1. Solid State Welding By A Nirala Email:-niralaiitk@gmail.com
Solid State Welding is a welding process, in which two work pieces are joined under a pressure providing an intimate contact between them and at a temperature essentially below the melting point of the parent material.

2. Advantages of Solid State Welding
Weld (bonding) is free from microstructure defects .
Mechanical properties of the weld are similar to those of the parent metals
No consumable materials (filler material, fluxes, shielding gases) are required.
Dissimilar metals may be joined .
Disadvantages of Solid State Welding
Expensive equipment

3. Types of Solid State welding
Friction Welding (FRW)
Ultrasonic Welding (USW)
Friction stir welding
Resistance welding

4. Friction Welding (FRW)
Friction Welding is a Solid State Welding process, in which two cylindrical parts are brought in contact by a friction pressure when one of them rotates. Friction between the parts results in heating their ends. Forge pressure is then applied to the pieces providing formation of the joint.

5. Material that can be welded in Friction Welding
Carbon steels , Alloy steels, Tool and die steels, Stainless steels, Aluminum alloys, Copper alloys, Magnesium alloys, Nickel alloys, Titanium alloys can be joined by Friction Welding.

6. Ultrasonic Welding (USW)
Ultrasonic Welding is a Solid State Welding process, in which two work pieces are bonded as a result of a pressure exerted to the welded parts combined with application of high frequency acoustic vibration (ultrasonic). Ultrasonic vibration causes friction between the parts, which results in a closer contact between the two surfaces with simultaneous local heating of the contact area. Interatomic bonds, formed under these conditions, provide strong joint.

7. Advantages of Ultrasonic Welding
Dissimilar metals can be joined.
Very low deformation of the work pieces surfaces.
High quality weld is obtained.
The process may be integrated into automated production lines.
Moderate operator skill level is enough.

8. Disadvantages of Ultrasonic Welding
Work pieces may bond to the anvil.
Only small and thin parts can be welded.

9. Friction stir welding (FSW)
Welding using friction as the major resource
No filler material involved
Welds created by,
a) Frictional heating
b) Mechanical deformation

10. Friction-stir welding (FSW)
It is a solid-state joining process (the metal is not melted)
In the process a rotating FSW tool is plunged between two clamped plates. The frictional heat causes a plasticised zone to form around the tool. The rotating tool moves along the joint line. A consolidated solid-phase joint is formed.
Friction Stir Welding transforms the metals from a solid state into a plastic state, and then mechanically stirs the materials together under pressure to form a welded joint

11. Principle Of Operation
In friction stir welding (FSW) a cylindrical, shouldered tool with a profiled probe is rotated and slowly plunged into the joint line between two pieces butted together.
The parts have to be clamped onto a backing bar in a manner that prevents the abutting joint faces from being forced apart.
Frictional heat is generated between the wear resistant welding tool and the material of the work pieces.

12. Principle Of Operation(contd.)
This heat causes the material to soften without reaching the melting point and allows traversing of the tool along the weld line.
The maximum temperature reached is of the order of 0.8 times of the melting temperature of the material.
It leaves a solid phase bond between the two pieces.
The process can be regarded as a solid phase keyhole welding technique since a hole to accommodate the probe is generated, then filled during the welding sequence.

13. Advantages Low distortion and shrinkage, even in long welds
Excellent mechanical properties in fatigue and tensile tests
No arc or fumes
No porosity
Can operate in all positions (horizontal, vertical, etc.), as there is no weld pool.
Energy efficient
One tool can typically be used for up to 1000m of weld length in 6XXX series aluminium alloys
No filler wire required
No gas shielding is also required for welding

14. Disadvantages Exit hole left when tool is withdrawn.
Less flexible than manual and arc processes
Work pieces must be rigidly clamped
Often slower traverse rate than some fusion welding techniques.
Cannot make joints which required metal deposition (e.g. fillet welds)

15. Resistance Welding (RW)
Resistance Welding is a welding process, in which work pieces are welded due to a combination of a pressure applied to them and a localized heat generated by a high electric current flowing through the contact area of the weld. Heat produced by the current is sufficient for local melting of the work piece at the contact point and formation of small weld pool (”nugget”). The molten metal is then solidifies under a pressure and joins the pieces. Time of the process and values of the pressure and flowing current, required for formation of reliable joint, are determined by dimensions of the electrodes and the work piece metal type. AC electric current (up to 100 kA) is supplied through copper electrodes connected to the secondary coil of a welding transformer.

16. 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)

17. Low strength of discontinuous welds;
Disadvantages of Resistance Welding:
Advantages of Resistance Welding:
High equipment cost;
Low strength of discontinuous welds;
Thickness of welded sheets is limited - up to 1/4” (6 mm);
High welding rates;
Low fumes;
Cost effectiveness;
Easy automation;
No filler materials are required;
Low distortions.

18. The most popular methods of Resistance Welding are: 
Spot Welding (RSW)
Flash Welding (FW)
Resistance Butt Welding (UW)
Seam Welding (RSEW)

19. 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). Spot welding is widely used in automotive industry for joining vehicle body parts.

20. Flash Welding (FW)
Flash Welding is a Resistance Welding (RW) process, in which ends of rods (tubes, sheets) are heated and fused by an arc struck between them and then forged (brought into a contact under a pressure) producing a weld. The welded parts are held in electrode clamps, one of which is stationary and the second is movable.

21. Resistance Butt Welding (UW)
Resistance Butt Welding is a Resistance Welding (RW) process, in which ends of wires or rods are held under a pressure and heated by an electric current passing through the contact area and producing a weld.
The process is similar to Flash Welding, however in Butt Welding pressure and electric current are applied simultaneously in contrast to Flash Welding where electric current is followed by forging pressure application. Butt welding is used for welding small parts. The process is highly productive and clean. In contrast to Flash Welding, Butt Welding provides joining with no loss of the welded materials.

22. Seam Welding (RSEW)
Seam Welding is a Resistance Welding (RW) 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).