How to: Plastic lens mold
How to: Plastic lens mold
(OP)
I wanted to know how, and what I would need to make a plastic lens mold for automotive purposes.For example. A mold to make a taillight pastic lens.Does anyone have a link to where I get buy all the stuff? .






RE: How to: Plastic lens mold
RE: How to: Plastic lens mold
Regards
pat pprimmer@acay.com.au
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RE: How to: Plastic lens mold
RE: How to: Plastic lens mold
The resin needs to have minimal shrinkage and a good surface finish.
You will need to make the mould in at least 2 pieces that fit together to form the inside and outside surfaces. The mould will need to be accurate so the section thickness is correct.
Once you have a mould, you can cast the parts from acrylic or Poly Methyl MethAcrylate or PMMA.
It should be partially polymerised before you start so you can control the exotherm and avoid forming bubbles due to the monomer boiling.
PMMA is the resin that is used for most original equipment taillight lenses and in sheet form is often known by the trade names of "Perspex" or "Plexiglass".
PMMA is very clear and transparent. You could add colours to the resin, but for multi colour lenses, you would need to cast them in individual colour pieces. If you want to do them in one piece, do them in clear then paint the inside surface with a transparent tint.
Regards
pat pprimmer@acay.com.au
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: How to: Plastic lens mold
You can get tints and add them for differsnt colors also.
RE: How to: Plastic lens mold
what advantage does PU have over acrylic.
How will you control yellowing after prolonged exposure to UV light.
Why are most OEM lights acrylic.
Regards
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: How to: Plastic lens mold
All headlamps and taillamps have UV protection additive put into the material before molding.
Even the prototype tooling for the lense moulds are made via the "Growing of the Pins" type tooling.
Now if you are looking at a lense to go on a garden tractor or such, then a "CUT" tool either alum. or steel can be used. You will still need to put the UV additive into the molding process or else the lense will turn yellow with time.
Regards
RE: How to: Plastic lens mold
i'm not sure the difference between alumilite and other plastics, but alumilite is most available to consumers. their website (alumilite.com) has lots of support material and step by step instructions for various casting problems. also, they answer most email inquiries (usually referring you to a FAQ on the website).
for your project you will need a CLEAR plastic resin, and some (orange) dye. alumilite offers ALUMILITE CLEAR, which you would have to purchase seperately.
here is your bare minimum shopping list:
$5 for orange dye. $25 for 32 oz. alumilite clear. 2 lbs of rtv silicon rubber, to make the mold, might be enouph (2 X $28).
additionally you will need some superglue, some material for housing the mold while the silicone cures (cardboard base and corrugated plastic walls is good), and you probably want some modeling clay, at least for sealing the mold box during cure, if not for helping to make a 2 PART mold.
so that is a minimum of probably about $100. however, i would recommend getting the kit too, to start with and learn ($70). also, if you want your lens to be really clear and free of obscuring air bubbles, you will have to PRESSURE CAST the piece during cure. i have never done this myself, but have looked into it. alumilite sells a "pressure pot" for this process, for $185. (i am not sure if this pot is large enouph for your purposes though). i'm sure there are other alternatives for a pressure pot, but homemade ones are not safe, as pressure is dangerous. to use the pressure pot you will need (according to alumilite): "an air compressor of at least 3.5 H.P. and a 1/4"coupling/adapter to attach to your air compressor". i will estimate that to be about another $100.
so pressure casting will probably add about $300 to you project cost, unless you already have those tools.
here's the diff between pressure cast and regular cast:
http://www.alumilite.com/howto.cfm?ID=18
RE: How to: Plastic lens mold
Cheers
RE: How to: Plastic lens mold
They are described above, along with some one eyed comercial promotion and absolute garbage.
Casting PMMA in a filled (low shrinkage) epoxy mould is the way to do this.
Regards
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: How to: Plastic lens mold
Ive probably done close to 200 different len's both for customers(in Lighting and Automotive) and with friends in custom fab shops.
If you already have a lens cover you want to modify, take it and modify it. When its ready, you can make a RTV Mold (silicone), and cast parts to your hearts content. One of the len's sets I did is still on a car after 4 yrs (still looks good). The tooling is still good (we even sold a few sets to recoup most of the cost).
There are many ways to get there from here. Dont let anyone scare you off.