topic Re: Mass & Weight in an assembly in Inventor Forum

Mass & Weight in an assembly

mahmoud.ts86 — Mon, 05 Dec 2022 15:08:20 GMT

In an assembly if i have the weight of every part added to iproperties and i cut a part of the assembly will that change the total weight ?

Re: Mass

Gabriel_Watson — Mon, 05 Dec 2022 03:07:44 GMT

As long a your assembly is updated to absorb the changes, the mass should be recalculated and thus reflect a change on the iProperty. Do you have an example to test with?

Re: Mass

mikejones — Mon, 05 Dec 2022 11:42:17 GMT

I think the answer is no if I have understood your question correctly.

Lets say you have a 100mm cube that you assign a mass manually to of 100kg and insert that cube into an assembly and remove 50mm off the height of the cube as an assembly feature cut you may expect the mass to be reduced to 50kg but it isn't, it will still report the mass as being 100kg. If the mass of the part was being calculated physically by inventor based on material density then the assembly cut would indeed give you the updated mass.

Mike

Re: Mass

CGBenner — Mon, 05 Dec 2022 12:14:21 GMT

@mahmoud.ts86

If the Mass value has been entered manually, it will not automatically update, as @mikejones mentioned. The only workaround for this I've ever seen was to change the part density by modifying the material or creating and assigning a custom material. By calculating what the density needs to be using d=m/v (density = mass/volume), you can sort of force the part to have the mass you want it to have. And since the value of Mass now is no loner manually entered, but is a result of this trickery, it should update when the model changes. It's a lot more work, and I haven't tried it since IV 2015 or so. I used to use this to force the Mass to be the known weight of dumb solids, usually STEP files of purchased parts. Manually entering Mass caused errors in the center of gravity, so this was a nice workaround.

Re: Mass & Weight in an assembly

Cris-Ideas — Mon, 05 Dec 2022 17:31:57 GMT

In the assembly mass of each part is added automatically by the software.

So mass of your assembly is what comes out from adding all your parts.

As far as I remember when you cut the assembly (extrude in assembly environment) mass is not updated based on this cut and it actually stays as per assembly without any cuts.

This operation most likely only removes parts of the geometry from rendering, and as assembly is a rigid body environment it calculates mechanical properties based on global properties of the parts (most likely).

What you can try (I did not) is to execute this cut in "Machining" environment of the "weldment" type assembly.

This potentially may have different result than for cut done in modelling environment of standard assembly.

(interesting BTW, I need to check).

Cris.

Re: Mass & Weight in an assembly

johnsonshiue — Tue, 06 Dec 2022 00:33:42 GMT

Hi! One workflow you may consider is to add a virtual component in the assembly. You can assign the added mass to the VC in the assembly. The mass of the rest within the assembly can stay computed. The total mass of this assembly will be based on the computed mass from all of the components except VC plus the manually added mass from the VC.

Would it help?

Many thanks!

Re: Mass & Weight in an assembly

mahmoud.ts86 — Tue, 06 Dec 2022 00:53:05 GMT

I give that a go and post an update if it works

Re: Mass & Weight in an assembly

mahmoud.ts86 — Tue, 13 Dec 2022 02:22:13 GMT

i figured out what was wrong if i leave the material weight as per default when i cut a piece out of the part the weight changes if i edit the weight in the physical tab to what the part actually weighs than it wouldn't change the weight after a cut.

thanks for your help.