Patent Description:
Over the past years, there has been an increasing interest in the use of lightweight materials in for instance the automotive and aerospace industry, where the main goal has been to reduce carbon emissions during transportation. For instance, it has been increasingly common that the vehicle or aircraft components are made of fiber composites.

When producing a fiber composite part, such as a car door or an aircraft component, it is important to have a controlled heating and ensure an even heat distribution throughout relevant areas of the part. There are several examples of molding tools for composite manufacturing in the prior art which all have different drawbacks. For instance, they suffer from large thermal mass to be heated up and cooled down, which means long cycle times and high energy consumption. Another common problem is uneven heating, which affects part performance and yield negatively. Large physical space demand and high capex investments are other common challenges with existing solutions as well as limitations in size or temperature.

Common heat sources are ovens, and heated autoclaves, heat cartridges, resistance wires, IR-lamps, all with their pros and cons. Environmental aspects are another important topic with certain energy sources, such as hot oil and high pressurized steam technologies.

Examples of composite production processes which typically uses the heat sources described and which suffer from the above-mentioned drawbacks are resin transfer molding and compression molding, normally used inside some type of press to keep two mold halves together. Other examples are vacuum infusion, vacuum bagging, and autoclave processing, where one of the mold halves is usually replaced by a flexible membrane or bag, or where the mold halves are pushed together by a pressure difference between the inside and the outside of the mold. <CIT>, <CIT> and <CIT> show known molding tools using induction heating means.

Hence, there is a need for improved molding tools for manufacturing of composite parts, which allow for short cycle times, are energy efficient and result in a high quality and yield, to enable cost efficient volume production. Further, the molding tools also need to be robust, cost efficient and easy to manufacture, with a long service life.

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.

According to a first aspect, a molding tool for producing a composite part using induction heating is provided. The molding tool comprises a mold having a contact surface adapted to be in contact with a material to be transformed into a composite part, and an outer surface; at least one coil or at least one wire of a coil arranged on the outer surface of the mold; and at least one clamping means having a first end, a second end and an intermediate section extending between the first end and the second end, wherein at least one of the first end and second end is attached to the outer surface of the mold using welding, brazing or soldering, so as to at least partly fixate the at least one coil to the outer surface of the mold; wherein the intermediate section at least partially encloses the at least one wire or coil to hold said at least one wire or coil in place on the outer surface of the mold; and wherein the at least one wire or coil are electrically insulated from the mold and in operative communication with at least one processing means.

According to a second aspect, a method of manufacturing a molding tool according to the above is provided. The method includes providing a mold, having a contact surface adapted to be in contact with a material to be transformed into a composite part, and an outer surface; providing at least one coil or at least one wire of a coil and arranging the same on the outer surface of the mold; providing at least one clamping means having a first end, a second end, and an intermediate section extending between the first end and the second end; attaching at least one of the first end and second end of the at least one clamping means to the outer surface of the mold using welding, brazing or soldering, so as to at least partly fixate the at least one coil to the outer surface of the mold; whereby the intermediate section at least partially encloses the at least one wire or at least one coil to hold said at least one wire or coil in place on the outer surface of the mold; and wherein the at least one wire or coil are electrically insulated from the mold and in operative communication with at least one processing means.

According to a third aspect, a method of using a tool for producing a composite part is provided. The method includes providing a molding tool having at least one clamping means according to the above; placing a fiber and plastic material on the contact surface of the mold; closing the mold; applying a consolidation pressure on the material to be processed; and inductively heating the mold containing the material according to a predetermined time-temperature profile to consolidate and/or cure the material to produce the composite part.

According to a fourth aspect, another method of using a tool for producing a composite part provided. The method includes providing a molding tool having at least one clamping means according to the above; placing a fiber material to be processed on the contact surface of the mold; closing the mold; applying vacuum pressure and infusing the fiber material with a plastic material, the plastic material thereby forming part of the material to be processed; and inductively heating the mold containing the fiber and plastic material according to a predetermined time-temperature profile to produce a composite part.

In general, an advantage of using the clamping means is to be able to speed up and automate the manufacturing process of the induction heated molding tools compared to gluing the coils to the outer surface of the mold, and to be able to reach temperatures where glue does not work, e.g. for thermoplastic composites with PA, PC or PET matrix or high-end matrices such as PEEK, PEI and PPS which are widely used in the aerospace industry. In other words, the clamping means should withstand high-temperature applications.

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

Molding tools are often used to produce composite parts of different shapes. Typical parts to be produced are automotive vehicle parts, sports equipment, drones or aircraft parts as well as wind energy components, such as for instance body panels and structural components, e.g. car doors, aircraft and wind mill wings etc.. Tools applicable within the inventive concept disclosed herein are shell tools and solid tools, with single or multiple cavities. The inventive concept is directed mainly towards inductively heated tools for the manufacturing of composite articles.

Embodiments of the invention will now be described with reference to the accompanying drawings. The invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. The terminology used in the detailed description of the particular embodiments illustrated in the accompanying drawings is not intended to be limiting of the invention.

Before turning into a detailed description on the molding tool and the novel and inventive way of attaching coils to the mold <NUM>, a molding tool in relation to a material will be briefly described with reference to <FIG>.

As illustrated in <FIG>, the mold <NUM>, as seen from a cross-section view, has a body with a contact surface <NUM> and an outer surface <NUM>. The mold body may be divided into several layers, which enables the transfer of heat from the outer surface <NUM> to the contact surface <NUM>. The contact surface <NUM> is an inner region of the mold <NUM> configured to be facing a material <NUM> which is to be transformed into a composite part A (as illustrated in <FIG>) during a molding process. The mold <NUM> may also be seen as a body having a cavity which is dimensioned and shaped into the desired shape of the part A to be produced. It is the contact surface <NUM> of the mold <NUM> which is configured to receive the material <NUM>. For instance, a part A to be produced in the mold <NUM> of the molding tool is a car door, or any other composite part. The mold <NUM> may contain more than one cavity and thereby it may produce several components in a single production cycle, still referred to as a material <NUM> being transformed into a composite part A.

Hereafter, the contact surface <NUM> will be called the front side of the mold and the outer surface <NUM> will be called the back side of the mold <NUM>. A coil assembly <NUM> is to be attached to the back side <NUM> of the mold, as soon will be further described. The heating of the molding tool is induced by the coil assembly <NUM> arranged on the back side <NUM> of the mold <NUM>.

<FIG> shows an embodiment where a coil assembly <NUM> is attached to a mold <NUM> of the molding tool. The attachment of the coil assembly <NUM>, which may include for instance a combination of main coils and perimeter coils, is illustrated by the dashed lines in <FIG>. The coils are attached to the back side <NUM> of the mold via clamping means. Preferably, at least one part/end of the clamping means is attached to the back side of the mold. For instance, the clamping means may be attached by welding, brazing or soldering. Optionally, the clamping means may be seen as a fixturing element onto which the at least one coil may be clipped or clamped in, see for instance <FIG> and <FIG>. Details on the clamping means is shown and described in relation to <FIG>.

Typically, the mold <NUM> is made at least partially of a material chosen from a group consisting of carbon fiber composite materials or metals. The material is preferably a material with significant electrical conductivity to be able to be heated by induction, for example more than <NUM> Siemens/meter.

If the mold <NUM> is made of a carbon fiber composite material, the mold <NUM> may be a carbon fiber reinforced plastic (CFRP). The fiber reinforcement can also be a hybrid of carbon and another type of technical fiber such as glass fiber, basalt fiber etc.. The fibers can be continuous or chopped, unidirectional plies or multi-axial layups or randomly oriented fibers. In a preferred embodiment the fibers are woven. Different types of fibers and layups have their particular advantages, such as stiffness, coefficient of thermal expansion (CTE), electrical and thermal properties, and preferably a carbon fiber with high thermal conductivity such as pitch carbon fiber or high thermal conductivity polyacrylic nitrile carbon fibers is used to simplify uniform temperature generation. Similar choice applies to the matrix material, where easy and low temperature processing is advantageous, as well as high temperature resistance and high glass transition temperature. Also low CTE and long durability or service life are important properties. Examples of matrices can be epoxies, bismaleimides, polyimides, benzoxazines, phenolics and also silicones, and thermoplastics or semicrystallines such as polycarbonate (PC), polyphenylene-sulfide (PPS), polyetereterkotone (PEEK) etc..

If the mold <NUM> is made at least partially of metal, it may typically be in steel, aluminum, or an alloy such as invar. Nickel or coated steel is also common, but any metal works and might be beneficial depending on the particular application. The purpose of using a metal or a carbon fiber composite material is that the molding tool, and more importantly its mold <NUM>, should be able to be heated inductively. Basically, the molding tool is a susceptor, meaning that it has the ability to absorb electromagnetic energy and convert it to heat. In this case, the molding tool is heated inductively via the coil assembly <NUM>. During the molding process, the material <NUM> to be processed, which is typically a mix of a fiber and polymeric material, is configured to be heated by the inductively heated molding tool. The material <NUM> to be processed may also be a fiber material which is infused with a resin later on in the molding process. In total, the resin, or plastic material, to be infused during the molding process is regarded as being part of the material <NUM> to be processed.

In some cases, the mold <NUM> and the material <NUM> to be processed may be of similar material and might also absorb heat directly from the induction. The material <NUM> to be processed will be discussed in more detail below. The mold <NUM> can be single-sided to reduce costs when the requirements on one of the sides of the part is lower than the other and provide a more simple molding tool. It may alternatively be double-sided depending on the process and requirements, either as two independent molding tools, tool halves or as one molding tool where at least one coil is connected together, despite mechanically it might be two individual molds <NUM>.

The material <NUM> to be processed in the mold <NUM>, will be heated mainly due to its contact with the contact surface <NUM> but might also absorb a certain amount of energy directly from the induction heating if it contains carbon fiber. The material <NUM> is typically a composite material based on a mix of fiber material and polymeric material. As a non-limiting example, the material may contain multiple fiber layers, e.g. <NUM> layers of glass or carbon fibers embedded in a thermoset or thermoplastic matrix. The material can be made of a woven web of fibers, or for example chopped fibers, organized or randomly oriented. Optionally, the web is nonwoven. The matrix may be for example epoxy, polyester (PET), polypropylene (PP), polyamide (PA), polycarbonate (PC) or it can be a high-end amorphous or semicrystalline thermoplastic material such as polyphenylenesulfide (PPS), polyetherimide (PEI) or polyetereterketone (PEEK) etc. The fibers can also be of any other technical textile, such as flax fibers, aramid, ultra-high molecular weight polyethylene, etc. As a non-limiting example, glass fibers may be used as a reinforcement in a polycarbonate based matrix. The composite materials can also be built by hybrid fiber reinforcement, for example glass fiber and carbon fiber. Typical processing temperatures ranges from just above room temperature to about <NUM> degrees C, but can be even higher depending on the matrix material.

The part A is produced in the molding tool by heating the material <NUM> to be processed under pressure. Put differently, when the material <NUM> is heated by the inductively heated molding tool, the part A is being produced, either because there is a matrix material already there when the process starts, or because it is added during the process using an infusion process. Preferably, the material <NUM> is processed under vacuum pressure to reduce the risk of voids, pin holes or insufficient wet out.

<FIG> shows a molding tool <NUM> that includes a mold <NUM>, a coil assembly <NUM>, and a clamping means <NUM>. The coil assembly <NUM> may include one or a plurality of coils <NUM>, <NUM>, <NUM>. This is illustrated in <FIG> as a first coil <NUM> and possibly also a second coil <NUM>, and third coil. The coil assembly <NUM> may include three, four, five coils or any other reasonable number of coils.

In the same way as the mold <NUM> might have any suitable size and shape for the application, the coils <NUM>, <NUM> might have any shape, size or configuration. Examples of coil configurations are layouts generating a transversal or longitudinal flux, or a combination thereof, generating local or global circulating currents in the mold <NUM>. In a preferred embodiment, the coil assembly <NUM> comprises more than one coil <NUM>, <NUM>, <NUM> covering parts of, or the entire back side of the mold <NUM>, where the current in each coil can be individually controlled to always achieve the desired mold <NUM> temperature in every location. This is exemplified in <FIG>. If the entire mold <NUM> is not being heated, it is preferred to have at least one coil covering the main area of the mold and at least one coil covering the perimeters of the heated area to be able to compensate for heat loss due to thermal conduction. Each coil might consist of one or multiple parallel wires (not shown) to ensure thermal management.

The clamping means <NUM> is configured to at least partly fixate the at least one coil <NUM>, <NUM> to the mold <NUM>. The clamping means <NUM> will be described more in detail with reference to <FIG>.

In one embodiment, the molding tool <NUM> is arranged with one or more main coils arranged on the back side <NUM> of the mold <NUM> using clamping means <NUM>. The main coils are electrically insulated from the mold <NUM> and are configured to inductively heat the mold <NUM> when a current is flowing through them. Preferably, the main coils are made of litz wires due to their flexibility and low losses at high frequencies. There can be one or several wires in parallel depending on the dimensions and application, to ensure a good efficiency of the system.

For instance, the molding tool <NUM> may include some kind of cooling means to cool down the temperature of mold <NUM> after a processing cycle. Cooling may be performed from the outer surface <NUM> using for example forced air and/or water or using cooling channels inside or in proximity with the mold <NUM> for transporting a cooling media being in gas and/or liquid form.

In order to further improve the inductive heating of the molding tool <NUM>, soft magnetic elements and electrically conductive elements (not shown) may be placed at predetermined areas along the coil assembly <NUM>. The soft magnetic elements are typically made of a magnetic material with small hysteresis losses. The soft magnetic elements are produced in a way to avoid induced currents in the material. Typical examples of soft magnetic materials are soft magnetic composites, sometimes referred to as powder cores, or soft ferrites. The relative permeability should be substantially larger than <NUM>, typically <NUM>-<NUM>. The electrically conductive elements are typically made of highly electrically conductive material such as copper or aluminum, aimed to induce currents without creating substantial losses. The soft magnetic and electrically conductive elements are used to achieve the desired heating pattern, to concentrate the magnetic flux density, to improve the efficiency of the induction heating system, to reduce stray magnetic fields and to shield the high frequency electromagnetic field to prevent undesired areas or materials to be heated up by induction.

Turning back to <FIG>, at least one processing means <NUM> is provided which is in operative communication with the coil assembly <NUM>. The processing means <NUM> controls and energizes the operation of the coil assembly <NUM> and thereby also the inductive heating process which heats the molding tool <NUM> and results in the production of a composite part A. The coil(s) of the coil assembly <NUM> may be coupled to one and the same processing means or to different processing means. The processing means <NUM> is configured to generate a high frequency current in the coil assembly <NUM>. Preferably, the processing means <NUM> is or comprises a frequency converter. The at least one processing means <NUM> is configured to generate an alternating voltage and current to the coil(s) so as to inductively heat the mold <NUM> of the molding tool <NUM> so that a part A can be produced. In some embodiments, one processing means <NUM> alone can control multiple coils. In other embodiments, several processing means <NUM> may be used to control the heating of the molding tool <NUM>.

Preferably, the processing means <NUM> comprises a certain intelligence in terms of some type of microcontroller or central processing unit, memory etc. and at least one type of interface (not shown) for operating the system, either as a human machine interface in terms of a graphical display, buttons, knobs or similar, or as a communication interface to be controlled from a surveillance system such as a PC or PLC.

Turning now to <FIG>, the clamping means <NUM> which clamps the coils <NUM>, <NUM>, <NUM>/wires <NUM>, <NUM>, <NUM> to the mold <NUM> will be described. The principle of clamping a coil <NUM>-<NUM> to the outer surface <NUM> of the mold <NUM> is applicable to all types of coils, for coils consisting of one or multiple wires <NUM>, <NUM>, <NUM>, clamped individually or together. Each clamping means <NUM> can be mounted on the mold to clamp one or several wires <NUM>, <NUM> of one coil <NUM>, one or several turns <NUM>, <NUM> of the same coil <NUM>, or several coils <NUM>, <NUM> together, or a combination.

<FIG> schematically illustrates a part of a molding tool having two wires <NUM>, <NUM> of at least one coil arranged in parallel, which are held together by a plurality of clamping means <NUM> along their longitudinal axis. The number of clamping means <NUM> may vary depending on several factors, such as the length of the coils the pattern of the coils and the size of the clamping means <NUM>. As an example only, the clamping means <NUM> are arranged at a distance of <NUM> from one another.

In <FIG>, each clamping means <NUM> has a first end <NUM> and a second end <NUM> which are attached to the back side <NUM> of the mold <NUM>, respectively, thereby clamping the wires <NUM>, <NUM> of at least one coil to the mold <NUM>. The first and second ends <NUM>, <NUM> may also be referred to as first and second side sections. Optionally, only one of the first and second ends <NUM>, <NUM> are attached to the back side of the mold.

An intermediate section <NUM> of the clamping means <NUM> is elevated enough with respect to the coils/wires <NUM>, <NUM> and the side sections <NUM>, <NUM> to fit the coils and at least one insulating element, and keep them tightly in place with respect to the outer surface <NUM> of the mold <NUM>. The intermediate section <NUM> may be rigid or flexible, as long as it keeps the coils in place during manufacturing of the composite part A. The elevation of the intermediate section <NUM> creates a void or a space between the center part of the clamping means <NUM> and the outer surface <NUM> of the mold <NUM>. In other words, the distance between the intermediate section <NUM> and the back side <NUM> of the mold <NUM> defines a space within which one or more wires of one or more coils, electrically insulating material, thermally insulating material, cooling channels, and the like may be arranged and clamped. The intermediate section <NUM> is preferably made of a material having a thickness being less than two times the skin depth of its material at an operating frequency of the electric current configured to flow through the coils to prevent or at least reduce self-heating of the clamping means from the induction coils.

The first end <NUM>, the second end <NUM> and the intermediate section <NUM> may either be formed as an integral body or separately from one another. At least parts of the clamping means <NUM> is made of metal with a relative magnetic permeability lower than <NUM>. The clamping means <NUM> are preferably made of stainless steel, titanium or copper. The clamping means are preferably attached to the mold <NUM> by welding, such as spot welding, MIG (metal inert gas) welding, MAG (metal active gas) welding, TIG (tungsten inert gas) welding, ultrasonic welding. Alternatively, the clamping means <NUM> may be attached by soldering, or brazing to the mold <NUM>. The mold is defined as the mold tool including inserts, fasteners or other arrangements mounted to it, onto which the clamping means can be attached by the welding, brazing or soldering. To be more specific, the mounted or integrated attachments described above are considered as parts of the outer surface <NUM> of the mold <NUM>. As an example, if the mold is made out of carbon fiber composites, it might have metal parts attached to it from the composite manufacturing or afterwards using for example gluing; metal parts onto which the clamps can be attached using the methods described above. As another example, if the molding tool is made of carbon fiber thermoplastics, clamping means <NUM> made partially or entirely of polymeric material can be welded to the back side <NUM> of the mold <NUM> using for example ultrasonic or induction welding.

Turning to <FIG>, a clamping means <NUM> is shown from a cross-section view. The first side section <NUM> of the clamping means <NUM> and the second side section <NUM> of the clamping means <NUM> are each attached to the back side <NUM> of the mold <NUM> on opposite sides with respect to the intermediate section <NUM> which extends between the two side sections <NUM>, <NUM>. In <FIG>, the intermediate section <NUM> has an inverted U-shape and a substantially squared cross-section. Optionally, as illustrated in other drawings, the intermediate section <NUM> may have a more rounded shape, such as an arc-shape or the like.

The first side section <NUM> of the clamping means <NUM> has an attachment surface 41a facing the outer surface <NUM> of the mold <NUM>. A weld interface <NUM> is provided between the first attachment surface 41a and the outer surface <NUM>. Similarly, the second side section <NUM> has a corresponding attachment surface 42a facing the outer surface <NUM> of the mold <NUM>, and a weld interface <NUM> is provided between the attachment surface 42a and the outer surface <NUM>, or a weld interface <NUM> is provided between the attachment surface 42a and a part of the first side section <NUM>. At the respective weld interfaces <NUM>, <NUM>, the clamping means <NUM> is welded to the back side <NUM> of the mold <NUM>. Optionally, as shown in <FIG>, the attachment surface 41a, 42a is welded to a weldable element, such as a metal strip, which is in turn adhered to the back side <NUM> of the mold <NUM>, defined as above, being a part of the mold <NUM>. For instance, a metal strip is glued to the back side <NUM>. The clamping means <NUM> may be attached to the outer surface <NUM> of the mold <NUM> by any one of welding, brazing or soldering.

Moreover, the first side section <NUM> and the second side section <NUM> have respective upper surfaces 41b, 42b facing away from the back side <NUM> of the mold <NUM>. The upper surfaces 41b, 42b may be subjected to a welding tool, such as a spot welder, welding electrode or ultrasonic tool, or other heat generator such as soldering iron or open flame. It might also be affected by a press force during the attachment process when the clamping means <NUM> is to be attached to the back side <NUM>.

The features disclosed in relation to <FIG> above, i.e. the side sections <NUM>, <NUM>, the intermediate section <NUM> and the attachment surfaces 41a, 42a are all common features with the embodiments shown in <FIG>.

<FIG> shares the features described in relation to <FIG> and displays a coil wire <NUM> clamped between the clamping means <NUM> and the back side <NUM> of the mold <NUM>. The coil wire <NUM> is surrounded by an electrically insulating material <NUM> provided all along the circumference of the wire <NUM> and the outer surface <NUM> of the mold <NUM>. As can be seen, the intermediate section <NUM> further at least partially encloses the electrically insulating material <NUM>. Moreover, the electrically insulating material <NUM> is not limited to be in contact with the inner part of the intermediate section <NUM>.

With reference to <FIG>, two wires <NUM>, <NUM> of at least one coil are arranged within the space defined by the distance between the intermediate section <NUM> and the back side <NUM> of the mold <NUM>. Between the wires <NUM>, <NUM> and the back side <NUM> of the mold <NUM>, a thermally <NUM> insulating material is provided. The main advantage of using such a material is that the mold can be heated to a temperature higher than what the wire can withstand, but it can also save energy otherwise spent on heating up the wire through conduction.

As mentioned previously, the first and second side sections <NUM>, <NUM> of the clamping means <NUM> may be welded to a weldable element, such as a metal strip <NUM>, <NUM>, which is in turn adhered to the back side <NUM> of the mold <NUM>, and considered being part of the back side <NUM> of the mold <NUM>. In one embodiment, the metal strips <NUM>, <NUM> are glued onto the back side <NUM> of the mold <NUM>. The weldable surface of each metal strip <NUM>, <NUM> faces the respective attachment surfaces 41a, 42a of the clamping means <NUM>. Between the attachment surfaces 41a, 42a and the weldable surfaces of the metals strip <NUM>, <NUM>, the weld interfaces <NUM>, <NUM> are provided. This is shown in <FIG>, which in all other senses is reflected in the embodiment disclosed in relation to <FIG>.

<FIG> shares the features disclosed in relation to <FIG>. However, in <FIG>, the intermediate section <NUM> has a more curved, or rounded shape, and abuts the electrically insulating material <NUM> along the majority of the circumference of the electrically insulating material <NUM> which covers the wire <NUM> of the coil. Just like in all embodiments disclosed herein, the electrically insulating material <NUM> covers the wire <NUM> at least in this area along the longitudinal extension of the wire <NUM>. In a region between the wire <NUM> of the coil with its surrounding electrically insulating material <NUM> and the outer surface <NUM> of the mold <NUM>, a thermally insulating material <NUM> is provided. In <FIG>, the thermally insulating material <NUM> is preferably an air gap.

Moving on to <FIG>, two wires <NUM>, <NUM> of at least one coil are arranged on the back side <NUM> of the mold <NUM>. A first side section <NUM> and a second side section <NUM> of the clamping means <NUM> are shown as an inverted T. In this embodiment, the intermediate section <NUM> of the clamping means <NUM> is pressed, riveted or bolted to the first and second side sections <NUM>, <NUM> at a press/bolt interfaces <NUM>, <NUM>, which are welded to the back side <NUM> of the mold <NUM> at their respective attachment surfaces 41a, 42a, thereby creating weld interfaces <NUM>, <NUM>. Alternatively, the first <NUM> and second side sections <NUM> are soldered or brazed to the back side <NUM> of the mold. The clamping means <NUM> may also be built up by several welded sections, where the intermediate section <NUM> is welded to the first and/or second side sections <NUM>, <NUM>.

In <FIG>, the intermediate section <NUM> of the clamping means <NUM> is claw-shaped and is adapted to receive two wires <NUM>, <NUM> of at least one coil. As for all embodiments disclosed herein, one single wire or more than two wires may be clamped by the clamping means <NUM>. In this particular embodiment, the clamping means <NUM> can form a space between the wires <NUM>, <NUM> and the back side <NUM> of the mold <NUM> acting as a thermal barrier. Preferably, the clamping means <NUM> is rather flexible so that the wires <NUM>, <NUM> can be clipped in a direction towards the back side <NUM> of the mold <NUM>, forming a firm attachment.

As illustrated in <FIG>, each wire may be associated with a cooling channel <NUM>, <NUM>, <NUM>. The cooling channel is either integrated in or arranged in close proximity to a corresponding wire <NUM>, <NUM>, <NUM> of at least one turn of at least one coil. The purpose of the cooling channel(s) is mainly for gas or liquid cooling, preventing overheating of the coil, heat generated by losses in the wire itself <NUM>-<NUM> or caused by thermal conduction from the hot mold <NUM>. The intermediate section <NUM> at least partially encloses the cooling channel similarly as it encloses the coil, as well as the electrically and thermally insulating elements <NUM>, <NUM>, <NUM>, <NUM>. In <FIG>, the coil/wire includes a cooling channel <NUM>. Put differently, the cooling channel <NUM> is integrated in the wire <NUM> of the coil. The wire <NUM> is surrounded by an electrically insulating element <NUM>, and between the electrically insulating element <NUM> and the back side <NUM> of the mold <NUM>, a thermally insulating element <NUM> is provided. In <FIG>, three wires <NUM>, <NUM>, <NUM> of at least one coil are provided. Each one of the wires <NUM>, <NUM>, <NUM> is surrounded by a respective electrically insulating element <NUM>, <NUM>, <NUM>. Instead of being integrated in the coils, cooling channels <NUM>, <NUM>, <NUM> are arranged in close proximity to the coils/wires. The cooling channels <NUM>, <NUM>, <NUM> are surrounded by a material preventing the cooling media from leaking out. This material can, be the same as the one of the electrically insulating elements <NUM>, <NUM>, <NUM> associated with the respective wire <NUM>, <NUM>, <NUM>.

A further embodiment is shown in <FIG> where a soft magnetic element and/or an electrically conductive element <NUM> is arranged between the wires <NUM>, <NUM> of at least one coil and the intermediate section <NUM> of the clamping means <NUM>. The intermediate section <NUM> at least partially encloses the soft magnetic element and/or at least one electrically conductive element <NUM>, just like it encloses the wires <NUM>, 212with their surrounding electrically insulating elements <NUM>, <NUM>.

Turning to <FIG>, a support <NUM> is welded to the back side <NUM> of the mold <NUM>. The support <NUM> is shaped in a way such that a wire <NUM> fits in a depression of the support <NUM>. In other words, the support <NUM> holds the coil wire <NUM> in place over the surface of the mold. However, the shape of the support <NUM> can have a lot of different shapes and is not limited to having a depression/groove or similar. The support <NUM> may be seen as a bridge which creates a physical distance and thereby separates the back side <NUM> of the mold <NUM> and the coil. A purpose of the support <NUM> is to achieve thermal insulation between the coil and the mold <NUM>. For instance, the support <NUM> may be made of the same material as the clamping means <NUM> and attached with the same method.

The embodiment shown in <FIG> corresponds to a large extent with the embodiment of <FIG>. In <FIG>, a soft magnetic element <NUM> is for example cast around the intermediate section <NUM> of the clamping means <NUM>. An electrically conductive element may be a copper tube clamped around the clamping means. Moreover, the whole clamping means <NUM> may be an electrically conductive element with the purpose of reducing power locally. This would require a clamping means thickness of more than two times the skin depth. Between the back side <NUM> of the mold and the soft magnetic element <NUM>, the wire <NUM> of a coil is clamped.

Moving on to <FIG>, the first side section <NUM> of the clamping means <NUM> is attached to the back side <NUM> of the mold <NUM> by any of the ways described above, i.e. by welding, brazing or soldering. As mentioned previously, like numbers refer to like elements. The second side section <NUM> of the clamping means <NUM> is attached to a mold surface which is orthogonal to the surface onto which the first side section <NUM> is attached. The clamping means <NUM> described herein can be attached to basically any geometrical surface and is adaptable to different mold geometries. In <FIG>, the wire <NUM> of a coil is located between the clamping means <NUM> and the back side <NUM> of the mold <NUM>. The intermediate section <NUM> has a substantially tip-like shape in this configuration. In another embodiment (not shown), the intermediate section <NUM> could have the shape of a smooth bend which conforms to the shape of the wire/coil to be clamped.

In some cases, as will be clear from <FIG>, only one of the side sections, such as the first side section <NUM> is attached to the mold <NUM>. In those cases, the other one of the side sections, such as the second side section <NUM>, either is formed as a free end or is in turn attached to another part of the clamping means, such as the first side section <NUM>, by any one of welding, brazing or soldering.

With reference to <FIG>, the first side section <NUM> of the clamping means is attached to the outer surface <NUM> of the mold <NUM> at a weld interface <NUM>. The second side section <NUM> is at least partially wrapped around the wire <NUM> of a coil and is in turn attached to the first side section <NUM> at another weld interface <NUM>. It may be that the upper surface 42b of the second side section <NUM> is facing the upper surface 41b of the first side section <NUM>. It may also be that the attachment surface 42a of the second side section <NUM> faces the upper surface 41b of the first side section <NUM>. In any case, the clamping means surrounds the wire/coil and is welded to itself as well as the mold.

In <FIG> and <FIG>, the first side section <NUM> of the clamping means is attached to the back side <NUM> of the mold <NUM> at a weld interface <NUM>. The second side section <NUM> is loose and clamps around the wire <NUM> of a coil to keep the wire <NUM> in place on the back side <NUM> of the mold. In <FIG>, the intermediate section <NUM> of the clamping means is substantially flat/square-shaped and in <FIG>, the intermediate section <NUM> of the clamping means is rather arc-shaped.

Moving on to <FIG>, the first side section <NUM> of the clamping means is attached to the outer surface <NUM> of the mold and the second side section <NUM> clamps the intermediate section <NUM> of the clamping means. For example, the first and second ends <NUM>, <NUM> are made of a round stud with one or several barbs and the intermediate section <NUM> is made of a thin metal sheet of a certain material, preferably with a thickness of less than <NUM> times the skin depth of the material at the operating frequency, containing a deformable hole or slot that can be forced over the barbs of the stud to lock a wire <NUM> in place.

In <FIG>, the first side section <NUM> of the clamping means is attached to the back side <NUM> of the mold and the wires <NUM>, <NUM> of at least one coil are clamped around the clamping means. This can be explained as follows. Two litz wires <NUM>, <NUM> are provided, through which a hole (not shown) is made through their cover, between the wires <NUM>, <NUM>. The second side section <NUM> of the clamping means is threaded through this hole. The wires <NUM>, <NUM> are held in place by means of bulb-like elements protruding outwards from the intermediate section <NUM> of the clamping means. This way, the coil(s) are held in place over the back side of the mold.

It is appreciated that the wires <NUM>, <NUM>, <NUM> described above may be surrounded by electrically insulating elements. From safety, security, EMC and functionality point of view, it is beneficial that the mold <NUM> and the coils <NUM>-<NUM> and electrically insulated from each other, meaning an electrical insulation that can typically withstand several thousands of volts, during the entire lifetime of the molding tool <NUM>. Certain types of wires, for example magnet wires or enameled wires, including litz wires already have an insulation layer due to the enamel coating, providing sufficient in some cases but not in others. In the case with litz wires, it is common to have a wrapping of for example silk, nylon, polyimide, aramid or similar to keep the strands together and to further improve the electrical insulation. Like cables, the wire can further have one or several solid polymeric layers, to improve the electrical and thermal insulation even more and to achieve for example resistance to cooling fluids or form leakage proof channels for cooling of the wire or by other reasons suitable for the application. The same reasoning applies in the case if the wire is a solid or hollow conductor such as a copper tube. Electrical and thermal insulation can also be loosely attached to the wire, partially or completely surrounding it, for example bonded or clamped in position. <FIG> schematically illustrates a selection of insulation types.

A method of producing a composite article, or part A, using the molding tool <NUM> is shown in <FIG>. In the method described in relation to <FIG>, the material to be processed, which is placed in the mold, is a mix of a fiber and plastic material. Another method is shown in <FIG>, where the material placed in the mold is a fiber material which, during the molding process, is infused with a plastic material, so that the plastic material then forms part of the material <NUM> to be processed. <FIG> offers a schematic view of parts of these methods.

In the methods illustrated in <FIG>, the material <NUM> to be processed may consist of technical fibers such as carbon, glass, aramid, ultra-high molecular weight polyethylene, flax or basalt fibers, or be a mix of fiber and plastic material. The material <NUM> may be a prepreg, sheet/bulk molding compound (SMC/BMC), comingled yarns, intermediate material or a separate fiber and plastic, where the plastic may for example be in the form of sheets or powder. The plastic component may be a thermoplastic or a thermoset and the fiber component may be fiber tows, multiaxial material, weave or random oriented fibers. The layup, number of layers, directions, size, and shape of the material <NUM> can vary a lot depending on the process and application, well known in the field. The material <NUM> can be put into the mold in a sequence, for example layer by layer or may be pre-formed before being put into the mold. The material <NUM> may, in addition to the fibers, also contain core/distance/sandwich material such as foam cores, honeycomb structures etc., common in many composite components, or metal inserts, typical for assembly purposes in the final application of the part A. The material <NUM> may even be transformed into a multi-material part A, containing both fiber composites and metal.

The method shown in <FIG> comprises the step of providing <NUM> a molding tool <NUM> having a mold <NUM> configured to be inductively heated by a coil assembly <NUM> which is attached to the mold <NUM> by a clamping means <NUM> according to the teachings herein. Optionally, a release agent is added to the molding tool <NUM> at this stage to facilitate separation of the produced part A from the mold <NUM>. The method further comprises placing <NUM> a material <NUM> to be processed on the contact surface <NUM> of the mold <NUM>. Preferably, the material <NUM> is a fiber and plastic material in the form of a pre-form with the similar shape as the contact surface <NUM>, easy to put into the mold.

In this case, where the plastic is already in the mold, i.e. as a matrix material incorporated in the fiber material placed in the mold, the method further comprises closing <NUM> the mold <NUM> and applying <NUM> consolidation pressure on the material <NUM> to be processed. The mold <NUM> may for instance be closed by another molding tool <NUM> halve or by a flexible membrane or bag.

Before applying <NUM> consolidation pressure on the material <NUM> to be processed, the method may further comprise a step of applying <NUM> a vacuum, or near vacuum pressure on the material <NUM>. Certain processes benefit from the reduced pressure, i.e. the vacuum pressure, on the material to remove entrapped air and thereby enhance wet out of the matrix on the fibers during the manufacturing process and thereby reduce the risk of dry-spots or voids in the produced part A.

The consolidation pressure may for example be applied by arranging a vacuum bagging unit on top of the material <NUM> and performing vacuum bagging. The consolidation pressure may also be applied by a press, an autoclave or just via atmospheric pressure if there is near vacuum pressure inside of the mold. In the latter case, the step of applying <NUM> consolidation pressure on the material <NUM> often means drawing vacuum in the molding tool <NUM>. In some cases, vacuum pressure is the same as consolidation pressure.

The method which is described in relation to <FIG> further comprises inductively heating <NUM> the mold <NUM> containing the material <NUM>. The heating may be done according to a predetermined time-temperature profile to consolidate and/or cure the material <NUM> to produce the composite part A. The mold <NUM> is heated by the coil assembly <NUM> which is in operative communication with the processing means <NUM> as discussed previously. The molding tool <NUM>, or its mold <NUM>, may be heated prior to, during and/or after the step <NUM> of applying pressure. Also, the pressure must not be constant during the entire process but can for example be increased when the material <NUM> is getting warmer to enhance part quality.

The mold <NUM> and the material <NUM> to be processed are held in this position in the molding tool <NUM> during a predetermined time period, typically to ensure sufficient temperature throughout the material and a proper consolidation/wet out of the fiber composite material. In the case of a thermoset, the resin, or plastic material, should be sufficiently cured before demolding, while in the case of a thermoplastic, the part becomes solid after being cooled down. Thus, eventually, a cured or consolidated material <NUM> is provided and forms the composite part A. This is shown schematically in <FIG>. There are a few applicable processes for the method, for example often referred to as compression molding, stamp forming, autoclave processing, out of autoclave processing, vacuum bagging, etc..

Now turning to <FIG>, a case where no matrix material is placed in the mold, i.e. in the case where the material <NUM> initially consists of fibers only, possibly in combination with core/distance/sandwich material or metal inserts etc. as described above. The method, after providing <NUM> a molding tool <NUM>, includes a step of placing the fiber material <NUM> in the mold. Afterwards, the mold is closed <NUM>, typically with another mold half, a flexible membrane or a bag. The closed mold may, as in the case described above, consist of a plurality of mold halves, bags or membranes, or a combination, together providing a sealed or semi-sealed mold assembly. In this case the material <NUM> placed on the contact surface <NUM> of the mold <NUM> may also be called a layup or pre-form of fiber material.

The method related to <FIG> further comprises the step of applying <NUM> a reduced pressure on the material <NUM>, preferably vacuum or near vacuum pressure. The evacuation of gas may be applied in single or a plurality of openings and may be performed only at this step or during the entire production process.

The method further comprises the step of infusing <NUM> the material <NUM> in the mold <NUM> with a matrix material, preferably a low viscosity resin of any type. The resin in this case may also be called a plastic material. This can be done using so called vacuum infusion, where the driving force is the pressure difference between the vacuum pressure in the mold and the surrounding pressure. The infusion can also be done using a higher pressure, up to several hundred bars, often referred to as resin transfer molding RTM, high pressure resin transfer molding HPRTM, vacuum assisted resin transfer molding VARTM etc. Similar to what was discussed in relation to <FIG> above, the method further comprises inductively heating <NUM> the mold <NUM> containing the material <NUM>.

In both of the methods described for producing a composite part A above, the step of heating <NUM> and applying pressure or infusing resin, i.e. the plastic material in the material <NUM> in the mold <NUM>, may occur simultaneously. The heating may be done according to a predetermined time-temperature profile to produce the composite part A. The mold <NUM> is heated by the coil assembly <NUM> which is in operative communication with the processing means <NUM> as discussed previously. The molding tool <NUM>, or its mold <NUM>, may be heated prior to, during and/or after the step of infusing the matrix material in the case of the method described in relation to <FIG>.

A warm tool is typically beneficial to reduce the viscosity of the resin, but typically also starts a chemical reaction to cure the resin, so different aspects apply depending on the application and choice of material. In a preferred case, a proper wet-out of the fibers by the resin is obtained, without dry-spots or voids. In this method, the typical matrix is a thermoset resin and requires the matrix to be cured. Novel plastics are continuously being developed and the method may also be used with hybrid thermoset/thermoplastic matrixes and also low viscosity thermoplastics.

All methods described herein may further comprise active or passive cooling <NUM> of at least a part of the molding tool <NUM> and/or the produced part A formed therein. Finally, the methods described further comprise demolding <NUM> the part A from the molding tool <NUM>. In certain applications, the part A can be demolded at the processing temperature, which is beneficial from a cycle time perspective. Contrarily, a reduced demolding temperature is often beneficial from a part quality perspective.

Part of the methods described above in relation to <FIG> and <FIG> are illustrated in <FIG>. The material <NUM> to be processed, i.e. a mix of a fiber material and a polymeric material, or a fiber material which is to be infused with a resin, or a plastic material, during the molding process as described above, is arranged <NUM> in the molding tool <NUM>. The fiber material may for instance be a carbon fiber or a flax fiber material. Preferably, the mix is in the shape of a pre-form, or a piece of a web. Alternatively, the molding tool <NUM> is arranged in a stream-lined system where webs of material are fed into the molding tool <NUM> in steps. Before heating, the material <NUM> is shown in dashed lines. The material might extend beyond the heated area of the molding tool <NUM>, or be located inside of the heated zone depending on the application. When the molding tool <NUM> is inductively heated <NUM> by the coil assembly driven by the processing means, the mix of fiber and polymeric material, i.e. the material <NUM> to be processed, is consolidated, or cured, to form a part A having a shape corresponding to that of the molding tool <NUM>. After being cured or consolidated, the material to be processed is shown as a solid line. Once the process temperature profile has been completed, the molding tool is cooled down <NUM> and the part A is removed, or demolded, <NUM> from the molding tool. The shape of the part A corresponds to the contact surface of the mold.

A method of manufacturing a molding tool <NUM> will now be described with reference to <FIG>.

In a first step, a mold <NUM> which is configured to be inductively heated is provided <NUM>. The mold <NUM> has a contact surface <NUM> and an outer surface <NUM>, or back side. In a next step, at least one coil <NUM>, <NUM>, <NUM> is provided <NUM> and arranged <NUM> on the back side <NUM> of the mold <NUM>. The coil <NUM>, <NUM>, <NUM> may be arranged in a desired pattern on the outer surface <NUM> of the mold <NUM>, such that a preferred heating pattern can be achieved. A magnetic field generated by this current is configured to induce currents in at least a portion of, or parts of, the mold <NUM> to be heated up.

The mold <NUM> is configured to be heated by an alternating electric current of a certain operating frequency, flowing through the at least one coil <NUM>, <NUM>, <NUM>, and the magnetic field generated by the alternating electric current is configured to induce currents in at least parts of the mold <NUM> to be heated.

As mentioned previously, the molding tool <NUM> includes a mold <NUM>, a coil assembly <NUM>, and a clamping means <NUM>. For instance, the coil assembly <NUM> includes one single coil. The coil assembly <NUM> may also include several coils.

The at least one coil <NUM>, <NUM>, <NUM> is electrically insulated from the mold <NUM>, and in operative communication with at least one processing means <NUM>.

In a preferred embodiment, the wires <NUM>, <NUM> of the et last one coil, <NUM>, <NUM> consists of litz wire, i.e. a wire built up by many thin strands, individually electrically insulated and twisted to reduce high frequency losses caused by skin and proximity effects. Furthermore, the method may further comprise the step of arranging at least one soft magnetic element and/or electrically conductive element <NUM> at predetermined regions along the at least one coil <NUM>, <NUM>, <NUM>.

Additionally, the method of manufacturing the molding tool <NUM> includes providing <NUM> at least one clamping means <NUM> having a first end <NUM>, a second end <NUM>, and an intermediate section <NUM> extending between the first end <NUM> and the second end <NUM> in a way described in relation to <FIG> above. Next, the method comprises attaching <NUM> at least the first end <NUM> of the at least one clamping means <NUM> to the outer surface <NUM> of the mold <NUM> using welding, brazing or soldering, so as to at least partly fixate the at least one coil <NUM>, <NUM>, <NUM> to the outer surface <NUM> of the mold.

In one embodiment, a molding tool for producing a composite part using induction heating is provided. The molding tool <NUM> includes a mold <NUM>, having a contact surface <NUM> adapted to be in contact with a material <NUM> to be transformed into a composite part A, and an outer surface <NUM>, or back side. The mold <NUM> is configured to be inductively heated by at least one coil <NUM>, <NUM>, <NUM> which is attached to the back side <NUM> of the mold <NUM> using clamping means <NUM> which are fastened to the mold <NUM>, preferably by welding. Optionally, the clamping means <NUM> are indirectly welded to the mold <NUM> by being welded to a weldable material which is in turn attached to the back side <NUM> of the mold. For instance, in the case of a composite mold, a glued metal strip <NUM>, <NUM> may serve as a weldable material (see <FIG>). The clamping means <NUM>, more specifically an intermediate section <NUM> of the clamping means <NUM>, may also be screwed, bolted, riveted or pressed onto separate parts that are welded to the mold surface <NUM>, such as for instance the T-shaped side sections <NUM>, <NUM> in <FIG>. Furthermore, the clamping means <NUM> may be in the shape of clips that clamp the coils <NUM>, <NUM>, <NUM> from below, i.e. the coils are clipped onto a clamping means <NUM> which is already in place on the outer surface <NUM> of the mold <NUM>, rather than first arranging the coils and clamping them later on. A further option of clamping is to attach multiple clamping means <NUM> using welding, brazing or soldering over the back side <NUM> of the mold <NUM> and threading the at least one coil <NUM>, <NUM>, <NUM> through each clamping means.

Claim 1:
A molding tool (<NUM>) for producing a composite part (A) using induction heating, comprising:
a mold (<NUM>) having a contact surface (<NUM>) adapted to be in contact with a material (<NUM>) to be transformed into a composite part (A), and an outer surface (<NUM>);
at least one coil (<NUM>-<NUM>) or at least one wire (<NUM>-<NUM>) of a coil (<NUM>-<NUM>) arranged on the outer surface (<NUM>) of the mold (<NUM>); and
at least one clamping means (<NUM>) having a first end (<NUM>), a second end (<NUM>) and an intermediate section (<NUM>) extending between the first end (<NUM>) and the second end (<NUM>), wherein at least one of the first end (<NUM>) and second end (<NUM>) is attached to the outer surface (<NUM>) of the mold (<NUM>) using welding, brazing or soldering, so as to at least partly fixate the at least one coil (<NUM>-<NUM>) to the outer surface (<NUM>) of the mold (<NUM>);
wherein the intermediate section (<NUM>) at least partially encloses the at least one wire (<NUM>-<NUM>) or coil (<NUM>-<NUM>) to hold said at least one wire (<NUM>-<NUM>) or coil (<NUM>-<NUM>) in place on the outer surface (<NUM>) of the mold (<NUM>); and
wherein the at least one wire (<NUM>-<NUM>) or coil (<NUM>-<NUM>) are electrically insulated from the mold (<NUM>) and in operative communication with at least one processing means (<NUM>).