Molding system with inductive heating

Abstract

A system for uniform temperature generation in an article or part to be formed by molding. The system (1) comprises a molding tool (10) with an electrically conductive element (11) and a heat generation means (12); and an inductor unit (20) comprising at least one coil (21) wound such that a current flowing in each winding of the at least one coil (21) is directed alternatingly in a positive and negative direction with respect to an adjacent winding of the at least one coil (21). The inductor unit (20) is configured to induce a current in the molding tool (10). Furthermore, the electrically conductive element (11) is configured to electrically bypass current induced in the molding tool (10) by the inductor unit (20), at an interface between the electrically conductive element (11) and the heat generation means (12).

Description

[0001] MOLDING SYSTEM WITH INDUCTIVE HEATING

[0002] TECHNICAL FIELD

[0003] The present invention relates in general to a system for uniform temperature generation in an article or part to be formed by molding.

[0004] BACKGROUND

[0005] A common problem associated with manufacturing of articles to be formed by molding are long cycle times, large energy consumption and / or expensive customization for each individual molding tool design. Alternatively, when techniques attempting to mitigate these problems are being employed, the articles formed are often left with areas that are either overheated or insufficiently heated. This is particularly problematic when forming fiber composite parts in which fibers and a matrix material, typically a thermoset or thermoplastic binder, are being molded through a curing or consolidation process. Overheated areas on the formed articles, often referred to as hot spots, may result in poor material quality in the articles. Depending on the application, such as in the aerospace industry, the vehicle mobility industry or in sports equipment, the poor quality may be detrimental to the overall function of the composite part. Correspondingly, insufficiently heated areas of the formed article may result in equally detrimental effects.

[0006] Within the field of composite manufacturing today, there is a challenge in that a large number of different geometries are required for the molding tools, although relatively few articles are produced in each tool. This means that the user of the processing setup of each molding tool requires the processing setup to be cheap. Further on, many materials used for these articles benefit from thermal cycling as well as an elevated pressure. As an example, a common technique used is to use a press to apply the required force on the molding tool, while heating and cooling is performed by heating and cooling of the entire press platens, or by special plates mounted in a press. To heat and cool the entire press platens is time and energy consuming, but also special heating and cooling plates represent a large thermal mass. This is particularly noticeable when the molding tool covers only a fraction of the heated platen in the press. For high-end thermoplastic composites, where temperatures in excess of 400 °C may be needed, a fast and reliable cooling of the molding tool can be challenging, in particular if there is a requirement on uniformity and good temperature control. From the above, it is understood that there is a need for improvements in the field of molding technology.

[0007] SUMMARY

[0008] An object of the present invention is to solve or at least mitigate the problems related to prior art. This object is achieved by means of the technique set forth in the appended independent claims; preferred embodiments being defined in the related dependent claims.

[0009] In an aspect, a system is provided, for uniform temperature generation in an article or part to be formed by molding. The system includes a molding tool comprising an electrically conductive element, and a heat generation means. Furthermore, the system includes an inductor unit comprising at least one coil wound such that a current flowing in each winding of the at least one coil is directed alternatingly in a positive and negative direction with respect to an adjacent winding of the at least one coil. The inductor unit is configured to induce a current in the molding tool. Moreover, the electrically conductive element is configured to electrically bypass current induced in the molding tool by the inductor unit, at an interface between the electrically conductive element and the heat generation means.

[0010] In an embodiment, the electrically conductive element is coated or plated on the heat generation means, or vice versa. This may be beneficial in cases where there is no pressure applied on the molding tool, and where proper electrical and thermal contact between the electrically conductive element and the heat generation means is to be ensured. It is also beneficial for easy handling, as well as to keep the thermal mass to a minimum. Furthermore, it enables a more sophisticated heating pattern, which is beneficial to achieve a uniform temperature on the molding surface when the molding tool varies in thickness.

[0011] In another embodiment, the electrically conductive element and the heat generation means are assembled from separate parts. Consequently, the molding tool can have unlimited shapes since the choice, amount and shape of the electrically conductive element and the heat generation means can be tailored to a certain application. This can be beneficial to be able to reuse certain parts of a tool when a number of similar molding tools are being used. It may also be beneficial to mitigate thermal distortion due to the combination of materials with different thermal expansion coefficients.

[0012] In yet an embodiment, the at least one coil of the inductor unit comprises wires that are electrically insulated from the molding tool. Preferably, the wires are litz wires. Litz wires are beneficial due to their flexibility and low losses at high frequencies. Moreover, they ensure a good efficiency in the system.

[0013] In a further embodiment, the at least one coil is embedded in an embedding material. Preferably, the embedding material is an electrically insulated material, or a material with an electrical resistivity high enough to prevent significant currents from being induced, resulting in undesired heat losses. This is beneficial in that the inductor unit can be used in several different locations.

[0014] In an embodiment, the inductor unit further comprises a plurality of electrically conductive parts and a plurality of soft magnetic parts. The conductive parts of the inductor unit contribute to the amplification of current to be induced in the heat generation means of the molding tool. The soft magnetic material is beneficial in that it contributes to the efficiency and performance of the inductor unit. The soft magnetic material also shields electromagnetic fields from heating undesired objects such as a press in cases where the molding tool is to be used in a press.

[0015] In yet an embodiment, the at least one coil is arranged in each of the electrically conductive parts of the inductor unit. This further contributes to the efficient heat generation in the molding tool by amplifying the current induced in the heating arrangement. It has a number of advantages, such as improvement of the heating pattern, and robustness to withstand mechanical loading when a press is used.

[0016] In another embodiment, the electrically conductive parts are arranged alternatingly in parallel with each other, separated by the soft magnetic parts of the inductor unit. This is advantageous in that the current can be further concentrated. Moreover, it provides the ability to separately activate versus deactivate certain areas of the inductor unit and thereby contribute to controlled heating of the molding tool. The electrically conductive parts are preferably insulated from each other as well as from the molding tool and other electrically conductive objects to avoid short circuit.

[0017] In a further embodiment, the inductor unit comprises a cooling channel provided in each electrically conductive part or in an adjacent element which is in thermal contact with the electrically conductive parts and / or the soft magnetic parts. By having cooling channels in each electrically conductive part, a controlled cooling of certain areas of the mold can be achieved.

[0018] In another embodiment, the system further comprises a thermal insulation arranged between the molding tool and the inductor unit to avoid undesired cooling power from being lost to the inductor unit. For lightweight molding tools, the inductor unit is preferably used to cool the molding tool through conduction. The thickness and properties of the thermal insulation may be selected as a trade-off between cool rate and power loss since there is a continuous conductive cooling effect on the molding tool.

[0019] In yet an embodiment, the molding tool further comprises a cooling channel in the electrically conductive element and / or the heat generation means. This provides efficient cooling directly in the molding tool. The design further allows for high processing temperatures of the molding tool, given the temperature rating of the thermal insulation.

[0020] In an embodiment, the system further comprises a cooling plate. Preferably, the cooling plate comprises at least one cooling channel. This is beneficial in that no intrusion needs to be made in the molding tool. In this case, the heat generation characteristics of the molding tool, i.e. the heat generating means and the electrically conductive element is rather transferred to the cooling plate.

[0021] In another embodiment, the heat generation means has a relative permeability > 10. The power generation and thereby the efficiency increases with increased permeability, and further on increases the difference in power generation in the electrically conductive element, thus reducing the edge effect.

[0022] In yet an embodiment, the heat generation means is a magnetic element and / or an element having a resistivity which is higher than the resistivity of the electrically conductive element. This causes a difference in power generation compared to in the electrically conductive element, thus reducing the edge effect. Further on, high electrical resistivity and high magnetic permeability of a metal object generally increases the efficiency of the system.

[0023] In a further embodiment, the resistivity of the heat generation means is at least two times higher than the resistivity of the electrically conductive element. Preferably, the resistivity of the heat generation means is at least three times higher, and more preferably at least four times higher than the resistivity of the electrically conductive element.

[0024] In another aspect, a system is provided, for uniform temperature generation in an article or part to be formed by molding. The system includes a molding tool, wherein said molding tool optionally comprises a heat generation means. Furthermore, the system includes an inductor unit comprising at least one coil wound such that a current flowing in each winding of the at least one coil is directed alternatingly in a positive and negative direction with respect to an adjacent winding of the at least one coil. The inductor unit is configured to induce a current in the molding tool. Moreover, the inductor unit further comprises a plurality of electrically conductive parts and a plurality of soft magnetic parts and where the at least one coil is arranged of the electrically conductive parts of the inductor unit.

[0025] In an embodiment, the electrically conductive parts are arranged alternatingly in parallel with each other, separated by the soft magnetic parts of the inductor unit.

[0026] In yet an embodiment, the inductor unit further comprises a cooling channel provided in each electrically conductive part or in an adjacent element which is in thermal contact with the electrically conductive parts and / or the soft magnetic parts.

[0027] In a further embodiment, the system further comprises a thermal insulation arranged between the molding tool and the inductor unit, preferably wherein the inductor unit is used to cool the molding tool through conduction.

[0028] In yet an embodiment, the electrically conductive element is made from extrusion.

[0029] The system(s) as described above are adaptable to different sizes of molding tools. At the same time, they exhibits a rather short cycle time as compared to conventional techniques used, thanks to the ingenious arrangement of electrically conductive elements and heat generation means in relation to the powerful inductor unit.

[0030] Furthermore, the system(s) can resist high temperatures. For instance via conductive cooling, fast, uniform and controlled cooling can be performed. This is done by controlling the induction power of the inductor unit.

[0031] An idea behind the invention is to provide a heating arrangement for heating of a molding tool, with a focus on flexible mold geometries, desired heat generation and edge effect control during heating. The overall purpose is to provide an arrangement that avoids hot spot creation in the article to be formed through heating, such as induction heating, and contributes to an even heating of the molding tool, independent of its size. If there is a uniform thickness, an even heating of the molding tool contributes to a uniform temperature generation in the article to be heated via the molding tool.

[0032] BRIEF DESCRIPTION OF THE DRAWINGS

[0033] By way of example, embodiments of the present invention will now be described with reference to the accompanying drawings, in which:

[0034] Fig. l is a block diagram of a system according to an embodiment,

[0035] Figs. 2-7 are cross-section views of the system according to different embodiments,

[0036] Figs 8-9 are zoomed in cross-section views of an inductor unit according to different embodiments,

[0037] Figs 10-12 are schematic illustrations of coil arrangements according to different embodiments,

[0038] Figs 13-15 are rear views of a molding tool having coating patterns according to different embodiments,

[0039] Fig. 16 is a perspective view of the system,

[0040] Fig. 17 is a perspective view of part of the system, where a cooling manifold has been hidden to show wires and cooling channels in the inductor unit, and Fig. 18 is a schematic illustration of the cooling channels in the inductor unit, including a manifold.

[0041] DETAILED DESCRIPTION OF EMBODIMENTS

[0042] With reference to Fig. 1, a system 1 for uniform temperature generation in an article to be formed by molding according to an aspect of the invention is shown. The system 1 may also be referred to as a heating arrangement system, or simply a heating arrangement. In particular, the system 1 includes a molding tool 10, and an inductor unit 20 provided for inductively heating the molding tool 10. The molding tool 10 and the inductor unit 20 are preferably manufactured separately. A processing means 50 may be included in the system for actuating the inductor unit 20, such as by applying an alternating or direct current to the inductor unit 20. In other words, the inductor unit 20 may be in operative communication with the processing means 50. Optionally, there may be more than one processing means 50 in the system 1. Alternatively, more than one inductor unit may be controlled by one or a group of processing means. The molding tool 10 may also be in operative communication with the processing means 50, for instance with the purpose of measuring temperature or other properties or for cooling the molding tool 10 after a molding cycle has been performed. Alternatively, the processing means 50 may be external to the system 1. For instance, the processing means 50 may be a frequency converter or the like. The processing means may further include a chiller, signal transmitters etc.

[0043] An overall purpose with the system 1 is to efficiently form articles in the molding tool 10, where temperature distribution is uniform during forming so that the article is homogenously heated. The articles to be formed by the molding tool 10 are indirectly heated by the inductor unit 20. In particular, the molding tool 10 is heated by the inductor unit 20, whereby the material, which is in contact with the molding tool 10 is heated indirectly by the inductor unit 20. For instance, the material to be formed may be a composite material, such as a fiber composite material, carbon fiber thermoplastic (woven or non-woven and / or semipreg or prepreg formats) or thermoplastic composite materials such as PEEK, PEKK and PAEK, preferably fiber composite material. The material to be formed may also be carbon fiber laminates, blanks, or organosheets. Optionally, the inductor unit 20 includes a support structure (not shown), which keeps all the elements of the inductor unit 20 in place at the same time contributes to a robustness of the system 1.

[0044] The molding tool 10 may have different thicknesses throughout the tool to produce articles or parts with complex shapes. In order to obtain a uniform heat generation across the entire molding surface of the molding tool 10, i.e. the surface of the molding tool 10 facing the material of the article or part to be produced, the inductor unit 20 may be adapted to locally increase or decrease the power density to take into account differences in the thickness of the molding tool 10. An increased power density results in more heat generation, whereas decreased power density results in less heat generation.

[0045] As illustrated schematically in Figs 2-7, the molding tool 10 includes an electrically conductive element 11, hereby referred to as electrical conductor 11, and at least one heat generation means 12, hereby referred to as a heat generator 12. Preferably, the electrically conductive element 11 and the heat generation means 12 are assembled from separate parts.

[0046] The electrical conductor 11 is preferably a non-magnetic material made of e.g. aluminium, copper, tungsten or a material coated or plated with such a metal. For instance, as shown in Fig. 2, the electrical conductor 11 may be arranged on top of the heat generator 12 in the molding tool 10, opposite to the inductor unit 20. Fig. 2A schematically illustrates the electrical conductor 11 as a layer having substantially the same thickness throughout a molding tool 10 body. Fig. 2B illustrates the electrical conductor 11 as a layer having different thickness at the edges with respect to a center portion of the molding tool 10. The black areas at a bottom of the heat generator 12 represent locally increased power density in the molding tool as a result of locally amplified induced current in the heating arrangement by the inductor unit 20, to take into account the difference in thickness in the molding tool 10 and still achieve a uniform heating profile of the entire surface of the molding tool 10.

[0047] Alternatively, as shown in Fig. 3, the electrical conductor 11 may be provided as an insert sandwiched between two heat generators 12. Another option, shown in Fig. 4, is that the electrical conductor 11 is plated onto the heat generator 12 according to a predetermined pattern that depends on the desired shape of the molding tool 10, such as the thickness of the molding tool 10. It may be that the electrical conductor 11 is coated or plated on the heat generation means 12. However, it may also be that the heat generation means is coated or plated on the electrical conductor 11.

[0048] On the other hand, the heat generator 12 may be described as a magnetic element 12. Alternatively, or additionally, the heat generator 12 may be an element 12 having a resistivity that is higher than the resistivity of the electrical conductor 11. The element having a resistivity that is higher than the resistivity of the electrical conductor

[0049] 11 will hereinafter be referred to as a highly resistive element 12. Moreover, the heat generator 12 may be made of a combination of the magnetic material and the highly resistive element 12. For example, the highly resistive element 12 may be either magnetic or non-magnetic, such as ferritic steel versus austenitic steel. In any case, the heat generator 12 has a resistivity that is at least two times higher than the one of the electrical conductor 11, preferably three times higher, and more preferably four times higher. Moreover, the relative permeability of the heat generator 12 is preferably above 10.

[0050] One property differentiating the generator 12 from the electrically conductor 11 is the amount of heat generation obtained from a high frequency current. Within reasonable limits, the heat generation increases with increasing resistivity as well as with increased magnetic permeability. Thus, the product of the magnetic permeability and the electrical resistivity should be higher in the generator than in the electrical conductor.

[0051] As an example, the heat generator 12 may be in the form of a steel or nickel plate. Alternatively, when the electrical conductor 11 is integrated in the heat generator

[0052] 12 in the form of a coating or insert, the heat generator 12 may have another shape and be made of e.g. steel, nickel or titanium. The heat generator 12 is heated by current inducing means, which is the induction unit 20. Preferably, the heat generator 12 of the molding tool 10 is in indirect contact with the inductor unit 20, for instance via a thermal insulation. In particular, the heat generator 12 is heated by induced high- frequency currents generated by the inductor unit 20. The heat is subsequently transferred to the electrical conductor 11 and short circuited therein to provide uniform heating throughout the molding tool 10.

[0053] According to a non-limiting example, the molding tool 10 may be built up in layers by different materials, such as a first layer of steel, a second layer of copper and a third layer of steel. In this configuration, the first and second layers act as the main features for heating the mold, whereas the third layer acts as a molding surface that is to be in contact with the material to be formed in the molding tool 10. In another nonlimiting example, the first layer is aluminium, the second layer is highly resistive nonmagnetic titanium or steel and the third layer is highly resistive magnetic ferritic steel.

[0054] For instance, the molding tool 10 may be made of an electrical conductor 11 such as aluminium, which is coated by a magnetic element 12 and / or highly resistive element 12, such as for instance steel or nickel. The coating may be made via electro plating, physical vapor deposition (PVD), chemical vapor deposition (CVD), cold spraying, or thermal spraying such as high velocity oxygen fuel (HVOF) spraying.

[0055] A combination of a magnetic and / or high resisitivty material and nonmagnetic, high conductivity material is beneficial for the efficiency of the molding tool 10. As a non-limiting example, the magnetic and / or high resisitivty material may be represented by a steel sheet whereas the non-magnetic, high conductivity material is represented by an aluminium mold. Alternatively, the magnetic and / or high resisitivty material may be represented by a steel / nickel mold having the high conductivity material as a copper plating.

[0056] The molding tools 10 according to what has been described above may be used with double sided tooling in a press, for example in compression molding or resin transfer molding. They may alternatively be used as a single sided tooling solution for vacuum molding, bladder molding or autoclave processing. The solution has advantages for processing of for example thermoplastic as well as thermoset composite parts.

[0057] Figs 2-9 also illustrate an inductor unit 20 schematically. The inductor unit 20 includes at least one coil 21 arranged in a way that the current flowing in each coil is directed alternatingly in a positive and negative direction relative to each other. In particular, the at least one coil 21 is wound such that a current flowing in each winding of the at least one coil 21 is directed alternatingly in a positive and negative direction with respect to an adjacent winding of the at least one coil 21. The different current directions are illustrated by dots and crosses in Figs 2-9. In Figs 2-4 and 8-9, only one wire 21 is shown, whereas in Figs 5-7, three wires 21 are shown. Optionally, there may be two wires 21 in the inductor unit 20, three wires 21 or more than three wires 21.

[0058] With reference to Fig. 10, a coil 21 is folded in a way that resembles a serpentine road which curves back and forth on itself. The coil 21 is arranged in a meander-like pattern in the inductor unit, such that an alternating electric current flowing through the coil 21 is to its major extent directed in, altematingly, opposite directions over the outer surface of the molding tool 10, following the meander-like pattern. The direction of the current is represented by arrows. Another example of coils 21 folded in a meander-like pattern is shown in Fig. 11, where two coils follow the same pattern, offset from each other. The inductor design may also feature a more two- dimensional (2D) pattern, shown in Fig. 12, showing yet another example of a meanderlike pattern of a coil 21. Also here, an alternating electric current flowing through the coil 21 is to its major extent directed in, altematingly, opposite directions over the outer surface of the mold, following the meander-like pattern. This is particularly advantageous when the heating in the different directions may be performed independently, enabling compensation of for example for higher cooling along the edges. The inductor unit 20 may include coil figurations such as those illustrated in Figs 10-12.

[0059] A purpose of the inductor unit 20, and particularly its coil(s) 21, is to induce a current in the molding tool 10, and in particular in the heat generation means 12 of the molding tool 10. The at least one coil 21 is preferably in operative communication with the at least one processing means 50 described in relation to Fig. 1 above. The coil(s) 21 of the inductor unit 20 include(s) wires that are electrically insulated from the molding tool 10, and from the heat generator 12 in particular. Preferably, the wires are litz wires. However, the wires may also be copper tubes or similar. Moreover, the coil(s) 21 is / are preferably embedded in an embedding material 22. Advantageously, the embedding material 22 is an electrically insulated material such as a fiber composite, a polymer, or a cement based or ceramic material. Preferably, the embedding material 22 has soft magnetic properties. Currents induced in the heat generator 12 by the inductor unit 20 are transferred through conduction into the electrical conductor 11 and concentrated therein. Instead of creating unwanted edge effects, causing undesired hot spots, the current is going in the electrical conductor 11 with only minor heat generation therein, thus the molding tool 10 is heated evenly. The conduction of currents in the electrical conductor 11 may also be referred to as a bypassing of the current.

[0060] The electrical conductor 11 of the molding tool 10 is configured to electrically bypass the current induced in the molding tool 10 by the inductor unit 20. The bypassing of the current occurs at an interface between the electrical conductor 11 and the heat generator 12. The interface may also be described as a boundary between the electrical conductor 11 and the heat generator 12, i.e. where the electrical conductor 11 and the heat generator 12 meet or intersect each other.

[0061] Preferably, the system 1 includes a thermal insulation 30 which is arranged between the molding tool 10 and the inductor unit 20, see Figs 2-7. Moreover, the molding tool 10 may further include a cooling device. This cooling device may be arranged either in the inductor unit 20 or in the molding tool 10. For instance, the cooling device may be integrated in the molding tool 10 or in a separate cooling plate 40 arranged below the molding tool 10. Cooling may be performed through gas or liquid media or a combination through cooling channels in the electrical conductor 11 and / or in the heat generator 12. Alternatively, the molding tool 10 may be moved to a separate cooling station after the molding process has been performed. In an another example, relating to a case where the molding tool 10 is arranged in a press, the whole press may be filled with water so that the molding tool 10 is temporarily sunk into a water bath for cooling.

[0062] As mentioned, a cooling channel may be provided in the electrical conductor 11 and / or the heat generator 12 (not shown) of the molding tool 10. In some embodiments, the cooling may also be provided in the system 1 in the form of a cooling plate 40 or cooling channels in the electrically conductive parts (see Figs 5-8). The cooling plate 40 may be provided with cooling channels 41 (see Figs 5-7 and 9).

[0063] Referring back to Fig. 2, an example of a system 1 having a molding tool 10 and an inductor unit 20 is shown, where the electrical conductor 11 is arranged on top of the heat generator 12. Inside the inductor unit 20 lies a coil 21 wound back and forth so that the current flowing therein is directed altematingly in opposite directions from the adjacent winding of the coil 21. Furthermore, the coil 21 is embedded in embedding material 22. Between the heat generator 12 of the molding tool 10 and the inductor unit 20, a thermal insulation 30 and a cooling plate 40 are facultatively arranged. This is indicated by the dotted lines. The molding tool 10 may optionally be provided with cooling channels (not shown). Alternatively, the molding tool 10 is cooled with the separate cooling plate 40.

[0064] The inductor unit 20 is similar in Figs 3-4 as in Fig. 2. The difference between the systems shown in Figs 2 as compared to Figs 3 and 4, respectively, lies in the configuration of the molding tool 10. In Fig. 3, the molding tool 10 is built up by a number of parts, including a heat generator(s) 12, and an electrical conductor 11. In particular, in Fig. 3, the electrical conductor 11 is sandwiched between the two heat generators 12. In Fig. 4, a heat generator 12 makes up the major part of the molding tool 10, where the electrical conductor 11 is coated, plated, or assembled on the sides of the heat generator 12.

[0065] Figs 5-7 resemble Figs 2-4 in that the molding tools 10 are illustrated similarly. This means that the molding tool 10 of Fig. 5 corresponds to the molding tool 10 of Fig. 2, the molding tool 10 of Fig. 6 corresponds to the molding tool 10 of Fig. 3, and the molding tool 10 of Fig. 7 corresponds to the molding tool 10 of Fig. 4. However, the inductor units 20 of Figs 5-7 differ slightly from the inductor units 20 shown in Figs 2- 4. In particular, the inductor unit 20 of the embodiments illustrated in Figs 5-7 is provided in a way that allows for conductive cooling of the molding tool 10 without moving it away from the inductor unit 20. It can also withstand higher temperatures since the coil and other temperature sensitive materials are easier to cool.

[0066] Referring to Figs. 5-7, the inductor unit 20 includes a plurality of electrically conductive parts 23 and a plurality of soft magnetic parts 24. The electrically conductive parts 23 are arranged altematingly in parallel with each other, separated by the soft magnetic parts 24. In each of the electrically conductive parts 23, three wires 21 are arranged, which are wound back and forth so that the current flowing in each winding 21 is directed altematingly in opposite directions from the adjacent winding of the coil 21, in a neighboring electrically conductive parts 23. The coil windings in each electrically conductive part 23 have their currents pointing in the same direction. The wires may be connected in parallel or in series or in some cases belong to separate coils. Two different coils may, in certain configurations, be placed in the same conductive part 23, beneficial to compensate for example for thickness variations of the molding tool 10. This is to enhance the heat generation by the inductor unit 20. There may be only one coil, two coils, or more than three coils in each electrically conductive part 23.

[0067] Explained differently, the inductor unit 20 shown in Figs 5-7 is built up by several wires 21 wound around an electrically conductive part 23, such as copper or aluminium. The electrically conductive parts 23 may be referred to as extenders, i.e. longitudinally extending elements of which only a cross-section is shown in the drawings. The extenders 23 face the molding tool 10, and in particular the heat generator 12, on all other sides surrounded by the soft magnetic material 24. This way, induced currents are forced to travel on the side of the extenders 23 facing the molding tool 10 / heat generator 12 to heat it up.

[0068] Similarly to Figs 2-4, a thermal insulation 30 is facultatively arranged between the heat generator 12 of the molding tool 10 and the inductor unit 20 in the embodiments illustrated in Figs 5-7. The thermal insulation 30 between the extenders 23 and the soft magnetic element 24 and the molding tool 10 / heat generator 12 is preferably used to prevent short circuits within the inductor unit 20 and create a continuous conductive cooling effect on the molding tool 10 as long as the temperature of the molding tool 10 exceeds that of the extenders 23.

[0069] Cooling channels 26 may be provided in each extender 23, see also Fig. 8. The cooling channels 26 may for instance provide forced liquid or gas cooling. Alternatively, as in Fig. 9, a cooling plate 40 may be arranged on the side of the inductor unit 20 opposite to the molding tool 10, where preferably cooling channels 41 are provided for conductive cooling. The cooling channels and the cooling plate may also be referred to as a cooler.

[0070] Optionally, the cooler may be provided in an adjacent element which is in thermal contact with the electrical conductor (not shown). The cooler may be a separate element or, if the molding tool is used in a press, the cooler may be part of the press platen, preferably with cooling channels for liquid or gas cooling.

[0071] Since the magnetic fields from an adjacent winding of opposite current direction may influence the heat generation negatively, this means that the windings close to the edge typically heat the workpiece with a higher power density then the rest of the windings, where there are opposite directed fields on each side. To avoid this effect, the winding close to an edge may beneficially be designed somewhat differently then the rest. Examples of solutions that may be employed is to increase the distance to between the wire and the molding tool (applies to embodiments shown in Fig 2-4) or electrically conductive parts and the molding tool (applies to embodiments shown in Fig 5-7), alternatively to locally change the geometry such as the width of the electrically conductive parts or the geometry or properties of soft magnetic elements. In Figs 8 and 9, the outer soft magnetic elements 24 have been shortened and replaced by a different material, here represented as white boxes at the top comers of the drawings. The added element may be a part of the electrically conductive element, a separate, electrically conductive element or a non-magnetic, non-electrically conductive element such as alumina or other ceramic material or glass fiber composite or other composite material.

[0072] Preferably, the molding tool 10 has the same or a relatively smaller dimension than the inductor unit 20. However, the inductor unit 20 may be provided with a perimeter coil to handle molding tools 10 that are dimensionally bigger than the inductor unit 20. Also, even if the molding tool 10 is bigger than the inductor unit 20, a coating pattern may be used to compensate for the dimensional discrepancies between the molding tool 10 and the inductor unit 20 of the system 1.

[0073] Moreover, in cases where the molding tool 10 has an uneven thickness, the concentration of heat in certain areas of the tool 10 may need fine tuning, which can be achieved by coating the electrical conductor 11 with a certain coating pattern. This concept will now be described in relation to Figs 13-15. The coating can be performed through plating, thermal spraying, laser cladding, CVD, PVD, adhesion bonding, as well as high energy rate methods such as fusion through electromagnetic or explosion processes. In cases where the component to be produced is contained in a closed mold, and in particular when the part to be formed in the molding tool 10 features three dimensional (3D) shapes, the molding tools 10 may have different thicknesses and / or thermal load in different regions of the mold. To obtain a uniform temperature in such molding tools, a non-uniform heat generation is beneficial. This can be achieved for example by having different coils 21 that can control the power generation of each zone independently from each other. Another option, which may be combined with the independent control of coils, is to control the heat generation by tailoring the molding tool 10 material and / or coating at different parts of the molding tool 10, see example in Fig. 2B.

[0074] In an embodiment (not shown), the inductor unit 20 may have a 3D shaped profile, allowing thin molding tools 10 to produce parts that are not flat. One particularly well-suited application is curved parts, commonly found in the aviation industry.

[0075] Figs 13-15 show examples of patterns that may be used to control heat generation in different areas of a molding tool 10. Black areas represent a material with high electrical resistivity, and / or high magnetic permeability, i.e. a highly resistive element 12. White areas represent areas with low electrical resistivity and / or low magnetic permeability relative to the material in the black marked areas, i.e. an electrical conductor 11. Depending on the inductor unit design and the sensitivity to the position and / or angle of rotation of the molding tool 10 relative to the inductor unit 20, the pattern may be adapted. Areas with a large concentration / density of material with high electrical resistivity and / or high magnetic permeability, i.e. black areas in Figs 13- 15, results in a relatively higher concentration of power generation as compared to an area that has not been coated, i.e. the white areas in Figs 13-15.

[0076] In a preferred embodiment shown in Fig. 13, the pattern represents a two dimensional (2D) shape, where a rotation of the molding tool 10 relative to the inductor unit 20 only has a minor effect on the heating pattern. This is particularly valid when the pattern features smaller areas of highly electrically conductive 11 and / or low magnetic permeable material distributed like islands on an ocean of high resistivity and / or high magnetic permeability material 12. The distribution of material properties may however be the opposite, even though the size of the high resistivity 12 and / or high magnetic permeability islands preferably are large relatively to the width of the coil wire to work well, since the current otherwise flows predominantly in the low-loss areas, i.e. the areas of the electrical conductor 11, see Fig. 14.

[0077] Referring to Fig. 15, as an alternative to a pattern of two different materials visible in the surface of the heated area of the molding tool 10, different thickness of the coating in different areas may provide the same functionality.

[0078] Yet another option is to use a larger number of materials for the coating, with a range of different properties, or a material that can be locally tailored, for example through doping, heat treatment bridging, or a mix of two material with different properties, mixed in different fractions at each location.

[0079] As mentioned briefly, the inductor unit 20 may have a number of coils 21, which enables independent heating zones, with or without temperature feedback. This enables compensation of varying molding tool 10 thickness, varying thermal losses as well as provides possibility to have different temperatures in different areas of the molding tool 10.

[0080] A method of producing an article or part to be formed by inductive molding in any of the systems 1 as described above may be performed as follows. First, a molding tool 10 and an inductor unit 20 are provided. Next, the inductor unit 20 is arranged on a back side of the molding tool 10, facing away from a molding surface on which the article or part is to be formed. The processing means 50 may be actuated to provide a current flow through the coil(s) 21 of the inductor unit 20. Subsequently, the currents are electromagnetically induced in the highly resistive or magnetic element 12 of the molding tool 10. As a result, the electrical conductor 11 is inductively heated. Thanks to the electrical conductor’s 11 ability of bypassing the current, the current is evenly spread out over the entire body of the electrical conductor 11 and thus provides a uniform heating of the molding tool surface which is in contact with the material of the article or part to be produced.

[0081] As mentioned, the molding tool 10 may be arranged in a press, autoclave, or vacuum bagged. After molding has been performed, an optional cooling step may be performed, using a cooling plate or any of the integrated features described above in the form of cooling channels in the molding tool 10 and / or the inductor unit 20.

[0082] All systems 1 including the molding tool 10 and the induction unit 20 as have been described above contribute to the mitigation of hot spots from boundary effects which are typically associated with induction heating, with the purpose of providing a uniform heating of the molding tool 10 and the article or part to be produced therein. The technique involves electrically bypassing the current induced by the inductor unit 20 in the heat generator 12 of the molding tool 10 by means of the electrical conductor 11. The bypassing of the current occurs at the interface, also referred to as boundary, between the electrical conductor 11 and the heat generator 12 in the molding tool 10, whether the boundary represents an entire layer, a spot, a line, a specific pattern or the like. It is the electrical conductor 11 that electrically bypasses the current, whether the electrical conductor 11 represents a major part of the tool 10, parts of the tool 10 (such as a coating or plating) or an intermediate layer in the tool 10 (such as an insert between two highly resistive element). This way, edge effects can be counteracted.

[0083] In a further aspect of the invention, the system 1 includes a molding tool 10, wherein said molding tool 10 optionally comprises a heat generation means 12. In such an example, the molding tool 10 does not comprise an electrically conductive element 11.

[0084] In an embodiment, the system 1 may further comprise an inductor unit 20 comprising at least one coil 21, wherein said coil 21 may be wound in a manner such that a current flowing in each winding of the at least one coil 21 is directed alternatingly in a positive and negative direction with respect to an adjacent winding of the at least one coil 21, wherein the inductor unit 20 is configured to induce a current in the molding tool 10. It is to be understood that adjacent may refer to any position as long as it is in proximity. The inductor unit 20 further comprises a plurality of electrically conductive parts 23, as defined previously, and a plurality of soft magnetic parts 24, as defined previously, and where the at least one coil 21 may be arranged in each of the electrically conductive parts 23 of the inductor unit 20. In an embodiment, the electrically conductive parts 23 may be arranged alternatingly in parallel with each other, separated by the soft magnetic parts 24 of the inductor unit 20.

[0085] In yet an embodiment, the inductor unit 20 may further comprise a cooling channel 26 provided in each electrically conductive part 23 or in an adjacent element which is in thermal contact with the electrically conductive parts 23 and / or the soft magnetic parts 24.

[0086] In a further embodiment, the system 1 may further comprise a thermal insulation 30 arranged between the molding tool 10 and the inductor unit 20, preferably wherein the inductor unit 20 may be used to cool the molding tool 10 through conduction.

[0087] In a yet further embodiment, the electrically conductive element may be made from extrusion, wherein extrusion is as understood by the skilled person in the technical field.

[0088] The inductor unit may have features for alignment of the molding tools and / or holes or attachment to clamp the molding tool, for example inside of a press. By clamping the tool to the inductor or press unit, then the opening of the mold is simplified.

[0089] The inductor unit may further be equipped with features which helps to load and unload the mold. Examples of features include spring loaded or pneumatic actuated rollers, cylindrical or ball type. Another solution to substantially reduce the friction between the mold and inductor unit is to use small holes for pressurized air to lift the molding tool from the surface.

[0090] Despite the aim is generally to create a uniform temperature, there are cases when a non-uniform temperature pattern is preferred, for example to control the resin flow during resin transfer molding or to control the melting front of thermoplastic composite processing to facilitate evacuation of gas. In one embodiment, the inductor unit is equipped with vacuum seals or completely contained inside of a vacuum chamber. Vacuum enhances the quality of a composite part by reducing the void content or may allow a lower consolidation pressure to be used with maintained part quality. The inductor unit and molding tool may also be contained inside of a pressurized chamber, often referred to as an autoclave. This is a common manufacturing method of composite parts, where large time and energy savings can be made by directly heating the molding tool and thereby be able to run the autoclave as a pressure vessel (without heating the air) rather that to use it as a pressure oven. Typically a bag is covering the part in which near vacuum pressure is applied while the surrounding air creates consolidation pressure. The bagging material may for example be a polymer or a metal. Support heating or thermal insulation of the area of the part being furthest away from the molding tool may be beneficial to reduce the temperature gradient through the material. The pressure may alternatively come from a pressurized bladder.

[0091] The embodiments of the inductor unit containing the electrically conductive parts and soft magnetic elements are preferably coated on the surface for electrical insulation and good wear resistance. This can be made for example by a polymer or ceramic coating, including enamel.

[0092] Cooling channels within the electrically conductive parts are preferably cooled with a cooling media coming alternatingly from each side of the tool, this is particularly beneficial for large tools to avoid a thermal gradient along the length or width of the molding tool due to increased temperature of the cooling media. The cooling channels may be connected to a manifold for uniform distribution of the cooling media.

[0093] The thermal insulation 30 may be designed with a sophisticated pattern of cutouts or other design features, including material with varying thermal properties along the insulation unit to tailor it for a desired cooling behavior. In this way, yet one more opportunity to control the temperature heating and cooling pattern is achieved.

[0094] A number of coils may be installed to be able to control the heating pattern accurately, one particularly interesting separate coil may be installed around the perimeter of the molding tool to be able to compensate for effects related to increased cooling power along the edge, but also larger thermal mass due to the design of the molding tool, typically with a surrounding wall around a cavity, alternatively some kind of frame to contain the material of the part being produced.

[0095] Another interesting opportunity with multi-material coatings refers to more advanced temperature control. For example the generator material may be selected to have a certain Curie temperature where it becomes non-magnetic. With a relatively thin coating, typically 10-1000 micrometers, the heating will more or less stopped when reaching that temperature since the skin depth will increase, and the properties of the electrical conductor will be dominating. Yet another option is to have a first high resistivity non-magnetic coating on the electrically conductive element, then a magnetic coating outermost. If the outermost layer is exposed to a magnetic field, from for example a direct current, then it may be forced to saturate, i.e. the magnetic properties are changing so that the heat generation is changed, typically reduced. This may be particularly good to be able to heat with a higher power density during ramp-up where the molding tool is thicker, and then change the power distribution when reaching a dwell temperature. With a clever coating pattern as illustrated in Figs 13-15 of materials with different electrical and or magnetic properties, then a desired temperature patterns can be ensured at all time.

[0096] The system(s) according to the present invention comprise a temperaturecycles plate that quickly heats up to over 450 °C, with fast, controllable cooling for efficient composite processing, featuring exceptional temperature uniformity and low thermal mass. Heat rates exceeding 600 °C / min and cool rate of 200 °C / min for precise, efficient thermal cycling.

[0097] The invention’s scalability enables production of parts from credit card-sized to large components like wing skins, all as single pieces with modest power requirements — substantially lower than traditional tools. This efficiency comes from keeping most of the tool cold and heating only a thin facesheet, potentially made from low-expansion alloy, free to slide on an insulation layer covering the support structure, which reduces CTE mismatch issues common in other solutions. A frame prevents squeeze-out, vacuum integration reduces porosity, and a cooled perimeter enables easy sealing.

[0098] Some of the key benefits of the present invention includes achieving up to 95% energy saving and reduced cycle times by 90% compared to systems currently in the technical field. Moreover, the system(s) give complete control of cooling cycles, high temperature range (at least 450 °C) and scalability from R&D to full production.

Claims

CLAIMS1. A system for uniform temperature generation in an article or part to be formed by molding, the system (1) comprising: a molding tool (10) comprising an electrically conductive element (11) and a heat generation means (12); and an inductor unit (20) comprising at least one coil (21) wound such that a current flowing in each winding of the at least one coil (21) is directed altematingly in a positive and negative direction with respect to an adjacent winding of the at least one coil (21), wherein the inductor unit (20) is configured to induce a current in the molding tool (10); wherein the electrically conductive element (11) is configured to electrically bypass current induced in the molding tool (10) by the inductor unit (20), at an interface between the electrically conductive element (11) and the heat generation means (12).

2. The system according to claim 1, wherein the electrically conductive element (11) is coated or plated on the heat generation means (12), or vice versa.

3. The system according to claim 1 or 2, wherein the electrically conductive element (11) and the heat generation means (12) are assembled from separate parts.

4. The system according to any one of the preceding claims, wherein the at least one coil (21) of the inductor unit (20) comprises wires that are electrically insulated from the molding tool (10), preferably wherein the wires are litz wires.

5. The system according to any one of the preceding claims, wherein the at least one coil (21) is embedded in an embedding material (22), preferably wherein the embedding material (22) is an electrically insulated material.

6. The system according to any one of the preceding claims, wherein the inductor unit (20) further comprises a plurality of electrically conductive parts (23) and a plurality of soft magnetic parts (24).

7. The system according to claim 6, wherein the at least one coil (21) is arranged in each of the electrically conductive parts (23) of the inductor unit (20).

8. The system according to claim 6 or 7, wherein the electrically conductive parts (23) are arranged alternatingly in parallel with each other, separated by the soft magnetic parts (24) of the inductor unit (20).

9. The system according to any one of claims 6-8, wherein the inductor unit (20) further comprises a cooling channel (26) provided in each electrically conductive part (23) or in an adjacent element which is in thermal contact with the electrically conductive parts (23) and / or the soft magnetic parts (24).

10. The system according to any one of the preceding claims, wherein the system (1) further comprises a thermal insulation (30) arranged between the molding tool (10) and the inductor unit (20), preferably wherein the inductor unit (20) is used to cool the molding tool (10) through conduction.

11. The system according to any one of the preceding claims, wherein the molding tool (10) further comprises a cooling channel in the electrically conductive element (11) and / or the heat generation means (12).

12. The system according to any one of the preceding claims, wherein the system (1) further comprises a cooling plate (40), preferably wherein the cooling plate (40) comprises at least one cooling channel (41).

13. The system according to any one of the preceding claims, wherein the heat generation means (12) has a relative permeability > 10.

14. The system according to any one of the preceding claims, wherein the heat generation means (12) is a magnetic element and / or an element having a resistivity which is higher than the resistivity of the electrically conductive element (11).

15. The system according to claim 14, wherein the resistivity of the heat generation means (12) is at least two times higher than the resistivity of the electrically conductive element (11), preferably at least three times higher, more preferably at least four times higher.

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