Mass calculation when derived assembly in a surface

[MIRKO_G]

I have a problem with derived parts of assemblies that I import as composite and then surfaces, where the physical iproperties, the mass value is retrieved that of the assembly and the density (looks like) an average value of the assembly.

If  I derive a part in a surface, the mass is correct =0 but why when i derived an assembly in a surface is not the same?

does anyone have any idea if there is a reason and if it is possible to correct?

  

[JDMather]

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@MIRKO_G wrote:

If  I derive a part in a surface, the mass is correct =0 but why when i derived an assembly in a surface is not the same?

does anyone have any idea if there is a reason and if it is possible to correct?

  

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That is interesting.

The only thing I can suggest is to override the Mass, but if you forget to do this - this could be a problem.

(It will maintain the override once you set it.)

[MIRKO_G]

for me this is not possible. if I need the derived assembly to create new solid features in the part, the mass cannot be 0.

[rogmitch]

This is something I asked the forum about a few years ago so it is a long standing issue.

One thing that is possible is to right click on the derived body (test.iam_Corp) in DERIVED testA.ipt and pick 'Copy to Construction' before deleting the original derived body.  The mass will now be zero but unfortunately the construction bodies are no longer associative 

RM

[JDMather]

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@MIRKO_G wrote:

for me this is not possible. if I need the derived assembly to create new solid features in the part, the mass cannot be 0.

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I misunderstood the question - I thought that you wanted it to be zero.

BTW - there is a bug in the forum that is causing your email to be displayed (this despite Autodesk assurances of confidentiality).  You might want to edit your profile username.

[rogmitch]

I think he means that as he adds new features the mass must then become non-zero.

Another oddity is that if you add additional solid features to the DERIVED testA.ipt the material dropdown in the iproperties panel remains inactive.  

RM

[MIRKO_G]

correct. i use the derived assembly as a surface skeleton to create the assembly references on the solid part.
mass and all physical properties do not need to be retrieved from the assembly.

certainly with inventor I can use other methods, such as adaptivity in assembly.
But the bug remains.

I find this problem in inventor version 2020, 2021 and 2022
I hope it gets noticed by Autodesk and fixed

[johnsonshiue]

Hi Folks,

This behavior exists on Inventor 2018 and earlier. This is because Shrinkwrap was a special mode of derive assembly (Composite). As a result, the mass prop for a Composite derive assembly part always came from the source assembly.

On 2019 and later, Shrinkwrap is no longer a special mode of derive assembly. Though Shrinkwrap substitute part's mass prop still comes from the assembly, the derive assembly part's mass prop is evaluated by the local geometry.

Many thanks!

[rogmitch]

Hi Johnson,

But if the 'derived assembly part's mass properties are now evaluated by local geometry' should that not mean that if the assembly parts are derived as surfaces the mass should be zero?  This is not the case for IV2022.

RM

[johnsonshiue]

Hi! I think you meant Composite, right? I am sorry if I gave you confusing information. Composite mass prop (mixed bodies) is always based on the source assembly, not by local geometry.

Many thanks!

[rogmitch]

Hi Johnson,

Yes, I should have said composite.  Thank you for the clarification regarding the mass prop source.

RM

[TomHia]

So in essence deriving an assembly as composite in order to use it as background for (especially) sheet metal parts is and will be impossible in Inventor? Unless you want to keep a list of component masses and update manually...