What plastic molding process?

[aspetuck]

I want to make a mold for a plastic piston mockup. It would be a solid hunk of plastic in the size and shape of a piston. In fact, there are several components I need to make molds for. What type of mold should I use? Could I CNC it? How would that impact the strength of the resulting product?

[Jersey Tom]

Why not rapid prototype this thing (these things)? E.g. SLA / the ubiquitous "3d printing."

Cutting molds is an expensive proposition most of the time. Better suited for larger scale production work. For one-offs, better to machine them from billet or rapid prototype (IMO)

[aspetuck]

Suppose I was interested in producing several dozen engine models, specifically of the ls7, out of plastic. What sort of mold would I use for pistons.

[Lycoming]

What exactly are these plastic models for?

[Greg Locock]

3d printing sounds the obvious approach. In general injection moulded plastic is not suited for small production runs. Would you consider vacuum formed sheet? That can be done very cheaply, but it is a pain to build models from.

Another process you might consider is to build a wooden pattern and sandcast them in aluminium. Obviously they'd then need to be machined like a real part

Here's a 3d shop

http://www.shapeways.com/model/198434/m ... terialId=6

[marcush.]

3D printing and all other RP processes will give a Rather Rough finish,nothing you could use for a Display methinks.
I'd consider a different Strategy here with a proper mold made of Aluminium or epoxy -with a good sufraface gelcoat.
I'm sure the Piston is very easy to Drag a mold from . The interesting Bit will be what to use for the
Actual Parts. Then ..there are some good epoxies around Maybe Aluminium Power filled and you may get a Perfect Plastik Look alike with no real Finishing work to be Performed.

[krisfx]

3D printing and all other RP processes will give a Rather Rough finish,nothing you could use for a Display methinks.
I'd consider a different Strategy here with a proper mold made of Aluminium or epoxy -with a good sufraface gelcoat.
I'm sure the Piston is very easy to Drag a mold from . The interesting Bit will be what to use for the
Actual Parts. Then ..there are some good epoxies around Maybe Aluminium Power filled and you may get a Perfect Plastik Look alike with no real Finishing work to be Performed.

You could use SLA, but it's quite brittle.

[tok-tokkie]

Consider polyurethane vacuum casting. I have access to a product development company that uses it to make prototypes and small production runs. They machine a master model, cast a silicon rubber 2 part mold then cast the urethane in that silicon mold. Urethane can be formulated to be elastic all the way to rigid.
Here is a link to their website. many products to see. (They also do high end 3-D printing, robot & cnc machining, glass fibre layup etc so not everything you see has been vacuum cast.)
http://www.skeg.com/vacuum_casting.htm

[Greg Locock]

He still hasn't told us what the models are for

[matt21]

Suppose I was interested in producing several dozen engine models, specifically of the ls7, out of plastic. What sort of mold would I use for pistons.

There is a supplier in the UK for small series molded plastic parts.
It is called Protomould: http://www.protomoulduk.co.uk/

You can directly upload your 3D-geometry as a step-file and get an offer including an analysis of feasibility.

We´re using this in our company for prototype parts.

[marcush.]

I´d guess all this is rather expensive stuff so wouldn´t it be more cost effective to just buy a Piston and make a Display of it? gearing up for modelmaking and actual production runs of parts + inevitable development cost this all will result into something easily detected as a plastic fake ...so where is the Point?