1. Other Aluminum Welding Processes

2. Resistance Welding Learning Activities View Slides; Lesson Objectives
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Lesson Objectives
When you finish this lesson you will understand:
Keywords

3. Weld Bonding
Adhesives are Epoxy, modified-epoxy, or elastomeric urethane adhesives, sometimes with fillers.
When conductive metal fillers are used, welding parameters are nearly the same as those used for welding without adhesives
This figure shows a spot weld in a single-lap weld-bonded joint. Spot welding pressure and heat displace the adhesive and allow metal fusion to form a nugget. The inner dashed circle outlines the weld nugget. The region between the two dashed circles in the figure, or the halo, is effectively unbonded because the displacement of adhesive and heating effects. Some small region of solid state bonding may occur at the innermost (hottest) of this region. However, often the presence of burned adhesive products prevents this solid state bonding. Beyond the halo is a region of transition to full adhesive thickness and adhesive bonding.
Messler, R, “Joining of Advanced Materials” Butterworth-Heinemann, 1993

4. Weld Bonding Advantages Increased static tensile and/or shear strength
Increased fatigue life
Gas tight or fluid tight bonds
Improved corrosion resistance
Complete interface bonding for load transfer
Disadvantages
High percent of irregular shaped nuggets
Higher percentage of expulsion
The advantages and disadvantages of the weld-bonding process are listed here. The disadvantages can be reduced by using an alternate process of welding first and then back-infiltrating with a low viscosity adhesive. But this requires an additional manufacturing step.
Alternate Process
Weld then back-infiltrate with low-viscosity adhesive
Messler, R, “Joining of Advanced Materials” Butterworth-Heinemann, 1993

5. Weld Bonding Variables That Can Effect Weld Bond Quality
Aluminum Alloy Type
Type of Adhesive
Presence of a Forming Lubricant
Metal Surface Treatment
Effect on
Weld Current (Heat) Required to Produce Weld
Strength of Weld
Listed above are the variable which can have an effect on the production or quality of weld made by weld bonding. The next slide shows some data obtained by McCleary and Hulting.
McCleary, S & Hulting, F, “Weldbonding of Aluminum Automotive Body Sheet”, SAE Paper , 1995

6. Lower Adhesive Resistance
Lower Surface
Resistance
Lower Adhesive Resistance
Higher Bulk
Resistance
Oil Film Higher
Resistance
The only welding parameter to truly vary with base metal or adhesive combination was the weld current. The average peak current is significantly lower for runs involving the 5182 alloy which has higher bulk resistance. There is also statistical evidence that the presence of a lubricant increased the interfacial resistance and reduced the current required, and the use of the Alcoa proprietary surface treatment which provides better adhesive bond durability also required higher currents. There was some variation in peak current noted for the different adhesive formulations, but this was not consistent, perhaps because of variations in the thickness of adhesive with various tests.
The resultant tensile strength of the weld bond did show variations as well. The higher UTS 6111 material had high strength levels. There was also some strength variations in the adhesives as noted. And finally, the absence of lubricant resulted in increased strength of the bond joint.
McCleary, S & Hulting, F, “Weldbonding of Aluminum Automotive Body Sheet”, SAE Paper , 1995

7. Roll Spot & Seam Welding Aluminum
Higher Current than Steel - lower resistance, shunting
Excessive travel speed can result in Al pick-up on wheel - Increase time between welds, reduce travel speed
Radius face wheel - face radii 1-10 inch
Clean wheels:
After every 3-5 revolutions - continuous
After eve4y revolution - Roll Spot welding
Or continuous cleaning
In roll spot and seam welding process, the effect of the lower resistance of the aluminum alloys is noted. As before, this mandates the use of higher current levels. This results in aluminum pick-up on the wheel electrodes necessitating frequent roll cleaning or dressing. The oxide layer which must be fractured and squeeze out also requires some change in the wheel electrode design to have a radius face rather than a flat face as well. Recommended radii are from 1 to 10 inch radii. Often a knurled drive roll on the seam welding apparatus will keep the electrode wheels cleaner longer so that fewer dressing interruptions are needed.

8. This table list some recommended procedures for seam welding of aluminum.
AWS Welding Handbook, Vol 3, 1996

9. Capacitor Discharge Stud Welding of Aluminum
Another process used is the capacitive discharge welding process especially for welding of aluminum studs. The capacitors in the control box are charged with AC and at the time of welding the capacitors are discharged through the stud to consummate the weld. There are three variants of this process as seen here. In the drawn arc, the stud touches the work piece and is retracted to draw an arc for a short time and then the stud is upset into the workpiece. Shielding gas is usually provided. In the initial contact mode the stud with an end projection is placed on the workpiece and current passed melting the projection as upset force is applied to the stud. In the initial gap method the stud is held off by a gap and is plunged into the weld as the capacitors discharge. This is the preferred method of small to medium size suds. Often multiple ground connections are used for even current flow.
Use AC to charge capacitors
Three Processes
Drawn Arc (inert gas shield)
Initial Contact
Initial Gap(preferred)
Two Ground Clams for even Current Distribution
AWS Welding Handbook

10. Capacitor Discharge Stud Welding of Aluminum
Here are examples of some of the capacitive discharge weldments.
Studs commonly made of Al-Mg Alloys (high strength good ductility)
Base metal 1100, 3000 & 5000 series low copper 7000 series
AWS Welding Handbook

11. This table lists some properties obtained by the capacitive discharge weld on several different aluminum materials.
AWS Welding Handbook

12. The microstructure shown here shows that good welds are made with capacitive discharge welding.
AWS Welding Handbook

13. A comparison of the welds obtained shows a good weld together with welds made with too high power and too low power.
AWS Welding Handbook

14. Flash Welding of Aluminum
Equipment similar to that used for steel
More rapid platen motion than for steel - softer material
Higher currents - less resistance
Electrodes fabricated from tool steel to prevent sticking
In flash welding, equipment similar to that used for steel flash welding can be used. Because the aluminum is softer, a more rapid platen motion is required than for steel and higher currents are required. The electrodes are usually fabricated from tool steels rather than copper to prevent alloying to copper and possible electrode clamp sticking.