Tip #3 - Hiding a Part in an Assembly (Going from zero to many parts, as needed by your design.)

(Note: This tip will work in both versions 2 and 3 of Mechanical Desktop®.)

Hello again and welcome to the third in our series of Mechanical Desktop® tips and tricks, Hiding a Part in an Assembly.  This tip addresses a need of ours that required different stiffening configurations for different casing sizes.   As the size of the casing grew, it's required stiffening went from none at all to several members.  This example will show you how to set up an assembly so that any part can be hidden when it is not needed.  Using this technique, you can generate complex models with various part configurations, all parametrically!

This model will start with the "morphing" structural member created in Tip #1.  We will create a simple plate sidewall and show you how to constrain the structural member to the plate to obtain the desired effects.  As a bonus, we will even incorporate the part arraying techniques from Tip #2 to demonstrate some of the flexibility of this method.

A short aside here....feature suppression, which will hide or suppress part features, is an important addition to Mechanical Desktop® 3.   That feature, although VERY useful will still not allow you to suppress the BASE feature of the part (and therefore the part itself) through the new table driven feature suppression. Using the combination of techniques described here will allow the user to fully control part visibility from Excel.  One of my main goals is to FULLY automate model creation from Excel......

What we will set out to do is create a casing side plate sub-assembly in 4 sizes with 4 stiffening configurations.  These are outlined in Table 1 below.

As stated before, we are starting with the part created in Tip #1 (Part Morphing).  Create this model as described or download the example files before starting.

A second aside here for all you structural engineers.....Yes, I know that the better configuration for the angle stiffener would be "leg out" ....I was too lazy to flip the profile since I already had the part created.... :-)

Step 1 - Modify the Structural Member Part
We must first add 2 Local Part Variables for the Structural Member or Stiffener part.   "no_of_stiffs" will define the number of stiffeners required.  "stiff_spacing" will define the spacing of the stiffeners. (If the number of stiffeners is equal to 1, this value is irrelevant.)   See Figure 1 for the initial values. (These values will correspond to Configuration #3). 

Figure 1 - AMVARS dialog showing the additional variables required for the structural part.

We must then update the table values in the Excel spreadsheet.   See Figure 2 for the configuration and values to enter.

Figure 2 - View of excel table information for Stiffener Part.

The last step is to set up the stiffener profiles for arraying so that the proper number of stiffeners appear.  Using AMARRAY, select the Angle profile.  Set the Number of Columns value equal to "no_of_stiffs" and the Spacing value equal to "stiff_spacing". (See Figure 3).  Repeat the command for the W beam profile using the same values.   The modifications to the stiffener part are now complete.

Figure 3 - AMARRAY dialog to array the stiffener profiles.

Step 2 - Create the Plate Part
Start a new part and name it PLATE.  Using the AMVARS command, create the LOCAL part variables as shown in Table 2.  The "hide_offset" variable controls the work plane that we will use to "hide" the stiffener part when it is not needed.  Normally, this work plane will be flush with the face of the plate (offset value = 0).  When we "hide" the stiffener, the stiffener profile dimensions will be set very small and the stiffener part will be pulled inside the plate part, hiding it from view.  All the other variables are self explanatory.

Now create the Excel table information for the plate part and link the part to the sheet you have created.  Figure 4 shows the Excel table for the Plate part.

Figure 4 - View of excel table information for Plate Part.

Now we can create the plate part.  Draw a rectangle, profile it and dimension with the "plate_width" and "plate_length" variables.  Extrude to a depth of "plate_thickness".   Now we must create the 2 work planes that the stiffener part work planes will be constrained to.  The first work plane will be the Cl/Edge work plane.  This will control the position of the first stiffener member on the face of the plate.  Create a work plane Planar Parallel/Offset from the left edge of the plate and set the offset value equal to the variable "stiff_offset". (Be sure that the plane offsets in the +X direction.). The second plane will be the Mate to Plate (Hide/Offset) work plane.  This will control weather the stiffener part is pulled inside the plate part or is flush with the front surface.  Create a work plane Planar Parallel/Offset from the front edge of the plate and set the offset value equal to the variable "hide_offset". (Be sure that the plane offsets in the -Z direction.).  When you are finished, the part should look like Figure 5.

Figure 5 - View of completed Plate Part.

Step 3 - Constrain the assembly.
Now all we have to do to finish is to constrain the stiffener part to the plate part.  Using flush assembly constraints with an offset value of 0, constrain the following planes/surfaces:

• The Cl/Edge work plane of the stiffener part to the Cl/Edge work plane of the plate part.
• The Mate to Plate work plane of the stiffener part to the Mate to Plate work plane of the plate part.
• The top edge of one of the profiles (I used the Angle in my example) of the stiffener part to the top edge of the plate part.

Using the browser or AMVARS, update both parts to Configuration 3 and use AMASSEMBLE to update the assembly constraints.  Figure 6 shows the results.  View the other configurations in a similar manner.

Figure 6 - View of assembly showing Configuration 3.

A final note on Mass Properties.
The Mass Properties readout of the Plate Part will be unaffected by "hiding" the stiffener profile inside it.  However, you may accidentally select both profiles if you use a crossing or window box.  This will cause an erroneous properties output.

If you would like to see screen shots of the other 3 configurations, Click Here.

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