What Is Pulsed Magnetic Welding?

PMW is a technique for creating solid-state welds in microseconds by accelerating of one electrically conductive metal surface against another metal surface.

Is it new?

No, the first PMW done in America was in 1967 on a 6 kJ MAGNEFORM® machine by Douglas Nuclear.

MAGNEFORM ® Machine similar to that used for first PMW.

How does it work?

An intense magnetic field is created through a discharge of electrical current into a coil. An eddy current is created in the conductive work piece. The current creates a magnetic pressure that puts the work piece to be welded in motion at speeds greater than 300M/Sec.

The action is similar to the repulsive force created when like poles of a permanent magnetic are pushed together.

Can you describe an application?

The process has been used for several applications. Two are described below.

Sealing of Aluminum Pressure Vessel

The requirement was to create a hermetically sealed pressure vessel using both mild steel and aluminum closures. The diameter was 2 inches [5cm]. The body was 6061 TO, and the closures 6061 T6 aluminum and 1010 steel. The welding was performed on the machine pictured above.

Before

After

Photomicrograph below show welded interface between closure and vessel body. Peel test shows the same part.

Welding Nuclear Fuel Pins
Magneform® built special production machines for the welding of the end closures of nuclear fuel pins. [See Weld Journal June 1978]. The first was for Westinghouse Hanford, the second for PNC, a Japanese nuclear fuel manufacturer.

Various combinations of materials were welded including 316 Stainless Steel, Inconel 706, PE 16, and RA 330. Diameter of the outer tube was 0.230 inches [5.84 mm]. A mild steel driver was used on the outside of the tube. Below is a photomicrograph of an un-etched section of a welded fuel pin. Follow the tube from the left till it disappears. The solid section is welded.

The following electron photomicrograph shows the weld interface at x1000 magnification.

Fuel Pin Welders Two types of machines were designed and manufactures for pin welding.

The Westinghouse Hanford Design

Fuel Pin Welders

The PNC Design.

The circular section to the right is to accommodate a glove box in which welding takes place.

What are the advantages of Magneform PMW?

Advantages:
1. The process in non-contact. Nothing touches the part.
2. Repeatability of the force is within one half of one percent.
3. Cycle time is a little as 6 seconds-that's over 1,000,000 parts per year per shift.
4. There is no heat-affected zone adjacent to the weld.
5. The process is very energy efficient. Energy cost is typically fractions of a cent per weld.
6. Dissimilar metals can be welded.

Photomicrograph above is aluminum [top] welded to steel [bottom]. *

7. Most Magneform® equipment used for welding can also be used for forming or mechanical joining.
8. Hermetic seals can be achieved.
9. No filler material [I.e. welding rod] or gases are necessary.

*Welded on 90 kJ Magneform machine similar to that at EWI.

What are the disadvantages?
There are of course a few disadvantages.
1. PMW is limited to good electrical conductors.
2. Parts need not be round but must provide a current path.
3. Process is limited to welding relatively thin walled materials.

Where are Magneform® products manufactured? All Magneform® products have been designed and built in San Diego California, USA since 1961. We have a full applications laboratory to serve you.