COMPACT INDUCTION HEATING SYSTEM WITH MOVABLE COIL

Abstract

An induction heating system for heating a component, the induction heating system having an alternating voltage supply device, a capacitor, a displacement unit, and an induction coil. The alternating voltage supply device supplies alternating voltage to a series resonant circuit which is formed by the capacitor and the induction coil. The displacement unit allows the induction coil to be displaced laterally in at least one direction relative to the component. The capacitor is situated between the displacement unit and the induction coil. A device for the additive manufacturing of a component uses such an induction heating system.

Claims

1. An induction heating system for heating a component, the induction heating system comprising: an alternating voltage supply device, a capacitor, a displacement unit, and an induction coil, wherein the alternating voltage supply device supplies alternating voltage to a series resonant circuit which is formed by the capacitor and the induction coil, wherein the displacement unit enables the induction coil to be displaced laterally in at least one direction relative to the component, and wherein the capacitor is arranged between the displacement unit and the induction coil.

2. The induction heating system as claimed in claim 1, wherein the alternating voltage supply device has an induction generator for generating an input alternating voltage and a transformer for converting the input alternating voltage into an output alternating voltage.

3. The induction heating system as claimed in claim 1, wherein the displacement unit has a rail and a slide, wherein the slide is designed to move on the rail and wherein the rail defines the direction along which the induction coil moves.

4. The induction heating system as claimed in claim 3, wherein an electrical contact between the rail and the slide is realized by a sliding contact.

5. The induction heating system as claimed in claim 1, wherein the displacement unit enables the induction coil to be displaced laterally in two directions relative to the component.

6. The induction heating system as claimed in claim 5, wherein the displacement unit enables the induction coil to be displaced over an entire surface of the component in plan view.

7. The induction heating system as claimed in claim 1, wherein the induction coil and the capacitor form an induction module which is displaceable by the displacement unit and are surrounded by a common housing.

8. The induction heating system as claimed in claim 1, wherein the series resonant circuit has, at least partially, liquid-cooled electrical lines.

9. The induction heating system as claimed in claim 1, wherein the induction heating system has a further capacitor which is located between the alternating voltage supply device and the displacement unit and, together with the capacitor between the displacement unit and induction coil, forms the capacitive resistance of the series resonant circuit.

10. A device for additive manufacturing of a component, comprising: a platform which is provided in order to apply a powder or wire metallic material thereon in layers, a primary heating device which is adapted to melt a powder or wire metallic material applied to the platform, and an induction heating system as claimed in claim 1, wherein the induction coil is traversable above the platform and is designed to heat the powder or wire metallic material applied to the platform.

11. The device as claimed in claim 10, wherein the primary heating device is designed as a laser beam source or an electron beam source, and wherein the induction coil defines a window through which a laser beam or electron beam of the laser beam source or electron beam source can pass and can heat the powder or wire metallic material applied to the platform.

12. The device as claimed in claim 10, wherein the primary heating device comprises a laser beam source or an electron beam source.

13. The induction heating system as claimed in claim 5, wherein the displacement unit enables the induction coil to be displaced laterally in two directions relative to the component, wherein the two directions are perpendicular to one another.

14. The induction heating system as claimed in claim 8, wherein the series resonant circuit has, largely, liquid-cooled electrical lines.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In the figures:

[0028] FIG. 1: shows a device for additive manufacturing of a component with an induction heating system according to the invention;

[0029] FIG. 2: shows an electrical circuit diagram of the induction heating system from FIG. 1; and

[0030] FIG. 3: shows an electrical circuit diagram of a conventional induction heating system.

DETAILED DESCRIPTION OF INVENTION

[0031] FIG. 1 (also referred to as FIG. 1) shows a device for additive manufacturing of a component 1 with an induction heating system according to the invention. The device comprises a platform which is provided in order to apply a powder or wire metallic material thereon in layers as well as a primary heating device which is designed to melt a powder or wire metallic material applied to the platform. These parts of the device are standard parts of a system for additive component manufacturing (also: additive manufacturing or 3D printing) and are not shown in FIG. 1 for the sake of clarity. Their configuration and connection relative to one another are well known to the person skilled in the art within the field of additive manufacturing, in particular selective laser melting.

[0032] The device further has an induction heating system for heating the material. Both preheating of the material which has not been melted yet and post-treatment of the material which has already been melted are possible with the induction heating system. In principle, inductive heating of the metallic material is also possible during melting by means of a laser beam source or electron beam source, for example.

[0033] The induction heating system has an alternating voltage supply device 10 which consists of an induction generator 11 and a transformer 12. The induction generator 11 generates alternating voltage with an effective voltage of several hundred volts up to several kilovolts. In this case, the current strength is moderate and is between 10 A and 100 A, for example. In order to achieve a high heating power through the induction coil, said coil must have a high current strength, which in particular is higher than 100 A, flowing through it. A transformer 12 is therefore connected to the induction generator 11. The transformer 12 converts the high voltage of the induction generator 11 into a lower voltage, which directly results in an increase in the current strength in the circuit at the output of the transformer 12. The circuit at the input of the transformer 12 is also referred to as a “generator circuit”; the circuit at the output of the transformer 12 as a “working circuit”.

[0034] The alternating voltage supply device 10 is connected to a displacement unit 30 by means of electrical lines, which are also referred to as supply lines 50 in the context of this application. The purpose of the displacement unit 30 is to make the induction coil 40 connected to it displaceable with respect to a stationary component 1. For this purpose, a first slide 32 and a second slide 35 can in each case be controlled by means of a control device. For the sake of clarity, the control device for the displacement unit 30 is not shown in FIG. 1 and it is also not explored in greater detail in this description, since it does not relate to the essence of this invention.

[0035] The first slide 32 is located on a first pair of rails 31 by means of two first sliding contacts 33. The sliding contacts 33 are made of an electrically highly conductive metal, for example, likewise the two rails of the first pair of rails 31. Copper can be specified as a suitable material for the sliding contacts 33 and the pair of rails 31, for example. The first sliding contacts 33 are for their part in turn connected to a second pair of rails 34 by means of electrical conductors 50. The second pair of rails 34 forms the bearing surface for the second slide 35, the second sliding contacts 36 of which are electrically connected to the rails of the second pair of rails 34. The second sliding contacts 36 are connected to the induction coil 40 by means of supply lines 50. The first slide 32 is moveable back and forth along a first displacement direction 37 (here corresponding to the x direction); the second slide 35 is moveable back and forth along a second displacement direction 38 (here corresponding to the y direction). For the induction coil 40, it follows that it is displaceable in a region (or: surface) defined by the displacement unit 30.

[0036] The induction coil 40 is not drawn to scale in FIG. 1 (as well as the alternating voltage supply device 10, for example) with respect to the other components. In most real cases, it will be significantly smaller. However, for the sake of clarity, it is drawn as a large, double-wound coil in FIG. 1. In this case, the induction coil defines a window 43 through its coil interior, through which window a laser beam can advantageously pass to the material which is to be treated.

[0037] One essential part of an induction heating system is a capacitor which, together with the induction coil, forms a series resonant circuit, also referred to as an RLC resonant circuit. Owing to the high currents which flow through the induction coil, the inductance of the coil is high and the capacitance of the capacitor must be selected to be correspondingly large. This results in a certain structural size and weight of the capacitor. As a result, in conventional induction heating systems, the capacitor(s) was (or were) built into the alternating voltage supply device, since the alternating voltage supply device with the induction generator and transformer already claimed a lot of space and also weight. The induction generator and transformer are also often surrounded by a common housing, so that the capacitor could also be accommodated and protected efficiently therein.

[0038] In the case of a stationary induction coil, i.e. an induction coil which is immovable relative to the alternating voltage supply device, well insulated, optionally water-cooled electrical cables can be used as electrical lines between the capacitor located at the alternating voltage supply device and the induction coil, for example, so that no voltage flashovers occur in the supply lines.

[0039] In the case of a moveable induction coil, i.e. an induction coil which is moveable relative to the alternating voltage supply device, water-cooled electrical cables may not be able to be used, since they are not suitable for frequently occurring movements. However, if contact rails and sliding contacts are used, this creates the problem of potential voltage flashovers, such that the maximum power in the resonant circuit must be limited, for example.

[0040] The idea of the present invention is not to place the capacitor 20 close to the alternating voltage supply device 10, as is conventional, but rather between the displacement unit 30 and the induction coil 40. One possible position is shown in FIG. 1 in a schematic manner.

[0041] FIG. 1 further shows a second capacitor which is referred to as an additional capacitor 21 hereinafter. It essentially serves as an additional capacitor in order to have more flexibility to set the capacitance of the resonant circuit.

[0042] It must be decided in each individual case whether sufficient space is available or can be provided in order to place the capacitor 20 and optionally the additional capacitor 21 between the displacement unit 30 and the induction coil 40. Should this be difficult, an attractive compromise, for reducing the risk of voltage flashovers, between, on the one hand, the structural constraints and, on the other hand, necessity can involve designing the capacitor 20 to be only just as large as possible and therefore placing a further capacitor close to the alternating voltage supply device 10, as is conventional. The total capacitance of the series resonant circuit is then formed from the capacitor 20 close to the induction coil and the further capacitor close to the alternating voltage supply device 10.

[0043] FIG. 2 (also referred to as FIG. 2) shows an electrical circuit diagram of the induction heating system from FIG. 1. The generator circuit is formed by the induction generator 11 and the one coil of the transformer 12. The working circuit is formed by the second coil of the transformer 12, the capacitor 20, the additional capacitor 21 and the induction coil 40. For the induction coil 40, both the ohmic resistance 41 and the inductive resistance 42 is marked in FIG. 2. The supply lines 50 also have an ohmic resistance and this is accompanied by ohmic losses (which for the most part are absorbed and dissipated by the water cooling of the supply lines 50). These ohmic losses are not marked in FIG. 2 because they do not constitute the essence of the invention. In FIG. 2, the displacement unit 30 is further symbolized by the shaded rectangle.

[0044] Owing to the placement of the capacitor 20 and the additional capacitor 21 between the displacement unit 30 and the induction coil 40, only the relatively low output alternating voltage of the transformer 12 is measured at a voltage measuring device 13 at the displacement unit 30—i.e. at the sliding contacts, for example, which are particularly susceptible to and critical for voltage flashovers. Bearing in mind the fact that in dry air, as a very rough rule of thumb, the likelihood of a voltage flashover is significantly increased for exposed contacts one millimeter apart from one another from approximately 1,000 volts, the risk of a voltage flashover in a structure as shown in FIG. 1 or FIG. 2 is negligible.

[0045] However, this does not apply to a structure as shown in FIG. 3 (also referred to as FIG. 3). FIG. 3 shows an electrical circuit diagram of a conventional induction heating system in which the capacitor 20 and the additional capacitor 21 are arranged “in front” of the displacement unit 30, i.e. between the alternating voltage supply device 10 and the displacement unit 30. All other components in FIG. 3 correspond to the components from FIG. 2, such that they are not repeated for reasons of scarcity.

[0046] As a result of the different placement of the capacitor 20 and the additional capacitor 21, in conventional systems, high voltages owing to the reactive voltage in the series resonant circuit are also measured in the supply lines 50 at the displacement unit 30, i.e. also at the sliding contacts 33, 36, for example. Since they are not virtual voltages but rather real applied voltages, they can also be detected by means of a voltage measuring device 13 which is placed on the displacement unit 30. In the case of correspondingly high inductance of the coil 41, capacitance of the capacitors 20, 21 and applied current strength, a reactive voltage can be generated which is in a range at which charge flashovers are likely.

[0047] In summary, owing to a skilled arrangement of its components, the present invention enables an induction heating system which, even in the case of a moveable induction coil, enables a high degree of operational safety without having to compromise on the maximum heating power.