This is the next phase of the University of Central Florida 2007 ASME Human Powered Vehicle Team's fairing construction. We will be using the "negative" tools we made the previous weekend to create parts that will resemble the plug we started with.
Thanks to Lockheed Martin Missile and Fire Control....
Video Large Scale Mold Making - Part 1
Video Mixing Polyester Resin
Photo: 2006 HPV Fairing next to 2007 Fairing (not yet complete)
Step 1: Planning
Take your glass and lay it out over your tool and see exactly how much you need. Then, cut your fiber for each necessary layer. For us - this required:
8 10' X 36" Sheets
8 6' X 11" Strips
8 6' X 16" Strips
Cut to fit Pieces of CoreMat
Remember, we have two tools to make one complete part (in two halves). So, this material is enough to do four layers of glass with core (3 glass layers, Core, 1 Glass Layer).
Step 2: Planning II
Next, we make the bag for vacuuming. This requires special materials - mainly the bag material and the vacuum tape used to make the bag from pieces. Making a bag requires that your surface is clean (to prevent puncture) and you must not walk, kneel or put excessive pressure on your bag as this can cause punctures.
As for making the bag - that deserves it's own instructable. I may not have enough to document it by itself - so it's a good idea to have a mentor to show your the ropes :D
Step 3: Tool Prep
1. Sand flange and plug interior - remove all PVA remnants from tooling
2. Wax flange and plug interior - just as we did when tooling
3. Spray on PVA - just like when tooling
4. Create a Resin Mixing Stand ready with pots, brushes, mixing sticks, gloves, etc.
It is not 100% necessary, however, building a support stand can be beneficial to your back. Some scrap lumber - even recycled from your tooling stand) cut to support the tool by the flange is all that is needed. That would be step 0 on this list.
You may already be saying - "But this is just like making a tool." You'd be right - except we're using woven glass, epoxy resin, and a core material.
Step 4: Begin Layup - GelCoat
1. Add desired amount of resin to a pot
2. Mix in Cabosil until it holds peaks
3. Add epoxy hardener
Apply gently with a brush. Remember, once you add hardener - the clock is ticking. You need to go from mixed to bagged ASAP.
The resin/silica is thixotropic - that is, when you apply pressure to it, it becomes thinner and easier to spread. This coating will provide a glass smooth like finish (assuming your tool is smooth too).
Once your coat is down -- apply a coat of regular resin.
Step 5: Layup
Overlapping should be about an inch. For continuity and strength, try to vary where the overlap occurs on each layer.
When you first lay down a sheet of fiber, use your hands and press it into the free resin below - manipulate the fiber cloth to get it in the desired position. Add additional resin as necessary with a brush. Finally, use squeegees to get large air bubbles out. Small bubbles (less than .5 inches) are nothing to worry about as the vacuum bag will take care of this.
Step 6: Layup II - Jobs
1. Resin Mixer
3. Fiber Layer (should be the same person/people that cut the glass)
4. Brush Cleaner (more on that later)
5. Resin Apply'erer
Some of these jobs can be shared - for instance, the person mixing resin can clean brushes in between batches and the person applying resin can help lay down fiber as needed. And Everyone (except the mixer) can help tease and manipulate the fiber into position when it goes down.
On the subject of brush cleaning. Clean your brushes and squeegees frequently as old resin will start curing before you're finished.
Step 7: Layup III Core
CoreMat soaks up resin and expands a bit. When it has been fully impregnated with resin, it turns a deep yellow color. Too much manipulation when coated with resin will damage the mat (much like rubbing wet paper towels).
To apply this type of core. Simple drench the area you will apply the core to with resin. Stick on the core and work in more resin until it's completely soaked.
Some other types of Core:
2. Honeycomb (of many types including paper, aluminum, etc.)
3. Steel or Aluminum (good for super strong mounting points)
5. K-mat (a scored foam with fiberglass back)
Step 8: Peel Off Bag Release and Breather
Roll out this plastic film to cover every square inch. Folds are nothing to worry about - just get everything covered. If you need to overlap pieces due to size - give yourself about six inches.
Now unroll your breather material. Your breather should NOT have any folds in it - if you need to, use tape to keep it in place. If you need to use more than once piece to cover the entire tool - you can overlap, just keep it to a minimum.
Finally, make sure some breather goes well over the flange - this will provide a location to mount the vacuum port and valve.
Step 9: Bagging
Cut a hole for your port/valve in a location that will have breather. At all times during this process, make sure your breather stays in position.
Begin applying vacuum. Making sure that the bag will not "bridge" any curves.
Bridging is what happens when there is not enough bag material to match a curve - so the bag jumps over the curve creating a high stress point on the curve and a location for resin to pool (bad).
To prevent bridging, create a location where the bag overlaps and creates a little envelope - as the vacuum presses down, it will pull this envelope apart.
NEVER allow the tape to "feel" the full vacuum. Be sure there's enough bag material near the tape to "suck down" on.
Step 10: Finishing Up
Too much resin is also a problem. At no time should resin enter the vacuum lines, valve etc. That, would be terrible.
Finally - the worst thing you can do is apply vacuum - realize you have a bridge and the release vacuum. This removes resin, adds air and then attempts to suck air out again with resin on top. So go slowly, don't apply vacuum all at once.
We flipped our tool so it would cure with minimal warping. Cure time is at least 16 hours with our resin.
Step 11: Putting Them Together
Gray spray paint marks where windows will be cut and formed out of PETG (similar to soda bottle plastic).