MDF Temp?

General Composites Discussions Composites Talk
#1

Hi All,

I have been charged with making some parts (3-4 parts max) off of a simple male mold. In the past I have just cut up a bunch of 1" thick MDF and sealed and effectively used the plug as a male mold, which is ideal for this type of part, but I now only use prepreg.

Question being, has anyone used MDF patterns for prepreg? I used low temp curing resin (variable from 180-250F). I was planning on coating with the same high temp laminating resin I used for my composite molds and then sanding/polishing. Does anyone know if the MDF can handle these temps safely?

Alternatively, can anyone reccomend another answer? Is there 1" thick tooling board? These do not need to be super-high quality molds, just get the job done.

Thanks!

#2

We use MDF quite often, although I try to avoid it. It starts to get a little sad at 90degC, so we try to cook at 80C and then demould and give it a slow ramp (0.5deg/min) to 120C to fully cure and raise the Tg.

#3

Thanks for the tip Brent. Anybody have an opinion if high quality hardwood plywood would fare better? I assume it would.

#4

Depends also on glue melting temperatures within plywood for example. there have been a few occasions while ive had a bit of timber in the oven at 120 and glue has run out of its joints, so certainly worth giving it a trail run i think

#5

I’ve used MDF fairly extensively, although as Moke said, reluctantly. A few things:

-Drying the MDF at temp before laminating it together can help with the high temp warpage, which means its prewarped and then shaped.
-Use epoxy and Micro at room temp (the slurry helps fill gaps), or adhesive film if the budget/resources allow.
-Cure under vacuum on a flat plate (again if resources allow)
-We’ve had good luck with urethane primers for creating a nice surface (or clear/teflon tape if you don’t need a nice surface)
-You’re probably going to need to envelope bag, although if you’re careful you can get a vacuum (ish) tight surface.

You should be fine for 3-4 parts if you don’t have difficult to release or fragile features. IF the features are small or you don’t have sufficient draft expect mold maintenance somewhere along the line.

Cheers,
Mike