Patent Description:
Many aircraft thermoplastic composite structures are formed using stiffeners comprised of a thermoplastic, a thermoplastic material, a metallic material, or the like to reinforce or stiffen the structure. These stiffeners typically provide the structure with resistance to compression buckling or bending, making the structure desirably less flexible when put under a shearing, tensile, or compressive stress, or the like. These stiffeners are joined to the thermoplastic structure by induction welding. Induction welding utilizes electromagnetic induction to heat a workpiece. An induction coil is energized with electrical current which generates an electromagnetic field that heats a workpiece and binds it to a thermoplastic structure. As a stiffener is laid up in a thermoplastic structure, induction welding can generate eddy currents which can heat the edges of the stiffener, leading to higher temperatures that can damage the thermoplastic structure.

<CIT> discloses a method of joining a skin panel and stringer comprising positioning the skin panel and the stringer on top such that it least partially overlays it and operating an induction welding system having a tool surface and a coil to weld the stringer to the skin panel by operating over a length of the stringer for a time period. A susceptor welding tape is positioned between the stringer and the skin panel.

<CIT> discloses Millimeter-wave radar simulator shielding box for intelligent automobile electromagnetic compatibility testing.

According to an aspect of the present invention, there is disclosed a method of joining a first workpiece to a second workpiece as claimed in claim <NUM>. Embodiments of this aspect of the invention are provided in claims dependent from claim <NUM>.

According to an aspect of the present invention, there is disclosed a method of joining a first workpiece to a second workpiece as claimed in claim <NUM>. Embodiments of this aspect of the invention in claims dependent from claim <NUM>.

The detailed description of exemplary embodiments herein makes reference to the accompanying drawings, which show exemplary embodiments by way of illustration. While these exemplary embodiments are described in sufficient detail to enable those skilled in the art to practice the disclosure, it should be understood that other embodiments may be realized and that logical changes and adaptations in design and construction may be made in accordance with this disclosure and the teachings herein. The scope of the disclosure is defined by the appended claims. For example, the steps recited in any of the method or process descriptions may be executed in any order and are not necessarily limited to the order presented. Also, any reference to attached, fixed, connected or the like may include permanent, removable, temporary, partial, full and/or any other possible attachment option.

<FIG> illustrates a nacelle <NUM> for a gas turbine engine according to various embodiments. The nacelle for a gas turbine engine may be suitable for an aircraft. The nacelle <NUM> can comprise a centerline A-A' <NUM>. Nacelle <NUM> can comprise an inlet <NUM>, a fan cowl <NUM>, and a thrust reverser <NUM>. The fan cowl <NUM> can comprise a stiffener <NUM> configured to reinforce the fan cowl <NUM>. In various embodiments, stiffeners as disclosed herein can be comprised of a thermoplastic, a thermoplastic composite material, a metallic material, or the like. Stiffener <NUM> comprises a thermoplastic composite material. Nacelle <NUM> can be coupled to a pylon <NUM>, which can mount the nacelle <NUM> to an aircraft wing or aircraft body. A nozzle <NUM> can surround a center body <NUM>, between which an engine exhaust stream exits to provide additional thrust.

Referring to <FIG>, a portion of an aircraft fan cowl <NUM> is illustrated according to various embodiments. In various embodiments, the fan cowl <NUM> can be comprised of a metallic material, a thermoplastic, a thermoplastic composite material, or the like. In various embodiments, the fan cowl <NUM> can be a thermoplastic composite structure. In such embodiments, the fan cowl <NUM> can include at least one stiffener <NUM> formed along an inner surface or skin <NUM> of the fan cowl <NUM>. The stiffener <NUM> can be formed along the skin <NUM> according to any desirable orientation, geometry, or symmetry, including, for example, a fully interconnected grid stiffening symmetry. A stiffener <NUM> in a fan cowl <NUM> is described, however, the stiffener <NUM> can be utilized in any other suitable aircraft structure, including for example, a fuselage, a wing, panels and substructures thereof, and the like. In various embodiments, stiffeners as disclosed herein can be comprised of a thermoplastic, a thermoplastic composite material, a metallic material, or the like. Stiffener <NUM> comprises a thermoplastic composite material.

Although <FIG>. and <FIG> may disclose stiffeners used within fan cowls, various embodiments of the below referenced methods and system can be applied to any other thermoplastic composite structures within a nacelle. In various embodiments, the below referenced methods and systems can be applied to an inlet inner barrel, a translating sleeve, and an inner fixed structure.

In reference to <FIG>, a first workpiece shown as a thermoplastic composite structure <NUM> can be coupled to a second workpiece shown as a stiffener <NUM> using an induction welding process. In various embodiments, stiffeners as disclosed herein can be comprised of a thermoplastic, a thermoplastic composite material, a metallic material, or the like. Stiffener <NUM> comprises a thermoplastic composite material. The stiffener <NUM> can comprise a stiffener width <NUM> and a stiffener length <NUM>. The stiffener width <NUM> and the stiffener length <NUM> can form a perimeter of the stiffener <NUM>.

In various embodiments, the thermoplastic composite structure <NUM> can further comprise a thermoplastic composite skin <NUM>. The stiffener <NUM> can further comprise a stiffener cap <NUM> and a stiffener web <NUM> disposed along the length of the stiffener cap <NUM>. In various embodiments, the stiffener web <NUM> may be offset along the y-axis from a surface of thermoplastic composite skin <NUM>, for example, at a substantially <NUM>-degree angle. In various embodiments, the stiffener web <NUM> may be offset from the thermoplastic composite skin <NUM> at any desirable angle, or any angle suitable for reinforcing a thermoplastic composite structure. The stiffener <NUM> can further comprise a stiffener flange <NUM> disposed outward in the positive x-direction from the stiffener web <NUM>. The stiffener can further comprise a first edge <NUM> and a second edge <NUM>.

In various embodiments, the stiffener flange <NUM> may be welded to the thermoplastic composite skin <NUM> at a welding region <NUM>. The thermoplastic composite skin <NUM> can degrade as the heat generated by induction welding reaches the edges of the stiffener <NUM>. This may be caused by inconsistent eddy currents generated along the thermoplastic composite skin <NUM>, as well as inconsistent heat generation at the welding region <NUM>. In various embodiments, a first removable metal mask <NUM> can be used in induction welding of the thermoplastic composite structure <NUM> to the stiffener <NUM> to reduce the eddy currents produced in the thermoplastic composite structure <NUM>. The first removable metal mask <NUM> can be positioned adjacent to the first edge <NUM> of the stiffener <NUM> in the negative z-direction and on top of the thermoplastic composite structure <NUM> in the positive y-direction. In various embodiments, a second removable metal mask <NUM> can be used in induction welding of the thermoplastic composite structure <NUM> to the stiffener <NUM> to reduce the eddy currents produced in the thermoplastic composite structure <NUM>. The second removable metal mask <NUM> can be positioned adjacent to the second edge <NUM> in the positive z-direction of the stiffener <NUM> and on top of the thermoplastic composite structure <NUM> in the positive y-direction.

In various embodiments, both the first removable metal mask <NUM> and the second removable metal mask <NUM> can be used during the induction welding process. The first removable metal mask <NUM> and the second removable metal mask <NUM> can be equal to or greater in length in the x-direction than the stiffener width <NUM>.

The first removable metal mask <NUM> and the second removable metal mask <NUM> can each comprise a metal mesh configured to at least partially overlay the thermoplastic composite structure <NUM>. The metal mesh can function similar to a faraday cage to attenuate the electromagnetic field that induces eddy currents during the induction welding process. This attenuation of the induced eddy currents in these localized areas can help reduce the temperature achieved in those localized areas. A metal mesh with a higher electrical conductivity can result in better attenuation of the electromagnetic field. A metal mesh with higher electrical conductivity can result from a metal mesh with higher density. The density of a metal mesh can be determined by the percentage of metal mass to empty space in the metal mesh. In various embodiments, the electrical conductivity of the metal mesh can be between <NUM> million siemens per meter and <NUM> million siemens per meter, between <NUM> million siemens per meter and <NUM> million siemens per meter, and <NUM> million siemens per meter and <NUM> million siemens per meter. In various embodiments, the metal mesh can comprise a conductive metal such as copper, aluminum and the like.

In various embodiments, the stiffener flange <NUM> may be welded to the thermoplastic composite skin <NUM> at a welding region <NUM>. In various embodiments, a removable metal mask <NUM> can be used in induction welding of the thermoplastic composite structure <NUM> to the stiffener <NUM> to reduce the eddy currents produced in the thermoplastic composite structure <NUM>. In <FIG>, the removable metal mask <NUM> is partially covering the thermoplastic composite structure. The removable metal mask <NUM> can be positioned adjacent to the first edge <NUM> and the second edge <NUM>, on top of the thermoplastic composite structure <NUM> in the positive y-direction, such that it masks the thermoplastic composite structure <NUM> and exposes the stiffener <NUM>. In various embodiments, the length and width of the removable metal mask <NUM> can greater than the stiffener length <NUM> and the stiffener width <NUM>, respectively.

The removable metal mask <NUM> can comprise a metal mesh configured to at least partially overlay the thermoplastic composite structure <NUM>. The metal mesh can have the same properties and composition as previously described for the metal mesh of the first removable metal mask <NUM> and the second removable metal mask <NUM>.

In reference to <FIG>, a removable metal mask <NUM> used in induction welding of a first workpiece to a second workpiece is shown. In various embodiments, the removable metal mask <NUM> can comprise a metal mesh <NUM> and a workpiece opening <NUM> disposed within the metal mesh <NUM>. The workpiece opening <NUM> is configured to at least partially mask a portion of the first workpiece and at least partially expose the second workpiece. The metal mesh <NUM> can have the same properties as described previously for the metal mesh of the first removable metal mask <NUM>.

The workpiece opening <NUM> can be the same or within <NUM>% of the size of the second workpiece. The metal mesh <NUM> can be configured to contact each perimeter edge of the second workpiece, such that there may not be any space in the zx-plane between the second workpiece and the removeable metal masks <NUM>.

In various embodiments, the removable metal mask <NUM> can comprise a metal frame <NUM>. In various embodiments, the metal frame <NUM> can comprise a metallic material. Exemplary metallic materials for the metal frame <NUM> include copper, copper alloys, aluminum, aluminum alloys, various iron alloys such as steel and the like. The metal frame <NUM> can be a solid metal frame or a hollow metal frame. In various embodiments, the metal frame <NUM> can comprise a frame width <NUM> and a frame length <NUM>.

In various embodiments, the frame width <NUM> can be greater than the second workpiece width. In various embodiments, the frame length <NUM> can be greater than the second workpiece length. Therefore, the workpiece opening <NUM> can be configured to expose the second workpiece and workpiece opening <NUM> may cover a portion of the first workpiece. Additionally, the removable metal mask <NUM>, as well as the removable metal masks <NUM>, <NUM>, and <NUM> can comprise various geometries including a rectangle, a square, a triangle and other shapes of the like.

In various embodiments, the first workpiece can be a thermoplastic composite structure such as thermoplastic composite structures <NUM> and <NUM>. In various embodiments, the second workpiece can be a stiffener such as stiffeners <NUM> and <NUM>.

With reference to <FIG>, and <FIG>, a cross section along the x-axis of a first workpiece shown as a thermoplastic composite skin <NUM> and a second workpiece shown as a stiffener <NUM> during an induction welding process <NUM>. The thermoplastic composite structure <NUM> can further comprise a thermoplastic composite skin <NUM>. In various embodiments, stiffeners as disclosed herein can be comprised of a thermoplastic, a thermoplastic composite material, a metallic material, or the like. Stiffener <NUM> comprises a thermoplastic composite material. The stiffener <NUM> can further comprise a stiffener cap <NUM> and a stiffener web <NUM> disposed along the length of the stiffener cap <NUM>. In various embodiments, the stiffener web <NUM> may be offset along the y-axis from a surface of thermoplastic composite skin <NUM>, for example, at a substantially <NUM>-degree angle. In various embodiments, the stiffener web <NUM> may be offset from the thermoplastic composite skin <NUM> at any desirable angle, or any angle suitable for reinforcing a thermoplastic composite structure. The stiffener <NUM> can further comprise a stiffener flange <NUM> disposed outward in the positive x-direction from the stiffener web <NUM>.

In various embodiments, the stiffener flange <NUM> may be welded to the thermoplastic composite skin <NUM> at a welding region <NUM> as shown in <FIG>. The welding region <NUM> can be disposed along the entire length or the partial length of the stiffener <NUM> in the z-direction. In various embodiments, a removable metal mask <NUM> can be used in induction welding of the thermoplastic composite structure <NUM> to the stiffener <NUM>. In various embodiments, the removable metal mask <NUM> can be the removable metal masks described previously as removable metal masks <NUM> and <NUM>.

In <FIG>, a cross-section of an induction welding tool <NUM> is shown. The induction welding tool <NUM> may have an induction welding tool surface <NUM> configured to interact with the stiffener flange <NUM> and the thermoplastic composite structure <NUM>. The induction welding tool <NUM> can be located proximate the stiffener flange <NUM> in the positive y-direction. In various embodiments, a coil <NUM> can be located proximate the thermoplastic composite structure <NUM> in the negative y-direction.

In various embodiments, the coil <NUM> may be configured to energize with electrical current. The energized coil <NUM> may be configured to generate an electromagnetic field that heats the induction welding tool <NUM>. In various embodiments, the heat generated by the coil <NUM> may be configured to enable the induction welding tool <NUM> to weld the stiffener flange <NUM> to the thermoplastic composite skin <NUM> at a welding region <NUM>.

With combined reference to <FIG>, a method <NUM> for joining a first workpiece to a second workpiece is disclosed. Method <NUM> includes the steps of positioning a second workpiece (shown as stiffener <NUM>) on top of the first workpiece (shown as thermoplastic composite structure <NUM>) in the positive y-direction (step <NUM>), positioning a removable metal mask <NUM> on top of the first workpiece (thermoplastic composite structure <NUM>) in the positive y-direction (step <NUM>), operating an induction welding tool <NUM> configured to weld at a welding region <NUM> of the second workpiece (step <NUM>), and removing the removable metal mask <NUM> (step <NUM>). In various embodiments, the first workpiece can be the thermoplastic composite structure <NUM> and the second workpiece can be the stiffener <NUM>.

In various embodiments, the step <NUM> can further comprise the stiffener <NUM> at least partially overlaying the top of the first workpiece. In various embodiments, the step <NUM> can further comprise the metal mesh, shown in <FIG> as <NUM>, configured to at least partially mask the thermoplastic composite structure <NUM> and at least partially expose the stiffener, shown in <FIG> as <NUM>.

In various embodiments, the induction welding may further comprise operating an induction welding tool <NUM> configured to weld at the welding region <NUM> of stiffener <NUM>, wherein an induction welding tool <NUM> operates for a length of the stiffener <NUM> in the z-direction for a welding period. The welding period can be adjusted depending on the operational temperature of the welding tool. For example, a welding tool <NUM> operating at a temperature above <NUM>° C can have a shorter welding period than a welding tool <NUM> operating at a temperature below <NUM>° C. In various embodiments, the induction welding tool <NUM> can comprises an induction welding tool surface <NUM> located proximate the second workpiece in the positive y-direction.

In various embodiments the induction welding tool <NUM> can comprise a coil <NUM> located proximate the first workpiece in the negative y-direction. In various embodiments, the coil <NUM> can be configured to energize with alternating current to generate an electromagnetic field. The electromagnetic field can be configured to heat the welding region <NUM>, wherein the heat generated by the coil is configured to weld at a welding temperature. In various embodiments, the welding temperature can be between <NUM>° C and <NUM>° C, between <NUM>° C and <NUM>° C, and between <NUM>° C and <NUM>° C. In various embodiments, when the induction welding tool <NUM> is at the welding temperature, the induction welding tool <NUM> can weld the stiffener <NUM> to the thermoplastic composite structure <NUM> at the welding region <NUM>. In various embodiments, the operating the induction welding tool (step <NUM>) can comprise welding the stiffener flange <NUM> to the thermoplastic composite skin <NUM>.

With reference to <FIG> and <FIG>, a cross section along the x-axis of a first workpiece shown as a thermoplastic composite structure <NUM> and a second workpiece shown as a stiffener <NUM> during an induction welding process <NUM>. The thermoplastic composite structure <NUM> can further comprise a thermoplastic composite skin <NUM>. In various embodiments, stiffeners as disclosed herein can be comprised of a thermoplastic, a thermoplastic composite material, a metallic material, or the like. Stiffener <NUM> comprises a thermoplastic composite material. The stiffener <NUM> can further comprise a stiffener cap <NUM> and a stiffener web <NUM> disposed along the length of the stiffener cap <NUM>. In various embodiments, the stiffener web <NUM> may be offset along the y-axis from a surface of thermoplastic composite skin <NUM>, for example, at a substantially <NUM>-degree angle. In various embodiments, the stiffener web <NUM> may be offset from the thermoplastic composite skin <NUM> at any desirable angle, or any angle suitable for reinforcing a thermoplastic composite structure. The stiffener <NUM> can further comprise a stiffener flange <NUM> disposed outward in the positive x-direction from the stiffener web <NUM>.

In various embodiments, the stiffener flange <NUM> may be welded to the thermoplastic composite skin <NUM> at a welding region <NUM> as shown in <FIG>. The welding region <NUM> can be disposed along the entire length or the partial length of the stiffener <NUM> in the z-direction. In various embodiments, a first removable metal mask and a second removable metal mask can be used in induction welding of the thermoplastic composite structure <NUM> to the stiffener <NUM>. The first removable metal mask and the second removable metal mask cannot be seen from the cutaway view in <FIG> as they extend along the zx-plane. However, in various embodiments, the first removable metal mask can be the removable metal mask <NUM> and the second removable metal mask can be the removable metal mask <NUM> as described previously.

With reference to <FIG>, a method <NUM> for joining a first workpiece to a second workpiece is disclosed. Method <NUM> includes the steps of positioning a second workpiece (shown as stiffener <NUM>) on top of the first workpiece (shown as thermoplastic composite structure <NUM>) in the positive y-direction (step <NUM>), positioning a first removable metal mask on top of the first workpiece (thermoplastic composite structure <NUM>) in the positive y-direction (step <NUM>), positioning a second removable metal mask on top of the first workpiece (thermoplastic composite structure <NUM>) in the positive y-direction (step <NUM>), operating an induction welding tool <NUM> configured to weld at a welding region <NUM> of the second workpiece (stiffener <NUM>) (step <NUM>), and removing the first removable metal mask and the second removable metal mask (step <NUM>). In various embodiments, the first workpiece can be the thermoplastic composite structure <NUM> and the second workpiece can be the stiffener <NUM>.

In various embodiments, the step <NUM> can further comprise the stiffener <NUM> at least partially overlaying the top of the first workpiece. In various embodiments, the step <NUM> can further comprise the first removable metal mask comprising a metal mesh as described for the first removable metal mask <NUM>, configured to at least partially mask the thermoplastic composite structure <NUM>. In various embodiments, the step <NUM> can further comprise the second removable metal mask comprising a metal mesh as described for the second removable metal mask <NUM>, configured to at least partially mask the thermoplastic composite structure <NUM>.

Claim 1:
A method of joining a first workpiece to a second workpiece, the method comprising:
positioning the second workpiece on a top of the first workpiece, wherein the second workpiece is configured to at least partially overlay the top of the first workpiece;
positioning a removable metal mask (<NUM>; <NUM>; <NUM>) on the top of the first workpiece, wherein the removable metal mask (<NUM>; <NUM>; <NUM>) comprises a metal mesh (<NUM>) configured to mask the first workpiece and expose the second workpiece through a workpiece opening (<NUM>) disposed within the metal mesh (<NUM>);
induction welding the first workpiece to the second workpiece at a welding region (<NUM>; <NUM>, <NUM>), wherein the induction welding further comprises:
operating an induction welding tool (<NUM>, <NUM>) configured to weld at the welding region (<NUM>; <NUM>, <NUM>) of the second workpiece, wherein an induction welding tool (<NUM>, <NUM>) operates for a length of the second workpiece for a welding period, wherein the induction welding tool (<NUM>, <NUM>) comprises:
an induction welding tool surface (<NUM>, <NUM>) located proximate the second workpiece, and a coil (<NUM>, <NUM>) located proximate the first workpiece, wherein the coil (<NUM>, <NUM>) is configured to energize with alternating current to generate an electromagnetic field, wherein the electromagnetic field is configured to heat the welding region (<NUM>; <NUM>, <NUM>), wherein the heat generated by the coil (<NUM>, <NUM>) is configured to weld at a welding temperature, by the induction welding tool (<NUM>, <NUM>), the second workpiece to the first workpiece at the welding region (<NUM>; <NUM>, <NUM>); and
removing the removable metal mask (<NUM>; <NUM>; <NUM>).