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Mass properties when no material is defined

Question asked by Loren Sackett on Jun 26, 2013
Latest reply on Dec 14, 2015 by Mike Pogue

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When I make a part and then go to mass properties it gives me a weight. Oftentimes this weight (mass) that SW tells me fails the sanity check. Then I will check and find that no material is defined.

Why does Solid Works spit out a weight when there is no material defined? Is there a logical reason for it to use the density it does when there is no material defined?

Part of me wishes that SW would throw out a warning when no material was defined rather than throwing out a random/wrong weight. On the other hand, when I measure the weight of a big assembly, I don't want to have to worry about defining a material for every little bolt, nut and washer.

What do you folks think about this?

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Jerry Steiger Jun 26, 2013 7:58 PM
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Loren,

I believe that the default material density for SolidWorks is 1 gm/cc. You can set up your part templates to have whatever density you like. Since a lot of our parts are Polycarbonate, I use a value of 1.20 gm.cc. I typically don't define a material, as the clear Polycarbonate appearance isn't good for most of our parts. When I work with other materials I have to remember to set the proper density, unless I go ahead and use a material.

I guess the existing SW way of handling weights works OK for me.

Jerry S.
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Kieran Choy Jun 26, 2013 8:18 PM
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When no material is specified, the density is 1000kg/m^3 or 0.001g/mm^3 (sorry if you use imperial), which is about the same as water.

If you want to set a default material, start a new blank part, assign the material of your choice (e.g. mild steel) and then Save As a part template. When you start new parts with this template your parts will already have the Mild Steel material (and density) applied.

You can Shift-Select multiple parts in the Assembly Feature Tree and then right-click and apply a material to all of these parts.

If you have SolidWorks Professional or Premium I think you can use Design Checker to ensure models have a material applied to them.
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Rob McGivern Jun 27, 2013 5:34 AM
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As already stated, SW uses a default material density, even with material has not been added.

My prefered approach would be.

Open new part.
Then > Tools > Options > Document Properties > Material Properties
then add some more zeros to the default density.

default is 0.001 kg/cm^3
I use something like 0.000000001 kg/cm^3

This means the part is much lighter. Then save this part out as a template.

It's the designers job to check they have added material to all the parts. I like to check the weight is correct, but before doing so I will create a BOM with the material as a property. This way I know all the parts have material applied.

Hope this helps
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- Randy Miller @ Rob McGivern on Dec 14, 2015 4:29 PM
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  We actually didn't want to underestimate mass of an assembly or part so we went the other way and increased the default density by several orders of magnitude so it would be obvious that some parts still needed materials assigned (i.e. 276771 g/cm^3). It works great to identify which parts have been overlooked, especially when looking in Assembly Visualization where you can see the list of all parts and sort highest mass to lowest!
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  - Mike Pogue @ Randy Miller on Dec 14, 2015 6:04 PM
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    Yeah, much better to have a part weight 1000x too much than to accidentally omit it from the weight budget.
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Loren Sackett Jul 1, 2013 12:02 PM
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Ahhh, the density of water. We use imperial units so I did not make that connection. Thanks for the input everyone.
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Mass properties when no material is defined

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