Metal mould for accurate carbon fiber boxes

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Metal mould for accurate carbon fiber boxes

http://www.talkcomposites.com/Topic23477.aspx

By pineirod - 6/9/2017 5:19:30 PM

Hi everybody,

I am new here and I would like to start with a problem we are having.

We are building carbon fiber boxes“alveoles”. We have already manufactured some, but the final dimensions are noacceptable, they are 600-700 microns bigger than they should and not straight.At the end some pictures of the results and manufacturing procedure.

200 microns prepreg (Fiber/fabric: Torayca M46J /plain weave, 43% of epoxy E022, Cured ply thickness: 0.180mm) was selected.

We wrap inner moulds “mandrels” andpress them with the outer mould. All wall must be 300microns thick.

We used aluminium for the innermoulds 7075 and for the outers stainless steel 304 (1.4301).

Now the idea is designing a newmould. Attached some pictures. We want to use different material with lowerthermal expansion coefficient. We heard about THYROPLAST 2738 EHT plus,but I couldn’t find a supplier (in Germany).

I read about plastic injectionmoulds. There are many types, with low CTE and hard. My first question is therecommendation for the material. We tighten with many screws, very strong. Themould will be used like 100 times.

The tolerances in the drawings are20microns. And surface finishing Ra 0.1 /N3

I appreciate any inputregarding the design.

Thank you

regards

PS: the pictures are from the mould we've been using so far and the drawing of the future we want to build.

By pineirod - 6/12/2017 10:07:56 AM

Hi,

We are curing the prepreg in a convection oven.

We first put the mould at 80ºC for an hour. Then take it out; put the last prepreg layer (the outer one, surrounding all the inner negative mandrels) at 120ºC for 3 hours. The oven is switch off and everything is let in the oven the whole night to cool down. Finally we put the mould in a freezer at -18ºC for un-mouldig (these mandrels are straight, we need to cool them to be able to remove them).

With the new design; the idea is keeping the oven at 80ºC or maximum 100ºC because of the thermal expansion. Here attached a list from Thyssenkrupp for plastic injection. P20 looks also a good candidate, but for the final selection I don't know. The options are overwhelming. I need some guidance for the decision.

Also we want to use the same material everywhere (inner and outer parts).

To my understanding we need, low CTE, easy machinability (for the high tolerances) and hardness. And of course possibility of buying small quantities in plates.

thank you

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