Basic Composites American Composites Manufacturers Association 1

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1 Basic Composites Study Guide

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3 Basic Composites When you apply to become a Certified Composites Technician, you take the first step towards achieving excellence in the composites industry, advancing your career, and pursuing comprehensive composites knowledge. The CCT program is designed to elevate standards in the industry by enhancing individual performance and recognizing those who demonstrate critical knowledge of the composites industry. The CCT designation is a noted symbol of education among employers, employees, and industry professionals. As the industry advances, being a CCT will become increasingly important. If you are committed to developing your career, attaining the CCT designation will allow others to recognize you as a certified composites industry professional. This Study Guide will cover the first steps in becoming a CCT by introducing you to the basic composites knowledge that will lay the foundation for your growth and understanding as you progress American Composites Manufacturers Association 1

4 Disclaimer The sole purpose of this Study Guide is to assist in the preparation for the CCT examination. It is not a formal code or standard of the American Composites Manufacturers Association nor is the information contained herein based upon such a code or standard. While the Study Guide reflects ACMA s understanding of current industry practices in general, nothing herein should be viewed as a recommendation by ACMA that any application, technique or process is appropriate in any particular circumstance. Similarly, the fact that a particular application, technique or process is listed in the Study Guide should not be viewed as an endorsement by ACMA of such application, technique or process. ACMA makes no claims concerning the accuracy or applicability of the information contained in the Study Guide and ACMA is not responsible for the results obtained from the use of such information. Determination of the suitability of the information in the Study Guide other than for the preparation for the CCT Examination is the sole responsibility of the user. This Study Guide is sold without warranties, express or implied, including but not limited to any implied warranty of merchantability or fitness for a particular purpose. ACMA expressly disclaims all such warranties. ACMA is not responsible for any damage or loss caused or alleged to be caused by the information contained herein. Accordingly, ACMA shall not be liable for any direct, indirect, incidental, special or consequential damages, resulting from the use of the Study Guide. ACMA does not accept any liability based on the designation conferred upon an individual who successfully completes the certification program. Any company recognizing the conference of such a designation is responsible for verifying any and all credentials and skills of anyone with the CCT designation American Composites Manufacturers Association 1010 North Glebe Road, Suite 450 Arlington, VA Phone: Fax: All rights reserved. No part of this book may be reproduced, in any form or by any means, without permission from the publisher. Printed in the United States 2

5 Table of Contents Module 1 General Composites Knowledge Sec 1: Composites Overview...7 Sec 2: The Composites Industry...9 Sec 3: What are Composites?...10 Sec 4: Why Composites are Different...12 Sec 5: The Advantages of Composites...13 Sec 6: History of the Composites Industry...15 Module 2 Composites Manufacturing Processes Sec 1: Overview...21 Sec 2: Open Molding...22 Sec 3: Closed Molding...27 Sec 4: Cast Polymer Molding...36 Module 3 Composites Materials Sec 1: The Polymer Matrix...43 Sec 2: Thermoset Resins...43 Sec 3: Overview of Polyester Resins...44 Sec 4: Initiators, Promoters, and Inhibitors Sec 5: Resin Additives...49 Sec 6: Gel Coat...50 Sec 7: Reinforcement Materials...51 Sec 8: Core Materials...54 Module 4 Quality Control and Troubleshooting Sec 1: The Approach to Quality...63 Sec 2: Quality Assurance System vs. Quality Control Program...65 Sec 3: Quality Terminology...65 Sec 4: Management Roles in Quality...68 Sec 5: Building a Quality System...72 Sec 6: Procedural Quality Control American Composites Manufacturers Association 3

6 Certified Composites Technician Basic Composites Study Guide Table of Contents Module 5 Composites Plant Safety Sec 1: Introduction to Shop Safety...85 Sec 2: Chemical Safety...87 Sec 3: Fire Prevention and Safety...93 Sec 4: Fluid Handling Equipment Safety...96 Sec 5: Electrical Safety...97 Sec 6: Power Tool Safety...99 Sec 7: Compressed Air Safety Sec 8: Lock-Out/Tag-Out Procedures Sec 9: Lift Truck Safety Sec 10: Manual Lifting Safety Sec 11: General Personal Safety Sec 12: Housekeeping and Safety Sec 13: Confined Space Entry Sec 14: Emergency Response Plan (ERP) Sec 15: Respiratory Protection Program Appendix I Conversion Charts Appendix II Glossary

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9 Certified Composites Technician Basic Composites Study Guide Module 1 General Composites Knowledge Section 1 Composites Overview General Composites Knowledge Manufacturers, designers, and engineers recognize the ability of composite materials to produce high-quality, durable, cost-effective products. Composite materials are found in many of the products used in our day-to-day lives, from the cars we drive to the boats, RVs, skis, and golf clubs we use on the weekends. Composites are also used in many critical industrial, aerospace, and military applications. In a marketplace in which demands for product performance are ever increasing, composite materials have proven to be effective in reducing costs and improving performance. Composites solve problems, raise performance levels, and enable the development of many new products. While these exact numbers change from year to year, composites manufacturing in the United States is roughly a $53 billion a year industry, and it is one of the few industries in which the U.S. is more advanced than most competitors abroad. There are around 6,000 composites-related manufacturing plants and materials distributors across the U.S, and these facilities employ more than 125,000 people. An additional 230,000 people are employed in businesses that support the composites industry, including materials suppliers, equipment vendors, and other support personnel. About 90 percent of all composites produced are comprised of glass fiber and either polyester or vinyl ester resin. 65 percent of composites are manufactured using the open molding method and the remaining 35 percent are produced using closed molding or continuous molding methods. The term cast polymer is generally used to describe a variety of materials including cultured marble, cultured onyx, cultured granite, cultured stone, and solid surface. These are commonly used to cast and fabricate sinks, vanities, countertops, bathtubs, shower stalls, floor tiles, and similar products. This segment of our industry also makes buttons, bowling balls, automotive grouts and putties, utility boxes, curbs and gutters, drainage systems, architectural building decorations, garden statuaries, and art sculptures. Composites are broadly known as reinforced plastics. Specifically, our industry s composite materials are composites with a reinforcing fiber in a polymer matrix. The matrix is the glue that holds the fiber in place. The polymer matrix is a resin, with polyester, vinyl ester, and epoxy resins most often being the matrix material 2009 American Composites Manufacturers Association 7

10 Module 1 General Composites Knowledge Certified Composites Technician Basic Composites Study Guide of choice. There are many specialized resins, such as Bisphenol A Fumarate, Chlorendic, furane or furfural alcohol phenolic, polyurethane, and silicone that are used for specific applications. Most commonly, the reinforcing fiber is fiberglass, although high-strength fibers such as aramid and carbon are used in advanced applications. Common household plastics such as polyethylene, acrylic, nylon, and polystyrene are known as thermoplastics. These materials may be heated and formed and can be re-heated and returned to the liquid state. Composites typically use thermoset resins, which begin as liquid polymers and are converted to solids during the molding process. This process, known as cross-linking, is irreversible. Because of this, these polymers cannot be melted and reshaped and are known as thermosets. Composite materials have fueled the growth of new applications in markets such as transportation, construction, corrosion-resistance, marine, infrastructure, consumer products, electrical, aircraft and aerospace, appliances, and business equipment. The benefits of using composite materials include: High Strength: Composite materials can be designed to meet the specific strength requirements of an application. A distinct advantage of composites over other materials is the ability to use many combinations of resins and reinforcements, and therefore to custom tailor the mechanical and physical properties of a structure. Light Weight: Composites are materials that can be designed to have light weight and high strength. In fact, composites are used to produce structures with the highest strength-to-weight ratios known to man. Corrosion Resistance: Composite products provide long-term resistance to severe chemical and temperature environments. Composites are often the material of choice for outdoor exposure, chemical handling applications, and severe environment service. Design Flexibility: Composites have an advantage over other materials because they can be molded into complex shapes at relatively low cost. The flexibility of creating complex shapes offers designers a freedom that is a hallmark of composites achievement. Durability: Composite structures have an exceedingly long life span. The longevity of composites, along with their low-maintenance requirements, is a major benefit in critical applications. There are many well-designed composite structures constructed over fifty years ago that are still in active use. 8

11 Certified Composites Technician Basic Composites Study Guide Module 1 General Composites Knowledge Today, the composites industry continues to grow as more designers, engineers, and manufacturers discover the benefits of using these unique materials. As a Certified Composites Technician, you will have the opportunity to be a part of this success, and you will benefit from your enhanced knowledge of the industry. Section 2 The Composites Industry The composites industry can generally be characterized by the markets that use composite products. Composites are used to manufacture thousands of products that fall into three broad categories: consumer composites, industrial composites, and advanced composites. Consumer Composites The composites industry has been producing consumer products such as boats, automobiles, and recreational products since the early 1950s. Typically, consumer composites involve products that require a cosmetic finish, such as boats, recreational vehicles, bathroom components, and sporting goods. In many cases, the cosmetic finish is an in-mold coating. Consumer products make up a large portion of the overall composites market. Industrial Composites A wide variety of composites products are used in industrial applications, where corrosion resistance and performance in adverse environments are critical. Generally, premium resins such as isophthalic or vinyl ester formulations are required to meet corrosion resistance specifications. There are other specialty resins that may be used depending upon the ultimate chemical resistance properties required. Fiberglass is almost always used as the reinforcing fiber. In this segment of the industry, cosmetic finishes are secondary to the performance of the product. Industrial composite products include underground storage tanks, scrubbers, piping, fume hoods, water treatment components, pressure vessels, and a host of other products. Advanced Composites This sector of the composites industry is characterized by the use of expensive, high-performance resin systems and high-strength, high-stiffness fiber reinforcement. The aerospace industry, including military and commercial aircraft, is the major customer for advanced composites American Composites Manufacturers Association 9

12 Module 1 General Composites Knowledge Certified Composites Technician Basic Composites Study Guide These materials have also been adopted for use in sporting goods, where highperformance equipment tools such as golf clubs, tennis rackets, fishing poles, and archery bows benefit from the light weight and high strength offered by advanced materials. There are a number of exotic resins and fibers used in advanced composites, but epoxy resin and aramid, carbon, or graphite reinforcement fibers dominate this segment of the market. Section 3 What Are Composites? The term composites can be used in several different ways, and the definition can range from general to very specific. Combining many individual photographs into one picture is known as a composite photograph because it is a combination of different components. Our industry s composite materials are also made up of a combination of different components. A broad definition of a composite is: Two or more dissimilar materials which when combined are stronger than the individual materials. Composites can be natural or synthetic (man-made). Wood is a good example of a natural composite. Wood is a combination of cellulose fiber and lignin. The cellulose fiber provides strength and the lignin is the matrix that bonds and stabilizes the fiber. Bamboo is a very efficient wood composite structure. Its components are cellulose and lignin, as in other types of wood, but bamboo is hollow, resulting in a very light yet stiff structure. Composite fishing poles and golf club shafts copy this natural design. Plywood is a man-made composite combining natural and synthetic materials. Thin layers of wood veneer are bonded together with adhesive to form flat sheets of laminated wood that are stronger than natural wood. Figure 1 The Cellular Structure of Wood 10

13 Certified Composites Technician Basic Composites Study Guide Module 1 General Composites Knowledge There are other man-made combinations of natural materials that form useful composites. Adobe bricks are a good example. The combination of mud and straw forms a composite that is stronger than either the mud or the straw by itself. The ancient Egyptians manufactured composites when they created bricks for the pyramids! Figure 2 In modern structures, concrete and steel combine to create buildings that are rigid and strong. This is a classic composite material where there is a synergy between materials. In this case, synergy means that the materials work together as a combination to be stronger and perform better than the individual materials. Concrete is rigid and has good compressive strength, while steel has high tensile strength. Combining the two creates a composite that is strong in both tension and compression. Another familiar composite product is the rubber tire. A typical car tire is a combination of a rubber compound and reinforcement such as steel, nylon, aramid, or other fibers. The rubber acts as the matrix, holding the reinforcement in place. While the broad definition of composites is accurate, it is too general. A specific definition of composites for our purposes is: a combination of fiber reinforcement and a polymer matrix. In many of our industry s products, polyester resin is the matrix and glass fiber is the reinforcement. The glass fiber provides strength and stiffness, and the resin provides shape and protects the fibers American Composites Manufacturers Association 11

14 Module 1 General Composites Knowledge Certified Composites Technician Basic Composites Study Guide Section 4 Why Composites are Different? Composites have different properties than other materials. Metals, for example, have equal strength in all directions. Composites can be custom-tailored to have strength in a specific direction. If a composite has to resist bending in one direction, most of the fiber can be oriented at 900 to the bending force. This creates a very stiff structure in one direction, allowing more of the material to be used where it counts. With metals, if greater strength is required in any direction, the material must be made thicker overall, which adds a great deal of weight. Figure 3 Figure 4 Composites also differ from metals due to the wide range of material combinations that can be used. Because of this, it is difficult to use a handbook approach to composites design. For example, if one were looking for a steel I-beam to span 20 feet and carry a 2000-pound load, you could simply open a structural steel handbook and choose the proper beam thickness and flange width from a chart. Composites are more complicated. There are many combinations of resins and reinforcements used in composites, and each specific material contributes to specific unique properties in the finished FRP product. The performance characteristics of composites can be varied to a tremendous degree, and there is no such thing as a generic or typical composite. The properties that make composites such highly adaptable engineering materials also make them more difficult to describe and specify. For composites products, the resin system is selected based on a variety of functional and cost requirements. There are a number of different resins used in composites, including polyester, vinyl ester, modified acrylic, epoxy, phenolic, and urethane. The list goes on; however, the important point to note is that 12

15 Certified Composites Technician Basic Composites Study Guide Module 1 General Composites Knowledge each of these resins has specific performance characteristics. For example, if a product needs to be corrosion-resistant, isophthalic or vinyl ester resin might be used. If high strength is critical, epoxy might be the resin of choice. If product cost is an issue, polyester resin is most commonly used. In the realm of polyester resins alone, different formulations will be used if cosmetics are important, if enhanced corrosion resistance is required, or if elevated temperatures will be encountered. In addition to different resins, various types of reinforcement fibers are used in composites. Glass fiber is used in over 90 percent of all composites. In the realm of glass fiber, there are many styles of reinforcement. Depending on the molding process and the strength requirements of the product, there are many options. Glass fiber is available in random fiber orientation in the form of chopped strand mat. There are also lightweight textile fabrics, heavy woven materials, knitted fabrics, and unidirectional fabrics that all serve specific purposes in composite design. When a variety of glass fiber is not sufficient to meet specifications, advanced fibers such as aramid or carbon fiber offer highlevel performance at a significant increase in price. To maximize the cost/benefit of composite products, the component materials must be custom tailored to the application. The ability to adapt composites over a wide range of requirements makes them different from other materials. Section 5 The Advantages of Composites Composites offer a number of advantages over traditional engineering materials. These beneficial characteristics have enabled the rapid acceptance of composites in many products. High Specific Strength Specific strength is a term that relates strength to weight. Composites have a higher specific strength than many other materials. To understand this, consider the following example. Compare a ¼ inch diameter steel rod to a ¼ inch diameter fiberglass composite rod. The steel rod will have higher tensile and compressive strength, but it will weigh more. If the fiberglass rod were increased in diameter to the same weight as the steel rod, it would be stronger. Per unit of weight, the composite rod is stronger than the steel American Composites Manufacturers Association 13

16 Module 1 General Composites Knowledge Certified Composites Technician Basic Composites Study Guide Figure 5 Ability to Form Shapes Composites can be formed into complex and accurate shapes easier than other materials. This gives designers the freedom to create any shape or configuration. Boats are a good example of the success of composites. Boats can be made out of a variety of materials wood, aluminum, steel, and even cement! Why are most pleasure boats today built from fiberglass composites? Composites can be easily molded into attractive, complex shapes. Inherent Durability How long do composites last? The answer: We do not know because we have not come to the end of the life of many original composites. There are many examples of composite boats, buildings, and other composite structures built in the 1950s that have now been in service for over 50 years. The bodies of the original 1953 Corvette are fiberglass and are still structurally sound. There are case histories of fiberglass ductwork being in service in chemical manufacturing plants for over 25 years operating in harsh chemical environments twenty-four hours a day, seven days a week. In 1947 the U.S. Coast Guard built a series of 40-foot patrol boats, using polyester resin and glass fiber. These boats were used until the early 1970s when they were taken out of service because the design was outdated. Extensive testing was done on the laminates after decommissioning, and it was found that only 2 percent-3 percent of the original strength had been lost after 25 years of hard service. How long do composites last? In many cases, over 50 years and still counting! 14

17 Certified Composites Technician Basic Composites Study Guide Module 1 General Composites Knowledge Low Relative Investment One reason the composites industry has been successful is because of the low relative investment in setting up a composites manufacturing facility. This has resulted in many creative and innovative companies in the field. Many of the largest composite molding companies began as small entrepreneurial companies that entered the industry because of the low initial investment. Many manufacturing processes, such as thermoplastic injection molding, require multimillion dollar investments in equipment to start out. Open molding of composites is possible with a much lower cost for equipment and molds. Although complying with modern regulations has added to the cost of being in the composites business, the overall cost to enter the industry is still less then many other manufacturing ventures. Section 6 History of the Composites Industry The use of natural composite materials has been a part of man s technology since the first ancient builder used straw to reinforce mud bricks. Below is a brief history of composites since that time. The 12th century Mongols made the most advanced weapons of their day: archery bows that were smaller and more powerful than their rivals. These bows were composite structures made by combining cattle tendons, horn, bamboo, and silk, which were all bonded together with natural pine resin. The tendons were placed on the tension side of the bow, the bamboo was used as a core, and sheets of horn were laminated to the compression side of the bow. The entire structure was tightly wrapped with silk using rosin (pine resin) adhesive. These 12th century weapons designers certainly understood the principles of composite design. Recently some of these 700-year old museum pieces were strung and tested, and they were found to be about 80 percent as strong as modern composite bows! (Source: Gerald Shook, Reinforced Plastics Tutorial). In the late 1800s, canoe builders experimented with gluing together layers of Kraft paper with shellac to form paper laminates. While the concept was successful, these materials did not perform well. Because the available materials were not up to the job, the idea faded. In the years between 1870 and 1890, a revolution occurred in chemistry. The first synthetic (man-made) resins were developed, which could be converted from a 2009 American Composites Manufacturers Association 15

18 Module 1 General Composites Knowledge Certified Composites Technician Basic Composites Study Guide liquid to a solid by polymerization. These polymer resins are transformed from the liquid state to the solid state by cross-linking the molecules. Early synthetic resins included celluloid, melamine, and Bakelite. In the early 1930s, two chemical companies, American Cyanamid and DuPont, worked on the further development of polymer resins. In the course of their experimentation, both companies independently formulated polyester resin for the first time. In the same time period, Owens-Illinois Glass Company began weaving glass fiber into a textile fabric on a commercial basis. Between 1934 and 1936, experimenter Ray Green in Ohio combined these two new products and began molding small boats, marking the beginning of modern composites. During World War II the development of radar required non-metallic housings, and the U.S. military advanced the fledgling composites technology with many research projects. Immediately following World War II, composites emerged as a major engineering material. The composites industry began in earnest in the late 1940s and developed rapidly through the 1950s. Most of the composites processing methods used today were developed by the year Open molding, hand lay-up, chopping, compression molding, filament winding, resin transfer molding, vacuum bagging, and vacuum infusion were all developed and used in production between 1946 and The products manufactured from composites during this period included boats, car bodies (Corvette), truck parts, aircraft components, underground storage tanks, buildings, and many other familiar products. 16

19 Certified Composites Technician Basic Composites Study Guide Module 1 General Composites Knowledge Study Module 1 Key Words Composites: A combination of a polymer matrix and fiber reinforcement. Thermoplastics: A non-cross-linked polymer resin. Thermosets: A cross-linked polymer resin. Matrix: The resin which holds the reinforcement fiber in place. Reinforcement: A fiber placed in a resin matrix. Polyester Resin: The most common resin used in composites. Vinyl Ester Resin: A premium resin for composites products, often used in corrosion applications. Glass Fiber: Reinforcement fibers made from molten glass, used to reinforce a resin matrix. Specific Strength: The strength of a material compared to its weight. Synthetic Resin: A man-made combination of chemicals. Polymerization: The conversion of a thermoset resin from liquid to solid. Cross-Linking: The molecular bonding that takes place during polymerization American Composites Manufacturers Association 17

20 Module 1 General Composites Knowledge Certified Composites Technician Basic Composites Study Guide Study Module 1 Questions 1. What percentage of overall composites production uses glass fiber and polyester or vinyl ester resin? 2. What is the difference between thermoplastics and thermosets? 3. How does the specific strength of composites compare to other materials? 4. What are the general differences between Consumer, Industrial, and Advanced composites? 5. What is the specific definition of composites? 6. Why are composites more complicated than other materials? 7. How long do composites last? 8. What are two composites products from early history? 9. When were most of the composites processes used today first developed? 18

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23 Certified Composites Technician Basic Composites Study Guide Module 2 Composites Manufacturing Processes Composites Manufacturing Processes Section 1 Overview There are two general divisions of composites manufacturing processes: open molding (sometimes called contact molding) and closed molding. With open molding, the composite materials are exposed to the atmosphere during the fabrication process. In closed molding, the composite materials are processed in a two-sided mold set or within a vacuum bag. There are a variety of processing methods within the open and closed molding categories: Open Molding Hand Lay-Up Manual Resin Application Mechanical Resin Application Chopped Laminate Process Atomized Spray-Up Non-Atomized Application Filament Winding Closed Molding Vacuum Bag Molding Wet Lay-Up Prepreg Vacuum Infusion Processing Resin Transfer Molding (RTM) Compression Molding Sheet Molding Compound (SMC) Bulk Molding Compound (BMC) Thick Molding Compound (TMC) Low Pressure Molding Compound (LPMC) Wet Lay-Up Compression Molding Pultrusion Reinforced Reaction Injection Molding (RRIM) Centrifugal Casting Continuous Lamination 2009 American Composites Manufacturers Association 21

24 Module 2 Composites Manufacturing Processes Certified Composites Technician Basic Composites Study Guide Cast Polymer Molding In addition to these composites, we also have the cast polymer industry. These molding methods sometimes use open molding and sometimes use closed molding. Cast Polymer Molding Gel Coated Cultured Stone Molding Solid Surface Molding Engineered Stone Molding Other divisions of molding processes can be made to further characterize composites fabrication techniques. Another way of categorizing processes is by the volume they produce: Low Volume Production Open Molding Vacuum Bag Molding Vacuum Infusion Molding Medium Volume Production Filament Winding Wet Lay-Up Compression Molding Resin Transfer Molding Centrifugal Casting High Volume Production Compression Molding (SMC/BMC/TMC/LPMC) Pultrusion Reinforced Reaction Injection Molding Continuous Lamination Section 2 Open Molding The heart of the open molding process is saturating a reinforcement fiber with resin and then using manual roll-out techniques to consolidate the laminate and remove entrapped air. The primary division in open molding is between hand layup and spray-up. 22

25 Certified Composites Technician Basic Composites Study Guide Module 2 Composites Manufacturing Processes In years past the terminology used to discuss hand lay-up and spray-up have been somewhat confusing. In order to clarify the methods being used, the industry has developed more accurate descriptions of the processes. The molding process is defined by the method of fiber reinforcement placement (i.e. by hand, or by chopping). If you are using roll stock materials (e.g., chopped strand mat or knitted fabric), the method is referred to as hand lay-up. Even if the resin is applied by spray application, by virtue of the reinforcement being applied by hand, the molding process is called hand lay-up. When using a chopper gun to apply the fiber reinforcement to the mold, the molding process is spray-up. Open Molding Process Definitions Official definitions for open molding processes depend on the application methods used to place the reinforcement. Hand Lay-Up Laminating Process: A composites manufacturing method using roll stock reinforcement, such as chopped strand mat, woven, knitted, or textile fabrics, where the reinforcement is placed by hand, then saturated with resin. Resin can be applied either by manual or mechanical means. Spray-Up (Chopping) Laminating Process: A composites manufacturing method using a chopper applicator, which cuts continuous strand roving into short fiber lengths and deposits a mixture of resin and cut fibers, known as chop, onto the mold surface. This process includes traditional atomized chopping (spray-up) as well as non-atomized flow chop application. Resin Application Definitions The Resin Application Method is defined by the means used to transfer resin to the mold. Manual Resin Application: The manual transfer of a thermoset resin from a container onto fiber reinforcement. This is bucket and tool application, with the resin being mixed in a container and manually applied to the laminate with a brush, paint roller, squeegee, or other tool American Composites Manufacturers Association 23

26 Module 2 Composites Manufacturing Processes Certified Composites Technician Basic Composites Study Guide Figure 1 Mechanical Resin Application: The application of a thermoset resin to a fiber reinforcement using a fluid delivery device. Controlled Spraying: Spraying resin as outlined in the ACMA Controlled Spraying Handbook. Three things are required to qualify: the spray gun pressure calibration must be verified, mold containment flanges must be in place, and operator training must be documented. All three elements must be in place in order to qualify as Controlled Spray Application. Uncontrolled Spraying: Spraying resin without all three elements in place: spray gun pressure calibration verification, mold containment flanges, specific operator training. Non-Atomized Application: Resin application without spraying, which includes the use of flow coaters, flow choppers, pressure fed rollers, or other nonspray application devices. Gel Coat Application: The application of gel coat products using atomized spray, with either controlled or uncontrolled spraying. Uncontrolled Spraying: Spraying gel coat without all three elements in place: spray gun pressure calibration verification, mold containment flanges, specific operator training. Controlled Spraying: Spraying gel coat as outlined in the ACMA Controlled Spraying Handbook. Three things are required to qualify: the spray gun pressure calibration must be verified, mold containment flanges must be in place, and operator training must be documented. All three elements must be in place in order to qualify as Controlled Spray Application. 24

27 Certified Composites Technician Basic Composites Study Guide Module 2 Composites Manufacturing Processes Hand Lay-Up Hand lay-up is an open molding method suitable for making a wide variety of composites products including: boats, tanks, bathroom components, housings, RV/truck/auto components, architectural products, and many other products ranging from very small to very large. Production volume per mold is low; however, it is feasible to produce substantial production quantities using multiple molds. Process Description Gel coat is first applied to the mold using a spray gun for a high-quality surface. When the gel coat has cured sufficiently, roll stock fiberglass reinforcement is manually placed on the mold. The laminating resin is applied by pouring, brushing, spraying, or using a paint roller. FRP rollers, paint rollers, or squeegees are used to consolidate the laminate, thoroughly wetting the reinforcement and removing entrapped air. Subsequent layers of fiberglass reinforcement are added to build laminate thickness. Low-density core materials, such as end-grain balsa, foam, and honeycomb, are commonly used to stiffen the laminate. This is known as sandwich construction. Molds Simple, single-cavity molds of fiberglass composites construction are generally used. Molds can range from very small to very large and are low cost in the spectrum of composites molds. Major Advantages This is the simplest composites molding method, offering low-cost tooling, simple processing, and a wide range of part sizes. Design changes are readily made. There is a minimum investment in equipment. With skilled operators, good production rates and consistent quality are obtainable. Spray-Up (Chopping) Spray-up or chopping is an open mold method similar to hand lay-up in its suitability for making boats, tanks, transportation components, and tub/ shower units in a large variety of shapes and sizes. A chopped laminate has good conformability and is sometimes faster to produce than a part made with hand lay-up when molding complex shapes. In the spray-up process, the operator controls thickness and consistency, therefore the process is more operatordependent than hand lay-up. Although production volume per mold is low, it is feasible to produce substantial production quantities using multiple molds American Composites Manufacturers Association 25

28 Module 2 Composites Manufacturing Processes Certified Composites Technician Basic Composites Study Guide Figure 2 Process Description: As with hand lay-up, gel coat is first applied to the mold and allowed to cure. Continuous strand glass roving and initiated resin are then fed through a chopper gun, which deposits the resin-saturated chop on the mold. The laminate is then rolled to thoroughly saturate the glass strands and compact the chop. Additional layers of chop laminate are added as required for thickness. Roll stock reinforcements, such as woven roving or knitted fabrics, can be used in conjunction with the chopped laminates. Core materials of the same variety as used in hand lay-up are easily incorporated. Molds These are the same molds as in hand lay-up: simple, single-cavity molds of fiberglass composites construction. Molds can range from very small to very large and are low cost in the spectrum of composites molds. Major Advantages This process uses simple, low-cost tooling, and simple processing. Portable equipment permits on-site fabrication with virtually no part size limitations. The process may be automated. Filament Winding Filament winding is an automated open molding process that uses a rotating mandrel as the mold. The male mold configuration produces a finished inner surface and a laminate surface on the outside diameter of the product. Filament winding results in a high degree of fiber loading, which provides high tensile strength in the manufacture of hollow, generally cylindrical products such as chemical and fuel storage tanks, pipes, stacks, pressure vessels, and rocket motor cases. 26

29 Certified Composites Technician Basic Composites Study Guide Module 2 Composites Manufacturing Processes Process Description Continuous strand roving is fed through a resin bath and wound onto a rotating mandrel. The roving feed runs on a trolley that travels the length of the mandrel. The filament is laid down in a predetermined geometric pattern to provide maximum strength in the directions required. When sufficient layers have been applied, the laminate is cured on the mandrel. The molded part is then stripped from the mandrel. Equipment is available for filament winding on a continuous basis with two axis winding for pressure cylinders. Filament winding can be combined with the chopping process and is known as the hoop chop process. Molds Filament winding uses mandrels of suitable size and shape, made of steel or aluminum, to form the inner surface of the hollow part. Some mandrels are collapsible to facilitate part removal. Major Advantages The process makes high strength-to-weight ratio laminates and provides a high degree of control over uniformity and fiber orientation. The filament winding process can be used to make structures that are highly engineered and meet strict tolerances. Because filament winding is automated, the labor factor for filament winding is lower than other open molding processes. Section 3 Closed Molding Vacuum Bag Molding The mechanical properties of open-mold laminates can be improved with vacuum bagging. By reducing the pressure inside the vacuum bag, external atmospheric pressure exerts force on the bag. The pressure on the laminate removes entrapped air, excess resin, and compacts the laminate. A higher percentage of fiber reinforcement is the result. Additionally, vacuum bagging reduces styrene emissions. Vacuum bagging can be used with wet-lay laminates and prepreg advanced composites. In wet lay-up bagging the reinforcement is saturated using hand lay-up, then the vacuum bag is mounted on the mold and used to compact the laminate and remove air voids. In the case of pre-impregnated advanced composites molding, the prepreg material is laid-up on the mold, the vacuum bag is mounted and the mold is heated or the mold is placed in an autoclave that applies both heat and external 2009 American Composites Manufacturers Association 27

30 Module 2 Composites Manufacturing Processes Certified Composites Technician Basic Composites Study Guide pressure, adding to the force of atmospheric pressure. The prepreg-vacuum bagautoclave method is most often used to create advanced composite aircraft and military products. Figure 3 Process Description In the simplest form of vacuum bagging, a flexible film (PVA, nylon, mylar, or polyethylene) is placed over the wet lay-up, the edges are sealed, and a vacuum is drawn. A more advanced form of vacuum bagging places a release film over the laminate, followed by a bleeder ply of fiberglass cloth, non-woven nylon, polyester cloth, or other material that absorbs excess resin from the laminate. A breather ply of a non-woven fabric is placed over the bleeder ply, and the vacuum bag is mounted over the entire assembly. Pulling a vacuum from within the bag uses atmospheric pressure to eliminate voids and force excess resin from the laminate. The addition of pressure further results in high fiber concentration and provides better adhesion between layers of sandwich construction. When laying non-contoured sheets of PVC foam or balsa into a female mold, vacuum bagging is the technique of choice to ensure proper secondary bonding of the core to the outer laminate. Molds Molds are similar to those used for conventional open-mold processes. Major Advantages Vacuum bag processing can produce laminates with a uniform degree of consolidation, while at the same time removing entrapped air, thus reducing the finished void content. Structures fabricated with traditional hand lay-up techniques can become resin rich and vacuum bagging can eliminate the problem. 28

31 Certified Composites Technician Basic Composites Study Guide Module 2 Composites Manufacturing Processes Additionally, complete fiber wet-out can be accomplished if the process is done correctly. Improved core bonding is also possible with vacuum bag processing. Vacuum Infusion Processing Vacuum infusion is a variation of vacuum bagging where the resin is introduced into the mold after the vacuum has pulled the bag down and compacted the laminate. The method is defined as having lower than atmospheric pressure in the mold cavity. The reinforcement and core material are laid-up dry in the mold. This is done by hand and provides the opportunity to precisely position the reinforcement. When the resin is pulled into the mold the laminate is already compacted; therefore, there is no room for excess resin. Very high resin-to-glass ratios are possible with vacuum infusion and the mechanical properties of the laminate are superior. Vacuum infusion is suitable to mold very large structures and is considered a low-volume molding process. Figure 4 Process Description The mold may be gel coated in the traditional fashion. After the gel coat cures, the dry reinforcement is positioned in the mold. This includes all the plies of the laminate and core material if required. A perforated release film is placed over the dry reinforcement. Next a flow media consisting of a coarse mesh or a crinkle ply is positioned, and perforated tubing is positioned as a manifold to distribute resin across the laminate. The vacuum bag is then positioned and sealed at the mold perimeter. A tube is connected between the vacuum bag and the resin container. A vacuum is applied to consolidate the laminate and the resin is pulled into the mold American Composites Manufacturers Association 29

32 Module 2 Composites Manufacturing Processes Certified Composites Technician Basic Composites Study Guide Molds Molds are similar to those used for conventional open-mold processes. Major Advantages Vacuum infusion can produce laminates with a uniform degree of consolidation, producing high strength, lightweight structures. This process uses the same low-cost tooling as open molding and requires minimal equipment. Very large structures can be fabricated using this method. Vacuum infusion offers substantial emissions reduction compared to either open molding or wet lay-up vacuum bagging. Resin Transfer Molding Resin transfer molding is an intermediate volume molding process for producing composites. The RTM process is to inject resin under pressure into a mold cavity. RTM can use a wide variety of tooling, ranging from low-cost composite molds to temperature controlled metal tooling. This process can be automated and is capable of producing rapid cycle times. Vacuum assist can be used to enhance resin flow in the mold cavity. Figure 5 Process Description The mold is gel coated conventionally, if required. The reinforcement (and core material) is positioned in the mold and the mold is closed and clamped. The resin is injected under pressure, using mix/meter injection equipment, and the part is cured in the mold. The reinforcement can be either a preform or pattern cut roll stock material. A preform is a reinforcement that is formed to a specific shape in a separate process and can be quickly positioned in the mold. RTM can be done at 30

33 Certified Composites Technician Basic Composites Study Guide Module 2 Composites Manufacturing Processes room temperature; however, heated molds are required to achieve fast cycle times and product consistency. Clamping can be accomplished with perimeter clamping or press clamping. Molds RTM can utilize either hard or soft tooling, depending upon the expected duration of the run. Soft tooling would be either polyester or epoxy molds, while hard tooling may consist of cast machined aluminum, electroformed nickel shell, or machined steel molds. RTM can take advantage of the broadest range of tooling of any composites process. Tooling can range from very low-cost to high-cost, long-life molds. Major Advantages This closed molding process produces parts with two finished surfaces. By laying up reinforcement material dry inside the mold, any combination of materials and orientation can be used, including 3-D reinforcements. Part thickness is determined by the tool cavity. Fast cycle times can be achieved in temperaturecontrolled tooling and the process can range from simple to highly automated. Figure 6 Compression Molding Compression molding is a high-volume, high-pressure method suitable for molding complex, fiberglass-reinforced plastic parts on a rapid cycle time. There are several types of compression molding that are defined by the type of material molded: sheet molding compound (SMC), bulk molding compound (BMC), thick molding compound (TMC), and wet lay-up compression molding. Compression molding tooling consists of heated metal molds mounted in large hydraulic presses American Composites Manufacturers Association 31

34 Module 2 Composites Manufacturing Processes Certified Composites Technician Basic Composites Study Guide SMC Figure 7 Process Description The mold set is mounted in a hydraulic or mechanical molding press. The molds are heated from 250o to 400o F. A weighed charge of molding material is placed in the open mold. The two halves of the mold are closed and pressure is applied. Depending on thickness, size, and shape of the part, curing cycles range from less than a minute to about five minutes. After cure, the mold is opened and the finished part is removed. Typical parts include automobile components, appliance housings and structural components, furniture, electrical components, and business machine housings and parts. Molds Tooling usually consists of machined or cast metal or alloy molds that can be in either single or multiple-cavity configurations. Steel molds are hardened and sometimes chrome plated for enhanced durability. The molds are heated using steam, hot oil, or electricity. Side cores, provisions for inserts, and other refinements are often employed. Mold materials include cast of forged steel, cast iron, and cast aluminum. Matched metal molds can cost 50 times as much as an FRP open mold, and tooling in the $50,000-$500,000 range is not uncommon. Major Advantages Compression molding produces fast molding cycles and high part uniformity. The process can be automated. Good part design flexibility and features such as inserts, ribs, bosses, and attachments can be molded in. Good surface finishes are obtainable, contributing to lower part finishing cost. Subsequent trimming and machining operations are minimized in compression molding. Labor costs are low. 32

35 Certified Composites Technician Basic Composites Study Guide Module 2 Composites Manufacturing Processes Pultrusion Pultrusion is a continuous process for the manufacture of products having a constant cross section, such as rod stock, structural shapes, beams, channels, pipe, tubing, fishing rods, and golf club shafts. Pultrusion produces profiles with extremely high fiber loading, thus pultruded products have high structural properties. Figure 8 Process Description Continuous strand fiberglass roving, mat, cloth, or surfacing veil is impregnated in a resin bath and then pulled (therefore the term pul-trusion) through a steel die by a powerful tractor mechanism. The steel die consolidates the saturated reinforcement, sets the shape of the stock, and controls the fiber/resin ratio. The die is heated to rapidly cure the resin. Many creels (balls) of roving are positioned on a rack, and a complex series of tensioning devices and roving guides direct the roving into the die. Molds Hardened steel dies are machined and include a preform area to do the initial shaping of the resin-saturated roving. The dies include heating which can be electric or hot oil. The latest pultrusion technology uses direct injection dies, in which the resin is introduced inside the die, rather than through an external resin bath. Major Advantages The process is a continuous operation that can be readily automated. It is adaptable to both simple and complex cross-sectional shapes. Very high strengths are possible, due to the fiber loading, and labor costs are low American Composites Manufacturers Association 33