required for further welds on the same flange because each weld becomes the shunt for the next weld. For this reason, the welds must be made in succession.

An alternative to attaching a shunt clamp is to clean the mating surfaces at the first weld site to allow current to flow as usual.

A-5 The shunt clamp must be relocated when a new series of spot welds will be made.

An exception to requiring a shunt only on the first weld is where the next weld is not close to a previous weld, such as when starting a new series of welds on another flange.

A-6 The heavy-gauge copper wire between the copper clamp pads make this clamp better suited for shunting than a regular locking pliers.

There are dedicated shunt clamps that are:

■ designed for the specific purpose of shunting.■ built with a heavy gauge copper wire and copper

tips for less resistance to the current flow than a regular steel clamp.

■ available from welding suppliers.


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A-7 Making an insulated clamp does not have to be any more compli-cated than wrapping tape around the clamp jaws.

If the joint must be fit-up while welding, all clamps other than the shunt clamp should be insulated. Insulated clamps:

■ prevent current from flowing through the clamp rather than the previous weld.

■ can be made by wrapping tape around the clamp jaws.

■ are available ready-made from some welding suppliers.

B-1 When the trigger is pressed to make a weld, there is an intense magnetic field around the arm sets and electrode tips.

There is a magnetic field where there is current flowing. With the STRSW process, upwards to 10,000 or more amps are flowing through the arms, electrode tips, and connecting cables.

Welds made deep into a panel require more current than welds made on a flange due to the magnetic field around the steel in the throat of the welding arms.

Topic B. Weld Characteristics

MAGNETIC FIELDSelect the Demonstration icon found on screen B-1 of your CD-ROM for a demonstration of magnetic fields when making a spot weld.

The magnetic field which surrounds the arms and cables when spot welding can affect pacemakers. Pacemaker wearers should con-sult their doctor before performing STRSW

operations. Also, be sure to remove watches and other jewelry before spot welding. The magnetic field can also affect cell phones.


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B-2 Nugget size, which is based on the thickness of the metal being welded (lower left), is measured with a vernier caliper (upper right).

The size of the nugget will vary depending on the thickness of the metal.

A general recommendation for a minimum nugget size is five times the thickness of one metal workpiece. For example, when spot welding two one-millimeter pieces, the nugget should have a diameter of at least 5 mm.

There may be a recommended nugget diameter chart from the vehicle maker. For example, the Chrysler Group and Ford have a nugget diameter chart.

To determine the size of the nugget made, a sample weld should be peeled apart and the pulled-out nugget measured with a caliper.

DIFFERENT NUGGET SIZESSelect the Demonstration icon found on screen B-2 of your CD-ROM for examples of different nugget sizes.

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B-3 Pitch is the distance between one weld and the next.

Pitch:

■ is the recommended distance between welds.■ varies depending on the metal thickness.■ if too short, may shunt some of the current through

the previous weld rather than between the elec-trode tips because current takes the path of least resistance. This can result in a weak weld.

■ as recommended on new construction, such as when fabricating sheet metal, is shown in a chart from the Resistance Welder Manufacturers’ Association (RWMA).

DIFFERENT PITCHESSelect the Demonstration icon found on screen B-3 of your CD-ROM for examples of welds made with different pitches.

Disconnect and isolate both battery cables before welding. Disable the passive restraint system. Due to the magnetic field around the

welding arms and cables, make sure the arms and cables are routed away from wiring harnesses and sensitive elec-tronic parts. Control modules within 305 mm (12") of the repair should be removed.


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Minimum Edge Distance (E)

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B-4 Edge distance is how far the spot weld is from the edge of the workpiece.

Edge distance:

■ is the minimum distance from the outside edge.

■ must allow enough metal to support the weld nugget, or the weld will be weak, even blow off the edge of the panel.

■ is shown on a chart from the RWMA for new part fabrication.

DIFFERENT EDGE DISTANCESSelect the Demonstration icon found on screen B-4 of your CD-ROM for examples of welds made at different distances from the edge.

B-5 A portion of the roof rail and A-pillar on two separate 2005 Chrysler 300 models show the original spot welds in nearly the exact same spots.

Some vehicle makers recommend replacement spot welds be made close to the original welds as pos-sible. Original spot weld locations are programmed and made while the specific vehicle is fixtured in one position. The weld layout may appear staggered. This is because weld layout is usually determined by strength requirements, not appearance.

Examples of vehicle makers that recommend match-ing the original spacing and location as closely as possible include the Chrysler Group and Ford. The screen photos show the driver door opening flange on two 2005 Chrysler 300 models. Notice that the spot weld locations are nearly identical.

Some vehicle makers recommend spacing replace-ment spot welds consistently, despite the original locations and number of spot welds. Land Rover, for example, recommends spacing all replacement spot welds 25–30 mm apart.


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B-6 If it is possible, compare the replacement panel to the original panel to determine where the replacement spot welds should be located.

To help match the original construction:

■ hold the replacement panel up to the original, if possible. There may be recommendations from the vehicle maker for proper spacing if the original panel is too damaged for comparison.

■ use a marker to transfer the original spot weld locations to the replacement panel. Add more weld locations as recommended. Locate replace-ment welds next to the original welds.

■ avoid original spot weld locations. The steel is thin, with changed characteristics, in these locations. As a result, repair spot welds made in the same location as original spot welds are not strong.

C-1 This test weld setup was made from sheet metal taken from the original damaged part.

To obtain the proper machine settings, make test welds:

■ before welding on a vehicle.■ duplicating the same conditions as on the vehicle

for metal type and thickness, coatings, and dis-tance from the edge.

SPOT WELDING PROCEDURESRefer to screen B-7v of your CD-ROM for a video on various recommended spot welding procedures.

Topic C. Test Weld Visual Inspection


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C-2 Some examples of weld defects include (clockwise from the top) metal throwout, deep indentation, and a pinhole.

Visual defects when inspecting a spot weld include:

■ excessive metal throwout.■ deep indentations.■ oblong weld shape.■ pinholes.

Any of these will result in a loss of weld strength.

C-3 The illustration shows that if there is too little clamping force, there will be metal throwout among other weld problems.

Inadequate force is a common cause for many weld defects. If the force is not high enough:

■ resistance increases due to the small air gaps between the workpieces. Higher resistance causes more heat.

■ it can cause defects such as burnthrough, metal throwout, cracks, and pinholes.

The result will be a weak weld.


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C-4 Metal throwout is molten metal that escaped before the weld had a chance to solidify.

Metal throwout occurs when part of the nugget is thrown out of the weld site. When the throwout is excessive, the weld may require dressing.

Causes of metal throwout include:

■ contaminated metal.■ poor fit-up.■ squeeze time too short.■ force too low.■ current too high.■ weld time too long.■ tip misalignment.

Wear leather gloves when inspecting spot welds with metal throwout, since the edges of the metal are sharp.

METAL THROWOUTSelect the Demonstration icon found on screen C-4 of your CD-ROM for an example of metal throwout.

C-5 The weld in the center has too deep of an indentation compared to the other welds.

The weld should be slightly concave. Deep indenta-tions on one or both sides of the workpieces may be caused by:

■ weld time too long.■ force too high.■ poor fit-up.■ excess current.

DEEP INDENTATIONSelect the Demonstration icon found on screen C-5 of your CD-ROM for an example of a spot weld made with too deep indentation.


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C-6 There are numerous causes for an oblong nugget (right), but it is usually because the electrode tips are not aligned (left).

The weld nugget should be round, not oval. Causes for an out-of-round weld nugget include:

■ misaligned arm set or electrode tips.■ electrode tips misaligned with the panels.■ poor fit-up.■ mushroomed electrode tips.

C-7 The metal throwout in this weld has created a small hole in the thin nugget that remains.

A pinhole or crack in the nugget area indicates a thin, weak nugget.

Causes of a pinhole or crack include:

■ hold time too short.■ force too low.■ contaminated metal.

PINHOLESelect the Demonstration icon found on screen C-7 of your CD-ROM for an example of a spot weld with a pinhole.


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C-8 This chart lists visual inspection problems and possible causes.

This chart is based on information from the Resistance Welder Manufacturer’s Association. Some of the machine settings listed are not adjustable on some machines.

Topic D. Test Weld Destructive Testing

D-1 Two tests that can be done in a shop setting on spot welds are a twist test (top right), and a peel test (bottom left).

With a spot weld, it is difficult to determine if the weld is good just by visual inspection. There may be some inner metal throwout or a cavity in the nugget that is not visible on the outside. A destruc-tive test is required to make the final determination of a good weld.

A lap shear test is the recommended method for accurately determining tensile shear strength. Lap shear testing equipment is not practical for a collision facility.

Two destructive tests that can be done without special equipment are a twist and peel test.

D-2 The twist test is done by securing the bottom coupon in a vise and twisting the top coupon off with a pliers. There should be tearout in one of the pieces (bottom).

A twist test:

■ is recommended by some Asian vehicle makers and welding equipment makers.

■ is done by spot welding two coupons together near one end with a single spot weld.

■ is done by twisting the top coupon off the bottom coupon laterally until it breaks free.

■ can be affected by the imprint of the electrodes in the steel. If this test is used, ensure that the metal thickness of each coupon is not reduced in thickness by more than 25%.

The weld should not just break apart. There should be tearout in one of the coupons.

TWIST TEST SAMPLESSelect the Demonstration icon found on screen D-2 of your CD-ROM for examples of test welds that have been twist tested.


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D-3 A peel test is done by securing the bottom test coupon in a vise and peeling the top coupon back with a pliers.

The peel test is another test that can be performed easily in a shop setting. The peel test is widely recognized as a reliable test by equipment makers. To do a peel test:

■ lap one coupon over another, and make a spot weld on the center edge of the top coupon.

■ peel the top coupon away from the bottom coupon using locking pliers or a similar tool.

Metal should pull out of one of the pieces, leaving a hole.

The test can also be skewed if there is an oblong nugget and the narrow end is positioned in the direc-tion of the pulling action.

PEEL TEST SAMPLESSelect the Demonstration icon found on screen D-2 of your CD-ROM for examples of test welds that have been peel tested.

D-4 One of the steps that might make a test weld successful is changing the equipment settings, such as increasing the metal thickness.

If the two pieces break apart cleanly or with too small of a tearout hole, inspect:

■ surface preparation. Is there good metal-to-metal contact? Is the metal clean?

■ fit-up. Gaps between the workpieces add resis-tance. There may be other indications if there is bad fit-up, such as metal throwout.

■ the welder settings. Adjust the metal thickness setting, current setting, or inlet pressure and make another test weld.

■ electrode tip condition. Steel imbedded on the tip will decrease the resistance. Other contamina-tion may have a similar effect. Dress the tip and make another test weld.

■ electrode tip alignment. If the tips are not meet-ing the workpieces at 90°, the weld will be weak. This may also make an oblong-shaped weld.

■ the power source. Other equipment being used in the facility at the time of the weld may affect the power available to the welder.

REVIEWRefer to screens E-1 and E-2 of your CD-ROM for review questions on making resistance spot welds.

Topic E. Review


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MODULE 4–WELD BONDING

Topic A. Weld Bonding Process

A-2 In the weld bonding process, adhesive is applied (top right), the panels are fit-up, and spot welds are made along the flange through the adhesive (bottom left).

Weld bonding:

■ combines adhesive and spot welds.■ may also include combining adhesive and

GMA (MIG) plug welds where spot welding cannot reach. Ford is one vehicle maker that recommends this combination. The GMA (MIG) welds are not made through the adhesive, a 25 mm area around each plug weld is kept free of adhesive.

More information on adhesive bonding of exte-rior panels without welds can be found in the I-CAR Live program Adhesive Bonding (ADH01). More information on weld bonding of exterior panels on Chrysler Group vehicles can be found in the I-CAR Live program Collision Repair Overview For Chrysler, Dodge, and Jeep Vehicles (DCX01). More information on weld bonding and GMA (MIG) weld bonding of exterior panels of the Ford F-150 can be found in the I-CAR Live program Collision Repair Overview For The 2004 Ford F-150 (FRD01).

A-3 The vehicle maker recommends a weld bonding repair on this rocker panel flange.

Weld bonding is done by the vehicle maker and rec-ommended for some repairs because the process:

■ reduces noise, vibration, and harshness (NVH).■ combines the advantages of the individual

processes. The adhesive creates a stiff structure, while spot welding eliminates the concern of the poor peel strength of the adhesive.

■ adds to corrosion resistance, since the adhesive may better seal the joint.


41

A-4 The adhesive used on this test sample contains glass beads, which helps keep a bond-line thickness between the coupons.

Use the adhesive recommended by the vehicle maker. Some considerations for adhesives selected for weld bonding include:

■ the ability to control the thickness. Adhesive applied too thick restricts the flow of current during welding. The use of spacers, such as glass beads in some adhesives, helps control adhesive thickness.

■ working and clamp time, which is how long from when the adhesive is applied to when curing begins. Although welds can be made through some cured adhesives, it is easier to spot weld while the adhesive is still wet. Since adhesive does not allow current flow, the adhesive burns away at the spot of the weld. This is easier with the adhesive still wet, as the adhesive is easily displaced with the current flow at the spot of the weld. Some types of adhesive, such as epoxy, require that all spot welds be completed while the adhesive is still wet, since epoxy is too hard to burn through when cured.

Recommended safety procedures should be followed when performing weld bonding. When using solvents, the technician should

be familiar with the Material Safety Data Sheet (MSDS) and the hazards of each product. Rubber gloves should be worn and skin contact avoided when working with adhesives. Fumes can be produced when welding metal, along with the fumes from the adhesive in the weld site, requiring proper respiratory protection.

Most adhesives used for this application are combustible, meaning they can catch fire. To avoid this, make sure to clean off excess adhesive squeeze-out when making test welds or during the repair.

A-5 This two-part adhesive recommended by Ford is dispensed using a dedicated gun.

Some other considerations for adhesives selected for weld bonding include:

■ a two-part product. The curing time of two-part adhesives does not totally depend on the ambient temperature and humidity. If the proce-dure requires that all spot welds be completed before full cure, shop conditions become an important consideration. Two-part products are typically recommended.

■ strength. Some weld bonding procedures specify a “structural” adhesive, which requires certain strength properties.

■ corrosion-resistant properties. Most adhesive applications require a bare metal flange. The adhesive must then be the corrosion-resistance and bonding agent in one.


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A-6 All of the coatings, including the zinc coating, are being removed from this Chrysler 300 B-pillar flange in preparation for weld bonding.

Whether following the adhesive maker’s or vehicle maker’s recommendations for preparing the flanges, the preparation steps may require:

■ grinding weld nuggets flush on the existing panel.

■ removing any adhesive, paint, E-coat, and other coatings, including the zinc coating. If using the first weld as a shunt, do not remove the zinc coating from the first weld site.

■ straightening the existing flange so there are no gaps during fit-up.

The panel should be dry-set, with clamps, to ensure there is proper fit-up. This will also ensure that there are enough insulated clamps for the procedure.

A-7 Since the adhesive being used on this inner flange is corrosion-resis-tant, it is spread over all the bare metal.

Follow the recommendations for applying the adhe-sive. This typically requires:

■ preparing the adhesive cartridge by leveling the plungers, attaching the mixing tip, and dispens-ing a bead about the length of the mixing tip to ensure proper mixing.

■ applying a small bead along the center of each mating flange.

■ spreading the adhesive out to make sure all the bare metal is covered. The adhesive now provides the only corrosion protection for the flange.

■ applying a third bead of adhesive on one panel to ensure proper bond-line thickness.


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A-8 The technician positions the replacement panel (top left), and slides it into a close fit with the existing panel (bottom right).

When positioning the panels:

■ if adjustment is required, slide the panel. Do not lift the panel to reposition. If the panel is lifted, air bubbles can become trapped inside the adhesive. If the panel is lifted, the adhesive must be removed and reapplied.

■ install clamps where necessary. The first clamp is usually the shunt clamp, unless the first weld area is left without adhesive.

A-9 Weld bond test samples can only be peel tested, not twist tested.

As is recommended with all spot welding procedures, make test welds before welding on the vehicle. Duplicate the same conditions that will be used on the vehicle. With these test samples:

■ a peel test is recommended, rather than a twist test.

■ the recommendation may be to make two welds and use the second weld as a measure. If a shunt clamp is used, shunting may weaken the first weld because some of the applied cur-rent flows through the shunt clamp rather than directly between the electrode tips. If the first weld is made without adhesive, it will not be indicative of the remaining welds. In either case, the second weld will be more of an indication of the strength of most of the welds.

■ follow the weld nugget size requirements from the vehicle maker.

WELD BOND TEST SAMPLESSelect the Demonstration icon found on screen A-9 of your CD-ROM for examples of weld bond test samples that have been peel-tested.


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NUGGET SIZE RECOMMENDATIONSSelect the Demonstration icon found on screen A-10 of your CD-ROM for an example of OEM weld nugget size recommendations when weld bonding.

A-10 The size of the nugget is measured with a vernier caliper.

One example of a weld nugget size recommen-dation from a vehicle maker is from the Chrysler Group. A chart in the “Welding and Weld Bonding” publication lists:

■ minimum weld nugget diameters depending on the thickness of the panels being weld bonded.

■ governing metal thickness (GMT) if the panels are of different thicknesses. GMT is based on the thinner gauge of two sheets or the middle gauge thickness if there are three sheets. The middle thickness is not necessarily the middle panel.

Another example of a weld nugget size rec-ommendation from the vehicle maker is the “Weld Nugget Chart” in the Ford Weld Bonding Procedures technical service bulletin (04-26-16).

It is recommended to measure the weld nugget using

A-11 After the test welds are proven successful, weld bonding is done on the vehicle using the same settings.

Making the spot welds:

■ is done before or after the adhesive is fully cured, though spot welding is easier during the wet time. Cured adhesive is an insulator and will require higher settings than when welding through wet adhesive.

■ on three panels through two layers of adhesive, is only possible when the adhesive is wet. Make test welds using the same setup to ensure the settings are correct.

■ may cause minimal burning of the adhesive. This is a vehicle and personal protection issue. Minor burning of the adhesive will not affect the integrity of the bond.

WELD BONDINGRefer to screen A-12v of your CD-ROM for a video on weld bonding.


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B-1 The marked spots on this replacement outer A-pillar show where the replacement spot welds will be located.

Vehicle maker recommendations for STRSW are generally to:

■ avoid original weld locations.■ not make single-sided welds.

Some vehicle makers, such as the Chrysler Group and Ford, recommend weld bonding for repairs. At least two vehicle makers, Audi and BMW, recommend replacing original weld-bonded joints with twice as many spot welds, using no adhesive.

Most vehicle makers now say to use the same number of welds as were used originally. This is due, in part, to the increased capabilities of today’s equipment. The recommendation is to usually locate the replacement welds as near as possible to the original welds. An example of an exception to that is Land Rover, which recommends spacing replacement welds 25–30 mm apart, regardless of the original locations.

B-2 Spot welds are being made on this front lower rail.

Vehicle maker recommendations for STRSW may also include:

■ equipment recommendations. These may be specific welders. Some of the welders may have software downloaded from the vehicle maker for specific welds. Specific technology may also be recommended. For example, some vehicle makers state to only use welders with inverter technology.

■ structural applications, but only if test welds made before the welds on the vehicle are proven adequate.

■ skip welding to avoid excessive heat buildup.

VEHICLE MAKER RECOMMENDATIONSSelect the Activity icon found on screen B-2 of your CD-ROM for examples of vehicle maker recommendations on spot welding.

Topic B. Vehicle Maker Recommendations


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Topic C. Choosing An STRSW Machine

C-1 Make sure there are legible and complete instructions for using the spot welding machine.

When choosing a resistance spot welder, make sure there is adequate current and clamping force available from the machine. If the repair facility works often on a certain make of vehicle, know the machine requirements from that vehicle maker.

Make sure the power to the facility matches the type of power configuration of the spot welder. For example, if the machine only makes good, strong welds with a three-phase power supply, three-phase power must be available to the facility. Three-phase power is not available in all areas.

Ensure that training and adequate technical support is available from the equipment maker.

C-2 There should be different size arm sets available that can be easily installed.

The electrode tips should be easy to maintain. A convenient solution for this from many welder manu-facturers is replaceable tips that can be sanded or filed lightly and replaced when they lose their shape.

There should be proper attachments available, such as arm sets, for vehicle access. Extension arms must be able to hold the same pressure as the shortest arm configuration, and guidelines provided where the pressure should be increased with longer arms.

To ensure that the machine will perform properly, perform test welds. Try to obtain a machine that can be used on a trial basis. This will allow the repair facil-ity to give it an adequate test on the vehicles and the types of damage repaired in the facility.

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