MAGNETIC PULSE TECHNOLOGY APPLIED TO WELDING AND FORMING

MAGNETIC PULSE TECHNOLOGY APPLIED TO WELDING AND FORMING

ABSTRACT

In 1947 researchers in USA working in the field of bullet containment discovered that an oblique impact of metal, accelerated to high velocity, produces a weld on impact with a stationary metal. This fact was utilized in the development of explosive welding which began in 1950. Magnetic pulse welding is analogous to explosive welding.

Magnetic pulse welding is a cold solid state process which although known for sometime is only recently being incorporated in industry as a mass production tool for both similar and dissimilar metal combinations.

The pulse magnetic field has many advantages over conventional methods in the metal working industry. The process makes use of a high velocity low angular impact between two metallic work pieces creating suitable conditions for the weld to take place.

BASIC PRINCIPLES

In the magnetic pulse welding process, a very high energy current is discharged through a cylindrical coil in which two tubular work pieces have been inserted. This high and extreme fast current when discharged through the coil creates strong magnetic forces between the coil and the outer tubular work piece. The outer tubular work piece is then accelerated under precisely controlled conditions into the work piece resulting in an oblique impact and thus, a solid state weld. In this collision the atoms of the two adjacent metals are propelled together with such force that they actually overcome their natural repulsion forces and result in a stable equilibrium as they share electrons. The process utilizes pressure, without heat and therefore avoids all the conventional heat induced deficiencies revealed in conventional welding methods, such as phase changes the formation of intermetallics, recrystallised grains, to produce a solid state bond.

This solid state bond is generally stronger than the parent materials themselves, as failure normally occurs in the weaker of the two metals and not at the welded interface. The absence of heat in the process makes it possible to weld metals with widely different melting temperatures, such as aluminum and steel. The process takes place at a very high velocity in less than 100 microseconds.

METALS COMBINATIONS WELDED

Some of the significant metals and alloys that have been commercially welded using MPW. However, it must be stated here, that the process is not in anyway limited to the material combinations. These combinations are simply based on work carried out by Pulsar

COMMERCIAL APPLICATIONS

The following are examples of typical applications for magnetic pulse welding

An example of a fuel filter made from 1100 series aluminum material.

These parts are normally tested under pressure pulse cycles of 7 atm for 300,000

Cycles.

A typical rectangular tube application for the automotive industry made with 6000 series aluminum. These parts have been tested destructively but although buckling in various modes occurs with different tests, the weld always remains intact

An aluminium (AL 5049) to stainless steel (AISI 316 L) tubular weld. This assembly has been burst tested, illustrating the high integrality of the joint. Failure occurs in the aluminium tube, remote from the weld

TYPICAL WELD INTERFACE

The typical weld interface may include interfacial waves and or flat undulated areas. The following presents a few examples of typical metallographic sections of weld interfaces obtainable for both similar and dissimilar metal combinations

BENEFITS OF THE MAGNETIC WELDING PROCESS

MP- weld provides the following benefits

W MP-Weld enables simpler design and also designs which were previously impossible by conventional means. It provides the advantages of higher strength to weight ratio. A metallurgical bond is produced without any heat affected. Therefore, the original heat treatment in this cold weld is maintained and thus better joint properties are achieved

Dissimilar materials combinations are available with this method and the complex joints may be replaced by simpler joints

Apart from higher process weld speed, there is a significant quality improvement with this system and there is no corrosion in the welded area

Finally in this GREEN process parts produced are more aesthetic than those of competing conventional process and do not require any post weld cleaning or finishing

MAGNETIC PULSE FORMING, CRIMPING AND PERFORATION

The arrangements for the flat forming and perforating, the equivalent system for tubular forming, perforating and crimping. In all these process, the work piece is accelerated by the same principal as described in the earlier section on welding except that energies are generally much lower. The die is a single sided, or in the case of tubular crimping work piece replaces the die

BENEFITS OF FORMING, CRIMPING AND PERFORATION USING MAGNETIC PULSE ENERGY

· Some benefits of magnetic pulse forming crimping and perforation

· High repeatability

· Non-contact operation

· Negligible spring back

· Improved ductility of the worked part

· Cheaper tooling

· No need for special workshop infrastructure

CONCLUSION

MPW produces a weld without heating up the parts involved without any filter metal, with limited surface treatment at high speed without any detrimental effects on the heat treatment of welded materials, has good repeatability and is stronger than the weaker of the parent metals being joined.Thus this process is a green process