Resin Infusion for headlight housings

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#1

I have been working for over a year now designing a headlight system for c4 corvettes. I have finished my design and now I am trying to work out the production process. Considering the multiple contours of my parts, I have leaned toward resin infusion to produce the housings. I have been doing some trial runs(just the infusion) with fiberglass mat, fiberglass cloth and carbon cloth. Here is a picture of the part I am trying to produce.

As you can see from the picture above, the part is quite complex, which makes hand layup impractical. I am looking for any good advice for making this part. Here is a picture of the mold design(my current molds are a little more refined).

The mold is four main sections with two small tabs that attach on the opposite side to create a mounting flange. I am also looking for good ideas to seal the mold cracks for the infusion process.

Where I’m at:
So far I have made a couple test runs with the resin infusion. Right now I am using uscomposites 635fast with fiberglass and carbon for testing. I have not been able to complete a successful test run so far. I have set up a flat surface with several layers of different cloths in a row to test the process. When I start the vacuum pump(thomas dual positive displacement) the bag seals tight with no apparent leaks. The 635 resin is at 80F. I open the resin inlet line and resin flows quickly into the bag. The fiberglass mat around the inlet line quickly saturates and then the process slows. The resin continues to fill the bag but does not flow through the part. My first suspicion is insufficient vacuum. After that I think the mat is not good enough flow media(but I have seen successful runs with just mat). Where is the best place to start troubleshooting. Could my pump be inadequate. Any past experience, good suggestions would be appreciated.

#2

Without discouraging you, you need a lot to learn. But that is no problem. You are at the right place.

-1. Do you have a picture of the part from the rear / bottom?

-2. Split moulds are a pig to infuse. Getting the split to be completely airtight is difficult. Enveloping the whole could be an option. Making a RTM double sided mould with inserts for the headlight cones could be a viable option as well.

-3. Some laminates are permeable enough to infuse, but many are not. Are your products weight-critical?
To overcome the permeability issue, you would need to use infusion mesh. However, the shape of the product will make it very difficult to use. I am thinking 1 or 2 layers of carbon, and a layer of drapable RTM mat here (Scott & Fyfe Polymat High Flow). Perhaps with VE instead of epoxy.

-4. Without knowing how much vacuum you were able to pull, it is really, really difficult to tell whether it is enough.

#3

1: if the resin is filling the BAG, but not the PART, leads me to think your mold is BELOW the resin bucket. If so, place the resin bucket below the part so it doesn’t siphon into the bag!!!
2: along with #1: not all mat is a good flow, there are tons of mats out there. Get some distro media.
4: I have never done split molds, but some people use clay, some use a thin rubber between the mold pieces to seal, I can suggest PVA in the crack, and if you can scrap off the excess. Heck if you are going to be post finishing the parts, you can just put a layer of thin tape, like flashbreaker I. release coat that as well :slight_smile: Another idea is to clean up the back side, and add tackytape to the seam. Might get resin in the cracks, but that can be sanded smooth…but at least the mold will be sealed.

Heck, maybe wax one side REAL well, bolt together, smear silicone over the other side, and squeegie it smooth…then you will have a slight gasket on one side?
3: as for vacuum, get a gauge. Infusion can work with lower vacuum levels, but will be slow, but can be done.

#4

Thanks for the fast replies. Here are pictures of the inside of the current molds and the backside pieces for creating flanges.



I really like the silicone idea. I think I will try waxing both sides of the mold flanges and then run a bead of silicone between. It should be pretty easy to wipe up the excess after the mold is bolted together. I can even use 1 hr clear silicone II which is fairly cheap. If that doesn’t give a good seal, nothing will.

I have flow media and a vacuum gage on order. The flow media should be here Thursday and the vacuum gage should get here next week. I think vacuum may be the primary issue since the resin flows pretty quick and then slows after an inch or two. I will also do trials with the flow media in different positions.

I am using a thomas vacuum pump that was rated at 28"hg but I have also seen the more conservative 24"hg for a similar pump. What is a good, not ridiculously expensive vacuum pump that pulls close to 30"hg. I will wait until after testing with the gage and ruling out other causes, but I would like to get some direction in case I do need to get a better pump.

#5

I got my vacuum gage and my other materials today. I tested the vacuum and it was 28-29"hg which was more than expected, so the pump is not an issue. I made another test run with the green flow media and various layers of carbon and fiberglass. The epoxy temp was 85F and I used stretchlon 200 for the bag. The resin flowed about 8in in less than 3 minutes so it would appear the major issue was distribution of vacuum under the bag, which the flow media seems to have corrected. I will now move on to testing the more complex part pictured above to work out any issues. I am thinking that I will distribute flow media 2in past the part in all directions to maximize vacuum and then make my resin inlet near the center. I will attempt to make a video of the process or at least take a couple pictures for clarity.

I have seen several demonstrations for gel coat just using microballoons or colloidal silica with epoxy. Has anyone tried this and what is the advantage/disadvantage compared to some of the epoxy gel coats on the market. What are some good options for epoxy gel coat. I am asking because these parts will need to be painted for final finish.

#6

If you are painting clear, then do not use any gelcoat.

If you are painting in colour, you could mix some talcum in an epoxy resin, or a bit of aerosil. I would not recommend microballoons, unless you are going to shape the part afterwards considerably. When painting you will find out why. (cratering of the paint on the microballoons)

The distro medium is not about equalising vacuum. The vacuum will find its way anyhow, air is a thin material.
It is all about bringing resin towards where you want it.

Point infusions towards the perimeter are very slow, and very dependant on inlet size (Darcy’s law). So keep that in mind when experimenting. An infusion from the perimeter inwards is way faster. (up to 16 times). However, the epoxy needs to be able to saturate the cloth, so slow can be good.

#7

Are these purley aire vents

#8

Here is what the headlight system looks like in the car.

I did another test with the full housings today(2 layers 11oz carbon; 1 layer 19oz carbon; 1 layer 12oz 45/45 fiberglass; 1 layer fiberglass mat). I used standard peel ply, green flow mesh and stretchlon 200. UScomposites635 at about 70F with fast hardener. Flow was pretty fast but I did have some issues with holes forming in the bag(That was a prime reason many people have given for going to the thicker stretchlon 700). The silicone seemed to work pretty well for sealing the mold sections. The mounting tabs did not infuse, but that could have been caused by the vacuum leaks. I will probably vary the infusion media and add some spiral wrap next time to see if I can get the mounting tabs to infuse. Last resort is separate production and then secondary bonding(not much experience with this so I am curious if anyone else has some proven methods).

Since carbon is pretty expensive, I am planning on making further housings with mainly fiberglass. I have had good results with 45/45/mat 12oz and I’m thinking of trying 45/45/mat 17-20oz to reduce the number of layers necessary. The goal is to get the process down to one hour per housing production time. 90 percent of the housings will be painted, so a good paintable gell coat is crucial.

I also made a vacuum cannister to mount my gage and an overflow catch out of 1.5" pvc. It is working great so far and it definitely limits cycle time on my pump. Pump is pulling around 29"hg so working great.

#9

Here is the infused headlight shell I made the other day. As you can see there are several void areas. Most of the voids I believe were caused by vacuum loss(holes in the stretchlon 200). I think I will try stretchlon 800 next time with more pleats next time since it is less prone to holes.

I will probably utilize secondary bonding next time for the mounting tabs. They add too much complexity to the infusion so I will probably make them separately. The 12oz 45/45 is very thin so I am considering the use of 17-20oz 45/45/mat for faster buildup. 12oz 45/45/mat worked pretty well for me so I am assuming the 17-20oz will still be pretty pliable.

#10

Its a shame thers a negative draft because these could be done with on mold otherwise but look good get them clear coated

#11

I ordered more supplies: 17oz 45/45/mat, 635 fast epoxy, a different core mat, several epoxy pigments, aluminum powder, aerosil cabosil. The fumed silica I have seems to be working well for making gel coat, so I am moving on to using the pigments and will maybe try some aluminum powder for the molds. Any experience in this area would be helpful.

I will be building another plug and then several more molds over the next couple weeks, so it will be a while before my next infusion run.

#12

Finally building molds again, so I should be due for another infusion run in about 2 weeks. I have made several test runs with very good results. I have tested 20oz carbon, 17oz 45/45/mat glass, and 2 types of coremat. So far my preference is 2 layers of 20oz carbon with one layer of nida core mat. Fairly strong and very light weight. I need 4 layers of the 17oz 45/45/mat glass with a layer of nida core mat to give similar stiffness. I may experiment a little with thicker nida core since two layers works pretty well. Has anyone had much experience with nida core over time. I just want to know if anyone has had delamination issues.

Also, I am using the green flow media right now and it is a little fast for full wetout. What does everyone else use.

#13

Green or blue for me and if its fast slow the infusion down

#14

Question…

What hgt resin are you using, some of those halogen headlights get up to a surface temperature in excess of 150f, with the internals above 400f.