need advice: model train bodies

[wlw3]

trying to find supplier for injection molded plastic model train bodies. We can get a prototype built or can get plans to be converted into CAD/CAM file.

What is lowest cost method for high quality reproduction in plastic? Steel molds are supposedly about 50-80k to make. We understand that aluminum and certain phenolic plastics are commonly used for highly detailed parts molds also. Other consideration is that we are probably interested in 1,000-2,000 units per mold, so super durability is not req'd. If we can sell more, we might upgrade on the next iteration.

Any suggestions for production techniques -- CAD approaches versus using a prototype? metal versus phenolic plastics molds? anything else? Any companies that come to mind that might be good at this. Any thoughts appreciated.

Also interested in having same parts cast in metal if we can do it easier or more cheaply than plastic.

 

[patprimmer]

You are in a difficult position re numbers.

You require to many parts in I expect a high level of detail for phenolic or epoxy moulds, but not enough to amortise the cost of a properly constructed production mould.

Possibilities are aluminium, mild steel or zinc, with the surface detail you require, but cheap construction re cooling and finish in non viewable areas.

A 2 pack epoxy, polyester or polyurethane casting resin might suit your required numbers better. These can be cast in silicone rubber moulds, themselves cast off a prototype model, carved from Kraft wood or wax or whatever.



Regards

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[wlw3]

thanks

we want to upgrade from the resin method, which we use and which works well, but is very limited in production capability (would take over a year to make 1,000 units)

I thought somebody might have a way to reduce tooling costs using either cheaper mold materials that retain detail but are easy to tool, or some way to use CAD/CAM to reduce the labor cost of the tooling.

will

 

[patprimmer]

CAD/CAM is extensively used in making moulds for injection moulding of plastics.

To increase production by the resin method, simply make multiple moulds. Once you have a pattern, it is relatively easy to knock of a few copies. In fact it is so obvious, I wonder if I have missed something.

Another problem I see with injection moulding is that I expect you have detail on the sides of your part, this detail will produce undercuts, making it impossible to open the mould without damaging the part, unless you have side cores. These side cores will leave wittiness lines on the part.

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.

 

[ornerynorsk]

You can probably go with a rapid molding vendor for 10,000 or less, depending on the size of the part being molded. Very fast, cheap, good for low volumes. They upgrade and maintain the mold as needed. You pay a little more per piece part, but you don't have the expense of high grade tooling.

 

[tkdesigner]

I have molded a few train parts in the past, but these were parts that had been previously die cast; the steel cavities were installed into some 5" X 8" MUD-type units, and the parts run in 33% GF nylon.
My brother has retired from molding, but has run a LOT of train parts using good quality aluminum molds; don't even think about having aluminum molds built using any lesser grades that 7000 series for cavities. 6061-T6 is useable for ejector plates, etc. I will mention this thread to him for comments.
I have run, and still run, mostly aluminum molds on a small 28-ton press. I have run hundreds of thousands of parts from some tools. The key is safety for the molds, and not running under flashing conditions; fix it, and then run. High tonnage and flashing molds are a bad combination.
What are the physical size of the parts? Rail car bodies, or smaller component attachments?

tkdesigner

 

[Plastserv]

One suggestion is that with your quantities why not consider making all the sides and tops flat and assemble them. This would work well for boxcars. There are some very fast cnc's lately that would make quick work of all the detail you desire. Make up a family mold out of prehard at least so that you minimize any smashing problems.