Shaped Composite Vehicle Skins and Method for High Rate Manufacturing of Same

A method for making large vehicle body sections, skins, and panels, including three dimensional sections, skins, and panels, using carbon fiber filaments comingled with thermoplastic polymer filaments to form comingled fibers. The first step is the manufacture of a composite preform using the comingled fibers. The comingled fibers are chopped by a fiber chopper unit mounted on a robot arm to create chopped comingled fibers that are sprayed and set on a preform mold to create a comingled fiber preform. The second step is forming the comingled fiber preform into a composite laminate using heat and pressure to consolidate the comingled fibers on a tooling surface. The disclosed method can be used for making large and contoured thermoplastic composite panels, skins, or sections suitable for light aircraft, automobiles, eVTOL's and other panel applications at a high production rate.

FIELD OF THE INVENTION

This invention relates generally to shaped composite laminates and methods for high rate manufacturing of same.

BACKGROUND OF THE INVENTION

Relatively small vehicles such as cars, airplanes, helicopters, and electric vertical takeoff and landing (eVTOL) urban transport aircraft require an external body shell structure to encapsulate the passengers and systems. There are many existing methods to make such vehicle external shell structures, such as formed metal, plastic, and composite materials. However, each such method has attributes and disadvantages depending on the vehicle requirements. Furthermore, for any given application, the material and manufacturing process must meet functional, cost, and manufacturing requirements.

For example, steel sheet metal has been the dominate automotive body panel manufacturing method because it is low cost, easily formed, highly durable, and the manufacturing method meets automotive production rate requirements. However, steel sheet metal is heavy and has a propensity to rust.

As another example, aluminum has been the dominate material for use in the manufacture of small aircraft and helicopter body shells and skins because aluminum is lightweight and can easily be formed to body panel shapes. However, aluminum body panels must be riveted to the supporting framework which is time consuming and costly. Furthermore, aluminum has corrosion and fatigue concerns.

Advanced composite materials such as carbon fiber and epoxy provide for a lightweight, strong, corrosion resistant, and fatigue resistant structure, but the materials and manufacturing processes are slow and more costly.

The body shell for urban transport vehicles and aircraft, such as eVTOLs, is a significant material and process challenge because the body shell must be very lightweight, strong, low cost, and capable of being manufactured at high rates. To be cost effective for an urban transport vehicle, it is desirable to be able to manufacture the body shell at rates close to one unit per hour.

A second objective for high-volume production of urban transport vehicles and aircraft, such as eVTOLs and other similar vehicles, is to make the body shell structure in as few segments as possible to eliminate assembly time and cost. To date, advanced composite body shell structures have not been made in large sizes and at costs and production rates suitable for the high rate of manufacture needed for urban transport vehicles and aircraft, such as eVTOLs.

The set of requirements for a high-volume produced vehicles such as automobiles, aircraft and urban mobility eVTOL aircraft are extensive. In addition to meeting basic requirements for function, strength, weight, cost, and manufacturing rate, modern products must meet a high standard of appearance and preferably be recyclable at end of life.

Thermoplastic matrix advanced composite materials have many attractive features for the body shell structure of small vehicles such as cars, airplanes, helicopters and eVTOL aircraft. Carbon fibers combined with a thermoplastic polymer such as polyetheretherketone (PEEK), polyaryletherketone (PAEK), polyphenylene sulfide (PPS), and polyetherimide (PEI) can make a strong, lightweight, and damage resistant body shell structure. Thermoplastic materials are also recyclable. As a material, thermoplastic composites potentially do not require long processing times like those for thermosetting polymer materials.

While thermoplastic composite materials offer many attractive features for a lightweight vehicle body shell, many significant processing challenges exist. For example, high molding pressures (200 psi+) and high molding temperatures (500 F+) are typically required to form and consolidate a carbon fiber thermoplastic material into a thin, high-strength composite laminate suitable for a vehicle skin panel. These processing requirements are not an issue for small parts. A hydraulic press can be used to create molding die pressure. Various means to heat and cool down a tool for a small part exist.

However, to make larger skin panels and parts, there exists a need and desire to create adequate heat, pressure, and cool down at a cost effective rate. Currently, large thermoplastic parts and skins are often consolidated in an autoclave so there is no reduction in processing time compared to thermosetting materials, and production rates are not suitable for high volume production. For these reasons, a new process that mitigates the high pressure and heat and cool cycle requirements for molding large thermoplastic composite laminates or vehicle skins is disclosed.

BRIEF SUMMARY OF THE INVENTION

The invention disclosed and described herein is directed to composite laminates and vehicle body panels, parts, and skins that are too large to be compression molded by conventional techniques and that would be too slow to produce if made by autoclave processing, and to a method for making same.

The disclosed invention can be used for making large thermoplastic composite laminates such as large and contoured thermoplastic composite panels or sections suitable for light aircraft, automobiles, eVTOL's and other panel applications at a high production rate.

While primarily directed at lightweight vehicle shell skins that are supported by frame structures, this invention can also be used for other vehicle component skins such as wing skins in certain applications where chopped fiber composite material strength is acceptable. In addition to making three-dimensional shells or skins, the disclosed method can also be used for making flat panels.

This method for manufacturing large thermoplastic laminates such as skin panels is divided into two primary processes. The first process is the manufacture of a composite preform, and the second process is consolidating that preform into a laminate.

The first process is the manufacture of a composite preform using carbon fiber filaments comingled with thermoplastic polymer filaments to form comingled fibers. The comingled fibers are chopped by a fiber chopping unit mounted on a robot arm to create chopped comingled fibers that are sprayed and set on a preform mold to create a comingled fiber preform.

The second process is forming the comingled fiber preform into a composite laminate using heat and pressure via a consolidation tool to consolidate the comingled fibers on a tooling surface.

The two-step process is optimized for high-rate production because it increases the production rate as the forming of the comingled fiber preform is occurring simultaneously with the consolidation of the composite laminate in two separate operations.

However, in an alternative embodiment, the comingled fibers can also be chopped and sprayed by fiber chopper unit directly onto consolidation tool if production rate is less of a concern. In this embodiment, two robot arms can be utilized concurrently, with the first robot arm preforming preform manufacture and the second robot arm then performing the consolidation process.

Prior art fiber chopping units only have one rotary drum with a fixed number of cutting blades so they can only cut one length of fiber at a time. Therefore, in another embodiment, an option to vary the length of the chopped comingled fiber to either be longer or shorter during processing is disclosed because in certain applications it may be desirable to use longer fibers in certain high structurally loaded areas and shorter fibers in other areas.

In this embodiment, the fiber chopping unit has two rotary drums built into the fiber chopper unit to cut different lengths of chopped comingled fibers. The smaller rotary drum is used to make short length chopped comingled fibers. The larger diameter rotary drum has fewer blades and therefore produces longer chopped comingled fibers. The rotary drums rotate on a rotating platform so one or the other can engage and bear against the drive drum.

The change in fiber length can also be controlled with computer numerical control along with the robot arm used for applying the chopped comingled fibers to the preform mold. Computer numerical control can be used to rotate one rotary drum out of use and bring the other into use thereby changing the length of fibers cut.

Another alternative embodiment for manufacturing large composite vehicle skins and parts using the two-step process disclosed herein is to utilize carbon fiber felt, or mat, with a Polyphenylene Sulfide (PPS) matrix in powder that is sprinkled throughout the carbon fiber felt as it is manufactured such that the polymer is evenly distributed amongst the carbon fiber fibers.

In other embodiments, other fiber forms and other thermoplastic polymers may be combined in a similar manner to make a felt-like material or mat that can be consolidated into a composite laminate using the two-step process disclosed herein.

Accordingly, one or more embodiments of the present invention overcomes one or more of the shortcomings of the known prior art.

For example, in one embodiment, a method of manufacturing a composite laminate comprises providing a plurality of carbon fiber filaments comingled with a plurality of thermoplastic polymer filaments to form a plurality of comingled fibers; chopping the plurality of comingled fibers with a fiber chopper unit mounted on a robot arm to form a plurality of chopped comingled fibers; spraying the plurality of chopped comingled fibers onto a preform mold; setting the plurality of chopped comingled fibers on the preform mold to form a comingled fiber preform; directing heat energy from a heating unit onto the comingled fiber preform to melt the plurality of thermoplastic polymer filaments; applying pressure to the comingled fiber preform to consolidate the comingled fiber preform; and cooling the comingled fiber preform to form a composite laminate.

In this embodiment, the method can further comprise controlling the fiber chopper unit using computer numerical control; applying pressure comprises rolling a roller over the comingled fiber preform; controlling the roller using computer numerical control; or controlling the heating unit using computer numerical control.

In another example embodiment, a method of manufacturing a composite laminate comprises providing a comingled felt comprising a plurality of carbon fibers and a thermoplastic polymer; forming the comingled felt into a preform shape; directing heat energy from a heating unit onto the comingled felt to melt the thermoplastic polymer; rolling the comingled felt with a compaction roller; and cooling the comingled felt to form a composite laminate.

In another example embodiment a composite laminate manufactured by a process comprises the steps of providing a plurality of carbon fiber filaments comingled with a plurality of thermoplastic polymer filaments to form a plurality of comingled fibers; chopping the plurality of comingled fibers with a fiber chopper unit mounted on a robot arm to form a plurality of chopped comingled fibers; spraying the plurality of chopped comingled fibers onto a preform mold; setting the plurality of chopped comingled fibers on the preform mold to form a comingled fiber preform; directing heat energy from a heating unit onto the comingled fiber preform to melt the thermoplastic polymer filaments; applying pressure to the comingled fiber preform to consolidate the comingled fiber preform; and cooling the comingled fiber preform to form a composite laminate.

In this embodiment, composite laminate manufactured by the process can further comprise controlling the fiber chopper unit using computer numerical control; applying pressure comprises rolling a roller over the comingled fiber preform; controlling the roller using computer numerical control; or controlling the heating unit using computer numerical control.

In another example embodiment a composite laminate manufactured by a process comprises the steps of providing a comingled felt comprising a plurality of carbon fibers and a thermoplastic polymer; forming the comingled felt into a preform shape; directing heat energy from a heating unit onto the comingled felt to melt the thermoplastic polymer; rolling the comingled felt with a compaction roller; and cooling the comingled felt to form a composite laminate.

Other objects, features, and advantages of the present invention will become apparent upon consideration of the following detailed description and the accompanying drawings.

DETAILED DESCRIPTION OF THE INVENTION

The following is a detailed description of embodiments to illustrate the principles of the invention. The embodiments are provided to illustrate aspects of the invention, but the invention is not limited to any embodiment. The scope of the invention encompasses numerous alternatives, modifications, and equivalents. The scope of the invention is limited only by the claims.

While numerous specific details are set forth in the following description to provide a thorough understanding of the invention, the invention may be practiced according to the claims without some or all of these specific details.

As shown inFIG. 1, the materials used for comingled fibers100, sometimes referred to as a carbon fiber tow, comprise carbon fiber filaments110comingled with thermoplastic polymer filaments120. In an example embodiment, the ratio of carbon fiber filaments110to thermoplastic polymer filaments120is roughly60percent to40percent by volume. However, higher or lower volume ratios for the thermoplastic polymer filaments120to the carbon fiber filaments110can also be used and be beneficial for some applications.

In one example embodiment, carbon fiber is used as a reinforcing fiber for aircraft, helicopters, eVTOL, and even lightweight automobiles. However, glass fibers with comingled thermoplastic filaments can also be used in an alternative embodiment.

Robot Application Machine

As shown inFIGS. 2 and 3, robot application machine200is used for chopping spraying, and applying comingled fibers100onto a preform mold220to make comingled fiber preform310as shown inFIG. 3.

As shown inFIG. 2, comingled fibers100are wound on comingled fiber supply spool210. The comingled fibers100are continuously delivered from comingled fiber supply spool210to fiber chopper unit230mounted on robot arm240. Fiber chopper unit230is electronically controlled, such as by a computer, to continuously apply short lengths of comingled fibers100at a high rate of speed to the preform mold220. In an example embodiment, the short lengths of comingled fibers100are one to three inches long.

In an alternative embodiment, carbon fiber filaments110and thermoplastic polymer filaments120can be independently fed through the fiber chopper unit230rather than comingling the two materials together into comingled fibers100. In another alternative embodiment, pre-impregnated carbon fiber often called tow-preg can be fed into the fiber chopper unit230. In the case of the tow-preg, it will be higher cost due to the pre-preg operation.

As shown inFIG. 11, in one example embodiment, fiber chopper unit230has a first rotary drum1110with a cutter blades1120such that it cuts comingled fibers100against drive drum1130one time with each revolution of first rotary drum1110to create chopped comingled fibers205. The number of cutter blades1120determines the length of the chopped comingled fibers205.

Fiber chopping unit230can also comprise a second rotary drum1140to cut different lengths of chopped comingled fibers205. In one example embodiment, the second rotary drum1140has a larger diameter than first rotary drum1110and fewer cutter blades1120, and therefore produces longer chopped comingled fibers205. The first rotary drum1110and second rotary drum1140can rotate on rotating platform1150to engage and bear against the drive drum1130as required to cut chopped comingled fibers205.

In one example embodiment, the length of chopped comingled fibers205can also vary by mechanically retracting one or more of cutter blades1120in the first rotary drum1110and/or second rotary drum1140used to cut the length of chopped comingled fibers205or by using computer numerical control to switch between first rotary drum1110and second rotary drum1140.

Compressed air provides the delivery of comingled fibers100through fiber chopper unit230. A binder material can be sprayed with chopped comingled fibers205so that the short lengths of lightweight chopped comingled fibers205adhere as they are blown onto the preform mold220.

In one example embodiment, preform mold220is a half circle or doom shape form for a lightweight air vehicle such as an eVTOL. In one embodiment, preform mold220can be made of metal hardware cloth, wire screen, or wire mesh that has been formed to the shape of the vehicle body.

Preform mold220is mounted to a work surface250that has a plenum270underneath it. Blower260pulls air from the inner space of the plenum270, which aids in adhering the chopped comingled fibers205to the outer surface of the preform mold220. In one example embodiment, blower260is a large squirrel cage type blower or other high volume, low pressure blower.

Preform Manufacture Process

At Step420, chopped comingled fibers205are applied or laid down on the surface of preform mold220. This step can be done using robot arm240for manipulating the fiber chopper unit230. The robot arm240is programmed to lay down chopped comingled fibers205on the preform mold220in a controlled and repeatable manner. This provides an improved method over conventional fiberglass chopped fiber spray-up which is typically done by hand.

In another embodiment, the amount of chopped comingled fibers205can be programmed to vary over the surface of the preform mold220. For example, the robot arm240can be programmed to not lay down chopped comingled fibers205in areas such as window openings, hatches, and door openings thereby avoiding material waste.

At step430, chopped comingled fibers205are set on the preform mold220to create comingled fiber preform310. This process can vary depending on the type of binder used in conjunction with fiber chopper unit230. In one embodiment, a water or solvent binder may require infrared heat for a few minutes to set the comingled fiber preform310. In other embodiments, infrared heat can be applied by overhead lamps or as an end effector on a robot arm. In one embodiment, the random orientation of the chopped comingled fibers205creates a quasi-isotropic composite laminate.

In Step440, the comingled fiber preform310is removed from the preform mold220and staged for the next part of manufacture. Making the comingled fiber preform310on a separate preform mold220improves the overall rate production since spray-up time is separated from the thermoplastic consolidation process.

Preform Consolidation Tool

As shown inFIG. 5, comingled fiber preform310is placed on consolidation tool500that accurately defines the Inner Mold Line (IML) or Outer Mold Line (OML) of the fully consolidated comingled composite laminate900, as desired for dimensional control.

In one example embodiment, consolidation tool500is made from carbon fiber so it has a low coefficient of thermal expansion (CTE), but other tool materials can be used. Consolidation tool500is integrally heated to optimize the consolidation process, although consolidation tool500is always kept at a lower temperature than the melt point of the thermoplastic polymer filaments120.

As shown inFIG. 6, roller610of consolidation tool500applies pressure to consolidate the comingled fiber preform310on finish surface630of consolidation tool500. Roller610is attached to robot arm620that is programmed to pass over the entire finish surface630. In one-embodiment, roller610is a hard or semi-hard roller.

Roller610applies line contact pressure on the comingled fiber preform310, and thus has high local consolidation pressure. Thus, a pneumatic cylinder spring can be incorporated into the end of robot arm620to provide compliance to the system.

Heating unit640applies heat from heat energy power source650to comingled fiber preform310.

Several options exist for heat energy from heat energy power source650through heating unit640suitable to melt the thermoplastic polymer filaments120of comingled fiber preform310. In one embodiment, directed heat energy is used. The directed heat energy can be supplied by a laser or pulsed light. An example of a pulsed light system is the Heraeus humm3™ pulsed light technology wherein the pulsed light is controlled in terms of energy, duration, and frequency. In one embodiment, a laser is used for the directed heat energy, although other directed heat energy methods may be used in alternative embodiments.

Consolidation Process

At step710, roller610and heating unit640are progressively passed over comingled fiber preform310with high pressure thereby pin-rolling the carbon fiber filaments110and thermoplastic polymer filaments120.

At step720, the directed heat energy from the heating unit640is focused just before the contact point of roller610. The directed heat energy of heating unit640heats and melts the thermoplastic polymer filaments120of the comingled fiber preform310.

The directed heat energy must be tailored with consolidation pressure and the rate of movement of the robot arm620to optimize the composite laminate900produced from the comingled fiber preform310. The amount of heat energy to put onto the comingled fiber preform310just ahead of roller610and the traverse speed of the roller is specific to each thermoplastic polymer filament120used. For example, PPS requires 500 F+ temperature and 200 psi to consolidate, and other materials like PEEK require in excess of 600 F and similar pressure. Once the process parameters and the allowable deviation is determined, then the robot arm620is programmed for that speed and heat input.

At step730, roller610applies pressure to consolidate the comingled fiber preform310and cool it back to a solid form. In one embodiment, roller610generates 200+ psi pressure required to adequately flow the melted thermoplastic polymer filaments120and produce a high strength relatively void free composite laminate900from the comingled fiber preform310.

At step740, when the entire surface of the fully consolidated comingled composite laminate900has been fully consolidated, it is ready for removal from the consolidation tool500.

Consolidation process700performs multiple functions. First, it melts and flows the thermoplastic polymer filaments120amongst the carbon fiber filaments110in the comingled fiber preform310. Second, it consolidates the carbon fiber filaments110and thermoplastic polymer filaments120of the comingled fiber preform310into fully consolidated comingled composite laminate900with low void content. Third, it is forming the fully consolidated comingled composite laminate900to the finish surface630. Fourth, it is creating a smooth surface on the fully consolidated comingled composite laminate900for the non-tool side of the vehicle body.

FIG. 8shows an example of a partially consolidated comingled composite laminate800.

FIG. 9shows an example of a fully consolidated comingled composite laminate900.

Alternate Embodiments

The two-step process of preform manufacture process400and consolidation process700is optimized for high-rate production because it increases production rate as the forming of comingled fiber preform310is occurring simultaneously with the consolidation of the composite laminate900in two separate operations.

However, in an alternative embodiment, the comingled fibers100can also be chopped and sprayed by fiber chopper unit230directly onto consolidation tool500if production rate is less of a concern. In this embodiment, two robot arms can be utilized concurrently, with one first preforming preform manufacture process400and the second then performing consolidation process700. The directed energy heat is still applied by heating unit640in the same manner with roller610consolidating the composite laminate900as describe herein.

As shown inFIG. 10, another alternative embodiment for manufacturing large composite vehicle skins and parts using preform manufacture process400with robot application machine200and consolidation process700with consolidation tool500is to utilize carbon fiber felt, or mat,1000with a Polyphenylene Sulfide (PPS) matrix in powder that is sprinkled throughout the carbon fiber felt1000as it is manufactured such that the polymer is evenly distributed amongst the carbon fiber fibers.

In other embodiments, other fiber forms and other thermoplastic polymers may be combined in a similar manner to make a felt-like material or mat that can be consolidated into a composite laminate900using preform manufacture process400with robot application machine200and consolidation process700with consolidation tool500.

Such materials in various forms are commercially manufactured and available in sheet form. An example is Mitsubishi Kyron TEX™. The Kyron TEX™ material is available in sheet form delivered on a roll. For example, the material can be manufactured as wide as six feet. The felt material can be cut to flat pattern shapes that can be joined together to approximate a three-dimensional shape such as a composite vehicle skin. The flat pattern shapes can be joined together by sewing or thermoplastic spot welding. When joined together the shaped felt will loosely approximate the shape of the vehicle.

The consolidation process700can be used to heat and consolidate the felt preform on the consolidation tool500. Multiple passes of the roller610and heating unit640may be required to reduce the loft of the felt down to a high strength consolidated laminate. The consolidation temperature and pressure applied is specific to the material and the thickness of composite laminate900to be produced. For example, a carbon fiber PPS comingled laminate processed in this manner will require at least 600 degrees Fahrenheit heat input to melt and flow the thermoplastic filaments and a roller line contact pressure equal to or greater than 200 psi.