Patent Description:
Composite materials, including carbon fiber epoxy impregnated laminates, are often used in applications requiring high strength and light weight, such as in the aerospace industry. At least some known composite structures are formed using a process known as hot drape forming. Hot drape forming typically includes heating one or more plies of flat pre-impregnated (i.e., prepreg) composite material, and forcing the composite material around a mandrel with a vacuum bag or a pressurized bladder device. When sufficiently heated, the plies can slide relative to one another in order to form a desired nonplanar shape. However, it is difficult and time consuming to form the sheet-like composite material into a non-planar composite structure while avoiding unacceptable buckling or wrinkling of the composite material.

<CIT> discloses, according to its abstract, "Systems and methods for drape forming a charge of composite material are disclosed herein. The systems include a forming mandrel, a charge support structure, a flexible and resilient forming membrane, a base, and a vacuum source. The charge support structure includes a flexible and resilient charge support membrane, a membrane suspension device, and a release structure. The release structure operatively couples the charge support membrane to the membrane suspension device when a tension on a peripheral region of the charge support membrane is less than a threshold tension and releases the charge support membrane from the membrane suspension device when the tension is greater than the threshold tension. Alternatively, and in place of the charge support structure, the systems include a means for supporting the charge of composite material. The methods include methods of drape forming a charge of composite material".

<CIT> discloses, according to its abstract, "A method for drape forming a laminated composite charge, the method including placing the laminated composite charge on a forming tool and redirecting forming forces applied to the laminated composite charge during drape forming to counteract wrinkle forming movement between plies of the laminated composite charge".

In a first aspect there is provided a drape forming apparatus as defined in claim <NUM> of the appended claims. In a second aspect there is provided a method as defined in appended claim <NUM>.

For relatively thick composite materials, uniform heating to a desired forming temperature using known drape forming apparatuses may be unattainable within a predetermined time threshold and/or without exceeding a predetermined maximum temperature. For example, a portion of a composite material closest to a heat source (e.g., a top ply) may quickly attain a desired forming temperature while a portion furthest from the heat source (e.g., a bottom ply) remains below the desired forming temperature.

A drape forming apparatus, flange forming device, and method of forming a composite material are disclosed herein that, in various examples, allow more uniform heating of the composite material in combination with controlled forming rate for avoiding wrinkling of the material. The composite structure may be used in a variety of implementations, especially those in which a controlled surface profile is desired (e.g., with minimal surface wrinkling), such as at an exterior of an aircraft. Representative applications include, without limitation, aeronautical components and control surfaces, including rudders, flaps, and wing surfaces. Other industries utilizing composite structures may also benefit from the improvements described herein.

A drape forming apparatus disclosed herein, such as for use in forming a composite structure, includes a forming tool having a first forming surface and a second forming surface nonplanar with the first forming surface. A tray is spaced apart from the forming tool and has a first side and a second side. The tray has a hinged end and a distal end, and is configured to pivot about the hinged end from a first position to a second position under an applied force such that the distal end moves away from the forming tool. The drape forming apparatus also includes a first heat source and a second heat source. The first side of the tray faces the first heat source when the tray is in the first position, and the second heat source is disposed at the second side of the tray. Accordingly, a composite material disposed on the tray is heated at both sides by the first and second heat sources, and pivots with the tray to be formed to the second forming surface. As the material is incrementally withdrawn from the tray at a controlled rate corresponding with the rate of pivoting, the portion moved furthest from the first heat source remains on the tray being heated by the second heat source until finally withdrawn. The two-sided heating provided by the drape forming apparatus may help to minimize a temperature gradient through the material, which is especially helpful when drape forming relatively thick composite materials.

Also disclosed herein is a device for use in forming a composite structure that includes a standoff and a tray having a first side and a second side, the tray having a hinged end and a distal end, the tray configured to pivot about the hinged end from a first position to a second position under an applied force. A heat source is secured to the second side of the tray.

A method of forming a composite structure, such as by utilizing the drape forming apparatus and flange forming device disclosed herein includes disposing at least one layer of composite material over a first forming surface of a forming tool so that a portion of the at least one layer of composite material is positioned on a first side of a tray coplanar with the first forming surface when the tray is in a first position, the tray having a hinged end and a distal end with the distal end nearer the first forming surface than the hinged end when the tray is in the first position. The method includes heating a first side of the at least one layer of composite material with a first heat source, the first side facing the first heat source when the tray is in the first position. The method further includes heating a second side of the at least one layer of composite material with a second heat source, the second heat source disposed at a second side of the tray. Under the method, a force is applied on the tray such that the tray pivots about the hinged end, the distal end moves away from the forming tool, and such that the portion of the at least one layer of composite material is withdrawn from the tray and is disposed against a second forming surface of the forming tool nonplanar with the first forming surface.

The above features and advantages, and other features and advantages, of the present teachings are readily apparent from the following detailed description of some of the best modes and other examples for carrying out the present teachings, as defined in the appended claims, when taken in connection with the accompanying drawings.

Disclosed herein are various examples of drape forming apparatuses, flange forming devices, and methods of forming composite structures that include two-sided heating of the composite material, and specifically, two-sided heating of a portion of the composite material to be formed as a flange. Especially when forming relatively thick, multi-ply composite material, a temperature gradient through the material could lead to undesirable wrinkling. By disposing a first heat source at one face of the composite material and a second heat source at an opposite, second face of the composite material, predetermined forming temperature and time ranges can be achieved, the heat sources may be separately controlled for more uniform heating and final properties of the composite structure, and production time goals can be achieved. Additionally, the improved heating arrangement may be integrated with features of the drape forming apparatus that allow a rate of forming of the flange portion to be controlled.

Referring to the drawings, wherein like reference numbers refer to like components, <FIG> is a side view illustration of a first example of a drape forming apparatus <NUM> that includes two flange forming devices <NUM>, one of which is shown in perspective view in <FIG>. In the implementation shown, a composite material <NUM> can be formed into a composite structure <NUM> with two flange portions, as shown in <FIG>, by utilizing both of the flange forming devices <NUM>. The flange forming device <NUM> on the right side of <FIG> has like components functioning in the same manner as those of the flange forming device <NUM> on the left side of <FIG>. In some examples, only one of the flange forming devices <NUM> is included, such as when a composite structure with only one flange portion is to be formed.

The flange forming apparatus <NUM> includes a forming tool <NUM> that has a first forming surface <NUM> and a second forming surface <NUM> nonplanar with and extending from the first forming surface <NUM>. In the example shown, the first forming surface <NUM> is an upper forming surface and the second forming surface <NUM> is a side forming surface that is substantially perpendicular to the first forming surface <NUM>. However, in an alternative implementation, the second forming surface <NUM> could extend from the first forming surface <NUM> at a different non-planar orientation. For example, the second forming surface <NUM> could be arcuate of otherwise contoured, could be disposed at a complementary angle to the first forming surface <NUM>, or could be disposed at any angle or orientation and have any shape relative to the first forming surface <NUM> that enables the drape forming apparatus <NUM> to function as described herein.

In the example shown, the forming tool <NUM> also has a third forming surface <NUM> nonplanar with and extending from the first surface <NUM>, and opposite to the second forming surface <NUM> as another side forming surface. The description herein of utilizing the flange forming device <NUM> shown at the left side of <FIG> to form a flange portion 14B to the second forming surface <NUM> applies equally to the like flange forming device <NUM> shown at the right side of <FIG> that is used to form a like flange portion 14C to the third forming surface <NUM>. The orientation of the forming surfaces <NUM>, <NUM>, and <NUM> in the example of the forming tool <NUM> as shown can be used to form a composite structure <NUM> having two arm portions extending from a main portion, defining a channel.

As described in further detail herein, at least one layer of composite material <NUM> is disposed on the forming tool <NUM> as shown in <FIG>. More specifically, a main portion 14A of the composite material <NUM> rests on the forming tool <NUM> while opposing flange portions 14B and 14C extend from the main portion 14A and are laterally outward of the first forming surface <NUM> in preparation for drape forming to the respective second and third side surfaces <NUM>, <NUM> of the forming tool <NUM>. The flange forming device <NUM> includes a standoff <NUM> spaced apart from the forming tool <NUM> by a predetermined distance <NUM>, also referred to as a gap. Both the forming tool <NUM> and the standoff(s) <NUM> may be secured in place on a platform <NUM> to maintain the predetermined distance <NUM>.

The flange forming device <NUM> also includes a pivotable tray <NUM> coupled to and supported by the standoff <NUM>. Each flange portion 14B, 14C rests on a respective pivotable tray <NUM>. Top surface <NUM> of the composite material <NUM> is furthest from the tray <NUM>, while a bottom surface <NUM> of the composite material <NUM> rests on the tray <NUM>. More particularly, the tray <NUM> is supported by the standoff <NUM> such that the tray <NUM> is pivotable relative to the standoff <NUM> about a pivot axis <NUM> best shown in <FIG>. The pivot axis <NUM> extends perpendicular to the plane of the page in <FIG>. The tray <NUM> has a first side <NUM> and a second side <NUM> opposite to the first side <NUM>. In the example shown, the first side <NUM> faces generally upward when the tray <NUM> is in the first position shown in <FIG>, and the second side <NUM> faces generally downward when the tray <NUM> is in the first position at the beginning of the drape forming process. The tray <NUM> has a hinged end <NUM> pivotably supported by the standoff <NUM> and a distal end <NUM> opposite from the hinged end. The tray <NUM> is configured to pivot about the pivot axis <NUM> near the hinged end <NUM>, moving within the gap <NUM> from the first position to a second position (shown in <FIG>) under an applied force <NUM> such that the distal end <NUM> moves away from the forming tool <NUM>.

To achieve desired material properties of the final composite structure after drape forming, including an absence of or reduction in significant wrinkles, the drape forming apparatus <NUM> provides two-sided heating of the flange portion(s) 14B, 14C, with first and second heat sources <NUM>, <NUM> disposed at respective opposing first and second sides <NUM>, <NUM> of the composite material <NUM> (e.g., at the top surface <NUM> and the bottom surface <NUM>). The heat sources <NUM>, <NUM> may be independently controllable and implementable with the controlled forming rate of the composite material <NUM> afforded by the pivoting tray <NUM> of the flange forming device <NUM>.

As shown in <FIG> the drape forming apparatus <NUM> includes a first heat source <NUM>. In the example shown, the first heat source <NUM> is at least one heat lamp fixed in position relative to the forming tool <NUM> and the standoff(s) <NUM>. When the tray <NUM> is in the first position of <FIG>, the first side <NUM> of the tray <NUM> faces the first heat source <NUM>. The drape forming apparatus <NUM> also includes a second heat source <NUM> disposed at the second side <NUM> of the tray <NUM>. In the example shown, the second heat source <NUM> is a heat pad that includes a resistance heating element <NUM>. For example, the resistance heating element <NUM> may be a wire and the heat pad <NUM> may include a base <NUM>, such as a silicone rubber base, in which the resistance heating element <NUM> is embedded and through which heat radiates to heat the tray <NUM>. As an alternative to or in addition to heating via a hear pad and a resistance heating element, the second heat source may heat the second side <NUM> of the tray <NUM> by convection heating, circulating heated fluid, or otherwise.

The second heat source <NUM> may be secured directly to the second side <NUM> of the tray <NUM> as in the example shown, such as with adhesive. The second heat source <NUM> may extend below the composite material <NUM> only to the far extent <NUM> when the tray <NUM> is in the first position, or may extend further laterally outward than the far extent <NUM>. In other examples, the second heat source <NUM> could be another mode of heating, such as at least one heat lamp disposed so that the second side <NUM> of the tray <NUM> faces the at least one heat lamp when the tray <NUM> is in the first position.

Optionally, heat output of the first heating source <NUM> and heat output of the second heat source <NUM> may be independently controlled by an electronic controller <NUM> operatively connected to each of the heat sources <NUM>, <NUM> such as by controlling electrical power to each heat source. For example, the second heat source <NUM> can thus be controlled to provide heat uniformly along the portion of the tray <NUM> to which it is secured regardless of the position of the tray <NUM> (e.g., whether at the first position, at an intermediate position, or at the second position). Similarly, power to the first heat source <NUM> may be controlled by the electronic controller <NUM> throughout the forming process and separately from the second heat source <NUM>. One or more temperature sensors, such as a thermocouple, may be positioned on or in the tray <NUM>, on or in the second heat source <NUM>, and/or on a membrane <NUM> described herein. The second heat source <NUM> is fixed to and moves with the tray <NUM> while the first heat source <NUM> is fixed in position relative to the forming tool <NUM> and the standoff <NUM>. While the first side <NUM> of the tray <NUM> is moving further away from the first heat source <NUM> during pivoting of the tray <NUM> from the first position to the second position, the second side <NUM> of the tray <NUM> remains fixed in position relative to the second heat source <NUM>.

With reference to <FIG>, during the drape forming process, the tray <NUM> is made to pivot as a result of a net force against the first side <NUM> of the tray <NUM> resulting from an applied force <NUM> of a membrane <NUM> and an opposing, resisting force <NUM> of a resistance device <NUM>. In an example, the membrane <NUM> may be a flexible, air-tight bladder to which a pressure differential may be applied, such as via a vacuum <NUM> applied at an interior surface of the membrane and/or a pressure applied at an exterior surface of the membrane, depending upon the sealing arrangement of the membrane <NUM> in the drape forming apparatus <NUM>. Alternatively or in addition, fluid pressure may be applied to the exterior of the membrane <NUM>. The membrane <NUM> is disposed over the forming tool <NUM>, the standoff(s) <NUM>, and the tray <NUM> on the first side <NUM> of the tray <NUM>, and therefore over the top surface <NUM> of the composite material <NUM> disposed on the forming tool <NUM> and the tray <NUM>. The membrane <NUM> is configured to exert the applied force <NUM> on the tray <NUM> in response to the controller <NUM> commanding a pressure differential on opposing sides of the membrane <NUM>. In <FIG>, the membrane <NUM> is shown in a first state with dashed lines, prior to the controller <NUM> initiating a vacuum and/or pressure on the membrane <NUM>. The membrane <NUM> is shown in solid lines in a second state in which the membrane <NUM> is engaged with and exerts an applied force <NUM> distributed against the top surface <NUM> of the composite material <NUM>, including the flange portions 14B, 14C, that encourages pivoting of the tray <NUM> from the first position to the second position (e.g., the applied force <NUM> is exerted downward on the tray <NUM>).

The resistance device <NUM> is coupled to the tray <NUM> and automatically or controllably (e.g., operable under the control of the controller <NUM>) exerts a resisting force <NUM> on the tray <NUM> opposite to the applied force <NUM>. The resisting force <NUM> resists pivoting of the tray <NUM> from the first position to the second position. In the example shown in <FIG>, the resistance device <NUM> is an adjustable resistance friction hinge having a hinge axis coincident with the pivot axis <NUM>. As shown in <FIG>, there may be multiple resistance devices <NUM> disposed along the length of the tray <NUM> and each aligned with the pivot axis <NUM>. The friction within the hinge of the resistance device <NUM> is representable by the resisting force <NUM> pushing upward on the tray <NUM> (e.g., resisting picoting from the first position to the second position).

The heat sources <NUM>, <NUM> may be controlled to ramp the temperature of the composite material <NUM> from room temperature to a predetermined forming temperature or to within a predetermined forming temperature range (e.g., within <NUM> degrees of a predetermined forming temperature), and then to maintain the composite material <NUM> at this temperature or within this range of temperatures for a predetermined period of time. Once the predetermined forming temperature or predetermined forming temperature range is achieved, the force <NUM> applied to the tray <NUM> may be simultaneously controlled to cause the tray <NUM> to pivot from the first position to the second position. The pivoting may be at a controlled rate, such as a constant rate, such as by controlling the vacuum and/or pressure acting on the membrane <NUM>. The resistance force <NUM> applied by the resistance device <NUM> may also be controlled or, in some examples, may be automatic, with only the applied force <NUM> of the membrane <NUM> controlled to control the rate of pivoting. Pivoting causes the flange portions 14B, 14C to withdraw from the trays <NUM> and form to the second and third forming surfaces <NUM>, <NUM>, respectively, at a rate (e.g., inches withdrawn per second) that corresponds with the rate of pivoting (e.g., angles per second) of the tray <NUM>. A near extent <NUM> of the flange portion 14B closest to the forming tool <NUM> when the tray is in the first position will initially withdraw, with the far extent <NUM> of the flange portion 14B that is furthest from the forming tool <NUM> when the tray <NUM> is in the first position (e.g., the side edge of the flange portion 14B) being the last to withdraw and form to the second forming surface <NUM> when the tray <NUM> is pivoted further toward the second position. The flange portion 14B is thus heated by the second heat source <NUM> longer at and near the far extent <NUM> than at and near the near extent <NUM>. However, the near extent <NUM> moves little if at all further from the first heat source <NUM> during forming while the far extent <NUM> moves further away from the first heat source <NUM> according to the controlled rate of pivoting of the tray <NUM>. Thus, the declining contribution of heat from the first heat source <NUM> in the direction from the near extent <NUM> to the far extent <NUM> is countered by the increasing contribution of heat by the second heat source <NUM> in the direction from the near extent <NUM> to the far extent <NUM>. The ability of the controller <NUM> to control the rate of withdrawal of the flange portion 14C from the tray <NUM> (e.g., by controlling the applied force) while also controlling the heat output of the first heat source <NUM> and the second heat source <NUM> enables control of the internal temperature profile of the composite material <NUM>, including the ability to prevent or limit a temperature gradient in the flange portion 14B between a temperature at the top surface <NUM> of the composite material <NUM> and a temperature at the opposite bottom surface <NUM> of the composite material <NUM>.

The composite material <NUM> may be any composite to be formed to a desired composite structure by drape forming, and may include a first material arranged in a matrix of a second material different from the first material, with the second material softening when heated to allow the composite material to be drape formed to a desired shape. In an implementation, the composite material <NUM> may be carbon fiber disposed in a resin matrix such as an epoxy resin matrix. For example, the composite material <NUM> may be laminated plates or sheets of carbon fiber impregnated with an epoxy resin matrix. Prior to drape forming, the composite material <NUM> may have an overall flat shape, such as a flat sheet. During drape forming, the resin matrix must be sufficiently heated to allow the composite material <NUM> to form to the shape of the forming tool <NUM>. For example, when there are multiple layers (e.g., plies) of carbon fiber material, these layers slide relative to one another as the material <NUM> is formed to the shape of the forming tool <NUM>. Heating and softening of the resin matrix material enables this reorientation of the carbon fiber material to adopt the final formed shape composite structure. Heating of the composite material <NUM> to a uniform predetermined temperature or temperature range and forming the material at a controlled rate, such as a predetermined uniform rate, can best avoid the formation of wrinkles in the material. The composite material <NUM> may have a predetermined, designated forming temperature or temperature range (e.g., based upon prior testing) that enables the requisite pliability of the composite material <NUM> during forming, and may also have a predetermined maximum forming temperature and/or a predetermined maximum time above a threshold temperature that, if either is exceeded, may result in insufficient material or aesthetic properties of the final formed composite structure <NUM>. Additionally, an excessively long heating time adds to the manufacturing cycle time. If the composite material <NUM> is relatively thick (e.g., whether it is a single layer (also referred to as a single ply) that is relatively thick, or multiple layers), heating of the composite material <NUM> to a predetermined forming temperature or temperature range from only one side may require an unsatisfactorily long cycle time and/or may cause the side closest to the single heat source to be at an elevated temperature for longer than is optimal to attain desired material properties in the final formed composite structure. The two-sided heating solution disclosed herein solves these issues while integrating the controlled pivoting of the tray <NUM> to enable more uniform heating and forming of the flange portions 14B and 14C as described. In some implementations, heating time may be shortened by <NUM> percent with the two-sided heating solutions disclosed herein.

The flange forming device <NUM> may include one or more position sensors disposed on the standoff <NUM>, on the tray <NUM>, and/or on the resistance device <NUM> to enable the controller <NUM> to monitor the position of the tray <NUM>, and then, based on the position information, control the pressure differential acting on the membrane <NUM> (and, in some examples, control the resisting force <NUM> of the resistance device <NUM>), to control the rate of pivoting of the tray <NUM> and the resulting rate of forming of the flange portion 14B against the side surface <NUM> (and the flange portion 14C against the side surface <NUM>). For example, the controller <NUM> may implement a uniform rate of forming by control of the pressure differential acting on the membrane <NUM> (e.g., control of the level of vacuum <NUM> applied to the membrane <NUM>).

<FIG> is a side view illustration of the drape forming apparatus <NUM> of <FIG> at an intermediate stage of forming a composite structure <NUM> (shown in <FIG>). The trays <NUM> are shown pivoted from the first position of <FIG> to an intermediate position, with the flange portions 14B, 14C of the heated composite material <NUM> beginning to be withdrawn from the trays <NUM> and change shape from the configuration in which they are coplanar with the main portion 14A to a partially bent configuration. As discussed, the near extent <NUM> gradually receives less direct heating by the tray <NUM> via the second heat source <NUM> while the far extent <NUM> moves further from the first heat source <NUM> but continues in contact with the tray <NUM>, receiving direct heat from the tray <NUM> via the second heat source <NUM> as the tray <NUM> pivots in the gap between the forming tool <NUM> and the standoff <NUM>.

<FIG> is a side view illustration of the drape forming apparatus <NUM> with the pivotable trays <NUM> pivoted further than the intermediate position of <FIG> to the final second position at a final stage of forming the composite structure <NUM>. The heat sources <NUM>, <NUM> may each be independently controlled to continue heating according to a desired temperature profile for a predetermined time. For example, power to the heat sources <NUM>, <NUM> may be controlled to set the heat output of each of the heat sources <NUM>, <NUM> to zero as the composite structure <NUM> cools in the final shape shown in <FIG>. The vacuum/and or pressure on the membrane <NUM> can be released and the composite structure <NUM> then removed from the forming tool <NUM> in its final, formed shape. The trays <NUM> can be moved to the first position in preparation for forming a subsequent composite structure with the drape forming apparatus <NUM>.

<FIG> is a side view illustration of a second example of a drape forming apparatus <NUM> with two-sided heating and pivotable trays <NUM> in a first position supporting a composite material <NUM>. The drape forming apparatus <NUM> is identical to and functions as described with respect to the drape forming apparatus <NUM> except that the first heat source is a heat blanket <NUM> disposed on the membrane <NUM> rather than the at least one heat lamp <NUM> of the drape forming apparatus <NUM>. The heat blanket <NUM> may be sized to extend over the composite material <NUM> at least to the far extent <NUM> of the composite material <NUM>. The heat blanket <NUM> may be controlled via the controller <NUM>, and may provide a uniform heat output over the top surface <NUM> of the composite material <NUM>, or may provide more heat over the flange portions 14B, 14C or an amount of heat that differs at different areas of the flange portions 14B, 14C as may be desired to achieve a predetermined temperature profile through the composite material <NUM>. In an implementation, heat may be applied by the heat blanket <NUM> to heat the membrane <NUM> prior to applying the pressure differential (e.g., via the vacuum <NUM>) to the membrane <NUM>.

<FIG> is a side view illustration of a second example of a flange forming device <NUM> for use in place of flange forming device <NUM> in the drape forming apparatus <NUM> or <NUM>, or for use in any of the other drape forming apparatuses disclosed herein. The drape forming device <NUM> includes a standoff <NUM> with a pivotable tray <NUM> secured to the standoff and shown in a first position. The tray <NUM> is hinged to the standoff at hinges <NUM> and pivotable relative to the standoff <NUM> about pivot axis <NUM> at a hinged end <NUM>. The hinges <NUM> may not be friction hinges as in <FIG>, as the flange forming device <NUM> instead includes a resistance device <NUM> that may be a linear actuator having one end <NUM> pivotably coupled to the standoff <NUM> and an opposite end <NUM> pivotably coupled to the tray <NUM>. Linear actuator <NUM> may be actuated by any suitable means such as, but not limited to, electrical and pneumatic. The resistance device <NUM> may be controllable by the controller <NUM> (shown in <FIG>) to provide the resisting force <NUM> on the tray <NUM> opposing the applied force <NUM> of the membrane <NUM> (see <FIG>), and resisting pivoting of the tray <NUM> from the first position of <FIG> to a second position of <FIG>, or may automatically resist pivoting to provide the resisting force <NUM>. The resistance device <NUM> is shown in a fully deployed position in <FIG> and a fully retracted position in <FIG>.

As shown in <FIG>, the flange forming device <NUM> includes an end wall <NUM> coupled to the tray <NUM> and disposed between the membrane <NUM> and the second heat source <NUM> when the flange forming device <NUM> is used in the flange forming apparatus <NUM> of <FIG>. The end wall <NUM> serves as a barrier that prevents the flexible membrane <NUM> from being pulled under the tray <NUM> during application of the pressure differential in order to prevent entanglement of the membrane <NUM> that would interfere with pivoting of the tray <NUM>, and prevent contact of the membrane <NUM> with the second heat source <NUM>. The end wall <NUM> is disposed inward of an end wall <NUM> of the standoff <NUM>, and pivots with the tray <NUM> inward of the end wall <NUM>. <FIG> is a side view illustration of the flange forming device <NUM> with the end walls <NUM>, <NUM> removed for clarity in viewing other features, and with the pivotable tray <NUM> in a second position.

Referring to <FIG>, the tray <NUM> has a lip <NUM> with an aperture <NUM> extending therethrough. The flange forming device <NUM> also includes a latching device <NUM> secured to the standoff <NUM> and operable to latch the tray <NUM> in the second position. The latching device <NUM> may be secured to an inner side of the tray <NUM>, an inner side of the end wall <NUM>, or to a bracket of the standoff <NUM> that is disposed inward of both end walls <NUM>, <NUM>. The latching device <NUM> may be operatively connected to the controller <NUM> and actuatable in response to a control signal provided by the controller <NUM> to deploy a latch <NUM> that extends through the aperture <NUM> when the tray <NUM> is pivoted to the second position of <FIG>, thereby latching the tray <NUM> in the second position. Alternatively, the latching device <NUM> may automatically latch such as by the lip <NUM> triggering the latch, or otherwise. Latching of the tray <NUM> in the second position prevents the resistance device <NUM> from causing any spring back of the tray <NUM> toward the first position so that the tray <NUM> will not contact the formed composite structure <NUM> as it is curing on the forming tool <NUM>. This ability to latch the tray <NUM> enables the standoff <NUM> to be placed close to the forming tool <NUM> (e.g., minimizing the gap <NUM>) so that the tray <NUM> supports the flange 14B very close to the forming tool <NUM> during pivoting of the tray <NUM>, which may help prevent wrinkles.

<FIG> show another example of an alternative flange forming device <NUM> for use in any of the drape forming apparatuses disclosed herein. The flange forming device <NUM> includes many of the same components as the flange forming device <NUM>, such as the pivotable tray <NUM> shown in a first position in <FIG>, the second heat source <NUM> configured as the heat blanket secured to the underside of the tray <NUM>, a standoff <NUM>, and a plurality of the resistance devices <NUM> configured as linear actuators each having one end coupled to the standoff <NUM> and an opposite end coupled to the tray <NUM>. The resistance devices <NUM> are shown in fully deployed positions in <FIG>, but may be retracted to the fully retracted position to move the tray <NUM> to a second position like that shown in <FIG>. An end wall <NUM> extends from the tray <NUM> and serves as a barrier that prevents the flexible membrane <NUM> from being pulled under the tray <NUM> during application of the pressure differential to protect entanglement of the membrane <NUM> that would interfere with pivoting of the tray <NUM>, and prevent contact of the membrane <NUM> with the second heat source <NUM>. The end wall <NUM> is disposed inward of the end wall <NUM> of the standoff <NUM>, and pivots with the tray <NUM> inward of the end wall <NUM>. As best shown in <FIG>, a pin <NUM> extends inward from the end wall <NUM> into a slot <NUM> formed in the end wall <NUM>. Another end wall like end wall <NUM> may be disposed at the opposite end of the flange forming device <NUM> but is not shown in <FIG> and <FIG>. The pin <NUM> and the slot <NUM> together function as a guide to help stabilize and limit movement of the tray <NUM> to the direction of pivoting. As can be seen in <FIG> and <FIG>, the flange forming device <NUM> is elongated. Although shown as relatively straight along its length, multiple flange forming devices of differing lengths and varying in width can be positioned together for manufacturing a flange portion of a nonlinear (e.g., arcuate) composite structure. Accordingly, the applied force <NUM> is distributed uniformly along the length of the elongated tray <NUM> by the multiple resistance devices <NUM>. Support brackets <NUM> are spaced along the length of the flange forming device <NUM> and are mounted to a front wall <NUM> to provide structural integrity. The resistance devices <NUM> extend through apertures <NUM> in the front wall <NUM>, and a variety of apertures <NUM> are disposed in the end wall <NUM>. The apertures <NUM>, <NUM> reduce the thermal mass of the standoff <NUM>. The heat output of the second heat source <NUM> disposed on the underside of the tray <NUM> and of the first heat source <NUM> of <FIG> may be controlled to provide the desired forming temperature of range of forming temperatures as described while accounting for the thermal mass of the standoff <NUM>.

<FIG> is a fragmentary side view illustration of a third example of a drape forming apparatus <NUM> including a fourth example of a flange forming device <NUM> including the standoff <NUM> and with a pivotable tray <NUM> in a first position supporting the composite material <NUM>. <FIG> is a fragmentary side view illustration of the drape forming apparatus <NUM> of <FIG> with the pivotable tray <NUM> in a second position and the composite structure <NUM> formed. The drape forming apparatus <NUM> includes many of the same components as the drape forming apparatus <NUM>, including the forming tool <NUM>, the membrane <NUM> (shown in fragmentary view), at least one first heat source <NUM>, and a standoff <NUM> similar to standoff <NUM>. The controller <NUM> and the vacuum <NUM> may also be included, and are not shown in <FIG>. The pivotable tray <NUM> has a first side <NUM> that faces the first heat source <NUM> when the tray <NUM> is in the first position of <FIG>. The second heat source <NUM> is secured to the opposite second side <NUM> of the tray <NUM> and pivots with the tray <NUM>. The tray <NUM> is connected to the standoff <NUM> and is pivotable relative to the standoff <NUM> via rotatable levers 372A, 372B. The rotatable levers 372A, 372B are each pivotably connected at one end to the tray <NUM> and at an opposing end to the standoff <NUM>. The hinged tray <NUM> is rotatable about a first pivot axis 335A and a second pivot axis 336A defined between rotatable levers 372A, 372B and retractable hinged tray <NUM>, and rotatable levers 372A, 372B are rotatable about pivot axes 335B, 336B defined between rotatable levers 372A, 372B and standoff <NUM>, thereby defining a range of motion for retractable hinged tray <NUM> to be fully retractable within standoff <NUM>. The side of the standoff <NUM> facing the tray <NUM> has an open cavity into which the levers 372A, 372B extend and into which the tray <NUM> retracts when in the second position. As such, the range of motion of the tray <NUM> is <NUM> degrees, and facilitates reducing friction between at least one layer of composite material <NUM> and retractable hinged tray <NUM> as at least one layer of composite material <NUM> is withdrawn therefrom and, because the tray <NUM> withdraws into the cavity of the standoff <NUM>, facilitates reducing the likelihood of the membrane <NUM> from becoming caught between standoff <NUM> and retractable hinged tray <NUM>. The composite material <NUM> is also shown in fragmentary view, and may extend further to the right in the drawing as the drape forming apparatus <NUM> may include another flange forming device <NUM> disposed on the opposite side of the tool <NUM> as that shown for forming another flange portion.

<FIG> is a side view illustration of a fourth example of a drape forming apparatus <NUM> including a fifth example of a flange forming device <NUM> having a pivotable tray <NUM> shown in a first position. <FIG> is a side view of the drape forming apparatus <NUM> of <FIG> with the pivotable tray <NUM> pivoted to an intermediate position. Pivoting may continue to a second position in which the tray <NUM> is disposed at an angle to the standoff <NUM> like tray <NUM> in <FIG>. The drape forming apparatus <NUM> includes many of the same components as the drape forming apparatus <NUM>, including the forming tool <NUM>, the membrane <NUM> (shown in fragmentary view), at least one first heat source <NUM>, and the standoff <NUM>. The controller <NUM> and the vacuum <NUM> may also be included, and are not shown in <FIG>. The pivotable tray <NUM> has a first side <NUM> that faces the first heat source <NUM> when the tray <NUM> is in the first position of <FIG>. The second heat source <NUM> is secured to the opposite second side <NUM> of the tray <NUM> and pivots with the tray <NUM>. The tray <NUM> is connected to the standoff <NUM> and is pivotable relative to the standoff <NUM> via a resistance device <NUM> that is an integral reinforcement of the tray <NUM>. Stated differently, the resistance device is a reinforced portion of the tray <NUM> disposed at pivot axis <NUM>. The tray <NUM> is a single unitary structure, and deflects when the applied force <NUM> is induced against elongated tray <NUM> by the pressure differential over the membrane <NUM>. As such, reinforced portion <NUM> provides the counteractive resisting force <NUM> to the tray <NUM> to control the rate of pivoting of the tray <NUM> without having any moving parts. Reinforced portion <NUM> may be fabricated from the same material as tray <NUM>, or may be fabricated from a different stiffer material. When fabricated from the same material, the tray <NUM> may be thicker at the reinforced portion <NUM> to increase the stiffness of the tray <NUM> at the reinforced portion. The composite material <NUM> is also shown in fragmentary view, and may extend further to the right in the drawing as the drape forming apparatus <NUM> may include another flange forming device <NUM> disposed on the opposite side of the tool <NUM> as that shown for forming another flange portion.

<FIG> is a side view illustration of a fifth example of a drape forming apparatus <NUM> including a sixth example of a flange forming device <NUM> having a pivotable tray <NUM> in an intermediate position. The tray <NUM> is hinged to the standoff <NUM> at hinge <NUM> and pivotable relative to the standoff <NUM> about pivot axis <NUM> at a hinged end <NUM>. The hinge <NUM> is not a friction hinge as in <FIG>. Pivoting may continue to a second position in which the tray <NUM> is disposed at an angle to the standoff <NUM> like tray <NUM> in <FIG>. The drape forming apparatus <NUM> includes many of the same components as the drape forming apparatus <NUM>, including the forming tool <NUM>, the membrane <NUM> (shown in fragmentary view), at least one first heat source <NUM>, and the standoff <NUM>. The controller <NUM> and the vacuum <NUM> may also be included, and are not shown in <FIG>. The pivotable tray <NUM> has a first side <NUM> that faces the first heat source <NUM> when the tray <NUM> is in a first position like that of <FIG> (e.g., a horizontal position). The second heat source <NUM> is secured to the opposite second side <NUM> of the tray <NUM> and pivots with the tray <NUM>. A resistance device <NUM> that is a linear actuator like linear actuator <NUM> of <FIG>, has one end 172B pivotably connected to the tray and an opposite end 172A pivotably connected to the standoff <NUM>. The resistance device <NUM> may be controllable by the controller <NUM> (shown in <FIG>) to provide the resisting force <NUM> on the tray <NUM> opposing the applied force <NUM> of the membrane <NUM> (see <FIG>), and resisting pivoting of the tray <NUM> from the first position to a second position like that of <FIG>, or may automatically resist pivoting to provide the resistance force <NUM>. Because the pivotably connected end 172A of the resistance device <NUM> is at an exterior of the standoff <NUM> in the gap <NUM> rather than within a cavity of the standoff <NUM> as in standoff <NUM> in <FIG> and standoff <NUM> in <FIG>, the gap <NUM> is larger than when standoffs <NUM> or <NUM> are used in order to enable the tray <NUM> to pivot to a second position at which the composite material <NUM> is fully withdrawn and formed to the second surface <NUM>. The composite material <NUM> is also shown in fragmentary view, and may extend further to the right in the drawing as the drape forming apparatus <NUM> may include another flange forming device <NUM> disposed on the opposite side of the tool <NUM> as that shown for forming another flange portion.

<FIG> is a side view illustration of a sixth example of a drape forming apparatus <NUM> including a seventh example of a flange forming device <NUM> that has the pivotable tray <NUM> in an intermediate position. The tray <NUM> is hinged to the standoff <NUM> at hinge <NUM> and pivotable relative to the standoff <NUM> about pivot axis <NUM> at hinged end <NUM>. Pivoting may continue to a second position in which the tray <NUM> is disposed at an angle to the standoff <NUM> like tray <NUM> in <FIG>. The drape forming apparatus <NUM> includes many of the same components as the drape forming apparatus <NUM>, including the forming tool <NUM>, the membrane <NUM> (shown in fragmentary view), at least one first heat source <NUM>, and the standoff <NUM>. The controller <NUM> and the vacuum <NUM> may also be included, and are not shown in <FIG>. The pivotable tray <NUM> has a first side <NUM> that faces the first heat source <NUM> when the tray <NUM> is in a first position like that of <FIG> (e.g., a horizontal position). The second heat source <NUM> is secured to the opposite second side <NUM> of the tray <NUM> and pivots with the tray <NUM>. A resistance device <NUM> is an inflatable bladder that is disposed between the standoff <NUM> and the tray <NUM> in the gap <NUM> and applies the resisting force <NUM> to the tray <NUM> opposing the applied force <NUM>. The resistance device <NUM> may be adhered to the second heat source <NUM> and the underside of the tray <NUM> not covered by the second heat source <NUM>. The inflatable bladder <NUM> may be selectively filled with any suitable fluid, which enables inflatable bladder <NUM> to bias against tray <NUM> and provide the counteractive resisting force <NUM> thereto. As pressure is applied by pressurized bladder <NUM>, tray <NUM> deforms inflatable bladder <NUM> as tray <NUM> pivots about pivot axis <NUM>. Pressure within the resistance device <NUM> may be varied via a valve <NUM> controlled by the controller <NUM>, or the valve <NUM> may automatically release fluid in response to the applied force <NUM> to decrease pressure, allowing the tray <NUM> to pivot to the second position under the applied force <NUM>. The composite material <NUM> is also shown in fragmentary view, and may extend further to the right in the drawing as the drape forming apparatus <NUM> may include another flange forming device <NUM> disposed on the opposite side of the tool <NUM> as that shown for forming another flange portion.

<FIG> is a functional block diagram flow chart illustrating an example of a method <NUM> of forming a composite structure such as composite structure <NUM> using any of the drape forming apparatuses and flange forming devices disclosed herein. The method <NUM> may begin at block <NUM>, disposing at least one layer of composite material <NUM> over a first forming surface <NUM> of a forming tool <NUM>. Block <NUM> is accomplished so that a portion of the at least one layer of composite material <NUM> is positioned on a first side of a tray coplanar with the first forming surface <NUM> when the tray is in a first position. The tray may be any of the trays <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>, disclosed herein having a hinged end and a distal end with the distal end nearer the first forming surface <NUM> than the hinged end when the tray is in the first position.

The method <NUM> then proceeds to block <NUM>, disposing a membrane <NUM> over the forming tool <NUM> and the tray. With the composite material <NUM> and the membrane <NUM> disposed as set forth in blocks <NUM> and <NUM>, the method <NUM> proceeds to blocks <NUM> and <NUM>, heating a first side <NUM> of the at least one layer of composite material <NUM> with a first heat source <NUM> in block <NUM>, the first side facing the first heat source <NUM> when the tray is in the first position, and heating a second side <NUM> of the at least one layer of composite material <NUM> with a second heat source <NUM> in block <NUM>, the second heat source <NUM> disposed at a second side of the tray. Blocks <NUM> and <NUM> may be carried out simultaneously to shorten the processing time.

Moreover, the heating conducted in blocks <NUM> and <NUM> may be done in a controlled manner. For example, in optional block <NUM>, the temperature may be monitored at the first side of the membrane <NUM>, or at the first side of the tray, or simply at the first heat source <NUM>, such as with one or more thermocouples operatively connected to the controller <NUM>. The controller <NUM> may determine whether a predetermined temperature has been reached or exceeded in block <NUM>. If the predetermined temperature has not been reached or exceeded, the method <NUM> can optionally adjust the heat output of the first heat source <NUM> in block <NUM>, and then moves to block <NUM> to continue heating the first side in block <NUM> until the predetermined temperature of block <NUM> is reached or exceeded.

Similarly, in optional block <NUM>, the temperature may be monitored at the second side of the membrane <NUM>, or at the second side of the tray, or simply at the second heat source <NUM>, such as with one or more thermocouples operatively connected to the controller <NUM>. The controller <NUM> may determine whether a predetermined temperature has been reached or exceeded in block <NUM>. The predetermined temperature of block <NUM> may be the same as or different than the predetermined temperature of block <NUM>. If the predetermined temperature has not been reached or exceeded in block <NUM>, the method <NUM> can optionally adjust the heat output of the second heat source <NUM> in block <NUM>, and then continue heating the second side of the composite material <NUM> in block <NUM> until the predetermined temperature of block <NUM> is reached or exceeded. For example, adjusting the heat output in blocks <NUM>, <NUM> results in controlling the heat output of at least one of the first heat source and the second heat source to limit a temperature gradient between the first side of the at least one layer of composite material and the second side of the at least one layer of composite material.

Once the requisite temperatures have been achieved in both blocks <NUM> and <NUM>, the composite material <NUM> is sufficiently heated for drape forming a flange portion 14B (and, optionally, 14C), and the method <NUM> proceeds to block <NUM>, applying a force <NUM> (e.g., applied force <NUM>) on the tray such that the tray pivots about the hinged end <NUM>, the distal end <NUM> moves away from the forming tool <NUM>, and such that the portion 14B of the at least one layer of composite material <NUM> is withdrawn from the tray and is disposed against the second forming surface <NUM> of the forming tool <NUM> that is nonplanar with the first forming surface to form a flange. As discussed, the drape forming apparatuses disclosed herein may be configured so that applied pressure is applied to an exterior surface of the membrane <NUM>, a vacuum is applied to an interior surface of the membrane <NUM> (e.g., at the side of the membrane where the tray is disposed), or both.

Simultaneously with block <NUM>, the method <NUM> may include block <NUM>, exerting a resisting force <NUM> on the tray via a resistance device coupled to the tray to control a rate of pivoting of the tray, the resisting force <NUM> opposing the force applied <NUM> on the tray. In one example, the rate of pivoting of the tray may be controlled to be uniform (constant) and a resulting rate of forming the portion of the at least one layer of composite material against the second forming surface is therefore uniform (constant). Any of the resistance devices <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> disclosed herein may be used. As the resistance force <NUM> exerted by some examples of the resistance devices <NUM>, <NUM>, and <NUM> may be varied, optionally, the controller <NUM> may monitor the rate of pivoting of the tray in block <NUM> with position sensors or the like, determine in block <NUM> whether the rate of pivoting (e.g., angles per second) is within a predetermined range, and if not, adjust either or both of the applied force <NUM> or the resistance force <NUM> in block <NUM> to control the rate of pivoting of the tray. For example, the rate of pivoting could be adjusted by increasing or decreasing the pressure differential applied to the membrane <NUM> (e.g., increase or decrease pressure or vacuum), increasing or decreasing the friction of the friction hinge <NUM>, increasing or decreasing the deployment rate of the linear actuator <NUM>, or increasing or decreasing the rate of deflation of the resistance device <NUM>. As another alternative, any of the resistance devices disclosed herein may be configured to automatically (e.g., not via the controller <NUM>) provide a resistance force <NUM> that is not variable by the controller <NUM>, but that is at a predetermined magnitude that allows the tray to pivot at a rate equal to a desired forming rate of the flange portion, which may be based on prior testing, and will not pinch the composite material between the membrane <NUM> and the tray as it pivots.

Optionally, the method <NUM> may include block <NUM>, determining whether the tray reaches a predetermined second position, which is a final position of the tray in which the flange portion 14B of the composite material <NUM> is fully withdrawn from the tray and, accordingly, in contact with the second forming surface <NUM> in the shape of the composite structure <NUM>. A contact sensor may be utilized to determine the position of the tray in block <NUM>.

Optionally, in some implementations, the method <NUM> may include activating a latching device <NUM> to latch the tray in the second position in block <NUM>. As discussed, latching prevents spring back of resistance devices such as pneumatic linear actuators and is beneficial when the gap <NUM> is minimal and the tray could otherwise contact the flange portion 14B on spring back, potentially deforming the flange portion 14B.

Claim 1:
A drape forming apparatus (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) for use in forming a composite structure (<NUM>), the drape forming apparatus (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) comprising:
a forming tool (<NUM>) having a first forming surface (<NUM>) and a second forming surface (<NUM>) nonplanar with the first forming surface (<NUM>);
a tray (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) spaced apart from the forming tool (<NUM>) and having a first side (<NUM>) and a second side (<NUM>), the tray (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) having a hinged end (<NUM>) and a distal end (<NUM>), the tray (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) configured to pivot about the hinged end (<NUM>) from a first position to a second position under an applied force (<NUM>) such that the distal end (<NUM>) moves away from the forming tool (<NUM>);
a first heat source (<NUM>, <NUM>) and a second heat source (<NUM>);
wherein the first side (<NUM>) of the tray (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) faces the first heat source (<NUM>) when the tray (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) is in the first position; and
wherein the second heat source (<NUM>) is disposed at the second side (<NUM>) of the tray (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>).