Small Part Stuck in Mold

Because thats how we learn.
Dont give up.

When you build plugs and moulds you need to learn to think inverted.

Work out where your split line is going to be, building a split mould just takes a little more time and planning.

1" for 28" sounds absolutely fine. build a wooden plug, use something pretty stable like MDF. radius all your corners , make sure you have no undercuts and use polyester bodyfiller to fill and fair it until 100 % happy.

Use a roller, or hand paint or spray if you can polyester fillercoat?primer - preferably two pack. Leave to harden overnight, sand with 800, 1000 and 1200 grit wet and dry sheet, use lots of clean water. Change your water often and also between grades of paper.

Machine or hand polish with a fine compound G3 or G10 Farecla is good for painted finish.
Minimum 5 x layers wax leaving to dry for 10 minutes between coats
Work out where your split line is going to be, nows the time to spend a bit on thinking rather than doing.

When youve worked out your line you need to put up a temporary flange at 90 degrees if possible along your split line, mdf, cardboard etc - you can tack it on with a hot glue gun. Fill any gaps with plasticine.
When happy with your flange, apply wax to the flange , a couple of coats and wax and polish as best you can, now apply PVA- the best way to do this is to use a soft sponge, and give it a lightish layer- dont make it too thick, wait for it to flash dry( you can use a hairdryer for this if it takes time-some are faster than others.)

When happy apply your gel coat - 2% cat ,not too thick and not too thin, you can always do a thinnish layer and when it gels add another layer. If you want the mould to last ie: a production mould do the first layer of gel in clear and the second layer the colour you want. The reason for this is that pigments soften the gelcoat so the mould doesnt last quite as long. Make it a different colour to your intended mouldings.ie:not white on white, black or orange are good
Once the gel has gone off after 20 minutes or so(must be squeaky to the touch)
add your first layer of glass, I prefer to use tissue for this but a lot of guys dont. Once gelled and you are happy you have no voids directly behind the gelcoat, continue with your layup. Your mould needs to ideally be 2.5 times the thickness of your intended article, but just use common sense to guide you on this. Leave overnight to cure.
Next day

pop temp flange off and clean the new flange if there is any residue plasticine, glue etc. , take a large drill or countersink bit and drill into your new flange at intervals, not right through, just enough to leave an imprint of a couple of mm into flange 1 - this will end up being your locating points and will ensure that your two parts can only fit together in 1 position.
Wax the new flange five or so times ensuring you get wax in and out again of your new locating points.
When satisfied give it a coat of PVA.
then repeat the whole scenario on the second part, gelcoating and laminating up against the new flange surface made by your first flange.
Leave overnight.

If you intend laminating timber etc to stiffen your mould body, then wait at least overnight so the laminate will be more cured otherwise you can get printhrough onto your mould surface from the back of the mould.

When the time comes to pop the mould , just make up loads of wooden, wedges of different thicknesses and insert them in between your two laminate flanges,one after the other, it helps if you have ground your flanges to a neat clean edge. You can then see exactly where to insert your screwdriver or whatever to start the splitting.
try and exert even pressure, over the entire mould, increasing it as you go along, until it pops.
If it doesnt pop immediately, increase pressure slightly on all your wedgies and go and have a coffee, chances are when you come back to it itll be lying in two halves- if it doesnt you can, water it, add compresed air, if really necessary you can drill a hole through the back of the mould and introduce air, but this is usually a last resort.

splitting a mould is the time to chill out, if you rush it, you'll spoil all your preparation work.
remember you cant rush mould building , unless you have been doing it for a while and know a few shortcurts, but even then its not advised.
Plan, your mould and take it easy.
You'll soon get the hang of it, once youve done it once the rest will come easier.
have fun
Itchy

 

Also, while you put pressure, smack it with a rubber mallet.

 

I would rebuild with about the same draft,3/8" corner radius.Use 2 pack paint,follow the advice about polishing given earlier.Without a sketch,to enable us to understand exactly the shape of your component,it is very difficult to make meaningful comments about split lines.
Be very cautious about hammering the mould to assist the release,star crazing can occur and this creates another problem.

 

I still feel one important thing is missing:

Use 2K PU paint AND LEAVE IT TO CURE FOR AT LEAST 1 WEEK.

I have seen too many stuck moulds which were made hastily.

For your radiusses: more is better, but I see square angled products pop out without any problem. They are just more tricky when applying gelcoat and laminate (corner bubbles)

Indeed water or air valves can help. I use the Composite Integration ones with good results (and they are replacable, only the base part gets laminated in).



About PVA: nice stuff, but with a good sealer and a good wax you should be able to do without, leaving the mould surface nice and smooth, and highly polished. But do use a mold release system which has a sealer. This is very important for good release.

Remember the mould will shrink around your product. Using a very conservative layup schedule will reduce shrinkage (1 layer a day) or use a rapid tooling system, and follow the procedure carefully. This will also make almost shrink-free moulds.

And take your time. If you do not have the time to do it right, where do you get the time to do it over?

 

Thanks for all the suggestions!

To address a couple thoughts:

This project took me two weeks (40-50hrs of work)...I felt was too long to make a small console mold...What would be the estimated time?

I thought the paint was cured on plug. I used Rust-Oleum Top Side Mfg Cure was 24 hrs...What is 2K PU paint? (Sorry to ask stupid questions)

I thought once you waxed and PVA the the plug you were good to go...the part didn't seem stuck just would not release...that is why I 'm temped to put water or air realease vent over split mold. I thought you could pop a mold off almost anything as long as it was waxed and PVA'd...

I know some of you suggested a new plug but I realy like the part and I'm despartly trying not to trash the plug. I have filled in the front hatch and put more radius where the console meets storage / baitwell.

I like the idea of water or air valve...

 

An air valve really is a time saver. It pops the middle of the part loose from the mould, untill there is a leak somewhere, but then usually you can lift the part from the mould. Also remember that a part shrinks itself loose from the mould. So releasing a mould from the plug is the hard thing. Pop it off is not the term I would use...

2K PU paint is a 2-part polyurethane paint. Those enamels take too long to cure properly, and can make a part stuck.

 

Would paint over the Rust-Oleum Top Side (Oil based) that is currently on the plug?

 

2-part polyurethane paint seems pricey ($50 qt ITERLUX ) for a plug....

 

Seems a normal price. Plugs are not cheap. If you want a high quality mould, you will need to start with a high quality plug... Prying a mould off of a plug in pieces, is not cheap either...

 

10-4 on that....

 

Did any of the old plug come off and stick to the first mold when you tore it off?

This seems like the problem..

 

No...once broken into smaller pieces it came off fine.

 

The surface on the plug looks great other than the pry marks!

 

SamSam
Split Mold? or Water/Air Mold Valve?

 

Can you attach a photograph?It would be a great deal easier to make constructive suggestions if we could see what you have in the workshop.