What is Explosive Welding?
Definition: Explosive Welding (also known as explosion welding or explosive bonding or explosive cladding) is a type of solid state welding process in which a controlled explosive detonation is used to force two metals together at high pressure.
Explosive welding is widely used for welding various metals with some corrosion resistant materials like stainless steel, nickel alloys, etc.
Explosive welding working principle
The working principle of explosive welding process is mentioned below.
Explosive Welding process works on the principle of metallurgical bonding.
Two surfaces which are to be welded are initially spaced at a smaller distance.
Explosive force produced by the explosion brings the surfaces together at a collision front.
The interfacial pressure at the collision front is more than the yield strength of the metals so that plastic deformation of metals occurs and welding takes place.
Explosive welding process
For obtaining good weld using explosive welding, the very first step is to know the properties of the metal to be clad with each other.
As shown in the diagram of explosive welding, the two metal plates which are to be welded are initially spaced at a smaller distance.
This smaller distance is known as standoff distance.
The frame containing explosive powder is attached to the surface of the upper metal sheet.
The detonator is attached and the setup is now ready for the explosive welding process.
As shown in the diagram, the explosion is detonated on the surface of the metal.
When the detonator is activated, the explosion takes place and it lasts for only a fraction of a second.
This high explosive force forces the top metal plate on the base metal plate with a very high velocity.
This creates a collision between the upper metal sheet and the base metal (which is at the bottom).
This collision pressure is so high that the deformation of metal occurs at the point of collision.
When the explosion occurs, the shockwave is created which is transmitted through the metal layers.
The velocity of collision should be lower than the velocity of the sound in the materials, otherwise the shockwave would interfere with the contact surfaces which prevents the bond formation.
This pressure created by the explosion is higher than the yield strength of the materials, and because of this the welding of metals takes place easily.
Due to the plastically deformed metal at the collision point, you may see the wave pattern with a naked eye too (see below image).
The plasma jet is required at the collision interface which cleans the metal surface and allows the pure metallic surfaces to join under extreme pressure.
In explosive welding process, the metallurgical bond is formed as a result of high pressure that causes the valence electrons to cross into each other’s sphere of influence.
Explosive welding process is also known as a variation of cold pressure welding process, because the entire process is carried out at room temperature.
By using an explosion welding process, dissimilar metals can also be welded (like copper to steel, titanium to stainless steel, etc.)
The impact pressure that occurs in explosive welding can be upto millions of psi.
Explosive used in explosive welding
The common explosives used in explosive welding process are mentioned in the table below.
|Explosives||Approximate detonation velocity (m/s)|
|RDX (Cyclotrimethylene trinitramine, C3H6N6O6)||8100 m/s|
|PETN (Pentaerythritol tetranitrate, C5H8N12O4)||8190 m/s|
|TNT (Trinitrotoluene, C7H5N3O6)||6600 m/s|
|Tetryl (Trinitrophenylmethylnitramine, C7H5N5O8)||7800 m/s|
|Lead azide (N6Pb)||5010 m/s|
|Ammonium nitrate (NH4NO3)||2655 m/s|
Having said that, now let’s see the advantages and disadvantages of explosive welding.
Advantages of explosive welding
Advantages of explosion welding process are mentioned below.
- Dissimilar metals which are difficult to weld by using other welding techniques, can be bonded by using explosion welding technique.
- This method requires minimum jigs and fixtures.
- Large surface can be bonded using explosive welding.
- Explosive welding does not create any effect on the properties of parent metal.
- Distortion of parent metal is minimum.
- The weld piece possesses higher bonding strength.
Disadvantages of explosive welding
Disadvantages of explosion welding process are mentioned below.
- The metals having high impact strength and ductility can only be welded using explosive welding technique.
- This process produces more noise and blast. So protection is required for the operator.
- Simple geometry can only be welded using explosive welding (simple geometry includes flat surface, cylindrical surface or conical surface)
Applications of explosive welding
Applications of explosion welding process are mentioned below.
- Used for joining of pipes and tubes in heat exchanger, pressure vessels, etc)
- Used in tube plugging.
- Used for remote joining in hazardous environment.
- For attaching fins to the surface of heat exchangers.
- Other applications of explosive welding include ship building industries, cryogenic industries, etc.
Explosive welding wave pattern: Image credit American welding society