Adding Parting Lines & Flanges to Original Part for Epoxy Mold

[doctorbombei]

Greetings, I am having some difficulty with flanges and parting lines for an epoxy mold of a body panel of sports car. Adding the flanges and parting lines is not a problem with hot glue and foam board, however, it is getting the epoxy & fiberglass to conform to every single contour. It takes the epoxy a while before it begins to tack and simply makes the process kind of nightmare-ish. I have gotten pretty good surface quality on this set of molds, but I can see where there are some gaps in a couple of corners. I need these molds to be accurate for a consistent fitment.

Ok, so I attempted to solve this problem by reinforcing the parting lines with wood and foam, and infusing the mold and this would have worked if it were not for my leaky envelope bag. The bracing apparently added some sharp points that poked some small holes in the bag during the infusion process. However, this is simply so time consuming and tedious to fabricate the bracing for these curvy parts. Do epoxy molds always have to be vacuumed? Seems that way. Does anyone have any advice/experience on epoxy molds and efficiently adding flanges+parting lines? What are you mold makers using for epoxy tooling gelcoat and epoxy resins?

Recently, I came across a company’s facebook post where they used epoxy tooling gelcoat and epoxy putty for creating a mold of a hood.

I have never seen this epoxy putty and can find little information about it. Anyone have any experience with epoxy putty or care to explain? I wonder how easy it would be to use this putty on something with more curvature, such as a fender or bumper?

Ultimately, my final solution to achieve the efficiency that I would like is to 3D scan the item, reverse engineer, and CNC foam plugs with built in flanges. Obviously, I will be exchanging money for efficiency, but I do have my own high resolution 3D scanner. Maybe you guys have suggestions?

[Hanaldo]

The putty is either from or the same as the epoxy tooling putty that Easy Composites sell. You can get the green epoxy tooling gel coat from them, and then they sell the putty in various size packs. It’s excellent to work with, possibly the easiest way to make moulds for a beginner. Gotta watch out for trapping air voids in both the gel coat and the putty, as they are both extremely thick and trap air very easily. They also aren’t a good option for producing large moulds (I’ve seen people like the above making bonnets etc before, but it really isn’t a cost effective solution at all) because it simply uses SO much of the stuff. For a big flat object like a bonnet, fibreglass fabric is a much more cost effective solution. For small moulds it is perfect.

It is however a great solution for the problem you are having - reinforcing tight corners. You can greatly save on time and costs by just using a little bit of the putty to reinforce the corners of your mould and give things a larger radius, and then lay up fabric over the larger easier sections of the mould.

[Infused]

I don’t even want to know how much that mold in materials costs with all that epoxy tooling putty.

[Hanaldo]

Can I just ask why you need an epoxy tool?

[doctorbombei]

I need superior, consistent and repeatable parts for high end projects. Polyester is simply not an option.

[Hanaldo]

Why not vinyl ester?

[AVT]

PTM&W has tooling putty as well, but all the points the others have made are accurate. It is rarely used for large tools. (unless you have a large budget and want to use it a limited amount of cycles)

Lots of info here: http://www.ptm-w.com/technical-papers.html

[kidpaint]

Other can possibly chime in, I havent done this, but have heard. Use strands out of roving and lay then up in the corners and angles to fill the void. Then lay your FG and resin up like normal after that.

[Hanaldo]

Yeah that works, but it’s incredibly time consuming. It’s better to make your own sort of ‘putty’. Just a bit of cab-o-sil and some calc carb mixed in with your resin to thicken it up, then chop up some strands of fibreglass (about 5mm long) in there as well until you’ve got a slurry that you can trowel on with a tongue depressor. You want it to be liquid enough that you aren’t getting strands of glass sticking up everywhere, but thick enough to fill the radius and not move once you’ve placed it there.

The trick is to get that done and then lay your glass over the top before the resin in the slurry begins to gel. This will allow you to press the fibreglass cloth down into the slurry and make a very strong corner. You get quick and good at it after a bit of practice, but the pre-made stuff from EC is a lot easier to begin with.

[doctorbombei]

Would you actually recommend vinyl ester for the tool?

[Hanaldo]

For sure, all my tools are done with a vinyl ester system. I would consider a proper vinyl ester tool (using proper vinyl ester gel coat, vinyl ester skin coat, and a high quality tooling resin such as Reichold) to be a top quality tool. Certainly it would depend a bit on the skill of the laminator, but I believe a wet-lay vinyl ester tools to be more forgiving and easier to construct than a wet-lay epoxy tool, hence generally of higher quality.

Of course if you need a really next level top-notch tool, then you’re talking more along the lines of pre-preg or infusion. It depends on what the application requirements are heat wise etc. But essentially if you are comparing a basic wet lay epoxy system vs a basic wet lay vinyl ester system, I would go the vinyl ester every time.

[Infused]

Interesting to know. I usually make my molds from poly and ever so slightly get some warping. I recently used epoxy to make a mold and it came out great but was a small part. I may try vinyl Ester since I like the stuff and also it’s a step up from poly. Although I can’t seem to find vinyl Ester tooling gel in the states, or haven’t looked hard enough.

[Hanaldo]

You’ll be able to get vinyl tooling gel in the states for sure. I’m sure fibreglast would have it. You’ll want tooling resin as well if you can find some. This stuff is very low shrink if you use it properly, I’ve got a few moulds with very important dimensional stability and haven’t had any issues with them. Only time I’ve ever noticed any sort of shrinkage was when I was rushing a mould and put it in the oven at 60 degrees for 2 hours and then demoulding it. This caused a bit of warping on the flanges, but nothing noticeable otherwise.