question on injection mold design / plate thickness issue

[al204]

Hello ProE users...


This time I have a question on injection molds. I have been assigned my first design project.

How can I estimate the thickness for the cavity plate? What should be the minimum plate thickness remaining after creating the cavity?


I work at a toolshop, most people here decide what plate thickness to use based on experience, because such thickness has worked before with a similar, etc.

However I need to present the technical argument on which I have based this decision.
I thought of calculating the minimum plate thickness (after creating the cavity) to allow it flexing 0,05 mm under a distributed constant force.
The constant force would be (injection pressure x projected area)...you think this is an educated way to justify such decision?? when you design a mold how do you decide what plate thickness to use?

Unfortunately we do not have a CAE software such as moldflow or moldex 3d. I would be using pro-mechanica for the flexing calculation.

thank you, best regards,

Al.
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[scooke]

Hi Alvaro



You are making assumptions which are not correct in terms of the force
generated by the pressure. The pressure across the cavity will be different
everywhere (highest near the gate and lowest at the last point to fill).
Also using injection pressure x projected area

takes no account of the viscosity effects of the melt, which dramatically
affects the forces applied to the die plate. Any such inputs into Mechanica
will give you incorrect results!



Unless the total mould height is critical (ie to fit the mould in a
particular machine), I think you are wasting your time (and the companies
money!) trying to save a few kg of tool steel. In my 30 years of experience
as a mechanical engineer working in the tooling industry I have seen far too
many moulds that are made with too thin die plates, and it is false economy
to save a few $ on tool steel compared to the cost of the toolmaking hours
that are put into that thin piece of steel!



Regards



Steve



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