Patent Publication Number: US-2022227078-A1

Title: System and method for promoting inter-ply slippage

Description:
RELATED APPLICATIONS 
     The present non-provisional patent application is related to and claims priority benefit of prior-filed US provisional patent application Serial Application No. 63/138,609, filed Jan. 18, 2021, titled SYSTEM AND METHOD FOR PROMOTING INTER-PLY SLIPPAGE. The above-referenced US provisional patent application is hereby incorporated by reference into the present patent application in its entirety. 
    
    
     BACKGROUND 
     Stamp forming is often used for rapid manufacturing of thermoplastic composite laminates, and drape forming is often used to rapidly layup thermosetting composites. In both applications, as part thickness increases, bend radius decreases, or angle of bending increases, the composites become prone to wrinkling on concave sides and bridging on convex sides of the formed part. Such wrinkling and bridging are considered rejectable conditions for aerospace parts. 
     Wrinkling is reduced by tensioning a part blank with springs or retainers attached via holes in manufacturing excess of the part blank. For example, knotted wire or clevis type clips pull on the entire thickness of the part blank. This reduces the ability of the part blank to “book” at the edge of the laminate. Booking is necessary to avoid wrinkling or bridging in bend regions due to the differing path lengths through the thickness after forming. 
     Complex, multi-piece tooling with side action can be used to minimize wrinkling and bridging by incorporating moving tool segments to strategically time laminate compaction. For example, pressure may be applied in a sequence that promotes inter-ply slippage while keeping molten material in tension to avoid wrinkling. This can be expensive, may require more maintenance than simple two-piece tooling, and may require extensive experience to design and operate properly. 
     SUMMARY 
     Embodiments of the invention solve the above-mentioned problems and other problems and provide a distinct advancement in the art of composite part forming systems. More particularly, the invention provides a composite part forming system that promotes inter-ply slippage between plies of a composite material blank. 
     An embodiment of the composite part forming system broadly comprises a female tool, an actuator, a male tool, and composite material tensioning system. The composite material tensioning system induces more tension to some of the plies depending on whether those plies are wrinkle prone or not. 
     The female tool includes concave radiused inner corners and convex radiused lead corners. The female tool is formed of a substantially rigid material configured for supporting composite material during layup and prior to and/or during curing. 
     The actuator is configured to urge the male tool and female tool together. In one embodiment, the actuator supports or suspends the male tool above the female tool and actuates the male tool downward toward the female tool. 
     The male tool includes convex radiused inner corners and concave radiused lead corners. The male tool is formed of substantially rigid material configured for shaping the composite material during layup and prior to and/or during curing. 
     The tensioning system comprises opposing first and second clevises and opposing first and second clevis pins. The tensioning system may also include biasing members (e.g., springs), cables, linkages, or similar components for applying tension in the composite material. 
     The first clevis is U-shaped or C-shaped and includes opposing holes for receiving the first clevis pin therethrough. The opposing holes loosely align with a tension hole in excess manufacturing portions of the composite material. The opposing holes are offset from each other in the direction of applied tension so that the first clevis pin is oriented at a non-perpendicular angle in the tension hole relative to the plies. 
     The first clevis pin is configured to be inserted through the opposing holes and tension hole to link the first clevis to the composite material. The first clevis pin is also configured to be oriented diagonally through the tension hole due to the offset positioning of the opposing holes. 
     The second clevis is U-shaped or C-shaped and includes opposing holes for receiving the second clevis pin therethrough. The opposing holes align with another tension hole in excess manufacturing portions of the composite material opposite the tension hole. Unlike the opposing holes of the first clevis, the opposing holes of the second clevis may be axially aligned so that the second clevis pin is perpendicular to the direction of applied tension. Alternatively, the opposing holes of the second clevis may be offset from each other similar to the opposing holes of the first clevis. 
     The second clevis pin may be substantially similar to the first clevis pin. The second clevis pin is configured to extend through the opposing holes of the second clevis and the tension hole of the composite material. 
     In use, the clevises are positioned at certain locations along the periphery of the composite material with the opposing holes of the clevises aligned with the tension holes of the composite material. The clevis pins are inserted into the opposing holes of the clevises and through the tension holes of the composite material. 
     The clevises are then pulled in opposite directions from each other to induce tension in plies of the composite material via the clevis pins. The clevis pins induce more tension to some of the plies depending on whether those plies are wrinkle prone or not (based on their position in the completed part). In this case, the upper plies are more susceptible to wrinkling due to their closer proximity to the male tool and thus are engaged with more tension by the diagonally oriented clevis than the lower plies. 
     The male tool is then moved by the actuator toward the female tool until the male tool and female tool are fully engaged with each other. The composite material complies with shape-forming features of the male tool and female tool so that the composite material takes a desired shape when the male tool and female tool are fully engaged with each other. The clevis pins may pull through the composite material when tension exceeds bearing strength of the composite material. 
     The above-described composite part forming system provides several advantages. For example, plies of the composite material that are on the inside of a bend (and thus are more susceptible to wrinkling) are stretched under more tension than plies in the middle or on the outside of the bend. This difference in tension endured by adjacent plies promotes inter-ply slippage, which prevents wrinkling and bridging. 
     The composite part forming system can be used in aircraft production, automobile production, and other applications that use thermoplastic composite stamp forming, thermosetting laminate hot drape forming, and the like. The composite part forming system also reduces scrap. 
     Another embodiment is a composite tensioning system broadly comprising a clevis and clevis pin in which the clevis is U-shaped or C-shaped and includes opposing holes that are aligned with each other for receiving the clevis pin perpendicularly therethrough. 
     The clevis pin is configured to extend perpendicularly through the aligned opposing holes and a tension hole of composite material. The tension hole is tapered on its outer side. That is, outer edges of the tension hole are initially closer to the clevis pin in plies that are more susceptible to wrinkling and farther away in plies that are less susceptible to wrinkling. To that end, the tension hole may be machined to a desired shape. 
     In use, the clevis pin induces more tension to some of the plies depending on whether those plies are wrinkle prone or not (based on their position in the completed part). In this case, the upper plies are more susceptible to wrinkling due to their closer proximity to the male tool and thus are engaged with more tension by the clevis pin than the lower plies according to the tapered outer sides of the tension holes. This difference in tension endured by adjacent plies promotes inter-ply slippage, which prevents wrinkling and bridging. 
     Another embodiment is a composite tensioning system broadly comprising a clevis and clevis pin in which the clevis is U-shaped or C-shaped and includes opposing holes that have different dimensions to accommodate the clevis pin. For example, one hole may have a relatively larger diameter while the opposing hole may have a relatively smaller diameter. 
     The clevis pin includes a number of step-down ledges and is configured to be inserted perpendicularly through the opposing holes of the clevis and a tension hole of composite material. The clevis pin thus forms a discrete tapered profile. 
     The clevis pin induces more tension to some plies of composite material depending on whether those plies are wrinkle prone or not (based on their position in the completed part). In this case, the upper plies are more susceptible to wrinkling due to their proximity to the male tool and thus are engaged with more tension by more prominent step-down ledges of the clevis pin. The lower plies are less susceptible to wrinkling and thus are engaged with less tension by the less prominent step-down ledges of the clevis pin. This difference in tension endured by adjacent plies promotes inter-ply slippage, which prevents wrinkling and bridging. The benefit is further enhanced by the larger engagement area with the higher tension plies since the larger area can provide more tension before the soft surrounding laminate deforms. 
     Another embodiment is a composite tensioning system broadly comprising and clevis pin in which the clevis is U-shaped or C-shaped and includes a single hole on side of the clevis. The clevis pin is configured to extend cantilever through the hole of the clevis and at least partially through a tension hole of composite material. The clevis pin does not extend fully through the tension hole when fully inserted. 
     In use, the clevis pin engages only some plies of composite material. In this way, the clevis pin induces more tension to some of the plies depending on whether those plies are wrinkle prone or not (based on their position in the completed part). In this case, the upper plies are more susceptible to wrinkling due to their proximity to the male tool and thus are engaged directly by the clevis pin. The lower plies are only indirectly under tension via the directly-engaged plies. This difference in tension endured by adjacent plies promotes inter-ply slippage, which prevents wrinkling and bridging. 
     Another embodiment is a composite tensioning system broadly comprising a cantilever pin including a neck and a head. The cantilever pin is configured to be attached to a wire on a distal end of the cantilever pin opposite the head. 
     The neck is configured to extend through a tension hole of composite material. The head is wider than the neck and is configured to anchor the cantilever pin in the tension hole or prevent the cantilever pin from being pulled through the tension hole. 
     In use, the wire pulls the cantilever pin via the distal end of the cantilever pin. The cantilever load induces more tension in some of the plies of composite material depending on whether those plies are wrinkle prone or not (based on their position in the completed part). To that end, the cantilever pin may rotate about a midplane. In this case, the upper plies are more susceptible to wrinkling due to their proximity to the male tool and are engaged with more tension by the distal end of the cantilever pin. The lower plies are less susceptible to wrinkling and thus are engaged with less tension by the cantilever pin or may be pushed into forming process. This difference in tension endured by adjacent plies promotes inter-ply slippage, which prevents wrinkling and bridging. 
     Another embodiment is a hot drape forming system broadly comprising a mold, an inflatable bladder, an actuator, and a composite tensioning system. The composite tensioning system may be substantially similar to one of the composite tensioning systems described previously. 
     The mold includes convex radiused inner corners and concave radiused lead corners. The mold is formed of substantially rigid material configured for shaping the composite material. 
     The inflatable bladder is positioned above the composite material opposite the mold and is flexible, malleable, or compliant to shape the composite material around the mold when the inflatable bladder is inflated or actuated (after being inflated) against the mold. The inflatable bladder may have a biasing shape to assist in pressing the composite material along sides of the mold. 
     The actuator is positioned above the inflatable bladder and is configured to move the inflatable bladder into engagement with the composite material. The actuator may be further configured to compress the inflatable bladder against the mold so the inflatable bladder shapes the composite material around the mold. 
     The composite tensioning system includes a biasing element, tension wires, and tension connectors (clevises and clevis pins or cantilever pins as described above). The composite tensioning system is configured to induce tension in the composite material as the composite material is draped over the mold via the inflatable bladder. 
     The biasing elements is configured to exert a tension force on the tension wires and may include springs, weights, pressurized or vacuum systems, or the like. The composite tensioning system is configured to move along the axis of movement of the inflatable bladder (e.g., downward) during forming to more effectively control an amount of tension on the composite material. 
     The tension wires connect the biasing elements to the composite material via the tension connectors for transferring the tension force from the biasing elements to the composite material. The tension wires are configured to at least partially wrap around the inflatable bladder as the inflatable bladder presses down the sides of the mold. 
     The tension connectors (clevises and clevis pins or cantilever pins as described above) connect the tension wires to the composite material. The tension connectors are configured to distribute tension to each ply in the composite material according to the ply&#39;s susceptibility to wrinkling. 
     This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the detailed description. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter. Other aspects and advantages of the present invention will be apparent from the following detailed description of the embodiments and the accompanying drawing figures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING FIGURES 
       Embodiments of the present invention are described in detail below with reference to the attached drawing figures, wherein: 
         FIG. 1  is an elevation view of a composite part forming system constructed in accordance with an embodiment of the invention; 
         FIG. 2  is another elevation view of the composite part forming system of  FIG. 1 ; 
         FIG. 3  is an elevation view of a composite part formed by the composite part forming system of  FIG. 1 ; 
         FIG. 4  is an enlarged elevation view of certain components of the composite part forming system of  FIG. 1 ; 
         FIG. 5  is an enlarged elevation view of certain components of a composite part forming system constructed in accordance with another embodiment of the invention; 
         FIG. 6  is an enlarged elevation view of certain components of a composite part forming system constructed in accordance with another embodiment of the invention; 
         FIG. 7  is an enlarged elevation view of certain components of a composite part forming system constructed in accordance with another embodiment of the invention; 
         FIG. 8  is an enlarged elevation view of certain components of a composite part forming system constructed in accordance with another embodiment of the invention; 
         FIG. 9  is an elevation view of a composite part forming system constructed in accordance with another embodiment of the invention; and 
         FIG. 10  is another elevation view of the composite part forming system of  FIG. 9 . 
     
    
    
     The drawing figures do not limit the present invention to the specific embodiments disclosed and described herein. The drawings are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of the invention. 
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     The following detailed description of the invention references the accompanying drawings that illustrate specific embodiments in which the invention can be practiced. The embodiments are intended to describe aspects of the invention in sufficient detail to enable those skilled in the art to practice the invention. Other embodiments can be utilized and changes can be made without departing from the scope of the present invention. The following detailed description is, therefore, not to be taken in a limiting sense. The scope of the present invention is defined only by the appended claims, along with the full scope of equivalents to which such claims are entitled. 
     Turning to  FIGS. 1-4 , a composite part forming system  10  constructed in accordance with an embodiment of the invention is illustrated. The composite part forming system  10  broadly comprises a female tool  12 , an actuator  14 , a male tool  16 , and composite material tensioning system  18 . 
     The female tool  12  may be a mold, layup tool, bladder, or the like and may have concave radiused inner corners  20  and convex radiused lead corners  22 . The female tool  16  may be made of a substantially rigid material configured for supporting a composite material blank (e.g., composite material  100 ) during layup and prior to and/or during curing. 
     The actuator  14  may be configured to urge the male tool  16  and female tool  12  together. In one embodiment, the actuator  14  supports or suspends the male tool  16  above the female tool  12  and actuates the male tool  16  downward toward the female tool  12 . 
     The male tool  16  may be a mold, layup tool, bladder, or the like and may have convex radiused inner corners  24  and concave radiused lead corners  26 . The male tool  16  may be made of a substantially rigid material configured for shaping the composite material  100  during layup and prior to and/or during curing. 
     The composite material tensioning system  18  broadly comprises opposing first and second clevises  28 A, B, and opposing first and second clevis pins  30 A, B. Two clevises and two clevis pins are shown, but any number of clevises and clevis pins may be used to apply tension in the composite material  100 . The composite material tensioning system  18  may also include biasing members, cables, linkages, or similar components for applying tension in the composite material  100 . 
     The first clevis  28 A is U-shaped or C-shaped and includes opposing holes  32 A,B for receiving the first clevis pin  30 A therethrough. The opposing holes  32 A,B loosely align with a tension hole  102  in excess manufacturing portions of the composite material  100 . The opposing holes  32 A,B may be offset from each other in the direction of applied tension so that the first clevis pin  30 A is angled in the tension hole  102 . 
     The first clevis pin  30 A is configured to be inserted through the opposing holes  32 A,B and tension hole  102  to link the first clevis  28 A to the composite material  100 . The first clevis pin  30 A may be straight and configured to be oriented diagonally through the tension hole  102  due to the offset positioning of the opposing holes  32 A,B. Alternatively, the first clevis pin  30 A may have an angled, bent, eccentric, tapered, or diagonal shape. The first clevis pin  30 A may also include a head or flange for preventing the first clevis pin  30 A from completely passing through the first clevis  28 A and tension hole  102 . The first clevis pin  30 A may be configured to be secured to the composite material  100  via linchpin or similar component. 
     The second clevis  28 B is U-shaped or C-shaped and includes opposing holes  34 A,B for receiving the second clevis pin  30 B therethrough. The opposing holes  32  align with another tension hole in excess manufacturing portions of the composite material  100  opposite the tension hole  102 . Unlike the opposing holes  32 A,B, the opposing holes  34 A,B may be axially aligned so that the second clevis pin  30 B is perpendicular to the direction of applied tension. Alternatively, the opposing holes  34 A,B may be offset from each other similar to the opposing holes  32 A,B. 
     The second clevis pin  30 B may be substantially similar the first clevis pin  30 A. The second clevis pin  30 B may be configured to extend through the opposing holes  34 A,B of the second clevis  28 B and the tension hole  102  of the composite material  100 . The second clevis pin  30 B may be straight or may have an angled, bent, eccentric, or tapered, or diagonal shape. 
     In use, the clevises  28 A,B are positioned at certain locations along the periphery of the composite material  100  with the opposing holes of the clevises  28 A,B aligned with the tension holes of the composite material  100 . The clevis pins  30 A,B are inserted into the opposing holes  32 A, B and  34 A, B of the clevises  28 A, B and through the tension holes of the composite material  100 . To that end, the tension holes may be drilled or machined into the composite material  100 . 
     The clevises  28 A,B may then be pulled in opposite directions from each other to induce tension in plies  104  of the composite material  100  via the clevis pins  30 A,B. Various tensioning arrangements are possible for applying force to each of the clevises  28 A,B to pull them in opposite directions. One example of a tensioning arrangement having biasing elements for pulling the clevises in opposite directions is described below in connection with  FIG. 5 . As another example, a lever may be used to produce shear in the periphery outside of the composite part to enforce the displacement to promote laminate booking. Importantly, the diagonally oriented clevis pin  30 A induce more tension to some of the plies depending on whether those plies are wrinkle prone or not (based on their position in the completed part). In the illustrated example, the upper plies are more susceptible to wrinkling and thus are engaged with more tension by the diagonally oriented clevis  28 A than the lower plies. 
     Ply tension may be a function of a ply&#39;s position in the composite material  100 . For example, a non-curved, diagonal clevis pin may apply linearly decreasing tension from one side of the composite material  100  to the opposing side of the composite material  100 . Alternatively, ply tension may increase by larger orders or may increase by a tapered amount. 
     The male tool  16  may then be moved by the actuator  14  toward the female tool  12  until the male tool  16  and female tool  12  are fully engaged with each other. The composite material  100  complies with shape-forming features of the male tool  16  and female tool  12  so that the composite material  100  takes a desired shape when the male tool  16  and female tool  12  are fully engaged with each other. The clevis pins  30 A, B may pull through the composite material when tension exceeds bearing strength of the composite material. 
     The above-described composite part forming system  10  provides several advantages. For example, plies of the composite material  100  that are on the inside of a bend (and thus are more susceptible to wrinkling) are stretched under more tension than plies in the middle or on the outside of the bend. This difference in tension endured by adjacent plies promotes inter-ply slippage, which prevents wrinkling and bridging. 
     The composite part forming system  10  can be used in aircraft production, automobile production, and other applications that use thermoplastic composite stamp forming, thermosetting laminate hot drape forming, and the like. The composite part forming system  10  also reduces scrap and tooling costs. 
     Turning to  FIG. 5 , a clevis  200  and clevis pin  202  constructed in accordance with another embodiment is illustrated. The clevis  200  may be U-shaped or C-shaped and includes opposing holes  204  that are aligned with each other. 
     The clevis pin  202  may be configured to extend perpendicularly through the aligned opposing holes  204  and a tension hole  302  of composite material  300 . The tension hole  302  may be tapered on its outer side. That is, outer edges of the tension hole  302  are initially closer to the clevis pin  202  in plies that are more susceptible to wrinkling and farther away in plies that are less susceptible to wrinkling. To that end, the tension hole  302  may be machined to a desired shape. 
     In use, the clevis pin  202  may induce more tension to some of the plies  304  depending on whether those plies are wrinkle prone or not (based on their position in the completed part). In the illustrated example, the upper plies are more susceptible to wrinkling and thus are engaged with more tension by the clevis pin  202  than the lower plies due to the tapered outer sides of the tension holes  302 . This difference in tension endured by adjacent plies promotes inter-ply slippage, which prevents wrinkling and bridging. 
     Turning to  FIG. 6 , a clevis  400  and clevis pin  402  constructed in accordance with another embodiment is illustrated. The clevis  400  may be U-shaped or C-shaped and includes opposing holes  404 . The opposing holes  404  may have different dimensions to accommodate the clevis pin  402 . For example, one hole may have a relatively larger diameter while the opposing hole may have a relatively smaller diameter. 
     The clevis pin  402  may include a plurality of step-down ledges  406  and may be configured to be inserted perpendicularly through the opposing holes  404  of the clevis  400  and a tension hole  502  of composite material  500 . The clevis pin  402  thus may form a discrete tapered profile. 
     The clevis pin  402  may induce more tension to some of plies  504  of composite material  500  depending on whether those plies are wrinkle prone or not (based on their position in the completed part). In the illustrated example, the upper plies are more susceptible to wrinkling and thus are engaged with more tension by more prominent ones of the step-down ledges  406  of the clevis pin  402 . The lower plies are less susceptible to wrinkling and thus are engaged with less tension by the less prominent ones of the step-down ledges  406  of the clevis pin  402 . This difference in tension endured by adjacent plies promotes inter-ply slippage, which prevents wrinkling and bridging. 
     Turning to  FIG. 7 , a clevis  600  and clevis pin  602  constructed in accordance with another embodiment is illustrated. The clevis  600  may be U-shaped or C-shaped and may include a single hole  604 . 
     The clevis pin  602  is configured to extend cantilever through the hole  604  of the clevis  600  and at least partially through a tension hole  702  of composite material  700 . The clevis pin  602  does not extend fully through the tension hole  702  when fully inserted. 
     In use, the clevis pin  602  may engage only some plies  704  of the composite material  700 . In this way, the clevis pin  602  may induce more tension to some of the plies depending on whether those plies are wrinkle prone or not (based on their position in the completed part). In the illustrated example, the upper plies are more susceptible to wrinkling and thus are engaged directly by the clevis pin  602 . The lower plies are only indirectly under tension via the directly-engaged plies. This difference in tension endured by adjacent plies promotes inter-ply slippage, which prevents wrinkling and bridging. 
     Turning to another embodiment of the invention illustrated in  FIG. 8 , one or both of the tensioning connectors of a tensioning system may comprise a cantilever pin  800  employed without the clevises used in the prior embodiments. Each cantilever pin  800  may include a neck  802  and a head  804 . Each cantilever pin  800  may be attached to a wire  806  on a distal end  808  opposite the head  804 . 
     The neck  802  may be configured to extend through a tension hole  902  of composite material  900 . The head  804  may be wider than the neck  802  and may anchor the cantilever pin  800  in the tension hole  902  or prevent the cantilever pin  800  from being pulled through the tension hole  902 . 
     In use, the wire  806  pulls the cantilever pin  800  via the distal end  808  of the cantilever pin  800 . The cantilever load may induce more tension in some of the plies  904  of composite material  900  depending on whether those plies are wrinkle prone or not (based on their position in the completed part). To that end, the cantilever pin  800  may rotate about a midplane. In the illustrated example, the upper plies are more susceptible to wrinkling and are engaged with more tension by the distal end  808  of the cantilever pin  800 . The lower plies are less susceptible to wrinkling and thus are engaged with less tension by the cantilever pin  800  or may be pushed into forming process. This difference in tension endured by adjacent plies promotes inter-ply slippage, which prevents wrinkling and bridging. 
     Turning to  FIGS. 9 and 10 , a hot drape forming system  1000  constructed in accordance with another embodiment is illustrated. The hot drape forming system  1000  broadly comprises a mold  1002 , an inflatable bladder  1004 , an actuator  1006 , and a composite tensioning system  1008 . The composite tensioning system  1008  may be substantially similar to the composite material tensioning system  18  described previously, and may likewise include clevises as described in connection with  FIGS. 1-4  or a system using a cantilever pin without a clevis, as described in connection with  FIG. 5 . 
     The mold  1002  may be a male layup tool, bladder, or the like and may have convex radiused inner corners  1010  and concave radiused lead corners  1012 . The mold  1002  may be made of a substantially rigid material configured for shaping the composite material  2000 . 
     The inflatable bladder  1004  may be positioned above the composite material  2000  opposite the mold  1002  and may be flexible, malleable, or compliant to shape the composite material  2000  around the mold  1002  when the inflatable bladder  1004  is inflated. The inflatable bladder  1004  may have a biasing shape to assist in pressing the composite material  2000  along sides of the mold  1002 . 
     The actuator  1006  may be positioned above the inflatable bladder  1004  and may be configured to move the inflatable bladder  1004  into engagement with the composite material  2000 . The actuator  1006  may be further configured to compress the inflatable bladder  1004  against the mold  1002  so the inflatable bladder  1004  shapes the composite material  2000  around the mold  1002 . 
     The composite tensioning system  1008  may include a biasing element  1014 , optional tension wires, and tension connectors  1016  (clevises and clevis pins or cantilever pins as described above). The composite tensioning system  1008  may be configured to induce tension in the composite material  2000  as the composite material  2000  is draped over the mold  1002  via the inflatable bladder  1004 . 
     The biasing elements  1014  may be configured to exert a tension force on the tension connectors  1016  via the tension wires and may include springs, weights, pressurized or vacuum systems, or the like. The composite tensioning system  1008  may be configured to move along the axis of movement of the inflatable bladder (e.g., downward) during forming to more effectively control an amount of tension on the composite material  2000 . 
     The tension wires may connect the biasing elements  1014  to the composite material  2000  via the tension connectors  1016  for transferring the tension force from the biasing elements  1014  to the composite material  2000 . The tension wires may be configured to at least partially wrap around the inflatable bladder  1004  as the inflatable bladder  1004  presses down the sides of the mold  1002 . 
     The tension connectors  1016  (clevises and clevis pins or cantilever pins as described above) may connect the tension wires to the composite material  2000 . The tension connectors are configured to distribute tension to each ply in the composite material  2000  according to the ply&#39;s susceptibility to wrinkling. 
     In use, the composite material  2000  may be connected to the tension wires via the tension connectors  1016 . Initial tension may be applied to the tension wires to suspend the composite material  2000  above the mold  1002 . This may reduce the need for heating the mold  1002  since cooling of the composite material  2000  can be delayed via the suspension. The initial tension may also assist in blank trellising in certain areas of the composite material  2000 . 
     The inflatable bladder  1004  may then be inflated. Alternatively, the inflatable bladder  1004  may be pre-inflated or permanently inflated. The actuator  1006  may also press the inflatable bladder  1004  against the composite material  2000 . 
     The biasing elements  1014  may induce additional tension into the composite material  2000  so that the composite material  2000  is subjected to a forming tension. Furthermore, the biasing elements  1014  and tension wires may be moved to change the origin of the tension force, thereby affecting the direction, intensity, and timing of the tension. 
     To promote early tensioning in the forming process, the tension wires may be pulled from a position that causes the inflatable bladder  1004  to quickly contact the tension wires. To promote late tensioning, the tension wires may be pulled from a position where the inflatable bladder  1004  does not contact the tension wires until later in the forming process or not at all. 
     The tension connectors  1016  (clevises and clevis pins or cantilever pins as described above) may induce more tension to some of the plies depending on whether those plies are wrinkle prone or not (based on their position in the completed part). In the illustrated example, the lower plies are more susceptible to wrinkling near the convex radiused inner corners  1010  and thus are engaged with more tension than the upper plies. This difference in tension endured by adjacent plies promotes inter-ply slippage, which prevents wrinkling and bridging. The tension connectors  1016  may pull through the composite material  2000  when tension exceeds bearing strength of the composite material  2000 , as seen in  FIG. 10 . 
     Although the invention has been described with reference to the embodiments illustrated in the attached drawing figures, it is noted that equivalents may be employed and substitutions made herein without departing from the scope of the invention as recited in the claims.