Explosive welding – also called explosion welding, explosion bonding or blast welding – joins two metal plates by driving one onto the other with a controlled detonation. The impact is so fast and so intense that the surfaces are cleaned and bonded in the solid state, without melting, within microseconds. It is the standard way to make clad plates and transition joints from metals that cannot be fusion welded together, such as titanium or aluminium on steel.
How explosive welding works
- Set-up: the cladding plate (the flyer) is placed parallel to the base plate with a small, precisely controlled gap – the stand-off distance. A layer of explosive is spread evenly over the flyer.
- Detonation: the explosive is initiated at one edge and the detonation front runs across the plate.
- Collision: behind the front, the flyer is accelerated across the gap and hits the base plate at a small angle. The collision point moves across the plate at the speed of the detonation.
- Jetting: at the collision point the pressure is so high that a thin layer of metal from both surfaces is squeezed out ahead of it as a jet. The jet carries away oxides and contamination, leaving clean metal surfaces that are pressed together.
- Bond: the clean surfaces bond at an atomic level. The result is a continuous metallurgical bond, typically with a characteristic wavy interface.
The parameters that matter
| Parameter | What it controls |
|---|---|
| Detonation velocity | Speed of the collision point – it must stay below the speed of sound in the metals so that a jet forms |
| Explosive load (thickness / density) | The velocity of the flyer plate and therefore the collision energy |
| Stand-off distance | How far the flyer accelerates before impact, and so the collision angle and velocity |
| Flyer and base thickness | The mass to be accelerated and the support behind the bond |
| Surface preparation | Clean, flat surfaces for a uniform bond |
Together these define a weldability window for each metal pair. Inside the window the interface is a continuous, wavy bond; with too little energy the plates do not bond, and with too much the interface can melt locally or the waves grow too large. Setting these parameters for each combination and thickness is the know-how of the cladding manufacturer.
Advantages
- Almost any metal pair: titanium, zirconium, tantalum, aluminium, copper and nickel alloys on steel – combinations that are impossible by fusion welding because they form brittle intermetallics.
- No melting, no dilution: both metals keep their chemistry and properties; there is practically no heat-affected zone.
- Large areas and thick layers: plates of many square metres, clad layers from about 1 mm to several tens of millimetres, on bases of hundreds of millimetres.
- Strong bond: the bond is typically at least as strong as the weaker of the two metals and passes shear, tensile and bend tests.
- Short lead times and small quantities: no rolling-mill campaign needed.
Limits
- Geometry: mainly flat plates and discs (and some cylindrical parts). Shells and heads are formed or rolled after cladding.
- Ductility: the flyer must be ductile enough to withstand the impact; very brittle metals are not suitable as cladding.
- Flattening: the impact deforms the plate, so clad plates are straightened afterwards.
- Site and safety: the process needs a licensed explosives site. Open-air explosive welding is noisy; doing it inside a vacuum chamber reduces noise and emissions.
Explosive welding in a vacuum chamber
In open-air explosive welding the air in the gap between the plates has to be pushed out by the collision. Shockwave bonds inside vacuum chambers: with the air removed, there is no air cushion or trapped gas at the interface, the bond is oxide-free and more consistent, and less explosive is needed. The closed system filters the reaction gases and greatly reduces noise. Read more about vacuum explosion bonding technology and the explosion bonding process.
What explosive welding is used for
- Clad plates for pressure vessels, columns and reactors – stainless, nickel alloy, titanium and zirconium on steel.
- Clad tube sheets for heat exchangers and condensers.
- Transition joints: Triplate® (aluminium–steel for ships), CryoClad® (cryogenic) and Triconnect® (electrical, aluminium smelters).
Have a combination in mind? Send the metals, thicknesses and sizes through our contact page.
Frequently asked questions
What is explosive welding?
A solid-state welding process in which a controlled detonation drives one metal plate onto another at high speed. The impact cleans both surfaces and bonds them at an atomic level without melting. It is also called explosion welding, explosion bonding or blast welding.
How does explosive welding work?
An explosive layer on the flyer plate is detonated from one edge. The flyer crosses a small gap and hits the base plate at an angle; at the collision point a jet of surface metal removes oxides, and the clean surfaces bond, usually with a wavy interface.
What are the advantages of explosive welding?
It joins almost any metal pair – including titanium, zirconium and aluminium on steel – without melting or dilution, over large areas and with thick layers, and with a bond at least as strong as the weaker metal.
What are the disadvantages of explosive welding?
It is limited mainly to flat plates and discs, needs ductile cladding metals and a licensed explosives site, and the plates must be straightened afterwards. Open-air bonding is noisy; vacuum chambers reduce noise and emissions.
Is explosion welding the same as explosive welding?
Yes. Explosive welding, explosion welding, explosion bonding, explosive cladding and blast welding all describe the same process.
Written by Joeri Hofstede, CEO of Shockwave Metalworking Technologies — vacuum explosion welding specialists since 1985.