Pandemic Project - Learning a new skill?

This is really informative - thanks for sharing. Definitely bookmarking this...

I said in the last post that I next made parts for the E30, but I forgot that I did some testing using core materials before I started that. 

I had been reading about the advantages of adding core materials to composites and watching the math show that by adding even minimal core thickness the stiffness of the part jumped exponentially. With the flat panel I had made I saw that the 3 layers of carbon - even laid up in the 0*-90*-0* orientation that I used was still really REALLY flexible. This came as somewhat of a surprise to me because when I started working with composites I thought of every F1 crash that I've seen that leaves shards of sharp carbon bits all over a race track which in my mind told me that while carbon fiber is strong, it also is some what brittle. Turns out that depending on certain properties that you can control you can influence this somewhat.

Anyway, getting to the point... core material is a way to add stiffness by making the product thicker but without adding layer upon layer of carbon. Which may get prohibitively expensive, or heavy. So I went out searching for a core material that might add a little bit of thickness but keep the weight down AND still allow me to easily do vacuum infusion. If you start searching there are SOO many core materials to choose from; various materials, resin uptakes rates, flexibility, thickness, etc.

I finally settled on trying a product called Lantor Soric TF. This is not the choice for making the lightest possible parts because it absorbs a lot of resin, but it is readily available, isn't crazy expensive per yard, and acts as the infusion mesh when doing a vacuum infusion, so it was what I decided to test out. 

The pictures of the lay up process are almost identical to the regular vacuum infusion, except I left out putting the green infusion mesh over everything because the core will allow the resin to flow throughout the part. 

Then it was time to infuse. The bag held much better this time, there isn't a boat load of yellow tape trying to patch things up. I also decided to mark on the bag (kind of looks like a topographic map if you look closely enough)

 how far the resin front had made it every 2 minutes. Because I wasn't sure how the resin would move through the core material I wanted some data on how fast it went so if I was doing a larger piece using this core again I could choose a resin with enough pot-life to prevent it from gelling before the part was fully infused. You can see that resin really slows down the longer it needs to travel (lines get a lot closer to each other as time goes on) so making sure that there is enough pot life does become a worry on large parts.

I used a space heater to apply a little bit of heat to help the cure happen a bit faster and then 24 hours or so later I pulled the vacuum bag off and had this:

This I was really happy with, no dry spots, no spots that got stuck to the glass, perfect for my use! Oh and I used a spread tow fabric as the layer that will be seen instead of the typical 2x2 twill that is kind of synonymous with the carbon fiber look. 

In the interest of gathering data again I setup a very non scientific (but informative) comparison between a 3 layer carbon sheet and the 3 layer carbon sheet with the 2mm Soric core. Looking at the bends in each piece you can see how much stiffer the core material makes things. Core material is in the foreground, non-core is in the background. Both pieces were exactly the same size and layup, only difference here is the core material.

And because I needed to use the new sheet I had just made I decided to make a door card for one of the other V8 944's. So the red car in the background now has door cards that look like this:

And yes, brass hardware has been replaced by black - I only had brass in the right thread pitch at the time :-)

Any idea how much cost in materials you have in the door card(s), with the Doric core? 
 

Also what do you use to cut the carbon to fit the correct size for the door cards? Dremmel with a cut off wheel? 

In reply to Somebeach (Forum Supporter) :

I would say that the carbon, core, and resin are about $200 worth of materials, although resin has gotten a lot more expensive lately so this might be a low estimate. This doesn't include all of the consumables that I used to vacuum bag though (peel ply, bagging tape, infusion mesh, tubes, mixing cups, etc, etc.)

I use a dremel with a cut off wheel. It creates a lot of dust that is carcinogenic and also conducts electricity so you have to be careful with your lungs and your tools. 

I've tried an oscillating tool as well, it creates less dust but I didn't feel like I had the same control in making cuts so I just keep using the dremel

In reply to alpinecoupe :

Thanks!

While I was messing around with learning infusion I was trying to make a mold of an extra E30 trunk lid that I had laying around. The current one that is on the race car was pretty trashed (drill through in multiple spots, had a nascar style spoiler haphazardly attached, etc) so I thought before we install this new metal one we had that I would try to make a mold and then make a carbon fiber version. 

So begins the mold making process again... As I mentioned before getting the surface of whatever you are making a mold of perfect is very necessary since the gel coat of the mold will pick up on the smallest of details. So I did some body filling/ sanding etc to get a good surface finish. Looked like this after I put the flange material on:

Seemed good to me, looked nice and glossy, put many layers of mold release wax on it, and I thought I was good to go!

Started in on the tooling gel coat and the 2nd layer of gel coat started to look like this as I was applying it...

Arrrgh... this is ruined.

In the composites world this is called "alligatoring" because when you pull the part from the mold the surface looks like alligator skin. There are soo many possible causes to this and I think that I committed many mold making sins on this one. But I am going to attribute this failure to 2 main things: 1. I used rattle can automotive clear coat to finish this mold. And while it looked really nice and shiny in that earlier picture the truth is that rattle can (1K) paints have a bad interaction with polyester based gel coats like I was using for this mold. And, 2. I applied my initial layer of gel coat way too thin. And as soon as I started in on the second coat the thing alligatored immediately.

So what to do? Start over.

Tooling gel coat is no joke, when it hardens it hardens, and when it reacts chemically with the paint layer that I had sprayed on my choices essentially were paint stripper or throwing the part away. I still wanted to make the mold so paint stripper it was!

I applied paint stripper a total of 7 times to the gel coat and eventually got to the point that I broke down the clear coat and paint underneath the gel coat and could scrape it off together. 

Ok, so now what? I have a trunk lid that has destroyed paint but I still want to make a mold of it. I know spray cans don't work so time to problem solve.

Thankfully I have a good friend, and fellow car enthusiast, that happens to work at a facility with a massive paint booth and access to epoxy primers. And he was willing to prime the trunk lid for me. After his handy work and then me putting a flange back on it looked like this:

Fingers crossed for gel coat...

First layer of gel coat on the newly primed and readied mold and we have success. 

Alright, this time we are good to go. Now it's just a whole bunch of fiberglass backing to make sure the mold is strong enough not to flex when I pull vacuum on it.

First a coat of fiberglass veil - this is very thin material that stops the "print through" of the chop strand mat into the gel coat. It also lays very easily so you can be sure that there are no air bubbles/ pockets between this layer and the gel coat layer. Air behind the gel coat means that it is more easily cracked at that location because there is nothing behind it to give it the strength that it needs. So veil first:

Then I laid up 5 or 6 layers of chop strand mat (CSM) fiberglass:

Once all the CSM was laid down I got nervous that perhaps I didn't make the mold quite thick enough. So I picked up a tip from the Throttle Stop Garage youtube channel that you can use pool noodles that have been cut in half on the mold and the fiberglass over them to provide extra strength. I couldn't find any pool noodles in my area because it was winter in Chicago but there was plenty of pipe insulation at my local big box store. I apparently didn't take a real good picture of this part of the mold but you can kind of see the black half tubes here beneath the fiberglass that I was about to wet out.

Let this fully cure for a long period of time, and then nervously came back to pop the trunk lid out... Nervously because let's be real, if this didn't work out I was out a significant amount of time and resources... plus I had already failed once before.

But thankfully the trunk lid popped out just fine. There were a couple of minor imperfections that had to be sanded out (I'll spare you the boring sanding pictures) and then the mold was polished up and ready to be chemically sealed.

Bruce Meyers used cardboard carpet tubes to add strength to the edge  under the "door area" of  his Manx buggy

In reply to californiamilleghia :

Absolutely! Other people making molds sometimes save and then use the cardboard tubes that the fiberglass and carbon fiber come shipped on. For the contours I needed around that 90-ish degree edge I went with the more malleable foam style. But I still keep all my tubes for future projects just in case.

Before I jumped into throwing carbon into the mold I read/ researched the different cores that I could use in the panel. I knew that I needed it to be stiff enough to hold a shape, and strong enough to withstand some higher speeds but instead of just doing many layers of carbon (which becomes expensive and can get heavy) I decided to use a foam core between the layers of carbon. As I talked about in an above post cores are great for exactly what properties I was looking for, but the Lantor Soric core I used before absorbs soo much resin that it would have really weighed the trunk lid down. So I was off to find a different material. 

Enter in the closed cell foam category. These are core materials that absorb very little (nearly no?) resin. So they add very little weight but still all the benefits of having the core. Divinycell is one brand that is particularly available here in the states, its a PVC based foam - they make various weights of foam and thicknesses so you can dial in the performance of the composite. I was talking with some people that make race car parts and they lead me to Rohacell, which is a PMI (polymethacrylimide) which allows it to have a higher heat tolerance, better chemical resistance, and if you use the "F" version then it takes up less resin than Divinycell, thus it's lighter.

I really wanted to try the Rohacell out, unfortunately, it is not as readily available in the states, because of this it's expensive. So I started looking to see if I could buy it in Europe/UK and have it shipped here. As it turned out buying a couple of sheets from a composites supplier in the UK and having it shipped here was LESS expensive than just buying divinycell foam from the regular suppliers I order from. I was a bit nervous when I sent the order that it was going to get held up in customs or take months and months to arrive but I place the order on a Friday and it was at my house in the middle of the US by Wednesday of the next week!

Now it was onto figuring out the layering of the carbon and the core. At first I thought I would do the core in one piece, and I read that you could use heat to mold the core but that just didn't work for me. I couldn't get the core to bend without crimping or cracking it. 

So I went with a 2 piece design, like this:

I also had purchased some spread tow carbon that I wanted to use as the outer most layer. I'd like to tell you about how much better the performance of this weave is (I do think there are benefits because it compresses flatter and should twist less) but honestly I used it because I think it looks cool.

In this picture I haven't really pushed the carbon into the mold very well, I did go back and make sure all of the edges were really tucked in and the carbon hadn't pulled away from the mold at all. If the carbon does pull away from the mold it is called "bridging" and leads to either a very resin rich area, or possibly an area where air bubbles get trapped so you get dry spots of fabric. Either way, things you want to avoid.

With the foam core because it doesn't absorb resin you have to drill holes in it so resin can flow through it and bond it to the layers of carbon. I drew a 2"x2" grid and drilled 1/8" holes at all the intersection points. And then started laying everything up. The layup for the trunk lid was Spread Tow Carbon-Twill weave carbon-Foam core-Twill weave carbon. So 3 complete layers of carbon, and a layer of foam core. I did get a recommendation to add an extra strip of carbon at the curve of the trunk lid so one place did get 4 layers, but not the whole thing.

Final layup:

Then it was on to the bagging and infusion. Next post!

Once all the layers of fabric were laid down then it was on to the consumables. Peel Ply (green silky fabric), then infusion mesh (green plastic that allows for resin to flow), then all the spiral tubing for the resin inlet line and vacuum outlet line. Then of course the vacuum bag.

Looked like this:

When running an infusion it seems that all the advice is to run the resin across the shortest path you can. So you can see I have the resin feed on the right hand side in this picture and the vacuum line set up on the left hand side, this allows the resin to run from the front to the back of the trunk lid as though it were on the car. I also extended the resin spiral tube and the vacuum spiral tube the full width of the trunk lid in the hope that the resin would evenly distribute as it ran.  

Once it was running it stayed pretty even:

Not perfectly even, the driver's side out paced the passenger but that isn't a problem at all. Eventually everything was fully wet out.

I did get a little worried when looking at the piece fully wet out because of those lighter spots that showed up in the exact pattern that I drilled the holes in the core material. Since I had never used this core before I wasn't sure at this point if those spots meant I was going to have a grid of dry spots or if things were going to be ok... A bit scary because if they are dry spots then this whole piece is trash.

Now it was time to leave the part to cure - I left it for 24 hours in my garage which is not temperature controlled - but due to the weather outside stayed at a very nice 80 degrees or so for the curing period. Ideally I would have been able to increase the temp while it was in the mold to cure it, or move it into the sun but there was no sun while it cured. 

24 hours later, with my wife cheering me on (she's the best!), I de-molded the biggest part I had ever infused!

Woo! It worked!

Definitely took some of the gel coat of the mold with it but those were spots on the flange that I had to repair so I am not too surprised by it. And also those were all places that were going to get trimmed off anyway. There was some bridging/ air bubbles at one of the edges but overall I think a very solid result for my first time using a core and making such a large piece. 

Out in the sun to give it some post cure heat:

And the underside as well:

Then it needed to be trimmed up:

A quick test fit on the car (it's not bolted on, nor pinned down):

And, to provide some perspective of weight savings, the complete stock trunk without the tool kit or the foam on it was about 22 lbs. Just the skin of this trunk was about 2.5 lbs after being trimmed, now I still will be adding the attachment points that use the stock hinges so the goal was to have it complete and be about 3.5 lbs. 

Figuring out the mounts and clear coat comes next since it'll be out in the sun and I don't want the resin to yellow...

Impressive!      You did well.

Thats looking really really good!!

Thanks!

For the mounts I wanted to use the factory hinges because I still need access to the trunk (that's where the fuel cell is installed). In order to do that I needed to build out an area for them to bolt onto. I also wanted to keep things as carbon fiber as I could so I figured that I would attempt to just build out the bolt on area from the metal trunk. To start I covered the corners in a type of tyvek tape - a little more sturdy than packaging tape - and then did a wet layup of 5-6 layers of carbon. Then vacuum bagged the corner. It looked like this:

I couldn't take pictures of the actual layup since I was doing a wet layup my hands were covered in epoxy. After letting them cure I needed to install nuts so I could use the stock bolts that hold the trunk to the hinge. I was able to buy these nuts that have extra large washers attached. They are specifically designed to be used with adhesive, thus the holes they have in them. So I fired up the adhesive gun and attached the 4 nut/washers and used the bolts to hold them tight to the carbon. Left them for another day to dry:

Then I used the same adhesive, and a bunch of clamps, and bonded the pieces above to the trunk lid:

And there it is all buttoned up. 

After that I wanted to have it clear coated so I drove it over to a friends shop who was clear coating some parts for himself and he threw on a couple layers of clear for me.

And that was that. Trunk lid complete!

Final weight with clear and hardware attached, 3.6 lbs:

Thanks for coming along this far!

Man i can only invision the hours involved in this but i love it too.

If you have spare time at all, follow the "Scrappy" build by Mike Patey. He built the entire skin in carbon fiber and every video drops hints and tricks to laying up CF for the best look/fit/final value.  

Is it possible to drill through CF? Just go slow? I envision making mounts for my APR mirrors out of CF as they are small and probably a good place to start for a first timer but would need to be drilled through for mounting hardware. 

Cool.....where did you get the special nuts ,?

thanks

I've definitely seen some of his carbon work! Good info for sure that can be applied across disciplines (planes to cars). 

DjGreggieP said:

Is it possible to drill through CF? Just go slow? I envision making mounts for my APR mirrors out of CF as they are small and probably a good place to start for a first timer but would need to be drilled through for mounting hardware. 

Yep, no special bits required either. I've used cheap harbor freight titanium coated ones, carbide, and everything in between. I will say that you can reduce the amount of fraying that happens if you start the hole on one side, then flip the piece and finish drilling from the opposite side. Not essential but does help the finish/ look. 

And if you want any help figuring out the mounts or anything feel free to reach out!

californiamilleghia said:

Cool.....where did you get the special nuts ,?

thanks

McMaster Carr (https://www.mcmaster.com/catalog/128/3531)

If you scroll a bit you'll see the "adhesive mount nuts"

I have seen others get similar ones in larger amounts on eBay but I went the McMaster route because I wanted to be sure of the quality since I'm hoping these 4 tiny things are going to hold on the trunk during track time. Also, McMaster is local to me so I can usually get same day delivery.