I made this custom intake tube for my Eclipse using a molding technique called "lost foam molding". Basiclly this is a one off mold were the "buck" or core is destroyed after the final piece is made. The foam is melted away with acetone.
I will start of by saying composite part making is very, very messy and time consuming and wasteful. It took me 3 weeks to make this one part. It maybe because I'm a novice at this but there is a lot of areas to cover and I did the best I could at taking pictures when I was covered in foam shavings and epoxy. I will try to explain everything they best I can and list everything out.
Supplies and why I used them:
Core- foam and spackle or some form of light filler.
Fiberglass (FG) cloth and sleeve material, Carbon Fiber (CF) sleeve material
Epoxy- I used West System 105,207 epoxy because its idiot proof when it comes to mixing and has a long pot life.
Sharpie pen- for layout
Packaging tape- preferable the clear 2" wide box tape, prevents the epoxy from sticking to the foam.
Release wax, PVA or some other release agent.- Added protection to prevent the epoxy from sticking to the tape.
Foam cutter- I bought my Hotwire cutter off Ebay for $20. There are plans on the internet to make your own. Razor knifes work but not as clean and easy as the hotwire.
1 roll of electrical tape or shrink wrap tape- used to compress final layup
Bleeder fabric- excess epoxy bleeds though this to the batting fabric.
Batting fabric- soaks up excess epoxy
Cardboard- for making templates
Good sharp scissors- I bought a $20 heavy duty pair at the local craft store, any good cloth shears will work and produce clean cuts in the fiberglass and CF.
Razor knife- trimming
Dremel tool with high speed abrasive wheels.
Mixing cups,paint brush's, stirrers, latex gloves, a GOOD paint/chemical style respirator, clean rags, 80,120,220,800,1200 grit sandpaper
I have been reading up on Composite (Fiberglass/ Carbon fiber) products, fabrication, and techniques for several months now and decided I was ready to make my first attempt. I wanted to produce something custom and unique. After moving things around in my engine bay I came up with a idea for a custom airbox that would draw air though a NACA style hood scoop.
First the core. The cheapest and best way I found to make a core was using high density blue house insulation foam. Its easy available at Lowe's or Home Depot and is cheap. Its easy to form with a hot wire foam cutter and sand paper. I first cut out a cardboard template of the shapes I wanted. since the air filter has a 4" hole and the coupler at the turbo inlet is 3" that is my stating point. The tube will start out with a 4" ID and neck down to 3"ID. I then used a "Hotwire" cutter to cut the shapes out of the foam. I then glued the pieces together with 3M spray adhesive. (note: This adhesive will eat away some of the foam if you spray it on too thick) NOTE: wear the respirator when cutting foam with hot wire cutter!!
I found it was best to cut the foam way over size to allow for shaping. After getting it to the desired shape. You can fill in area's with spackle or plaster. I used this because it is easy to apply doesn't react with the foam, easy to sand and doesn't cost much. I don't suggest BONDO because once its hard it hard to sand and if to think you will never get it out.
Next start sanding with 80 grit sand paper it cuts fast though the foam and produces a smooth surface. If you can sand it down to the shape you want without using any filler your better off than I was. If not use the filler to fill in voids or add shape were needed and sand again. The one big pain in the butt with the filler is that I took an overnight drying before I could sand it. One thing to note FG, CF does not like sharp corners and will not form to them without a fight and F-ing up the fabric weave. Make your shapes, surface transitions as smooth as possible for easy layup. Check and triple check to make sure you have clearance and everything lines up.
Once the plug is were you want it start taping it up using the clear package tape. Pay attention to the radius's and any sharp areas. Make sure you try to clean(vacuum cleaner, damp cloth) as much of the sanding dust as possible off the plug before taping, I found using the razor knife and a heat gun will help form the tape, but be careful the heat gun will melt the foam. Don't worry about lines or overlaps from the tape it will not be seen after layup.
I made aluminum pipe ends because I was worried the FG pipe would crush or break. I know think it was overkill but wanted the added insurance.
Have your plug on a stand that will allow you to gain access to all areas for wet-out.
Next comes the first layer of FG. Make a rough measurement of the length of sleeve needed. and then add about 7" to ether end. Have all of your pieces cut and ready in order for layup. ( this also When the sleeve expands it shortens and the weave will start to separate. You don't want to come up short here or you will have to scrap the whole thing.After fighting with the sleeve to get it to slip over the plug I came up with the bag condom. Take a CLEAN grocery bag, garbage bag and slip it over the plug to cover it all the way. Doing so covers up any shape edges and allows for a smooth surface for the material to slide over. I destroyed the first sleeve before I figured this out. After the sleeve is all the way on pull the bag off carefully to make sure it doesn't snag anywhere.
Next mix up your epoxy I used about 6 pumps of resin and hardener. Thats the great thing about the West epoxy its a 1 to 1 pump ratio, no measuring, just pump. If you can count you can mix the perfect ratio. The temperature will affect pot life ( the time before the epoxy starts to gel and harden). It was about 50 degree's in my garage and the pot lasted a good hour before it gelled.
With a clean paint brush start applying epoxy from the center towards the ends in a blotting application, heavily saturating the fabric with epoxy. brushing it on moves the weave around and separates it. You will have trouble with the sleeve lifting from the plug and bunching up in areas where bends are, will will address that later. Just get it as close as possible.
With strips of FG cloth maybe 3" wide lay on top of the weave at a 45 degree angle of the sleeve weave, this creates a cross axis matrix that adds strength to the part. I used 3 layers of FG 1 sleeve and 2 with strips of cloth. With the brush blot the cloth until you see the epoxy bleed though and throughly wet-out the fabric. You should not have to add any epoxy to the fabric just make sure everything is throughly wetted-out. You should have all areas covered and overhang from the FG sleeve and fabric.
Now with latex gloves on you may need to "massage" the fabric and epoxy to get it to stay in place and to insure that it is totally wetted out. Getting the sleeve to form to the plug and stay there was a real pain and took a lot of delicate handling.
Next apply the bleeder fabric, making sure all the plug is covered. Overlapping is a good idea. You do not want anything coming in contact with the wetted-out FG other than the bleeder fabric.
Next is the batting fabric. Same deal here cover all of the plug.
Now remember that roll of electrical tape? Remember me saying that the FG will lift from the plug? This is a poor man's vacuum bagging technique. Starting from the CENTER of the plug start wrapping the electrical tape around the plug with reasonable tension on the tape, don't over kill it. You want to move from the center out to prevent bunching of the fabric and to push the excess epoxy out and away from the fabric. This will prevent the fabric from lifting off the plug before the epoxy has a chance to harden by compressing it with the tape. Also by using the bleeder and batting fabric you are reducing weight and getting close to that ideal 1 to 1 resin to cloth ratio. I have a vacuum bagging setup but was worried that the fabric would bunch up after vacuum was applied, and I had never seen anyone Vacuum Bag a composite tube before.
More to come since I can only upload 10 pictures at a time............
And my editing sucks, more photos to come
