Solid-state Welding

Coextrusion welding (CEW) Dissimilar metals are extruded through the same die.

Cold pressure welding (CW) Dissimilar metals are extruded through the same die.

Diffusion welding (DFW) is a solid state welding process by which two metals (which may be dissimilar) can be bonded together. Diffusion involves the migration of atoms across the joint, due to concentration gradients. The two materials are pressed together at an elevated temperature usually between 50 and 70% of the melting point. The pressure is used to relieve the void that may occur due to the different surface topographies. The method was invented by the Soviet scientist N.F. Kazakov in 1953. Specific tooling is made for each welding application to mate the welder to the workpieces.

Explosion welding (EXW) is a solid state (solid-phase) process where welding is accomplished by accelerating one of the components at extremely high velocity through the use of chemical explosives. This process is most commonly utilized to clad carbon steel plate with a thin layer of corrosion resistant material (e.g., stainless steel, nickel alloy, titanium, or zirconium). Due to the nature of this process, producible geometries are very limited. They must be simple. Typical geometries produced include plates, tubing and tube sheets

Magnetic pulse welding (MPW) is a welding process that uses magnetic forces to drive two workpieces together and weld them together. The welding mechanism is most similar to that in explosion welding

Forge welding (FOW) is a solid-state welding process that joins two pieces of metal by heating them to a high temperature and then hammering them together. The process is one of the simplest methods of joining metals and has been used since ancient times. Forge welding is versatile, being able to join a host of similar and dissimilar metals. With the invention of electrical and gas welding methods during the Industrial Revolution, forge welding has been largely replaced.

Forge welding between similar materials is caused by solid-state diffusion. This results in a weld that consists of only the welded materials without any fillers or bridging materials.

Forge welding between dissimilar materials is caused by the formation of a lower melting temperature eutectic between the materials. Due to this the weld is often stronger than the individual metals.

The temperature required to forge weld is typically 50 to 90 percent of the melting temperature. Steel welds at a lower temperature than iron. The metal may take on a glossy or wet appearance at the welding temperature. Care must be taken to avoid overheating the metal to the point that it gives off sparks from rapid oxidation (burning).

Friction welding (FRW) is a class of solid-state welding processes that generates heat through mechanical friction between a moving workpiece and a stationary component, with the addition of a lateral force called “upset” to plastically displace and fuse the materials. Technically, because no melt occurs, friction welding is not actually a welding process in the traditional sense, but a forging technique. However, due to the similarities between these techniques and traditional welding, the term has become common. Friction welding is used with metals and thermoplastics in a wide variety of aviation and automotive applications.

Friction-stir welding (FSW) is a solid-state joining process (meaning the metal is not melted during the process) and is used for applications where the original metal characteristics must remain unchanged as far as possible. This process is primarily used on aluminium, and most often on large pieces which cannot be easily heat treated post weld to recover temper characteristics.

It was invented and experimentally proven at The Welding Institute UK in December 1991. TWI holds a number of patents on the process, the first being the most descriptive.

Hot pressure welding (HPW) Metals are pressed together at elevated tempeartures below the melting point in vacuum or an inert gas athmosphere

Hot isostatic pressing (HIP) is a manufacturing process used to reduce the porosity of metals and increase the density of many ceramic materials. This improves the material’s mechanical properties and workability.

The HIP process subjects a component to both elevated temperature and isostatic gas pressure in a high pressure containment vessel. The pressurizing gas most widely used is argon. An inert gas is used, so that the material does not chemically react. The chamber is heated, causing the pressure inside the vessel to increase. Many systems use associated gas pumping to achieve the necessary pressure level. Pressure is applied to the material from all directions (hence the term “isostatic”).

For processing castings, the inert gas is applied between 7,350 psi (50.7 MPa) and 45,000 psi (310 MPa), with 15,000 psi (100 MPa) being most common. Process soak temperatures range from 900 °F (482 °C) for aluminum castings to 2,400 °F (1,320 °C) for nickel-based superalloys. When castings are treated with HIP, the simultaneous application of heat and pressure eliminates internal voids and microporosity through a combination of plastic deformation, creep, and diffusion bonding; this process improves fatigue resistance of component. Primary applications are the reduction of microshrinkage, the consolidation of powder metals, ceramic composites and metal cladding. Hot isostatic pressing is also used as part of a sintering (powder metallurgy) process and for fabrication of metal matrix composites.

Roll welding (ROW) Bimetallic materials are joined by forcing them between two rotating wheels.

Ultrasonic welding (USW) is an industrial technique whereby high-frequency ultrasonic acoustic vibrations are locally applied to workpieces being held together under pressure to create a solid-state weld. It is commonly used for plastics, and especially for joining dissimilar materials. In ultrasonic welding, there are no connective bolts, nails, soldering materials, or adhesives necessary to bind the materials together.