Explosive Welding

Introduction

Principle of Explosion Welding

Salient Features of Explosion Welding

Explosives Materials

Advantages & Disadvantages

Applications

Contents

Explosion welding is a solid-state process that produces a high velocity interaction of dissimilar metals by a controlled detonation.

Introduction

This eliminates the problems of heat effects & micro-structural changes (as in fusion welding).

Oxides found on material surfaces must be removed by effacement or dispersion

Fig. Explosive Welding

Principle of Explosion Cladder metal can be placed parallel or

inclined to the base plate. Explosive material is distributed over top of

cladder metal. Upon detonation, cladder plate collides

with base plate to form weld. Waves are generated so due to mechanical

bonding joining takes place. A single detonation cap can be used to

ignite the explosive.

Placement of Cladder metal-parallel Standoff distance

predetermined and unique to material combination• Achieved by placing shims

between plates• Shims designed to be

consumed by explosion wave and do not affect weld

Usually ranges between 0.5-2 times the thickness of cladder plate

Cladder must reach critical velocity before impact

Salient Features The high velocities are promoted by carefully

detonated explosives. The process can be done in vacuum to reduce

sound & blast. Typical impact pressure are millions of psi. Well suited to metals that are prone to brittle

joints when heat welded such as,• Al on steel• Ti on steel

Typical explosive forms• Plastic flexible sheer• Cord• Pressed shapes• Cast shapes• Powder/granular

Detonation velocity is a function of• Explosive type• Composition of explosive• Thickness of explosive layer

Assuring a Good weld Three types of Detonation wave welds:

• Shock wave develops if sonic velocity is greater than 120% of material sonic velocity (type 1)• Detached shock wave results when

detonation velocity is between 100% and 120% of material sonic velocity (type 2)• No shock wave is produced if detonation

velocity is less than material sonic velocity (type 3)

Explosive material High velocity (4572-7620 m/s)• Trinitrotoluene (TNT)• Cyclotrimethylenetrinitramine (RDX)• Pentaerythritol Tetranitrate (PETN)• Datasheet• Primacord

Mid-low velocity (1524-4572 m/s)• Ammonium nitrate• Ammonium perchlorate• Amatol• Nitroguonidine• Dynamites• Diluted PETN

Advantages of Explosion Welding

• Very large work pieces can be welded.• (Al + Steel) materials can be welded. • Can bond many dissimilar, normally unweldable

metals.• Material melting temperatures and coefficients

of thermal expansion differences do not affect the final product.• Process is compact, portable, and easy to

maintain.

• Welding can be achieved quickly over large areas.• No need for surface penetration.• Backer plate has no size limits.• Inexpensive.• The strength of the weld joint is equal to or

greater than the strength of the weaker of two metals joined.• No heat-affected zone (HAZ).

Disadvantages of Explosion Welding

• Metals must have high enough impact resistance and ductility• The geometries welded must be simple-flat,

cylindrical, conical• The cladding plate can’t be too large• Noise & blast can require worker protection,

vacuum chambers, buried in sand/water.

Applications• Cladding of base metals with thinner alloys e.g.

cladding of Ti with mild steel.• Seam and lap welds.• Reinforcing aerospace materials with dissimilar

metal ribs.• Heat exchangers.• Tubular transition joints.• Used as a repair tool for repairing leaking tube-

to-tube sheet joints.• Spot welding.• Flat plates.• Joining of pipes in socket joints.

Common industries that use Explosion Welding

• Petroleum Refining• Chemical Processing• Hydrometallurgy• Aluminum Smelting• Shipbuilding• Electrochemical

• Oil & Gas• Power Generation• Cryogenic Processing• Pulp & Paper• Air conditioning &

Chillers• Metal Production

Examples

Examples

3” Diameter AI/SS Ring Copper/Stainless 12” UHV Assembly