Advice needed with mould?

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#1

Hi guys.

The local motorcycle muffler builder asked me once again to make him CF exhaust can end caps. He gave me an aluminium mould he had made from a solid piece of aluminium and cnc. However, the guy that used to do it before me damaged the mould with wedging screwdrivers into the mould. So the whole mould is full of rough tooling marks. I tried to get rid of it, but it’s still visible. These tooling marks are not visible in the composite parts so it’s not that bad. But the problem is, this mould can only make one part at a time, and this is a problem because he orders 30 parts at a time. It takes me 24 hours to make one cap, resulting in a 30 day procedure.
So I decided to make a new mould out of fibre glass and gel coat, but first I need some plugs. I decided to make some plugs with a polyurethane plastic casting agent. After it cured it was stuck in the mould, but like properly stuck. I tried everything to get it out, resulting in an oven for 1 hour at 180 degrees Celsius. Obviously it melted and fell out.
On closer inspection I noticed the problem. The mould has a negative draft/pull angle, the edges are closing up. That is not supposed to be the case, so the guys that machined the mould, screwed up.
So now I’m trying to make plugs using epoxy and composites, because the composites plugs tend to come out easier, because it can flex.
I want to build a mould which can produce 4 parts at once, that way it’s more time effective and less effort.
However, the plugs I’m pulling from the current aluminium mould shows a negative edge angle, and that means my new mould is also going to have them.
The client doesn’t want to sort out the mould, he says it set him back $300, and that mould worked fine all the years. So if i want a new mould I must make it myself, or give the contract to the other 10 guys wanting it.
What’s your take on it? Must I carry on with a one at a time crooked mould, or make a mould that can carry 4 parts at a time? Will a composite mould benefit me in conjunction with the aluminium mould, regarding quality of the parts?
The parts that I need to make are 2 layers 200grm of 2x2 twill weave and epoxy resin. Here is some picks of what I’m making and how the mould looks like. And a sketch of the negative draft angle.
Any suggestions will be greatly appreciated.

#2

Hang on bro…the tool is aluminum and can be polished to a mirror finish, you can remove the gashes.

We use aluminum tools all the time, we have sanded moulds as rough as starting with scotch pad, remember, CNC mills do not cut mirror finishes, they ALL leave tooling paths which must be sanded out.

You can never ever produce a composite mould which would compete with an aluminum for the same level of effort.

Search around Youtube and watch some vids of the polishing methods on aluminum tools, for example (not the best, but you get the drift)

[ame=“http://www.youtube.com/watch?v=PWQVBSoXlEc”]Mirror Finish on Milled Aluminum! Machined on TAIG CNC bencthop Mill - YouTube[/ame]

Also, on the aluminum tool, there is no reason why you cannot turn it over every 30 to 45 minutes. You can make 10 caps a day easy…

First step, sand that mould (wet) from 320 to 2,000 - then buy a metal polishing kit and use the black compound, red compound and if need, blue compound. It will be a mirror.

Change your resin over to an epoxy, the part is small so get a fast hardener, something with a potlife of 8 to 10 minutes (this is if you are vacuum infusing it), buy a small heating element, place another block of aluminum between the heating coil and the mould block so it is not direct heat and apply enough heat to the aluminum to bring it within the limits of the resin, usually 150 degree’s, ours goes as high as 275 degree’s - review the spec sheets, you will want a high Tg value.

Once the part is shot, move the mould to the heating element, let stand 20 to 30 minutes, remove mould from heat, now you need to cool the mould, we have a plate which runs glycol chilled we put the moulds on, a garden hose with running water also works, so you can place the mould under the running water, in 3 to 5 minutes you can handle it by hand. Remove the bag, peel & flow media, pop the part.

Start over again…30 more times. If given the choice of a composite or aluminum tool, always go aluminum…there are times I can run 20 or 30 parts between waxes on the tool, they pop out by hand, now wedge of force needed (granted yours has a bit of a draft to it which will require some force) but regardless, fix the aluminum mould, you are WAY better off.

PS…before the comment of expansion of materials, heat etc…comes up, it’s a muffler cap, not a space shuttle part. Trust, crank heat to it and pop them out every 30 minutes…PM if you need help or specifics, I cannot post pics of our moulds but I can def walk you through this and show some of the older moulds we ran, with tooling paths to mirror finish and the turn-over rate. I can also send you the data sheets on the resin we use, you can ask your supplier to find a similar version.

Remember:

  1. Watch vids on how to sand aluminum (always wear a mask btw)
  2. Wet sand your mould
  3. Polish your mould
  4. Wax and lay-up
  5. Shoot the part and put heat to it
  6. Pop part
  7. Profit
#3

That is some of the best advice I got from this forum! Thanks SLS, you gave me new hope. Im using Gurit Ampreg 21 epoxy resin, been using it for years, because I do wet lay ups. However, I see a 50 degrees celcius temp factor on their data sheets. Its winter in South Africa now, so outside air temp is around 14 degrees celcius. Im using their fast hardner, and with this temp its only curing after 16 hours. Its a good idea to switch to another resin.

#4

its a real bummer they couldnt put a better lip on the mould… i suppose if you wanted later to, after making 5 or 6 parts make your own custom mold with the parts lined up together using tooling gel process then due infusion setup that goes through them all at one time… it would be a ton more work but if you plan on doing 100s of parts then in the long run its worth it… also you would want to change your epoxy over to a infusion type which is thinner based and will go quicker or use vinyl ester infusion resin which also works well and is alittle cheaper then epoxy

#5

I can only repeat what SLS told you, but I would like to add that when sanding with 320, get rid of the negative draft. It will kick you in the face sooner or later.

This mould screams for press moulding by the way. Throw in resin, throw in fabrics, press on the top mould, done.

#6

^^ I have never had much luck with press moulding, mainly because of surface defects in the part afterwards. I firmly believe it was from not having enough pressure but there is only so much clamps can provide. A true press with a true tool to handle a few hundred tons would work but then the tool design needs to account for run-offs and you need a serious block of metal, the job needs to produce $bank$ to warrant it.

I will say, I use to run composite tools, now I strongly, strongly suggest aluminum for everything (within reason), small parts and I don’t even flinch, I go 2024-T6, draw up the design in Rhino or Solidworks, send the design out or cut it ourselves. The difference in surface quality, gloss, less voids and more importantly turn-over makes it worth the extra dollars.

I remember turning parts 5 to 6 hours in composite tools thinking I was a champ, now I turn the moulds every 30 to 45 minutes - way more efficient.

#7

No sweat…you should charge the guy for fixing the mould also, he likely won’t know it makes life easier for you but keep to your 30 days quoted, pound out 10 a day for 10 days and you’ll have a hundred, throw them on the shelf and when he orders you show up with them…he will like you and not look elsewhere. From there push for more of his work, manufacturers who work with metal mainly always revert back to it by the way. So when dealing with them, companies like muffler manufacturers, or who have a product produced in steel, put the tooling back on them and advise they can make the tool, you can provide the drawing and design, but have them cut it.

They don’t really live in our world, making a tool with 10 layers of glass which eats up the whole day laying one after the other. Then the potential for a void here or there also if the part is at all semi-difficult. You can’t put heat to composites like you can aluminum in a McGyver way.

So long as expansion is not hypercritical and the like, it is the way to go. Like I mentioned, if you need some guidance PM me.

One last tid bit, we actually have to sometimes clamp the part in the mould when go to pull the peel ply and flow media, we actually pull the part right out of the mould from the minor force of the peel ply “stuck” to the back of the laminate, seriously, I kid you not. If you can get the mould to a mirror, you won’t even need to clear coat it unless it is required (exposed and all to UV), you can however source resins which are UV stable and don’t yellow. With the gloss from the mould surface, just trim and ship.

Good luck

#8

3 years back when I started making these caps it was a press mould set up. Mainly because I had no vacuum pump. So it was a male plug, and female mould. The male plug was 0.6mm smaller than the mould. Wet lay-up, two layers of CF, press in the male plug, excess resin squeezes out. But then something weird happened. The first 10 parts came out, absolutely perfect, not even the smallest pinhole. Then all of a sudden it was an F up! When i removed the part from the mould, pieces of resin will break of and stay behind in the mould, sometimes as big as a finger nail. I tried everything, better release wax, agent, frekote, you name it. Different resin, heat, more pressure on the male plug (2000pounds), nothing helped. It came out a mess. I had all kinds of experts here, and all of them scratched their heads. The most plausible explanation I got was that aluminium is pores, and that’s why??? Then I gave it back to the client, and told him he should find someone else. But after 3 years it came back to me, because the new guy charged him $40 a piece. The other guy had the same issue, but he just flooded the part with clear coat afterwards.
The current parts I’m pulling from this mould with vac bag are more or less the same result. There is a lot of ‘dry spot’ and pinholes. Although it’s not dry spots, its spots where the resin and the CF separated?
My initial idea behind the composite mould was to be able to design and built it the way I like it, and the way I’m used to work. But if you guys tell me to stick with the aluminium mould, then i will do so. Give me ideas how to heat up this mould, you have seen it. Do i put it flat on my domestic stove hot plate?

#9

For heating it yes, just place another block of aluminum between the coil of the hot plate and the aluminum mould for the cap. Bear in mind the aluminum plate may bond to the bag with the heat (envelope bagging method) if you are not using a bag which is rated for it. If you are bagging the top perimeter than you are fine.

Not sure why you had probs with the press mould, I will say 2,000 lbs of pressure is not much for a press mould design, the wet lay-up method with a press mould is not ideal in my opinion, I have never had a consistent result from it. Not saying people haven’t, just not for me…I like the vacuum infusion method and RTM ways. Would love to do a press mould using a shot of fibers impregnated with resin, like the “forged composites” method as they say, a little rich for my blood though and I don’t have a 250 tonnes press around.

#10

PREPREG!!!
but that lip is going to suck.