Induction welding
Encyclopedia
Induction welding is a form of welding
that uses electromagnetic induction
to heat the workpiece. The welding apparatus contains an induction coil
that is energised with a radio-frequency electric current
. This generates a high-frequency electromagnetic field
that acts on either an electrically conductive or a ferromagnetic
workpiece. In an electrically conductive workpiece, such as steel
, the main heating effect is resistive
heating, which is due to magnetically induced currents called eddy current
s. In a ferromagnetic workpiece, such as plastic doped with ceramic
particles, the heating is caused mainly by hysteresis
as the magnetic component of the electromagnetic field repeatedly distorts the crystal
line structure of the ferromagnetic material. In practice, most materials undergo a combination of these two effects.
As suggested above, nonmagnetic materials such as plastic
s can be induction-welded by implanting them with metallic or ferromagnetic compounds, called susceptor
s, that absorb the electromagnetic energy from the induction coil
, become hot, and lose their heat
to the surrounding material by thermal conduction.
Induction welding is used for long production runs and is a highly automated process, usually used for welding the seams of pipes. It can be a very fast process, as a lot of power can be transferred to a localised area, so the faying surfaces melt very quickly and can be pressed together to form a continuous rolling weld.
The depth that the current, and therefore heating, penetrates from the surface is proportional to the frequency of the current flowing in the coil. The temperature of the metals being welded and their composition will also effect the penetration depth. This process is very similar to resistance welding
, except that in the case of resistance welding the current is delivered using contacts to the workpiece instead of using induction.
Welding
Welding is a fabrication or sculptural process that joins materials, usually metals or thermoplastics, by causing coalescence. This is often done by melting the workpieces and adding a filler material to form a pool of molten material that cools to become a strong joint, with pressure sometimes...
that uses electromagnetic induction
Electromagnetic induction
Electromagnetic induction is the production of an electric current across a conductor moving through a magnetic field. It underlies the operation of generators, transformers, induction motors, electric motors, synchronous motors, and solenoids....
to heat the workpiece. The welding apparatus contains an induction coil
Induction coil
An induction coil or "spark coil" is a type of disruptive discharge coil. It is a type of electrical transformer used to produce high-voltage pulses from a low-voltage direct current supply...
that is energised with a radio-frequency electric current
Electric current
Electric current is a flow of electric charge through a medium.This charge is typically carried by moving electrons in a conductor such as wire...
. This generates a high-frequency electromagnetic field
Electromagnetic field
An electromagnetic field is a physical field produced by moving electrically charged objects. It affects the behavior of charged objects in the vicinity of the field. The electromagnetic field extends indefinitely throughout space and describes the electromagnetic interaction...
that acts on either an electrically conductive or a ferromagnetic
Ferromagnetism
Ferromagnetism is the basic mechanism by which certain materials form permanent magnets, or are attracted to magnets. In physics, several different types of magnetism are distinguished...
workpiece. In an electrically conductive workpiece, such as steel
Steel
Steel is an alloy that consists mostly of iron and has a carbon content between 0.2% and 2.1% by weight, depending on the grade. Carbon is the most common alloying material for iron, but various other alloying elements are used, such as manganese, chromium, vanadium, and tungsten...
, the main heating effect is resistive
Electrical resistance
The electrical resistance of an electrical element is the opposition to the passage of an electric current through that element; the inverse quantity is electrical conductance, the ease at which an electric current passes. Electrical resistance shares some conceptual parallels with the mechanical...
heating, which is due to magnetically induced currents called eddy current
Eddy current
Eddy currents are electric currents induced in conductors when a conductor is exposed to a changing magnetic field; due to relative motion of the field source and conductor or due to variations of the field with time. This can cause a circulating flow of electrons, or current, within the body of...
s. In a ferromagnetic workpiece, such as plastic doped with ceramic
Ceramic
A ceramic is an inorganic, nonmetallic solid prepared by the action of heat and subsequent cooling. Ceramic materials may have a crystalline or partly crystalline structure, or may be amorphous...
particles, the heating is caused mainly by hysteresis
Hysteresis
Hysteresis is the dependence of a system not just on its current environment but also on its past. This dependence arises because the system can be in more than one internal state. To predict its future evolution, either its internal state or its history must be known. If a given input alternately...
as the magnetic component of the electromagnetic field repeatedly distorts the crystal
Crystal
A crystal or crystalline solid is a solid material whose constituent atoms, molecules, or ions are arranged in an orderly repeating pattern extending in all three spatial dimensions. The scientific study of crystals and crystal formation is known as crystallography...
line structure of the ferromagnetic material. In practice, most materials undergo a combination of these two effects.
As suggested above, nonmagnetic materials such as plastic
Plastic
A plastic material is any of a wide range of synthetic or semi-synthetic organic solids used in the manufacture of industrial products. Plastics are typically polymers of high molecular mass, and may contain other substances to improve performance and/or reduce production costs...
s can be induction-welded by implanting them with metallic or ferromagnetic compounds, called susceptor
Susceptor
A susceptor is a material used for its ability to absorb electromagnetic energy and convert it to heat . This energy is typically radiofrequency or microwave radiation used in industrial heating processes, and also occasionally in microwave cooking...
s, that absorb the electromagnetic energy from the induction coil
Induction coil
An induction coil or "spark coil" is a type of disruptive discharge coil. It is a type of electrical transformer used to produce high-voltage pulses from a low-voltage direct current supply...
, become hot, and lose their heat
Heat
In physics and thermodynamics, heat is energy transferred from one body, region, or thermodynamic system to another due to thermal contact or thermal radiation when the systems are at different temperatures. It is often described as one of the fundamental processes of energy transfer between...
to the surrounding material by thermal conduction.
Induction welding is used for long production runs and is a highly automated process, usually used for welding the seams of pipes. It can be a very fast process, as a lot of power can be transferred to a localised area, so the faying surfaces melt very quickly and can be pressed together to form a continuous rolling weld.
The depth that the current, and therefore heating, penetrates from the surface is proportional to the frequency of the current flowing in the coil. The temperature of the metals being welded and their composition will also effect the penetration depth. This process is very similar to resistance welding
Resistance welding
Electric resistance welding refers to a group of welding processes such as spot and seam welding that produce coalescence of faying surfaces where heat to form the weld is generated by the electical reistance of material vs the time and the force used to hold the materials together during welding...
, except that in the case of resistance welding the current is delivered using contacts to the workpiece instead of using induction.