Help Planning Mold/Part - Sunroof delete panel

General Composites Discussions Composites Talk
#1

I’m new to composites work for the most part. This will be my second project. My first project was abandoned over 10 years ago, and I’ve got a newfound interest in making composites parts. I’m an engineer and a very hands on person, so this sort of thing is right down my alley.

This particular project will be to produce a lightweight composite sunroof delete panel for my autox car. I’d like to fix it permanently to the roof. I have an existing metal sunroof to use as a plug, with a few modifications. My sunroof fits flush with the roof, and is sealed with an edge seal. On the inside of the sunroof there is a gutter type features to catch and drain any water that makes it past the seal. I want my part to overlap the roof by ~1" and be adhered/sealed to the roof, thus eliminating any edge seals and gutter system.

Here is the sunroof hole.

IMG_4930.jpg by Kevin Sobkowiak, on Flickr

Another of the hole.

IMG_4935.jpg by Kevin Sobkowiak, on Flickr

Closeup of the hole.

IMG_4940.jpg by Kevin Sobkowiak, on Flickr

Sunroof to use as plug.

IMG_4941.jpg by Kevin Sobkowiak, on Flickr

Now here are my questions.

  1. I can’t use the metal sunroof as is for a plug, I’ll need to extend it ~1.5" in all directions so it will overlap the roof. I was thinking about various methods of flanging it and filling it with clay, but I’m not sure how I’d get a perfect contour/surface to use as a proper plug. What method would you recommend?

  2. I’m planning on using vacuum infusion for the part, using 2 layers of 6oz twill weave carbon, then 1/8" divinymat core, then 1 or 2 layers of 6oz twill weave carbon in a sandwich. The core will not extend all the way to the edge that will be sealed down, just in the large mainly flat area in the middle. Would you do 2 layers, core, two layers, or recommend some other layup schedule. I was somewhat curious if 2, core, 1 would be adequate for a sunroof.

  3. What method of attachment would you use to mount it to the roof. The seal must be waterproof, that is a requirement. I have thought about using self-sealing rivets, and using RTV between the roof and composite flange. I’ve also thought about using roughing up the roof surface under the overlap and using a structural epoxy, but I’m not sure how well it will bond and deal with chassis flex. I don’t want the part to fly off at high speed, so I’m not sure about that method. Any thoughts or recommendations.

#2

That’s a nice project…if it we’re me doing it, I would do this.

Take the metal sunroof and flange it with a decent size flange, you will need that anyways if you plan to infuse it so you have an area to attach the bag too. Once you shoot the part from the mould, you can trim the flange back to the size you desire for the overlap on the roof of the car and you’re done…For the flange I would just attach some foam and hot glue PET plastic down to the edge of the part. You can use model clay to fill the little gap in. Since it sounds like you are only going to make a few parts out of the mould there is no need to over engineer it. However, a nice flange goes a long way to asthetics of the part and if you use the flange to attach it you’ll want it smooth.

For the lay-up, 2 & 2 works, you might find the part to be a little thick though depending on the bulker you plan to use. See what some of other guys say, I think you would be fine with 5.7oz carbon, 8.9oz glass like a #7781 style next, your laminate bulker and a another layer of the 8.9oz glass. Any reason why you want to use that type of core? A laminate bulker like a nida-core can work as well, I think it maybe cheaper also.

Any plans to finish the backside of the panel since you will see it from the inside of the car? Could just paint it out…

As far as attaching it, I don’t think I would rivet it, try looking at PTM&W ES6292 A/B, it is specifically designed for an application like you have…from the website:

“ES6292 is a very tough adhesive, so it works well in applications where severe stresses and vibration are involved. It is not brittle when cured, and has very good resistance to peel forces. It has good thixotropy, and fills gaps in uneven bond lines withour sagging or run out during cure. ES6292 performs well at both high and low temperatures, so it is useful for applications where the bonded structure is exposed to environmental extremes. This is a fire retardant system, and meets requirements of UL-94 Specification.”

Plus, the tensile shear on it is over 2,100psi but that is glass to glass, glass to metal will be different but I think safe enough for your application. This company also has specific adhesives for glass to metal bonding. You can ring there technical department for more info.

Hope that helps…

#3

Thanks for the quick reply. I was speaking with a friend over dinner today and he also suggested another method for sealing/attachment. He thought it would be nice to make the part an exact replica of the current sunroof, or maybe slightly larger. Mount it flush like the stock metal ones mounts, and then just fill the seam with some sort of black RTV to waterproof it. I assume it would be easiest to use secondary bonding to attach some brackets to the underside of it to fix it to the roof using the stock attachment studs. That may be the easiest method, and it won’t have any visible rivets which is a plus.

As for why Divinymat, I’m not sure. I’ve read that that product was made specifically for vac infusions of sandwich core layups, and would conform nicely to my contours. I’ve never done this before so if there is something better for my project, I’m all ears.

I’m not really concerned with the inside surface finish even though it will be seen in the car. This project is part of a larger weight reduction of the car. The interior has already been removed besides critical components. I’m hoping this project goes well and I can continue to make more lightweight parts. I need to drop 400 lbs off the car to get to min weight for my class.

#4

Depending on how serious you are as for using this as a race device, weight and stiffness go hand in hand. Weight, the lighter and lower the better. Stiffness, the stiffer the better so the vehicle will better respond to chassis tuning as long as you add the least amount weight possible.
I would make the part fit flush in the cavity and bond & rivet to the shell. You would be amazed how much a roof adds to the stiffness o a vehicle even with a roll cage inside of it. Next weight loss program is to loose the rear hatch glass, I bet there is at least 40lbs there.
For the tool I would place the lid on the car tape a 4" border and lay it up on the chassis. As long as you use plastic around the rest of the roof you should be able to make the plug W/o damaging the paint. Once done you will have enough there with a flat flange to make your part.

Have fun! Post some pictures when you get it done.

#5

Here is what I’ve done so far. I made a plywood table to work from, to create my plug. I made it over 6" larger all around than I need, to make sure I have ample flange space on the mold.

In this picture you can see two silver parts on the assembly. Those silver parts are nuts, that mount the sunroof assembly to the roof structure. What I did was measure the vertical distance between the contact surface of the nut, and the edge of the sunroof at that location. That way I’d know what the spacing from the edge of the sunroof to the flange I’ll be building onto the plug. All 4 ended up exactly 1.1875".

IMG_4961.jpg by Kevin Sobkowiak, on Flickr

Then I removed the metal sunroof from the assembly and placed it on the plywood table. I then added 1/8" to the 1.1875" so that when the mold is made the flange will be 1/8" too tall. This will make the part that it produces protrude 1/8" above the flush roof line. I am doing this to account for any variations car to car, and my measurements accuracy. I can always add shims to bring it down to flush when I mount it, but I cannot make it stick up higher, so I’m erring to the side of too tall. Here it is shimmed to correct height.

IMG_4982.jpg by Kevin Sobkowiak, on Flickr

The next steps are to attach it to the wood shims to keep it in place during the rest of the buck making process. Then I’ll need to fill in the vertical gaps with something. I also need to make the vertical edges have a slight angle to them, of a few degrees to make the parts release from the mold easy. I’m not sure what I’ll use for the vertical surface building, any good suggestions? I also need to slightly extend the sunroof about 1/8" all around, to make the fit inside the roof hole a bit tighter. Right now its about 1/4" gap all around.

IMG_4988.jpg by Kevin Sobkowiak, on Flickr

I’ll post more as it happens.

#6

Are u saying make a mold of the rear window and make it in carbon ??

#7

I would go about this completely differently.

  1. Install oem sunroof in car. Fill and smooth gaps with clay. Apply release agent. Lay up on roof, extend past the opening by 8" in each direction (4" for finished part, 4" flange). This is your mold.
  2. Lay up 2 layers of 200gsm (5.7 ounce) 2x2 twill in the mold, cure, demold, trim edges.
  3. Remove oem sunroof from car, lay part in position, be careful with alignment. Trace around the opening onto the underside of the part.
  4. Place a piece of 1" PU foam over the roof opening, trace onto foam from underneath. Cut and smooth the foam to just inside the line you traced out.
  5. Epoxy foam to underside of part. Vacuum infuse another 2 layers of 2x2 twill over the foam, extending about 2" out onto the flat section. The part is finished.
  6. Check part fit. Maybe bevel the edges a little bit where they meet the roof. Sand the roof a little where the part overlaps it to provide bonding surface. Fix part to roof using appropriate adhesive. Apply adhesive under the “flange” and in the vertical gap around the foam core. Clear coat roof+part.

End result should be a part that matches the contour of the roof, no ugly rivets, nice and secure.

#8

No sorry I meant replace with a Pollycarbinate sheet. Take a look at the guys who supply bodywork for stock cars dirt modified’s etc. they are thin and usually pretty cheap and oversize enough to cut it down to fit most import hatches. We used them years ago and saved a lot of weight.

Don

#9

Poly or lexan is good Needs to be 4mm thick at most tracks in the uk

#10

I mounted the sunroof to the plywood with expanding foam. I placed a 25 lb weight on each side directly above the shims I used to get the height right. And I put another 15 lbs in the middle. Here it is all trimmed up.


IMG_4999.jpg by Kevin Sobkowiak, on Flickr

Long story short, foam was a very bad idea even with the weights on top. The force of the reaction is so strong that my plywood ballooned and the sunroof did too. Not great. I had to cut the bottom out of the plywood and pull all the foam out. The sunroof went back into shape thankfully. I also had to cut out some foam on the long edges to get the shape to come back to stock. It did, but I was sweating it pretty good. Here is a pic of the foam all cut out (besides 2" around the edges to keep it mounted).

IMG_5002.jpg by Kevin Sobkowiak, on Flickr

Then I needed to box in the sides, and make it 1/8" larger all around to reduce the gap when installed in the car. I used 1/8" thick hardboard and glued it with Locktite construction adhesive. That actually worked pretty well. For the corners I had to cut 3/8" wide strips and glue them in place individually.

IMG_5003.jpg by Kevin Sobkowiak, on Flickr

All edges bonded on, and the first coat of body filler. I’ve got a lot of work to do on this to make it a quality surface finish, but I’ll get there in a few days hopefully.

IMG_5007.jpg by Kevin Sobkowiak, on Flickr

This photo shows two things, one is the corner edging. The other is the crosshairs and circle around it. Those are the locations of the mounting studs in the car. That is where I’ll drill a hole in my part. I’m planning on putting some sort of spike onto the plywood before I make the mold, that way it will give me a “center punch” on my part so I can drill the holes accurately.

IMG_5006.jpg by Kevin Sobkowiak, on Flickr

#11

Might be worth double checking that your hardboad is following the same angle as the opening of the roof.

Are you going to arch the flange so that it contacts the underside of the roof skin in a similar way as the sunroof flange bolted in, or just have the four bolts? It might take less sealant if it followed the roof.

Are you flanging the back half of the mold, to be cut off to slide over the metal shelf in the roof? Did the roof have to be popped open to install over that metal shelf?

#12

The opening of hte roof is almost completely vertical. I’m making the mold with a 5 degree draft angle to make de-molding easy. I checked and made sure there would be clearance before I did that. The flange will be completely flat, formed by the plywood in my plug. I do plan on cutting off the flange on the back side to fit. Yes, the sunroof did not have to be popped open to remove, I just had to lower the front side first, then the rear was able to slide forward and drop down over the shelf.

#13

Small update. Lots of bondo work. I roughed in the visible sunroof surface. I am nearly completed with the sides. I just have a bit of finish sanding to do there. I included a 5 degree angle on the side pieces to give the mold some proper draft angle so the parts would pop out of the mold easier. I also finished squaring off the corners from widening it 1/8".


IMG_5130.jpg by Kevin Sobkowiak, on Flickr

This shows the widening by 1/8" all around.

IMG_5131.jpg by Kevin Sobkowiak, on Flickr

And another of the 1/8" widening, and the sides.

IMG_5134.jpg by Kevin Sobkowiak, on Flickr

#14

Another small update, although this one took me quite a bit of time. I finished out all the surfaces to 220 grit paper. I took it to 80 grit with bondo, then skimmed it with a glazing putty and took to 220 grit. The sunroof was quite a bit rougher than it seemed when it was installed on my bar. Either way, its 100x better than it was, and hopefully will make for some nice parts that I pull from the mold.

Next step is high build primer, 400, 800, 1000, 1500, 2000, buff.


IMG_5229.jpg by Kevin Sobkowiak, on Flickr

The sunroof was really a complex surface to finish out nicely, curves in every direction, and transitions from convex to concave, etc. These next two pics show the shape of the sunroof.

IMG_5232.jpg by Kevin Sobkowiak, on Flickr


IMG_5233.jpg by Kevin Sobkowiak, on Flickr

And this one shows the corner edge blends. The inside corner is just to ease the layup. The outside corner will be somewhat visible, and I tried to match the radius of the corner of the sunroof hole.

IMG_5234.jpg by Kevin Sobkowiak, on Flickr

#15

I primed the plug and I’m waiting another for it to dry/cure before I sand it to 2000 grit paper, then polish. I’ve got a question about release agent. I was reading that PVA is not recommended due to surface finish concerns. What would you recommend I use for release? Just a bunch of layers of wax?

#16

Primed with many coats of high build primer. Should be sufficient to get sanding up to 2000 grit and then polishing/waxing. I was in a rush and ended up painting right over my mounting hole location marks before I center punched them. Looks like I’ll be sanding down to the wood to find my marks and then touching up those areas. Won’t matter too much though since it won’t be visible when installed, but it pisses me off when I do stupid xxxx.


IMG_5242.jpg by Kevin Sobkowiak, on Flickr


IMG_5243.jpg by Kevin Sobkowiak, on Flickr


IMG_5246.jpg by Kevin Sobkowiak, on Flickr

#17

I spy with my little eye an FD in the back ground! Looks good dude! i thought about doing the same project with my track car but i havent had time. keep up the good work!

#18

Looks good but you should get an industrial vacuum cleaner going while you sand. It looks like you have dust everywhere!

#19

And sanded to 2000 grit. Then buffed with some meguiars polish on the surface that will show when installed. Bare primer just doesn’t buff out that nice, I suppose since there isn’t any clear.


IMG_5250.jpg by Kevin Sobkowiak, on Flickr

What mold release wax would you recommend for this plug? Meguiars?

#20

What kind of primer did you use? When I use duratec with the high gloss additive I can get the surface pretty shiny after polishing.

You should be good with pretty much any mold release wax. I use partall and PVA.