Direct tooling OOA mold material

[Lander Hollevoet]

thread327-391908
For the production of a very small serie (max 2 products), I will be using OOA, vacuum bag only CF prepreg. I will be using a cure of 70°C and a post cure of 90°C. The tooling material I will be using has a CTE of 25 µm/m°C. The minimal draft angle of my object is 2°.

As I don't have a lot of experience in this matter, I would like to know if the difference in thermal expansion between the carbon fiber ant the tooling board would cause problems? Or is it nessecary to use a better (more expensive) tooling board?

 

[Compositepro]

This is a complex topic and the answer to your question depends on the exact details of your part and cure process. If your are making a flat plate CTE does not matter very much.

 

[RPstress]

25 micro-m/m/deg C is about like aluminum. A multidirectional carbon laminate will be about 2 micro-m/m/deg C if it's a symmetric layup. The initial cure of 70 deg (a temp difference of about 50 deg C) will define the temp the part cools from. Any curvature will cause spring-in. Since you have a draft angle you presumably have 90 degree corners with flanges. These will spring in by about half a degree irrespective of the tool material. This is very rough and shouldn't be affected much by the cte of the tool. Process modelling is always tricky. I'd recommend making a trial cure of a part (use a cheap but representative geometry if cost is a problem) and assess the spring.