METHODS AND APPARATUSES FOR FORMING CORRUGATED THERMOPLASTIC SHEETS AND CELLULAR STRUCTURES

A method of forming a corrugated thermoplastic matrix composite sheet includes preheating a thermoplastic matrix composite sheet including a thermoplastic matrix and a reinforcement material to at least about a melting temperature of the thermoplastic matrix; preheating at least one of a pair of complementary corrugating tools to at least about a glass transition temperature of the thermoplastic matrix; compressing the preheated thermoplastic matrix composite sheet between the pair of complementary corrugating tools to form a corrugation in the thermoplastic matrix composite sheet; and holding the corrugation between the pair of complementary corrugating tools until a portion of the thermoplastic matrix composite sheet having the corrugation is below the melting temperature of the thermoplastic matrix to form the corrugated thermoplastic matrix composite sheet.

BACKGROUND

Honeycomb cores are made of composite material or metals and are often used in the construction of aircraft parts. For example, honeycomb cores are used to make acoustic panels in a nacelle for attenuating engine noise. Honeycomb cores are sandwiched between pairs of skins and attached to the skins adhesives and/or fasteners. However, these types of securement methods can be inconsistent in terms of rate, strength, and weight.

SUMMARY

In some embodiments, a method of forming a corrugated thermoplastic matrix composite sheet includes preheating a thermoplastic matrix composite sheet including a thermoplastic matrix and a reinforcement material to at least about a melting temperature of the thermoplastic matrix: preheating at least one of a pair of complementary corrugating tools to at least about a glass transition temperature of the thermoplastic matrix: compressing the preheated thermoplastic matrix composite sheet between the pair of complementary corrugating tools to form a corrugation in the thermoplastic matrix composite sheet; and holding the corrugation between the pair of complementary corrugating tools until a portion of the thermoplastic matrix composite sheet having the corrugation is below the melting temperature of the thermoplastic matrix to form the corrugated thermoplastic matrix composite sheet.

In another embodiment, an apparatus for forming a corrugated thermoplastic sheet. The corrugated thermoplastic sheet is formed from a sheet of thermoplastic with reinforcement material embedded therein. The apparatus includes a first heating element, a first corrugating tool, a second corrugating tool, and a second heating element. The first heating element is configured to heat a portion of the sheet to at least about a melting temperature of the thermoplastic. The first corrugating tool has a male mold for imparting a trough in the sheet. The second corrugating tool has a complementary female mold that receives the male mold. The second heating element is configured to heat the male mold or the female mold to at least about a glass transition temperature of the thermoplastic.

In yet another embodiment, an apparatus for forming a corrugated thermoplastic sheet includes a first continuous track assembly, and a second continuous track assembly. The first continuous track assembly includes a belt with a first set of cleats for engaging a first side of a portion of a thermoplastic sheet. The second continuous track assembly includes a belt with a second set of cleats that are complementary to the first set of cleats for engaging a second side of the portion of the thermoplastic sheet. The second side being opposite to the first side of the thermoplastic sheet.

In some embodiments, a method of forming a thermoplastic cellular structure includes positioning a lower surface of a trough of a first corrugated thermoplastic sheet against an upper surface of a crest of a second corrugated thermoplastic sheet: positioning a support against a lower surface of the crest of the second corrugated thermoplastic sheet; and pressing a thermoplastic welding element against an upper surface of the trough of the first corrugated thermoplastic sheet so that at least a portion of the lower surface of the trough of the first corrugated thermoplastic sheet melts and bonds to at least a portion of the upper surface of the crest of the second corrugated thermoplastic sheet.

In another embodiment, an apparatus for forming a thermoplastic cellular structure includes elongated supports and thermoplastic welding elements. The elongated supports extend parallel to one another and have coplanar top surfaces. The thermoplastic welding elements are operable to melt thermoplastic and have coplanar bottom surfaces that face the top surfaces of the elongated supports.

In yet another embodiment, a method of forming a thermoplastic cellular structure includes positioning a lower surface of a trough of a first corrugated thermoplastic sheet next to an upper surface of a crest of a second corrugated thermoplastic sheet: pressing the lower surface of the trough of the first corrugated thermoplastic sheet against the upper surface of the crest of the second corrugated thermoplastic sheet; and heating a portion of the trough of the first corrugated thermoplastic sheet so that at least a portion of the lower surface of the trough of the first corrugated thermoplastic sheet melts and bonds to at least a portion of the upper surface of the crest of the second corrugated thermoplastic sheet.

DETAILED DESCRIPTION

Turning toFIG.1, a corrugated sheet10constructed according to an embodiment is depicted. The corrugated sheet10comprises thermoplastic and a reinforcement material. The thermoplastic includes any type of thermoplastic, depending on the application. In embodiments, the thermoplastic includes polyetheretherketone (PEEK), polyaryletherketone (PAEK), or polyetherketoneketone (PEKK). However, embodiments of the invention include thermoplastics having varying processing temperatures and performance capabilities. The reinforcement material includes continuous fiber, such as glass fiber, carbon fiber, boron fiber, aramid fiber, or ceramic fiber. Multiple corrugated sheets may be positioned with their troughs and crests (discussed in further detail below) facing one another to form a stack12.

Embodiments of the invention include methods and apparatuses for welding the sheets10of the stack12to form a cellular structure14. The cellular structure14defines cells16having any number of shapes without departing from the scope of the invention. In embodiments, the cellular structure14is a honeycomb with hexagonal columnar cells16, as depicted inFIG.1. In some embodiments, the sheets10form sinusoidal waves to define ogee-shaped cells, square waves to define rectangular cells, or the like. The widths of the cells16vary depending upon the application. In embodiments, the widths of the cells16are 3.18 millimeters (about an eighth of an inch) to about 6.35 millimeters (about a quarter of an inch). In some embodiments, the widths of the cells16are about 304.8 millimeters (about a foot wide).

The cellular structure14is advantageously welded to thermoplastic skins. This enables the use of thermoplastics in structures that require sandwich panels with structurally sound bonds without the use of mechanical fasteners or adhesives. The cellular structure14can be implemented in any number of applications, such as in automotive structures, wind turbine structures, structural/architectural components for construction projects, sporting goods, and other applications.

Turning toFIG.2, an apparatus18constructed according to an embodiment of the invention is depicted. The apparatus18is operable to form corrugated sheets10from reinforced thermoplastic material20. The thermoplastic material20is any of the thermoplastic materials discussed above, including reinforced thermoplastic. The apparatus18includes a mobile support22for supporting a roll of thermoplastic material20, a tensioning device24, a housing or oven26, a first heating element28, a second heating element30, and a pair of complementary corrugating tools32,34.

The mobile support22holds the roll of thermoplastic20and is spaced apart from the corrugating tools32,34. The mobile support22is an axle or bearing that allows the roll of thermoplastics20to unroll so that the thermoplastic shifts toward, unfurls, or moves towards the corrugating tools32,34when the corrugations are being formed. In embodiments the thermoplastic is reinforced with continuous fiber, such as carbon fiber, the sheet10does not stretch well. Thus, the thermoplastic20needs to be able to shift toward the tools32,34as the corrugations are formed. In other words, the corrugations are formed by folding additional material, not stretching the material. This is advantageous for application requiring high levels of control over the thickness of the cellular structure14and necessary when the sheet is reinforced with continuous fiber. Embodiments of the invention include other types of mobile supports, including mobile clamps, as discussed elsewhere herein.

The tensioning device24provides tension to the thermoplastic sheet20. The tensioning device24comprises a biasing element36secured to a dancer pulley38that maintains constant tension as the material20is pulled into the corrugating tools32,34.

The oven26houses the heating elements28,30and the corrugating tools32,34and helps control the temperature around the thermoplastic sheet and the processing area. The oven26includes an inlet40through which the thermoplastic sheet20is received and an outlet42through which the formed corrugated sheet10exits.

The first heating element28is configured to heat a portion of the sheet20to at least about a melting temperature of the thermoplastic20. The melting temperature is different for different types of thermoplastics. In embodiments, the first heating element28is configured to heat the thermoplastic20up to eight hundred degrees Fahrenheit (800° F.). As used herein, “at least about the melting temperature” is ninety-five percent (95%) of the actual melting temperature of the thermoplastic material or higher. The first heating element28is supported on the oven26at the inlet40thereof. In some embodiments, the first heating element28includes infrared lamp heaters, hot gas/hot air heaters, or high-powered lasers.

The second heating element30is configured to heat at least one of the molding surfaces of the corrugating tools32,34. The tools32,34are heated so that the corrugated thermoplastic sheet10is cooled in a controlled manner. In embodiments, the second heating element30is configured to heat the molding surfaces of the corrugating tools32,34to at least about a glass transition temperature of the thermoplastic. As used herein, “at least about the glass transition temperature” is ninety percent (90%) of the actual glass transition temperature of the thermoplastic material or higher. In embodiments, the second heating element30is configured to heat the molding surfaces of the corrugating tools32,34to at least about a glass transition temperature of the thermoplastic up to 95% of the melting temperature of the thermoplastic material. In embodiments, the second heating element30is configured to heat the thermoplastic material to about halfway through the glass transition temperature of the thermoplastic material and the melting temperature of the thermoplastic material. In embodiments, the second heating element30includes a motor43outside the interior of the oven26that drives a fan44for blowing heated air onto the corrugating tool32. In some embodiments, the apparatus18includes multiple heating elements configured to heat both corrugating tools32,34.

The first corrugating tool32—cooperatively with the second corrugating tool34—forms a corrugation46in the sheet20. The first corrugating tool32comprises a continuous track assembly having a pair of pulleys48,50spaced apart from one another and a belt or linked chain52comprising a plurality of cleats54. One or more of the pulleys48,50drive the belt52so that the belt52shifts about the pulleys48,50. In some embodiments, a motor (not shown) drives at least one of the pulleys48,50. The cleats54engage a first side56of the thermoplastic material20. The cleats54have any number of different shapes, depending on the desired shape of the cells of the cellular structure.

The second corrugating tool34is complementary to the first corrugating tool32. The second corrugating tool34comprises a continuous track assembly having a pair of pulleys58,60spaced apart from one another and a belt or linked chain62comprising a plurality of cleats64. One or more of the pulleys58,60drive the belt62so that it shifts about the pulleys58,60. In some embodiments, a motor drives at least one of the pulleys58,60. In some embodiments, the motor that drives the pulleys48,50also drives pulleys58,60through one or more belts or gears so that the pulleys operate synchronously. The cleats64engage a second side66of the thermoplastic material20and are complementary to the cleats54of the first corrugating tool32. The cleats54,64may be complementary due to their relative orientation about their respective pulleys and/or due to the positions of the pulleys (as depicted). The cleats64have any number of different shapes, depending on the desired shape of the cells of the cellular structure.

The corrugating tools32,34hold the corrugations46in the cleats54,64until the portion of the sheet20having the corrugation46is below the melting temperature of the thermoplastic. In embodiments, this is accomplished due to the cleats54,64forming and engaging the corrugation46and pulling or shifting the corrugation46as their respective belts shift about their respective pulleys. The pulleys are spaced apart at long enough distances so that the cleats54,64hold the corrugation46for a necessary distance at an operating speed so that the thermoplastic20of the corrugation46cools below the melting temperature of the thermoplastic. In some embodiments, the distance is long enough so that the thermoplastic20of the corrugation46cools to the glass transition temperature of the thermoplastic. In embodiments, the distance the corrugation46travels is at least twice as long as the length of the sheet required to form the corrugation46. In embodiments, the apparatus18includes idler rollers68and biasing members70that apply constant pressure to the belts52to maintain a pressure on the corrugated sheet10as the cleats54,64hold the corrugation46. In embodiments, the biasing members70include actuators or hydraulic cylinders. The cleats54,64disengage from the formed corrugation46at the end of the forming distance, and the portion of the sheet10having the corrugation46is pushed out of the outlet42of the oven26.

An apparatus18A constructed in accordance with another embodiment of the invention is shown inFIG.3. The apparatus18A comprises some similar components as apparatus18: thus, the components of apparatus18A that correspond to similar components in apparatus18have an ‘A’ appended to their reference numerals.

The apparatus18A is operable to form corrugated sheets10from thermoplastic material20. The thermoplastic material20is any of the thermoplastic materials discussed above, including reinforced thermoplastic material. The apparatus18A includes a mobile support22A for supporting the thermoplastic sheet20, an end clamp24A, a first heating element28A, second heating elements30A, and a pair of complementary corrugating tools32A,34A.

The mobile support22A holds a portion of the sheet20not being formed and is spaced apart from the corrugating tools32A,34A. The support22A is configured to shift toward the corrugating tools32A,34A so that the portion of the sheet20not being formed shifts toward the corrugating tools32A,34A when the sheet is compressed. In embodiments, the support22A includes a clamp72A, a mobile chassis74A, and a track76A. The other end of the sheet20is secured via the fixed end clamp24A. Every time the sheet20is bent to form a corrugation, the rest of the sheet and the support22A are pulled towards the corrugating tools32A,34A.

The first heating element28A is configured to heat a portion of the sheet20to at least about a melting temperature of the thermoplastic20. The first heating element28A is a mobile heater that is operable to extend between the tools32A,34A and retract out from between the tools32A,34A. The melting temperature is different for different types of thermoplastics. In embodiments, the first heating element28A is configured to heat the thermoplastic20up to eight hundred degrees Fahrenheit (800° F.). In some embodiments, the first heating element28A includes infrared lamp heaters, hot gas/hot air heaters, or high-powered lasers.

The second heating elements30A are configured to heat at least one of the molding surfaces of the corrugating tool32A. The heating elements30A comprise heated blocks or platens having any number of heat sources, including electric heaters, infrared heaters, or induction heaters. As discussed above, the tool32A is heated so that the corrugated thermoplastic sheet10is cooled in a controlled manner. In embodiments, the second heating elements30A are configured to heat the molding surfaces of the corrugating tool32A to at least about a glass transition temperature of the thermoplastic. In embodiments, the second heating elements30A are configured to heat the molding surfaces of the corrugating tool32A to at least about a glass transition temperature of the thermoplastic up to and including the melting temperature of the thermoplastic material. In embodiments, the second heating elements30A are configured to heat the tools32A so that the thermoplastic material is cooled in a controlled manner to about halfway through the glass transition temperature of the thermoplastic material and the melting temperature of the thermoplastic material.

The first corrugating tool32A includes a plurality of individually shiftable cleats54A that each form a corrugation in the sheet20. The cleats54A engage a first side56of the thermoplastic material20to form the corrugation46(depicted inFIGS.4B-4F). The cleats54A have any number of different shapes, depending on the desired shape of the cells of the cellular structure. The second corrugating tool34A comprises cleats64A that are complementary to—and operable to receive—the cleats54A. The second corrugating tool34A is positioned on a press base78A. The cleats64A engage the second side66of the sheet20when the opposing cleats54A push against the first side56of the sheet20. The corrugating tools32A,34A include any number of cleats54A,64A without departing from the scope of the invention. Further, any portion or the entirety of the corrugating tool34A can be actuated toward tool32A without departing from the scope of the present invention.

Turning toFIG.4A, the first heating element28A is positioned between the tools32A,34A to heat the thermoplastic sheet20. The first heating element28A heats the portion of the sheet20that is between a first cleat54A and corresponding cleats64A. Turning toFIG.4B, a first cleat54A is actuated toward the second tool34A. The first cleat54A engages the first side56of the sheet20and extends into a space defined by adjacent bottom tool cleats64A. The adjacent cleats64A engage the second side66of the sheet20. The cleats54A,64A form a first corrugation46in the sheet20. As the cleat54A engages the sheet20, the tension of the sheet causes the clamp72A and chassis74A to shift toward the tools32A,34A. While the first corrugation46is formed, the heater28A heats the portion of the sheet20where a second corrugation is to be formed.

Turning toFIG.4C, a second cleat54A is actuated toward the second tool34A. The second cleat54A and adjacent cleats64A engage the sheet20to form a second corrugation46in the sheet20, and the clamp72A and chassis74A shift toward the tools32A,34A. Meanwhile, the heater28A heats the portion of the sheet20where another corrugation is to be formed.

Turning toFIG.4D, another cleat54A is actuated toward the second tool34A. The second cleat54A and adjacent cleats64A engage the sheet20to form another corrugation46in the sheet20, and the clamp72A and chassis74A shift toward the tools32A,34A. Meanwhile, the heater28A heats the portion of the sheet20where another corrugation is to be formed. Turning toFIG.4E, the aforementioned operations are repeated until all the cleats54A of the tool32A have engaged the sheet20. The tools32A,34A hold the corrugations46until the portions of the sheet20having the corrugations are below the melting temperature of the thermoplastic to form the corrugated thermoplastic sheet10, as depicted inFIG.4F.

An apparatus80constructed in accordance with another embodiment of the invention is shown inFIG.5. The apparatus80is operable to form a cellular structure14(depicted inFIG.1) from corrugated reinforced thermoplastic sheets10,11and comprises a support structure82and a welding tool84.

The support structure82comprises a first tool support86, elongated supports88, and a second tool support90. The elongated supports88extend from the first tool support86and are operable to extend into or be inserted into spaces defined by the crests of the sheets10,11. Turning toFIG.6, the elongated supports88extend generally parallel to one another and have substantially coplanar top surfaces92. The contour of the top surfaces92generally match the bottom surfaces of the crests of the corrugated sheets10. In embodiments, the top surfaces92are parallel to bottom surfaces of the crests of the corrugated thermoplastic sheets10. First ends94of the elongated supports88are secured to the first tool support86, and the other ends96extend past the sheets10and are supported by the second tool support90(as depicted inFIG.5) when the welding tool84presses against the sheets11, as discussed in further detail below: In embodiments, the supports88comprise metal, steel, aluminum, or any material that can withstand high temperatures and are rigid. In embodiments, the supports88are I-beam shaped, U-shaped, or rectilinear. The second support tool90is vertically shiftable relative to the sheets10to support the elongated supports88at any vertical location relative to the sheets10.

Turning back toFIG.5, the welding tool comprises a press platen98, a plurality of stanchions100connected to the platen98, and a plurality of thermoplastic welding elements102secured to the stanchions. The press platen98is operable to be actuated towards the supports88to weld sheets and away from the supports88in order to load additional corrugated sheets.

Turning toFIG.7A, the thermoplastic welding elements102are operable to melt the thermoplastic of the corrugated thermoplastic sheets. The welding elements102have bottom surfaces104that are generally coplanar and face the top surfaces92of the elongated supports88. In embodiments, the thermoplastic welding elements102comprise ultrasonic welding heads, induction welding heads, or hot knives.

The platen98is operable to shift towards the elongated supports88. The thermoplastic welding elements102press against upper surfaces110of troughs108of the corrugated thermoplastic sheet11so that at least portions of the lower surfaces112of the troughs108of the sheet11melt and bond to at least portions of the upper surfaces110of the crests106of the bottom corrugated thermoplastic sheet10. As used herein, when in the orientation indicated by the arrow; the crests106are the portions of the corrugated sheets10,11that are convex relative to and extend toward the platen98, and the troughs108are the portions of the corrugated sheets10,11that are concave relative to and extend away from the platen98. The upper surfaces110are on the sides of the corrugated sheets10,11that face toward the platen98, and the lower surfaces112are on the sides of the corrugated sheets10,11that faces away from the platen98.

Turning toFIG.7B, the platen98is actuated to hold the thermoplastic welding elements102pressed against the corrugated sheet11so that the welding elements102and the elongated support elements88squeeze the sheets10,11. The sheets10,11are held clamped under pressure until they are welded together and then until their temperatures drop below the melting temperature of the thermoplastic of the sheets10,11. In embodiments, the welding elements102and the elongated supports88squeeze the sheets10,11together until the temperature of the sheets10,11drop below the halfway between the glass transition temperature and the melt temperature of the thermoplastic of the sheets10,11to maximize the crystallinity formation rate in the weld.

The elongated supports88are pulled out of the crests106of the sheet10and inserted into the spaces defined by the crests106of second sheet11for welding another sheet13, as depicted inFIG.7C. The welding elements102are then pressed against the troughs108of the third sheet13to weld the third sheet13to the second sheet11. These operations are repeated until the cellular structure14having the desired number of layers is formed, as depicted inFIGS.7D-7G.

The flow chart ofFIG.8depicts the steps of an exemplary method800of forming a corrugated thermoplastic sheet. In some alternative implementations, the functions noted in the various blocks may occur out of the order depicted inFIG.8. For example, two blocks shown in succession inFIG.8may in fact be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order depending upon the functionality involved. In addition, some steps may be optional. The method800is described below, for ease of reference, as being executed by exemplary devices and components introduced with the embodiments illustrated inFIGS.1-4F.

Referring to step801, a portion of a sheet comprising thermoplastic and a reinforcement material is preheated to at least about a melting temperature of the thermoplastic. The sheet is heated via a first heating element configured to heat a portion of the sheet to at least about a melting temperature of the thermoplastic. In embodiments, the first heating element comprises a mobile heater configured to extend between corrugating tools to heat the portion of the sheet the tools are about to engage. In some embodiments, the first heating element is located proximal to an inlet of an oven that houses corrugating tools and through which the sheet is operable to enter. In some embodiments, the first heating element includes infrared lamp heaters, hot gas heaters, hot air heaters, or high-powered lasers.

Referring to step802, at least one of the corrugating tools is preheated to at least about a glass transition temperature of the thermoplastic. In embodiments, the corrugating tool is heated via a second heater configured to heat the tool so that a surface that engages the sheet is at least about the glass transition temperature. In embodiments, the second heating element is configured to heat the thermoplastic material to about halfway through the glass transition temperature of the thermoplastic material and the melting temperature of the thermoplastic material. In embodiments, the second heating element includes a fan for blowing heated air onto the corrugating tool. In embodiments, the second heating element includes electric heaters, infrared heaters, or induction heaters. In some embodiments, this step includes heating both corrugating tools.

Referring to step803, the preheated portion of the sheet is compressed between the corrugating tools to form a corrugation in the sheet. In embodiments, the corrugating tools comprise continuous track type tools, as discussed above in reference toFIG.2. Alternatively, the sheet is compressed between linearly actuated tools with cleats, as discussed above in reference toFIGS.3-4F.

Referring to step804, the corrugation(s) are held between the tools until the portion of the sheet having the corrugation is at least below the melting temperature of the thermoplastic. In embodiments, the thermoplastic is held stamped down and cooled until the thermoplastic goes below the glass transition temperature of the thermoplastic. In embodiments, this step includes shifting the first and second sets of cleats of the tools with their respective belts a distance with the corrugation held therebetween and disengaging at least one of the tools from the preheated sheet.

The method800may include additional, less, or alternate steps and/or device(s), including those discussed elsewhere herein.

The flow chart ofFIG.9depicts the steps of an exemplary method900of forming a cellular structure from corrugated thermoplastic sheets. In some alternative implementations, the functions noted in the various blocks may occur out of the order depicted inFIG.9. For example, two blocks shown in succession inFIG.9may in fact be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order depending upon the functionality involved. In addition, some steps may be optional. The method900is described below, for ease of reference, as being executed by exemplary devices and components introduced with the embodiments illustrated inFIGS.5-7G.

Referring to step901, an outer surface of a crest of a first corrugated thermoplastic sheet and an outer surface of a trough of a second corrugated thermoplastic sheet are positioned next to one another (as depicted inFIGS.7A and7B). In embodiments, multiple crests of the first corrugated thermoplastic sheet are positioned next to multiple troughs of the second corrugated thermoplastic sheet.

Referring to step902, elongated supports are inserted into crests of the first corrugated sheet. The supports are positioned against inner surfaces of the crests of the first corrugated thermoplastic sheet. In some embodiments, this step includes positioning a tool support against the undersides of the ends of the elongated supports that stick out from the sheet.

Referring to step903, thermoplastic welding elements are pressed against inner surfaces of the troughs of the second corrugated thermoplastic sheet so that at least portions of the outer surfaces of the troughs of the second corrugated thermoplastic sheet melt and bond to at least portions of the outer surfaces of the crests of the first corrugated thermoplastic sheet. In some embodiments, the thermoplastic welding elements are operable to melt the thermoplastic and have coplanar bottom surfaces that face the top surfaces of the elongated supports. The thermoplastic welding elements and the supports cooperatively squeeze the two corrugated thermoplastic sheets when welding them. The corrugated thermoplastic sheets are held together until they are welded together. Once welded, the corrugated thermoplastic sheets are held together at least until their temperatures drop below the melting temperature of the thermoplastic of the sheets to ensure strong welds. In embodiments, the welding elements and the elongated supports are used to squeeze the sheets together until the temperature of the sheets drop below the glass transition temperature of the thermoplastic of the sheets.

Referring to step904, one or more of the previous steps are repeated with additional corrugated thermoplastic sheets until a cellular structure with a desired thickness is formed. This step includes positioning outer surfaces of troughs of another corrugated thermoplastic sheet and outer surfaces of crests of the previously-welded corrugated thermoplastic sheet next to one another. This step also includes removing the supports from the spaces defined by the previously-welded crests of the previously-welded sheet and inserting the supports into the spaces defined by the crests of the thermoplastic sheet above the previous one. This step includes pressing the thermoplastic welding elements against inner surfaces of the troughs of the next corrugated thermoplastic sheet so that at least portions of the outer surfaces of the troughs of the next corrugated thermoplastic sheet melt and bond to at least portions of the outer surfaces of the crests of the previously-welded corrugated thermoplastic sheet.

The method900may include additional, less, or alternate steps and/or device(s), including those discussed elsewhere herein.

Although the invention has been described with reference to example embodiments illustrated in the attached drawing figures, it is noted that equivalents may be employed and substitutions made herein without departing from the scope of the invention as described and claimed herein.