Introduction to induction brazing

The induction brazing It is a technique that basically consists of heating two or more parts through the practical use of Eddy currents and hysteresis cycles of ferromagnetic materials or electrical conductors. In them, a current is induced through the use of coils through which a certain alternating electric current circulates. This high-frequency induced current heats the material due to its internal resistance; heat can also be produced by repeated changes in the magnetic domain of ferromagnetic materials.

In other articles we have already talked about welding, about its different types and other issues. Today we will focus precisely on this particular topic in order to answer the following question: What is the induction brazing?

The traditional method allows parts to be welded together without the need to use electrodes. It is important to clarify that this method works only if the metals of both pieces allow them to be alloyed. When this does not occur, an intermediate material is sought that offers alloy for both metals.

Induction Brazing Apparatus

The appliances of welding by induction consist of a transformer and a coil connected to the transformer by means of a thick wire. The operating principle is simple: the parts to be welded are heated by electrical induction, until they reach the melting temperature in the area to be welded.

In all cases, alternating current and an electronic oscillator are used that pass high-frequency alternating current through the coil; the rapidly changing magnetic field thus generated penetrates the object, generating currents induced by Faraday’s law, called eddy currents.

The heating of the pieces is produced by two different effects: the resistivity of the material, which opposes the passage of electric currents, and the change of the magnetic domain in those ferromagnetic materials.

In any case, the pieces, after being heated for a certain time, reach the melting temperature in the area to be welded. When this occurs, they can be joined permanently and by fusion, thereby achieving a welding clean, efficient and fast.

Advantages over other welding methods

• Reduced power consumption.
• Lower cost of production, cleaning, maintenance and supplies.
• Lower gas emission.
• Automation feasibility.

There are two methods of induction brazing: direct and strong welding. We will see both methods below.

direct welding

It is the union of two or more pieces of the same metal by simple fusion between them, that is, without the use of a filler material.

This method is generally used to sew steel tubes, in which case, in addition to the induction coil, two rollers are used that force the tube to close after passing through the coil, where it reaches the temperature of fusion.

Preparation of the surfaces to be welded

• The surface of both parts must be clean, polished and fitted to size.
• The shape and arrangement of the welding to do to choose the most suitable coil. Welding two tubes together is not the same as joining two L profiles.
• Parts must be firmly attached. The success of induction brazing it depends on none of the pieces moving once attached.

Performing direct induction brazing

Both pieces are placed in such a way that the surfaces to be welded are exactly below or in the center of the induction coil.

The process of welding by passing high frequency current through the coil. Special care must be taken to select the appropriate power for the job, according to the thickness and materials of the pieces.

When the surfaces to be welded reach the melting temperature, one of the two pieces must be pushed gently, in order to press so that the material penetrates evenly into each microcavity.

It only remains to cut off the high frequency current and wait for the joint to cool down.

It should be checked to make sure there are no cracks or unwelded areas.

brazing

Unlike the direct weldingIn this case, flux and filler material are used to join both pieces.

Induction brazing – joining of steel tubes using copper as filler metal

This type of welding It is particularly useful for those cases in which the different materials do not offer a ligation, but they do with a third material, which is the filler.

Preparation of the pieces

• The surface of both parts must be clean, polished and fitted to size.
• The shape and arrangement of the welding to do to choose the most suitable coil. Welding two tubes together is not the same as joining two L profiles.
• Parts must be firmly attached. The success of welding it depends on none of the pieces moving once attached.
• Flux should be applied to the surface of both pieces. The objective of its application is to avoid the oxidation of the surfaces to be welded.

Carrying out brazing

After applying the flux, and with the filler material already placed around the surface to be welded (in the case of two tubes), the passage of current through the coil begins.

According to the materials to be welded, the time and temperature will be determined —see the table below— for this induction brazing.

If the pieces to be joined do not allow the previous placement of the filler material, it must be applied while both pieces are under the induction current.

Once both pieces are joined, the current can be turned off, taking special care not to move the pieces until they are relatively cool.

Remember that it is not necessary to cool the welding with water or oil, nor is it required to remove any type of slag; the use of flux and the same process of induction brazing they will make it unnecessary.

Induction Brazing Temperature Chart