Magnetic Pulse Welding | Diagram | Equipment | Applications | Pros & Cons

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.

History

Magnetic Pulse Welding came to the 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.

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Complete Process

MPW technique is based on a very short electromagnetic pulse whose value is less than 100µs. The pulse is obtained via 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 produce 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

Magnetic Pulse welding diagram-TWW

Factors that lead to Solid State Welding

Factors of Solid State Welding
  • Microstructure refinement
  • Local re-crystallization
  • Slip bends
  • Micro twins
  • Dislocation cells

Necessary Conditions for Stronger Welds

Several conditions need to be attained to obtain a strong weld, the list is given below.

Jetting condition

The collision should be subsonic, unlike the local materials where a 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.

High-Pressure regime

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.

Explosive Welding

Collision angle & velocity are constant in explosive welding.

Magnetic Pulse Welding

Collision angle & velocity continuously vary in this welding.

Equipment used in magnetic pulse welding

  • Capacitor Bank

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

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

  1. Compression coil
  2. Plate Coil
  3. Expansion coil

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Process Parameters

The two main process parameters for this welding technique are

  1. Collision angle
  2. 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

  1. Charged Electrical Energy
  2. The frequency of discharged current
  3. Material dimensions
  4. Material type
  5. Gap between materials
  6. Surface condition
  7. Electric conductivity
  8. Elongation strength
  9. 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

Magnetic Pulse Welding Machine-TWW

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Advantages & Disadvantages of Magnetic Pulse Welding

Advantages
  • It is a faster Welding technique
  • Stronger welding joints are formed
  • Heat is not required in MPW
  • No filler metal is required in MPW
  • Shielding gas is also not  required in MPW
  • No flux is required in MPW
  • Formation of brittle intermetallic phase in not required in this technique
  • High-quality welds are formed in both similar & dissimilar metals
  • It is an efficient welding technique
  • Properties of joining materials remain same
  • Preparation of the parts is not required
  • Post weld finishing is also not required at all
  • There are high chances that the process can be made automatic
  • For mass production, it is advantageous to give high productivity
  • It has better process tolerances
  • It has high repeatability
  • It doesn’t contain any distortion
  • It forms cold welds with no heat affected zones
  • High-quality welds are formed
  • There is no smoke, no radiation & no spark in this technique
  • Corrosion is not formed in the weld area
  • Zero residual stresses are present
Disadvantages
  • The parts must overlap to form a joint
  • Only those materials can be used as flyers which are electrically conducting
  • It has Lack of flexibility for differing geometries
  • High magnetic fields are dangerous
  • This technique creates more noise
  • Expensive Tools are used in this technique

Applications of Magnetic Pulse Welding

Applications

Its applications include

  • The word welding in this technique is kinda misleading, this technology is suitable for a variety of applications; therefore it is referred to as MAGNETIC PULSE TECHNOLOGY.
    1. No heat is involved in this technique so dissimilar materials can be welded using this like aluminum/steel & aluminum/copper etc.
    2. It can also be used for surface treatment of materials like vinyl coated materials &anodized aluminum.
    3. It is also used for joining of outer tubular components onto inner tubular components.
    4. This technique can be applied to the automotive industry for the development of lightweight vehicle bodies & components
    5. It can also be used in electronic devices as well.
    6. Its applications are also being expanded to home appliances as well.
    7. This technique can replace already being used in the market like brazing, friction welding, roll bonding & explosive welding.

    New development of the inductors & switches increased the commercial implementations of the technique. Engineers have found a variety of the applications for this technique which is solid state & cold welding process at a time.

Real World Application Examples of Magnetic Pulse Welding

Magnetic pulse welded HVAC pressure vessel

Magnetic pulse welded HVAC pressure vessel

Magnetic pulse welded space frame

Magnetic pulse welded space frame

Conclusion

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.

Read more about Types of Welding Joints

Summary
Magnetic Pulse Welding | Diagram | Equipment | Applications | Pros & Cons
Article Name
Magnetic Pulse Welding | Diagram | Equipment | Applications | Pros & Cons
Description
Magnetic pulse welding is a solid-state welding process that is accomplished via high impact velocity. It is also useful for dissimilar materials welding.
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The Welding World
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