Mass properties.

Has anybody seen problems with 2003 SP3 reporting incorrect mass properties
in an assembly where parts have configuration driven material properties,
i.e., a steel and aluminum version of the same part? I ran across this
today.

 

Paul,

Thanks. This will help. The problem was repeatable within the session until
we deleted all configurations and had to manually change each part to get
the assembly MP to change. Didn't matter whether the MP were changed in the
default config or any of the others, it was stuck.

I didn't think to try shutting down SW and restarting it.

 

If I might ask, how are you able to set different material properties for
part configurations? I didn't think this was possible. If it is, I would
love to know how to do it.

Greg Wedeking

 

It is pretty simple:

1. Create/activate configuration
2. Set mass property while that config is active.
3. goto 1 till done.

Since there is no documentation on this and no configuration control while
setting material properties one could look at this as a serious bug or a
feature. It is a serious bug in that a multi configuration part could have
different and unintended mass properties in various configurations. It is a
feature if you need different mass properties in different configurations.

SW2003 SP3.0

I couldn't find any mention of this one way or the other in the KB, online
help or in the list of SPRs.

There are two big questions:

1. If a company is using this "functionality" and it gets "fixed" how is it
to be handled?

2. If a company wants to check its assemblies with multi-configuration parts
for the correct mass properties how do they do it?

And while we are at it, how are mass properties set for Toolbox parts? Do
they use the default part template? If so, what if it is set for plastic or
aluminum? We are finding a lot of fasteners in assemblies with plastic
densities.

 

...snipped

I've noticed this for some time. My Toolbox parts have density of 0.0361273
lb/in^3 (1000 kg/m^3). But since I don't have a part template with this
density, it looks like Toolbox is arbitrarily using this value.

I just created a PEM fastener that is explicitly aluminum, and it comes up
with the same density. Just another case of kicking the product out the
door? I thought that Toolbox was better supported back when Cimlogic owned
it.

On a similar subject, I was surprised to find that the individual parts made
with the split part command do not inherit the density of the parent part.
In fairness, the user *is* prompted to choose a template for the child
parts, but it would be much more intuitive if an option were available (or
the default) to overwrite the parent part's document properties onto the
child parts.

Art Woodbury

 

Greg,

We found a reference in the help to configuration specific mass
properties. This is the only thing in the documentation that I have
been able to find on the subject. Here is a quote from Summary Info –
Custom and Configuration Specific:

You can add system-defined, configuration-specific mass properties as
a custom property, using either the Custom or Configuration Specific
tabs. Use the Configuration Specific tab to display with other
configuration-specific properties. Mass properties use the following,
system-generated format:

SW<mass property>@ @configuration@model

Further testing here is showing that the ability to set mass
properties on a configuration specific basis is limited to setting
mass properties through TOOLS/MASS PROPERTIES dialog box. Setting
density in TOOLS/OPTIONS/DOCUMENT PROPERTIES/MATERIAL PROPERTIES or
even viewing density there will globally set all densities to whatever
value is displayed. This may explain some of the problems we have been
having with assemblies showing incorrect mass properties.

 

If this thread has you confused 2004 can ice the cake. 2004 has a material
editor in addition the other interfaces to setting density. Here is a list:

1. Density can be set/checked in TOOLS/OPTIONS/MATERIAL PROPERTIES. Doing so
will set the density in all configurations to whatever value is displayed.
2. Density can be set/checked in TOOLS/MASS PROPERTIES/OPTIONS. Doing so
will set the density only in the currently active configuration
3. Density can be set/checked by assigning a material in the new material
editor. Doing so will set density across all configurations. In addition
the editor does not display material properties in the currently set units,
it is always SI.
4. Density can be checked throught the API. I have only looked into VB and
have not found a way to set density. Someone else may know how to do this.
As I recall the results were a bit sporadic across configurations.

Note: it would be nice to be able to access the correct density for a part
and to set it through the API. We wanted to write a macro to enable
checking large assemblies for correct density in all the parts and have
been unable so far.

It would also be nice to have the typical dialog show up when setting
density giving a choice of setting all configs, this config or selected
configs. Especially in the design phase this is really helpful in testing
different material choices.

These conclusions are based on my testing. Others may want to confirm the
results, especially in 2004 and the API.

 

The toolbox addin has to be activated.

There is an SPR on this now.

 

I think you can still set density (on a part-level basis) through setting
user prefs:

swPart.SetUserPreferenceDoubleValue swMaterialPropertyDensity, dDensity

I'm also curious about whether SW2004 will give us access to setting density
by configuration through the API, so I'll look a little further.

Regards,
Brenda

 

Clarification question--
You were actually able to change the density for only one configuration when
you used tools-mass properties-options? When I try it (SW2004 sp0), I'm
getting the density changes showing up in the other non-active configs as
well.

In general it's seeming to me that the same paradigm still holds where most
mass properties can change by configuration as the geometry/size changes,
but material density is a constant for all configs. If this isn't the case,
I'd love to learn more.

Regards,
Brenda

 

There is one other prerequisite, the Toolbox addin must be activated.
Without it, SW works as intended and as you experienced. I just learned
that today.

As you can see, truly documenting a problem can take time and a lot of
trouble.

We where actually using the ability to have configuration dependent material
properties to explore what using different materials in the assembly would
do to the overall weight. This might make sense for a plastic assembly or
in our case where trading steel for aluminum might help us meet a weight
target. With the emphasis now on embedding FEA in CAD this kind of thing
makes a lot of sense.