Explosion welding : A Solid State Welding Process

Solid State Welding

1. Explosion Welding Presented By :- Deepam Goyal Nitesh Parmar Department of Mechanical Engineering NITTTR , CHANDIGARH

2. Introduction History Terminology Principle of Explosion Welding Salient Features of Explosion Welding Explosives Materials Advantages & Disadvantages Applications References Contents

3. 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. Surface atoms of two joining metals must come into intimate contact to achieve metallic bond. Fig. Explosive Welding

4. 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 explosion welding, received the patent in 1964 and began commercial production of bi-metallic explosion welded clad in 1965. Detaclad licensed the process and was bought by Dynamic Materials Corporation (DMC). Other companies have merged with DMC and acquired the current name DMC Groupe SNPE making them a worldwide company.

5. 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

6. 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..

7. 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..

8. 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.

9. 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

10. Cladder placement-Angled Where: Vc = collision velocity V D = detonation velocity V p = plate Collision velocity α = preset angle β = dynamic bend angle γ = collision angle

11. 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

12. 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.

13. 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.

14. 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

15. Contd.. Sonic velocity of cladding material can calculated using: Where: K = Adiabatic bulk modulus ρ = Cladding material density E = Young’s Modulus of cladding material ע = Poisson’s ratio of cladding material

16. Contd.. Types of Bond: Straight, direct metal-to-metal : B est 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.

17. Assuring a Good weld Three types of Detonation w ave 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)

18. Contd.. Type 1 Material behind shock wave is compressed to peak pressure and density Creates significant plastic deformation locally and results in considerable ‘shock hardening’ Type 2 & 3 Pressure is generated ahead of collision point of metals When subject to large pressures, metal ahead of collision point flows into spaces between plates and takes form of high-velocity jet Effaces material and removes unwanted oxides and other unwanted surface films No bulk diffusion and only localized melting

19. 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

20. 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.

21. 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).

22. Disa dvantages 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.

23. 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.

24. Contd.. Any metal with sufficient strength and ductility can be joined

25. 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

26. Examples

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

28. REFERENCES Parmar, R.S. "Explosion Welding." Welding Processes and Technology . Third ed. New Delhi: Khanna, 2012. 389-403. Print. Kalpakjian Seope, Schmid Steven R.: “ Manufacturing Engineering & 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, Umesh Publication s, New Delhi, New Delhi, 2006.

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