NASA CASE NO.

PRINT FIG.

NOElCE

The invention disclosed in this document resulted from research in aeronautical

and space activities performed under programs of the National Aeronautics and Space

Administration. The invention is owned by NASA and is, therefore, available for

licensing in accordance with the patent licensing regulations applicable to U.S.

Government-owned inventions (37 CFR 404.1 el seq.).

To encourage commercial utilization of NASA-owned inventions, it is NASA

policy to grant licenses to commercial concerns. Although NASA encourages

nonexclusive licensing to promote competition and achieve the widest possible

utilization, NASA will provide the necessary incentive to the licensee to achieve early

practical application of the invention.

Address informational requests for this invention to the Technology

Applications Team, NASA Langley Research Center, Code 200, Hampton, Virginia

23681-0001.

Address applications for license to the Patent Counsel Office, Mail Stop 212,

3 Langley Boulevard, Hampton, Virginia 23681-0001.

Serial No.: 08/411,231

Filed: 03/21/95

(NASA-Case-LAR-15259-1) CQNPOSITE

PREPREG APPLICATION DEVICE Patent

Application (NASA. Langley

Research Center) 14 p

laRC

N95-Z_|92

Unclas

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G3/24 0069679
LAR 15259-1-CU AWARDS ABSTRACT 

COMPOSITE PREPREG APPLICATION DEVICE 

A heated shoe and cooled pressure roller assembly for composite prepreg 

application is provided. The shoe assembly includes a heated forward contact 

surface having a curved pressure surface. The following cooled roller provides a 

continuous pressure to the thermoplastic while reducing the temperature to 

approximately 5°C below glass transition temperature. Electric heating coils 

inside the forward portion of the shoe heat a thermoplastic workpiece to 

approximately 100°C above the glass transition. Immediately following the heated 

contact surface, a cooled roller cools the work. The end shape of the heated shoe 

tends to prevent slag buildup and maintain a uniform, relaxed stress fabrication. 

Inventor: Donald A. Sandusky 

Home address: f ?5-#8-Memmac-fraiI 1213 Christina Mill Drive 

Employer: WM & Mary 

Inventor: Joseph M. Marchello 

Home address: 6 Rhoda Court 

Hampton, Virginia 23664 

SS#: 

Employer: 

0 

ODURF 

Initial Evaluator: 

Newark, DE 19711 

Serial No.: 081411,231 

Filed: March 21, 1995 
LAR 15259-1-CU -1 - PATENT APPLICATION

COMPOSITE PREPREG APPLICATION DEVICE

Origin_ of_the Invention

5 The invention described herein was made by contractor employees in

the performance of work under a NASA contract. In accordance with

35 USC 202, the contractor elected not to retain title.

10

Background of_the Invention

The invention is related to the field of composite fabrication and in

particular to devices providing product release, void compression and

residual stress management in thermoplastic composites.

15 Description of RelatedArt

20

25

The state of the art application devices were developed for thermoset

technology. They are not functional for thermoplastic in situ fabrication

because they cannot cause the appropriate heat transfer and squeeze flow

mechanisms to occur. Thermoplastics have become a material of

preference in certain fabrications, particularly lay-up of aerospace

structures. Thermoplastics exhibit beneficial characteristics including more

resilient and resistance to impact fractures, the ability to shape or mold,

resistance to heat and fire, and retention of these characteristics at high

temperatures. Recent thermoplastic matrix composites have withstood

frictional temperature approaching that required for Mach 2 flight.

To achieve this level of performance with thermoplastic components,

it is necessary to provide a material with uniform thickness, free of internal

flaws, uniformly compacted, and with a low and uniform level of residual
LAR 15259-1-CU

stress.

-2- PATENT APPLICATION

Summa[y_o[the Invention

5 It is an object of the present invention to provide a composite prepreg

application device which expels or compresses voids from thermoplastic

composites.

It is another object of the invention to provide a composite prepreg

application device which controls residual stress.

10 It is yet another object of the invention to provide a composite

prepreg application device with improved product release during composite

lay-up.

It is a further object of the invention to provide a composite prepreg

application device which facilitates melt flow of the incoming prepreg during

15 composite lay-up.

It is still another object of the invention to provide a composite

prepreg application device which applies both high temperature and high

pressure simultaneously during composite lay-up.
LAR 15259-1-CU -3- PATENT APPLICATION

It is another object of the invention to provide a composite prepreg

application device which applies both high pressure and a high cooling

gradient immediately following the high temperature and pressure lay-up.

Accordingly, the invention is a device for composite prepreg

5 application comprising a moving electrically heated shoe assembly having

an attached cooled roller. The electrically heated shoe assembly is operated

by a conventional robotic control mechanism known in the art. The special

shape of the shoe provides a substantial transverse pressure load as a

continuous pressure gradient to the prepreg material, that is, a continuously

10 increasing load. The heated shoe is maintained at a temperature above

(approximately 100°C above) the glass transition temperature for the

material being fabricated. Immediately following the tip of the heated shoe,

a cooled roller both applies pressure and reduces the temperature slightly

below (approximately 5°C below) the glass transition temperature. The

15 invention applies heat to a composite prepreg material with smoothly

increasing pressure so as to reach a temperature above glass transition for

purposes of causing wet outflow and consolidation and thereafter,

immediately applies cooling to below glass transition temperature while

maintaining a steady pressure on the material.

2O

Brief Description of theDrawings

25

For a more complete understanding of the present invention and for

further objects and advantages thereof, reference is now made to the

following description taken in conjunction with the accompanying drawings

in which:

FIG. 1 is a side view of the composite prepreg application device;

FIG. 2 is a side view of an alternative configuration of the application

device;
LAR 15259-1-CU -4- PATENT APPLICATION

FIG. 3 is a side view of the application device as installed on a

conventional robotic control mechanism; and

FIG. 4 is a cutaway side view of the application device.

5 Dstailed Description of the ln_ention

Referring now to Fig. 1, the composite prepreg application device,

designated generally by the reference numeral 10, is shown with its major

components. The device comprises an attachment base 11 which is

10 adapted for attachment to a conventional robotic lay-up machine. The

attachment base 11 has support arms 13 on either end for attaching a

pressure roller 15. A heated shoe assembly 16 is located on the fore

section of the attachment assembly 11. The heated shoe assembly uses an

electrical heater in the preferred embodiment, but any suitable heat source

15 may be substituted. The pressure roller 15 is cooled by a cooling fluid

delivered through support arms 13. During operation of the device, the

heated shoe assembly 16 raises the temperature of the paver-coated

prepreg tow 17 above the glass transition temperature, thereby providing

a molten plastic to the composite 19 immediately behind the tip 18 of the

20 heated shoe assembly. The heated shoe assembly has an elongated curving

tow guide having a sharpened tip or trailing edge. This shape provides the

steadily increasing pressure while the sharpened tip disperses slag

preventing any build-up. Immediately thereafter, the composite reaches the

pressure roller 15 where it is simultaneously compacted and cooled below

25 glass transition temperature. The process allows the production of high

quality, uniform lay-ups free of voids and free of variations in thickness or

surface smoothness.

Referring now to Fig. 2, an alternate embodiment 20 of the invention

is shown using a second cooling arrangement. The attachment base 21
LAR 15259-1 -CU -5- PATENT APPLICATION

contains the heated shoe assembly as in the first embodiment, however, the

pressure roller 25 has no internal cooling. Cooling is provided, instead, by

a cooling shoe 26 which receives a cooling fluid directly from the

attachment base 21. The temperature control of the incoming prepreg tow

5 17 is accomplished as in the preferred embodiment. The temperature of the

prepreg tow is raised above glass transition temperature, depicted by point

27, and then is immediately cooled, under pressure to a temperature below

glass transition temperature, depicted by point 28. During lay-up, the entire

lay-up structure may be moved, or the robotic machine may move the

10 application device. In the case of application device movement, the

direction of movement is to the left in each figure, depicted by arrow 29 in

Fig. 2.

The attachment of composite prepreg application device 10 when

installed on a typical robotic lay-up machine may be seen by reference to

15 Fig. 3. For attachment to a typical conventional robotic lay-up machine, the

attachment base is a block shaped to be held by the conventionally known

chucks commonly used on these machines. The block or bit forming the

attachment base is fitted with electrical ports and cooling ports for providing

heating energy and cooling energy to the applicator shoe and roller,

20 respectively. The robotic machine 30 is used to apply powder-coated

prepreg ribbon to a typical aerospace structure 31. As depicted here, the

device 10 in this embodiment applies multiple ribbons of prepreg tow 17.

By adapting the guide surface of the heated shoe, multiple side-by-side

strips of prepreg tow may be applied simultaneously.

25 A side section of the application device 10 in Fig. 4 shows the

internal components of the device. For reference, prepreg tow 17 is

referenced along with the attachment base 11 and the cooled roller 15

supported by arm 13 forming composite 19. Internally, a heating element

41 is located at the tip of the heated shoe. The upper portion 42 of the
LAR 15259-1-CU -6- PATENT APPLICATION

heated shoe assembly acts as a guide for the incoming prepreg tow 17. An

electrical connecting wire 43 provides a means of attaching the heating

element 41 to a power supply. The cooling liquid is supplied to the cooled

roller through an insulated area by coolant tube 45.

5 The advantage and features of the application device are numerous.

The device allows the immediate transition of a powder-coated prepreg tow

line to above glass transition temperature and immediately thereafter,

provides an under pressure temperature decrease to below glass transition

temperature. The result is a uniform application of the ribbon with a

10 uniformly filled material. Internal voids are minimized or eliminated. The

surface is uniformly even and the material thickness is likewise maintained

at a uniform value. The heated shoe assembly, having a curvilinear contact

surface, provides for a smoothly and steadily increasing pressure (a

continuous pressure gradient) on the work piece. This continuous pressure

15 gradient is applied while the heating of the work piece to approximately

100°C above the glass transition temperature for the particular work piece.

The prepreg lay-up is thereby maintained at a precise pre-selected pressure

during the glass transition. The cooling roller of the device is positioned

immediately behind the heated shoe contact surface. This positioning

20 allows pressure to be continuously applied to the work piece during both

heating through glass transition and then cooling down below glass

transition. There is no point during the heat up/cool down cycle where the

material is not under pressure with the exception of the very small physical

space separating the shoe contact surface and the roller. Additionally, the

25 trailing edge of the shoe tip tends to disperse any slag prior to any

significant buildup. As a result, a very high quality material is produced,

free of void area, and free of residual stresses.

Although the invention has been described relative to a specific

embodiment thereof, there are numerous variations and modifications that
5

LAR 15259-1 -CU -7- PATENT APPLICATION

will be readily apparent to those skilled in the art in the light of the above

teachings. It is therefore to be understood that, within the scope of the

appended claims, the invention may be practiced other than as specifically

described.

What is claimed as new and desired to be secured by Letters Patent

of the United States is:
LAR 15259-1-CU PATENT APPLICATION

COMPOSITE PREPREG APPLICATION DEVICE

Abstractof the Invention

5 A heated shoe and cooled pressure roller assembly for composite

prepreg application is provided. The shoe assembly includes a heated

forward contact surface having a curved pressure surface. The following

cooled roller provides a continuous pressure to the thermoplastic while

reducing the temperature to approximately 5°C below glass transition

10 temperature. Electric heating coils inside the forward portion of the shoe

heat a thermoplastic workpiece to approximately 100°C above the glass

transition. Immediately following the heated contact surface, a cooled roller

cools the work. The end sharpened shape of the heated shoe trailing edge

tends to prevent slag buildup and maintain a uniform, relaxed stress

15 fabrication.
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