Surface Body as derived part shows mass and changes density in part file.

[Anonymous]

Hi, 

I have an assembly file sbody.iam that is imported as a derived part into a part file. 

It shows mass in the part file and affects the density of the part file. I thought a surface body had no mass?

Is there a way to alter or to make sure the sbody.iam is represented as a reference(sinilarly to the feature in BOM in an iam file). 

[Xun.Zhang]

Hi Jm,

Ah, it seems a limitation so far to remove the mass property during shrinkwrap or derive, the alter native solution more like Copy object to a composite face and delete the derive or shrinkwrap node to clean up the mass.

Hope it helps!

By the way, could you share me a case why you would like to have the assembly in without mass property? From representation perpective, it contains mass in the original assembly and it should be accumulate in the target part as well, is it true for you?

[Anonymous]

Thanks Xun, 

So if you make a composite surface of something, it is for my purpose to trace/project the properties of a body down to for instance make a base for filling of ballast in a tank, as the ballast water must be separate from the steel of the tank. I would like to know the weight and properties of COG of the ballast water in the tank. 

I am confused with the purpose of a composite surface/surface body if it has no thickness, how can it have mass??? 

If i would like to have the mass of the .iam or .ipt for that sake (the derived part) - i would then have double weight in the ultimate assembly file where i combine the ballast and the tank. (the tank is the .iam file here). 

As i underlined, the tank (.iam file) is purely the skeleton for the tank. But a workaround is to derive the tank into the ballast ipt. Then when i have traced it, delete the tank from the ballast ipt. But again, it would be very simple task to just tick off on the derived part (do not include mass properties in the derive command).

Still having difficulties understanding the purpose of a composite surface/surface body which has no thickness...

[Xun.Zhang]

Yes, your comments make sense to me as well, contacting the project team right now to have a better understanding.

Thanks for those valuable comments!

[johnsonshiue]

Hi! This particular behavior was designed to support Shrinkwrap Substitute workflow. Basically, Inventor captures the bodies in the entire and puts them in a Composite node. And, the mass property is linked to the source assembly. As a result, the mass property would not change when a Shrinkwrap Substitute is active.

Many thanks!

[Xun.Zhang · Accepted solution]

Hello again,

Johnson is right, but for your case, it seems to add a new option to ask user to retrieve mass property or not is a better enhancement candidate, does it make more sense to you?

Thanks!

[Anonymous]

Hi Johnson and Xun,

I understand why now, it makes sense. However i think it would be quite simple to add as you mention Xun, an option for including/excluding mass properties of the derived part, or add a function called "ghost" body. It is probably less complicated to add this as exclude/include mass properties, but that is not my expertise.  

This would only be applicable in the event of deriving into a part file, as in an assembly you can select the part to be reference. 

How is this process taken from here? 

Are you including this as a suggestion to the project team?

[rayessle]

Seems that if you derive an assembly into a surface part then the mass is carried over. If however you derive a part into a surface part then the mass is not carried over. So as a workaround if you derive the Assembly into a new part then derive this new (derived) part into another new (surface) part the mass disappears.

Regards

Ray Esslemont

Inventor 2018

[LSA-skan]

Waow... We don't derive assemblies very often, so we just found out about this now in 2023. and tracking this back to 2018, and it still haven't been adressed is quite shoking to me. There must be more people using inventor, that do not want the mass from a derived asselmbly carried over to the part...? I understand why it was made this way, but i don't understand why there hasn't been made an option to disable the mass export...?

[johnsonshiue]

Hi! This is specific to deriving an assembly as a composite node (mixed body). The physical properties do indeed carry over from the source, since it is a shrinkwrap/substitute representation of the source assembly.

If you don't want the source assembly to influence the derived assembly part, you should set the output to individual solid bodies or merge solid body.

Many thanks!

[LSA-skan]

Hi Shiue

Thanks for the quick reply 🙂

im using the derived assembly to make a new part, that uses geometry from the assembly. So im only interested in the geometry and not the parts themselves. Changing the derived Assembly to multiple bodies, single body or composite feature, doesnt help. the mass is still carried over. I could maybe, as one suggests, make the derive assembly in to a single part and the drive that to the new part, but that is just a temporary workaround in my opnion. 

[johnsonshiue]

Hi! I am sorry I am confused. If you use Derive Assembly, only the Composite option will carry over the assembly mass prop. Other output options (solids) should allow you to set the material style and evaluate the mass accordingly.

For Simplified (or Shrinkwrap) substitute parts, they represent the source assembly in a different way. As a result, the mass prop always comes from the source assembly.

If you have an example that exhibits a behavior deviating above descriptions, that will be a bug. Please share it with me directly [email protected]. I would like to understand the behavior better.

Many thanks!