Induction forging
Encyclopedia
Induction forging refers to the use of an induction heater
to pre-heat metals prior to deformation using a press or hammer. Typically metals are heated to between 1100 °C (2,012 °F) and 1200 °C (2,192 °F) to increase their malleability and aid flow in the forging die.
is a non-contact process which uses the principle of electromagnetic induction
to produce heat in a workpiece. By placing a conductive material into a strong alternating magnetic field
, electrical current is made to flow in the material, thereby causing Joule heating
. In magnetic materials, further heat is generated below the Curie point
due to hysteresis losses. The generated current flows predominantly in the surface layer, the depth of this layer being dictated by the frequency of the alternating field and the permeability
of the material.
In order to select the correct power it is necessary to first calculate the thermal energy
required to raise the material to the required temperature in the time allotted. This can be done using the heat content of the material which is normal expressed in KW hours per tonne the weight of metal to be processed and the time cycle. Once this has been established other factors such as radiated losses from the component, coil losses and other system losses need to be factored in. Traditionally this process involved lengthy and complex calculations in conjunction with a mixture of practical experience and empirical formula
. Modern techniques utilise finite element analysis and other computer aided modeling techniques, however as with all such methods a thorough working knowledge of the induction heating process is still required.
requirements regarding the cross sectional ∆T it is possible to calculate or create a model to establish the heat time required. In many cases the time to achieve an acceptable ∆T will exceed what can be achieved by heating the components one at a time. A range of handling solutions including conveyors, in line feeders, pusher systems and walking beam feeders are utilised to facilitate the heating of multiple components whilst delivering single components to the operator at the required time cycle.
Subject to the required throughput, handling systems can vary from simple 2 or 3 station pneumatic pusher systems to walking beams and conveyors.
Typical parts processed by in line billet heating:
Typical parts processed by single shot billet heating:
Induction heater
An induction heater is a key piece of equipment used in all forms of induction heating. Typically an induction heater operates at either medium frequency or radio frequency ranges. Three main components form the basis of a modern induction heater including the power unit , the work head and the...
to pre-heat metals prior to deformation using a press or hammer. Typically metals are heated to between 1100 °C (2,012 °F) and 1200 °C (2,192 °F) to increase their malleability and aid flow in the forging die.
Process
Induction heatingInduction heating
Induction heating is the process of heating an electrically conducting object by electromagnetic induction, where eddy currents are generated within the metal and resistance leads to Joule heating of the metal...
is a non-contact process which uses the principle of 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 produce heat in a workpiece. By placing a conductive material into a strong alternating magnetic field
Magnetic field
A magnetic field is a mathematical description of the magnetic influence of electric currents and magnetic materials. The magnetic field at any given point is specified by both a direction and a magnitude ; as such it is a vector field.Technically, a magnetic field is a pseudo vector;...
, electrical current is made to flow in the material, thereby causing Joule heating
Joule heating
Joule heating, also known as ohmic heating and resistive heating, is the process by which the passage of an electric current through a conductor releases heat. It was first studied by James Prescott Joule in 1841. Joule immersed a length of wire in a fixed mass of water and measured the temperature...
. In magnetic materials, further heat is generated below the Curie point
Curie point
In physics and materials science, the Curie temperature , or Curie point, is the temperature at which a ferromagnetic or a ferrimagnetic material becomes paramagnetic on heating; the effect is reversible. A magnet will lose its magnetism if heated above the Curie temperature...
due to hysteresis losses. The generated current flows predominantly in the surface layer, the depth of this layer being dictated by the frequency of the alternating field and the permeability
Permeability (electromagnetism)
In electromagnetism, permeability is the measure of the ability of a material to support the formation of a magnetic field within itself. In other words, it is the degree of magnetization that a material obtains in response to an applied magnetic field. Magnetic permeability is typically...
of the material.
Power consumption
Power supplies for induction forging vary in power from a few kilowatts to many megawatts and, depending on the component geometry, can vary in frequency from 50 Hz to 200 kHz. The majority of applications use the range between 1 kHz and 100 kHz.In order to select the correct power it is necessary to first calculate the thermal energy
Thermal energy
Thermal energy is the part of the total internal energy of a thermodynamic system or sample of matter that results in the system's temperature....
required to raise the material to the required temperature in the time allotted. This can be done using the heat content of the material which is normal expressed in KW hours per tonne the weight of metal to be processed and the time cycle. Once this has been established other factors such as radiated losses from the component, coil losses and other system losses need to be factored in. Traditionally this process involved lengthy and complex calculations in conjunction with a mixture of practical experience and empirical formula
Empirical formula
In chemistry, the empirical formula of a chemical compound is the simplest positive integer ratio of atoms of each element present in a compound. An empirical formula makes no reference to isomerism, structure, or absolute number of atoms. The empirical formula is used as standard for most ionic...
. Modern techniques utilise finite element analysis and other computer aided modeling techniques, however as with all such methods a thorough working knowledge of the induction heating process is still required.
Output frequency
The second major parameter to be considered is the output frequency of the power source. As the heat is predominantly generated in the surface of the component it is important to select a frequency which offers the deepest practical penetration depth into the material without running the risk of current cancellation. It will be appreciated that as only the skin is being heated time will be required for the heat to penetrate to the centre of the component and that if too much power is applied too quickly it is possible to melt the surface of the component whilst leaving the core cool. Utilising thermal conductivity data for the material and the customers specified homogeneity (physics)Homogeneity (physics)
In general, homogeneity is defined as the quality or state of being homogeneous . For instance, a uniform electric field would be compatible with homogeneity...
requirements regarding the cross sectional ∆T it is possible to calculate or create a model to establish the heat time required. In many cases the time to achieve an acceptable ∆T will exceed what can be achieved by heating the components one at a time. A range of handling solutions including conveyors, in line feeders, pusher systems and walking beam feeders are utilised to facilitate the heating of multiple components whilst delivering single components to the operator at the required time cycle.
Advantages
- Process controllability - Unlike a traditional gas furnace the induction system requires no pre-heat cycle or controlled shutdown. The heat is available on demand. In addition to the benefits of rapid availability in the event of a downstream interruption to production the power can be switched off thus saving energy and reducing scaling on the components.
- Energy efficiency - Due to the heat being generated within the component energy transfer is extremely efficient. The induction heater heats only the part not the atmosphereAtmosphereAn atmosphere is a layer of gases that may surround a material body of sufficient mass, and that is held in place by the gravity of the body. An atmosphere may be retained for a longer duration, if the gravity is high and the atmosphere's temperature is low...
around it.
- Rapid temperature rise - High power densities ensure that the component reaches temperature extremely rapidly. Scale is reduced as are surface defects and undesirable effects on the surface metallurgyMetallurgyMetallurgy is a domain of materials science that studies the physical and chemical behavior of metallic elements, their intermetallic compounds, and their mixtures, which are called alloys. It is also the technology of metals: the way in which science is applied to their practical use...
.
- Process consistency - The induction heating process produces extremely uniform consistent heat this improves accuracy of the forging and can in extreme cases reduce post forging machining allowances and have a positive effect on die life.
Bar end heating
Bar end heating is typically used where only a portion of the bar is to be forged. Typical applications of bar end heating are- Hot heading of bolts
- Anti roll bars
- Mining tools
Subject to the required throughput, handling systems can vary from simple 2 or 3 station pneumatic pusher systems to walking beams and conveyors.
Billet heating
In the induction billet heater the whole of the billet or slug is heated. Normally for short billets or slugs a hopper or bowl is used to automatically present the billets in line to pinch rollers, chain driven tractor units or in some cases pneumatic pushers. The billets are then driven through the coil one behind the other on water cooled rails or ceramic liners are used through the coil bore which reduce friction and prevent wear. The length of the coil is a function of the required soak time, the cycle time per component and the length of the billet. In high volume large cross section work it is not unusual to have 4 or 5 coils in series to give 5 m (16.4 ft) of coil or more.Typical parts processed by in line billet heating:
- Small crankshafts
- Camshafts
- Pneumatic and hydraulic fittings
- Hammer heads
- Engine valves
Single shot
For long billets, single shot heating can be used. This process utilises similar systems to bar end heating except that the whole of the billet is driven into individual coils. As with bar end heating the number of coils is governed by ∆T required and the thermal properties of the material being heated.Typical parts processed by single shot billet heating:
- Lorry axles
- Marine camshafts
See also
- ForgingForgingForging is a manufacturing process involving the shaping of metal using localized compressive forces. Forging is often classified according to the temperature at which it is performed: '"cold," "warm," or "hot" forging. Forged parts can range in weight from less than a kilogram to 580 metric tons...
- Induction hardeningInduction hardeningInduction hardening is a form of heat treatment in which a metal part is heated by induction heating and then quenched. The quenched metal undergoes a martensitic transformation, increasing the hardness and brittleness of the part...
- Induction shrink fittingInduction shrink fittingInduction shrink fitting refers to the use of induction heater technology to pre-heat metal components between and thereby causing them to expand and allow for the insertion or removal of another component. Typically the lower temperature range is used on metals such as aluminium and higher...
- Induction heaterInduction heaterAn induction heater is a key piece of equipment used in all forms of induction heating. Typically an induction heater operates at either medium frequency or radio frequency ranges. Three main components form the basis of a modern induction heater including the power unit , the work head and the...