1. Resistance Welding
Resistance Welding is a pressure welding technique using high current and low voltage
The current passing through the two overlapping workpieces causes local heating and tempeature of the metallic pieces raises to the fusion point due to resistance offered by the workpieces to flow of current
Subseqent aplplication of pressure results in permanent joinining of the workpieces by the formation of weld without the use of filler material
Workpieces are placed between two rods or wheels(rolls), which serve as conductor for producing welds AC electric current is supplied through copper electrodes or rolls connected to the secondary coil of a welding transformer.
It is used for welding thin sheets of similar metallic materials

2. Voltage : 0.5 to 10 V
At Amp
H = Amount of heat generated at the contacting area of the elements to be welded ( Joules)
I = current ( Amperes )
R = resistance of the ckt at contacting area ( ohms)
T = time for which electric current passes through the joint. ( sec ) ( sec )

3. Advantages of Resistance Welding: High welding rates; Low fumes;
The following metals may be welded by Resistance Welding:
Low carbon steels - the widest application of Resistance Welding
Aluminum alloys
Medium carbon steels, high carbon steels and Alloy steels (may be welded, but the weld is brittle)
Advantages of Resistance Welding:
High welding rates;
Low fumes;
Cost effectiveness;
Easy automation;
No filler materials are required;
Low distortions.
Disadvantages of Resistance Welding:
High equipment cost;
Low strength in case of discontinuous welds;
Thickness of welded sheets is limited - up to 1/4” (6 mm);

4. Resistance spot welding Resistance seam welding
Applications :
Resistance Welding (RW) is used for joining vehicle body parts, fuel tanks, domestic radiators, pipes of gas oil and water pipelines, wire ends, turbine blades, railway tracks. Types of Resistance Welding are:
Resistance spot welding
Resistance seam welding
Resistance butt welding 1. Upset welding
2. Flash welding
Resistance projection welding

5. Diameter of the weld spot is in the range (3 - 12 mm).
Figure : Resistance welding, showing the components in spot welding, the main process in the RW group.

6. Spot Welding Cycle (a) Spot welding cycle,
Figure : (b) plot of squeezing force & current in cycle (1) parts inserted between electrodes, (2) electrodes close, force applied, (3) current on, (4) current off, (5) electrodes opened.

7. Typical car body has about 10,000 spot welds

8. Resistance Spot Welding (RSW)
Spot Welding is a Resistance Welding (RW) process, in which two or more overlapped metal sheets are joined by spot welds. The method uses pointed copper electrodes providing passage of electric current. The electrodes also transmitt pressure required for formation of strong weld. Diameter of the weld spot is in the range 1/8” - 1/2” ( mm).
It consist of a transformer core having primary and secondary
Winding. One end of secondary winding is connected to upper
Electrode and other electrode is connected to lower electrode.
The workpieces to be weld are pressed between tips of the electrodes and high current at low voltages is passed through the workpieces.
Due to resistance offered by the workpieces ( sheet metal ) to
the flow of current , the temperature at the contact surfaces rises to fusion point and the weld is completed on freezing.The operation is repeated by changing the position of the workpiece plate to get the weld at another point.
Spot welding is widely used in automotive industry for joining vehicle body parts and in metal furniture.

9. Resistance Welding Seam
Electrodes are a pair of rotating copper rolls between which sheets to be welded are passed
The seam weld joints are continuous
It is used to weld components such as a fuel tank shells & other application which require the joint to be leak proof
Spot
The electrodes are a pair of copper rods between which the sheets to be welded are positioned
The welding takes place at discrete intervals
It is used for components such as flat sheets , panels as in car bodies.

11. Figure : Resistance seam welding (RSEW).

12. Resistance Seam Welding
Side view
Resistance Seam Welding

13. Seam Welding (RSW)
Seam Welding is a Resistance Welding process of continuous joining of overlapping sheets by passing them between two rotating electrode wheels. Heat generated by the electric current flowing through the contact area and pressure provided by the wheels are sufficient to produce a leak-tight weld.
Seam Welding is high speed and clean process, which is used when continuous tight weld is required (fuel tanks, drums, domestic radiators,gasoline tanks, automobile muffler ).

14. Resistance Butt Welding
It is of two types
1. Upset welding
2. Flash welding

15. Upset Butt Welding

16. Resistance Butt Welding (UW)
Upset Welding is used to join the pieces end to end
The process is best suited to rods , pipes and many other parts
Of uniform cross section.
In upset butt welding , the parts are clamped and brought in solid contact and current is applied so that the heat is generated through
the contact areas of the parts.
When the temperature of the interface reaches to plastic state, the
current is switched off and the two parts are pressed together firmly. This results in lateral flow of the surfaces oxide layers. This action of pressing together is called upsetting.
Butt welding is used for welding small parts. The process is highly productive and clean.

17. Flash Butt Welding

18. Flash Welding (FW)
Flash welding is similar to upset welding except that the heat is
obtained by means of an arc than the simple resistance heating.
The two parts are brought together and the power supply is switched on.
As the parts are moved closer , flashing or arcing raises the temperature of the parts to a welding temperature.
Now power is switched off and two parts are rapidly pressed (forced)
together causing a small upset. This squeezes out liquid metal and oxides ,
formed on the joint surfaces and the two parts are welded together.
Thick pipes, ends of band saws, frames, aircraft landing gears are produced
by Flash Welding.

19. Resistance Projection Welding
Figure : Resistance projection welding (RPW): (1) start of operation, contact between parts is at projections; (2) when current is applied, weld nuggets similar to spot welding are formed at the projections.
A resistance welding process in which coalescence occurs at one or more small contact points on parts
Contact points determined by design of parts to be joined .May consist of projections, embossments, or localized intersections of parts