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OPTICast UNIT 4: Selecting Geometric Design Variables

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Geometric design variables are those parts of the model that you will allow to change in size during the optimization process. The most obvious choice for this would be riser/feeder size, but could also include things such as gate size, or even a part of the casting geometry itself, if you can adjust that feature separately.

When you select the Geo. Design Tab from the Create/Edit Optimization Project window, you will see something similar to this:

The general procedure is to first use the model building tools to select a part of your model that you want to be a geometric design variable, then click on the add variable button on the Geo. Design tab. You can choose to have the geometric design vary in the horizontal and/or vertical direction. You need to tell the system where the design is locked, or pinned, by clicking with the mouse. Let’s see how this would work with our plate casting.

As an example, let’s create a geometric design variable that will consist of both the riser and the riser contact. First, on the Model Building Icon Menu, click on the arrow to choose Select Shape Mode. Then, holding down the CTRL key, click on both the riser and the riser contact to select them at the same time. The riser and contact should change color, as shown in the figure on the next page, to indicate that they have both been selected.

Once the features are selected in the Model Builder, click on the add variable button. The system will add a new Geometric Variable to the list with a default name that you can rename if you like. The system will also set up defaults, including high and low limits for the change in vertical and horizontal scales, as well as the Pin Point Location, about which the scaling takes place.

The default values for upper and lower limits for the vertical and horizontal scales are 1.5 and 0.5 times the current size of that dimension. So, for example, if the riser was originally 4 by 4 inches in height and diameter, the system would be able to modify the riser size between 2 by 2 inches and 6 by 6 inches.

To change the name of the variable, simply type over the default name listed in the Name box. This will automatically change the name listed in the Variable List.

The Pin Point Location can be specified in two ways. First, if you know where you want the Pin Point, you can simply type in the X, Y and Z coordinates for the point. If you do not know the exact location, you can use the Pick Point function to find it.

To use the Pick Point function, you need to first expose the location you want to choose in the Model Builder. For example, we’d like the Pin Point to be at the center of the bottom of the riser contact. To see this location we need to rotate the model up, select the plate section, and select Show Hide, to temporarily hide the casting, so we can see the bottom of the contact. Then, check the Pick Point box on the Geo. Design tab and click the mouse on the bottom center of the contact. The coordinates of that location will then be entered onto the tab. The figure on the next page shows typical results.

This example shows that the default name was changed to Riser Size, and that the Upper and Lower Limits for the riser height and diameter were left at their default values. The Pin Point Location was selected using the mouse. Notice that the location is very close to 4, 4, 2, which would be the exact location. Such small variations will not make any difference in the simulations and can be safely ignored.

It should be noted that Select Shape Mode is a ‘sticky’ function; i.e., that mode stays in effect until it is de-selected using the mouse. When removing the casting from view to pick the base of the riser contact, you may need to move into and/or out of Select Shape Mode more than once. If the Create/Edit Optimization Project window gets in the way, you can move it by dragging on the title bar until the part of the model you need is visible.

If more variables are desired, they are added in the same way, by selecting the geometric feature, then choosing add variable from the Geo. Design Tab. To reduce optimization time, keep the number of variables to a minimum. And, if possible, use linked geometries, as described in the next section.

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