Solid State Welding Process: Principle, Types, Application, Advantages and Disadvantages

Solid-state welding processes are those welding processes in which no external heat is applied and the joining of workpiece takes place in solid-state. In these welding processes, no filler metal is used and welding does not involve a molten state of base material or filler material. The weld formation takes place due to the intermolecular diffusion process in which, the interface molecules of workpieces flow from high concentration region to low concentration region due to applied pressure. Some methods are used to produce heat which accelerates the diffusion process at mating surfaces. This type of welding process does not affect the mechanical or physical properties of parent material thus these are widely used in industries application. These are ideal joining processes for heat-sensitive material.

Solid-State Welding Process:

Principle:

Mainly metal joining process is classified into two types. The first one is the liquid state welding process in which, metal workpieces are heated until its melting temperature and the metal to metal joint form due to solidification of melted workpieces together.  Sometimes this process uses filler material which is melted with the base material and allows solidity, which makes a permanent strong joint. The other one is a solid-state welding process in which no molten or liquid state involves and metal joining process takes place due to the application of high pressure into solid-state. The metal to metal joint form due to the intermolecular diffusion process at the interface surfaces. This is the basic principle of it.

solid state welding

Types:

We have discussed the main principle of solid-state welding processes. All-solid-state welding processes work on the same principle but the method of applying pressure and heat is different in all these processes. According to the application of energy, this welding process can be classified into the following types.

Forge Welding:

Forge welding works on the basic principle of forging. In this type of welding process, both welding plates heated simultaneously quite below its melting temperature. This heating deforms the workpieces plastically. Now a repeated hammering on these plates applied together. This hammering starts diffusion process between plates and repeated continuously until the whole joint is created. It was used to weld iron or steel workpieces into ancient times.

Friction Welding:

As the name implies, this welding uses friction heat to accelerate the diffusion process. In this type of welding, a rotating workpiece brings in contact with a stable workpiece. Due to the high friction force at the contact surfaces, a high amount of heat generates. The friction is applied until the plastic form at an interface surface is achieved. After this heating process, a continuously increasing pressure force applied to these workpieces until the whole joint is formed. This welding mostly used to join steel bars, tubes, etc. One of the most important types of friction welding is friction stir welding in which, a non-consumable rotating tool is used to applied friction of welding plates.

Ultrasonic Welding:

Ultrasonic welding is also a solid-state welding process in which the energy of ultrasonic waves is used to join two workpieces. In this process, ultrasonic vibration creates dynamic shear between the interface surfaces. This will create local plastic deformation and friction between plates which is used to create a joint at the interface part.

ultrasonic welding

Explosive Welding:

This welding uses explosive energy to joint two plates. In this process both the welding, plates placed one over another such that the welding surface is in contact with one another. Now a buffer plate is placed over the upper surface of the welding plate which protects welding plates form high impact force of explosive. The explosive is placed over the buffer plate. When the explosion starts, a high-pressure wave generates which deform the interface surface of welding plates plastically and form a metallurgical bond between these plates. This joint is stronger than the parent material. It is mostly used to weld large welding area.

explosive welding

Diffusion Bonding:

Diffusion means the flow of any material form a high concentration region to a low concentration region. This is the basic principle of diffusion bonding. In this welding method, both the welding plates are placed one over another in the presence of high pressure and temperature for a long time. This high pressure starts diffusion between interface surfaces of welding plates. This diffusion accelerates by the high temperature which is much below the melting temperature of base plates. No molten state involves in this type of welding and weld joint is formed in the pure solid-state.

diffusion welding

Application:

Solid-state weldings are used everywhere in mechanical industries. It is widely used in aerospace and marine industries for structure work. It is widely used in automobile industries for most of the fabrication work. Explosive welding used to join a large welding plate that can’t be possible or uneconomical by other methods like arc welding or gas welding. Friction welding is used to join tubes, shafts, etc. These processes are further used to join dissimilar material used in various industries. Hydraulic piston, connecting rod, driveline, truck roller bushes, pump shaft, gear lever, drill bit, etc. are friction welded.

Advantages and Disadvantages:

Advantages:

• Solid-state welding can be easily automated.
• This produces a high strength joint without applying external heat.
• They are used to weld both similar and dissimilar material.
• Provide a good surface finish.
• They do not use any filler metal or flux as used in arc welding.
• Mostly these processes do not affect the properties of parent materials.

Disadvantages:

• High equipment cost or set up cost.
• Welding preparation is more critical.
• Complicated and special fixtures are required for different processes.
• Mostly, this process can’t be used for mass production due to slow welding speed.