System and method for welding thermoplastic components to create composite structure

A system and method for welding thermoplastic components by positioning and moving a heated plate between the components to melt their respective faying surfaces, and as the plate moves, pressing the components together so that the melted faying surfaces bond together as they cool and re-solidify, thereby creating a composite structure. The plate has a heated portion which is positioned between and heated to melt a portion of the first and second faying surfaces. A manipulator mechanism moves the plate along an interface from between the portion to between a series of subsequent portions of the first and second faying surfaces, thereby welding the thermoplastic components along the entire interface to create the composite structure. The heated portion may contact the faying surfaces and melt them through conduction, or may be suspended between them and melt them through radiation and convection.

FIELD

The present invention relates to systems and methods for creating composite structures, and more particularly, embodiments concern a system and method for welding thermoplastic components by positioning and moving a heated plate element between the components to melt the respective faying surfaces, and as the plate element moves, pressing the components together so that the melted faying surfaces bond together as they cool and re-solidify, thereby creating a composite structure.

BACKGROUND

Thermoplastics are polymers, typically synthetic resins, that melt when heated and solidify when cooled. Thermoplastic laminate components can be welded by heating and then cooling faying surfaces between the components to bond them together to form composite structures. The most common techniques for thermoplastic composite welding are induction welding, ultrasonic welding, and resistance welding, but each of these techniques suffers from particular disadvantages.

Induction welding using a susceptor involves incorporating a foreign material into the weld line, which has undesirable effects on structural integrity and reliability. Induction welding without using a susceptor can be difficult to control and requires substantial engineering and design to determine the correct coil and heat sink configuration to avoid temperature control problems and resin degradation or poor welds. Further, nearby metal, such as a lightning strike protection conductor, can act as a susceptor and cause additional heat distribution issues. Ultrasonic welding requires an energy director in the weld line, results in lower strength welds, can distort fiber alignment, and is difficult to use for continuous welds. Resistance welding using a carbon fiber resistive element in the weld line creates continuous welds with good strength. However, resistance welding is difficult to use in production processes because the entire resistance circuit is heated simultaneously and therefore must be clamped and supported throughout the entire welding process. Further, provisions for making reliable electrical bonds to the fibers are not conducive to automation, and individual locations are not temperature controlled, and instead, the entire circuit is on a single channel. Further, it is generally important to avoid degrading/deconsolidating the laminate components due to overheating, so techniques that generate too much heat beyond the faying surfaces may require heat mitigation (e.g., heat sink technology).

Traditional hot plate welding is another common technique in which an entire weld area is heated at the same time with a contoured plate and then the melted surfaces are brought together. However, this can result in difficulty initially aligning and thereafter maintaining the positions of the thermoplastic components due to the instability of the melted faying surfaces. It is also known to weld the seams of products made of thermoplastic fabrics, such as tents, tarps, and parachutes. However, the nature of the materials makes this welding process substantially different than materials welded using the techniques described above. In particular, the fabrics are much more flexible and are initially separated and brought together at the time of welding, while the materials at issue are relatively stiff (one may even be a stiffener structure) and are already aligned and maintained in particular positions at the time of welding.

SUMMARY

Embodiments address the above-described and other problems and limitations by providing a system and method for welding thermoplastic components by positioning and moving a heated plate element between the components to melt the respective faying surfaces, and as the plate element moves, pressing the components together so that the melted faying surfaces bond together as they cool and re-solidify, thereby creating a composite structure.

In one embodiment, a system is provided for welding a first thermoplastic component to a second thermoplastic component along an interface to create a composite structure. Broadly, the system may include a plate element and a manipulator mechanism. The plate element may have a heated portion which may be positioned between a portion of a first faying surface of the first thermoplastic component and a second faying surface of the second thermoplastic component. The heated portion may be heated to an operating temperature which is sufficient to melt the portion of the first and second faying surfaces. The manipulator mechanism may move the plate element along the interface from between the portion of the first and second faying surfaces, which then cool and bond together, to between a series of subsequent portions of the first and second faying surfaces, and thereby weld the first thermoplastic component to the second thermoplastic component along the interface to create the composite structure.

Various implementations of this embodiment may include any one or more of the following features. The heated portion the plate element may have a thickness of approximately between 0.01 inches and 0.03 inches. The heated portion of the plate element may be heated using joule heating. The system may further include a first temperature sensor which may determine the operating temperature of the plate element, and a second temperature sensor which may determine an adjacent temperature of the first and second thermoplastic components.

In a first or “contact” implementation, at least the heated portion of the plate element may be in physical contact with the portion of the first and second faying surfaces, and may melt the portion of the first and second faying surfaces through conduction. A front portion of the plate element may have a rake angle to control any excess melted thermoplastic material from the first and second faying surfaces. The rake angle may be approximately between 10 degrees and 50 degrees.

In a second or “gap” implementation, at least the heated portion of the plate element may be suspended between and not in physical contact with the portion of the first and second faying surfaces, and may melt the portion of the first and second faying surfaces through radiation and convection. The system may further include a spacer element which may create a gap between the first and second faying surfaces, wherein at least the heated portion of the plate element is located in the gap. The spacer element may be an unheated front portion of the plate element, and/or the spacer element may include one or more circular rollers. The system may further include an air nozzle configured to introduce a stream of air or inert gas between at least the heated portion of the plate element and the first and second faying surfaces so as to enhance convection and reduce oxidation. The system may further include one or more holes in the plate element to enhance convection.

The manipulator mechanism may further include a guide roller configured to guide movement of the plate element along the interface between the first and second faying surfaces. The manipulator mechanism may further include a pressure roller configured to press the first and second faying surfaces together behind the plate element as the plate element is moved along the interface. The manipulator mechanism may further include a cooling nozzle configured to deliver a cooling fluid to accelerate cooling of the first and second faying surfaces behind the plate element as the plate element is moved along the interface. The manipulator mechanism may further include an inert gas nozzle configured to deliver an inert gas to displace oxygen around the heated portion of the plate element. The system may further include a support surface configured to be positioned behind the first thermoplastic component, wherein the support surface is flexible so as to accommodate a deflection of the first thermoplastic component as the plate element is moved between the first and second faying surfaces.

This summary is not intended to identify essential features of the present invention, and is not intended to be used to limit the scope of the claims. These and other aspects of the present invention are described below in greater detail.

DETAILED DESCRIPTION

The following detailed description of embodiments of the invention references the accompanying figures. The embodiments are intended to describe aspects of the invention in sufficient detail to enable those with ordinary skill in the art to practice the invention. Other embodiments may be utilized and changes may be made without departing from the scope of the claims. The following description is, therefore, not limiting. 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.

In this description, references to “one embodiment”, “an embodiment”, or “embodiments” mean that the feature or features referred to are included in at least one embodiment of the invention. Separate references to “one embodiment”, “an embodiment”, or “embodiments” in this description do not necessarily refer to the same embodiment and are not mutually exclusive unless so stated. Specifically, a feature, structure, act, etc. described in one embodiment may also be included in other embodiments, but is not necessarily included. Thus, particular implementations of the present invention can include a variety of combinations and/or integrations of the embodiments described herein.

Broadly characterized, embodiments provide a system and method for welding thermoplastic components by positioning and moving a heated plate element between the components to melt the respective faying surfaces, and as the plate element moves, pressing the components together so that the melted faying surfaces bond together as they cool and re-solidify, thereby creating a composite structure. In contrast to traditional hot plate welding which heats the entire weld area at the same time, embodiments utilize the motion of the plate element and the stiffness of the components and/or an underlying support surface to provide a clamping force against the plate element to join the melted surfaces. Further, unlike in traditional hot plate welding, there may be little or no movement of the components themselves because the faying surfaces are kept together and are only separated by the thin plate element moving between them during the welding process. Although described herein in the example context of manufacturing aircraft, the present technology may be adapted for use in substantially any suitable application (in, e.g., the automotive and/or ship-building industries) involving welding thermoplastic components.

Referring initially toFIGS. 1 and 2, an embodiment of a system20is shown for welding a first thermoplastic component22to a second thermoplastic component24to construct a composite structure26. In one example application, the first component22may be an aircraft stringer or other relatively rigid component, and the second component may be an aircraft skin or other relatively flexible component. The system20may include a plate element28and a manipulator mechanism30. The plate element28may be configured to be positioned between an initial or current portion32aof a first faying surface34of the first thermoplastic component22and a second faying surface36of the second thermoplastic component24, and to be heated to an operating temperature which is sufficient to melt the portion32aof the first faying and second faying surfaces34,36.

The thickness of the plate element28may depend, at least in part, on the natures of the first and/or second components22,24and the particular application and requirements of the welding process. In general, it may be desirable for the plate element28to be relatively thin so as to minimize the deflection of the first and/or second components22,24as the plate element28moves between them. Relatedly, the maximum ability of the first and/or second component22,24to deflect may determine an upper limit on the thickness of the plate element28. In various implementations, the plate element28may have a thickness of approximately between 0.005 inches and 0.05 inches, approximately between 0.01 inches and 0.03 inches, or approximately 0.02 inches. The thickness of the plate element28may also depend, at least in part, on the nature and design of the manipulator mechanism30which supports the plate element28. For example, a cantilevered plate element may be relatively thicker to avoid buckling, while a plate element supported on both ends may be relatively thinner. The plate element28may be constructed of substantially any suitable material, such as nichrome, titanium, Inconel, stainless steel, or other high temperature, corrosion resistant metal. In one implementation, the plate element28may be constructed of a material having a relatively high electrical resistance to facilitate joule (or resistance) heating.

The plate element28may be heated by one or more heating circuits. More specifically, the plate18may be joule heated to an operating temperature by passing an electric current through the material of the plate. The operating temperature of the plate28may depend, at least in part, on the natures of the first and/or second components22,24and the particular application and requirements of the welding process. In general, the operating temperature may be sufficient to melt the first and second faying surfaces34,36and accomplish the desired weld. Thus, the minimum operating temperature may be the melting point of the first and second faying surfaces34,36, and the maximum temperature may be determined by the ability to transfer enough heat sufficiently quickly so to avoid degradation/decomposition of the first and second components22,24due to the heat. In particular, it may be desirable to heat the first and second faying surfaces34,36while minimizing heating of the bodies of the first and second components22,24.

The temperature of the plate element28may be measured by one or more first sensors40(shown inFIGS. 3 and 4) at one or more locations on the plate element28. Multiple measurements at different points may be desirable if the plate element28loses more heat in one region than in another region due to, e.g., a heat sink effect. In one implementation, one or more thermocouples may be used to measure the temperature of the plate element28. Relatedly, multiple independently controllable heating circuits may be used to heat the plate element28to better compensate for any such differences in temperature across the plate element28, and to allow for greater flexibility in how the faying surfaces34,36are heated. The temperature of the first and second faying surfaces34,36may be at least as relevant as the temperature of the plate element, in which case the temperature of the first and second faying surfaces34,36may be measured by one or more second sensors42(shown inFIGS. 3 and 4) at one or more locations on the faying surfaces34,36. In one implementation, one or more optical temperature sensors may be used to measure the temperature of the first and second faying surfaces34,36.

In one implementation, additional resin may be introduced and melted between the faying surfaces34,36to facilitate bonding. This additional resin may be provided in the form of injected liquid resin, solid resin film, or an additional layer of prepreg (i.e., an extra layer of fiber and resin).

In a first or “contact” implementation, shown inFIG. 3, the plate element28may be generally in physical contact with the faying surfaces34,36while the plate element28moves between and heats the faying surfaces34,36through conduction. In the contact implementation, a front portion44of the plate element28may be provided with a rake angle to direct or otherwise control any excess thermoplastic resin material from the first and second faying surfaces34,36. More specifically, the rake angle may sweep the excess resin to the centerline of the weld where it may be squeezed out of the way, which promotes the ejection of air from between the first and second components22,24. In various implementations, the rake angle may be approximately between 10 degrees and 50 degrees, or approximately between 20 degrees and 40 degrees.

In a second or “gap” implementation, shown inFIGS. 4, 15, and 16, the plate element28may be generally suspended between and not in physical contact with the faying surfaces34,36as the plate element28moves between and heats the faying surfaces34,36through radiation and convection. In the gap embodiment, a spacer element46may be provided to create a gap in which at least the heated portion of the plate element28moves, and thereby prevents the faying surfaces34,36from physically contacting at least this heated portion of the plate element28. In one implementation, the spacer element44may be provided by thickening or shaping an unheated front portion of the plate element28to separate the faying surfaces34,36around the heated portion of the plate element28. In another implementation, the same spacing effect may be accomplished by physically forcing (e.g., pulling or pushing) the first and/or second faying surfaces34,36apart. In another implementation, a wedge or roller element48may be provided at the leading edge of the plate element28to create the gap. As shown inFIG. 16, the roller element48may include a plurality of rollers which may be offset from each other so that some of the rollers54roll across the first faying surface34and others of the rollers56roll across the second faying surface36. Such as roller element advantageously avoids dragging across and potentially damaging or contaminating the faying surfaces34,36. One advantage of the gap embodiment is that it avoids physical, high temperature contact which could otherwise damage or misalign the fibers of the first and second thermoplastic components. However, the gap embodiment may require a higher operating power than the contact embodiment due to convection heat losses. In various implementations, an air nozzle80may introduce air into the gaps between the plate element28and the faying surfaces34,36to enhance convection, and/or one or more holes82may be provided in the plate element34,36itself to enhance convection.

Referring also toFIGS. 5-15, the manipulator mechanism30may be configured to move the heated plate element28between the first and second faying surfaces34,36, from one end of the interface58of the first and second components22,24to the other end, such that the plate element28heats and melts the portion32aof the first and second faying surfaces34,36, and such that as the plate element28is moved along the interface58, the heated and melted portions of the first and second faying surfaces34,36bond together as they cool and re-solidify behind the plate element28. The manipulator mechanism30may support the plate element28on both sides of the plate element, as shown inFIGS. 5-10, or may support the plate element28only on one side (i.e., cantilevered), as shown inFIGS. 11-14. The manipulator mechanism20may move the plate element28at a rate of movement that maintains the plate element28in position for a sufficient time to heat the faying surfaces34,36to the melting temperature. The movement rate may be substantially continuous or potentially variable in order to better maintain particular temperatures. The rate of movement may depend on such factors as the operating temperature of the plate element28and the rate of heat transfer from the plate element28to the faying surfaces34,36. Further, the manipulator mechanism30may move the plate element28at a speed that maintains the operating temperature with the available power or may adjust the power to support the desired movement speed in a closed control loop such that the peak temperature (plate temperature) and the adherend surface temperature after the passage of the plate element28are both within the appropriate temperature range for obtaining a strong weld without degrading the thermoplastic components22,24.

The manipulator mechanism20may further include a guide roller62configured to guide movement of and ensure desired positioning of the plate element28between the first and second faying surfaces34,36. In one implement, the guide roller62may roll over a surface of one of the components22,24. The first and second components22,24may be positioned by tooling, or the manipulator mechanism30may include a guidance feature to position one of the components relative to the other. In one implementation, the manipulator mechanism20may further include a compliance spring, arm, or cylinder or similar compliance element64configured to maintain the guide roller62in contact with the surface of the component22,24as the plate element28is moved. Relatedly, the system20may further include one or more temporary or permanent fasteners66a,66bpositioned at the extreme ends of the first and second components22,24as desired or necessary to maintain the component22,24in proper alignment, though permanent fasteners may limit how closely the weld can approach these ends.

In one implementation, the manipulator mechanism30may use only localized pressure applied by the manipulator mechanism30because the mass of the material being heated is less than with most other welding methods and no foreign material is being introduced. In another implementation, the manipulator mechanism30may further include a pressure roller70configured to press the melted first and second faying surfaces34,36together behind the plate element28as the plate element28is moved along the interface58by the manipulator mechanism30, thereby facilitating the bonding together of the cooling first and second faying surfaces34,36. The pressure applied by the pressure roller70may depend on the nature of the first and second components34,36. In particular, stiffer components may require greater pressure. In one implementation, the pressure applied by the pressure roller may be at least 1 bar.

In one implementation, the manipulator mechanism20may further include a cooling nozzle72configured to deliver a cooling fluid, such as compressed air, refrigerant, or water, may be impinged against the first and second components22,24to accelerate cooling as desired or necessary. In one implementation, the manipulator mechanism20may further include an inert gas nozzle74configured to deliver an inert gas into the weld area in order to displace the oxygen in the weld area and thereby reduce the potential for oxidation and/or fire during the heating and consolidating phases. In one implementation, the system20may further include a support surface76position beneath, behind, or otherwise adjacent to the second component36. The support surface76may be compressible or otherwise flexible so as to accommodate a deflection of the second component36as the plate element28moves between first and second faying surfaces34,36. For example, in the example application in which the first component is a stringer and the second component is a skin, because the skin is much more flexible than the stiffener, the skin may be placed on the support surface76, and the support surface76may compress or otherwise flex to accommodate the deflection of the skin, while also providing a constant reaction force against the plate element28and the melted weld line. The support surface76may itself rest upon a flat or contoured tool78.

Referring toFIG. 17, the system20may function substantially as follows to weld the first thermoplastic component22to the second thermoplastic component24along the interface58to create the composite structure26. Additional functionality of the system20may be reflected in the steps of the method200discussed below. Broadly, the heated portion of the plate element28may be positioned between the portion32aof the first faying surface34of the first thermoplastic component22and the second faying surface36of the second thermoplastic component24, as shown in222. The heated portion may be heated to the operating temperature which is sufficient to melt the matrix of the first and second faying surfaces34,36, as shown in224. The manipulator mechanism30may move the heated portion of the plate element28along the interface58from between the portion32aof the first and second faying surfaces34,36to between the series of subsequent portions32b-32eof the first and second faying surfaces34,36, as shown in230. As the plate element28is moved along the interface58, the portion of the first and second faying surfaces34,36behind the plate element28is no longer exposed to the operating temperature and so begins to cool and re-solidify and bond together, as shown in236, which results in the first thermoplastic component22being welded to the second thermoplastic component24along the interface58to create the composite structure26.

The system20may include more, fewer, or alternative components and/or perform more, fewer, or alternative actions, including those discussed elsewhere herein, and particularly those discussed in the following section describing the method220.

Referring again toFIG. 17, an embodiment of a method220is shown for welding a first thermoplastic component22to a second thermoplastic component24along an interface58to create a composite structure26. The method220may be a corollary to the functionality of the system20described above, and may be similarly implemented using the various components of the system20. Broadly, the method220may proceed substantially as follows.

A heated portion of a plate element28may be positioned between a portion32aof a first faying surface34of the first thermoplastic component22and a second faying surface36of the second thermoplastic component24, as shown in222. The heated portion may be heated to an operating temperature which is sufficient to melt the matrix resin of the portion32aof the first and second faying surfaces34,36without exceeding a decomposition temperature of the first and second components22,24, as shown in224. The heated portion may be heated by joule heating or by substantially any other suitable technique, and the resulting heat may be transferred to the portion32aof the first and second faying surfaces34,36by conduction or radiation or convection. In an implementation in which heat is transferred from the plate element28to the first and second faying surfaces34,36by convection, an air nozzle80or similar mechanism may be used to introduce a stream of air or other inert gas between at least the heated portion of the plate element28and the first and second faying surfaces34,36so as to enhance convection and/or reduce oxidation, as shown in226. In one implementation, an inert gas nozzle74or similar mechanism may be used to deliver an inert gas to displace oxygen around the heated portion of the plate element28, as shown in228.

A manipulator mechanism30may move the heated portion of the plate element28along the interface58from between the portion32aof the first and second faying surfaces34,36to between a series of subsequent portions32b-32eof the first and second faying surfaces34,36, as shown in230. As the plate element28is moved along the interface58, the portion of the first and second faying surfaces34,36behind the plate element28is no longer exposed to the operating temperature and so begins to cool and re-solidify and bond together, as shown in236, which results in the first thermoplastic component22being welded to the second thermoplastic component24along the interface58to create the composite structure26. In one implementation, a guide roller62or similar mechanism may be used to guide movement of the plate element28along the interface58between the first and second faying surfaces34,36, as shown in232.

A first temperature sensor40may be used to determine the operating temperature of the heated portion of the plate element28, and a second temperature sensor42may be used to determine a temperature of the first and second thermoplastic components22,24, as shown in234, and this information may be used to control the heating of the heated portion of the plate element28and the speed with which the manipulator mechanism30moves the heated portion along the interface58.

In one implementation, a pressure roller70or similar mechanism may be used to apply a pressure to press the cooling first and second faying surfaces34,36together behind the plate element28to enhance bonding as the plate element28is moved along the interface58, as shown in238. In one implementation, a cooling nozzle72or similar mechanism may be used to deliver a cooling gas or other fluid to accelerate cooling of the first and second faying surfaces34,36behind the plate element28to hasten re-solidification and bonding as the plate element28is moved along the interface58, as shown in240.

The method220may include more, fewer, or alternative actions, including those discussed elsewhere herein.

Although the invention has been described with reference to the one or more embodiments illustrated in the figures, it is understood that equivalents may be employed and substitutions made herein without departing from the scope of the invention as recited in the claims.