Explosion Welding

Presented By:-Deepam GoyalNitesh Parmar

Department of Mechanical EngineeringNITTTR , CHANDIGARH

Introduction

History

Terminology

Principle of Explosion Welding

Salient Features of Explosion Welding

Explosives Materials

Advantages & Disadvantages

Applications

References

Contents

Explosion welding is a solid-state processthat produces a high velocity interaction ofdissimilar metals by a controlled detonation.

Introduction

This eliminates theproblems of heat effects& micro-structuralchanges (as in fusionwelding).

Oxides found on material surfaces must be removed byeffacement or dispersion.

Surface atoms of two joining metals must come intointimate contact to achieve metallic bond.

Fig. Explosive Welding

History Arnold Holtzman and a team at DuPont in Delaware

put a lot of research into developing the process.

Holtzman filed for a US patent in 1962 for explosionwelding, received the patent in 1964 and begancommercial production of bi-metallic explosionwelded clad in 1965.

Detaclad licensed the process and was bought byDynamic Materials Corporation (DMC).

Other companies have merged with DMC andacquired the current name DMC Groupe SNPEmaking them a worldwide company.

Component Terminology

Base component

• Joined to cladder

• Remains stationary

• Supported by anvil

Cladding metal

• Thin plate in direct contact with explosives

• Can be shielded by flyer plate

Flyer plate

• Sacrificial plate placed between explosive material and

cladder plate

• Used to protect cladder metal

Interlayer

• Thin metal layer

• Enhances joining of cladder to base plate

Anvil

• Surface of which the backer rests during explosion

Contd..

Anvil

• Surface of which the backer rests during explosion

Standoff

• Distance between cladder and base plate before explosion

Bond Window

• A range of variable in process such as velocity, dynamic

bend, and standoff distance that result in successful weld

Bonding Operation

• Detonation of explosives that result in a weld

Contd..

Principle of Explosion Cladder metal can be placed parallel or inclined to the

base plate.

Explosive material is distributed over top of claddermetal.

Upon detonation, cladder plate collides with baseplate to form weld.

Waves are generated so due to mechanical bondingjoining takes place.

A single detonation cap can be used to ignite theexplosive.

Placement of Cladder metal-parallel

Standoff distance predeterminedand unique to material combination

• Achieved by placing shimsbetween plates

• Shims designed to be consumedby explosion wave and do notaffect weld

Usually ranges between 0.5-2 timesthe thickness of cladder plate

Cladder must reach critical velocitybefore impact

Cladder placement-Angled

Where:Vc = collision velocityVD = detonation velocity

Vp = plate Collision velocity

α = preset angleβ = dynamic bend angleγ = collision angle

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

Contd.. This process doesn’t work well for,

• Brittle metals with < 5% tensile elongation

• Charpy V-notch value < 10 ft.lb.

Important factors are critical Velocity, stand off distance

& critical angle.

If two materials can be brought close enough together,

they will bond at a molecular level.

High velocity explosives require smaller gaps b/w plates,

and buffers such as rubber and Plexiglas are used.

Contd..

Angled interfaces are only used for high velocity

explosives.

The detonation velocity should not exceed 120% of the

sonic velocity in the metal.

There is a maximum velocity for welding, above this the

thermal effects weaken the joint.

To efficiently use explosives the plate separation is ½ to 1

times the cladding plate thickness.

Contd.. 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

Contd..

Sonic velocity of cladding material can calculated using:

Where:K = Adiabatic bulk modulusρ = Cladding material densityE = Young’s Modulus of cladding materialע = Poisson’s ratio of cladding material

Contd..Types of Bond:

Straight, direct metal-to-metal : Best type of bonding but

difficult to obtain when collision velocity less than critical

velocity.

Wavy : Interface is strong and the interface has waves.

Straight, but with a continuous layer : Weaker bond that

results when the collision velocity is too high and the alloy

bonds are strong.

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)

Contd.. Type 1

• Material behind shock wave is compressed topeak pressure and density

• Creates significant plastic deformation locallyand results in considerable ‘shock hardening’

Type 2 & 3

• Pressure is generated ahead of collision pointof metals

• When subject to large pressures, metal aheadof collision point flows into spaces betweenplates and takes form of high-velocity jet

• Effaces material and removes unwantedoxides and other unwanted surface films

• No bulk diffusion and only localized melting

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.

Contd..

• 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 sheetjoints.

• Spot welding.

• Flat plates.

• Joining of pipes in socket joints.

Contd..

• Any metal with sufficient strength and ductility can be joined

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

REFERENCES• Parmar, R.S. "Explosion Welding."Welding Processesand Technology. Third ed. New Delhi: Khanna, 2012.389-403. Print.

• Kalpakjian Seope, Schmid Steven R.: “ManufacturingEngineering & Technology” Pearson Education India,2009, pp 832.

• Sharma, P.C. A textbook of production Technology. 7.New Delhi: S.Chand & Company Ltd, 2011, 373-374.Print.

• Moeed, K.M., Manufacturing Science, UmeshPublications, New Delhi, New Delhi, 2006.

Email ID:-bkdeepamgoyal@gmail.comer.nitesh41@gmail.com