Help needed with stree analysis of a granite strengthening rib inside Extrusion

[delco]

Hello , I am trying to see what effect filling a 80160 with epoxy granite.

I have designed the granite infill to be a lattice core inside to help with dampening and rigidity in a aluminum extrusion but have no way to quantify if it will work.

looking for someone who can take my fusion files for the extrusion and the lattice inside and determing how the twisting forces will change if any.

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[PrestonSMA]

I for one would not be using Aluminum for the Framework...

It has 2 times the Coefficient of Thermal Expansion as Steel or Iron.

Thus, with any temperature changes of the machine...it is going to move
much more with Aluminum than Steel...

How many Professional CNC machines do you see made of Aluminum...Zero
for that reason alone...

Regards,

Preston

[peteeng]

Hello Delco - Unfortunately modelling dampening is a difficult thing to do unless you have very good mechanical properties for the materials and are using a transient non linear solver. Your epoxy granite will have a modulus anywhere from 10-40GPa plus it will be stiffer in compression then in tension a further complication for analysis. The external geometry is the main stiffness geometry, adding stuff to the inside does not help much. The stiffness is a 4th power equation ie the inside stuff doesn't do much the outside does it all. All you can do is use the linear FE to determine what a filled vs a hollow section will be in terms of stiffness. Plus you can run a modal analysis to see what the possible vibration modes and frequencies are. Then there is the economics. Epoxy is very expensive but not stiff and the aggregate you use is not stiff and the composite you make is not stiff compared to the aluminium. If you read the Milli thread I go through a lot of this stuff plus tests... In short I would not recommend you go down this path.

I have done quite a bit of modal analysis on construction extrusions and they always have wobbles with the small edges and free ends. I would not use these to build a machine if you are seeking a low vibration high stiffness machine. The extrusions themselves are not efficient for their cost or weight. Std square extrusion is much stiffer and cheaper. They are convenient but not the best thing to use. I suggest you think again about how to build a machine....

Peter

Preston - just because the CoE is higher then ferrous metals is not a good reason not to use it. There are companies that use Aluminium extensively on very expensive machines, look at Datrons. Comes down to thermal management simple eg keep in a thermally stable area or complex have liquid cooled components... Peter