Power to Handle Complex Geometry
For the software to be usable for plastic part design, it must be powerful enough to handle the complex geometry. The system must possess round, draft and complex surfacing capabilities.

The ability to sweep and loft surfaces and solids are typically necessary.
Import, Diagnose and Repair Geometry
Unfortunately, we can’t get away from this. Inevitably you will get files from customers or suppliers that will be in a format not native to the 3-D CAD system you are using. Modeling often begins with importing the model and then diagnosing and repairing it. Look for systems that include tools to run import diagnostics and even automatically repair and zip gaps in surfaces.

Most times, you will have to do some manual repair, so look for tools that make this easier. For example, some tools offer feature recognition for imported geometry, the ability to automatically select and remove rounds and the ability to automatically re-trim the edges once the rounds have been removed. This is especially helpful to mold designers who must add draft to a customer part that already has rounds and is drafted improperly.

Specialized Mold Design Functions
Mold design typically follows a series of steps, and there are particular features and functions that mold designers look for to get their jobs done faster. Besides importing and repairing data, and modeling complex geometry, mold designers need other specialized mold design functions such as parting lines, parting surfaces and splitting that are unique to mold design. Let’s look at these specialized functions in more detail.

Create the Mold Parting Line
The parting line is the foundation for all other mold geometry to follow. Although many parting lines can be determined by eye, there are many situations in which the parting line is not as obvious. Systems that can create parting lines automatically typically perform a draft analysis based on user-defined pull direction by finding the boundary between positive and negative draft. Unfortunately, this does not always give you the solution you want. Often the draft on the part is not correct or there are multiple possible draft solutions. Some systems allow manual interactions in the automated mode, which allow the moldmaker to apply his own skills for questionable areas, and even get feedback as to whether the parting line is complete or not.

Create the Mold Shutoff Surfaces
Steel-to-steel shutoffs are some of the toughest geometry to model in a mold. Look for software that allows automatic and interactive shutoff surface creation. The ability to toggle through shutoff surfaces that are created automatically by the system significantly speeds up parting surface creation

Create the Mold Parting Surface
The main parting surface is usually based on the parting line. Again, as with parting lines and shutoff surfaces, automated functionality with the ability for the user to manually interact is best. Areas where surfaces cannot be created automatically, or where the automated surface creation is unacceptable, require surfaces to be created manually. Organization of parting surfaces is important. Look for software that allows you to create “folders” to help organize and keep track of parting surfaces.

Split the Mold
Now that the appropriate surfaces have been created—including shutoff and main parting surfaces—the system should be able to automatically calculate how to split the mold block into solid geometry.
Add Geometry to Handle Undercuts (Slides, Lifters and Cores)
Before modeling any inserts, cores or pins, an undercut analysis (see next section) should be performed on the core and cavity blocks to determine if any side cores or lifters are required. The creation of core geometry is usually achieved by sketching the outline of the core on an appropriate planar face or plane. This is then extruded through the mold block cutting out a solid. The user should be able to add draft in the pull direction for a side core by including it in their sketch of the core profile. In some CAD software, draft in the retract direction for the side core is handled automatically by the system with an ability to input an appropriate draft angle.