Induction Brazing

induction brazing

What is Brazing?

Brazing is the process of joining two similar or dissimilar metals thorough heating and melting a filler that has a lower melting temperature than the base metal. By comparison, welding involved melting a filler and some of the actual base metal to bond it. Though properly brazed joints are not as strong as welded joints, brazing has minimal effect on the metals being bonded.

Historically, brazing material has a bit of a mixed reputation due to the weaker bonds than welding. However, modern brazing techniques are a far cry from previous generations. While still less strong than welds, there are plenty of situations where brazing is preferred.

So what is Induction Brazing?

There are three different techniques of brazing: Torch, Furnace, and Induction.

Torch brazing is the most commonly used. However, it requires experienced operators to pull of well. Because an open flame is used in torch brazing, it also comes with higher regulatory and safety concerns.

induction brazing

Torch brazing

Furnace brazing is also a common technique. It allows quality brazing of large batches of components. Furthermore, it doesn’t require skilled operators and multiple joints can be brazed at once. However, joints need to be closely fit to braze properly. Lastly, the surface of the material has to be spotless to prevent flaws in the brazing.

Induction brazing is the latest addition. An electrically conductive metal is heated by rapidly passing magnetic fields through it. Without getting too technical, electromagnets and oscillators are used for this.  The resulting electric currents generated inside the metal are referred to as “eddy currents.” These currents generate heat within the metal being brazed.

Induction brazing resolves many of the issues arising from torch and furnace brazing. Unlike torch, it doesn’t require an experienced operator. Compared to furnace, it has a smaller equipment footprint, utilizes less energy, and allows for a more accurate process.

This technique is fast, repeatable, and efficient. Furthermore, induction allows for a non-contact process for joining electrically conductive metals. These include copper-to-aluminum, aluminum-to-aluminum, copper-to-copper, brass-to-copper, brass-to-copper, steel-to-copper, steel-to-brass and steel-to-steel.

Advantages

  • High speed process of joining
  • Low cost
  • Ability to localize heat
  • Safer than torch and furnace brazing
  • Does not require an experienced operator
  • Good accuracy and repeatability

Disadvantages

  • Not all materials are compatible with induction brazing
  • Induction brazing is a low volume process compared to furnace brazing

Induction heating works on electrically conductive materials, usually this limits the process to metals but there are ways of bypassing these limitations.

The ease with which a material can be heated by induction depends on the electrical resistivity and their magnetism. Ferrous metals are therefore much easier to heat than aluminium. Likewise, carbon steels will heat more readily than stainless steels. Ceramics are not usually brazed by induction but can be brazed to ferrous metals relatively easily.

induction brazing

Brazing practice at the Gary, Indiana plant of the Tubular Steel Corporation. circa 1943

Things to Consider

Type of metal

The power and heating rate required will be determined by the type of metal of the work piece. High resistivity metals strongly resist the current flow that is required in induction brazing and heat builds up quickly in these metals. Steel and iron will heat faster than low resistivity metals such as aluminum, copper, and brass, which require more power.

Size of the metal

The size of the piece determines the induction heating system’s operating frequency. Brazing smaller parts requires higher frequency (>50 kHz), while larger parts require lower frequency (>10 kHz) to achieve more heat penetration. You should also consider the thickness of the metals to be brazed. With conductive materials, about 85% of the heating effect occurs on the surface, meaning thinner pieces typically heat faster than thicker pieces. Therefore, larger or thicker parts will take longer to reach the brazing temperature compared to smaller or thinner parts.

Magnetic Metals

In addition to the heat induced by eddy currents in induction brazing, magnetic materials also produce heat through what is referred to as the hysteresis effect. Because of this effect, magnetic materials heat faster than non-magnetic ones.

Coil design

The design of the coil used in induction brazing is crucial to ensure even heating of the brazed components.The coil should be individually designed for each braze joint in order to maximize the efficiency; coils may be as simple as a single round section to much more complex shapes. The closer in proximate the coil is to joint the more efficient the brazing process will be.