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Now, when you open the block's file, there will be the indentation, or space, deleted through the Cavity function. If the mold's size was not large enough to accommodate the part, you can edit the size of the mold in its respective file.
TBA: Screenshots
Complex Mold (with a more complex part) - TBA
Example of For the complex mold, we will be using an aerobody as the example, as this will aid the transition of building molds for the end goal. The process is quite similar to creating a Simple Mold, however, the challenging part will involve the planning and creation of separation markings, which will determine how the molds are created and have easily identifiable points to how it is connected/mounted to the rest of the car.
(Part updated on March 8, 2019,) the 3D model that is used in this example is: AerobodyAestheticModel_REV2B.SLDPRT, the current version of the MSXIV aerobody. Since this part is created already, you will only need to create the base for the mold, i.e. a rectangular block. It is recommended that the dimensions of the box is not too far fetched from the width and length of the portion of the aerobody that the mold will be made from. While this makes it more convenient for the part to be centered into the block without needing to make major changes to the block's dimension, always aim for a block with larger dimensions than smaller.
To start, create a New Part in SolidWorks. Choose the Front Plane and using the 
option. Note, in this case, we use Front Plane because the part we want to mold, the bumper, is in that plane. For the side panels of the car, you would use the Right/Left Planes, and for the top and the bottom of the car, you would use the Top Plane. For other areas, you would need to create your own plane to be optimal for the aerobody. In this example, the dimensions were 2000 mm x 1500 mm with an Extruded Boss/Base of 1000 mm.
The part is now ready to be used in an assembly with the model. In a new Assembly document, place the aerobody onto the document first. Next, go to Insert Components and select the block you had created previously. Place this in a location that is close to the part of the aerobody that is to be molded. In this case, place the block close or overlapping with the bumper. Move the block around, changing the view plane as required so that the bumper is approximately centered into one of the faces with the largest surface areas. Make sure the car does not go through the block, i.e. you cannot see it from the other side. In terms of depth of the intersection of the block, for now, allow the overlap to be just enough for the front of the bumper. See light blue outline of the part in the second image:
Making sure the two parts, the block and the aerobody, are connected, select the block and go to Assembly > Edit Component. You will notice that the aerobody part is now an outline rather than a solid body.
Go to Insert > Features > Cavity. A property manager will appear and asks you to select a part that will make the cavity. Select the aerobody.
Keep the Scale Parameters as 0.00% for now. Note, this function can be used to create draft angles. Click the green checkmark when done.
By default, you will still be in the Edit Component view. You will see that the aerobody is still outlined, but there is now a cavity within the block. When exiting the view, both parts will be solid. Moving the block away from the aerobody part, you will see the details of the aerobody in the cavity.
NOTE: You cannot save and keep the cavity if the two parts are not connected. In this step, undo until the parts are connected right after the cavity is created.
When saving, be sure to rebuild the parts. This will allow the changes to be reflected to the block in its original part file.
You have created your first mold of the aerobody!