Method of friction stir welding using an exothermically reactive sealant and friction stir weld joint having an exothermically reacted sealant

BACKGROUND OF THE INVENTION

1) Field of the Invention

The present invention relates to the joining of structural members by friction stir welding and, more particularly, relates to the sealing of friction stir welding joints between structural members, for example, to increase the strength and corrosion-resistance of the members.

2) Description of Related Art

The joining of structural members often results in an interface that is susceptible to intrusion by chemicals, moisture, or other fluids and particulates. For example, in the aircraft industry, joints between structural members are often formed by overlapping two or more structural members, forming holes through the members, and disposing rivets or other fasteners through the holes. Although the overlapping members may correspond closely to one another at their interface, each interface nevertheless typically defines a narrow space or crevice-like gap through which moisture, chemicals, debris, and other foreign materials can be received, possibly resulting in increased corrosion of the structural members and the fasteners. Therefore, a sealant such as a caulk-like organic material can be disposed in each interface to seal the interface and prevent the entry of foreign materials therein. The sealant can be disposed before or after the joint is formed, though in some cases the sealant is preferably disposed before joining because the geometrical configuration of the structural members may prevent access to one or both sides of the interface after joining. In some cases, the sealant may be squeezed from the interface during joining, leaving unfilled voids in the interface, which can be difficult to identify and fill, especially if one or both sides of the joint cannot be accessed after joining. Further, even if the sealant does fill the interface, the sealant can dry out and deteriorate or otherwise work free from the joint over time.

A friction stir weld joint can be formed by overlapping the structural members, rotating a friction stir welding pin extending in a direction generally perpendicular to the interface of the members, and urging the pin through the members along the interface. The pin generates sufficient friction with the structural members to plasticize a portion of the members, and the plasticized material is mixed by the pin. As the plasticized material cools, a friction stir weld joint is formed, characterized by a mixed portion having a refined grain structure, referred to as a nugget. The nugget is typically not as wide as the interface of the overlapping members, and the members therefore define spaces in the interface in which corrosion can occur, similar to the space proximate to the rivet joints described above. A sealant can be disposed in the spaces; however, if the sealant is disposed before welding, care should be taken to avoid introducing the sealant into the nugget of the joint as conventional sealants can negatively impact the strength and/or corrosion resistance of the joint. For example, masking tape can be placed on the area of the structural members where the nugget will be formed, the sealant can be disposed on the structural members, and the masking tape can then be removed to generally leave a clean area for forming the nugget. This process is time consuming. Further, even if such precautions are taken, as the members are placed and urged together to form the joint, some of the sealant can be squeezed into the interface and mixed with the plasticized material of the joint, thereby reducing the quality of the weld joint. In addition, as described above, voids can result in the interface during joining or the sealant can be loosened from the interface subsequently.

<patcit id="pcit0001" dnum="US6308882B1"><text>US-B1-6 308 882</text></patcit> discloses a method of forming a friction weld joint and also mentions to use a powder as exothermic sealant for joining components of dissimilar materials, but does not solve the above problems.

Thus, there exists a need for an improved method for forming a corrosion resistant joint in a structural member. The method should be compatible with friction stir welding, and should not be overly time consuming. Further, the method should result in a strong bond between the structural members without excessively reducing the quality of the joint.

BRIEF SUMMARY OF THE INVENTION

An object of the invention is therefore to provide an improved method for forming a joint in a structural member. This object is achieved by a method according to claim 1. Advantageous features and their combinations are described in the claims dependent therefrom. A further object is to provide an improved strong bond between the structural members. This object is achieved by a joint according to claim 18. Advantageous embodiments and their combinations are described in its dependent claims.

The present invention provides a sealed joint and a method for forming a joint between structural members. A sealant formed of an exothermic material is disposed in an interface between faying surfaces of the structural members and reacted to form a seal and/or a bond in the interface. The sealant can fill the spaces between the structural members to prevent the entry of chemicals, moisture, debris, and other substances, thereby reducing the likelihood of corrosion of the joint or structural members at the interface. Further, the sealant is reacted during the formation of a friction stir weld joint between the members.

The joint is formed by disposing the sealant in the interface and exothermically reacting the sealant in the interface. The structural members, which can be formed of a variety of materials including aluminum, aluminum alloys, titanium, titanium alloys, steel, and the like, are friction stir welded to form a joint between the faying surfaces, with the joint being at least partially sealed by the sealant.

The sealant, which can include aluminum, nickel, oxygen, or other materials, can be disposed as a foil, such as a multilayer foil, or as a fluid that can include a plasticizer. Further, the sealant can be provided on a substrate that is then used to dispose the sealant onto one or both of the faying surfaces. The sealant can be disposed with a thickness of between about 0.0005 and 0.020 inches (0.00127 and 0.0508 cm), and some of the sealant can be reacted outside the interface to form a fillet seal on one or more edges of the interface. For example, the faying surfaces can be urged together before the sealant is reacted so that some of the sealant is squeezed from the interface and subsequently exothermically reacted to form a seal on at least one edge of the interface.

The exothermic reaction of the sealant is initiated by heating the sealant to an initiation temperature, and is initiated during friction welding the structural members. Friction stir welding of the structural members can heat the members to the initiation temperature and thereby start the exothermic reaction. The exothermic reaction of the sealant can have a maximum temperature that reaches or exceeds about 1200 °F (649 °C).

In addition, a braze material can be provided in the interface with the sealant. The braze material has a melting temperature that is generally lower than a melting temperature of the structural members so that the braze material is bonded to the faying surfaces during the exothermic reaction of the sealant. The braze material can include, e.g., bronze, copper, aluminum, or nickel.

The present invention also provides a friction stir weld joint that connects first and second faying surfaces of one or more structural members formed of materials such as aluminum, aluminum alloys, titanium, titanium alloys, or steel. A friction stir weld joint connects the faying surfaces at the interface, and an exothermically reacted sealant in the interface at least partially seals the friction stir weld joint therein. The sealant, which can include materials such as aluminum, nickel, and oxygen, can substantially fill the interface. Further, the sealant can seal the faying surfaces outside the interface, e.g., as a fillet seal on the edges of the interface. The friction stir weld joint can have a nugget area characterized by a refined granular structure, and the friction stir weld joint can extend through the structural members in a direction substantially perpendicular to the interface. Further, a braze joint formed of bronze, copper, aluminum, nickel, or the like can be provided between the faying surfaces proximate to the friction stir weld joint such that the braze joint at least partially seals the interface.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

Having thus described the invention in general terms, reference will now be made to the accompanying drawings, which are not necessarily drawn to scale, and wherein: <ul id="ul0001" list-style="none"><li><figref idref="f0001">Figure 1</figref> is a perspective view illustrating two structural members partially joined by a friction weld joint according to one embodiment of the present invention;</li><li><figref idref="f0002">Figure 2</figref> is a section view in elevation of the weld joint between the structural members of <figref idref="f0001">Figure 1</figref>;</li><li><figref idref="f0002">Figure 3</figref> is a perspective view illustrating a sealant partially disposed on a structural member according to another embodiment of the present invention;</li><li><figref idref="f0003">Figure 4</figref> is a section view in elevation of two structural members configured for joining according to another embodiment of the present invention; and</li><li><figref idref="f0004">Figure 5</figref> is a block diagram illustrating the operations for forming a joint according to one embodiment of the present invention.</li></ul>

DETAILED DESCRIPTION OF THE INVENTION

The present invention now will be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all embodiments of the invention are shown. Indeed, this invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. Like numbers refer to like elements throughout.

Referring now to the figures and, in particular, <figref idref="f0001">Figure 1</figref>, there is shown an apparatus for forming a joint <b>10</b> to connect first and second structural members <b>20, 22.</b> Two structural members are typically joined by the method of the present invention, but a single structural member can be joined, for example, a tubular member or otherwise curved member with adjoining edges. Alternatively, three or more structural members can be joined, and the structural members can be arranged in various configurations. As illustrated in <figref idref="f0001">Figure 1</figref>, the first structural member <b>20</b> is disposed so that a faying surface <b>24</b> of the first structural member <b>20</b> overlaps a faying surface <b>26</b> of the second structural member <b>22</b> and the two structural members <b>20, 22</b> form an interface <b>28</b> therebetween. A friction stir welding tool is used to form a friction stir weld joint <b>12</b> between the structural members <b>20, 22.</b> The friction stir welding tool <b>50</b> includes a rotatable pin <b>52</b> extending from a shoulder <b>54.</b> The pin <b>52</b> is inserted through the interface <b>28</b> generally perpendicular to the interface <b>28,</b> e.g., at an angle of about 3-5° from a line normal to the interface <b>28.</b> An anvil (not shown) or other support can be disposed against the second structural member <b>22</b> to oppose the friction stir weld tool <b>50.</b> The friction stir welding tool <b>50</b> is then urged in a direction <b>55</b> against the first structural member <b>20</b> and advanced in a direction <b>56</b> along the interface <b>28</b> of the structural members <b>20, 22</b> as the pin <b>52</b> rotates in a direction indicated by reference numeral <b>57.</b> The motion of the pin <b>52</b> generates frictional heat, which plasticizes material from the structural members <b>20, 22,</b> and the plasticized material is mixed by the pin <b>52.</b> As the plasticized material cools and hardens, the friction stir weld joint <b>12</b> is formed, the friction stir weld joint <b>12</b> comprising part of the joint <b>10</b> that connects the two structural members <b>20, 22</b> as shown in <figref idref="f0002">Figure 2</figref>. The friction weld joint <b>12</b> includes a nugget region proximate to the path of the pin <b>52,</b> the nugget region being characterized by a refined granular structure.

The process of friction stir welding for joining structural members <b>20, 22</b> is known in the art and is described, for example, in <patcit id="pcit0002" dnum="US5460317A"><text>U.S. Patent No. 5,460,317 to Thomas, et al</text></patcit>.. The weld joint <b>12</b> formed by the configuration shown in <figref idref="f0001">Figure 1</figref> is generally referred to as a lap joint, i.e., a joint generally perpendicular to the interface of overlapping members. In other embodiments of the present invention, other weld joints can alternatively be formed by friction stir welding.

The structural members <b>20, 22</b> can define any of a variety of shapes such as sheets, plates, blocks, and the like. The members <b>20, 22</b> can be formed of metals, such as aluminum, titanium, alloys thereof, or steel. Alternatively, the members <b>20, 22</b> can be formed of non-metallic materials, including polymers, composite materials, and the like. Further, the members <b>20, 22</b> can be formed of similar or dissimilar materials, i.e., each of the members <b>20, 22</b> can be formed of the same or different materials. For example, according to one embodiment of the invention, one of the members <b>20, 22</b> is formed of a metallic material and is joined to another one of the members <b>20, 22</b> that is formed of a non-metallic material. The members <b>20, 22</b> can be joined to create an assembly used for various applications including frames, panels, skins, airfoils, and the like for aeronautical and aerospace structures such as aircraft and spacecraft, for marine vehicles, automobiles, and the like. In some applications, the members <b>20, 22</b> are joined in geometrical configurations that make difficult, or prevent, subsequent access for inspecting or treating the joint <b>10.</b> For example, the structural members <b>20, 22</b> can be overlapped and joined to form a partially or fully closed body such as a tube or an airplane wing.

Although the faying surfaces <b>24, 26</b> of the structural members <b>20, 22</b> can correspond closely in contour and the faying surfaces <b>24, 26</b> can be clamped tightly together, the interface <b>28</b> is characterized by spaces or voids <b>14</b> between the surfaces <b>24, 26</b> where the weld joint <b>12</b> is not formed, i.e., on either side of the weld joint <b>12.</b> According to one embodiment of the present invention, a sealant <b>40</b> is disposed between the structural members <b>20, 22</b> at the interface <b>28</b> thereof. The sealant <b>40</b> can be disposed on one or both of the faying surfaces <b>24, 26</b> of the structural members <b>20, 22,</b> and can be disposed over part or all of the area of the interface <b>28,</b> including the region of the friction stir weld joint <b>12.</b> Thus, the sealant <b>40</b> can fill the spaces <b>14</b> between the faying surfaces <b>24, 26</b> of the structural members <b>20, 22.</b> The sealant <b>40</b> prevents chemicals, moisture, debris, and other substances from entering the spaces <b>14,</b> and the sealant <b>40</b> thereby prevents corrosion or other damage that can be caused by those substances.

Preferably, the sealant <b>40</b> is formed of a material that can be chemically reacted exothermically. Such exothermically reactable materials can include beryllium, nickel, aluminum, boron, copper, magnesium, molybdenum, palladium, rhodium, silicon, titanium, zirconium, and the like. For example, the sealant <b>40</b> can be formed of compounds or mixtures of titanium and boron; aluminum, nickel, and copper; nickel and aluminum; zirconium and aluminum; nickel and silicon; molybdenum and silicon; palladium and aluminum; rhodium and aluminum; titanium and aluminum; and the like. In particular, the sealant <b>40</b> can be ZrAl₃, ZrAl₂, TiAl, a mixture of titanium and boron, or various other exothermically reactable compounds, mixtures, and materials containing elements listed above and/or others. The sealant <b>40</b> can also include various chemicals, e.g., to prevent or reduce oxidation of metals in the sealant <b>40</b> and/or to at least temporarily bind the members <b>20, 22</b> so that a better metallic bond results in the joint <b>10.</b>

The energy released during the exothermic reaction can be sufficient for sustaining the reaction so that once the reaction is initiated, all or substantially all of the sealant <b>40</b> in the interface <b>28</b> reacts. The exothermic reaction of the sealant <b>40</b> can also be sufficient for melting the sealant <b>40</b> and/or portions of the structural members <b>20, 22,</b> depending on the maximum reaction temperature of the sealant <b>40</b> and the melting temperature of the structural members <b>20, 22.</b> For example, in one embodiment of the present invention, the structural members <b>20, 22</b> are formed of aluminum or aluminum alloys and are sealed by a sealant <b>40</b> that reaches a maximum temperature of between about 1200 °F (649 °C) and 2000 °F (1093 °C) during the exothermic reaction. In another embodiment, structural members <b>20, 22</b> formed of titanium or titanium alloys are sealed by a sealant <b>40</b> that reaches a maximum temperature of between about 2000 °F (1093 °C) and 3500 °F (1927 °C) during the exothermic reaction. Unalloyed aluminum and titanium melt at temperatures of about 1220 °F (660 °C) and 3270 °F (1799 °C), respectively. Therefore, in some cases, the sealant <b>40</b> partially melts the structural members <b>20, 22</b> at the interface <b>28</b> and forms a diffusion bond therewith. Alternatively, if the reaction temperature is less than the melting temperature of the structural members <b>20, 22,</b> the sealant <b>40</b> can be melted to fill the interface <b>28</b> without melting the structural members <b>20, 22.</b>

In either case, the sealant <b>40</b> can substantially fill the interface <b>28,</b> thereby sealing the interface <b>28</b> and preventing the entry of debris, moisture, and the like. Further, the sealant <b>40</b> can be joined to the structural members <b>20, 22</b> forming a joint therebetween. If the sealant <b>40</b> is reacted before friction welding of the structural members <b>20, 22,</b> the joint formed by the sealant <b>40</b> can hold the structural members <b>20, 22</b> in place while friction welding is performed. Further, regardless of when the sealant <b>40</b> is reacted, the joint formed by the sealant <b>40</b> can enhance the strength of the overall joint <b>10</b> between the structural members <b>20, 22.</b> That is, the sealant <b>40</b> can connect the structural members <b>20, 22</b> over a portion of the interface <b>28</b> that is not joined by friction welding, thereby supplementing the strength of the friction weld joint <b>12.</b>

The sealant <b>40</b> can be formed and disposed as a film, a paste, a powder, and the like. For example, the sealant <b>40</b> can be formed as a foil or film having tens, hundreds, or thousands of layers. Alternatively, the sealant <b>40</b> can be formed as a paste or other fluid, such as a powder suspended in a plasticizer fluid. Further, the sealant <b>40</b> can be disposed as a film, powder, fluid, or the like onto or in a substrate <b>42</b> that is subsequently used to dispose the sealant <b>40</b> onto one or both of the faying surfaces <b>24, 26.</b> As illustrated in <figref idref="f0002">Figure 3</figref>, the substrate <b>42</b> can be a thin, flexible, tape-like sheet of polymer or paper material. Alternatively, the substrate <b>42</b> can be a porous or gauze-like material, which can at least partially absorb the sealant <b>40</b> therein. As shown in <figref idref="f0002">Figure 3</figref>, the sealant <b>40</b> can be disposed as a layer having uniform thickness on the substrate <b>42,</b> and the substrate <b>42</b> can then be coiled to form a roll <b>44.</b> Subsequently, the substrate <b>42</b> can be unrolled and placed on one or both of the structural members <b>20, 22</b> with the sealant <b>40</b> between the member <b>20, 22</b> and the substrate <b>42.</b> In other embodiments, the sealant <b>40</b> can be disposed on the substrate <b>42</b> as the substrate <b>42</b> is dispensed from a coil and/or by a feeder device, with the substrate <b>42</b> then being positioned on the structural member(s) <b>20, 22.</b> As shown in <figref idref="f0002">Figure 3</figref>, the substrate <b>42</b> can be peeled from the member <b>22</b> in a direction <b>43,</b> leaving the sealant <b>40</b> on the faying surface <b>26</b>. Alternatively, the structural members <b>20, 22</b> can be configured for joining with the substrate <b>42</b> therebetween, and the substrate <b>42</b> can be combusted or otherwise destroyed during the exothermic reaction of the sealant <b>40</b> and/or friction welding of the structural members <b>20, 22.</b>

The amount of sealant <b>40</b> disposed on the faying surfaces <b>24, 26</b> can vary, but in one embodiment of the invention, a layer of between about 0.0005 and 0.020 inches (0.00127 and 0.0508 cm) is disposed. The sealant <b>40</b> can be disposed over all or part of the faying surfaces <b>24, 26</b>, including the portion of the interface <b>28</b> that is welded to form the friction weld joint <b>12</b> of the joint <b>10</b>, although in some cases the sealant <b>40</b> may positively or negatively affect certain mechanical properties of the friction weld joint <b>12.</b>

The exothermic reaction of the sealant <b>40</b> is initiated during the structural members <b>20, 22</b> are friction stir welded to form the weld joint <b>12</b>. For example, according to one embodiment of the present invention, the sealant <b>40</b> is disposed on the faying surfaces <b>24, 26</b>, the structural members <b>20, 22</b> are positioned so that the faying surfaces <b>24, 26</b> are opposed to define the interface <b>28</b> therebetween, and the exothermic reaction is then initiated. Initiation of the exothermic reaction is achieved by heating the sealant <b>40.</b> As noted above the exothermic reaction releases sufficient thermal energy to sustain the reaction, and therefore no additional energy nedd be supplied.

The friction stir welding is performed at least partially during the exothermic reaction. In particular, the sealant <b>40</b> is disposed, the structural members <b>20, 22</b> is positioned to define the interface <b>28,</b> and the friction welding is then performed such that the friction welding provides sufficient thermal energy to initiate the exothermic reaction. The exothermic reaction can then occur at a rate that is equal to or different than the rate of the friction welding. For example, once initiated, the exothermic reaction of the sealant <b>40</b> may finish within a few seconds or less, while the friction stir welding continues at a slower rate.

Preferably, the sealant <b>40</b> substantially fills the interface <b>28</b> and thereby seals the interface <b>28</b> to prevent moisture and debris from entering the interface <b>28</b>. Further, as shown in <figref idref="f0002">Figure 2</figref>, the sealant <b>40</b> can form a seal <b>46</b> that extends outside the interface <b>28,</b> e.g., at one or more edges of the interface <b>28</b> to further protect the interface <b>28</b> from corrosion or other damage to the structural members <b>20, 22</b>. In this regard, the sealant <b>40</b> can be disposed outside the interface <b>28</b>. For example, if the sealant <b>40</b> is disposed as a foil or paste-like fluid, the sealant <b>40</b> can be disposed on portions of the structural members <b>20, 22</b> that are extend beyond the area of the faying surfaces <b>24, 26</b>. According to one embodiment of the present invention, the sealant <b>40</b> is disposed as a paste onto the faying surfaces <b>24, 26</b>, and the structural members <b>20, 22</b> are positioned with the faying surfaces <b>24, 26</b> in an opposed configuration to define the interface <b>28.</b> The structural members <b>20, 22</b> are then urged together, for example, by clamping the structural members <b>20, 22</b> together. The paste sealant <b>40</b> substantially fills the interface <b>28</b> and some of the sealant <b>40</b> is squeezed from the interface <b>28</b> at the edges of the interface <b>28</b>. Excess paste sealant <b>40</b> can be removed from the edges of the interface <b>28,</b> but some sealant <b>40</b> is left outside the interface <b>28.</b> Thus, when the paste sealant <b>40</b> is reacted, a bead of sealant <b>40</b> at the edge of the interface <b>28</b> forms a fillet seal <b>46.</b> In other embodiments of the present invention, such a fillet seal <b>46</b> can alternatively be formed using conventional sealants, such as a caulk-like or resinous material.

As illustrated in <figref idref="f0003">Figure 4</figref>, a braze material <b>48</b> can also be provided in the interface <b>28</b> with the sealant <b>40</b> before the sealant <b>40</b> is reacted to form a braze joint between the structural members <b>20, 22</b>. Typically, the braze material <b>48</b> is characterized by a melting temperature that is lower than the melting temperature of the structural members <b>20, 22</b>. Thus, the particular braze material <b>48</b> for a particular joint <b>10</b> can be selected according to the materials of the structural members <b>20, 22</b> and the sealant <b>40</b>. For example, the braze material <b>48</b> can include bronze, copper, aluminum, and/or nickel. The braze material <b>48</b> can be provided as part of the foil, paste, powder, or other constitution of the sealant <b>40.</b> For example, thin sheets of the braze material <b>48</b> can be layered within the foil of the sealant <b>40</b>, or particles of the braze material <b>48</b> can be mixed with a sealant <b>40</b> that is a powder or paste. Thus, the braze material <b>48</b> can be disposed onto one or both of the faying surfaces <b>24, 26</b> together with the sealant <b>40.</b> Alternatively, the braze material <b>48</b> can be provided separately in the interface <b>28,</b> e.g., as a separate sheet that is layered with the foil sealant <b>40</b>, as a powder or paste that is disposed on the faying surface opposite the sealant <b>40,</b> or otherwise. In any case, the sealant <b>40</b> can have a reaction temperature that is higher than the melting temperature of the braze material <b>48,</b> and the sealant <b>40</b> can be disposed in a quantity such that sufficient heat is released during the exothermic reaction to melt the braze material <b>48</b> so that the braze material <b>48</b> is brazed or otherwise bonded to the structural members <b>20, 22,</b> thereby joining the structural members <b>20, 22.</b> Before, during, or after the exothermic reaction of the sealant <b>40</b> and, hence, the joining of the structural members <b>20, 22</b> by the braze material <b>48,</b> the joint <b>12</b> can be formed, as described above by friction stir welding. Thus, the braze material <b>48</b> enhances the strength of the joint <b>10</b> between the structural members <b>20, 22.</b>

<figref idref="f0004">Figure 5</figref> illustrates the operations for forming a joint according to one embodiment of the present invention. It is understood that some of the operations can be omitted from the method, and additional operations can be performed, without departing from the scope of the present invention. As indicated in Block <b>100,</b> a sealant is disposed in an interface defined by first and second faying surfaces of at least one structural member. The sealant can be disposed as a foil or fluid, and can be disposed with a substrate. The sealant can be disposed with a thickness of between about 0.0005 and 0.020 inches (0.00127 and 0.0508 cm) and can fill, or substantially fill, the entire interface. Further, some of the sealant can be disposed outside the interface, e.g., by squeezing the members together after disposing the sealant, so that the sealant forms a fillet seal outside the interface. In some embodiments of the invention, a braze material is also disposed in the interface with the sealant. See Block <b>110.</b> An exothermic reaction of the sealant is initiated so that the sealant at least partially seals the interface between the faying surfaces. See Block <b>120</b>. The reaction can be initiated by heating the sealant to an initiation temperature. In one embodiment, the exothermic reaction is characterized by a maximum temperature of at least about 1200 °F (649 °C). The at least one structural member is friction stir welded to form a joint between the first and second faying surfaces, the joint being at least partially sealed by the sealant. See Block <b>130.</b> The friction stir welding initiates the exothermic reaction of the sealant, or the sealant can be reacted before or after the friction welding.

Many modifications and other embodiments of the invention set forth herein will come to mind to one skilled in the art to which this invention pertains having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the invention is not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims.