Source: http://www.google.com/patents/US5863635?dq=6,163,776
Timestamp: 2017-04-26 21:11:45
Document Index: 48156013

Matched Legal Cases: ['art 10', 'art 10', 'art 10', 'art 10', 'art 10', 'art 10', 'art 500', 'art 500', 'art 500', 'art 500', 'art 500', 'art 1555', 'art 1555', 'art 1555', 'art 1555']

Patent US5863635 - Composite detail having Z-pin stubble - Google PatentsSearch Images Maps Play YouTube News Gmail Drive More »Sign inPatentsI improve the impact shock resistance of bonds between composite elements by including Z-pin reinforcement. I prepare stubbled composite structure by using peel plys over the appropriate surface of the composite during pin insertion using conventional processes. I then use the stubbled composite structure...http://www.google.com/patents/US5863635?utm_source=gb-gplus-sharePatent US5863635 - Composite detail having Z-pin stubbleAdvanced Patent SearchTry the new Google Patents, with machine-classified Google Scholar results, and Japanese and South Korean patents.Publication numberUS5863635 APublication typeGrantApplication numberUS 08/812,639Publication dateJan 26, 1999Filing dateMar 7, 1997Priority dateMay 31, 1996Fee statusPaidAlso published asUS5968639, US5980665Publication number08812639, 812639, US 5863635 A, US 5863635A, US-A-5863635, US5863635 A, US5863635AInventorsJames J. ChildressOriginal AssigneeThe Boeing CompanyExport CitationBiBTeX, EndNote, RefManPatent Citations (12), Referenced by (56), Classifications (52), Legal Events (4) External Links: USPTO, USPTO Assignment, EspacenetComposite detail having Z-pin stubble
US 5863635 AAbstract
1. A prefabricated aerospace composite detail part, comprising:(a) cured and consolidated, fiber-reinforced organic matrix resin aerospace composite structure; (b) Z-pin fiber reinforcement protruding from at least a portion of the resin composite to define a bond line to provide stubble; areal density of said Z-pin reinforcement is between about 0.375 and 150% and (c) an uncured resin padup covering and protecting the stubble. 2. The detail part of claim 1 further comprising a compressible foam core backing the composite.
3. The detail part of claim 1 wherein the stubble defines a strip along the composite.
4. The detail part of claim 1 wherein the Z-pin reinforcement is in an interlaced arrangement.
5. The detail part of claim 2 wherein the foam is polyimide or polystyrene.
6. The detail part of claim 1 wherein the Z-pin reinforcement has a Young's modulus of elasticity of at least about 107.
7. The detail part of claim 1 wherein the padup includes a susceptor heatable by magnetic induction.
8. The detail part of claim 1 wherein the areal density of Z-pin reinforcement differs in different areas of the stubble.
This application is a division of application Ser. No. 08/658,927 filed May 31, 1996.
Boeing described a process for organic matrix forming and consolidation using induction heating in U.S. No. 5,530,227. There, prepregs were laid up in a flat sheet and were sandwiched between aluminum susceptor facesheets. The facesheets were susceptible to heating by induction and formed a retort to enclose the prepreg preform. To ensure an inert atmosphere around the composite during curing and to permit withdrawing volatiles and outgassing from around the composite during the consolidation, the facesheets are sealed around their periphery. Such welding unduly increased the preparation time and the cost for part fabrication. It also ruined the facesheets (i.e., prohibited their reuse which added a significant cost penalty to each part fabricated with this approach). So, Boeing described in U.S. Pat. No. 5,599,472 a technique that readily and reliably sealed the retort without the need for welding and permits reuse of the facesheets in certain circumstances. This "bag-and-seal" technique applies to both resin composite and metal processing.
Boeing can perform a wide range of manufacturing operations in its induction heating press. These operations have optimum operating temperatures ranging from about 350° F. (175° C.) to at least about 1850° F. (1010° C.). For each operation, the temperature is held relatively constant for several minutes to several hours. Controlling the input power fed to the induction coil provides temperature control, but a better and simpler way capitalizes on the Curie temperature. By judicious selection of the metal or alloy in the retort's susceptor facesheets, we can avoid excessive heating irrespective of the input power. With improved control and improved temperature uniformity in the workpiece, we produce better products. The method capitalizes on the Curie temperature phenomenon to control the absolute temperature of the workpiece and to obtain substantial thermal uniformity in the workpiece by matching the Curie temperature of the susceptor to the desired temperature of the induction heating operation being performed. This temperature control method is explained in greater detail in U.S. patent application Ser. No. 08/469,986.
Prior art disclosing thermoplastic welding with induction heating is illustrated by U.S. Pat. No. 3,966,402 and 4,120,712. In these patents, conventional metallic susceptors are used and have a regular pattern of openings of traditional manufacture. Achieving a uniform, controllable temperature in the bond line, which is crucial to preparing a thermoplastic weld of adequate integrity to permit use of welding in aerospace primary structure, is difficult with conventional susceptors.
The exponential decay of the strength of magnetic fields dictates that, in induction welding processes, the susceptible structure closest to the induction coil will be the hottest, since it experiences the strongest field. Therefore, it is difficult to obtain adequate heating at the bond line between two graphite carbon fiber reinforced resin matrix composites relying on the susceptibility of the fibers alone as the source of heating in the assembly. For the inner plies to be hot enough to melt the resin, the outer plies closer to the induction coil and in the stronger magnetic field are too hot. The matrix resin in the entire piece of composite melts. The overheating results in porosity in the product, delamination, and, in some cases, destruction or denaturing of the resin. To avoid overheating of the outer plies and to insure adequate heating of the inner plies, we use a susceptor of significantly higher conductivity than the fibers to peak the heating selectively at the bond line. An electromagnetic induction coil heats a susceptor to melt and cure a thermoplastic resin (also sometimes referred to as an adhesive) to bond the elements of the assembly together.
Large scale parts such as wing spars and ribs, and the wing skins that are bonded to the spars and ribs, are typically on the order of 20-30 feet long at present, and potentially can be as much as 100 feet in length when the process is perfected for commercial transport aircraft. Parts of this magnitude are difficult to produce with perfect flatness. Instead, the typical part will have various combinations of surface deviations from perfect flatness, including large scale waviness in the direction of the major length dimension, twist about the longitudinal axis, dishing or sagging of "I" bean flanges, and small scale surface defects such as asperities and depressions. These irregularities interfere with full surface area contact between the faying surfaces of the two parts and actually result in surface contact only at a few "high points" across the intended bond line. Applying pressure to the parts to force the faying surfaces into contact achieves additional surface contact, but full intimate contact is difficult or impossible to achieve in this way. Applying heat to the interface by electrically heating the susceptor in connection with pressure on the parts tends to flatten the irregularities further. Still, the time needed to achieve full intimate contact with the use of heat and pressure is excessive, can result in deformation of the top part, and tends to raise the overall temperature of the "I" beam flanges to the softening point. When softened, they begin to yield or sag under the application of the pressure needed to achieve a good bond Boeing's multipass thermoplastic welding process described in U.S. Pat. No. 5,486,684 (which I also incorporate by reference) enables a moving coil welding process to produce continuous or nearly continuous fusion bonds over the full area of the bond line. The result is high strength welds that we produce reliably, repeatably, and with consistent quality. This multipass welding process produces improved low cost, high strength composite assemblies of large scale parts fusion bonded together with consistent quality. It uses a schedule of heat application that maintains the overall temperature of the structure within the limit in which it retains its high strength. Therefore, it does not require internal tooling to support the structure against sagging which otherwise could occur when the bond line is heated above the high strength temperature limit. The process also produces nearly complete bond line area fusion on standard production composite material parts having the usual surface imperfections and deviations from perfect flatness. The multipass welding process eliminates fasteners and the expense of drilling holes, inspecting the holes and the fasteners, inspecting the fasteners after installation, sealing between the parts and around the fastener and the holes; reduces mismatch of materials; and eliminates arcing from the fasteners.
A structural susceptor allows us to include fiber reinforcement within the weld resin to alleviate residual tensile strain otherwise present in an unreinforced weld. The 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, we prefer 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. 9,717,191, which I incorporate by reference.
In U.S. Pat. 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 pattern of indentations usually in the form of interlinked equilateral triangles. The scoring is sufficiently deep and 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.
In U.S. patent application Ser. No. 08/660,060, entitled "Joining Composites Using Z-pinned Precured Strips," Pannell describes bond line reinforcement achieved by using precured strips to carry the Z-pins. Pannell position his strips between two detail parts and joins the three piece assembly with bonding, cocuring, or welding. I incorporate this Pannell application by reference.
The present invention introduces 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, I remove the peel plys to expose the stubble. Then, I assemble the several elements in the completed assembly to define the bond line.
In my Z-pin bonding process, I prepare a precured composite that has Z-pins (or "stubble") protruding from the detail along the intended bond line. To insert the pins in their intended location, I use an insertion process like one of those described in U.S. patent application Ser. Nos. 08/618,650 or 08/582,297 or any other suitable insertion process. My basic approach is shown in FIGS. 8-10. I can also use Avila's pin insertion tool (FIG. 15). Before describing the pin insertion process in detail, I will first describe how I use the Z-pinned detail parts to prepare bonded assemblies.
The function and properties of the Z-pins are described in my copending applications Ser. Nos. 08/618,650 and 08/582,297 which I incorporate by reference. 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.
Now turning to FIG. 1, the Z-pin bonding process uses a composite detail part 10 having a region 12 of Z-pin stubble along the intended bond line for connecting part 10 with other detail parts. Each Z-pin generally protrudes about 1/16 inch above the surface of part 10 (like the Indian "bed of nails") for ultimate insertion into the facing parts at the joint, but the height can change with the intended application. To protect the stubble during manufacture and inventory prior to laying up the assembly for bonding, I cover the stubble with Teflon peel plys 14 and the residue of the pin-carrier foam 16 which I use to hold the pins prior to their insertion into the detail part 10.
The pins in the stubble 12 may be normal to the surface of part 10 or interlaced or highly ordered, as described in Boeing's copending application Ser. Nos. 08/618,650 and 08/628,879. That is, the pins can assume any desired arrangement. The density of pins is also variable to suit the application. Differences in the orientation of pins, their length, their strength, their density, etc. can change in different regions of the bond line. That is, the areal density of pins might be 1.0% on the left side of the part in FIG. 1 while being 1.5% on the right side. Alternately, the pin density might be higher around fasteners or might be higher near the edges of the bond line as opposed to along the centerline. Also, of course, the orientation may change at different regions along the bond line and orientations might even be mixed together, if desired.
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, I introduce a bond padup strip 20, typically of the same materials 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 (in which cases bonding is a cocuring process) or might be any suitable adhesive bonding material. The padup strip might be a resin encased susceptor of the type shown in FIGS. 13 & 14 and as Boeing uses in its thermoplastic welding operations. In this case, the detail parts would generally be precured.
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 flange 10a. Shawn Pannell describes in his application "Joining Composites Using Z-Pinned Precured Strips," Ser. No. 08/660,060, that 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 I insert the pins into the spar and panel prior to their curing.
FIGS. 6 and 7 illustrate another embodiment of the present invention with reference to the 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 FIGS. 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.
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 U.S. patent applications Ser. Nos. 08/209,847 or 08/460,788, (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. patent application Ser. No. 08/585,304 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. The Young's modulus of elasticity for the Z-pins is generally greater than 107. 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, I can use metal foil or metal foil/resin laminated composites. The metal foil in such cases might be welded to metallic Z-pins in the fashion described in my copending U.S. patent application Ser. No. 08/619,957 entitled "Composite/Metal Structural Joint with Welded Z-Pins."
FIGS. 8-10 illustrate a preferred process for inserting the Z-pins into a detail part to leave a stubble interface. The detail part 500 (here a laminated panel having several layers of prepreg) is mounted on a work surface or layup mandrel 550 with appropriate release films between the part and tool. Another release film 600 caps the detail part 500 and separates the part 500 from a Z-pin preform 650 (i.e., a foam loaded with Z-pins 130 in a predetermined orientation). A rigid caul plate or backing tool 700 completes the assembly. All the layers are then wrapped in a conventional vacuum bag film 750 which is sealed to permit drawing a suction within the closed volume surrounding the assembly.
As shown in FIG. 9, in an autoclave under elevated temperature and pressure, the foam in the Z-pin preform 650 crushes and the Z-pins 130 are driven into the uncured detail part 500. After completing the cure cycle, the detail part 500 is cured and has the Z-pins 130 anchored within it. The crushed foam 650 and release ply 600 protect the stubble until assembly of the detail parts is desired. Thus, the process of FIGS. 8-10 yields a cured detail part having a stubble field. Other processes can be used to achieve the same result, including ultrasonic insertion into precured thermoplastic laminates as described in the prior art or Boeing's other, copending Z-pin applications.
I made 3/16 inch quasi-isotropic composite test specimens from AS4/3501-6having 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, on one-half of the specimens, I did not insert Z-pins. I assembled two of the stubbled parts around an AS4/3501-6 uncured scrim padup about 0.090 inch thick with the stubble from each part overlapping. I bonded the assembled parts using the conventional bonding cycle. Then, I cut the resulting bonded assembly 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, I discovered that some pins were bent, which I believe lowered the reinforcing value (reduced the load I measured). I also believe that I could prepare even better bonds (i.e., joints) using higher pressure during the bonding cycle.
FIGS. 15∝17 illustrate Avila's pin insertion tool that I can use to form detail parts having pin stubble. Avila's tool 1500 incudes a housing 1505 holding a sliding piston 1510 which is reciprocal between a loading position for receiving a pin-carrying foam 1550 in a cavity 1515 and an insertion position where the piston moves upwardly to crush the foam and to insert the pins 1545. Seals 1520 permit the piston 1510 to slide along the walls of housing 1505 when pneumatic pressure is applied through inlet 1525 to chamber 1530 behind the piston. Motion of the piston 1510 toward removable cure tool 1535 is arrested with stop 1540 which also serves to control the depth of insertion of pins 1545 in the pin-carrying foam 1550 into the detail part 1555. The stop 1540 contacts replaceable stop 1560 that seats in the fixed support frame of the cure tool 1535 that is rigidly attached to the housing 1505 as the fixed wall defining cavity 1515. The replaceable stop allows adjustment of the depth of penetration of the pins into the detail part 1555. The cure tool 1535 fits rigidly in a matching receiving surface in the frame and does not move when piston 1510 moves upwardly. Yet, cure tool 1535 is replaceable to permit controlled insertion of different Z-pin orientations or different insertion depths into the detail part 1555. During pin insertion through movement of the piston 1510, the detail part 1555 is held rigidly on the surface of the cure tool 1535 so that the Z-pins 1545 are positioned correctly.
Avila's tool might include a shearing ram on the contact surface between the cure tool and the detail part or at the interface between the cure tool and the pin-carrying foam for cutting the pins after their tool-foam insertion. In the alternative where the ram is at the cure tool-foam interface, the width of the cure tool becomes a reliable gauge for setting the height of the stubble, since this much of the pins will protrude when the detail part is removed from the tool.
Avila's pin insertion tool is especially beneficial when making relatively large production runs of detail parts. The tool reduces part-to-part variation by inserting the Z-pins accurately and repeatedly where they are designed to be. Avila's tool is described in greater detail in U.S. patent application Ser. No. 08/657,859 entitled "Tooling for Inserting Z-Pins," which I incorporated by reference.
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B29C65/76, B29C66/1122, B29C70/24, B29C70/44, B29C66/721, B32B7/04, B29C66/3034, B29C65/3644, B29C66/81455, B29C65/364, B29C65/5057, Y02T50/433, B29C65/4815, B29C65/483, B29C2035/0811, B29C2035/0816Legal EventsDateCodeEventDescriptionJul 25, 2002FPAYFee paymentYear of fee payment: 4Aug 13, 2002REMIMaintenance fee reminder mailedJul 26, 2006FPAYFee paymentYear of fee payment: 8Jun 28, 2010FPAYFee paymentYear of fee payment: 12RotateOriginal ImageGoogle Home - Sitemap - USPTO Bulk Downloads - Privacy Policy - Terms of Service - About Google Patents - Send FeedbackData provided by IFI CLAIMS Patent Services