Inductively heated slip sheet and method of using the same

Abstract

To provide a method and apparatus for non-autoclave curing of a composite part by using a simple and inexpensive machine tool.SOLUTION: An induction curing system comprises a slip sheet and a power supply. The slip sheet comprises: a lay-up surface configured to receive a composite material; a tool interface surface configured to interact with an upper surface of a tool; a rigid body extending between the lay-up surface and the tool interface surface; and an induction coil circuit within the rigid body of the slip sheet. The induction coil circuit is configured to heat the lay-up surface to a temperature sufficient to cure the composite material. The induction coil circuit has a diameter selected to generate heat using a power supply having a frequency less than 150 kHz. The rigid body is configured to support the composite material during transport of the composite material. The power supply is coupled with the induction coil circuit, and is selected based on the diameter of the induction coil circuit.SELECTED DRAWING: None

Description

[Technical Field]

[0001] FIELD OF THE DISCLOSURE The present disclosure relates generally to composite manufacturing, and more particularly to curing composite materials using induction heated slipsheets. [Background technology]

[0002] Composite parts may be cured in ovens or autoclaves, in which heat is applied to the part while it is supported on a curing tool that maintains the part's shape during the curing process. Techniques have been developed for curing composite parts without the need for an oven or autoclave, but these techniques are limited to curing relatively small parts and / or require relatively complex and / or expensive machine tooling.

[0003] It would therefore be desirable to have a method and apparatus that takes into account at least some of the above-mentioned problems, as well as other possible problems. For example, it would be desirable to have a method and apparatus for curing composite parts outside of an autoclave that employs relatively simple and inexpensive machine tooling. Summary of the Invention

[0004] An embodiment of the present disclosure provides a method for forming a composite part. A composite material is laid up on a layup surface of a slipsheet disposed on a layup support. The composite material laid up on the slipsheet is transported to a tool, where the slipsheet comprises a rigid body configured to support the composite material during transport. The slipsheet is secured to the tool such that a tool interface surface of the slipsheet contacts a top surface of the tool. The composite material on the slipsheet is cured using heat generated by an induction coil circuit within the rigid body of the slipsheet while the slipsheet is secured to the tool.

[0005] Another embodiment of the present disclosure provides an induction hardening system. The induction hardening system includes a slipsheet and a power source. The slipsheet includes a layup surface configured to receive a composite material, a tool interface surface configured to interact with an upper surface of a tool, a rigid body extending between the layup surface and the tool interface surface, and an induction coil circuit within the rigid body of the slipsheet. The rigid body is configured to support the composite material during transport. The induction coil circuit is configured to heat the layup surface to a temperature sufficient to harden the composite material. The induction coil circuit has a diameter selected to generate heat using a power source having a frequency of less than 150 kHz. The power source is coupled to the induction coil circuit. The power source is selected based on the diameter of the induction coil circuit.

[0006] Yet another embodiment of the present disclosure provides an induction hardening system. The induction hardening system includes a slipsheet. The slipsheet includes a layup surface configured to receive a composite material, a tool interface surface configured to interact with an upper surface of a tool, a body extending between the layup surface and the tool interface surface, and an induction coil circuit within the body of the slipsheet. The induction coil circuit is configured to heat the layup surface to a temperature sufficient to harden the composite material. The induction coil circuit includes a conductor for receiving an electric current and generating a magnetic field in response to the electric current, and a susceptor wire wound along at least a portion of the length of the conductor. The susceptor wire has a diameter greater than 0.05 inches.

[0007] These features and functions may be realized independently in various embodiments of the present disclosure or may be combined in yet other embodiments, further details of which can be seen in connection with the following description and drawings.

[0008] The novel features believed characteristic of the illustrative embodiments are set forth in the appended claims, however, the illustrative embodiments and preferred modes of use, further objects and features thereof will best be understood by reading the following detailed description of illustrative embodiments of the present disclosure when read in conjunction with the accompanying drawings. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is an illustration of an aircraft depicted in accordance with an illustrative embodiment; [Figure 2] FIG. 1 is a block diagram of a manufacturing environment in which an illustrative embodiment may be implemented. [Figure 3] FIG. 1 is an illustration of a composite component in an induction hardening system in accordance with an illustrative embodiment; [Figure 4] FIG. 1 is an illustration of an induction hardening system in accordance with an illustrative embodiment. [Figure 5] FIG. 1 is a cross-sectional view of a slipsheet of an induction curing system according to an exemplary embodiment. [Figure 6] FIG. 1 is a cross-sectional view of a slipsheet of an induction curing system according to an exemplary embodiment. [Figure 7] FIG. 1 is an illustration of a cross-sectional view of a composite material laid up on a slipsheet on a layup support in accordance with an illustrative embodiment. [Figure 8] 1 is a cross-sectional view of removing and transferring a composite material on a slipsheet from a layup support in accordance with an illustrative embodiment; [Figure 9] 1 is an illustration of a cross-sectional view of transferring a composite material on a slipsheet from a layup support in accordance with an illustrative embodiment; [Figure 10] FIG. 10 is a cross-sectional view of placing a rigid cowl within an induction hardening system in accordance with an illustrative embodiment; [Figure 11] FIG. 1 is a cross-sectional view of placing a heated blanket in an induction hardening system in accordance with an illustrative embodiment. [Figure 12] 1 is an illustration of a flowchart of a method for forming a composite part in accordance with an illustrative embodiment. [Figure 13]FIG. 1 is an illustration of an aircraft manufacturing and service method in the form of a block diagram in accordance with an illustrative embodiment; [Figure 14] FIG. 1 is an illustration of an aircraft in the form of a block diagram in which an illustrative embodiment may be implemented; DETAILED DESCRIPTION OF THE INVENTION

[0010] The illustrative embodiments recognize and take into account one or more different considerations. The illustrative embodiments recognize and take into account that in manufacturing composite structures, plies of composite material are typically laid up on a tool. The plies may be laid up in tape, tow, or other suitable form. In some cases, resin may be infused or pre-impregnated into the fiber plies. Composite materials pre-impregnated with resin are commonly referred to as prepregs.

[0011] Various layers of prepreg may be laid up in various orientations and different numbers of layers may be used depending on the thickness of the composite structure being produced. The layers may be laid up using automated layup equipment such as a tape layup machine or fiber placement system.

[0012] In thermosetting composites, after the various layers are laid up on a tool, the composite layers are cured. Thermosetting materials are cured when exposed to temperature and / or pressure, thereby forming the final composite structure.

[0013] The illustrative embodiments recognize and take into account that for large composites, layers of the composite are laid up and cured on the same tool. The tools used in curing thermosetting composites are configured to withstand the temperatures and pressures of curing and may be referred to as "high thermal capacity tools." The illustrative embodiments recognize and take into account that high thermal capacity tools are high cost tools. The illustrative embodiments recognize and take into account that building multiple high thermal capacity tools is a large upfront investment.

[0014] The illustrative embodiments recognize and take into account that laying up composite material using automated layup equipment is time consuming. The illustrative embodiments recognize and take into account that downtime for automated layup equipment is inefficient and expensive. The illustrative embodiments recognize and take into account that laying up composite material and curing the composite material on the same high thermal mass tool can result in downtime for the automated layup equipment. The illustrative embodiments recognize and take into account that laying up composite material and curing the composite material on the same high thermal mass tool can result in reduced throughput.

[0015] Composite parts may be cured in an oven or autoclave, in which heat is applied to the part while supported on a curing tool that maintains the part's shape during the curing process. The illustrative embodiments recognize and take into account that curing composite materials using an autoclave may use at least one of an undesirable amount of time or an undesirable amount of energy.

[0016] The illustrative embodiments recognize and take into account that, while techniques have been developed for curing composite parts without the need for ovens or autoclaves, these techniques are limited to curing relatively small parts and / or require relatively complex and / or expensive tooling.

[0017] The illustrative embodiments recognize and take into account that it may be desirable to lay up and cure the composite material on two different tools. By having a dedicated layup location, downtime for automated layup equipment may be reduced.

[0018] The illustrative embodiments recognize and take into account that transferring composite material between tools may be accomplished using "pick and place" machine tools. The illustrative embodiments also recognize and take into account that for large composite layups, it may not be possible to transfer the composite layup using pick and place equipment. Transferring a large composite layup between tools would use transfer equipment that is undesirably complex and / or undesirably expensive.

[0019] The exemplary embodiments recognize and take into account that it may be desirable to utilize a lower frequency power source. The exemplary embodiments recognize and take into account that power sources providing currents having frequencies in the range of 20-100 kHz are less expensive. The exemplary embodiments recognize and take into account that power sources providing currents having frequencies less than 9 kHz are below the band regulated by the Federal Communications Commission (FCC).

[0020] The illustrative embodiments recognize and take into account that there is also a need for methods and apparatus of the type described above that are well suited for curing relatively large parts outside of an autoclave using induction heating and smart susceptors to provide precise and uniform temperature control during the curing process. The illustrative embodiments recognize and take into account that there is also a need for machine tooling to move large composite layups between a layup support and a curing tool.

[0021] Referring now back to Figure 1 , an illustration of an aircraft is depicted in accordance with an illustrative embodiment. Aircraft 100 has wings 102 and 104 attached to fuselage 106. Aircraft 100 includes engines 108 and 110 attached to wing 102 and wing 104, respectively.

[0022] The fuselage 106 has a tail section 112. A horizontal stabilizer 114, a horizontal stabilizer 116, and a vertical stabilizer 118 are attached to the tail section 112 of the fuselage 106.

[0023] Aircraft 100 is an example of an aircraft having large composite components that may be manufactured using induction heated slipsheets and methods of use. For example, portions of fuselage 106, wing 102, or wing 104 may be manufactured using exemplary embodiments of induction heated slipsheets and methods of use.

[0024] Referring now to Figure 2, a block diagram of a manufacturing environment in which an illustrative embodiment may be implemented is depicted. Manufacturing environment 200 is a manufacturing environment in which components of aircraft 100 may be manufactured. For example, fuselage 106, wing 102, or a portion of wing 104 may be manufactured using induction hardening system 202 in manufacturing environment 200.

[0025] Induction hardening system 202 includes a slipsheet 204. Slipsheet 204 includes a layup surface 206 configured to receive a composite material 208, a tool interface surface 210 configured to interact with a top surface 212 of a tool 214, a body 216 extending between layup surface 206 and tool interface surface 210, and an induction coil circuit 218 within body 216 of slipsheet 204. Induction coil circuit 218 is configured to heat layup surface 206 to a temperature sufficient to harden composite material 208.

[0026] Layup surface 206 has a shape configured to be the outer mold line of composite material 208. Layup surface 206 is formed of material 220. Layup surface 206 is formed of any desired material for laying up composite material 208. Layup surface 206 is formed of material 220 that does not undesirably interact with composite material 208. In some illustrative embodiments, composite material 208 is laid directly on layup surface 206. In other illustrative embodiments, a release layer or other layer of material is disposed between composite material 208 and layup surface 206.

[0027] The composite material 208 is cured on the slipsheet 204. The layup surface 206 is formed of a material 220 configured to withstand the curing temperatures and pressures of the composite material 208.

[0028] In some illustrative embodiments, material 220 is the same as material 222 of body 216. In these illustrative embodiments, layup surface 206 is the exterior surface of body 216.

[0029] In some illustrative embodiments, material 220 forming layup surface 206 is different from material 222 forming body 216. In these illustrative embodiments, layup surface 206 is a layer of material 220 bonded to material 222 of body 216. When material 220 is different from material 222, material 220 is present in slipsheet 204 to provide desired material properties. In some illustrative embodiments, material 220 is present to increase the service life of slipsheet 204. In some illustrative embodiments, material 220 is present to increase the durability and reduce wear of layup surface 206 from repeated use. In some illustrative embodiments, material 220 is a metal bonded to material 222 to increase the service life of slipsheet 204.

[0030] Tool interface surface 210 is configured to contact top surface 212 of tool 214. Tool interface surface 210 is a mirror image of top surface 212 of tool 214. In some illustrative embodiments, tool interface surface 210 is an exterior surface of body 216. In these illustrative embodiments, tool interface surface 210 is formed of material 222.

[0031] In other illustrative embodiments, tool interface surface 210 is formed of a material different from material 222. In some illustrative embodiments, tool interface surface 210 is formed of insulating layer 224. When present, insulating layer 224 is disposed on tool interface surface 210 to minimize heat loss to tool 214 and improve the thermal efficiency of slipsheet 204. When present, insulating layer 224 is disposed on tool interface surface 210 to reduce the transfer of heat to tool 214. When present, insulating layer 224 may include any suitable insulating material, such as, but not limited to, silicone.

[0032] Slipsheet 204 is secured to tool 214 during curing of composite material 208. Tool 214 is configured to withstand the curing temperatures and pressures of composite material 208. Tool 214 may be referred to as a "high heat capacity tool" due to its use in curing thermosetting composite materials. A high heat capacity tool will be more expensive to manufacture than a tool not manufactured to withstand the curing temperatures and pressures. For example, a tool not configured to withstand high temperatures and pressures may be formed from less expensive materials. For example, a tool not configured to withstand high temperatures and pressures may be formed using less expensive manufacturing methods.

[0033] During curing of the composite material 208, an induction coil circuit 218 within the slipsheet 204 generates heat to cure the composite material 208. The induction coil circuit 218 comprises a conductor 226 for receiving an electric current 228 and generating a magnetic field in response to the electric current 228. The induction coil circuit 218 further comprises a susceptor 230. In some exemplary embodiments, the susceptor 230 comprises a susceptor wire 232 wrapped along at least a portion of the length of the conductor 226.

[0034] The characteristics of the induction coil circuit 218 are selected based on at least one of the desired temperature for curing the composite material 208, the desired parameters for the power source 234, and the design for the body 216 of the slipsheet 204. The induction coil circuit 218 is designed to generate heat such that the layup surface 206 reaches a temperature sufficient to cure the composite material 208. The susceptor 230 is formed of a material selected to have a Curie temperature sufficient to cure the composite material 208.

[0035] The susceptor 230 may extend along the length of the conductor 226 within the body 216. Application of a current 228 to the conductor 226 generates an alternating magnetic field that is absorbed by the material from which the susceptor 230 is formed, causing the susceptor 230 to be inductively heated.

[0036] The flow of current 228 through conductor 226 results in the creation of a magnetic field that surrounds susceptor 230. Eddy currents generated within susceptor 230 as a result of exposing it to the magnetic field inductively heat it. The magnetic material from which susceptor 230 is formed preferably has a high magnetic permeability and a Curie temperature that corresponds to the desired temperature to which composite material 208 will be heated by slipsheet 204. Susceptor 230 and conductor 226 are preferably sized and configured such that at temperatures below the Curie temperature of the magnetic material, the magnetic permeability of the material causes the magnetic field to be concentrated within susceptor 230.

[0037] As a result of the susceptor 230's proximity to the conductor 226, the concentration of magnetic fields results in relatively large eddy currents within the susceptor 230. The induced eddy currents result in resistive heating of the susceptor 230. The susceptor 230 inductively heats the body 216 and the composite material 208 in thermal contact with the layup surface 206. Heating of the susceptor 230 continues during application of the current 228 until the magnetic material approaches its Curie temperature. Once the Curie temperature is reached, the susceptor 230 becomes non-magnetic, at which point the magnetic field is no longer concentrated within the susceptor 230. The induced eddy currents and associated resistive heating are reduced to a level sufficient to maintain the temperature of the susceptor 230 at the Curie temperature.

[0038] Conductors 226 may extend through body 216 in a serpentine pattern, a snake-like pattern, a circular coil configuration, or any other desired pattern. In other exemplary embodiments, conductors 226 may form portions of the warp and weft of reinforcing fibers within body 216 of slipsheet 204. Conductors 226 are connected to a power source 234 for generating electric current 228. Electric current 228 may have an amperage between about 1 ampere and about 1000 amperes at a frequency 238 between about 1 kHz and about 300 kHz and a voltage between about 10 volts and about 300 volts, although electric current may be provided at frequencies, amperages, and voltages outside of such ranges. In one exemplary embodiment, electric current 228 has a frequency 238 of 150 kHz or less. In one exemplary embodiment, electric current 228 has a frequency 238 of 100 kHz or less. In one exemplary embodiment, electric current 228 has a frequency 238 of 9 kHz or less.

[0039] The susceptor wire 232 is helically wrapped along the length of the conductor 226 or along any portion of the conductor 226. The helically wrapped susceptor wire 232 may comprise a continuous wire wrap along at least a portion of the length of the conductor 226. In some exemplary embodiments, the susceptor wire 232 is wrapped around the conductor 226 such that adjacent ones of the wraps define a gap therebetween. The gap is about 20 percent or greater of the diameter 240 of the susceptor wire 232.

[0040] The susceptor wire 232 comprises a continuous wire wrapping helically wound around at least a portion of the length of the conductor 226 and defining gaps therebetween, such that the circumferential position of each wire wrapping is spaced apart from adjacent wire wrappings at the same circumferential position. A magnetic field passes through the gaps between the wire wrappings, thereby promoting the flow of eddy currents within the susceptor wire 232. The susceptor wire 232 is composed of a magnetic material having a Curie temperature, and the susceptor wire 232 is inductively heated in response to the magnetic field.

[0041] The susceptor wire 232 is preferably electrically insulated from the conductor 226 and may be mounted substantially coaxially thereon. In some exemplary embodiments, the susceptor wire 232 may be non-coaxially mounted thereon. The susceptor wire 232 may be maintained in a fixed position relative to the conductor 226 by a matrix material (not depicted) that forms part of the induction coil circuit 218. The susceptor wire 232 may be maintained in a fixed position relative to the conductor 226 by encapsulating the susceptor wire 232 within the material 222. In some exemplary embodiments, the susceptor wire 232 is electrically insulated from the conductor 226 by the material 222 having a relatively high thermal conductivity and a relatively low electrical conductivity. The material 222 may be selected from any desired material having sufficient rigidity and the desired thermal conductivity. In some embodiments, the material 222 is a cured composite material.

[0042] The thermoset composite material 222 of the body 216 includes a thermoset resin and reinforcing fibers, which may include at least one of graphite fibers, fiberglass fibers, or any other desired reinforcing fibers.

[0043] The magnetic material from which the susceptor wire 232 may be formed may be selected from at least one of nickel, iron cobalt, molybdenum, chromium, or other desired magnetic material having a Curie temperature corresponding to the curing temperature of the composite material 208. The susceptor wire 232 may be formed as a single strand wire, as a braided wire, or in any other desired design that may be helically wrapped around the conductor 226.

[0044] Inductive coil circuit 218 is designed to fit within body 216. Inductive coil circuit 218 has a diameter 236. Diameter 236 is small enough to fit within body 216. Inductive coil circuit 218 is arranged within body 216 in any suitable manner. In some exemplary embodiments, inductive coil circuit 218 is arranged in a serpentine pattern, a snake-like pattern, a circular coil configuration, or any other arrangement that facilitates desired spacing between adjacent portions of conductor 226.

[0045] In some exemplary embodiments, the induction coil circuit 218 is designed to select desired parameters for the power supply 234. The slipsheet 204 is configured to be sufficiently rigid to carry the composite material 208. Thus, the induction coil circuit 218 may be designed regardless of the flexibility of the induction coil circuit 218. The induction coil circuit 218 may have a larger diameter, i.e., diameter 236, than a flexible heating circuit, such as the induction heating circuit 242 of the heating blanket 244.

[0046] The sizes of the components of the induction coil circuit 218, including the conductor 226 and the susceptor 230, are based on several assumptions. In some exemplary embodiments, scaling the induction coil circuit 218 is based on the following assumptions: the diameter 240 of the susceptor 230 is five times the skin depth at 20° C.; a lower frequency 238 current 228 uses an inversely proportionally higher magnetic field to generate the same power; and a higher magnetic field scales proportionally with the current 228 and the cross-sectional area of ​​the litz wire 246. The diameter 240 of the susceptor 230 directly affects the amount of heat generated by the susceptor 230 and the change in heat output at the Curie temperature of heating. A larger diameter susceptor (>20 times the skin depth) will heat very efficiently and provide the most heat because heat is based on the volume of the susceptor. However, a larger diameter will show little change in heat output with increasing temperature at the Curie point. A small diameter susceptor (<2 skin depth) will have a strong change in heating at the Curie point but will output very little heat because the volume of susceptor material is smaller. Five skin depths may provide a balance between the change in heating at the Curie point and providing enough heat to raise the temperature when the part acts as a heat sink. In some other exemplary embodiments, the various ratios for diameter 240 may be different.

[0047] The materials and sizes of the components of the induction coil circuit 218 are selected based on at least one of the temperature desired to cure the composite material 208, the dimensions of the body 216, and the current 228 to be supplied. In some exemplary embodiments, the conductors 226 are selected to use a power source 234 that has at least one of lower cost or less regulation. For example, the diameter 248 and material of the conductors 226 may be selected to utilize a power source 234 that provides a current 228 having a frequency of 150 kHz or less. In some exemplary embodiments, the diameter 248 and material of the conductors 226 may be selected to utilize a power source 234 that provides a current 228 having a frequency of 100 kHz or less. By utilizing a power source that provides a current having a frequency of 100 kHz or less, the cost of the power source 234 may be reduced. In some exemplary embodiments, the diameter and material of the conductors 226 may be selected to utilize a power source 234 that provides a current having a frequency of 9 kHz or less. A power source that provides a current having a frequency of 9 kHz or less may have less regulation. In some example embodiments, the power source 234 coupled to the induction coil circuit 218 is selected based on the diameter 236 of the induction coil circuit 218 .

[0048] In some exemplary embodiments, conductor 226 takes the form of a litz wire 246. In some exemplary embodiments, a diameter 248 of litz wire 246 is selected to establish desired characteristics for power supply 234. In some exemplary embodiments, a diameter 248 of litz wire 246 is selected so that power supply 234 is a lower cost power supply having a frequency 238 in the range of 20-100 kHz. In some exemplary embodiments, litz wire 246 has a diameter 240 of approximately 0.111 inches. In some exemplary embodiments, a diameter 248 of litz wire 246 is selected so that power supply 234 is an unregulated power supply having a frequency 238 of less than 9 kHz. In some exemplary embodiments, litz wire 246 has a diameter 240 of approximately 0.235 inches.

[0049] In some exemplary embodiments, the diameter 240 of the susceptor wire 232 is selected to establish desired characteristics for the power source 234. In some exemplary embodiments, the diameter 240 of the susceptor wire 232 is selected so that the power source 234 is a lower cost power source having a frequency 238 in the range of 20-100 kHz. In some exemplary embodiments, the susceptor wire 232 has a diameter in the range of 0.03 to 0.07 inches. In some exemplary embodiments, the diameter 240 of the susceptor wire 232 is selected so that the power source 234 is an unregulated power source having a frequency 238 of less than 9 kHz. In some exemplary embodiments, the susceptor wire 232 has a diameter greater than 0.05 inches.

[0050] The slipsheet 204 includes a rigid body 250 extending between the layup surface 206 and the tool interface surface 210. The rigid body 250 is configured to support the composite material 208 during transport. The induction coil circuit 218 is within the rigid body 250 of the slipsheet 204. The induction coil circuit 218 is configured to heat the layup surface 206 to a temperature sufficient to cure the composite material 208. The induction coil circuit 218 has a diameter 236 selected to generate heat using a power source 234 having a frequency less than 150 kHz. The power source 234 is coupled to the induction coil circuit 218. The power source 234 is selected based on the diameter 236 of the induction coil circuit 218.

[0051] In some illustrative embodiments, slipsheet 204 further includes an insulating layer 224 connected to rigid body 250 of slipsheet 204. In these illustrative embodiments, insulating layer 224 forms tool interface surface 210.

[0052] In some illustrative embodiments, induction hardening system 202 further comprises a number of rigid cowls 252. The number of rigid cowls 252 can be used to form an inner mold line of composite material 208. When present, the number of rigid cowls 252 are used to form a second side of composite material 208 opposite a first side of composite material 208 formed on layup surface 206. In these illustrative embodiments, composite material is disposed between layup surface 206 and the number of rigid cowls 252. As used herein, "number" when used in reference to items means one or more items. Thus, the number of rigid cowls 252 includes one or more rigid cowls.

[0053] As depicted, some rigid cowls 252 include rigid cowls 254. Rigid cowls 254 include cowl induction coil circuits 256 within a rigid body of rigid cowls 254. In this illustrative embodiment, cowl induction coil circuits 256 are configured to heat rigid cowls 254. In some illustrative embodiments, rigid cowls 254 use cowl induction coil circuits 256 to heat composite material 208 during curing of composite material 208. In some illustrative embodiments, curing composite material 208 includes heating via induction coil circuits 218 and cowl induction coil circuits 256.

[0054] In some illustrative examples, induction hardening system 202 includes a heating blanket 244 that conforms to composite material 208. Heating blanket 244 includes an induction heating circuit 242. Induction heating circuit 242 is flexible so as to conform to composite material 208. Sizing of the components of induction heating circuit 242 is based on the desired flexibility of induction heating circuit 242 and heating blanket 244.

[0055] In some illustrative embodiments, cowl induction coil circuit 256 is configured to utilize power source 234. The rigidity of rigid cowl 254 allows cowl induction coil circuit 256 to have a larger diameter than induction heating circuit 242. In some illustrative embodiments, cowl induction coil circuit 256 is configured to utilize a power source configured to provide a current having a lower frequency than power source 258 configured to provide a current having frequency 260 to induction heating circuit 242.

[0056] The flexibility of the induction heating circuit 242 limits the frequency 260 of the power source 258. In some exemplary embodiments, the frequency 238 of the current 228 provided by the power source 234 is lower than the frequency 260 of the current provided by the power source 258.

[0057] To lay up composite material 208, slipsheet 204 initially resides on layup support 262. Composite material 208 is laid up on layup surface 206 by any desired automated composite layup tool. After composite material 208 is laid up on layup surface 206, slipsheet 204 is removed from layup support 262.

[0058] In some illustrative embodiments, several rigid cowls 252 are placed on the composite material 208 before removing the slipsheet 204 from the layup support 262. In other illustrative embodiments, several rigid cowls 252 are placed on the composite material 208 after the slipsheet 204 holding the composite material 208 is transferred from the layup support 262.

[0059] In some illustrative embodiments, the heating blanket 244 is placed over the composite material 208 before the slipsheet 204 is removed from the layup support 262. In other illustrative embodiments, the heating blanket 244 is placed over the composite material 208 after the slipsheet 204 holding the composite material 208 is transferred from the layup support 262.

[0060] The slipsheet 204, supporting the composite material 208, is then placed in contact with the tool 214 and secured to the tool 214. The slipsheet 204 may be secured to the tool 214 in any desired manner. In some exemplary embodiments, the slipsheet 204 is secured to the tool 214 using a mechanical system. In some other exemplary embodiments, the tool 214 further comprises a vacuum system 264 configured to hold the slipsheet 204 against the top surface 212 of the tool 214. The vacuum system 264 may include holes, channels, or any other desired type of vacuum distribution system within the tool 214.

[0061] If several rigid cowls 252 are present, several rigid cowls 252 are placed on the composite material 208 before curing the composite material 208. If a heating blanket 244 is present, the heating blanket 244 is placed on the composite material 208 before curing the composite material 208.

[0062] After securing slipsheet 204 to tool 214, an electric current 228 is provided to induction coil circuit 218. Induction coil circuit 218 includes a conductor 226 for receiving electric current 228 and generating a magnetic field in response to current 228. A susceptor wire 232, helically wrapped along a portion of the length of conductor 226, is inductively heated in response to the magnetic field.

[0063] The induction curing system 202 can be used to cure the composite material 208 without the need for an oven, autoclave, or similar large heated enclosure. In some exemplary embodiments, the induction curing system 202 is used within a pressure vessel 266. In other exemplary embodiments, the induction curing system 202 is used in conjunction with a vacuum bagging system.

[0064] The composite material 208 is then rapidly heated to a cure step while gas pressure is applied, as determined by an appropriate cure kinetics model. A smart susceptor, or susceptor 230, provides thermal leveling at a pre-specified cure temperature. While the susceptor 230 continues to drive the temperature of the slipsheet 204 to the desired cure temperature, a gentle circulation of a gaseous pressurized medium at ambient temperature within the cure vessel, or pressure vessel 266, sweeps away any exothermic heat generated during cure.

[0065] Once the desired state of cure is achieved in the composite material 208, the resulting composite part can be cooled rapidly because the body of the tool 214 is not heated and the gas in the pressure vessel 266 is at ambient temperature. The composite part formed from the composite material 208 and slipsheet 204 is then removed from the pressure vessel 266, and the part is then debagged and sent for inspection and trimming.

[0066] Induction curing system 202 generally includes a slipsheet 204 supported on tool 214, several rigid cowls 252, and a heating blanket 244. In the illustrated embodiment, composite material 208 may be substantially flat or may have one or more curves or undulations. Composite material 208 may include, for example, without limitation, stacked plies of fiber-reinforced polymer resin, such as, without limitation, carbon fiber epoxy, or other thermosetting resin that must be heated to a preselected temperature to achieve cure.

[0067] The induction curing system 202 may include one or more thermal sensors. One or more sensors, such as sensor 268, may be included to sense the temperature of at least one of the heating blanket 244, the slipsheet 204, the number of rigid cowls 252, or the composite material 208.

[0068] One or more controllers may be included within induction hardening system 202 to control the operation of each induction heating component of induction heating elements 270. For example, controller 272 may adjust the frequency 238 of the current 228 applied to induction coil circuit 218 as a means to vary or control the rate of heating of susceptor 230, and thereby control the rate of heating of composite material 208. While a single controller, i.e., controller 272, may be provided to regulate the operation of induction heating components 270, each induction heating component may have a dedicated controller.

[0069] The example of induction hardening system 202 in Figure 2 is not meant to impose physical or architectural limitations on the manner in which an illustrative embodiment may be implemented. Other components in addition to or in place of the components shown may be used. Some components may not be required. Furthermore, blocks are presented to illustrate some functional components. When implemented in an illustrative embodiment, one or more of these blocks may be combined, divided, or combined and divided into different blocks.

[0070] In some exemplary embodiments, some rigid cowls 252 include varying amounts of rigid cowls. In some exemplary embodiments, some rigid cowls 252 include two or more rigid cowls. In some exemplary embodiments, at least one rigid cowl of some rigid cowls 252 does not include an induction coil circuit. In some exemplary embodiments, some rigid cowls 252 do not provide heat to cure composite material 208.

[0071] In some illustrative embodiments, some rigid cowls 252 are optional. In these illustrative embodiments, heating blanket 244 may be placed directly on composite material 208.

[0072] 2 , a vacuum bag assembly may be placed over the heating blanket 244. The vacuum bag assembly may include a bagging film that covers the heating blanket 244 and may be sealed to one of the layup surface 206 of the slipsheet 204 or the top surface 212 of the tool 214. A vacuum probe and vacuum gauge may extend from the bagging film to a vacuum generator to provide a means for drawing a vacuum on the bagging film for application of pressure and to draw out volatiles and other gases that may be generated as a result of heating the uncured composite material 208. Drawing a vacuum on the bagging film may be performed to consolidate the composite material 208 against the slipsheet 204 during the curing process.

[0073] Although slipsheet 204 is depicted as having induction coil circuits 218, slipsheet 204 may have any desired amount of induction coil circuits. In some exemplary embodiments, slipsheet 204 may have multiple induction coil circuits with different Curie temperatures. In some exemplary embodiments, slipsheet 204 may have independently controlled induction coil circuits for locally heating composite material 208 on slipsheet 204.

[0074] In some exemplary embodiments, slipsheet 204 includes a second induction coil circuit. In these exemplary embodiments, induction coil circuit 218 includes conductor 226 and susceptor wire 232 having a first Curie temperature, and the second induction coil circuit includes a second conductor and a second susceptor wire having a second Curie temperature. In these exemplary embodiments, the first Curie temperature is different from the second Curie temperature. In some exemplary embodiments, the first Curie temperature is a cure temperature and the second Curie temperature is a lay-up temperature.

[0075] Referring now back to Figure 3, a composite part within an induction hardening system is depicted in accordance with an exemplary embodiment. Induction hardening system 300 is one physical implementation of induction hardening system 202 of Figure 2. Induction hardening system 300 includes slipsheet 302, tool 304, several rigid cowls 306, and heating blanket 308. Slipsheet 302 is one physical implementation of slipsheet 204 of Figure 2. Tool 304 is one physical implementation of tool 214 of Figure 2. Several rigid cowls 306 are one physical implementation of several rigid cowls 252 of Figure 2. Heating blanket 308 is one physical implementation of heating blanket 244 of Figure 2.

[0076] As depicted, the number of rigid cowls 306 includes rigid cowl 310, rigid cowl 312, rigid cowl 314, and rigid cowl 316. As depicted, each of the number of rigid cowls 306 includes at least one respective induction circuit. Each of the number of rigid cowls 306 may be inductively heated by at least one induction circuit present within the respective rigid cowl. The number of rigid cowls 306 may be referred to as a number of inductively heated rigid cowls.

[0077] Composite material 318 is placed on slipsheet 302. Composite material 318 is laid up on layup surface 320 of slipsheet 302. Composite material 318 is cured on layup surface 320 of slipsheet 302. During curing of composite material 318, slipsheet 302 is inductively heated to cure composite material 318 on layup surface 320.

[0078] Heating blanket 308 is flexible and conforms to composite material 318. Due to the flexible and conforming nature of heating blanket 308, its periphery leans over the outer edge of composite material 318, effectively sealing it to slipsheet 302 substantially completely around composite material 318 to thermally close composite material 318. During curing, slipsheet 302 and heating blanket 308 are each inductively heated to heat composite material 318 from both sides of composite material 318.

[0079] During curing of the composite material 318, the heating blanket 308 is inductively heated to cure the composite material 318. In some exemplary embodiments, the power supply for the heating blanket 308 is different from the power supply for inductively heating the slip-sheet 302. The heating blanket 308 includes a flexible induction coil circuit. The diameter of the induction coil circuit affects the flexibility of the heating blanket 308. The diameter of the conductor, the diameter of the susceptor, and the distance between the conductor and the susceptor affect the diameter of the induction coil circuit. The diameter of the induction coil circuit in the heating blanket 308 is small enough to allow the desired flexibility of the heating blanket 308. The diameter of the induction coil circuit affects the characteristics of the power supply for supplying current to the induction coil circuit of the heating blanket 308.

[0080] Slipsheet 302 is sufficiently rigid to maintain an outer mold line for composite material 318. In some exemplary embodiments, slipsheet 302 is sufficiently rigid to transport composite material 318 to tool 304.

[0081] The induction coil circuit of the slip sheet 302 does not have a size limitation to meet the desired flexibility. The induction coil circuit of the slip sheet 302 can be designed to have a larger diameter than the induction coil circuit of the heating blanket 308. The larger diameter of the induction coil circuit can change the characteristics of the power source for delivering current to the induction coil circuit. A larger diameter induction coil circuit can utilize a lower frequency power source.

[0082] In some exemplary embodiments, the heating blanket 308 and the slipsheet 302 use different power sources with different characteristics. In some exemplary embodiments, each of the several rigid cowls 306 utilizes the same power source. In some exemplary embodiments, each of the several rigid cowls 306 utilizes the same power source as either the power source for heating the heating blanket 308 or the power source for the slipsheet 302.

[0083] The example induction hardening system 300 in Figure 3 is not intended to impose physical or architectural limitations on the manner in which an illustrative embodiment may be implemented. Other components in addition to or in place of the components shown may be used. Some components may not be required. Furthermore, blocks are presented to illustrate some functional components. When implemented in an illustrative embodiment, one or more of these blocks may be combined, divided, or combined and divided into different blocks.

[0084] In some illustrative embodiments, some rigid cowls 306 are optional. In these illustrative embodiments, heating blanket 308 may be placed directly on composite material 318.

[0085] In some illustrative embodiments, at least one of the number of rigid cowls 306 does not include a respective induction coil circuit, ie, at least one of the number of rigid cowls 306 does not provide heat to cure the composite material 318.

[0086] Referring now back to Figure 4, an example of an induction hardening system is depicted in accordance with an exemplary embodiment. In view 400, induction hardening system 402 includes slipsheet 404 and tool 406. Slipsheet 404 is one physical implementation of slipsheet 204 from Figure 2. Tool 406 is one physical implementation of tool 214 from Figure 2.

[0087] In some exemplary embodiments, slipsheet 404 is the same as slipsheet 302 in Figure 3. In some exemplary embodiments, tool 406 is the same as tool 304 in Figure 3.

[0088] Slipsheet 404 has a layup surface 408 configured to receive a composite material (not depicted). Layup surface 408 is configured to form outer mold line (OML) tooling for the composite material (not depicted). Slipsheet 404 is sufficiently rigid to support the composite material as it is transported to tool 406.

[0089] The tool 406 has an upper surface 410 configured to receive the slipsheet 404. The upper surface 410 is configured to interact with a tool interface surface 412 of the slipsheet 404.

[0090] Tool 406 may be referred to as high heat capacity tooling. Tool 406 is formed from a material configured to withstand the curing temperatures of the composite material. In some exemplary embodiments, tool 406 is also formed from a material configured to withstand increased pressure. In some exemplary embodiments, tool 406 is formed from at least one of a composite material or a metal.

[0091] Slipsheet 404 is one non-limiting example of a slipsheet that may be used with tool 406. Slipsheets of various designs may be used with tool 406. Each slipsheet may have a layup surface configured to form an exterior mold line for a respective composite structure. Each slipsheet will have a tool interface surface configured to interact with top surface 410 of tool 406. Each slipsheet may have a desired amount of induction coil circuitry configured to cure the composite material on its respective layup surface. By utilizing removable slipsheets, changes to the composite structure may be made without fabricating another expensive, high-thermal-capacity tool. Fabricating another slipsheet may be less expensive than creating another high-thermal-capacity tool.

[0092] Referring now back to FIG. 5, a cross-sectional view of a slipsheet of an induction hardening system is depicted, according to one exemplary embodiment. View 500 is a cross-section through the slipsheet, namely slipsheet 502. Slipsheet 502 is one physical implementation of slipsheet 204 of FIG. 2. In some exemplary embodiments, slipsheet 502 is the same as slipsheet 302 of FIG. 3. In some exemplary embodiments, view 500 of slipsheet 502 is a cross-section through slipsheet 404 of FIG. 4.

[0093] Slipsheet 502 includes a layup surface 504 configured to receive a composite material (not shown), a tool interface surface 506 configured to interact with an upper surface of a tool, a body 508 extending between layup surface 504 and tool interface surface 506, and an induction coil circuit 510 within body 508 of slipsheet 502.

[0094] The induction coil circuit 510 is configured to heat the layup surface 504 to a temperature sufficient to cure the composite material (not shown). The induction coil circuit 510 includes a conductor 512 for receiving an electric current and generating a magnetic field in response to the electric current. The induction coil circuit 510 also includes a susceptor wire 514 wrapped along at least a portion of the length of the conductor 512.

[0095] The material and size of the conductor 512 are selected based on at least one of the temperature desired to cure the composite material, the dimensions of the body 508, and the current to be supplied. In some exemplary embodiments, the conductor 512 is selected to use a power source with at least one of lower cost and less regulation. For example, the diameter and material of the conductor 512 may be selected to utilize a power source that provides a current having a frequency of 150 kHz or less. In some exemplary embodiments, the diameter and material of the conductor 512 may be selected to utilize a power source that provides a current having a frequency of 100 kHz or less. By utilizing a power source that provides a current having a frequency of 100 kHz or less, the cost of the power source may be reduced. In some exemplary embodiments, the diameter and material of the conductor 512 may be selected to utilize a power source that provides a current having a frequency of 9 kHz or less. A power source that provides a current having a frequency of 9 kHz or less may have less regulation.

[0096] Increasing the diameter of conductor 512 reduces the frequency of the current to generate magnetic current in conductor 512. However, increasing the diameter of conductor 512 also reduces the flexibility of conductor 512. In this exemplary embodiment, induction coil circuit 510 resides within slipsheet 502. Slipsheet 502 is configured to be rigid enough to provide an exterior mold line for the composite material on layup surface 504. Thus, conductor 512 and induction coil circuit 510 can be increased in size without regard to flexibility.

[0097] Increasing the diameter of the conductor 512 also increases the diameter of the induction coil circuit 510. In some exemplary embodiments, the diameter of the induction coil circuit 510 is 0.18 inches or greater. A diameter of the induction coil circuit 510 of 0.18 inches or greater allows for a lower cost power source to provide current to the induction coil circuit 510. In some exemplary embodiments, the diameter of the induction coil circuit 510 is 0.38 inches or greater. A diameter of the induction coil circuit 510 of 0.38 inches or greater allows for a power source below the Federal Communications Commission (FCC) band (9 kHz) to provide current to the induction coil circuit 510. In some exemplary embodiments, the induction coil circuit 510 has a diameter selected to generate heat using a power source having a frequency less than 150 kHz. In some exemplary embodiments, the induction coil circuit 510 has a diameter selected to generate heat using a power source having a frequency less than 100 kHz. In some exemplary embodiments, the induction coil circuit 510 has a diameter selected to generate heat using a power source having a frequency in the range of 20 kHz to 100 kHz. In some exemplary embodiments, the induction coil circuit 510 has a diameter selected to generate heat using a power source having a frequency less than 9 kHz.

[0098] When the diameter of the conductor 512 is increased, the diameter of the susceptor wire 514 is also increased. In some exemplary embodiments, the susceptor wire 514 has a diameter greater than 0.03 inches. In some exemplary embodiments, when the susceptor wire 514 has a diameter greater than 0.03 inches, a lower cost power supply can be used to provide current to the induction coil circuit 510. In some exemplary embodiments, the susceptor wire 514 has a diameter greater than 0.05 inches. In some exemplary embodiments, the susceptor wire 514 has a diameter greater than 0.07 inches. In some exemplary embodiments, when the susceptor wire 514 has a diameter greater than 0.07 inches, a power supply below the Federal Communications Commission (FCC) regulated band (9 kHz) can be used to provide current to the induction coil circuit 510.

[0099] In some illustrative examples, body 508 is referred to as a rigid body. In these illustrative examples, body 508 is configured to support the composite material during transport. In these illustrative examples, body 508 is formed of a material that forms a rigid body configured to support the composite material during transport, and has a thickness sufficient to form the rigid body. Body 508 is formed of a thermosetting composite material. The thermosetting composite material of body 508 includes a thermosetting resin and reinforcing fibers. The reinforcing fibers may include at least one of graphite fibers, fiberglass fibers, or any other desired reinforcing fibers.

[0100] As depicted, slipsheet 502 further includes a metal layer 516 connected to body 508 of slipsheet 502. In this illustrative example, metal layer 516 forms layup surface 504. The material for metal layer 516 is selected such that metal layer 516 increases the resistance of layup surface 504. Metal layer 516 is configured such that the resistance of metal layer 516 is greater than the resistance of body 508 that the composite material forms.

[0101] As depicted, slipsheet 502 further includes an insulating layer 518 connected to body 508 of slipsheet 502. In this illustrative example, insulating layer 518 forms tool interface surface 506. Insulating layer 224 forms tool interface surface 210 to minimize heat loss to tool 214 and improve the thermal efficiency of slipsheet 204. Insulating layer 224 forms tool interface surface 210 to reduce the transfer of heat to tool 214. Insulating layer 224 may include any suitable insulating material, such as, but not limited to, silicone.

[0102] The example of sleep seat 502 in Figure 5 is not intended to impose physical or architectural limitations on the manner in which an exemplary embodiment may be implemented. Other components in addition to or in place of the components shown may be used. Some components may not be required. Furthermore, blocks are presented to illustrate some functional components. When implemented in an exemplary embodiment, one or more of these blocks may be combined, divided, or combined and divided into different blocks.

[0103] For example, metal layer 516 is optional. In some illustrative embodiments, metal layer 516 is not present. In other illustrative embodiments, layup surface 504 is formed by body 508. In other illustrative embodiments, layup surface 504 is a coating applied to body 508 to provide at least one of enhanced durability.

[0104] As another example, insulating layer 518 is optional. In some illustrative embodiments, insulating layer 518 is not present. In other illustrative embodiments, tool interface surface 506 is formed by body 508.

[0105] As yet another example, the induction coil circuit 510 can instead be formed within a woven smart susceptor system. In some non-illustrated exemplary embodiments, the smart susceptor system can be warp and weft threads within the composite material of the body 508.

[0106] Referring now back to FIG. 6, a cross-sectional view of a slipsheet of an induction hardening system is depicted, according to one exemplary embodiment. View 600 is a cross-sectional view through the slipsheet, namely, slipsheet 602. Slipsheet 602 is one physical implementation of slipsheet 204 of FIG. 2. In some exemplary embodiments, slipsheet 602 is the same as slipsheet 302 of FIG. 3. In some exemplary embodiments, view 600 of slipsheet 602 is a cross-sectional view of slipsheet 404 of FIG. 4.

[0107] Slipsheet 602 is similar to slipsheet 502 of Figure 5, but has two different types of induction coil circuits. By providing two different induction coil circuits, slipsheet 602 is configured to heat to two different temperatures.

[0108] The slipsheet 602 comprises a layup surface 604 configured to receive a composite material (not shown), a tool interface surface 606 configured to interact with an upper surface of a tool, a body 608 extending between the layup surface 604 and the tool interface surface 606, a first induction coil circuit 610 within the body 608 of the slipsheet 602, and a second induction coil circuit 611 within the body 608 of the slipsheet 602.

[0109] The first induction coil circuit 610 is configured to heat the layup surface 604 to a temperature sufficient to cure the composite material (not shown). The first induction coil circuit 610 includes a conductor 612 for receiving an electric current from a first power source and generating a magnetic field in response to the electric current. The first induction coil circuit 610 also includes a susceptor wire 614 wound along at least a portion of the length of the conductor 612.

[0110] The material and size of conductor 612 is selected based on at least one of the temperature desired to cure the composite material, the dimensions of body 608, and the current to be supplied. In some example embodiments, conductor 612 is selected to use a first power source that has at least one of lower cost or fewer regulations.

[0111] The second induction coil circuit 611 is configured to heat the layup surface 604 to a layup temperature for the composite material (not shown). In some illustrative embodiments, the second induction coil circuit 611 is configured to receive current from a second power source separate from the first power source. In some illustrative embodiments, the second induction coil circuit 611 is configured to receive current from the first power source. The second induction coil circuit 611 enables operation of the slipsheet 204 as a heated platform for layup of the composite material 208. The second induction coil circuit 611 comprises a conductor 613 for receiving current from the power source and generating a magnetic field in response to the current. The second induction coil circuit 611 also comprises a susceptor wire 615 wrapped along at least a portion of the length of the conductor 613.

[0112] The material and size of each component of the second induction coil circuit 611 may be selected based on the considerations discussed in connection with the first induction coil circuit 610. For example, the selection of the size and type of conductor 613 may take into account at least one of the temperature desired to heat the composite layup slipsheet 602, the dimensions of the body 608, and the current to be supplied.

[0113] In some illustrative examples, body 608 is referred to as a rigid body. In these illustrative examples, body 608 is configured to support the composite material during transport. In these illustrative examples, body 608 is formed of a material that forms a rigid body configured to support the composite material during transport, and has a thickness sufficient to form the rigid body. Body 608 is formed of a thermosetting composite material. The thermosetting composite material of body 608 includes a thermosetting resin and reinforcing fibers. The reinforcing fibers may include at least one of graphite fibers, fiberglass fibers, or any other desired reinforcing fibers.

[0114] As depicted, slipsheet 602 further includes a metal layer 616 connected to body 608 of slipsheet 602. In this illustrative example, metal layer 616 forms layup surface 604. The material for metal layer 616 is selected such that metal layer 616 increases the durability of layup surface 604. Metal layer 616 is configured such that the durability of metal layer 616 is greater than the durability of body 608, which the composite material forms. As depicted, tool interface surface 606 of slipsheet 602 is formed by body 608 of slipsheet 602.

[0115] The example of sleep seat 602 in Figure 6 is not intended to impose physical or architectural limitations on the manner in which an illustrative embodiment may be implemented. Other components in addition to or in place of the components shown may be used. Some components may not be required. Furthermore, blocks are presented to illustrate some functional components. When implemented in an illustrative embodiment, one or more of these blocks may be combined, divided, or combined and divided into different blocks.

[0116] For example, metal layer 616 is optional. In some illustrative embodiments, metal layer 616 is not present. In other illustrative embodiments, layup surface 604 is formed by body 608. In other illustrative embodiments, layup surface 604 is a coating applied to body 608 to provide at least one of enhanced durability.

[0117] As another example, an insulating layer may be added, hi some exemplary embodiments, the insulating layer forms the tool interface surface 606.

[0118] As yet another example, the first induction coil circuit 610 and the second induction coil circuit 611 may be positioned differently within the body 608 than as depicted. In one non-depicted example embodiment, the second induction coil circuit 611 may be positioned above the first induction coil circuit 610.

[0119] In some exemplary embodiments, the induction coil circuit 610 and the second induction coil circuit 611 have different Curie temperatures. In some exemplary embodiments, the second induction coil circuit 611 includes a second conductor, i.e., conductor 613, and a second susceptor wire, i.e., susceptor wire 615. The susceptor wire 615 has a second Curie temperature. In this case, the first Curie temperature of the susceptor wire 614 is different from the second Curie temperature. In some exemplary embodiments, the first Curie temperature is a curing temperature and the second Curie temperature is a lay-up temperature.

[0120] 7-11 present an illustrative example of laying up, transferring, and curing a composite material on a slipsheet 702, i.e., composite material 706. Referring now back to FIG. 7, a cross-sectional view of a composite material laid up on a slipsheet on a layup support is depicted according to an illustrative embodiment. In view 700, slipsheet 702 is positioned on layup support 704 to receive composite material 706. Automated laminating equipment 708 lays composite material 706 onto layup surface 710 of slipsheet 702. Layup surface 710 of slipsheet 702 acts as an outer mold line for composite material 706.

[0121] Slipsheet 702 is one physical embodiment of slipsheet 204 in Figure 2. Composite material 706 is one physical embodiment of composite material 208 in Figure 2. Layup support 704 is one physical embodiment of layup support 262. In some illustrative examples, layup support 704 is not a "high thermal mass tool." When layup support 704 is not a "high thermal mass tool," layup support 704 has a lower cost than a curing tool.

[0122] 8, an illustration of a cross-sectional view of removing a composite material on a slipsheet from a layup support is depicted in accordance with an illustrative embodiment. In view 800, slipsheet 702 is being removed from layup support 704.

[0123] As can be seen in view 800, slipsheet 702 is stiff enough to support composite material 706. Layup surface 710 of slipsheet 702 maintains its shape during transport of composite material 706. The shape of composite material 706 is maintained during transport of composite material 706.

[0124] By removing slip sheet 702 after laying composite material 706 but before curing composite material 706, layup support 704 is available to accept another slip sheet. By removing slip sheet 702 when layup of composite material 706 is complete, downtime of automated layup equipment 708 is reduced. By removing slip sheet 702 when layup of composite material 706 is complete, the efficiency of automated layup equipment 708 is increased. By removing slip sheet 702 when layup of composite material 706 is complete, the throughput of the manufacturing system is increased. The volume of composite parts produced over time will be increased by reducing downtime of automated layup equipment 708.

[0125] Referring now back to FIG. 9 , a cross-sectional view of removing a composite material on a slipsheet from a layup support is depicted in accordance with an illustrative embodiment. In view 900, slipsheet 702, carrying composite material 706, is lowered onto tool 902. Tool 902 is a curing tool. Tool 902 is a "high heat capacity tool." Slipsheet 702 is lowered until a tool interface surface 904 of slipsheet 702 contacts a top surface 906 of tool 902. After interface surface 904 of slipsheet 702 contacts top surface 906 of tool 902, slipsheet 702 is secured to tool 902.

[0126] 10, an illustration of a cross-sectional view of placing a rigid cowl in an induction hardening system is depicted in accordance with an illustrative embodiment. In view 1000, slipsheet 702 is secured to tool 902.

[0127] In view 1000, several rigid cowls 1002 are positioned on composite material 706. The several rigid cowls 1002 are one physical implementation of the several rigid cowls 252 of FIG. 2. As depicted, the several rigid cowls 1002 include rigid cowl 1004, rigid cowl 1006, rigid cowl 1008, and rigid cowl 1010. As depicted, each of the several rigid cowls 1002 includes at least one respective induction circuit. Each of the several rigid cowls 1002 may be inductively heated by the at least one induction circuit present within the respective rigid cowl. The several rigid cowls 1002 may be referred to as several inductively heated rigid cowls.

[0128] 11 , a cross-sectional view of placing a heated blanket within an induction hardening system is depicted in accordance with an exemplary embodiment. In view 1100, heating components of induction hardening system 1102 are positioned. In view 1100, induction hardening system 1102 includes slipsheet 702, several rigid cowls 1002, and a heating blanket 1104. Heating blanket 1104 overlies and is in thermal contact with a second side of composite material 706. Several rigid cowls 1002 also contact the second side of composite material 706. An outer edge of heating blanket 1104 extends outward beyond the edge of composite material 706 and overlaps a portion of layup surface 710 of slipsheet 702.

[0129] The example components of induction hardening system 1102 in Figures 7-11 are not meant to impose physical or architectural limitations on the manner in which an illustrative embodiment may be implemented. Other components in addition to or in place of the components shown may be used. Some components may not be required. Furthermore, blocks are presented to illustrate some functional components. When implemented in an illustrative embodiment, one or more of these blocks may be combined, divided, or combined and divided into different blocks.

[0130] For example, the size, shape, curvature, location, amount of reinforcement, and shape of reinforcement within composite material 706 are not limited to those depicted in composite material 706. Composite material 706 can have any desired size, shape, and curvature of reinforcement, and any desired location, amount, and shape.

[0131] 10 and 11 , several rigid cowls 1002 and heating blankets 1104 are placed on composite material 706 while slip-sheet 702 is on tool 902. In other illustrative embodiments, several rigid cowls 1002 or at least one of heating blankets 1104 are placed on composite material 706 before slip-sheet 702 is placed on tool 902. In some illustrative embodiments, several rigid cowls 1002 are placed on composite material 706 before slip-sheet 702 is removed from lay-up support 704. In some illustrative embodiments, heating blankets 1104 are placed on composite material 706 before slip-sheet 702 is removed from lay-up support 704.

[0132] In some exemplary embodiments, slipsheet 702 is transported to an intermediate tool between layup support 704 and tool 902. In some exemplary embodiments, while slipsheet 702 is on the intermediate tool, at least one of several rigid cowls 1002 or heating blankets 1104 is placed on composite material 706 before placing slipsheet 702 on tool 902. In some exemplary embodiments, several rigid cowls 1002 are placed on composite material 706 while slipsheet 702 is on the intermediate tool. In some exemplary embodiments, heating blanket 1104 is placed on composite material 706 while slipsheet 702 is on the intermediate tool.

[0133] In other illustrative embodiments, the heating blanket 1104 may extend over the slipsheet 702 and may overlap a portion of the tool 902. In some illustrative embodiments, at least one of the rigid cowl 1002 or the heating blanket 1104 is optional.

[0134] Referring now back to FIG. 12 , a flowchart of a method for forming a composite part is depicted in accordance with an illustrative embodiment. Method 1200 may be performed to manufacture a composite part for aircraft 100 of FIG. 1 . Method 1200 may be performed using components of induction hardening system 202 of FIG. 2 . Method 1200 may be performed using components of induction hardening system 300 of FIG. 3 . Method 1200 may be performed using components of induction hardening system 402 of FIG. 4 . Method 1200 may be performed using slipsheet 502 of FIG. 5 . Method 1200 may be performed using slipsheet 602 of FIG. 6 . Method 1200 may be performed using induction hardening system 1102 shown in FIGS. 7-11 . Method 1200 may be performed as described with respect to FIGS. 7-11 .

[0135] The method 1200 lays up a composite material on a layup surface of a slipsheet disposed on a layup support (operation 1202). The layup surface of the slipsheet is formed from at least one of the material of the body of the slipsheet or an additional material connected to the body of the slipsheet. In some exemplary embodiments, the layup surface of the slipsheet is a metal layer connected to the body of the slipsheet. In some exemplary embodiments, the layup surface is a coating applied to the body of the slipsheet. In some exemplary embodiments, the layup surface of the slipsheet is formed from the composite material of the body of the slipsheet.

[0136] The method 1200 transports the composite material laid up on a transfer slipsheet to a tool (operation 1204), where the slipsheet comprises a rigid body configured to support the composite material during transport, the slipsheet being stiff enough to maintain the shape of the composite material as it is transported.

[0137] Method 1200 secures the slipsheet to the tool (operation 1206) such that the tool interface surface of the slipsheet contacts the top surface of the tool. The tool interface surface is formed from at least one of the material of the body of the slipsheet or an additional material connected to the body of the slipsheet. In some exemplary embodiments, the tool interface surface of the slipsheet is formed from an insulating layer. In some exemplary embodiments, the tool interface surface is formed from the composite material of the body of the slipsheet.

[0138] Method 1200 cures the composite material on the slipsheet while the slipsheet is secured to the tool using heat generated by an induction coil circuit within the rigid body of the slipsheet (operation 1208). The induction coil circuit within the rigid body uses an electric current to generate heat. More specifically, a conductor generates a magnetic field in response to the electric current, and a susceptor generates heat in response to the magnetic field. Method 1200 may then end.

[0139] In some illustrative examples, method 1200 positions a number of rigid cowls over the composite material before curing the composite material (OPERATION 1212). In some illustrative examples, after performing OPERATION 1212, curing the composite material includes heating the composite material using heat generated by a number of induction coil circuits in the number of rigid cowls (OPERATION 1214).

[0140] In some illustrative embodiments, method 1200 places a heating blanket over the composite material and the number of rigid cowls (OPERATION 1216). In some illustrative embodiments, after performing OPERATION 1216, curing the composite material includes inductively heating the composite material using the heating blanket (OPERATION 1218).

[0141] In some examples, securing the slipsheet to the tool includes at least one of holding the slipsheet in place using a mechanical constraint and pulling the slipsheet against the tool interface surface using a vacuum (operation 1220). In some example examples, securing the slipsheet to the tool includes placing an insulating layer connected to the rigid body of the slipsheet in contact with the top surface of the tool (operation 1222).

[0142] In some exemplary embodiments, curing the composite material on the slipsheet includes providing a current having a frequency between 1 kHz and 150 kHz (OPERATION 1224). In some exemplary embodiments, curing the composite material on the slipsheet includes providing a current having a frequency less than 9 kHz (OPERATION 1226). In some exemplary embodiments, method 1200 further includes heating the slipsheet during layup of the composite material using a second induction coil circuit on the slipsheet (OPERATION 1228). In this case, the induction coil circuit and the second induction coil circuit have different Curie temperatures.

[0143] As used herein, the phrase "at least one of" used in conjunction with enumerated items means that various combinations of one or more of the enumerated items may be used, and that only one of each enumerated item may be required. For example, without limitation, "at least one of item A, item B, and item C" may include item A, item A and item B, or item B. This example may also include item A, item B, and item C, or item B and item C. Of course, any combination of these items may be present. In other examples, "at least one of" may be, for example, without limitation, "two items A, one item B, and ten items C," "four items B and seven items C," or other suitable combinations. An item may be a specific object, body, or category. In other words, "at least one of" means that any combination of items, or some items, from the list may be used, but not all of the listed items are required.

[0144] The flowcharts and block diagrams in the various illustrated embodiments illustrate the structure, functionality, and operation of some possible implementations of apparatus and methods in an illustrative embodiment. In this regard, each block in a flowchart or block diagram may represent at least one of a module, a segment, a function, or a portion of an operation or step.

[0145] In some alternative implementations of an exemplary embodiment, one or more functions described in a block may occur out of the order described in the figures. For example, in some cases, two blocks shown in succession may be executed substantially simultaneously, or the blocks may sometimes be performed in reverse order depending on the functionality involved. Also, other blocks may be added in addition to the blocks shown in a flowchart or block diagram. Some blocks may be optional. For example, operations 1212 through 1218 may be optional.

[0146] An exemplary embodiment of the present disclosure may be described with reference to aircraft manufacturing and service method 1300 shown in Figure 13 and aircraft 1400 shown in Figure 14. Referring first back to Figure 13, an aircraft manufacturing and service method is depicted in accordance with an exemplary embodiment. During pre-production, aircraft manufacturing and service method 1300 may include specification and design 1302 and material procurement 1304 of aircraft 1400 in Figure 14.

[0147] During production, component and subassembly manufacturing 1306 and system integration 1308 of the aircraft 1400 occurs. The aircraft 1400 then undergoes certification and delivery 1310 and is placed into service 1312. While in customer service 1312, the aircraft 1400 is scheduled for routine maintenance and service 1314, which may include modification, reconfiguration, refurbishment, and other maintenance and service.

[0148] Each process of aircraft manufacturing and service method 1300 may be performed or implemented by a system integrator, a third party, and / or an operator. In these examples, the operator may be a customer. For purposes of this specification, a system integrator includes, but is not limited to, any number of aircraft manufacturers and major system subcontractors; a third party includes, but is not limited to, any number of vendors, subcontractors, and suppliers; and an operator may include an airline, a leasing company, a military organization, a service organization, etc.

[0149] Referring now to Figure 14, an example aircraft is depicted in which an illustrative embodiment may be implemented. In this example, aircraft 1400 is manufactured by aircraft manufacturing and service method 1300 in Figure 13 and may include an airframe 1402 having a number of systems 1404 and an interior 1406. Example systems 1404 include one or more of a propulsion system 1408, an electrical system 1410, a hydraulic system 1412, and an environmental system 1414. Any number of other systems may also be included.

[0150] Apparatus and methods embodied herein may be used during at least one stage of aircraft manufacturing and service method 1300. One or more illustrative embodiments may be manufactured or used during at least one of component and subassembly manufacturing 1306, system integration 1308, service 1312, or maintenance and service 1314 in Figure 13 .

[0151] A portion of airframe 1402 of aircraft 1400 may be formed by method 1200. Method 1200 may be performed during component and subassembly manufacturing 1306. Induction hardening system 202 may be used to form composite structures during component and subassembly manufacturing 1306. Composite structures formed using method 1200 are in service and utilized in service 1312. Method 1200 may be performed during maintenance and service 1314 to form replacement parts.

[0152] Exemplary embodiments provide advantages in the manufacturing of composite structures. Tool surface-type self-heating slipsheets provide rapid and accurate component curing. This more agile process helps accommodate accelerated production rates. Induction-heated slipsheets provide faster and more efficient heat application than autoclaves or ovens.

[0153] The slip sheet acts as a layup surface and is used to transfer the layup from the lower cost layup mandrel to the higher cost curing tool, thereby reducing costs.

[0154] The composite material is laid up on a slipsheet using a low-cost layup mandrel. The layup is transported to a layup curing tool, where the slipsheet is secured for processing of the composite. The tool with the slipsheet and composite material can be moved into a pressure vessel. Any heating blankets and slipsheets are connected to the required induction power supplies. The composite layup can be vacuum bagged. Heating of the slipsheets and blankets is initiated.

[0155] The composite is then rapidly heated to the cure step while gas pressure is applied, as determined by an appropriate cure kinetics model. A smart susceptor provides thermal leveling at a pre-specified cure temperature. A gentle circulation of a gaseous pressurized medium at ambient temperature within the cure vessel sweeps away any exothermic heat release during cure, while the smart susceptor continues to drive the temperature of the slipsheet and blanket to the desired cure temperature. As used herein, a smart susceptor is constructed of one or more materials that efficiently generate heat until a threshold (i.e., Curie) temperature is reached.

[0156] Once the desired state of cure is achieved, the composite part can be cooled rapidly because the body of the tool is not heated and the gas in the pressure vessel is at ambient temperature. The composite part and tool are then removed from the pressure vessel, and the part is then debagged and sent for inspection and trimming.

[0157] The present invention further includes embodiments according to the following clauses: Article 1. A method (1200) of forming a composite part, comprising: laying up (1202) a composite material (208) on a layup surface (206) of a slipsheet (204) disposed on a layup support (262); conveying (1204) the composite material (208) laid up on the slipsheet (204) to a tool (214), the slipsheet (204) comprising a rigid body (250) configured to support the composite material (208) during conveyance; securing (1206) the slipsheet (204) to the tool (214) such that the tool interface surface (210) of the slipsheet (204) contacts the top surface (212) of the tool (214); and A method (1200) comprising curing (1208) the composite material (208) on the slipsheet (204) using heat generated by an induction coil circuit (218) within the rigid body (250) of the slipsheet (204) while the slipsheet (204) is secured to the tool. Article 2. The method (1200) of clause 1 further includes placing (1212) several rigid cowls on the composite material (208) before curing the composite material (208), and curing the composite material (208) includes heating (1214) the composite material (208) using heat generated by several induction coil circuits within the several rigid cowls. Article 3. The method (1200) of clause 2 further includes placing (1216) a heating blanket (244) over the composite material (208) and the number of rigid cowls, and curing the composite material (208) includes inductively heating (1218) the composite material (208) using the heating blanket (244). Article 4. 4. The method (1200) of any one of clauses 1 to 3, wherein curing the composite material (208) on the slipsheet (204) comprises supplying (1224) a current (228) having a frequency (238) between 1 kHz and 150 kHz. Article 5. The method (1200) of any one of clauses 1 to 4, wherein securing the slipsheet (204) to the tool (214) includes at least one (1220) of using a mechanical constraint to hold the slipsheet (204) in place and using a vacuum to pull the slipsheet (204) against the tool interface surface (210). Article 6. A method (1200) according to any one of clauses 1 to 5, wherein fixing the slipsheet (204) to the tool (214) includes placing (1222) an insulating layer (224) connected to the rigid body (250) of the slipsheet (204) in contact with the top surface (212) of the tool (214). Article 7. 7. The method (1200) of any one of clauses 1 to 6, wherein curing the composite material (208) on the slipsheet (204) comprises supplying (1226) a current (228) having a frequency (238) of less than 9 kHz. Article 8. 8. The method (1200) of any one of clauses 1 to 7, further comprising using a second induction coil circuit (611) of the slip sheet (204) to heat (1228) the slip sheet (204) during the layup of the composite material (208), wherein the induction coil circuit (218, 610) and the second induction coil circuit (611) have different Curie temperatures. Article 9. An induction hardening system (202) comprising a slipsheet (204) and a power source (234), the slipsheet (204) comprising: a layup surface (206) configured to receive a composite material (208); a tool interface surface (210) configured to interact with an upper surface (212) of a tool (214); a rigid body (250) extending between the layup surface (206) and the tool interface surface (210), the rigid body (250) configured to support the composite material (208) during transport of the composite material (208); and an induction coil circuit (218) within the rigid body (250) of the slipsheet (204) configured to heat the layup surface (206) to a temperature sufficient to cure the composite material (208), the induction coil circuit (218 having a diameter (236) selected to generate heat using the power source (234) having a frequency (238) of less than 150 kHz; The power source (234) is coupled to the induction coil circuit (218) and is selected based on the diameter (236) of the induction coil circuit (218). Article 10. 10. The induction hardening system (202) of clause 9, wherein the slip sheet (204) further comprises an insulating layer (224) connected to the rigid body (250) of the slip sheet (204), the insulating layer (224) forming the tool interface surface (210). Article 11. 11. The induction hardening system (202) of clause 9 or 10, further comprising a rigid cowl (254), the rigid cowl (254) comprising a cowl induction coil circuit (256) within a rigid body of the rigid cowl (254), the cowl induction coil circuit (256) configured to heat the rigid cowl (254). Article 12. 12. The induction hardening system (202) of any one of clauses 9 to 11, further comprising a heating blanket (244) conforming to the composite material (208), the heating blanket (244) comprising an induction heating circuit (242). Article 13. 13. The induction hardening system (202) of any one of clauses 9 to 12, further comprising the tool (214), the tool (214) further comprising a vacuum system (264) configured to press the slipsheet (204) against the top surface (212) of the tool (214). Article 14. 14. The induction hardening system (202) of any one of clauses 9 to 13, wherein the power source (234) has a frequency (238) of less than 9 kHz. Article 15. 15. The induction hardening system (202) of any one of clauses 9 to 14, wherein the top surface (212) of the tool (214) is configured to receive a composite material (208). Article 16. 16. The induction hardening system (202) of any one of clauses 9 to 15, wherein the slipsheet (204) further comprises a metal layer (516) connected to the rigid body (250, 508) of the slipsheet (204, 502), the metal layer (516) forming the layup surface (206, 504). Article 17. 17. The induction hardening system (202) of claim 16, wherein the rigid body (250) is formed of a composite material (208). Article 18. The induction coil circuit (218) a conductor (226) for receiving an electric current (228) and generating a magnetic field in response to said electric current (228); 18. An induction hardening system (202) according to any one of clauses 9 to 17, comprising a susceptor wire (232) helically wound along at least a portion of the length of the conductor (226), the susceptor wire (232) having continuous wire coverings defining gaps therebetween such that the circumferential position of each wire covering is spaced apart from the covering of an adjacent wire at the same circumferential position, the magnetic field passing through the gaps between the wire coverings, thereby promoting the flow of eddy currents in the wire (232), the wire (232) being composed of a magnetic material having a Curie temperature and being inductively heated in response to the magnetic field. Article 19. 19. The induction hardening system (202) of any one of clauses 9 to 18, wherein the induction coil circuit (218, 610) comprises a conductor (226, 612) and a susceptor wire (232, 614) having a first Curie temperature, and the slip sheet (204) further comprises a second induction coil circuit (611), the second induction coil circuit (611) comprising a second conductor (613) and a second susceptor wire (615) having a second Curie temperature, and the first Curie temperature is different from the second Curie temperature. Article 20. 20. The induction hardening system (202) of claim 19, wherein the first Curie temperature is a hardening temperature and the second Curie temperature is a lay-up temperature. Article 21. An induction hardening system (202) comprising a slip sheet (204), the slip sheet (204) comprising: a layup surface (206) configured to receive a composite material (208); a tool interface surface (210) configured to interact with an upper surface (212) of a tool (214); a body (216) extending between the layup surface (206) and the tool interface surface (210); and 1. An induction hardening system (202) comprising: an induction coil circuit (218) within the body (216) of the slipsheet (204), the induction coil circuit (218) configured to heat the layup surface (206) to a temperature sufficient to harden the composite material (208), the induction coil circuit (218) comprising a conductor (226) for receiving an electric current (228) and generating a magnetic field in response to the electric current (228), and a susceptor wire (232) wrapped along at least a portion of the length of the conductor (226), the susceptor wire (232) having a diameter (240) greater than 0.05 inches. Article 22. 22. The induction hardening system (202) of claim 21, further comprising a heating blanket (244) conforming to the composite material (208), the heating blanket (244) comprising an induction heating circuit (242). Article 23. 23. The induction hardening system (202) of claim 22, wherein the induction coil circuit (218) of the slip sheet (204) is configured to generate heat in response to a current (228) having a frequency in a first range, and the induction heating circuit (242) of the heating blanket (244) is configured to generate heat in response to a current having a frequency in a second range, the first range of frequencies being outside of and separated from the second range of frequencies. Article 24. 24. The induction hardening system (202) of clause 23, wherein the first range of frequencies is less than 9 kHz. Article 25. 25. An induction hardening system (202) as described in any one of clauses 21 to 24, wherein the body (216) is a rigid body (250), the rigid body (250) being sufficiently hard to support the composite material (208) during transport of the composite material (208).

[0158] The description of various exemplary embodiments has been presented for purposes of illustration and description and is not intended to be exhaustive or to limit the embodiments to the form disclosed. Many modifications and variations will be apparent to those skilled in the art. Moreover, various exemplary embodiments may provide different features as compared to other exemplary embodiments. The selected one or more embodiments have been chosen and described in order to best explain the principles and practical applications of the embodiments and to enable others skilled in the art to understand that the disclosure of the various embodiments, together with various modifications, is suitable for the particular use envisioned.

Claims

1. 12. A method (1200) of forming a composite part, comprising: laying up (1202) a composite material (208) on a layup surface (206) of a slipsheet (204) disposed on a layup support (262); conveying (1204) the composite material (208) laid up on the slipsheet (204) to a tool (214), the slipsheet (204) comprising a rigid body (250) configured to support the composite material (208) during conveyance; securing (1206) the slipsheet (204) to the tool (214) such that a tool interface surface (210) of the slipsheet (204) contacts a top surface (212) of the tool (214); and The method (1200) includes curing (1208) the composite material (208) on the slipsheet (204) using heat generated by an induction coil circuit (218) in the rigid body (250) of the slipsheet (204) while the slipsheet (204) is secured to the tool.

2. 12. The method (1200) of claim 1, further comprising: placing (1212) a number of rigid cowls over the composite material (208) prior to curing the composite material (208), and curing the composite material (208) comprises heating (1214) the composite material (208) using heat generated by a number of induction coil circuits in the number of rigid cowls.

3. 3. The method (1200) of claim 2, further comprising: positioning (1216) a heating blanket (244) over the composite material (208) and the number of rigid cowls, and curing the composite material (208) comprises inductively heating (1218) the composite material (208) using the heating blanket (244).

4. 4. The method (1200) of any one of claims 1 to 3, wherein curing the composite material (208) on the slipsheet (204) comprises supplying (1224) a current (228) having a frequency (238) between 1 kHz and 150 kHz.

5. 2. The method (1200) of claim 1, wherein securing the slipsheet (204) to the tool (214) comprises at least one (1220) of holding the slipsheet (204) in place using a mechanical restraint and pulling the slipsheet (204) against the tool interface surface (210) using a vacuum.

6. 2. The method (1200) of claim 1, wherein securing the slipsheet (204) to the tool (214) includes placing (1222) an insulating layer (224) connected to the rigid body (250) of the slipsheet (204) in contact with the top surface (212) of the tool (214).

7. 10. The method (1200) of claim 1, wherein curing the composite material (208) on the slipsheet (204) comprises supplying (1226) a current (228) having a frequency (238) of less than 9 kHz.

8. 12. The method of claim 1, further comprising: using a second induction coil circuit (611) of the slip-sheet (204) to heat (1228) the slip-sheet (204) during the lay-up of the composite material (208), wherein the induction coil circuit (218, 610) and the second induction coil circuit (611) have different Curie temperatures.

9. An induction hardening system (202) comprising a slipsheet (204) and a power source (234), the slipsheet (204) comprising: a layup surface (206) configured to receive a composite material (208); a tool interface surface (210) configured to interact with an upper surface (212) of a tool (214); a rigid body (250) extending between the layup surface (206) and the tool interface surface (210), the rigid body (250) configured to support the composite material (208) during transport of the composite material (208); and an induction coil circuit (218) within the rigid body (250) of the slipsheet (204) configured to heat the layup surface (206) to a temperature sufficient to cure the composite material (208), the induction coil circuit (218) having a diameter (236) selected to generate heat using the power source (234) having a frequency (238) of less than 150 kHz; The power source (234) is coupled to the induction coil circuit (218) and is selected based on the diameter (236) of the induction coil circuit (218).

10. 10. The induction hardening system of claim 9, wherein the slipsheet further comprises an insulating layer connected to the rigid body of the slipsheet, the insulating layer forming the tool interface surface.

11. 11. The induction hardening system (202) of claim 9 or 10, further comprising a rigid cowl (254) comprising a cowl induction coil circuit (256) within a rigid body of the rigid cowl (254), the cowl induction coil circuit (256) configured to heat the rigid cowl (254).

12. The induction hardening system (202) of claim 9, further comprising a heating blanket (244) conforming to the composite material (208), the heating blanket (244) comprising an induction heating circuit (242).

13. 10. The induction hardening system (202) of claim 9, further comprising the tool (214) further comprising a vacuum system (264) configured to hold the slipsheet (204) against the top surface (212) of the tool (214).

14. 10. The induction hardening system (202) of claim 9, wherein the power source (234) has a frequency (238) of less than 9 kHz.

15. The induction hardening system (202) of claim 9, wherein the top surface (212) of the tool (214) is configured to receive a composite material (208).

16. 10. The induction hardening system of claim 9, wherein the slipsheet further comprises a metal layer connected to the rigid body of the slipsheet, the metal layer forming the layup surface.

17. The induction hardening system (202) of claim 16, wherein the rigid body (250) is formed of a composite material (208).

18. The induction coil circuit (218) a conductor (226) for receiving an electric current (228) and generating a magnetic field in response to said electric current (228); 10. The induction hardening system of claim 9, comprising a susceptor wire (232) helically wrapped along at least a portion of the length of the conductor (226), the susceptor wire (232) comprising successive wire wraps defining gaps therebetween such that a circumferential position of each wire wrap is spaced from an adjacent wire wrap at the same circumferential position, the magnetic field passing through the gaps between the wire wraps thereby promoting the flow of eddy currents in the wire (232), the wire (232) being composed of a magnetic material having a Curie temperature and being inductively heated in response to the magnetic field.

19. 10. The induction hardening system of claim 9, wherein the induction coil circuit (218, 610) comprises a conductor (226, 612) and a susceptor wire (232, 614) having a first Curie temperature, and the slip sheet (204) further comprises a second induction coil circuit (611) comprising a second conductor (613) and a second susceptor wire (615) having a second Curie temperature, and the first Curie temperature is different from the second Curie temperature.

20. An induction hardening system (202) comprising a slip sheet (204), the slip sheet (204) comprising: a layup surface (206) configured to receive a composite material (208); a tool interface surface (210) configured to interact with an upper surface (212) of a tool (214); a body (216) extending between the layup surface (206) and the tool interface surface (210); 1. An induction hardening system (202), comprising: an induction coil circuit (218) within the body (216) of the slipsheet (204), the induction coil circuit (218) configured to heat the layup surface (206) to a temperature sufficient to harden the composite material (208), the induction coil circuit (218) comprising a conductor (226) for receiving an electric current (228) and generating a magnetic field in response to the electric current (228), and a susceptor wire (232) wrapped along at least a portion of a length of the conductor (226), the susceptor wire (232) having a diameter (240) greater than 1.27 mm (0.05 inch).

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