Source: http://www.google.com/patents/US5919413?dq=6016038
Timestamp: 2015-08-01 20:48:25
Document Index: 103919913

Matched Legal Cases: ['art.\n6', 'art. 12', 'art 10', 'art 1855', 'art 1855', 'art 1855', 'art 1855']

Patent US5919413 - Method for inserting Z-pins - Google PatentsSearch Images Maps Play YouTube News Gmail Drive More »Sign inAdvanced Patent SearchPatentsI achieve positive, accurate placement of Z-pins in resin composite parts using a tool to guide the pins from the foam preform into the part. The tool has a reciprocating piston for crushing the foam to insert the pins and uses a positive stop to control penetration depth and positioning of the Z-pins....http://www.google.com/patents/US5919413?utm_source=gb-gplus-sharePatent US5919413 - Method for inserting Z-pinsAdvanced Patent SearchPublication numberUS5919413 APublication typeGrantApplication numberUS 08/997,046Publication dateJul 6, 1999Filing dateDec 23, 1997Priority dateMay 31, 1996Fee statusLapsedAlso published asUS5832594Publication number08997046, 997046, US 5919413 A, US 5919413A, US-A-5919413, US5919413 A, US5919413AInventorsSteven J. AvilaOriginal AssigneeThe Boeing CompanyExport CitationBiBTeX, EndNote, RefManPatent Citations (11), Referenced by (34), Classifications (44), Legal Events (5) External Links: USPTO, USPTO Assignment, EspacenetMethod for inserting Z-pins
US 5919413 AAbstract
1. A method for inserting a plurality of Z-pins to provide Z-direction fiber reinforcement into a resin composite part from a foam preform, comprising the steps of:(a) seating the preform on a positioning tool to align bores on an entry side in the positioning tool with the Z-pins of the preform; (b) positioning the part adjacent to the bores on an egress side of the positioning tool; and (c) driving the Z-pins through the bores of the positioning tool into the part by compressing the foam between a piston and the positioning tool. 2. The method of claim 1 wherein the Z-pins are inserted into the part to a predetermined depth by driving the piston against a tooling stop.
3. The method of claim 1 further comprising heating the part under elevated pressure to cure the resin while the part is on the tool.
4. The method of claim 1 further comprising the step of:guiding each Z-pin with a converging funnel nozzle formed into the entry side of the positioning tool into a respective bore sized to receive such Z-pin. 5. The method of claim 1 wherein driving the Z-pins inserts the Z-pins into the part substantially normal to the X-Y plane defined by fiber reinforcement in the part.
6. The method of claim 1 wherein the Z-pins are stainless steel, titanium, copper, graphite, epoxy, composite, glass, or carbon.
7. The method of claim 3 further comprising the step of:dislodging the cured part from the tool using ultrasound. 8. A method for inserting a plurality of Z-pins to provide Z-direction fiber reinforcement into a resin composite part from a pin-carrying foam preform, comprising the steps of:(a) loading the preform into a pin insertion tool; (b) sliding a piston in the tool to crush the preform and to drive the Z-pins into a pin placement guide plate having a plurality of bores, each bore receiving one Z-pin; (c) continuing to crush the preform with the piston to insert the Z-pins into the part in an entry surface registering with the guide plate. 9. The method of claim 8 further comprising the step of:stopping crushing motion of the piston into the preform with a tooling stop. 10. The method of claim 8 further comprising the step of:curing resin in the part at an elevated temperature and pressure within the tool following insertion of the Z-pins. 11. The method of claim 8 further comprising the stop of:creating stubble on the part on an emergence surface of the part by inserting the Z-pins completely through the part. 12. The method of claim 1 wherein the Z-pins extend completely through the part to define stubble on an entry side and emergence side of the part.
The present application is a divisional application of U.S. patent application Ser. No. 08/657,859, filed May 31, 1996, Now U.S. Pat. No. 5,832,594.
The present invention relates to reinforced composites, and, more particularly, to using pin insertion tooling to insert Z-pins reliably, accurately, and reproducibly into detail parts or precured strips.
In contrast, thermoplastic welding, which eliminates fasteners, joins thermoplastic composite components at high speeds with minimum touch labor and little, if any, pretreatments. The welding interlayer (comprising the susceptor and surrounding thermoplastic resin either coating the susceptor or sandwiching it) also can simultaneously take the place of shims required in mechanical fastening. As such, composite welding promises to be an affordable joining process. For "welding" a combination of thermoplastic and thermoset composite parts together, the resin that the susceptor melts functions as a hot melt adhesive. If fully realized, thermoplastic-thermoset bonding will further reduce the cost of composite assembly.
Significant effort has been expended in developing inductor and susceptor systems to optimize the heating of the bond line in thermoplastic assemblies. Induction coil structures and tailored susceptors have now been developed that provide adequate control and uniformity of heating of the bond line. One difficulty remaining to perfecting the process for producing large scale aerospace structures in a production environment involves control of the surface contact of the faying surfaces of the two parts to be welded together. The timing, intensity, and schedule of heat application is controlled so the material at the faying surfaces is brought to and maintained within the proper temperature range for the requisite amount of time for an adequate bond to form. Intimate contact is maintained while the melted or softened material hardens in its bonded condition.
A structural susceptor includes fiber reinforcement within the weld resin to alleviate residual tensile strain otherwise present in an unreinforced weld. This susceptor includes alternating layers of thin film thermoplastic resin sheets and fiber reinforcement (usually woven fiberglass fiber) sandwiching the conventional metal susceptor that is embedded in the resin. While the number of total plies in this structural susceptor is usually not critical, Boeing prefers to use at least two plies of fiber reinforcement on each side of the susceptor. This structural susceptor is described in greater detail in U.S. Pat. No. 5,717,191, which I incorporate by reference.
The need for a susceptor in the bond line poses many obstacles to the preparation of quality parts. The metal which is used because of its high susceptibility differs markedly in physical properties from the resin or fiber reinforcement so dealing with it becomes a significant issue. The reinforced susceptor of U.S. Pat. No. 5,808,281 (which I also incorporate by reference) overcomes problems with conventional susceptors by including the delicate metal foils (0.10-0.20 inch wide�0.005-0.010 inch thick; preferably 0.10�0.007 inch) in tandem with the warp fibers of the woven reinforcement fabric. The foil is always on the remote side of the fabric because it is between the warp thread and the weave threads. This arrangement holds the foils in place longitudinally in the fabric in electrical isolation from each other yet substantially covering the entire width of the weld surface while still having adequate space for the flow and fusion of the thermoplastic resin. Furthermore, in the bond line, the resin can contact, wet, and bond with the reinforcing fiber rather than being presented with the resinphilic metal of the conventional systems. There will be a resin-fiber interface with only short runs of a resin-metal interface. The short runs are the length of the diameter of two weave fibers plus the spatial gap between the weave fibers, which is quite small. Thus, the metal is shielded within the fabric and a better bond results. In this woven arrangement the foil can assume readily the contour of the reinforcement. Finally, the arrangement permits efficient heat transfer from the foil to the resin in the spatial region where the bond will focus.
Foster-Miller has been active in basic Z-pin research. U.S. Pat. No. 5,186,776 describes a technique for placing Z-pins in composite laminates involves heating and softening the laminates-with ultrasonic energy with a pin insertion tool which penetrates the laminate, moving fibers in the laminate aside. The pins are inserted either when the insertion tool is withdrawn or through a barrel in the tool prior to its being withdrawn. Cooling yields a pin-reinforced composite. U.S. Pat. No. 4,808,461 describes a structure for localized reinforcement of composite structure including a body of thermally decomposable material that has substantially opposed surfaces, a plurality of Z-pin reinforcing elements captured in the body and arranged generally perpendicular to one body surface. A pressure plate (i.e., a caul plate) on the other opposed body surface drives the Z-pins into the composite structure at the same time the body is heated under pressure and decomposes. I incorporate U.S. Pat. Nos. 4,808,461 and 5,186,776 by reference.
A need exists for a method to form a sandwich structure that (1) resists distortion and separation between layers, in particular, separation of the facesheets from the core; (2) maintains high structural integrity; (3) resists crack propagation; and (4) easily accommodates the removal of portions of core, as required by specific applications. The method should allow the structure to be easily manufactured and formed into a variety of shapes. In commonly owned U.S. patent application Ser. No. 08/582,297 (which I incorporate by reference), Childress described such a method of forming a pin-reinforced foam core sandwich structure. Facesheets of uncured fiber-reinforced resin (i.e., prepreg or B-stage thermoset) are placed on opposite sides of a foam core. The core has at least one compressible sublayer and contains a plurality of Z-pins spanning the foam between the facesheets. Childress inserted the Z-pins into the facesheets during autoclave curing of the face sheet resin when a compressible sublayer is crushed and the back pressure applied trough the caul plate or other suitable means drives the Z-pins into one or both of the facesheets to form a pin-reinforced foam core sandwich structure. By removing some of the foam core by dissolving, eroding, melting, drilling, or the like to leave a gap between the facesheets, he produced his corresponding column core structure.
In U.S. No. 5,589,016, Hoopingarner et al. describe a honeycomb core composite sandwich panel having a surrounding border element (i.e., a "closeout") made of rigid foam board. The two planar faces of the rigid foam board are embossed or scored with a scoring pattern of indentations usually in the form of interlinked equilateral triangles. The scoring is sufficiently deep numerous to provide escape paths for volatiles generated inside the panel during curing and bonding of the resin in the facesheets to the honeycomb core and peripheral foam. The scoring prevents the development of excessive pressure between the facesheets in the honeycomb core that otherwise would interfere with the bonding. I incorporate this application by reference.
Rorabaugh and Falcone discovered two ways to increase the pulloff strength in foam core sandwich structure. First, they form resin fillets around the fiber/resin interfaces at the contact faces of the foam core by dimpling the foam to create a fillet pocket prior to resin flow during curing. Second, they arrange the pins in an ordered fashion such as a tetrahedral configuration or a hat section configuration. In tetrahedral or hat section configurations, the pins not only provide a tie between the two skins but they also provide miniature structural support suited better for load transfer than normal or random off-normal (interlaced) or less ordered pin configurations. With ordering of the pins, they produce anisotropic properties. More details concerning their Z-pin improvements are available in their commonly owned U.S. patent application Ser. No. 08/628,879 entitled "Highly Ordered Z-Pin Structures," now abandoned, which I incorporate by reference.
In U.S. Pat. No. 5,868,886 entitled "Z-Pin Reinforced Bonds for Connecting Composite Structures," Childress introduced Z-pin mechanical reinforcement to the bond line of two or more composite elements by prefabricating cured composite elements that include protruding Z-pins (or stubble) along the element face that will contact the bond line. The stubble is formed by including peel plys on this face during pin insertion using, for example, the process described in U.S. patent application Ser. No. 08/582,297, entitled "Pin-Reinforced Sandwich Structure." When connecting the element to other composite structure, Childress removed the peel plys to expose the stubble. Then, he assembled the several elements in the completed assembly to define the bond line. The problem with this Childress method is that it introduces the Z-pins to the detail parts which forces modification of their manufacturing processes and tools.
Pannell discovered a method to achieve Z-pin reinforcement using ordinary detail parts. Described in U.S. Pat. No. 5,876,540 (which I incorporate by reference), Pannell use precured Z-pin strips to produce the reinforced joining of prefabricated composite detail parts in adhesive bonding, cocuring, or thermoplastic welding processes. The strips have pin stubble projecting on opposed faces. The strips eliminate the need to incorporate the stubble into the detail parts, which would be difficult with manufacturing operations like resin transfer molding (RTM) or fiber placement. The strips are compatible with all major joining processes, are easy to manufacture, are easy to store, and have lasting shelf-life.
In Childress's Z-pin bonding process, he prepares a precured composite detail part that has Z-pins (or "stubble") protruding from the detail along the intended bond line. To insert the pins in their intended location, he uses an insertion process like one of those described in U.S. Pat. No. 5,736,222 or U.S. patent application Ser. No. 08/582,297 or any other suitable insertion process. In Pannell's Z-pin bonding process, he makes precured strips that have stubble fields on opposed surfaces. Pannell positions the precured strip along the bond line between two conventional detail parts.
The function and properties of the Z-pins are described in U.S. Pat. No. 5,736,222 or U.S. patent application Ser. No. 08/582,297. In Z-pin bonding, the resins should be compatible with the intended joint. The Z-pins might be the same material as the reinforcing fibers in the composite detail parts or can be different, as the situation dictates.
As shown in FIG. 3, when the assembly of the spar 10a and panel 18 are bonded, the Z-pins in the stubble 12 penetrate into the uncured panel 18. In the circumstance where the panel 18a is precured, as shown in FIGS. 4 and 5, Childress uses a bond padup strip 20, typically of the same material as the detail parts being joined. The padup strip 20 is uncured during assembly and functions to bond the precured, thermoset detail parts when the bonding process is complete. The padup strip can be an uncured thermosetting resin prepreg with bonding becoming a cocuring process or might be any suitable adhesive bonding material. If the detail parts are thermoplastic, the pad up strip 20 might be a thermoplastic prepreg or a thermoplastic welding susceptor.
As best shown in FIG. 5, the spar detail part 10a includes a stubble surface so that the padup strip 20 ends up having pins extending upwardly from the panel 18a as well as downwardly from the spar 10a. As Shawn Pannell describes in his application Ser. No. 08/660,060, the pins might be carried in the padup strip with stubble on both faces with longer, integral pins if the detail parts are thermoplastic rather than being inserted into the spar and panel prior to their curing.
FIGS. 6 and 7 illustrate bonding of a wing skin to a spar. FIG. 6 shows an exploded view of the wing skin 100, padup strip 20, and spar 200 while FIG. 7 shows a typical cross-section taken along the bond line. While FIG. 6 & 7 illustrate a wing skin-spar joint, the process is applicable to any joint. This embodiment describes bonding using a sandwich core structure for the wing skin to produce the stubble region and subsequent bonding of the skin to the spar with an uncured padup strip in a cocure, adhesive bonding, or welding operation.
As best shown in FIG. 7, the skin 100 comprises a sandwich core structure of the type described in U.S. patent application Ser. No. 08/582,297 having outer face-sheets 105 & 110, crushable foam layers 115 and 120, and a central foam core 125 with Z-pins 130 extending through all five layers. Stubble on the interface surface is achieved by crushing layers 115 and 120 more than the combined thickness of facesheets 105 and 110 during the autoclave cycle when the pins are inserted into the facesheets. Of course, after curing, the central foam 115, 120 and 125 might be dissolved to make a column core skin structure.
The facesheets 105 & 110 are positioned adjacent the foam core 115, 120 and 125. Boeing usually uses a layer of adhesive to attach adjoining layers. The pin-reinforced foam core is formed using known methods (e.g., stitching or needling) or purchase it from companies such as Foster-Miller, Inc., in Waltham, Mass., and can be scored according to the Hoopingarner method to provide channels for venting of volatiles during curing.
If a high density sublayer 125 is included, it usually should be made of a material that will not crush during autoclave curing. Obviously, the precise temperatures and pressures to be used during autoclave curing will affect the selection of the material used to form the high density sublayer. Further considerations to be taken into account when selecting an appropriate high density sublayer material include whether the high density sublayer is to be removed after autoclave processing and the preferred method for removing it. Typically it is high density polystyrene or polyimide foam. It might be (i) syntactic foam having internal reinforcing spheres, (ii) a fiber-reinforced resin prepreg or composite, (iii) a fiberform or microform ceramic such as described in U.S. Pat. Nos. 5,376,598; 5,441,682; and 5,041,321 or in copending commonly owned U.S. patent application Ser. No. 08/209,847 or U.S. Pat. No. 5,863,846, (iv) a metal foil, (v) a metal foil resin laminate of the type described in U.S. Pat. No. 4,489,123 or U.S. Pat. No. 5,866,272 entitled "Titanium-Polymer Hybrid Laminates," or (vi) a foam filled honeycomb core. The central sublayer 125 might also be a honeycomb core with the cells arranged normal to the plane of the facesheets. As Hoopingarner suggests, the core might be a combination of these alternatives, like a central honeycomb core bordered by a foam closeout frame. If the high density sublayer is a prepreg or a composite, the product itself is a laminated composite. In such case, generally the resin in the facesheets would be the same as the resin in the high density sublayer.
The Z-pins 130 (here and in all the embodiments) may be any suitably rigid material, e.g., stainless steel, titanium, copper, graphite, epoxy, composite, glass, carbon, etc. Additionally, the Z-pins may be barbed, where appropriate, to increase their holding strength in the facesheets.
Various procedures are available for laying up the composite facesheets. Since such procedures are generally known to those skilled in the arts they are not described here. Although thick, metal sheets do not work well as facesheets, metal foil or metal foil/resin laminated composites are possibilities. The metal foil in such cases might be welded to metallic Z-pins in the fashion described in U.S. Pat. No. 5,862,975 entitled "Composite/Metal Structural Joint with Welded Z-Pins."
Boeing made 3/16 inch quasi-isotropic composite test specimens from AS4/3501-6 having 0.5% areal density, 16 mil diameter T300/3501-6 Z-pins with sufficient surface peel plys to yield 0.080 inch stubble. As a control, one-half of the specimens did not include Z-pins. Two stubbled parts were assembled around an AS4/3501-6 uncured scrim pad up about 0.090 inch thick with the stubble from each part overlapping, and bonded using a conventional bonding cycle. Then, the bonded assemblies were cut into 1�10 inch coupons, thereby having some pin-reinforced, bonded coupons and some coupons lacking pin reinforcement.
TABLE 1______________________________________Specimen  Load   Comments______________________________________Pinned: 1     5.4   2     4.8   3     2.86   *Failed in the laminate above the bond lineUnpinned:   4     2.75   5     3.64   6     3.49______________________________________
Ignoring specimen 3, the Z-pin reinforcement at this relatively low density improved the bond strength with this Mode 1 fatigue measure by about a 45% increase in the peel strength. Upon analysis of the pinned specimens, some pins were bent, which lowered the reinforcing value (reduced the measured load). Better bonds (i.e., joints) could be prepared using higher pressure during the bonding cycle.
I prepared additional specimens using AS4/3501-6 prepreg with 2% by area 0.020 diameter titanium Z-pins inserted into a spar cap. This spar was then cured at 350 degrees F. with Z-pin stubble left exposed on the spar cap. The Z-pin stubble was 0.20 long. This cured spar was then placed on an uncured skin laminate 0.30 inches thick, with the Z-pin stubble placed against the uncured skin. The spar, associated spar tooling, and skin were then vacuum bagged and autoclave cured at 350 degrees F., using a 100 psi autoclave pressure. The vacuum and autoclave pressure drove the spar down onto the uncured skin and inserted the Z-pin stubble into the skin. The cured final part was then trimmed for pull testing.
The precured strip 99 constitutes a plurality of plys of fiber-reinforced resin or a laminated resin-metal foil composite or any of the other constructions I discussed for the core of the sandwich structure in a pin-carrying foam. The strip 99 can be whatever thickness is appropriate, but typically is about 26-5 plys thick. Z-pins 130 extend in stubble fields on opposed faces of the strip 99.
The Childress process for Z-pinning requires that one side of the part be directly accessible to cure pressure or that at least one side of the part be precured to embed the Z-pins. There are many situations in assembly of aerospace composite structure where the need for internal tools precludes use of the Childress concept. For example, as shown in FIG. 16, an inaccessible flange occurs at the bond line between a C-channel 113 and a hat section 119. In this circumstance, however, a precured strip 99 readily allows a Z-pinned joint. The flange is inaccessible because the C-channel is filled with a tool 123 (FIG. 17) during cure and the hat section 119 is fastened to a skin panel to leave a closed volume. Collapse of a foam to drive the pins into the aligned parts is difficult to achieve while retaining close location tolerances for the mated parts.
For joining graphite-epoxy detail parts, the body of the precured strip 99 should be two plys of cured graphite/epoxy fabric. The plys are cured at the same time the pins are inserted with heat and pressure. Pannell places the prepreg on a silicone backing atop a hard tooling surface, and places a pin-carrying foam atop the prepreg. He completes the assembly with a rigid caul plate before enclosing all the layers with a vacuum bagging film that connects with a seal to the tooling surface. The pins from the pin-carrying foam are driven into the fabric generally in an autoclave under heat and pressure. The thickness of the silicone backing controls the penetration of the pins and produces a precured strip with the desired, opposing stubble fields.
FIGS. 18-20 illustrate my pin insertion tool that I can use to form detail parts having pin stubble or to make Pannell's precured strips. My tool 1800 includes a housing 1805 holding a sliding piston 1810 which can reciprocate between a loading position for receiving a pin-carrying foam 1815 in a cavity 1820 and an insertion position where the piston 1810 moves upwardly to crush the foam and to insert the pins 1825. The foam 1815 is of the Foster-Miller type previously described and is loaded onto the piston in cavity 1820. Seals 1830 permit the piston 1810 to slide along the walls of housing 1805 when pneumatic pressure is applied through inlet 1835 to chamber 1840 behind the piston. Motion of the piston 1810 toward removable cure tool 1845 is arrested with stop 1850 which also serves to control the depth of insertion of pins 1825 in the pin-carrying foam 1815 into the uncured detail part 1855 (or Pannell prepregs). The stop 1850 contacts replaceable stop 1860 that seats in the fixed support frame of the cure tool 1845 that is rigidly attached to the housing 1805 at the fixed wall defining cavity 1820. The replaceable stop 1860 allows adjustment of the depth of penetration of the pins into the detail part 1855. The cure tool 1845 fits rigidly in a matching receiving surface in the frame and does not move when piston 1810 moves upwardly. Yet, cure tool 1845 is replaceable to permit controlled insertion of different Z-pin orientations into the detail part 1855. During pin insertion through movement of the piston 1810, the detail part 1855 is held rigidly on the surface of the cure tool 1845 so that the Z-pins 1825 are positioned correctly.
As the piston 1810 moves upwardly to compress the pin-carrying foam 1815 against the cure tool 1845, the Z-pins 1825 in the foam register with an associated hole 1905 (FIGS. 19 or 20) in the cure tool 1845. To assure registration between the pin 1825 and hole 1905, each hole has a funnel nozzle 2005 to guide the pin into the hole and into its proper orientation in the detail part.
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