Unlike other forms of joining, explosion welding does not depend on melting or plastic deformation but is instead achieved by impelling the cladding plate against the substrate material through the energy generated by an explosive discharge. The explosion creates a high energy impact between the two metals.
The parts to be joined need to be place at the correct angle to each other before the explosive shockwave pushes the two metals together at a speed of around 100 m/s.
The high interfacial pressure at the point of contact (or collision front) between the cladding plate and the substrate plate must be greater than the yield strength of both materials for plastic deformation within the surface layers to occur. A jet of highly softened metal is formed at the collision front and is projected in front of it as it progresses rapidly across the weld interface. As the plasma jet progresses, it thoroughly cleans the surfaces, thus permitting solid phase bonding to occur between the two materials as their atoms are pushed together.
The primary advantage of explosion welding is in producing bonds between metal combinations that may not be weldable using other methods.
The method allows for large areas to be joined very quickly without melting either material, and thereby preserving the material properties of both.
Explosion welding also creates clean welds as the surface material of both metals are expelled during the process.
Explosion welding is limited in the geometries it can join, with typical geometries produced including plates, tube sheets and tubing.
In addition, this joining method requires an extensive knowledge of explosives to be performed safely, while regulations for the use of high explosives may need special licensing.
While many forms of welding date back several centuries, explosion welding is a relatively new process, having been created in the decades following the Second World War.
The roots of this joining technique began during World War I when it was observed that pieces of shrapnel were welding themselves to armour plating as a result of the explosive forces acting upon the shrapnel. The lack of extreme heat acting on the shrapnel led to laboratory investigations to take place after World War II to try and duplicate the process, with a patent for the explosion welding process being granted to DuPont in 1964.
The explosive welding technique has found major use for cladding low cost plate (usually carbon steel) with more expensive corrosion resistant materials. This clad plate is typically used in the chemical and petrochemical industries as tube sheet for heat exchangers.
Because bonding occurs in the solid phase, it is possible to weld metals with different melting points. Some of the common clad layers deposited onto steel plate include aluminium, bronze, copper, titanium, nickel alloys and zirconium. Alternatively, explosive welding can be used to repair or plug tubes in heat exchangers on-site, where conventional welding methods are difficult to use.
A solid state process, like friction welding, explosion welding occurs when a component is accelerated towards another at a high velocity through the use of chemical explosives.
It is commonly used to clad materials such as carbon steel with a thin layer of corrosion-resistant material.
Ideal for joining dissimilar metals, this process does not change the material properties as with other more conventional welding methods. It is, however, only suitable for joining parts with simple geometries and also requires a good knowledge of explosives to perform safely.
What is Explosion Welding Used For?
Explosion welding is mainly used for preparing billets or blanks, but it can also be used to join simple parts like pipes or for securing tubes in tube-plates. It is used to join dissimilar materials that can be difficult to join using other methods.
It is widely used to clad low cost plate (such as carbon steel) with more expensive, corrosion-resistant materials like stainless steel. This cladded plate finds uses in industries such as the petrochemical and chemical industries as well as for tube sheet for heat exchangers.
When was Explosive Welding Invented?
Explosion welding was invented in the years following the Second World War, with a patent being granted for the process in 1964. However, the origins of explosive welding date back to World War I when it was noticed that pieces of shrapnel were welding themselves (rather than being embedded) to armour plating as a result of being propelled by explosive forces.
Are there any Welding Techniques Similar to Explosive Welding?
Because explosion welding not melt either of the metals being joined, it is often compared to other non-fusion welding techniques, such as friction welding. Explosive welding instead works through plasticising the interface between the metals, leaving their properties intact.