Apr. 21, 2025
Chemicals
The first step when looking at fiberglass projects is to decide what is important. Are you concerned about weight? Is strength the most important? Do you need it to be abrasion, corrosion or UV resistant? Do you want to build up thickness quickly? Answering questions like these first will help you choose the best reinforcement and resins for your project.
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To make a durable composite laminate you need to have both a reinforcement and a resin. Reinforcements include fiberglass cloth, fiberglass mat, carbon fiber and aramid. Resin holds the reinforcement together and helps it conform to the wanted shape. The most popular resins are polyester, vinyl ester and epoxy.
Many things will determine what fiberglass reinforcement you choose. It will depend on where you are applying it, what properties you need, why you will be using it, the type of resin you want to use and the cost.
Fiberglass cloth, also known as fiberglass fabric, is low in weight and becomes strong when combined with resin. It works well for building composite parts, making molds and for fiberglass repairs. The lower weight fabrics are great for waterproofing. It becomes transparent when resin is added. The heavier fabrics are stronger and build up thickness quicker.
The 6, 7.5 and 10 ounce plain weave fabrics are the most commonly used. They have a simple plain weave pattern that is uniform in strength both horizontally and vertically. This pattern has warp and fill yarns that are interlaced over and under each other in alternating fashion. The plain weave is the easiest to handle since it does not unravel as much as the other weaves when cut.
Most fabrics are sold by the yard and come in 38”, 50” and 60” widths. There is also the option of fiberglass tape. The widths on these range from 1” to 12” and come in 50 yard rolls. Fiberglass tape has selvage edges to keep it from un-raveling and do not have an adhesive backing. They are used with resin just like the regular fabrics.
Chopped strand mat is also known as fiberglass mat. It is made up of short strands of fibers that are randomly oriented and held together with a resin binder. The resin binder needs styrene to dissolve properly. This makes it incompatible with epoxy resin. It is only compatible with polyester and vinyl ester resin which contains styrene. When polyester or vinyl ester resin is added to the mat, the binder dissolves and the fibers can be moved around. This makes it easy to conform to tight curves and corners.
Chopped strand mat is the most affordable fiberglass and is frequently used in mold construction or projects where thickness is needed. It is meant for non-structural application as it does not have much strength. If you need strength you should choose a woven cloth or you could mix the two. Mat can be used between layers of woven fabric to help build thickness quickly and to aid in all layers bonding well together.
Mat is also often used as the first layer, right before the gelcoat, in a laminate to hide print through from heavier fabrics. Print through is when the fabric weave texture shows through the resin. Mat is also easy to handle and can be torn instead of cut.
Carbon fiber is known for being light weight, strong and for having great cosmetics. It is often used in the automobile, sporting goods and aerospace industry. A yard of carbon fiber cloth has millions of microscopic filaments all bundled together. For example, in a 3k fiber fabric, each bundle of fiber has filaments in it. Each filament carries part of the load. The bundles are woven together to form a strong fabric.
In cars, the 2x2 twill weave carbon fiber fabric is used to make hoods and dashboards. Usually, the carbon fiber is only there for its good looks. It doesn’t add strength or durability. It looks especially nice when it has a glossy clear coat on top of it.
Carbon comes in 3k, 6k and 12k varieties. The larger the k the larger the weave.
Kevlar® has great impact, heat and abrasion resistance. It also has excellent tensile strength, but poor compression strength. Kevlar® is used in bullet-proof vests, motorcycle racing cloth and gloves, kayaks and canoes. If a project needs abrasion resistance Kevlar® can be a good option.
One thing to note is that Kevlar® can be very difficult to cut. A separate pair of scissors should be used.
Woven roving is a heavy, coarse plain weave cloth that comes in 18 and 24 oz weights. It is made up of bundles of roving that are woven together loosely at 90 degrees and is ideal for laminating large flat areas. It is a great option to use in boat building, especially when used in conjunction with chopped strand mat. The mat will help the woven roving adhere well to subsequent layers and fill in the voids. Just be aware that if you use it with mat, it will not be compatible with epoxy resin.
Woven roving builds up thickness quickly and provides strength. A drawback is that there can be some crimping in the woven bundles. These crimp points can fracture. It is also a very heavy fabric that does not conform to curves.
Knitted fabric is bundled and stitched together. It wets out fast and provides maximum directional strength. It saves time in multi-layer layups. There is no crimping since the fabric is stitched instead of woven.
Knitted fabric is also a good option in boat building and in the composite industry. The most common knitted fabric is DBM . The is a 17 ounce +/-45 bias fabric with a 3/4 ounce chopped strand mat stitched to it.
Knitted fabric is compatible with polyester, vinyl ester and epoxy resin. It is compatible with epoxy even though it has mat with it. The mat that is stitched to the fabric does not have a styrene binder like the regular chopped strand mat.
The resin that is chosen also depends on many variables. Some of those variables are similar to the ones used when choosing a reinforcement- where you are applying it, what properties you need, why you will be using it and cost. It will also depend on the type of reinforcement you want to use, whether you will be finishing with a gel coat or not and whether you need it to be corrosion, abrasion or UV resistant. If it is a repair, it will depend on what resin was originally used. Once you have made a list of what is important to you in your laminate, you can research the different types of resins available.
The most commonly used resin is polyester. It is the easiest to use when compared to vinyl ester and epoxy resin. It is also the most economical. Polyester resin has a quick cure and adds dimensional stability. It has many different uses and is often used in building/repairing boats, car bodies, patio decks, surfboards, kayaks, decorative surfaces, outdoor ponds, bath tubs, plus more. If you will be finishing with a gel coat, it is important to use either polyester or vinyl ester resin as your laminating resin. Gel coats are polyester resins and will not adhere well if epoxy resin is used first.
There are several grades of polyester resins including ISO (isophthalic) and Ortho (orthophthalic). The most popular is the Ortho General Purpose Laminating Resin.
Ortho general purpose laminating resin is used for a wide variety of general fiberglass applications. It cures with a surface tack which holds the reinforcement in place and helps the multiple layers adhere well to each other. Another benefit to the surface tack is that it is not necessary to sand between layers. If you need a hard tack free surface, wax can be added (surface agent or surface seal) to the resin. This is typically done on the final layer. A Finishing resin can be used for the final layer as well. There is wax in a Finishing resin that rises to the top when cured and seals off the air thus providing that hard-finished surface. There will be no tack.
ISO (isophthalic) resin is a superior grade polyester laminating resin. It has higher heat distortion, is more impermeable to moisture and has better corrosion resistance. ISO resin also has a better tensile strength. It is often used in mold making because it is a stiffer resin and less likely to distort. It is also used on pipes or parts that require the higher corrosion and temperature resistance.
Surfboard Resin is another popular polyester. It is a water clear, UV and impact resistant resin. It provides some flex to help resist impact damage and also has UV inhibitors to protect the water clear appearance.
****Polyester and vinyl ester are not compatible with epoxy resin. Epoxy can be applied over polyester and vinyl ester resin for repairs etc., but not vice versa.
Vinyl ester resin falls between the polyester and epoxy resin when it comes to different characteristics and cost. It has a longer molecular chain than polyester resin which helps it absorb impact better than polyester and it shrinks less. There is also less chance of de-lamination when using VE resin. Vinyl ester can be used as a final coat after polyester resin to create a better water barrier.
Vinyl Ester resin is also more resistant to solvents and water degradation. It is typically used in boat hulls, gas tanks, kayaks, canoes and other items that will be exposed to chemicals such as fuel or water for extended periods of time.
VE resin is a tougher resin because of its longer molecular chains. It can withstand repeated bending better than both polyester and epoxy resin. Vinyl ester resin cures with a tack.
The price falls in between polyester and epoxy resin. It costs more than polyester resin and less than epoxy resin.
MEKP (methyl ethyl ketone peroxide) is the necessary catalyst for polyester and vinyl ester resins and gel coats. Without MEKP there will not be the needed chemical reaction that turns the liquid resin into a solid. It is designed for a room temperature cure.
More or less catalyst can be added depending on how long of a pot life and working time is desired. Pot life is the amount of time it takes before the resin hardens in a mixing cup. Unlike epoxy resin, polyester and vinyl ester cure time can be manipulated by the amounts of MEKP added. Typically, catalyst is used between 1.25% to 1.75% (1 2/3 ounce to 2 1/3 ounces per gallon).
The less MEKP added, the longer the pot life/working time will be. The more MEKP added, the shorter the pot life and working time. Be careful when adding more or less than the recommended amounts. Too much catalyst and the finished product can be prone to fractures or the resin in the cup will form a rubbery material before it can be used. If not enough catalyst is added, your resin will never cure. Cure time can be affected also by how thick the product is and how much resin is mixed per batch. It is best to work in smaller quantities.
The ideal temperature to work in is 70 degrees. It is not recommended to work in temps under 60 degrees Farenheit and the product could cure too fast if the temperature is above 80 degrees Farenheit.
***MEKP is hazardous. It needs to be handled with care.
Epoxy resin is an advanced system that comes in two parts. The resin side is typically designated as the ‘A’ side. The ‘B’ side is the hardener side. It comes in a variety of mix ratios including 2:1 or 4:1 ratios by weight or volume. For example, a gallon of Part A would require a half gallon of Part B with a 2:1 by weight system.
Epoxy resin is stronger than polyester and vinyl ester resin and is ideal for high performance and light weight parts. It is water resistant and has good flexibility. It has great bonding capability and a fast wet out. Epoxies have a low odor compared to other resins. One of the only downsides to epoxy is that it is more expensive than polyester and vinyl ester resin. It can be used with carbon fiber, Kevlar and fiberglass cloth (NOT compatible with chopped strand mat).
There is a choice of three different hardeners for epoxy resin: fast, medium and slow. Which speed of hardener chosen depends on the working temperature, the desired working time and the needed drying time. Epoxies dry with a full surface cure.
It is ideal to work in temperatures around 75-80 degrees. It is also important to warm up the resin and the working surface to room temperature if it is too cold. Mixing cold resin will create many air bubbles. The room and surface should stay warm through the whole curing process (approx. 3 days).
Measuring the correct ratio of A:B is EXTREMELY important. Most problems that occur with improper cure is due to not measuring the correct ratio or not mixing thoroughly. When mixing, the sides and bottom of the mixing cup should be scraped down well.
***It is very important that you do not add extra hardener to try and speed up the cure time. This will ruin your project. Instead, heat up the room to accelerate the process.
Working with fiberglass and resin can be hazardous if you are not careful. It is imperative to work in a well-ventilated area. The styrene in polyester and vinyl ester resins evaporate into the air during lay-up. Strong fumes come from the styrene and it is highly flammable. The same rules apply when working with epoxy. While the fumes are not as strong, it can still be hazardous to work with.
It is important to wear proper safety clothing to protect you from fumes and from getting hazardous material on your skin. Always wear a good respirator mask to protect from the fumes during the laminating process. You should also wear a respirator mask when cutting fiberglass, spraying gel coat or resin, working with solvents or sanding the finished laminate.
Wear gloves when working with fiberglass and resin. Nitrile gloves work best with epoxies. Also, eye protection is a must. Getting resin or catalyst in your eyes can cause permanent damage. Just the fumes alone could irritate your eyes making it very uncomfortable to work. Make sure the protective eye wear you choose is shatter proof.
Material Safety Data Sheets (SDS) are available for all hazardous materials including resin and MEKP. Read these carefully. They contain the known health and safety hazards, first aid measures, handling and storage instructions etc.
***A good recommendation is to keep a fire extinguisher and some sand in the shop. There is always a chance of fire. Plastic fires cannot be put out easily with water.
There are many different accessories you will need depending on your project. Some of these include mixing and measuring cups, spreaders, squeegees, rollers and brushes.
Graduated measuring cups are great when mixing and measuring resin. Stir sticks or tongue depressors can be used to stir the resin thoroughly.
Squeegees and spreaders are helpful when working with fiberglass and resin. The squeegee and spreader will help spread and evenly saturate the fabric.
A roller is also used to evenly saturate the fabric and will in addition help get rid of air pockets and excess resin in the fabric. If you have too much resin, spots without resin or bubbles in your finished product, you run the risk of it being weak and breaking. Using a good roller will help in creating a strong finished product.
There are several different roller options including deluxe aluminum rollers, corner rollers and barrel rollers. Deluxe aluminum rollers have grooves or fins to help distribute resin and get rid of air trapped within the fabric weave. The aluminum rollers are recommended when increased pressure is needed particularly on larger applications.
Corner rollers are designed for concave surfaces and filets where flat rollers are not effective. They eliminate bubbles in critical inside corners. They save time when rolling out non-flat surfaces.
Barrel rollers are also designed for curved and concave surfaces where flat rollers are not effective. They are wider in the middle and smaller on the ends. Radius/barrel rollers are perfect for small areas. They have deep fins.
Depending on your project, you may need some other items to complete your job-
Mold Release (PVA film or paste wax)
Surface seal (wax to create a tack free surface)
Link to Yourun Synthetic Material
Styrene Monomer (thins gel coat or resin for spraying)
Gel Coats or pigments
Acetone
Fillers (glass bubbles, fumed silica, milled glass fibers etc. to create a putty)
Once you have picked out all of your supplies, you are ready to prep your area and start the layup process. If you have any questions on the process, you can us at .
Do not use polyester or vinyl ester resin on Styrofoam. The styrene in the polyester or vinyl ester resin will melt it. Epoxy resin should be used.
Resin has a short shelf life. Try to store the resin in a cool dry place, or refrigerate (do not freeze) it to extend the life of the resin. When using Vinyl Ester resin, be sure to use it quickly after purchasing. Vinyl Ester has a shelf life of 3 months.
One of the most important steps when working with fiberglass is surface preparation. Your surface must be clean and dry. The surface needs to be free of contaminates such as dust, existing paint, grease, oil etc. You can prepare your surface by sanding with a coarse sand paper and power sander. It can be time consuming but well worth it. Clean the surface with acetone to remove dust or grease.
Based on the composite materials manufacturer and type of manufacturing method and the desired characteristics of the composite part, reinforcement material can be processed into different forms. Generally speaking, processed reinforcement materials can be classified into two main sub-categories:
Continuous fibers are commonly used when strength and stiffness are required. In the design process, designers use the orientation of the fibers to strengthen parts in the direction in which they are being loaded. When strength and stiffness are not a concern, discontinuous fibers products are often used and usually offer benefits in manufacturing speed.
Tow/Ribbon
This form has spooled bundles of individual filaments. The number of filaments per bundle is usually the main defining feature which differentiates tows from one another. This form is typically used in filament winding processes to produce cylindrical structures. Tows are also used for localized reinforcement or repairs. In some manufacturing methods (spray-up lamination) tows are cut into small fiber lengths and sprayed with a mixture of resin.
Woven Fabrics
These fabrics are processed by taking individual tows and woven bi-directionally, thus producing strands that are perpendicular to one another (0° strands and 90° strands). The two most common styles of woven fabric are:
Plain Weave: In this arrangement, each 0° strand alternately passes over and under each 90° stand. This arrangement is repeated over the entire woven fabric width and length. This produces a symmetrical pattern and uniform material properties in the 0° and 90° directions. This weave is easier to produce than most other weaves but results in a large amount of fabric ‘crimp’ (geometric reduction in length of woven fabric compared to full strand due to fiber curvature in the over and under arrangement). Since fibers produce the most strength when they are aligned with the load, this arrangement reduces the mechanical properties of the material when compared to other weaves. Plain weaves have good stability and offer easier handling, but are more difficult to drape around complex curvature.
Twill Weave: In this arrangement, each 0° stand alternatively passes over and under two 90° stands in a repeating pattern along the width and length of the fabric. This type of weave produces less fabric ‘crimp’ and twill weaves generally have improved mechanical properties over plain weaves. The arrangement has reduced stability and are more difficult to handle. They are easier to drape around curves but careful handling must be used to ensure gaps and porosity is not introduced in the manufacturing process.
Non-woven Fabrics
These fabrics are processed by taking individual tows and creating an arrangement using nylon stitches, or through the use of a mild adhesive. And then organized in a uni-directional (0°) or bi-directional (0° and 90°) arrangement.
Fiber Mat
This processed form typically contains chopped filaments of reinforcement material which is suspended in a binding agent. The amount of chopped filament, length of filaments, and the type of binder will determine the properties and manufacturing methods suitable for a particular mat. These materials are easy to work with and reduce the amount of time required to produce a laminate. Mats can also be produced from continuous fibers, whereby the fibers are randomly dispersed.
A veil is a special type of fiber mat which contains fine fibers and is usually used on the surface of a laminate to reduce the fiber imprint and improve the surface finish.
The matrix material suspends and binds the reinforcement material and hardens to determine the shape of the final part. Compared to the reinforcement material, the matrix material is relatively weak and lacks stiffness. In a loading scenario, the matrix material holds the fibers in place and transfers load between fibers and layers. Matrix material in composite part manufacturing is typically polymer based and hardens from a liquid state in the presence of a hardening agent, air, or heat.
Polymer matrix materials can be broken into two main categories, thermoset and thermoplastic.
Thermoset polymers are most popular in current composite parts. These polymers begin in a liquid state and cure to form a 3 dimensional molecular network. This process is termed as cross-linking and it produces a dimensionally stable solid which has the advantage of being resistant to heat and chemicals. In addition, the 3 dimensional network of molecular bonds gives these forms of polymers good mechanical strength properties. Most polyesters, vinyl esters, and epoxies resins used in industry are thermoset polymers.
Thermoplastic polymers are typically heated to above 500 °C and formed into the part shape. These polymers offer an advantage in being faster to produce as the curing process consists of only cooling. These polymers are not temperature resistant and will melt to a viscous liquid if exposed to high temperature. Some polyester resins are thermoplastic polymers.
Currently, the main matrix materials being used in industry are polyesters, vinyl esters, and epoxies resins. The resin system is selected based on the application and the final part properties required. Fillers and additives can often be added to most resin systems, and obtain characteristics such as flame resistance.
Polyester Resins
Polyester resins are the most widely used resin system. These resins are roughly half ester polymers blended into styrene monomers. In the molecular structure, the styrene enables the cross-linking by bonding between neighbouring polyester chains at specific reactive sites along the chain. Typical polyester resins require a catalyst agent to begin the cross-linking process with the styrene. This process is termed polymerization. Polyester resins offer a good price point and a quick cure time compared to other resin systems. This resin system works well in the presence of water and can be tailored to be chemical resistant. Polyester resins offer reasonable adhesive and mechanical properties compared to other resin systems.
Vinyl Ester Resins
Vinyl ester resin systems carry the same backbone structure as polyester resin systems, but have most of the reactive sites on the ends of the base polymer chain. In addition, vinyl ester resins have fewer ester groups which make it more resistant to water. Vinyl ester resins offer improved crack inhibiting abilities over polyester resins due to the location of cross-linking. With cross-linking only happening at the ends of parallel chains, vinyl ester resin systems are able to absorb more energy before cracks begin to form from an impact. As well, vinyl ester resins offer improved adhesion and mechanical stiffness and strength over a polyester resin.
Epoxy Resins
Epoxy resins are similar to vinyl ester resin systems in the manner that reactive sites exist at the ends of the base polymer chain. The main difference between these resin systems is the absence of ester groups in the base chain. Instead, epoxide groups are found at the reactive sites. Epoxy resins are also different in the manner that they require a hardener agent which is an amine group which is mixed with the resin to allow for it to cure. The ratio of the hardener to the resin is important as any excess of either component will remain uncured. Epoxy systems offer superior adhesion and mechanical stiffness and strength. In addition, with the absence of ester groups, the epoxy system performs extremely well in marine applications and are resistant to many industrial chemicals.
Gel coats are often used in conjunction with polyester and vinyl ester resin systems and are a thermoset plastic. They serve as a protective and aesthetic topcoat which protects the matrix and the reinforcement material from UV light and chemical degradation. They can also be tinted and dyed to replicate any colour and offer a significant advantage over paint in both labour and cost for finishing a composite part. In addition, in the event of damage to the top coat, gel coats can be resurfaced and restored far quicker and at a lesser cost than painted surfaces.
Gel coat is sprayed or brushed on in a thick (10-20mm) layer directly onto the prepared mold surface prior to lamination. The desired thickness is typically built up to 2 or 3 layers with sufficient time between coats. The rest of the lamination process remains unchanged and the overall part finish upon release is greatly improved.
Core material is often adhered in between ‘skins’ of reinforced plastic. Cores are typically used to add thickness to parts at little penalty of weight or cost. Adding core greatly improves the flexural (bending) stiffness and strength of a part.
When a material is being loaded in bending, the top surface of the material is being compressed while the bottom surface is being stretched. The further apart the top and bottom surfaces of a part in bending are spaced from each other, the greater the stiffness and strength of the part. In this form of loading, the core material sees what is known as a shear load as the top and bottom of the material is being pulled in opposite directions.
Core materials range widely based on the application, lamination method, and environmental conditions.
PVC Foam
PVC (polyvinyl chloride) cores are a chemical/moisture resistant, closed cell foam which offers good shear strength and adhesive properties. These cores are a rigid thermoset but can be thermoformed easily with the use of heat and pressure. They are manufactured in a variety of thicknesses and densities and are compatible with most resin systems and lamination methods.
SAN Foam
SAN Foam (Styrene acrylonitrile) cores are a closed cell, lightweight foam core which offers excellent chemical resistance. They are often used in very demanding manufacturing where high heat or high pressure is required. SAN has the unique property of being a thermoplastic and can easily be molded using heat.
Honeycomb Cores
Honeycomb cores can be manufactured from a variety of material but are typically produced from aluminum or a Kevlar based paper known as Nomex. The cells are arranged in a honeycomb pattern which offers a good compromise between strength and weight. These cores can easily be bent and molded to complex shapes. With hand lamination’s and resin infusion lamination methods, this type of core is susceptible to being saturated with resin.
Wood Cores
Wood cores offer very good compressive strength and shear properties at the expense of weight. End grain Balsa wood is typically used. This type of core is frequently used in local loading scenarios where high compressive stresses are expected. In addition, this core is often used at discontinuous locations such as bolt holes and other local stress concentrators. Balsa cores treated with sealers can be used in environments with moisture and can be used with most resin systems and manufacturing methods.
Fabric Cores
Fabric cores and mats are typically far thinner than other core materials. They are usually referred to as ‘bulking’ materials as opposed to a core, and add marginal thickness to the laminate. They are mostly polyester woven sheets which are closed cell so they will not absorb resin during the lamination process. These cores are flexible and conform to bends and curves in a part. Fabric cores are typically very low density and not used where high core shear strength is required.
Composite parts manufacturing methods have been adapted to meet the needs of the part and material. Almost all manufacturing methods require the need for a mold to designate the shape of the composite part. You can specifically learn more about “what is composite manufacturing” guide that covers this extensively.
Molds (or tools) are designed around the final part which is to be produced, the manufacturing method selected, and the required accuracy of the finished part. In the composites industry there are two main designations for tooling….namely, hard and soft tools.
Hard tools are made from ceramics, metals and high density woods. They require a larger initial investment in both material and machining costs. These types of tools are typically used repeatedly and the material is selected based on the robustness required for the mold. In addition, the material is selected based on the manufacturing method (ie. for a temperature cure part, the correct tooling material must be used for simultaneous thermal expansion). These types of tools are also able to hold dimensional tolerances better.
Soft tools are made from foams, composites or other machinable mediums which will wear and degrade as more parts are manufactured. These tools are lower cost and not as well suited for holding strict dimensional tolerances.
Tools preparation is essential to the final finish of the part. New tools are prepared for use by first polishing the surface to a desired roughness index. The roughness of the tooling surface has a direct impact on the surface roughness which will be imprinted on the part. Next the surface is sealed with an interfacial coating which fills very small scale pits and scratches. A release agent is then applied to the tool surface which allows the part to be removed after a full cure. The interfacial layer provides a good surface for the release agent to adhere to. Traditionally, release agents were a consumable material and would need to be applied after each part is removed from a tool. Recently, semi-permanent release agents are being used which can last up to 20 parts, and can be left on the mold surface when a new coat is required.
There are constantly new methods for composite part manufacturing as the diversity or parts and applications grow. In general, most manufacturing methods can be classified into the following categories:
Open Mold/Hand Lamination
This is the most basic form of lamination. Plies of reinforcement material and core are stacked in a prescribed sequence and wet out with the resin system layer by layer over top of a prepared mold. The completed laminate is then allowed to cure based on the requirements for the resin system. This curing processes can be aided by the use of heat.
This method is typically used for custom one-off parts and small production runs. Hand lamination requires no complex machinery, tools, or consumables. This process produces some variation in part quality and strength due to inconsistency in resin distribution and entrapment of air voids between layers. Hand lamination’s are also difficult to efficiently scale up in production quantity as they are a labour intensive process. Efficiency for this process can be improved by using a spray on resin system and by having reinforcement material pre-cut prior to the lamination.
Spray-Up Lamination
This form of lamination utilizes a pneumatic spray gun which chops strands of reinforcement material and a mixture of resin directly onto the mold surface. This method usually begins with an application of a gel coat on the mold surface. A mixture of resin, catalyst and chopped reinforcement material is then sprayed over top of the mold and compacted using a roller. Core and subsequent layers can be applied to add additional stiffness. Typically the laminate is then allowed to cure at room temperature or in an oven based environment, depending on the requirements of the resin. The part is then removed and the mold can be prepared for the next manufacturing cycle.
This method reduces the time required to complete a lamination. In addition it is suitable for larger parts as this method allows for a large coverage area. Spray-up lamination methods utilize discontinuous fibers which greatly reduces the strength of a part. In addition, due to inconsistencies in spraying, tolerances can be difficult to maintain. There are also health and environmental concerns over this form of manufacturing as large amounts of styrene content is released into the atmosphere.
Wet Bagging
Similar to a hand lamination, this process requires reinforcement plies to be wet out with a resin system layer by layer over top of a prepared mold. Prior to the resin curing, a consumable release ply, resin absorption material, and vacuum bagging film is placed over top of the final ply of reinforcement material. The vacuum bagging film is then sealed to the ends of the mold using an air tight mastic tape. A vacuum is then used to draw out air from between the mold surface and the vacuum bagging film, thus applying pressure and removing voids of air entrapped between plies of reinforcement material. Vacuum port positioning and the use of ‘breather’ material in strategic locations is important to ensure equal vacuum pressure is applied across the entire part.
This process greatly improves inter-laminar bonds resulting in greater structural integrity. For this method of lamination, a resin system with the appropriate cure time must be selected to ensure the plies can be thoroughly wet out and bagged prior to cure. Resin systems can be designed to offer different cure times.
Resin Infusion
In a resin infusion lamination, dry plies of reinforcement material and core are placed in the correct sequence over top of a prepared mold surface. The mold is also strategically fitted with a resin supply line and a vacuum draw line. The laminate is then covered with a porous releasing ply, and a flow medium which allows for the flow of resin during the infusion process. An air tight vacuum bag is then fitted which seals around the part and the supply and draw lines. Air is then evacuated out from the draw line while catalyzed resin is injected from the opposite end of the part. Resin supply and vacuum pressure are monitored carefully during this process to ensure the entire part is uniformly wet out with resin and has equivalent vacuum pressure throughout the part. Once the correct amount of resin is injected, the supply line is sealed off and the laminate is allowed to cure under a regulated vacuum pressure and temperature conditions.
This method allows for larger, more complex parts to be manufactured compared to hand lamination and wet bagging methods. In addition, part quality and consistency is improved as resin uniformity and the curing cycle are more closely regulated between parts. This method is suited for both small and large production runs and is increasingly being automated. This method has many variants such as Resin Transfer Molding (RTM), Vacuum Assisted Resin Transfer Molding (VARTM), and Resin Injection Molding (RIM) which all have similar processes but differ in how and when the resin is injected and distributed. Increasingly, a matching male and female mold technique is being employed in fully automated settings to allow labour and consumables such as vacuum bagging film to be reduced.
Autoclave Cure
Autoclave cure techniques are most commonly used with pre-impregnated (prepreg) reinforcement material such as prepreg carbon fiber when very high quality parts are required. This form of material has an un-catalyzed resin film which is applied to one or both sides of the reinforcement material by the manufacturer. This material is always stored in a climate controlled environment as the resin is catalyzed by heat. These materials have a prescribed shelf-life.
During the lamination process, the prepreg and core material is placed over top of a prepared mold surface in the prescribed sequence and orientation. A slight amount of tack is present on the surface of the prepreg allowing it to hold its place on the mold surface without voids and gaps being created. Fine contours and tight corners are laminated using the help of a heat gun to ensure the prepreg covers the entirety of the mold surface. Since the prepreg material has the perfect amount of resin for the amount of reinforcement material, any gaps or voids will remain unfilled in the finished part, thus making the initial uncured lamination process the limiting factor in the parts final quality. A film adhesive is often used between prepreg material and the core to ensure a quality bond is formed. In an autoclave cure, the laminate and mold are fitted with a vacuum bag which draws out air during the curing process. The mold and the entire part is placed inside of the autoclave which has control over the pressure and temperature of the environment. The autoclave has the advantage of producing conditions above 1 atmosphere (14.7 psi) during the curing process, allowing for more force to be applied on the part surface thus reducing voids and improving the inter-laminar bonds. This increased force is only typically required for extremely high grade parts and is almost exclusively used in aerospace and performance automotive settings.
In an autoclave cure cycle, the temperature is ramped up to an intermediate temperature causing the impregnated resin viscosity to drop, enabling it to flow and wet out the fibers of the reinforcement material. The temperature is then raised to the final cure temperature where the resin begins to catalyze and form chemical bonds. This process is carefully monitored using thermocouples to ensure that all areas of the part see the correct temperature conditions for a complete cure.
Autoclave processes require expensive prepreg material which has a limited shelf-life. In addition, there is a large capital cost associated with procuring equipment for an autoclave production run. Typically, parts will also spend upwards of 8 hours to go through a full autoclave cure cycle thus lowering the productively and usage of the autoclave and mold.
Oven Cure
Similar to autoclave cures, oven cures can be used to manufacture parts from pre-impregnated reinforcement material. An oven cure is typically used when the additional force of a high pressure atmosphere is not required. This dramatically reduces the initial capital cost for the production of prepreg parts. Oven cures are also often used with standard resin systems in certain applications where specific properties of the final cured part are required.
Composite parts are often trimmed and finished to the desired specification after final cure. Like metals and other materials, composites can be cut, trimmed, sanded and machined.
In low volume production runs, hand trimming, sanding and finishing is commonly used. These methods do not scale up well and are extremely labour intensive. They also cause health concerns due to exposure to fine particulate matter.
Composite parts are frequently brought down to exact dimensions through the use of precision automated part trimming tools which are able to remove material from ends and produce clean holes. The finished part is free of stray fibers or built up resin. Composite parts can also be brought down to final dimensions using sheet metal manufacturing methods such as a water jet which leaves behind clean, smooth edges.
When very precise fits and tolerances are required, composite parts can be machined using traditional machining methods. Typically, compression style tool bits are used to maintain the structure and distribution of reinforcement material in the polymer matrix. For drilling holes, an orbital style bit is used to prevent de-lamination and improve the dimensional accuracy throughout the hole depth.
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