Magnetic Pulse Welding Definition#1
The type of welding process which uses magnetic forces to weld two work-pieces together is called Magnetic pulse welding. It is a type of solid-state, cold welding process. Its mechanism is similar to explosion welding technique.
Magnetic Pulse Welding Definition#2
Magnetic pulse welding technique uses electromagnetically generated forces to produce a solid-state weld at room temperature. This technique is completed in microseconds.
Magnetic Pulse Welding came to existence when the automated industry began to use a solid-state welding process in early 1970. MPW was unknown in the industry till 1970 & its journey begun only 40 years ago. This technique is very useful due to its various advantages; one of the best advantages is it can be completed in no time & dissimilar metals can be joined as well.
Basic Working Principle
MPW is a solid-state welding technique which is accomplished by a magnetic pulse that produces a high-velocity impact on two materials that result in a true metallurgical bond. This technique is based totally on a theory of Lorentz forces which states that
“An electrically charged particle, moving in a magnetic field undergoes a force normal to the direction of the magnetic field & to the direction of movement.”
𝐹=𝑞 (𝑣 𝑥 𝐵 )
F is the force, q is the charge, v is the velocity & B is the magnetic field in the equation.
Download Magnetic Pulse Welding PDF from Here
MPW technique is based on a very short electromagnetic pulse whose value is less than 100µs. The pulse is obtained via a fast discharge of capacitors through low inductance switches into a coil. This pulsed current with a very high amplitude & frequency produces a magnetic field of very high density which creates an eddy current in any of the one workpiece, which is being joined together.
In effect to this eddy current repulsive Lorentz forces are produced which produces acceleration because of the excessive magnetic stress that is greater than the yielding strengths of materials, because of this one of the workpiece collides with the opposite piece with a collision pace up to 500m/s.
In MPW high plastic deformation is developed along with high shear strain & oxides disruptions because of the jet & high collision zone temperature. These factors led to the solid-state weld.
Dissimilar metals can also be welded since heat is not involved in this technique.
Magnetic Pulse Welding Diagram
Factors that lead to Solid State Welding
Necessary Conditions for Stronger Welds
Several conditions need to be attained to obtain a strong weld, the list is given below.
The collision should be subsonic, unlike the local materials where speed of sound produces a jet.
No fusion during a collision
Heat shouldn’t be present at the time of high pressure otherwise it can cause locally melt & re-solidify the materials. Welds produced in this way are not stronger instead they are weaker.
To avoid crimped parts formation the impact velocity should be adequate enough to attain hydrodynamic regime.
Difference between Magnetic Pulse Welding & Explosion Welding
The main difference between the two welding types is collision angle & Velocity.
Equipment used in magnetic pulse welding
The capacitor bank is used for charging to extreme levels of energy. If a high electromagnetic pressure is required then extremely low self-inductance capacitors are used. These devices can store charges up to a maximum level that depends upon the operator. This produces a high current pulse in the coil within 100 microseconds. To reduce energy expenditure a high current discharge switcher is also employed on the power source.
Working coil is used to discharge the extreme levels of energy. The development of the working coil depends upon the quality of the weld that is required. That’s why it is very important since quality depends upon its preparation. It actually includes shape, electrical & mechanical properties of the material.
Types of Working coils
- Compression coil
- Plate Coil
- Expansion coil
Download Magnetic Pulse Welding PPT from Here
The two main process parameters for this welding technique are
- Collision angle
- Impact velocity
To achieve a successful weldment, the designs of the impact velocity & impact angle are very important.
Impact velocity is related to both pressure & kinetic energy which is used to accelerate the outer material, impact velocity is determined by apparatus specifications.
The angle between the materials can be determined based on the geometry of the materials.
Apparatus parameters are also processed parameters. They include
- Charged Electrical Energy
- The frequency of discharged current
- Material dimensions
- Material type
- Gap between materials
- Surface condition
- Electric conductivity
- Elongation strength
- Coil inductance
When materials collide with optimal process parameters a jet is created & it causes perfect oxides & air ejection resulting into cleaned surfaces that are free of air contaminations.
Impact of High Velocity
Impact at high velocity overcomes the forces between the atoms of the material & brings atoms together with greater intensity so that electrons are shared between the two materials & strong weldment is formed.
Magnetic Pulse Welding Machine images
Watch Complete Video Here
Advantages & Disadvantages of Magnetic Pulse Welding
Applications of Magnetic Pulse Welding
Real World Application Examples of Magnetic Pulse Welding
Magnetic pulse welded HVAC pressure vessel
Magnetic pulse welded space frame
MPW is a solid state welding process that is accomplished via high-velocity impact on the materials. One of the main advantages that make this welding technique versatile is its ability to be used for dissimilar materials. Also, there is no heat affected zone in this welding technique. This welding technique has many advantages but its applications in the industry are low.