NBSIR 87-3686

.Research Information Center

iNational Bureau of Standards

Gaithersburg, Maryland 20899

October 7, 1987

Peter Beardmore

Donald Hunston

I'i DO i "—^

"

MAR 1 !J ww

Polymer

Composite

Processing

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

Institute for Materials Science and Engineering

NBSIR 87-3686

POLYMER COMPOSITE PROCESSING

An Industry Workshop

Held at NBS, Gaithersburg, MD

October 7, 1987

Peter Beardmore* and Donald Hunston

Ford Motor Company

Scientific Research Lab.

Dearborn, MI 48121

U. S. Department of Commerce

National Bureau of Standards

Institute for Materials Science and Engineering

Polymers Division

Gaithersburg, MD 20899

Issued February 1988

INDUSTRY WORKSHOP ON POLYMER COMPOSITE PROCESSING

Peter Beardmore

Ford Motor Co

.

Scientific Research Lab.

P. 0. Box 2053

Dearborn, MI 48121-2053

Donald Hunston

National Bureau of Standards

Institute for Materials Science and Engineering

Polymers Division

Gaithersburg, MD 20899

Report from workshop held at

National Bureau of Standards

October 7 , 1987

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

Institute for Materials Science and Eng ine e r ing

Polymers Division

Gaithersburg, MD 20899
SM

id
TABLE OF CONTENTS

Description Page

Summary 4

Introduction 6

Opportunities and Challenges 6

Purpose of Workshop 7

Information Sought 7

Program 9

Workshop Presentations 9

Questionnaire on Processing Methods 11

Questionnaire on Scientific

and Technical Barriers 11

Overview of NBS Reach Program 12

Current Activities 12

Processing Studies 13

Structural Characterization Studies 13

Performance Property Studies 14

Expansion of NBS Research Program 14

Industrial Perspective: Automotive 15

Cost is a Major Factor 15

Most Promising Processing Methods 15

Important Requirements for the Future 16

Industrial Perspective: Electronics 17

Dimensional Stability is Critical 17

Other Important Requirements 18

Industrial Perspective: Aerospace 19

Automation is Major Trend 19

New Materials and Processing Methods 20

Standard Tests and Data Validation 21

Industrial Perspective: Fabricators 21

Most Promising Processing Methods 22

Heat Flow and Fiber Orientation .......... 22

New Materials ..... 23

1
. Page

Discussion. . . . . . . . . . . . . . . . . . . . . . . „ „ . 2 4

Workshop Composition 24

Processing Methods. .... .......... 24

Questionnaire Results ............... 26

Comparisons by Industry .............. 26

Aerospace .................. 26

Automotive 26

Electronics ................. 27

Thermoplastics. ............... 27

Five Most Promising Processing Methods. ...... 27

Two Technologies that Complement Processing .... 28

Scientific and Technical Barriers ............ 29

Need to Better Understand Processing. ....... 29

Questionnaire Results ............... 29

Six Most Important Barriers ............ 31

Material Processing Parameters. ....... 31

Temperature Gradients and Heat Flow ..... 31

Fiber-Matrix Interface. ........... 32

Standard Tests, Data Validation,

and Data Bases ............... 32

Morphology 32

Surface Quality and Dimensional Tolerances. . 33

Materials with Potential for the Future ...... 33

Conclusions . .......... 34

Processing Methods 34

Scientific and Technical Barriers ......... 35

Appendix I: Attendance List 37

Appendix II: Questionnaires 39

Questionnaire 1 ................. 39

Questionnaire 2 ................. 40

Questionnaires . . . . . . . . . . . . . . . . . . 42

2
ACKNOWLEDGEMENT

The authors wish to express their appreciation to Mary Conneran,

Joan Ruff, and Dr. S. S. Chang for providing the arrangements and

organization that made the Workshop a success.
SUMMARY

This Workshop seeks to expand the use of polymer composites by

analyzing the critical need for improved processing . The Workshop Goals were to identify:

The most promising Processing Methods for the future

The critical Barriers to their implementation

The Attendees represent 23 different companies including composite

users, suppliers, and fabricators.

Five Processing Methods were selected as most important for the

future

:

Pressure Molding

Transfer Molding

Filament Winding

Thermo forming

Pul t rus ion

Two Technologies that Complement Processing were also noted as very

important

.

Alternative Sources of Energy Input

Resin Coating of Fibers

The Workshop concluded that the Most Critical Technical Barriers to

implementation of improved processing are inadequate understanding

o f : Resin Flow and Fiber Orientation

Temperature Gradients and Heat Flow

Fiber-Matrix Interface

Data Validation, Test Standardization

Morphology Control

Surface Quality, Dimensional Tolerances

Additional information in these areas is needed to implement process

control and automation which the Workshop felt were keys to mo r

e

rapid, reliable, and cost effective processing .

4
The Workshop also identified three classes of materials that should

be watched for future potential : Thermoplastics

Liquid Crystalline Polymers

Molecular Composites

Companies represented at the workshop were :

ALCOA AT&T

BF Goodrich Boe ing

Chrysler Dexter

DuPont Ferro

Ford GenCorp

General Electric Grumman

Hercules Hysol Composites

IBM Int e r e z Lockheed Martin Marietta

3M Phillips Petroleum

Rockwell International

United Technologies

SAMPE

5
INTRODUCTION

In the past few years, government organizations, professional

societies, and commercial groups have conducted studies to

identify critical areas of emerging technologies that are vital to

the international competitiveness of U.S. industries. Composites

rank at or near the top of these lists. Although the U.S.

presently enjoys a technological lead in some areas of composite

technology and applications, the rest of the world is rapidly

gaining on the U.S. and have now achieved equality in a number of

important areas. The reports on emerging technologies emphasize

the need for the U.S. to exploit the potential of composites to

maximize international competitiveness.

Opportunities and Challenges

The area of composites which has the most potential in the

next 5 to 15 years is mass-produced, commercial products using

polymer based composites. Although considerable U.S. effort has

concentrated on the development of DOD and aerospace applications

for composites, much of the resulting information is of limited

value for commercial applications where the primary emphasis is on

cost effectiveness rather than performance with cost as a

secondary factor. Manufacturing plays a critical role in the cost

for these materials, so more rapid, cost effective, and reliable

processing is often regarded as the single most important barrier

to expanded use in commercial application.

The pressure for rapid implementation of these highly

beneficial materials has led to rapid growth rates where the

applications have out stripped the development of the

corresponding science and technology base. It is now generally

recognized that a major effort to improve this science base is

essential, since the rapid growth rates can be maintained only by

6
extending the application of composites to the more cost sensitive

commercial markets.

Purpose of Workshop

It is necessary to focus on those aspects of the science base

which will have direct impact on the development of more cost

effective fabrication. To identify these areas, this Industry

Workshop was held at the National Bureau of Standards on October

7, 1987. Since polymer composites can be applied in a wide range

of industries, and each will have a slightly different set of

problems and constraints. It is important to identify common

problems whose solution will have a broad impact. These problems

can then be given highest priority. To this end, the Workshop was

organized with representatives from a variety of users,

manufacturers and suppliers in the composites field. The users

included the automotive, electronics, and aerospace industries

while the suppliers were manufacturers of resins and fibers.

Companies that prepare starting materials such as pre impregnated

fiber tape and cloth were represented as were companies that

fabricate small parts for the larger industrial users.

There were a total of 25 attendees representing 23 companies.

A full attendance list is given in Appendix I. In addition,

comments were supplied by a number of industrial people who could

not attend but expressed great interest in the workshop.

Information Sought

The meeting was organized so the results would reflect the

position of industry. Two questions were addressed. First, what

are the generic processing methods that will be of most interest

to industry during the next 5 to 15 years? Second, what are the

scientific and technical barriers that hinder the implementation

and effective use of these methods? The answers to these

7
questions are of interest to many people in the composites field

but will also help the National Bureau of Standards (NBS) identify

specific projects for their expanded composites research program.

8
PROGRAM

The workshop was a day long meeting divided into two parts

with presentations and focused discussions in the morning and

general discussions aimed at reaching a consensus in the

afternoon. The program is given in Table I. In preparation for

the meeting attendees were given the opportunity to identify the

processing methods and technical barriers expected to be important

to their industry or the industries they supply in the next 5 to

15 years. This information was combined with results generated

during the discussions to prepare questionnaires that were

distributed at appropriate points in the meeting. The results

help focus the discussion and assure that everyone had an

opportunity to contribute. The questionnaires are included as

Appendix I I

.

Workshop Presentations

The initial presentations in the meeting described the

purpose of the workshop, the current NBS composites program, and

the general plans for future expansion of this effort. The first

questionnaire was then distributed. It listed all of the

processing methods suggested by attendees on their application

forms. The audience was ask to add any important processing

methods that were not already listed and indicate which methods

they felt would be important to their industry or the industries

they supply in the future.

Presentations then followed by representatives from 4

industry sectors: automotive, electronics, aerospace, and

fabrication. The speakers gave a general overview from the

9
TABLE I: PROGRAM

Composite Processing Workshop

October 7, 1987

Lecture Room D

Administration Building

Cochairmen: Peter Beardmore , Ford, and Donald Hunston, NBS

Questions to be addressed:

What are the generic processing methods that will be

important to your industry in the future (i.e. 5 to 15 years)?

What are the long-term technical and scientific barriers that

must be overcome to fully utilize these methods?

Time Description

8 : 30

9 : 00

Registration

Welcome to NBS Ray Kammer, Deputy

Director of NBS

9 : 10 Introductions & Charge to Workshop Les Smith, Chief

Polymers Div. , NBS

9 : 25 Background of NBS Composites Don Hunston, NBS

Program and Initiative

9 : 55 Questionnaire on Processing Methods

10 : 00 Industry Prospective on Processing Methods and Problems

11:00

Automotive Carl Johnson, Ford

Electronics Don Barr, IBM

Coffee

Aerospace Sam Dastin, Grumman

Fabricators Joe Reardon, Hysol

12:00 Questionnaire to Rank Processing Methods

and Identify Technical Barriers

12:15 Lunch

1:15 Questionnaire to Identify Scientific and Technical

Barriers

1 : 30

1 : 35

Results from Ques t ionna i r e to Rank Processing Methods

Discussion of Processing Methods Ranked as Most Important

1 : 55

2 : 00

3:15

3 : 30

3 : 45

Results from Questionnaire to Identify Barriers

Discussion of Scientific and Technical Barriers

Coffee

Chairmen's Summary

Adj ourn
perspective of their industry, and following each presentation,

knowledgeable members of the audience augmented the presentation

with comments based on their own experience and expertise.

Questionnaire on Processing Methods

The second questionnaire which listed all of the processing

methods identified during the morning was then distributed. The

attendees were asked to indicate in priority order the methods

that they felt would be most important to their industry or the

industries they supply in the next 5 to 15 years. Equal ratings

were given when an attendees felt 2 or more techniques were

equally important. To analyze these results, 5 points were given

for each first place rating, 4 for each second place rating, etc.

The results provided a list indicating what techniques the

attendees, as a group, considered most important. Since the

questionnaires also obtained information about the attendee's

background, some inferences concerning differences in priorities

between industries could also be made.

Questionnaire on Scientific and Technical Barriers

The third questionnaire listed all of the technical barriers

mentioned by attendees on their application forms or in the

morning's discussions was completed after lunch. Each person was

asked to identify those barriers which are hindering or will

hinder the implementation of the composite processing methods

identified earlier in the meeting. The time frame of interest was

again 5 to 15 years. The results were analyzed by constructing a list of items that were rated as important by the largest number

of people.

The results of the second and third questionnaires were then

discussed, and a consensus as to which processing methods and

technical barriers were most important was sought. The sections

that follow will present brief summaries of the presentations, a

11
description of the questionnaire results, and a report of the

final conclusions, and a discussion of the efforts that achieved

this consensus.

OVERVIEW OF NBS RESEARCH PROGRAM

The first presentation in the workshop was a review of the

current NBS composites research program and an outline of the

preliminary thinking for program expansion.

Polymer composites represent an important emerging technology

where major opportunities exist for applications in the commercial

sector. In many cases the impediment that hinder the expanded use

of these materials involve questions of measurement methods and

test data. As a result NBS has had a composites research program

for a number of years. The potential for these materials has now

reached the point, however, where a major expansion of the NBS

effort is needed. Current plans call for growth of this program

in 1988 by a factor of 2 to 3 with further growth in 1989 being

considered. An important use for the conclusions from this

workshop will be to help NBS define research projects that provide

the type of information needed by industry. Cooperative programs

will also be encouraged.

Current Activities

The research projects in the NBS program are divided into

three tasks which focus on processing, structure, and performance.

The overall objective is to investigate how the properties of a composite depend on the internal structure produced by the

processing and the properties of the fibers and the matrix. Such

relationships are the key to more effective processing as well as

improved performance. The programs draw on the strength of NBS in

the measurement field. A complete description of the NBS program

is contained in the Polymer Division's Annual Report, but a brief

overview will be given here.

12
Processing Studies: In the area of processing, the projects

focus on cure monitoring for thermosets and consolidation

monitoring for thermoplastics. The objectives are threefold: to

develop new measurement methods which offer important

improvements, to maintain a variety of monitoring techniques for

calibration and testing of methods under development, and to apply

multiple monitoring techniques -to the study of model systems so a better fundamental understanding of the events that occur during

processing can be obtained. There are currently 10 different

process monitoring techniques available in this program. These

methods characterize systems on sensitivity levels ranging from

the covalent bonds that are involved in chemistry to the

macroscopic viscosity that controls flow and consolidation. The

results generated in these projects provide measurement techniques

with potential for on-line process control and an understanding of

processing events which can be useful in designing new fabrication

procedures

.

Structural Characterization Studies: In the task on

structure the objective is to characterize the composite so that

this information can help bridge the gap between processing and

properties. A knowledge of the structure can help explain why a given set of properties results from a particular processing

cycle. The structures of interest includes flaws, voids, fiber

orientation and dispersion, morphology, crystallinity, and the

molecular networks structure present in cross-linked systems. The

current work involves the development and use of small angle

neutron scattering to determine the network structure of thermoset

resins. This represents the first time such structure can be

characterized. For specific materials the technique has already

revealed the effects of changing the processing conditions and the

molecular level deformations that occur when the sample is loaded

to levels just below the failure point. The results are useful

for developing p r oc e s s ing - s t r uc tur e

- p r op e r ty relationships.

13
Performance Property Studies: In the task on performance the

objective is to study the behavior of composites in terms of the

properties of their fibers and resins. Although all aspects of

behavior are of interest, fracture is of particular concern. A

major current program is investigating toughened composites which

utilize high fracture energy resins to improve the composite

behavior. The experiments help explain both why the resins are

tough and how this behavior is translated into the composite.

This information provides a valuable tool for predicting composite

properties and generating improved resins.

Expansion of NBS Research Program

The proposed expansion in the NBS composites program will

focus on processing. The major change will be in the processing

task where several processing facilities will be constructed. The

results from this workshop will help determine what types of

processing facilities would be most appropriate in terms of the

future needs of industry. These facilities will be used to

experimentally address the scientific and technical barriers that

limit processing efficiency. The workshop results will provide

industry's priorities for these technical barriers. In the

preliminary planning for this program, three possible areas were

identified. First, the need to develop a better understanding of

the events that occur during processing appears to be an important

area. Second, the application of the process monitoring

techniques, developed in the current NBS program, to on-line

monitoring represents a possible program direction that takes

advantage of previous work. Third, the extension of on-line

process monitoring to process control through the development of

process models is also an exciting possibility.

The structure and properties tasks in the NBS program will

also be affected by the expansion since samples must be

characterized to establish the relationships between processing

14
and performance. One focus of the program expansion will be the

characterization of structure. This draws heavily on NBS's

measurement expertise. Examples of areas where such

characterization are needed include: network structure for

thermosets, crystallinity for thermoplastics, defects and

crystallinity for fibers, and adhesion and morphology for

interface regions. Research in the current program has already

developed unique measurement tools for some of these properties,

but much more work needs to be done.

INDUSTRY PERSPECTIVE: AUTOMOTIVE

In the automotive industry it will be difficult for

composites to compete in terms of appearance and cost with metal

stamping for s emi - s t rue tur a 1 components such as body panels. Dent

resistance is an advantage of composite body panels, however,

structural parts offer the biggest opportunity for composites.

The key to success in the automotive area for all types of

composite parts is cost effectiveness. The specific needs for

cost effective fabrication are high speed processing methods, low

cost fibers, and resins that are suitable for rapid processing.

Cost is a Major Factor

There are two important features of composites that can

contribute to the goal of cost effective processing: the relative

ease of making design changes and the ability to integrate many

components into a single part. Design changes are important

because the current trends are toward more models and more

frequent model changes. The use of composites facilitates large

scale integration but imaginative processing methods are often

required

.

Most Promising Processing Methods

Two processing methods are felt to offer the most promise for

the time period between 5 and 15 years from now: compression

15
molding and transfer molding. Compression molding has the

advantage that it is an established procedure. Unfortunately, it

also has two important disadvantages. First, with present

technology the part size and complexity are limited. This

controls the cost reductions that are possible without the

development of new technology. Second, the parts made by

compression molding are predominately 2 dimensional since the

complexity and thickness in the third direction are limited.

The second processing technique that shows promise for

automotive applications is transfer molding. Four factors make

this method particularly attractive. First, relatively low

pressure is required because only the pure resin is transferred.

Second, accurate placement of the reinforcement can be achieved

with complex variations in type and orientation throughout the

part. Third, a high degree of complexity is possible not only for

the reinforcement but also for the shape. Finally, the part can

be 3 dimensional since deep forms can be used. The major

shortcoming for transfer molding is that the preparation of the

reinforcement preform is often time consuming and labor intensive.

For simple performs a stamping process can be used, but more

complex performs with positional variations in the kind and

orientation of the reinforcement must now be prepared by hand.

Ultimately, this process must be automated.

In automotive processing both thermosets and thermoplastics

are being considered. Thermoplastics have advantages such as

stability during storage, possible simplifications in repair, and

the potential for an excellent surface finish. Thermosets, on the

other hand, have low viscosities during processing, so they can

achieve the flow necessary to make larger and more complex parts.

Important Requirements for the Future

Two other areas of importance for automotive applications of

composites are crash management and adhesive bonding. Crash

16
management is being addressed through the design of structures

that can absorb energy and thereby minimize injury to the

vehicle's occupants. Crack management considerations influence

the designs that must be fabricated and consequently, the

processing required. Adhesive bonding is important because it

increases flexibility in both design and manufacturing. The

desired high production rates require rapid cure materials that

need a minimum of surface preparation. In addition more data are

needed on long term durability and environmental effects on

adhesively bonded joints.

One final point of concern in automotive applications is the

need to generate a superior surface finish on those sections of a part that are visible in the application (it is worth noting that

many parts are not visible). Processing plays a major role in

determining surface finish so the effects of processing on surface

quality are a subject of major concern.

INDUSTRY PERSPECTIVE: ELECTRONIC

The applications of composites in the electronics field are

very broad and range from equipment housings to chip encapsulation

and circuit boards. A wide variety of processing methods are

needed. For example, housings may be made by injection molding,

circuit boards by press or autoclave fabrication, and chip

encapsulation by transfer molding.

Dimensional Stability is Critical

An important characteristic of the electronics industry is

the short time required for technology to move from the high end

systems to the mass market equipment. Consequently, much can be

learned about the processing needs for the future by considering

today's problems in the high technology systems. One example is

multilayer circuit boards. The current state-of-the-art boards

are large, 50 cm or 60 cm on each side, and can contain as many as

17
20 conducting and 20 non-conducting layers. The electronic

components mounted on the board are interconnected through complex

patterns created in the conducting layers and connections between

these layers made via a large number of small holes, 0.4 mm in

diameter, drilled through the board. There can be 20,000 or more

such holes in each board. The holes are plated with conducting

material to provide an electrical path. Since each hole must make

electrical contact with some layers and not with others, the

criteria for alignment and dimensional stability are extremely

severe. As this technology moves to larger volume equipment, the

need for increased production speeds grows and the challenges

become even greater.

Dimensional stability is also a concern for less

sophisticated composite parts. One reason for this lies in

another important trend for the future in the electronics

industry, i.e. a move to fiber optics for connections. The use of

fiber optics will require a high degree of alignment for proper

signal transfer.

Other Important Requirements

In addition to dimensional stability, there are a number of

other problems areas where a better understanding of the science

involved represents the key to progress. The dielectric constant

of a material is important for electronic applications since this

controls design factors such as circuit density. To optimize the

dielectric constant, however, requires a knowledge of structureproperty relationships that does not now exist. Thermal expansion

and high temperature performance are also important parameters for

electronic applications. Electronic systems often undergo thermal

cycles that can cause problems. The most severe thermal shock

occurs during processing when connections are soldered.

Chemical resistance is another concern of particular interest

for electronics. The circuitry is generally introduced by

18
processes which involve exposure to chemical agents for the

addition or removal of circuit layers. Any composite materials

present must therefore be resistant to these fluids. A fifth area

of importance for electronics is interface behavior. On circuit

boards the electronics must be well bonded to the base composite

layer, and interconnections must provide reliable contacts.

Proper control of the interfaces present in these situations

requires a better understanding of the features that control the

interaction between two materials.

One final topic with strong implications for the electronics

industry is the application of process control to the fabrication

of composite components. Such control is needed to improve the

speed and reliability of fabrication. Achieving this goal,

however, requires a better understanding of the resin flow during

processing, and how this flow can be modeled and controlled.

INDUSTRY PERSPECTIVE: AEROSPACE

The use of composite components in aerospace has a longer

history than in other industries, but important challenges remain.

Although applications in structural parts have received the most

attention, composites also find widespread use in nons t rue tur a

1

parts. Thus the processing methods of interest to aerospace

extends from sophisticated autoclave fabrication to simple

compression molding. In both structural and nons true tur al

applications, the needs are for low weight and reduced cost. With

structural parts, features such as damage tolerance and

crashworthiness are also important while nons true tur a 1 parts can

have a wide range of requirements, such as surface finish, heat

resistance, strength, etc., depending on the application.

Automation is Major Trend

The aerospace market is characterized by low production and

high performance, but cost is also a concern. Perhaps the most

19
important trend in aerospace processing today is the move to

process automation. Two major driving forces for this move are

reduced cost and increased reliability. The highly labor

intensive fabrication procedures initially used are now being

replaced by production facilities with a high degree of robotics.

The drive for automation gives rise to a need for an

increased scientific understanding of processing. Effective

automation is much easier when the process is understood.

Moreover, such knowledge is essential for implementing process and

control, and this is important to take full advantage of

automation. Consequently, automation, processing science, and

process control are closely linked areas where advancements will

have direct impact on composite fabrication.

New Materials and Processing Methods

Two other trends in aerospace are the introduction of new

materials and the development of new processing methods. There

are two important factors behind the drive for new materials: the

desire for higher temperature capabilities and the need for

improved properties such as damage tolerance. The materials being

developed are in two general classes: multicomponent, toughened

thermosets and high temperature thermoplastics. In both cases the

improvements in properties are often coupled with increased

difficulties in processing. This results in a need to develop new

or modified fabrication techniques and a better understanding of

the events that occur during processing so that effective

fabrication cycles can be designed.

An example of the development of new or modified processing

methods results from the requirement that some partially

crystalline thermoplastics must be cooled rapidly to achieve the

desired morphology. The use of heated head tape laying machines

and LASER assisted tape laying processes (the LASER providing

localized heat) offer considerable promise. Non- autoc lave curing

20
is a technique modification being studied in several programs. A

third example is advanced types of pressure molding that are being

sought as replacements for certain autoclave procedures. Although

these and other new methods may offer considerable promise, many

also increase the complexity of processing. Consequently, the

need for a better understanding is important if the potential of

these new methods is to be fully explored.

Standard Tests and Data Validation

One final topic worth mentioning is test method

standardization and data validation. The cost of certifying a

material for structural use in airplane construction is extremely

high. Since each company must separately evaluate and qualify

some of the same materials with their own tests, this cost is

often duplicated. To make matters worse a composite must be

specified not only in terms of the resin and fiber involved but

also by how these constituents are processed. This greatly

increases the number of possible materials and thus the cost of

testing and evaluation. With regard to processing there are three

areas where problems associated with testing are a concern:

specification development and evaluation of raw materials, the

acquisition of material property data for the design of processing

cycles, and the characterization of fabricated parts to evaluate

the success of fabrication.

Although many groups are actively involved in efforts to

develop materials data and the associated data bases, there are

important questions that remain unaddressed. Two examples are the

lack of a method to unique ly define a composite material and the

absence of standardized tests in many important areas.

INDUSTRIAL PERSPECTIVE: FABRICATORS

Fabricators are often smaller companies that specialize in

making certain types of parts for major users but can also be

21
divisions of larger companies that either use composites or supply

the starting materials. During the discussion in this section of

the workshop three topics were addressed: potentially important

processing methods for the future, fabrication problems related to

materials and fibers, and new material systems that have potential

for composites.

Host Promising Processing Methods

In the future, current processing methods like compression

molding and injection molding will continue to find major use by

fabricators although improvements in these techniques will

undoubtedly be made. Transfer molding is a particularly promising

method for the future because it has flexibility for use with new

resin and fiber systems. Powder technology for prepreg

preparation shows potential for use with materials that are

particularly difficult to handle by normal methods. Such

materials often have outstanding properties but cannot be utilized

because processing by conventional methods is so difficult.

Future fabrication procedures will also employ alternative forms

of heat generation. Controlling energy input is important for

effective processing, and sources such as LASERS and microwave

radiation offer potential for greater control.

Heat Flow and Fiber Orientation

When processing thermosets, an important consideration is the

combined effect of applied heat and the heat generated internally

by the exothermic chemical reactions. Since the reaction rates

are controlled by temperature, it is important to have the proper

temperature history throughout processing. It is extremely

difficult to achieve acceptable temperature histories at all

points within the part, particularly with thick components. To

address this problem requires improvements in our basic

understanding and modeling capability. Another problem is the

control of fiber orientation, dispersion, and degradation during

processing. This is particularly critical in fabricating short

22
fiber composites. The ability to predict fiber behavior in such

processes needs to be improved. Better models to relate the

effects of fiber length and orientation to the properties of the

composite are also needed. Such models are particularly useful

for separating those processing parameters that really do affect

performance in the composites from those that do not.

New Materials

Future processing will need to deal with new material systems

such as polymer blends, allows, and interpenetrating networks.

Such materials offer improved properties but their complexity will

require more exacting process control. Consequently, a better

scientific understanding of these materials and how they behave

during fabrication is required.

23
DISCUSSION

Following the industry overviews, the Workshop turned to open

discussion aimed at reaching a consensus. The first step was to

report the results of the questionnaires. In addition to

answering questions about processing methods and barriers, the

results also provided information on the expertise of the Workshop

attendees. It is instructive to examine these results first.

WORKSHOP COMPOSITION

In the 25 attendees, 14 listed themselves as composite users

and 6 as suppliers while 5 indicated they were involved in both.

When ask about their primary market, 5 specified aerospace, 4

automotive, 3 electronics, 2 fabrication, 8 a mixture of markets,

and 3 designated thermoplastics as their prime interest. Those

indicating a mixture of markets listed not only the applications

mentioned above but also sporting goods, marine uses, and

industrial products. In general, therefore, the workshop

represented a highly diverse group with a relatively balanced

range of interests.

PROCESSING METHODS

The workshop discussion led to a consensus on the five most

important processing methods for the future. These are listed in

Table II. The common trait that links all five methods is their

potential for development into systems capable of rapid

production. In addition the workshop identified two technologies

that complement processing. The attendees felt these

technologies, which are also listed in Table II, held great

promise for the future. A discussion of these conclusions, and

the process that led to them is given below.

24
TABLE II: PROCESSING METHODS AND TECHNOLOGIES SELECTED AS MOST

IMPORTANT FOR FUTURE (5 TO 15 YEARS)

PROCESSING METHODS

Pressure Molding

Compression Molding

Autoclave Molding

Transfer Molding

Reactive

Nonreactive

Filament Winding

Thermoforming

Pul trus ion

IMPORTANT TECHNOLOGIES THAT COMPLEMENT PROCESSING

Alternative Sources of Energy

Resin Coating of Fibers

Preparation & Processing

25
Questionnaire Results

The first step in this process was for the workshop to

consider the results from the second questionnaire which asked

attendees to prioritize the list of processing methods in terms of

potential for the future. The nine methods with the highest

ratings in order of decreasing priority are:

Compression Molding

Resin Transfer Molding

Alternative Sources of Heat

Filament Winding

Autoclave Molding

Resin-coated Fibers

Thermoforming

Reactive Transfer Molding

Pul trus ion

The first two methods were rated significantly higher than the

remaining seven.

Comparisons by Industry

Aerospace: Some interesting differences could be noted among

the various industry segments. The processing methods identified

as important by the aerospace group differed from the general list

only in that transfer molding was ranked 10th and reactive

transfer molding was not listed while high temperature processing

and adhesive bonding were included. It is interesting to note the

importance given to adhesive bonding, here as well as in the

earlier discussion during the automotive section. Nevertheless,

adhesion bonding is not generally thought of as a processing

technique

.

Automotive: Those responding for automotive interests also

produced a list quite similar to the general ratings. The

26
differences were that long fiber processing and SMC forming were

included while filament winding and autoclave molding were not.

Electronics: The responses associated with the electronics

industry listed fewer processing techniques. The focus was on

compression molding, resin transfer molding, and injection

molding. Surprisingly, injection molding did not appear in the

top items on the lists from other industry groups.

Thermoplastics: The list from the thermoplastics sector did

not include transfer molding and autoclave processing, but powder

impregnation of fibers was rated very highly. Clearly,

difficulties associated with the preparation of high quality

prepreg are important for this industry segment.

Five Most Promising Processing Methods

Although the differences outlined above are interesting, the

most significant observation is the strong similarities that exist

among the lists. This commonality made it much easier to achieve

a consensus. Beginning with the general list from the

questionnaire, the workshop first decided to combine

resin transfer molding with reactive transfer molding and list

both under the heading of transfer molding. It was felt that much

of the technology involved in the two methods shared a common

base, and the problems are also quite similar. The discussion

then focused on compression molding. It was decided to combine

compression molding and autoclave molding under the term pressure

molding. In both cases the combination of heat and pressure are

used to create the final part. Of particular interest to the

workshop was the potential for future improvements in autoclave

molding that would simplify the processing and improve the speed.

It was suggested that some future high speed processes might move

out of the autoclave environment and take on some of the

characteristics of compression molding.

27
Transfer molding and pressure molding were rated

significantly higher than the other three techniques in the list

from the questionnaire: thermoforming, filament winding, and

pultrusion. Nevertheless, these three methods received widespread

enthusiasm from attendees representing a variety of industries.

It was noted in the discussion that all five methods have the

potential for development into systems capable of rapid

production. This was clearly a key factor for the attendees.

Two Technologies that Complement Processing

The workshop then discussed resin coated fibers and

alternative sources of heat. It was decided that these are not

processing techniques but are better described as technologies

that aid and complement processing. Since they were so highly

rated a separate category was established for these two items.

The discussion first retitled alternative sources of heat to

alternative sources of energy input to include all possibilities.

The list of potential sources included microwave, dielectric, and

ultrasonic generators and LASERs . The energy supplied could be

used either to initiate or promote chemical reactions in

thermosets or to melt materials or change viscosities in

thermoplastics. A major advantage of such approaches is the

potential to gain better control over the energy input in terms of

the time period involved, the area where the energy is applied,

and its intensity. This will be increasingly advantageous as

process control and automation are implemented.

The other technology discussed was resin coating of fibers,

such as in prepreg fabrication. The attendees considered this

topic to be very important because new procedures could improve

both processing speed and versatility. A number of such

procedures are currently in development. They include commingled

fibers, fibers prepared with resin coatings, and powder processing

to prepare prepreg. The workshop felt that the development of

such methods should be encouraged.

28
SCIENTIFIC AND TECHNICAL BARRIERS

The items identified by the workshop as the most important

scientific and technical barriers to improved processing are

summarized in Table III. These barriers represent areas where the

attendees felt there was an urgent need for scientific study to

improve our knowledge and understanding. This is needed for the

development of improved processing methods, the implementation of

on-line process control, and the application of automation for

increased processing speed and reliability. A discussion of these

barriers and the workshop's efforts in developing this list are

g iven below.

Need to Better Understand Processing

The first conclusion in the workshop's discussion was that

the most critical barriers involve deficiencies in our

understanding of the chemical and physical changes that occur

during processing. The task then was to determine in which areas

an increase in our knowledge would have the most effect on

improving fabrication and developing on-line process control.

Questionnaire Results

To assist in identifying these areas, the results of

questionnaire 3 were presented. In order of decreasing priority

the eight most important items listed by the attendees were:

Adhesion and Fiber/Matrix Interface

Resin Flow Behavior

Data Validation/Data Base Systems

Temperature Profile and Thermal Gradient Control

Heat Transfer and Thermal Conductivity

Toughening Mechanisms

Fiber Alignment and Control

Phase Separation

29
TABLE III: RESULTS FOR SCIENTIFIC AND TECHNICAL BARRIERS

MOST IMPORTANT BARRIER IS INABILITY

TO UNDERSTAND AND CONTROL THESE FEATURES

Material Processing Parameters

Resin Flow

Flow Behavior in Composite

Fiber Distribution and Orientation

Temperature Gradients and Heat Flow

Temperature Profiles & Gradients

Heat Flow and Thermal Conductivity

Energy Input (Curing or Melting)

Adhesion - Fiber/Matrix Interface

Data Validation - Database Development - Test

Standardization

Mo rpho 1 o gy

Phase Separation (Toughened Systems)

Crystallinity

Surface Quality - Dimensional Tolerances

POTENTIALLY IMPORTANT MATERIALS FOR THE FUTURE

Thermoplastics

Liquid Crystalline Polymers

Molecular Composites

30
The results did not show any particular pattern by industry,

and this probably facilitated efforts to reach a consensus. The

first step in this process was to note that several of the topics

were specific examples of more general areas which had wide spread

interest among attendees. These areas were identified, and then

the discussion focused on filling the gaps and omissions that were

present in the list.

Six Most Important Barriers

Material Processing Parameters: The workshop first examined

the importance of resin flow behavior and the effects of fiber

alignment. The attendees felt that the control of these

parameters was critical to successful processing. The current

state of our understanding can and should be improved to show how

these parameters relate to performance, and how they should be

controlled during processing to achieve the desired results. The

flow behavior of both the resin itself and the resin in the

composite needs to be studied. The workshop grouped these topics

together under the title Material Processing Parameters, and

ranked the need to develop a scientific understanding of this area

very highly

.

Temperature Gradients and Heat Flow: The workshop then

reached a consensus that more needs to be learned about

temperature profiles and gradients, heat flow, and thermal

conductivity within parts during processing. This is particularly

important in thick parts where it may be quite difficult to

achieve uniform cure. Although the temperature history within the

sample is critical to processing, our current understanding does

not permit the modeling and control that is needed. The use of

alternative sources of energy input, as discussed earlier, could

have a major impact here.

31
Fiber-Matrix Interface: The workshop felt that fiber-matrix

interface properties, such as adhesion, have a direct effect on

composite performance. At present only the simplest correlations

can be made. It is important to increase our knowledge and

modeling capability in this area. In addition, there is a need to

identify parameters that affect the interface properties so that

they can be controlled both through the proper choice of starting

materials and the appropriate processing.

Standard Tests, Data Validation, and Data Bases: The area of

data validation and data base development was then discussed by

the workshop. The attendees felt this was a critical area and

identified test method standardization as another major aspect of

the problem. Many attendees expressed concern about difficulties

in specification testing for acceptance of starting materials and

performance testing of composites to determine if processing was

successful. The discussion concluded by expressing a strong

belief that this area needed to be addressed.

Morphology: The topics of toughening mechanisms and phase

separation were also rated highly in the questionnaire. The

connection between these two items and processing is that

toughening is generally accomplished through the use of additives,

many of which phase separate, and the morphology of these

multicomponent systems controls the toughening. It is critical to

know what morphology is needed, and how it can be generated during

fabrication. A closely related area is the control of

crystallinity in partially crystalline thermoplastics. The

development of crystallinity during processing must often be

controlled to achieve the desired performance in the finished

composites. At present, a largely empirical approach is used to

develop processing procedures for both types of systems, but this

is not very efficient and makes it difficult to translate

processing procedures to new materials. To improve this

32
situation, a better scientific understanding of these effects is

required

.

Surface Quality and Dimensional Tolerances: The workshop

discussion also concluded that dimensional control and

reproducibility are vital to a wide range of applications.

Examples include the fabrication of circuit boards for electronic

applications and the generation of high quality surface finishes

on automotive parts. Although such components can be manufactured

today, the processing is expensive, slow, and not successful for

all applications. In the future greatly increased speeds and

decreased costs will be required, and this means a better

understanding of and control capability for the factors that

influence dimensional tolerance and surface quality will be

needed

.

Materials with Potential for the Future

The final topic discussed in the workshop was the potential

of three new classes of materials: thermoplastics, liquid

crystalline polymers, and molecular composites. The attendees

felt that new processing requirements will be needed to take full

advantage of this potential. Thermoplastics are already

considered in much of the preceding discussion, but the other two

classes of materials may give rise to needs not covered here.

Consequently, developments related to these materials need to be

watch closely.

33
CONCLUSIONS

The workshop described in this report addresses the need for

improved processing of polymer based composites by identifying

areas where advances would have the most impact. To do this, two

questions were asked. First, what are the generic processing

methods that will be of most interest to industry during the next

5 to 15 years? Second, what are the scientific and technical

barriers that hinder the implementation and effective use of these

me thods ?

The workshop participants represented 23 different companies

involving a wide range of users, suppliers, and manufacturers.

The meeting employed overview presentations, questionnaires, and

discussions to reach a consensus among the attendees.

Processing Methods

Five processing methods that all attendees considered

important for the future were identified. Two of these were rated

highest: pressure molding and transfer molding. Pressure molding

includes both compression molding and autoclave processing while

transfer molding includes both reactive and non-reactive

materials. The three remaining processing methods were given

roughly equal ranking; they are thermoforming, filament winding,

and pultrusion. A major common feature for all five techniques is

their potential for development into rapid, cost effective

production methods.

In addition to the five selected processing techniques, the

workshop also identified as very imp ortant two technologies that

complement processing. The first is alternative sources of energy

input to initiate or facilitate processing. Examples cited

include the use of microwave, dielectric and ultrasonic sources or

34
LASERS. The second technology identified as important is the

preparation of the resin-fiber starting materials. Three examples

were mentioned: powder processing for prepreg manufacture,

commingled fibers, and resin coated fibers.

Scientific and Technical Barriers

The workshop concluded that the most critical scientific and

technical barriers are deficiencies in our understanding of the

events that occur during processing. Six areas were identified

where these deficiencies have the most adverse effects on

processing and, consequently, represent the primary barriers to

improved fabrication. These deficiencies are particularly

important because they hinder the implementation of process

control and automation which are the keys to more rapid and

reliable processing.

The attendees felt the most important problem is the need to

understand and control resin flow and fiber orientation during

processing. The second area where improvements are needed is

modeling and control of temperature and heat flow. The concerns

here ranged from temperature levels and gradients during

processing to the use of alternative sources of energy input.

Fiber-matrix adhesion is the third most important area cited by

the workshop while data validation, data bases development, and

standardized tests was ranked fourth. The control of morphology

during processing was listed next. Such control is particular

needed for crystallinity and phase separation in two phase

toughened systems. Control of finish and dimensional tolerances

is the final area identified. This is of particular concern to

the automotive and electronics industries, but others expressed

interest as well.

One final point is the suggestion that three classes of

materials offers significant potential for the future and should

be watched closely: thermoplastics, liquid crystal polymers, and

35
molecular composites. The first category is already included in

much of the discussion above. The second and third, however, are

newer and other problems may emerge.

36
APPENDIX I: ATTENDANCE LIST

Don Barr

IBM

T 5 0 257 -3

1701 North St.

Endicott, NY 13760

Peter Beardmore

Ford

Scientific Research Lab.

P.0. Box 2053

Dearborn, MI 48121-2053

Paul J. Biermann

Chairman, Baltimore -Washington

SAMPE Chapter

Applied Physics Laboratory

Johns Hopkins University

14-704 Johns Hopkins Rd

Laurel, MD 20707

David Boll

Hercules Inc

.

Aerospace Products Group

Bacchus Works

Magna, UT 84044-0098

Walt Brueggeman

Ferro Corporation

7500 E. Pleasant Valley Rd

.

Independence, OH 44131

Samuel Dastin

Grumman Aerospace Corporation

Mail Stop B10-25

Bethpage, NY 11714

J. William Davis

3M Technical Center

Research and Development

Bldg. 201-1F-02

St. Paul, MN 55144-1000

Thomas Dudek

GenCorp . Inc

.

2990 Gilchrist Road

Akron , OH 44305

Mahammad Ibrahim

Martin Marietta Labs.

Research and Development Lab.

1450 S. Rolling Road

Baltimore, MD 21227

Carl F. Johnson

Ford

Scientific Research Lab.

Room S - 2046

P.0. Box 2053

Dearborn, MI 48121-2053

Tim W . J ohns on

Phillips Petroleum Co.

Research and Development

155 C PL

Bartlesville, OK 74004

Chuk Leung

Rockwell International Science

Center

1049 Camino Dos Rios

Thousand Oaks, CA 91360

Jean Lynn

Chysler Motor Corp.

12800 Chysler Dr.

Detroit, MI 48013-1118

Louis T. Manzione

AT&T

Bell Laboratories

Room 7E-205

600 Mountain Avenue

Murray Hill, NJ 07974

37
Richard G. Parker

BF Goodrich

BF Goodrich Research Center

9921 Brecksville Rd

.

Brecksville, OH 44141

Joe Reardon

Hysol Composites Inc.

17960 Englewood Dr.

Cleveland, OH 44130

Charles L. Ryan

ALCOA Laboratories

ALCOA Technical Center

Bldg C

Alcoa Center, PA 15069

George Schmitt

IBM

T22/257-2

1701 North St.

Endicott, NY 13760

Dan Scola

United Technology Research

Center

Mai 1 S top 24

Silver Lane

East Hartford, CT 06108

J ame s R . Scott

Boeing Commercial Airplane Co.

P.0. Box 3707, MS 73-43

Seattle, WA 98124-2207

Dave Shimp

Int e r e z Inc

.

9800 Bluegrass Pkwy

.

Louisville, KY 40299

Allan Shultz

General Electric

Corporate R&D

K-l 4B37

1 River Road

Schenectady, NY 12345

Fred Tervet

Lockhe e d - C a 1 i f o r n i a Company

Dept. 47-17

Bui Iding 3 6 9 B - 6

Burbank, CA 91520

Stanley J. Wilcox

E.I. DuPont de Neumours & Co.

Textile Fibers Dept.

Bldg 702

Chestnut Run

Wilmington, DE 19707

Raymond Wong

Dexter- Hy s o

1

Aerospace & Ind. Products Div.

2850 Willow Pass Road

P.0. Box 312

Pittsburg, CA 94565

NBS Observers

:

Ray G . Kamme r Deputy Director

Administration Bldg.,

Room A 1 1 34

Gaithersburg, MD 20899

Lyle H. Schwartz

Director, Institute for

Materials Science & Eng.

Materials Bldg. , Room B309

Gaithersburg, MD 20899

Leslie E. Smith, Chief

Shu-Sing Chang

Brian Dickens

Bruno Fanconi

Charles C . Han

Donald Hunston

Fred I . Mops ik

Darrell H. Reneker

J ohn A . Te sk

Wen - 1 i Wu

Polymers Division

Po lyme r Bldg.

Gaithersburg, MD 20899

38
APPENDIX II: QUESTIONNAIRES

QUESTIONNAIRE 1

INDUSTRY WORKSHOP ON COMPOSITE PROCESSING

Survey of Processing Methods

Are you a supplier or user

What industry sector (sectors) can you respond for

In the following list please indicate which processing methods you

feel will be important to your industries or the industries you

supply. Consider the time frame of 5 to 15 year. Please add any

additional techniques we have not included even if you do not

select them as important to the industries you know.

Methods Selected Industry

( ies ) Pul t rus ion

Inter leavered yarn preparation and processing

Resin coated fiber preparation and processing

Autoclave molding

Powder molding

Thermoforming

SMC forming

Resin transfer molding

Reactive transfer molding

Injection molding

Reactive injection molding

Compression molding

Vacuum assisted, matched me tal - mo lding

3-D Weaving/Braiding

Filament winding

High temperature processing

Alternative sources of heat, i.e.

,

microwave, dielectric, ultrasonic heating

Focussed/diffused heating

39
QUESTIONNAIRE 2

INDUSTRY WORKSHOP ON COMPOSITE PROCESSING

Priorities for Processing Methods

Are you a supplier or user

What industry sector (sectors) can you respond for

Based on your knowledge and the discussions at this Workshop,

please indicate your opinions as to the order of priorities in the

processing techniques important to your industries or the

industries you supply. Start with 1 for the most important and go

up through as many techniques as appropriate. Feel free to rate

more than one method with equal priority and to add any comments

or explanations that you think would be useful.

Selected

Methods Ranking Indus try ( ie s

)

Pultrusion __________ ___________

Extrusion __________ _____________ Inter leavered yarn preparation and

processing __ Commingled fiber processing

Resin coated fiber preparation and

processing _________

Autoclave molding _______ _____________ Powder molding _________

Thermoforming

Superforming ________

SMC forming

Long fiber molding

Short fiber molding ___________ _______

Resin transfer molding ___________ Reactive transfer molding _________

Injection molding

Reactive injection molding

Compression molding __________ High precision molding _________

Vacuum molding

Vacuum assisted, matched metalmolding ________ __

3-D Weaving/Braiding

Filament winding

40
Tape laying and placement

High temperature processing

Alternative sources of heat, i.e.,

microwave, dielectric, ultrasonic

heating

Focussed/diffused heating

Liquid crystalline/rigid rod

polymer processing

Molecular composite processing

Sequential processing

Precomp action/Densif ication

Adhesive bonding

Fastening method

Powder impregnation of roving

RIM pultrusion of thermoplastics

41
QUESTIONNAIRE 3

INDUSTRY WORKSHOP ON COMPOSITE PROCESSING

Survey of scientific and technical problems

The following list includes scientific and technical problem areas

that have been suggested. Please add any additional items that

you think are important even if they are not a concern for your

particular industries. Time frame is again 5 to 15 years.

Next mark those items which are relevant to your industry. If the

item is "primarily associated" with one of the processing methods

you ranked as important on the previous page, please indicate

this.

specific

Problems and Needs important to proc

.

me thod

Materials Properties

Flow behavior

Crystallization

Phase separation ____________ Reaction kinetics • ___________ ___________ Heat transfer and thermal conductivity ____________ __________ Data validation/data base system ___________ ___________

Automated Process Control - Resin

Flow

Phase separation

Crystallinity

Temperature profile & gradients

Fiber alignment and Control

Fast curing

Uniform curing

Better heat transfer

High temperature processing and reactions

Adhesion and fiber/matrix interface

Toughening mechanism

Fiber damage

Geometry control

42
NBS-114A (REV. 2 -80

U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

SHEET (See instructions)

1. PUBLICATION OR

REPORT NO.

2. Performing Organ. Report No. 3. Publication Date

NBSIR 87-3686 FEBRUARY 1988

4.

TITLE AND SUBTITLE

Industry Workshop on Polymer Composite Processing

5.

AUTHOR(S)

Peter Beardmore and Donald Hunston

6.

PERFORMING ORGANIZATION (If joint or other than NBS, see instructions)

national bureau of standards

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

7. Contract/Grant No.

8o Type of Report & Period Covered

9.

SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street. City, State, ZIP)

10.

SUPPLEMENTARY NOTES

j Document describes a computer program; SF-185, FIPS Software Summary, is attached.

11.

ABSTRACT (A 200-word or less factual summary of most significant information . If document includes a significant

bi bl iography or literature survey, mention it here)

This report describes the proceedings of an Industry Workshop held at the

National Bureau of Standards on October 7, 1987. The Workshop sought to

facilitate the expanded use of polymer composites by analyzing the urgent need

for improved processing. The Workshop goals were to identify the most

promising processing methods for the future and the critical barriers to their

implementation. The attendees represent 23 different companies including

composite users, suppliers, and fabricators. Five processing methods were

selected as most important for the future: pressure molding, transfer molding,

filament winding, thermoforming, pultrusion. In addition, two technologies

that complement processing were also chosen as very important: resin coating

of fibers; alternate sources of energy input. The Workshop concluded that the

most critical barriers to implementation of improved processing are inadequate

understanding of: resin flow and fiber orientation; temperature gradients and

heat flow; fiber-matrix interface; data validation, test standardization;

morphology control; surface quality, dimensional tolerances. Increased

knowledge in these areas is needed to implement process control and automation

which the Workshop felt were keys to more rapid, reliable, and cost effective

processing

.

12.

KEY WORDS (Six to twelve entries; alphabetical order; capitalize only proper names; and separate key words by semicolon s) Autoclave molding; automation; composites; compression molding; filament winding;

polymer; process control; processing; pultrusion; thermoforming; transfer molding

13.

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'

i For Official Distribution. Do Not Release to NTIS

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20402.

[Xj Order From National Technical Information Service (NTIS), Springfield, VA. 22161

14. NO. OF

PRINTED PAGES

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