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Resistance welding of aluminium and aluminium alloys (Group 16)
of Aluminum and
PED16 - Second Year – Material Technology Project
• Aluminum in industry
• Resistance welding (Definition ,Principle ,Types)
• Spot (RSW) in automotive industry
• Conditions and rules must be applied in Spot welding of AL
• Contact-Resistance Measurement
• Equipment for RSW of aluminum
• Electrodes for (RSW) aluminum
• Problems connected with electrodes by Spot (RSW)
• Arc-Cleaning Method of Spot Welding Aluminum
• Defects in spot welds
Aluminum In Industry
• According to the newest studies, automotive industry
tends to use light alloys like aluminum and magnesium
alloys. Companies more often use aluminum as an
alternative material for vehicle body.
• The most popular method of joining body sheets is
resistance spot welding. Aluminum and its alloys series
5xxx and 6xxx can be connected by this technique.
Resistance Welding (Principle)
• Electrical heating combined with pressure
(RSW) Principle cont.
• The general heat generation formula in
Where: I = Electrical current (Ampair)
R= Electrical resistance (Ohm)
t = Weld time (HZ)
K= thermal expansion coefficient
(1) Very little warpage of the metal (Sheet metal).
(2) The process can accurately controlled and the
weld constantly uniform.
(3) Suitable for all automatic production.
(4) Clean and environmentally friend.
(5) Operator safety because of law voltage.
• Types (all types based on the same principle )
(1) Spot welding (Most common in industry)
Spot (RSW) in automotive industry
• Resistance Spot Welding (RSW) is widely used
in the high-volume manufacture of sheet metal
products. The automotive industry has relied on
RSW as a principal joining method for many
decades. A typical car contains between 2000
and 3000 spot welds.
• General Motors Yukon (SUV), with lightweight
spot welded all-aluminum rear door (tailgate).
Manufactured at 500,000 units per year.
Spot (RSW) in automotive industry
• Advantages of RSW in high-volume automotive
(1) Inexpensive (per-weld cost ~€ 0.05)
(2) Rapid process (< 1 second per weld)
(3) Ease of automation (flexible process)
(4) No per-weld consumables (i.e. no
issues of piece-cost, inventory, additional
weight or recycling difficulties)
(5) Low training costs (in manual
Conditions and rules must be applied in
Spot welding of AL
• Resistance Spot Welding of aluminum and its
alloys involves applying high power welding
guns because welding current must be 2–3
times higher than in case of steel but the welding
time is 1/3 weld time of steel.
• The main of that is 3 times higher than in case of
steel its thermal and electrical conductivity. It
means the electric parameters (current and
voltage) must be controlled more precisely in
narrower window of time.
• Because of the resistance of the oxide layers and its effect
on resistance welding, it is quite important to know the contact
and total resistance of the sheet samples to be welded. This
device uses low currents through the weld while measuring
the voltage drop and thus calculating the weldment initial
Equipment for RSW of aluminum
• AL Can be spot welded by all conventional RSW
systems and power supplies, if they meet the following :
(1) High electrode force (4-8 KN)
(2) High welding current (20-45 KA)
(3) Minimal deflection in gun arms (<1 mm)
(4) Efficient water cooling of electrodes ,gun arms ,& all
(5) Low-friction force actuator, to maintain weld force as
electrodes move during weld formation (i.e. good follow-
Electrodes for (RSW) aluminum
• (Because of Lower Resistance of Aluminum
Than Steel, More Current is Needed to Make the
• The Main properties of ideal electrodes:
(1) Max electrical and thermal conductivity
(2) Max hardness or resistance to deformation
(3) Tip design which reduce wear
(4) Minimum tendency to alloy with the
material being welded
Alloys used as a material in AL spot
• The copper alloy RWMA Class I (a copper-
cadmium alloy) has found wide acceptance as
electrode material for aluminum spot, roll-spot and
• The RWMA Class II copper alloy, which is heat-
treatable and available in cast form, has also been
used by many fabricators for spot, roll-spot and
seam welding. Because of superior hardness, this
is especially true for the latter two welding
processes which results in greater electrode life.
Properties of Some Copper-Alloy Electrodes
Arc-Cleaning Method of Spot Welding Al
• High frequency arc:
Arc cleaning is a relatively new approach to the resistance welding
aluminum alloys. This approach is the result of the sputtering action
of positively charged argon ions which displaces the oxide from the
negatively charged sheet surface, as shown in figure ,Although this
technique has shown considerable success, additional equipment
and power sources are required
Defects in spot welds
• Unconformities which can appear in spot welds
cause the spot welds can have less strength and
can lead into total destruction of manufacturing parts
of cars bodies.
• The typical unconformities of spot welds are :
(1) Cold weld
(2) Small-diameter nugget
(3) bad shape of welding nugget
(4) cracks inside/around welding nugget
(5) deep indentation of welding electrodes in
• the RSW process of AL and its alloys is
finding a wide range of applications in
joining technology. Its offered new
perspectives for innovative working and
opportunities for cost saving and high
productivity particularly in vehicle