Selection of solid state welding processes Process Selection Selection of solid state welding processes depends on the following factors : Performance of the welding processes under existing conditions Advantages of the processes involved Durability of the welds produced Materials to be welded Economic viability of the process

Solid state welding Diffusion welding(DFW): Two parts are held together under pressure at elevated temperature. Friction welding(FRW): By heat of friction between two surfaces two parts joined. Ultrasonic welding(USW):Moderate pressure between two parts hold together and an ultrasonic oscillation frequency send through in the direction parallel to the surface of contact. Forge welding(FOW): Heat and pressure applied. First the item is heated and hammered. Cold welding(CW):Only pressure is applied. Explosion Welding (EXW):A layer of explosives placed between layers of materials.

Advantages of Solid State Welding 1.Eliminates liquid phases Example: cold welding, friction welding, ultrasonic welding, diffusion welding and explosion welding 3.Can be performed with little or no deformation in some cases Example: diffusion welding 4.Some solid state processes can weld large areas in a single welding operation Examples: diffusion welding and explosion welding 2.Makes the joining of many dissimilar metal combinations possible Example: friction welding, explosion welding, diffusion welding. 5.Some solid state welding processes are relatively rapid Example: ultrasonic welding, cold welding and friction welding

Ultrasonic Welding

Ultrasonic welding Uses rapid vibrations to break up surface films and heat the surfaces, allowing them to bond Figure : Ultrasonic welding (USW): (a) general setup for a lap joint; and (b) close‑up of weld area.

Ultrasonic Welding In this high frequency ( ultrasonic ) vibrating energy is applied to overlapping metals into weld area to be joined The parts to be joined are clamped together between a Welding tip and a supporting member ( anvil ) 2. The core if ultrasonic transducer is coupled to work through A bar having suitably-shaped tip ( welding tip ) 3. The tip applies a transverse pressure between work pieces and simultaneously ultrasonic vibration ( 10 -75 KHz ) is then applied to tip 4. It causes vibration in metal molecules to raise temperature Sufficient to form a strong union between the face of the material In contact which results in spot type weld due to localized heating by high velocity rubbing.

Ultrasonic Welding Advantage This process doesn’t require any flux or filler metals, electric arc Disadvantage It is only used for welding thin strips and foils

Uses pressure and frictional heat caused by mechanical rubbing, usually by rotation Figure : Friction welding (FRW): (1) rotating part, no contact; (2) parts brought into contact to generate friction heat; (3) rotation stopped and axial pressure applied; and (4) weld created.

Friction Welding In friction welding process, the parts to be welded are kept in contact and rotated relative to each other. The interface is heated up due To rotating friction ( sliding & rubbing ) The two pieces ( perfectly clean ) to be welded Together are mounted in chucks on same horizontal Axis ( perfectly axial alignment ) .and are brought in contact face to face. One piece is held rigidly by fixed chuck and other is rotated by rotating Chuck at the desired speed with help of motor After the desired temp is attained , an axial pressure is applied to complete the weld. After welding is completed, the welded parts Rotate together as one piece until stopped

The process is mainly used for joining round bars face to face Friction Welding

Explosion Welding (EXW) process in which rapid coalescence of two metallic surfaces is caused by the energy of a detonated explosive No filler metal used No external heat applied No diffusion occurs - time is too short Bonding is metallurgical, combined with mechanical interlocking that results from a wavy interface between the metals Commonly used to bond two dissimilar metals, in particular to clad one metal on top of a base metal over large areas

Figure Explosive welding (EXW): (1) setup in the parallel configuration, and (2) during detonation of the explosive charge.

Definition of Explosion Welding Detonator Explosive standoff distance A solid-state welding process that produces coalescence by high velocity interaction of the work pieces produced by a controlled detonation. prime component Base component Component arrangement for explosion welding

Principles of Explosion Welding Detonator Welding arrangement consists of three components - Base component Prime component Explosive. Base component remains stationary, supported by anvil. Explosive prime component Base component Component arrangement for explosion welding

Principles of Explosion Welding Prime component is placed either parallel or at an angle to the base. Explosive is distributed over top surface of prime component. Upon detonation, prime component collides with base component to complete welding. Detonation Prime component Weld Jet Base component Action between components during explosion welding.

Process Variables and Controls Explosive Pressure Variables Collision Velocity Collision Angle Prime Component Velocity These are Controlled By: Component Mass Explosive Charge Initial Geometry - Standoff Distance or Angle V = charge velocity

Explosives Used for Welding High Velocity 14750-25000 ft/s Trinitrotoluene (TNT) Cyclotrimethylenetrinitramine (RDX) Pentaerythritol tetranitrate (PETN) Composition B Composition C4 Primacord Low to Medium Velocity 4900-14750 ft/s Ammonium nitrate Ammonium nitrate sensitized with fuel oil Ammonium perchlorate Amatol Amatol and sodatol diluted with rock salt to 30 to 35% Dynamites Nitroguanidine Dilute PETN

Effect of Velocity on Explosion Weld Geometry

In Parallel Arrangement Standoff = 1/2 to 1.0 times clad

In Angular Arrangement Angle = 1 to 8 Degrees

Wave Height Larger Standoff and Greater Angle Generally Leads to Greater Wave Heights

Wavy weld interface

Applications of Explosion Welding Any metal of sufficient strength and ductility can be joined. Cladding flat plates constitutes the major commercial application. Can be used to clad cylinders on inside or outside surface. Transition joints can be made. Tube to tube sheet joints in heat exchangers.

Finished vessel fabricated from explosion clad plate. Explosion welded 12 inch diameter 3003 aluminum to A106 grade B steel tubular transition joint.

Forge welding Forge welding(FOW): Heat and pressure applied. First the item is heated and hammered.

Diffusion welding Diffusion welding(DFW): Two parts are held together under pressure at elevated temperature process uses heat and pressure, usually in a controlled atmosphere, with sufficient time for diffusion and coalescence to occur Limitation: time required for diffusion can range from seconds to hours