Introduction to Explosive Welding

Amit Joshi

(B.E Mechanical, A.M.I.Prod.E)

Dept. of Metallurgical Engineering & Material Science,

Indian Institute of Technology - Bomby.

Introduction

Explosive welding is a solid state welding process, which uses a controlled explosive detonation to force two metals together at high pressure. The resultant composite system is joined with a durable, metallurgical bond.

Explosive welding under high velocity impact was probably first recognized by Garl in 1944. Explosive welding was first recognized as a possibility in 1957 in the United States when it was observed by Philipchuck that metal sheets being explosively formed occasionally stuck to the metal dies. Between that and now the process has been developed fully with large applications in the manufacturing industry.

It has been found to be possible to weld together combinations of metals, which are impossible, by other means.

The Process

This is a solid state joining process. When an explosive is detonated on the surface of a metal, a high pressure pulse is generated. This pulse propels the metal at a very high rate of speed. If this piece of metal collides at an angle with another piece of metal, welding may occur. For welding to occur, a jetting action is required at the collision interface. This jet is the product of the surfaces of the two pieces of metals colliding. This cleans the metals and allows to pure metallic surfaces to join under extremely high pressure. The metals do not commingle, they are atomically bonded. Due to this fact, any metal may be welded to any metal (i.e.- copper to steel; titanium to stainless). Typical impact pressures are millions of psi. Fig. 1 shows the explosive welding process.

Explosives

The commonly used high explosives are –

Explosive	Detonation velocity , m/s
RDX (Cyclotrimethylene trinitramine, C₃H₆N₆O₆	8100
PETN (Pentaerythritol tetranitrate, C₅H₈N₁₂O₄)	8190
TNT (Trinitrotoluene, C₇H₅N₃O₆)	6600
Tetryl (Trinitrophenylmethylinitramine, C₇H₅O₈N₅)	7800
Lead azide (N₆Pb)	5010
Detasheet	7020
Ammonium nitrate (NH₄NO₃)	2655

Applications

1) Joining of pipes and tubes.

2) Major areas of the use of this method are heat exchanger tube sheets and pressure vessels.

3) Tube Plugging.

4) Remote joining in hazardous environments.

5) Joining of dissimilar metals - Aluminium to steel, Titanium alloys to Cr – Ni steel, Cu to stainless steel, Tungsten to Steel, etc.

6) Attaching cooling fins.

7) Other applications are in chemical process vessels, ship building industry, cryogenic industry, etc.

Advantages

1) Can bond many dissimilar, normally unweldable metals.

2) Minimum fixturing/jigs.

3) Simplicity of the process.

4) Extremely large surfaces can be bonded.

5) Wide range of thicknesses can be explosively clad together.

6) No effect on parent properties.

7) Small quantity of explosive used.

Limitations

The metals must have high enough impact resistance, and ductility.
Noise and blast can require operator protection, vacuum chambers, buried in sand/water.
The use of explosives in industrial areas will be restricted by the noise and ground vibrations caused by the explosion.
The geometries welded must be simple – flat, cylindrical, conical.