Monday, March 19, 2012

Composite material construction book

I've recently come across this book While most books on composites approach the subject from a very technical standpoint, beginning composites presents practical, hands-on information about these versatile materials. From explanations of what a composite is, to demonstrations on how to actually utilize them in various projects, this book provides a simple, concise perspective on molding and finishing techniques to empower even the most apprehensive beginner. Topics include: What is a composite, why use composites, general composite types and where composites are typically used. The basics section also includes information on choosing the best resin/fiber system and the different types of both resin and fiber. Health and safety is a major consideration for any composite book. Author John Wanberg covers threats to both breathing and skin contact and how those contacts can be avoided when working with modern composite materials. First-time composite workers will need a work space and this book describes how to setup a shop that is both composite-friendly and safe. Once the shop is established, it’s time to begin using typical wet- layup and molding techniques. Creating useful composite parts starts with a good design, a topic that must be mastered before useful parts can be manufactured. Among the useful parts demonstrated here are both motorcycle and automotive components. The construction of these parts is documented in step-by-step fashion with an abundance of photographs - no step is left out. Any part created in a mold must be first removed from the mold, and second, finished and trimmed. Surface sanding and finishing makes up an entire chapter, ensuring that the composite parts you manufacture are not only light and extremely strong, but good looking as well.

Wednesday, March 14, 2012

DIY Carbon Fiber Materials

Part 3: Tools & Equipment for DIY Carbon Fiber Projects

This section will focus mostly on wet lay-up overlay carbon fiber projects, and not on other vacuum bagging, vacuum infusion or using pre-pregs (dry carbon fiber). For vacuum bagging or vacuum infusion, the same tools will be needed as below, only with the addition of your vacuum bagging/infusion equipment. At this time, DIY Carbon does not sell nor support vacuum bagging/vacuum infusion equipment, and you will need to research & obtain this equipment on your own. If we sense enough demand to expand our offerings to sell vacuum bagging/vacuum infusion equipment, we will also expand this section of our Carbon Fiber Tutorial.

Your Workspace:

First and foremost, an appropriate workspace is fundamental to the success of your project. A wet lay-up can be very messy, so do not try this on your dining room table (unless you are prepared to scrape dried resin off of your table). Another key component of your workspace is the fumes that are produced by the resins, as well as the temperature and humidity of the room.  Most resin systems work best at around 75 degrees Fahrenheit with low humidity – warmer temperatures will shorten your working time and curing time, and colder temperatures will increase your working time and curing time. If your workspace is too cold, the resin may never cure at all. What works well for many people is to perform the wet lay-up/overlay process in a moderate to slightly cool room, then allow the pieces to cure in a warmer room, or even under hot lamps to accelerate the curing phase.

If using PER or VER resins, be sure to work in a well ventilated space using the proper safety equipment, fume hoods, fans, or other ventilation procedures to protect yourself from the VOCs being emitted by the reactions of the polyester/vinylester and the MEKP hardener.

Another key component of your workspace is that you’ll want it to be in a clean, dust-free environment. There is nothing worse than having dust or debris land on a wet part, and having that piece of debris curing into the final product. Maintaining a dust & dirt free environment will minimize any imperfections or foreign materials introduced to the curing piece of CFRP.

Lastly, a well lit environment will help you avoid mistakes, and notice imperfections. Use plenty of light!

Tools & Equipment Needed:

DIYCarbon provides you almost everything you’ll need in our comprehensive kits. Aside from a few simple hand tools which you likely have lying around the house, everything from the carbon fiber fabric to nirtle gloves and a particle mask are all provided in our kits, making them perfect for a complete amateur, or a seasoned carbon fiber veteran looking to create a new part. However, we have provided a comprehensive list of tools & equipment that you should obtain, whether through us or otherwise, if you choose to embark on creating your own carbon fiber parts:

Carbon Fiber Fabric – in the weave pattern, size & weight of your choice. You should have more than enough to cover the surface of the part plus a little extra.

Epoxy Resin & Hardener – preferably professional grade epoxy resin that is UV treated.

Mixing Materials – mixing cups, mixing sticks, and measurement cups will help you achieve the correct ratio of resin to hardener.

Cutting Equipment – to prepare your fabric to make the proper shape to fit your mold, you’ll want a handy array of (sharp) cutting equipment such as box cutters, utility knifes, scissors, and similar tools.

Measurement Equipment – simple tools such as pencils, sharpies, rulers and tape measures will help you plan your cuts into the fabric and make sure you are not wasting any extra material.  Measure twice, cut once.

Gloves – resin is messy and potentially dangerous – gloves are strongly recommended. DIYCarbon kits come with nirtle gloves which are thicker than standard latex gloves to keep your hands safe.

Hand Tools – a standard set of hand tools is recommended, just in tase. Mallets, hammers, flat head screw drivers an pliers can get you out of a pinch depending on the part being overlaid or mold being used. Another extremely useful tool are a set of (or several sets of) clamps to help hold things in place as they cure.

Brushes – bristled brushes work best for applying the resin, although foam brushes will work fine too for smaller projects.

Sanding tools – once the resin has cured, you will likely need to sand off imperfections. Have plenty of sandpaper from coarse to very fine as well as wet sand paper that you can sand your parts smooth with are crucial. A dremel or rotary tool can be great for removing drips or large imperfections as well. Sanding blocks and a particle mask are also very good ideas.

Clean up tools – acetone will go a long way for cleaning up any resin spills or sticky tools. Likewise a strong hand soap is a good idea if you don’t have some, such as gojo .

Advanced Tools

Vacuum Bagging or Vacuum Infusion Equipment – there are many components involved in creating a working vacuum bagging or vacuum infusion setup. This can be costly, but for certain parts that require extreme precision or have irregular or complex shapes, this investment is necessary to achieve the end product.

Mold Making Equipment – a mold can be made many, many different ways. As long as you have a shapeable, non-porous material that won’t decompose or warp over time, you can likely make a mold out of it. Due to the endless possibilities we won’t even attempt to name them all, but common materials such as wood, metal, or plastic are commonly used to create molds.

Part 3 Conclusion

As you’ve probably heard a million times, having the right tools is essential to creating any project. The right tools will save you time, create a better finished project, and are sometimes critical to your safety. Before you start any carbon fiber project, ensure your workspace is clean, your tools are ready to use and easily accessible, and that everything is in order. Due to the limited working time of resin once a hardener/catalyst is introduced, it is essential to have all of your ducks in a row before you begin working on your project.

Production of Carbon FIber Pieces

Part 2: Carbon Fiber Production Basics

There are several ways to produce finished carbon fiber reinforced plastic (CFRP) parts – the most common for hobbyists is a wetlay (or sometime referred to as an overlay), although many other options exist but are generally only used for projects of considerable scale or quantity. In this section we will give a brief overview of each, although if you are planning on using a DIYCarbon kit, you will be using a Wet lay-up/Overlay and skip the rest of this section (unless of course you are interested, then please read on!).

Wet lay-up or Overlay – A basic Wet-layup or overlay is the most common method for hobbyist or DIYers looking to create carbon fiber parts as it does not require any specialty equipment. In this process you will overlay the carbon fiber over an existing part. You will want to make sure the part you overlay has smooth, non-porous surfaces that the wet carbon fiber fabric can be laid against. In this process you will combine your epoxy resin & hardener, then soak the carbon fiber fabric in the resin/hardener mix. You will then take the soaked carbon fiber fabric and lay it up over the part. You may choose to lay-up several layers of carbon fiber fabric at once, but the resin & layers will only bond to each other if they resin hasn’t cured yet. After allowing the resin to cure, you will need to remove the mold, sand and then finish the carbon fiber reinforced plastic in the method you prefer (be it paint, clear-coat, or any other kind of surface finishing). The downside to this method is that the part you overlay is part of the final product, so it does not save any weight and in fact adds a marginal amount of weight. This method is perfect for aesthetic applications of carbon fiber like automotive interior trim, as you can ensure an OEM-like fit and finish and reuse the OEM mounting points, while only gaining a trivial amount of weight.

Molds & Patterns – This process is much like an overlay, only instead of overlaying an existing part, you create a mold (also known as a plug, a pattern, a master, or a buck) that is used to create the part. The mold is then removed from the final product, requiring no core or base product that gets overlaid. There are several ways to create a mold – commonly materials include wood, metal, or plastic. The materials for the mold should be easily shapeable, resistant to the materials being used, non-porous, and strong enough to uphold their original shape over multiple uses (poorly made molds will warp or become distorted over time, causing the final product to be misshaped). The mold needs to be perfect in cases of creating replica automotive parts like hoods or interior parts, otherwise the final product will not fit correctly or possibly not fit at all.

Vacuum Bagging – In this process, the wet-laid carbon fiber and its mold are sealed in a plastic bag, of which all air is removed, thus pressing together the wet carbon fiber against the mold to ensure a void-free covering.  The advantage is that the fiber is vacuum pressed against the mold, preventing any wrinkles, bubbles, or irregular shaping – the final product will take on the exact shape of the mold. The disadvantage of this method is that it requires extra equipment including the vacuum bagging, a pump to create the vacuum, breather cloth, peel-ply, and many other materials. There are several resources around the internet on how to create a simple vacuum bagging system using a tire pump for a bicycle, although obviously there is more advanced equipment available as well. This system is great for very complicated parts that have lots of uneven contours, odd shapes, or need to be extremely precise.

Vacuum Infusion – In this process, carbon fiber is laid dry onto the mold, and the vacuum is created before the resin is introduced (in Vacuum Bagging, the resin is applied before the vacuum pressure). Once a complete vacuum is achieved between the carbon fiber and the mold, the resin is then injected into the vacuum where it covers the carbon fiber, then the extra resin is then sucked out of the vacuum sealed mold.  There are several advantages to this method over Vacuum Bagging, most notably that less resin is used (minimizing weight) and the procedure is much less messy than vacuum bagging where the carbon fiber still has to be wet-laid. The disadvantages are again cost & equipment – much more specialty equipment is required to create a vacuum infusion system, and maintenance on the equipment is more involved since resin (which will harden & cure) is injected through it.

Pre-Pregs (Pre-Impregnated Fabrics) – unlike other methods, this method is entirely “dry” and when you hear of “dry carbon fiber” this is how it is created. With Pre-pregs, the fabric is pre-impregnated with a resin system that will cure when heat is applied to it. Generally the pre-preg material is frozen and stored in very cool temperatures until it is ready to be cured, and then baked in an oven at extremely hot temperatures. This process gives you much more control over the process and allows you to use stronger resins than a wet lay-up, and will be 20-30% stiffer and stronger than an equivalent-thickness wet laminate. The disadvantage of this method is again cost, as well as equipment to bake the material. Applications such as (high quality) mass produced carbon fiber hoods, F1 race parts, and airplane/aerospace parts will use pre-pregs to create a highly controlled, extremely high quality end part on a large scale.

Part 2 Conclusion

There are several ways to create parts, all of which depend on your budget, the scale of the project, and the complexity of the part being created. For the purposes of the rest of this guide, we will be concentrating on wet-laid carbon fiber projects that use overlays or simple molds which will be ideal for most small projects done by DIYers and hobbyists. Many of the principles throughout this guide can easily be expanded to vacuum bagging and vacuum infusion as well.

Some Basics of creating carbon fiber parts

What is Carbon Fiber?

Raw carbon fiber is a composed to extremely thin fibers that are twisted together to form a “yarn”, which to the naked eye looks like one single strand of fiber. These yarns, or strands, are then woven together to form the carbon fiber fabric you will see in the DIYCarbon kits – they are often woven together in a criss-cross over-and-under weave style, which is known as “plain weave” although variations such as the twill weave (over-two, under-two) and basket weave are common as well.  This fabric of interwoven fibers is called raw carbon fiber, and can be used to create automotive parts by applying an epoxy resin which hardens the fabric to create a finished piece of carbon fiber reinforced plastic.

Finished Carbon Fiber is a Composite Material

Finished Carbon Fiber is a composite – that is, a material made up of two dissimilar materials, that when combined, yield inherent advantages greater than either material individually. In the case of carbon fiber, those materials are the raw carbon fiber fabric itself, and the epoxy resin it is combined with to create the final product, known as Carbon Fiber Reinforced Plastics (CFRP). Other composites include fiberglass, Kevlar, and graphite reinforced polymers – these composite materials are used in many applications over plastic, wood or metal due to their ability to be easily molded and advantages in weight savings and strength over those more common materials.

For the purposes of this overview, we will be focusing solely on carbon fiber, although in many cases the advice and concepts apply to other composites as well. As you likely know, Carbon Fiber is used in many automotive applications for its great strength to weight ratio, yielding a lightweight yet strong material for body & interior panels. For racing purposes, carbon fiber is generally used for larger parts, as the weight savings becomes negligible with smaller parts, and the production of carbon fiber can often become expensive. However, the allure of carbon fiber attracts all sorts of automotive enthusiasts for a variety of purposes, both functional and non-functional, due to both the allure of it being a very advanced material, and the brilliant depth and shine of a carefully finished carbon fiber product.

Raw Carbon Fiber versus Carbon Fiber Reinforced Plastics

Carbon fiber in raw form is a soft, pliable fabric much like any other fabric (think of a blanket), and can be easily draped or wrapped around just about anything (such as interior trim, a body panel, or even a person). Once introduced to a “matrix” such as an epoxy resin, it then becomes a composite material known as Carbon Fiber Reinforced Plastic. In this state, the carbon fiber is no longer a soft, pliable fabric but it becomes a hardened, strong, and unpliable material, much like the finished carbon fiber products you see on race cars. Simply put, raw carbon fiber (fabric) is the before, and carbon fiber reinforced plastics is the after. For purposes of this website, we’ll use “carbon fiber” and “carbon fiber reinforced plastic” somewhat interchangeably, but it’s important to note that technically speaking, the former is referring to just the raw, unfinished fabric, whereas the latter is referring to the composite material after epoxy resin has been applied and hardened.

One big advantage of working with raw carbon fiber, especially for DIY projects, is that it is very easy to mold into the shape you want, and can be wrapped over just about anything as an overlay. The disadvantage is that once the epoxy resin has been applied and it becomes a carbon fiber reinforced plastic, there is no flexibility whatsoever, and you’re pretty much stuck with the shape it hardened in. Carbon Fiber is not a flexible material, and there are no “do-overs” once the epoxy has set.

Types of Carbon Fiber

There are many types of carbon fiber, which we’ll explore now. Carbon Fiber can vary by the style the yarns are woven together (weave patterns), the weight of the carbon fiber, and the size of each yarn in the carbon fiber fabric.

Weave Patterns

Plain Weave (1×1) – the most common style of weave. Each yarn (or strand) is woven in a simple over-and-under weave style creating little squares. It is a simple over one strand, under one strand pattern, as shown in the picture.
Twill Weave (2×2) – With a twill weave, each yarn travels over-two, and then under-two other yarns, as opposed to a over-one, under-one ratio for plain wave. This creates a slightly different texture .
Harness/Satin Weave (Anythingx1) – Each yarn travels over two or more yarns, then under one. For example, if it travels over 3 and then under 1, it would be a 3×1, or 4HS. Harness Satin is commonly abbreviated as HS, and the number is derived by adding the numbers before it. An 8HS weave then, would be a 7×1 weave, where each yarn travels over 7 other yarns, and then under one yarn.
Basket Weave – very similar to the plain weave, but with two yarns under, and then two yarns over, almost like a double plain weave.
There are certain functional advantages to each type of weave, although for most purposes outside of aerospace use, it really comes down to aesthetics and personal preference as to which you weave you should choose.

Weave Weights

The weave weight is the actual weight of 1 square yard of raw carbon fiber fabric. The heavier the weight, the more fibers are woven into each individual yarn (known as the size), generally creating thicker strands that will have an effect both visually and to the strength of the finished carbon fiber reinforced plastic.

The most common weights for automotive applications are:

8 oz – the vast majority of aftermarket car parts on the market
12 oz – the minimum standard DIYCarbon or oCarbon sells (unless a colored weave…)
20 oz – the rarest of the bunch
Weave Sizes

The size is referring to how many pieces of fiber are in each yarn (or strand). A size of 3K means that there are 3,000 fibers in each yarn. Obviously, the greater the size, the thicker the yarn, and the greater the weight of 1 square yard of fabric as well. The greater the size, the greater the weight.

It is more common to purchase carbon fiber by weight than size, although they pretty much go hand in hand, and by knowing the weight you can often deduce the size. For instance, an 8oz weave generally has a yarn size of 6k, meaning 6,000 fibers per yarn (or strand). A 20oz weight is often around a 12k size, or 12,000 fibers per yarn.

Colors (Carbon-Kevlar Hybrids)

A common misconception is that carbon fiber comes in different colors – it doesn’t. Each yarn of carbon fiber is black – although it may look silver to the naked eye based on how the light reflects on the weave, it isn’t – there is no silver yarn, carbon fiber only comes in black.

Often you will see different colors available such as red, blue, or yellow. This colored carbon fiber isn’t really carbon fiber, it is a Carbon-Kevlar hybrid. The Kevlar can come in different colors and is woven together with the (black) carbon fiber yarns to create the multi-colored look.

What is (Epoxy) Resin?

To turn raw carbon fiber into a finished piece of carbon fiber reinforced plastic, you must add the magical ingredient of resin to harden the fiber. If you’ve never worked with epoxy resin before, it is a gel-like substance that you will brush over the fiber, and once it hardens the fiber and resin will become a finished piece of carbon fiber reinforced plastic. It can be very messy & sticky, especially if you’ve never worked with it before, which is why mixing sticks, gloves, and special mixing containers are recommended, as well as a clean & adequate work-space that you are okay with getting dirty (do not try this in your living room).

Epoxy resin works in a pretty simple way – you have a resin and a hardener. The hardener (or sometimes referred to as a catalyst) is added to the resin in a pre-set ratio, such as two parts resin to one part hardener. Separately, both the resin & hardener are gel-like liquids, but once the resin & hardener have been mixed together, a chemical reaction will occur and the liquids will become a solid. Sometimes, particularly with fast-drying resins, a noticeable amount of heat will be generated during this exothermic reaction, so be sure to read the safety & warning labels of all of the products you are using before mixing the resin & hardener. You generally have a certain window of time before the chemical reaction completes and the resin becomes too solid to work with (known as the “working time” of a resin), which means that once you have mixed the resin & hardener together you need to work efficiently, and only mix small batches of resin at a time that you can fully use up within the resin’s stated working time.

Generally the working time of a resin, and the time for it to fully cure are vastly different. You may only have 20 minutes of working time before the resin is too hard to work with anymore, but it may take a few days for the resin to fully cure and the chemical reactions to fully complete before you can begin working with the piece again – this would be called the “curing time.” You can accelerate the curing time applying moderate heat to the resin, but it’s important to allow the resin to fully cure before moving to the next stage. Another important note is that once the resin has fully cured, no more resin should be added to the part – the cured resin and the uncured resin will be unable to bond correctly, and the second layer of resin will be limited in its performance and may peel off or decompose rather quickly. Any and all resin you intend to add to a part should be done before the resin has been able to cure completely.

Choosing a Resin

There are several commonly used resins you can choose from – all of which have their pros and cons. At oCarbon and DIYCarbon all kits & parts we sell use professional grade UV treated epoxy resins as we have found this to be the best for automotive applications in terms of strength and minimizing yellowing & fading to producing a high quality finished product that will last a very long time.

One common misconception that is perpetuated by those who make low-cost carbon fiber parts is that certain resins will “never yellow or fade.” This is 100% false – all resins will fade or yellow when exposed to ultra-violet (UV) light, as the UV light breaks the chemical bonds in the resin’s molecules.  The speed & severity of yellowing/fading can be minimized substantially by which resin you choose, as well as introducing UV inhibiting chemicals into the resin to help minimize UV damage. Even OEM carbon fiber parts from manufacturers such as Lamborghini, Pagani, Ferrari or Audi will yellow or fade over time, especially parts exposed to extreme heat such as engine covers, or parts exposed to a lot of sunlight such as roofs and hoods in hot climates such as deserts.

Resin choice is just as important as your choice in raw carbon fiber – it takes both pieces to make a finished part after all. There are three categories of commonly used resins – Polyester Resin (PER), Vinylester Resin (VER), and Epoxy Resin. Within each category there are also varying levels of quality at corresponding levels of price, but for now we’ll focus purely on the types of resin to choose from.

Polyester Resin (PER)

Inexpensive, but the lowest in strength & performance – Polyester Resin (PER) is the most commonly used resin in mass-production due to its low cost and adjustable cure time. Polyester is very resistant to UV light and can be used in applications that are subjected to prolonged exposure to direct sunlight. PER is mixed with a catalyst/hardner called MEKP (methyl ethyl keytone peroxide), and you can adjust the ratio of polyester resin to MEKP to alter the working & cure times, depending on your needs.

The main drawback of PER is its low strength – as PER cures, it shrinks considerably, compromising the strength of the finished product. It is generally not recommended to use it with high-performance fabrics such as carbon fiber. It is also very sticky & tacky when working with it, which can make it unusually messy for novices. A final drawback is that PER releases higher levels of Volatile Organic Compounds (VOCs) which can be harmful to your health & respitory system, so be sure to work in a well ventilated area wearing a mask if you choose to use PER as your resin.

Vinylester Resin (VER)

Middle of the pack – VER is a little more expensive than Polyester Resin with improvements in strength & chemical properties, but not as strong as Epoxy Resin. VER is best described as an “upgraded version of PER” as you will achieve slight increases in strength & performance but otherwise many of the properties are the same (they both use MEKP as a hardener, for instance). Because of this, it is used in projects where PER would otherwise be used, but the builder once a slightly more strong product, such as boat hulls and storage tanks. Like PER, Vinylester also shrinks considerably during curing, causing decreases in strength, and VER also emits VOCs which may be harmful to your health.

Epoxy Resin

The highest cost & the highest quality – unlike PER and VER, the hardener used with epoxy resin actually bonds the resin & hardener together. This creates superior strength although it requires very precise measuring of resin to hardener, unlike PER and VER where you can mix resin to hardener in different ratios. Epoxy resin has much lower amounts of shrinkage while curing, creating superior strength over PER and VER. Because of its superior strength, Epoxy Resin is generally recommended for any high performance application such as aircraft, automotive, or structural uses. Because carbon fiber is a high performance (and exotic) fabric, it is generally recommended that you use epoxy resin with carbon fiber – using PER or VER with carbon fiber is like filling up your “premium fuel only” car with 87 or 89 octane – it can be done, but if you care about performance, it isn’t recommended.

Epoxy Resins tend to have very low VOC emissions, making them more safe to work with, especially for the hobbyist who may not have the proper safety equipment for PER or VER otherwise. The one disadvantage of epoxy resins that is worth mentioning is that they are more vulnerable to UV light damage relative to PER or VER, and require additional protection methods such as mixing in UV treatments to help prevent premature yellowing or fading. All kits & parts sold through DIYCarbon & oCarbon have UV inhibitors mixed in.

Part 1 Conclusion

In part 1 of our guide we have given you an overview of what makes carbon fiber unique, the basics of how a finished piece of carbon fiber reinforced plastic (CFRP) is produced, and the various choices in carbon fiber fabric and resins that exist. Both DIYCarbon & oCarbon allow you to pick the carbon fiber fabric of your choice according to weave pattern, weight, and other choices, although for all carbon fiber applications we recommend using epoxy resin for its superior strength and quality. Now that we have given you the necessary information to pick the right materials, it is time to discuss the basics of how to produce carbon fiber.

Part 1 Definitions/Glossary:

·         Raw Carbon Fiber – carbon fiber fabric before an epoxy resin is applied

·         Carbon Fiber Reinforced Plastics – carbon fiber after epoxy resin has been applied & hardened

·         Composite Materials – any product made of two or more different materials, such as raw carbon fiber and epoxy resin

·         Yarn – to the naked eye, the yarn looks like one single strand of fiber, although it is really several thousand fibers all twisted together to form one yarn. Also known as a pic, or bundle.

·         Weave weight – how much 1 square yard of carbon fiber fabric weighs, in ounces.

·         Weave size – how many fibers are in one yarn.

·         Weave pattern – the pattern in which yarns are woven together, such as a plain weave (1×1), a twill weave (2×2), or a harness satin (HS) weave (anythingx1).

Tuesday, March 6, 2012

Another review of how to vacuum bag carbon fiber, fiberglass, or kevlar

A lot of people ask us how do you make carbon fiber parts.
Here is a great video showing the process to vacuum bagging carbon fiber hoods, trunks, or anything else. This process is also useful for other composite materials such as fiber glass, kevlar, or others. Vacuum bagging produces a light product, as the breather material soaks up excess resin. The result is not only a light part, but one that is stronger as well. This technique also prevents air bubbles from forming in the finished product. Most professional construction of carbon fiber components use a vacuum bagging method.