Thermal influence on tolerance stack-up 1

[Azzazil]

Hello, I have doubt with calculation of minimal gap due to tolerance stacking but under thermal impact on high temperatures.
Attached is sketch drawing with two examples one example is calculating radial direction of tolerance stack-up of rod and tube and second one is calculating liner stack-up of parts in simple assembly.

Calculation is conducted for first example with tolerances that we have smallest inner diameter of tube and highest diameter of rod and I am checking what is final gap when parts are heated on 120°C. For second example tolerances for parts are used when they are at max plus tolerance. What is confusing me is this case where I have assembly how to properly calculate his thermal expansion when I have formula for thermal expansion Δl = α*l0*(t1-t0)where α is coefficient of thermal expansion and it is specific only for one material of one part not for assembly where we have couple parts with different materials. Does anybody have idea how to proper calculate this when we have thermal expansion for assembly?
Attached is also my calculation with marked cells what is confusing me.

 

[greenimi]

Use CETOL software

Include the Effects of Thermal Expansion in your Model with CETOL 6σ v11.2
CETOL 6σ v11.2 tolerance analysis software adds thermal expansion, and improves feature collector, and floating joint tools
MCKINNEY, Texas – April 21, 2022 – Sigmetrix, experts in mechanical variation management, announced their latest version of CETOL 6σ tolerance analysis software, version 11.2, is now available for immediate download.


CETOL 6σ is the world’s most powerful tolerance analysis software and was specifically developed to promote manufacturing efficiency and productivity. Designers and engineers use CETOL 6σ to see the impact that tolerance changes will have on their overall assembly. The cutting-edge technology enables product development teams to optimize their design and manufacturing goals so they can deliver higher quality and more precisely engineered products.

https://www.sigmetrix.com/press-rel...-expansion-in-your-model-with-cetol-6s-v11-2/

 

[Azzazil]

Will demo version be enough to do analysis?

 

[greenimi]

Will demo version be enough to do analysis?

No idea. You have to try.... or ask Sigmetrix

 

[3DDave]

There are two problem types to solve.

One is the steady state temperature which simply changes the part dimensions and can be done by simply scaling part models by the amount of expansion. However this only works for isotropic materials - that is materials that are uniform in all directions - and not for materials such as oriented fiber composites. For non-composite materials, just scale each part according to the thermal coefficient of expansion and that gives the nominal gap at the related temperature.

The other one is much more difficult - transient thermal analysis where the parts aren't all the same temperature and/or when the parts have a temperature gradient. These cases can cause parts to become bent or oval or other difficult to analyze shapes. These are typically managed by finite element transient thermal analysis. The worst case can be on temperature increase or temperature decrease and may be worst in different areas under each case.

It would surprise me if CETOL was using finite element methods or transient response analysis.

 

[Azzazil]

Thanks 3DDave, I didn't work with FEM programs to check transient thermal analysis but good point when I had time I will also try to check that but at the moment I don't have.
Also your approach for scaling parts is good point, in my case I manage to get some reasonable results when I propose for example 2 that parts 1 & 2 are constrained on ends and I set absolute value for assembly length to 48 mm without tolerances in that case when I have thermal impact it will count for worst case and gap will be minimum as possible.