How I took my first steps in making a carbon fiber part
My name is Pavel. I am in the business of making carbon fiber or, as they call it, carbon fiber, and I am happy to share my experiences.
I made my first attempts to master this technology about a year and a half ago. A lot of time has passed since then and it is even more pleasant to remember the first steps. In this post I will tell you about my first educational self-made project of a part from composite of epoxy resin and basalt fiber.
The idea to do with carbon fiber has arisen earlier, about three years ago. I nurtured it for a long time and at some moment decided. The first month of my own attempts and watching videos on youtube led to a lot of spent material, resin, fabrics, harnesses, etc. It turned out that even a carbon fiber plate by vacuum infusion is not so easy to make. After a little torture, I realized that it would be nice to find professionals to learn from this experience. I found the right guys, got to know each other and plunged myself into the learning process. I never got such a buzz out of university. Two months had passed, the alphabet was learned, the lectures were written down, the lab work was done and I set sail on my own. By that time I had already found my first customer. And before that everything was rosy. Then the battle began, and this will be discussed below.
My first project – continuation of the study, but in the field conditions. I agreed to make a part out of composite to reduce its weight. The part went to a mobile laser machine. The machine was a suitcase on wheels and was supposed to be constantly transported between work sites. By the way, it is used for laser surfacing of molds; a steel matrix edge was worn out – we brought a laser, set it up, adjusted and surfaced the worn-out area with a special wire.
Let’s get back to the process.
The part is a plate with complex grooves and selections, where the optics of the laser machine is set.
To make something out of carbon, you first have to make a matrix – the reverse of the original surface of the part. And then to put the carbon fabric on the matrix and impregnate it with resin.
Опишу создание матрицы коротко и скажу лишь, что работа шла три этапа: мастер-модель из пенопласта -> черновая матрица -> черновая деталь -> the working matrix.
This is what the working die looked like.
It is a fiberglass matrix with a flange thickness of 5-6 mm and a ground layer of gelcoat on the outside.
To make a part using this die, you must first prepare the patterns. Such a complex shape does not allow you to put the carbon fabric in one piece. To qualitatively match the geometry, you need to prepare a large number of small pieces of fabric – the patterns. In total, I made about 300 cutouts – that’s about 60 pieces per layer, and there were 5 layers. By the way, for the first time I used basalt fabric instead of carbon fabric. It’s easier, and the piece itself was for painting, so the finesse of the carbon pattern was unnecessary.
This is what the basalt fabric looked like with a layer of glue and marked patterns.
Yes, there were a lot of them, and even more work.
When all 300 cutouts were prepared, cut and fitted, it was time to lay and glue them onto the matrix. But first the die had to be cleaned of dirt, grease stains, and other things.
Then, the cleaned matrix is coated with a special release agent – wax. This is to ensure that the part is not permanently glued to the die, but can be carefully removed from it without damage. I used a liquid wax based on PVA. The wax is applied in layers of 3 to 5, depending on the brand and type.
Then I began arranging the cutouts. Layer by layer, in a certain order, I glued small pieces of fabric to the matrix, until it was all covered with a basalt shell.
By the way, the glue was also a special aerosol for infusion.
Although the patterns were made using a template, I still had to check each layer and adjust it a bit in place.
In the previous photo, you can see how the patterns come off. No matter how much glue you put on the last layer, you are sure to lose some of the patterns. This directly affects the quality of the piece. To avoid this, during impregnation a vacuum bag is assembled around the part – a clever layered structure for feeding and distributing epoxy, pumping out air, creating a reliable hold.
The bag is assembled from several layers: sacrificial fabric, which serves as a buffer for the resin and regulates the impregnation rate; perforated film for quick separation of technical layers from the part body; conductive mesh – fast resin delivery over the surface; trunk and spiral tubing to supply resin from the outside and pump air out of the bag. This entire pie is covered with vacuum film, which is secured and sealed with a sealing harness over the matrix flange.
Before assembling the bag, you need to think carefully about the scheme of feeding and pumping resin: how many feed points, how to draw the feed lines, where to make a fast course of resin, and where it is necessary to slow down for a guaranteed impregnation. It’s a terribly fascinating process, both to plan and to watch the resin flow. I let the resin run from the top points of the part, and I positioned the pumping lines from the flanges of the die.
When the bag is assembled, it should be pumped out and checked for leaks. It is not always possible to assemble an airtight bag on the first try. This time I even had to redo the bag, as the first bag burst with a sharp fiberglass needle from the back of the die. This is what the assembled and pumped bag looks like, ready to be impregnated with epoxy.
And this is how it looks while the resin is flowing.
The impregnation process can go from a dozen minutes to several hours. I impregnated two parts in parallel and the infusion took a little over an hour.
You have to watch the process to see when to speed up the resin flow, when to slow it down, and when to shut it off to add more resin to the system.
Keeps you in suspense until the last minute, because you don’t know if the whole part has time to soak in before the resin thickens.
The whole thing looks like a tambourine (marker) dance. But here all the light areas have darkened, the resin has shown up in the tubes on the way to the pump, which means you can breathe out and shut off the resin supply. After that we leave the part to dry for at least a day and leave with a pleasant feeling and anticipation.
After a couple of days I take apart the bag and take out the part. For the first disassembly I spent a huge amount of time – probably a whole day of swearing and fussing. I had a lot of trouble getting the intricately shaped part out, but when I did, I was smiling ear to ear.
This is what it looked like after disassembly and first fitting with the laser nodes.
Then I had to mill grooves, holes for buttons and magnets, and trim the contour. This is a separate story with milling tooling, basing and positioning on the part.
Then I had to mill grooves, holes for buttons and magnets, and trim the contour. This is a separate story with milling tooling, basing and positioning on the part.
Weighted sighting:
The final glued part before painting with the laser assembly looked like this.
And the final version after painting.
In the end, the training project took about 8 months, a decent amount of money for materials, tools, equipment, and my work. I immediately treated it as an investment and did not worry too much. I managed to save weight from 10 kg to 1.2 kg. It is obvious that to make such a part from composites by vacuum infusion method is absolutely inexpedient in terms of labor intensity and cost. The experience is invaluable. To make a part of such complexity from the first time is a great luck and not less big work. I haven’t taken on such large-scale stuff since, but I use the experience of those months every day.
As the saying goes, if you’re willing to do something for free and at night, maybe this is the one.
Instructions for the carbon lamination trial kit
We recommend setting up the process on the sample machines before doing the lamination on the specimen part, and afterwards, get to work.
All work with this kit can be divided into several steps, which will be described in more detail below:
Working with epoxy compound is recommended at 20-25 degrees for optimum viscosity of the epoxy compound. A piece of carbon cloth should be prepared before applying and diluting the resin. The size of the fabric should be 3-5 cm larger than the surface of the part to be covered. As it is easy to break the uniformity of carbon fabric weaving, it is recommended to prepare a template from paper, try it on and then proceed to cutting the carbon fabric.
The curing agent and epoxy resin must be mixed separately before mixing (resin for at least half an hour to an hour, curing agent for at least 10 minutes).
Transparent, low viscosity epoxy L – designed for work with fiberglass, carbon fiber, aramid fiber (kevlar). Also ideal for bonding wood, metal, ceramics, plastics, etc. Suitable for manual lamination, pressure and vacuum forming. New quality: nonylphenol free!
The resin easily impregnates the fiber, contains no solvents or fillers. It has high static and dynamic strength.
Technological process: all common methods of production: manual lamination, vacuum forming, compression.
Suitable for all types of reinforcement materials: carbon, glass fabrics, aramid fabrics (Kevlar), basalt fabrics, etc.
The heat resistance ranges from 60°C (using S, L hardener) up to 130°C (using EPH 161 hardener and post hardening process).
– L hardener. 40 minute viability, resin: hardener mixing ratio 100: 40 by weight, 100:45 by volume.
– EPH 161 Hardener. 90 minutes Viability, resin: hardener mixing ratio 100: 25 by weight.
The examination showed that the system “epoxy L + hardener S”, “epoxy L + hardener L”, “epoxy L + hardener EPH500” is not cytotoxic (does not destroy the cell structure), this is important when used for medical purposes.
The well-proven R&G epoxy L in combination with GL 2 hardener has been approved by Germanische Lloyd for the construction of boats and wind turbine blades
When using blue epoxy with hardener, mixing proportions: 100:50 by weight, 100:57 by volume.
Washing. Before starting work, wash in water with dishwashing detergent and rinse thoroughly in hard-to-reach places with a sponge or unnecessary toothbrush.
Degreasing. It is necessary to degrease the surface of the product, which may be contaminated with invisible to the human eye dirt, interfering with the interaction of the plastic and the epoxy compound. To do this, use degreaser and a cloth. Put the degreaser on the cloth and carefully wipe the whole product, paying special attention to the edges and hard-to-reach places (if any).
Sanding the product. We create a roughness (risk) on the surface of the product for better adhesion of epoxy materials. For this purpose we use sandpaper №120. Particular attention is paid to the edges and hard-to-reach places. The entire surface of the product must be thoroughly scrubbed.
Processing of joints. It is necessary to cover the joints of the part that are in contact with other parts with painter’s tape so that after finishing the epoxy layers it is easy to remove the remains of the carbon fiber from the joints and insert the part into the factory seating.
Product mount. It is necessary to come up with a fastener for the product to be worked on so that the surfaces of the product can be handled comfortably. During the epoxy compounding process, the product must be fixed still. The fastener is selected based on the product being worked on. It can be a regular pencil glued with superglue to the inside of the workpiece or a painter’s tape glued with an angle to the inside of the workpiece.
Re-degrease the product. Use the degreaser and the degreaser cloth from the kit. Apply the degreaser to the cloth and carefully wipe the entire piece, paying special attention to edges and hard-to-reach places.
To stir the transparent compound without bubbles, we recommend assembling and cutting a “mixer” from the mixer wand and nylon ties (included in the kit). If the wand has no corners in the cut (round cross-section), it is necessary to give the wand a square cross-sectional shape.
The first layer of the mixture has the function of gluing the carbon fabric to the part and dyeing the part black so that the light areas of the part do not show through the fabric.
If the color of the coated surface is not black, it is recommended to use tinting agent. The amount is calculated based on the color of the surface – from 1 to 3% of the epoxy mixture mass. First mix the tint with the hardener not in a plastic cup and only then add the already tinted hardener to the resin and stir it up. Example: you add (20 g L resin + 8 g L hardener) * 1% = 0.28 g of tint) to 8 g of hardener.
In a plastic cup we mix the resin with the colored hardener in the proportions by weight, for L resin and L hardener 100:40, for L resin and EPH161 hardener 100:25. Mix thoroughly with a flat spatula until the mixture is uniform. Allow mixture to stand for 2-3 minutes.
Apply the composition to the surface evenly, covering all areas of the surface of the part with a non-greasy layer, avoiding lapping and drips.
Drying of the adhesive composition on the rip is 2-3 hours. “On the go” means that the compound is already in a state of gel, when you touch it does not stain, but the surface of the product is still very sticky and remains a trace on the surface after touching. It is important not to miss this point.
When the adhesive layer reaches the “sticky” state, it is necessary to apply a cloth and roll it firmly with a roller. If the roller is stained with a sticky substance – rinse with solvent. Especially pay attention to bends, corners, corners, because after drying you will not be able to glue the fabric.
Cut the glued carbon fabric, leaving 2 to 3 centimeters to hang down from the edges of the piece. Treat the edges of the carbon fabric with painter’s tape so that the threads do not stick out.
You can start soaking immediately after gluing or if the piece has difficult edges, let it dry for 20-24 hours and only then proceed with impregnation.
For better removal of bubbles from the epoxy compound it is recommended to work in a room with a temperature of +24 degrees Celsius, or slightly warm the resin before mixing with a hair dryer (not a building one, but a household one), or in a water bath.
Mix the compound. A homemade device is used to obtain a bubble-free compound (see “preparation”).
The mixture in the cup should completely cover the “mixer” (about 30 ml of compound). At medium speed with a screwdriver stir the mixture to a uniform mass (1-2 minutes per side). In case of uneven mixing the composition will not polymerize and the parts will be ruined.
Apply the composition on the cloth, spread it with a brush. The brush should not be “dry”. The layer on the fabric should be greasy, abundant, as the material absorbs the epoxy composition.
When the condition of the previous layer reaches the state “on the peel” it is necessary to apply the next layer. If there are bubbles, you can slightly heat the surface of the composition with a hairdryer. Remove larger bubbles with a toothpick or stick.
If the moment is missed, wait until the composition is completely dry (24 hours), degrease with a cloth with degreaser, mat with a sponge until a completely uniform matte surface, degrease with a cloth with degreaser. After that, you can apply coats again.
The number of layers depends on your taste and to give a “lens” effect to the product. Epoxy compositions are applied in 3-6 words. After obtaining an even surface layer we proceed to the processing of the edges.
Treat the surface and the edges of the part to produce only after the epoxy dries completely (24 hours):
Before applying varnish, if you do touch the product, it must be degreased. Carefully read the can varnish instructions. Shake the bottle with varnish for 3 minutes before work. At a distance of 20-25 cm from the part lacquer is applied, beginning with the ends of 2-3 layers. The first layer we apply a light dusting. The interlayer exposure time is 5-10 minutes. Particular attention is paid to the edges and hard-to-reach places. Do not paint over the part to avoid its stains. Drying time at room temperature is 12 hours. The ends of the composite can be tinted with a black permanent marker.
