Picking the Right Mold-Design Tools for SolidWorks

February 10, 2004 | Comments

In an April 2002 article titled, “Mold design automation for SolidWorks,” we described two sophisticated packages from third parties that help design injection molds. SolidWorks 2004 introduced its own set of tools for mold design. In light of these new SolidWorks capabilities, do mold designers still need to buy Manusoft’s Imold or MoldWorks/SplitWorks from R&B Limited?

The answer depends on the types of molds your company designs. For simple tools, SolidWorks’ standard functions might be adequate. Designers of complex tools with intricate parting lines, sliding and lifting surfaces, cavities that must be cut with electrical discharge machining, hot runners, and complex cooling channels could benefit from the advanced design aids available from independent software firms. In this report, we’ll review the differences between SolidWorks’ standard capabilities and those available from third parties to help you make the right choice.

The mold-design process

Mold design with three-D CAD software can be divided into two main tasks: designing the core and cavity inserts and designing the injection-mold assembly. Core and cavity inserts form the actual surfaces of an injection mold. They conform to the shape of the finished part with allowance for shrinkage as the molded material cools. The inserts are forced together by a mold press prior to casting a part. After the part is cast and has cooled sufficiently, the press separates the core and cavity inserts to release the finished part.

Core and cavity inserts below are for the molded part shown above.
Core and cavity inserts below are for the molded part shown above.



The injection-mold assembly is a movable framework that holds the core and cavity inserts in the molding press and allows the mold to open and close. It also supports the systems that feed molten material to the mold cavity and supply coolant to remove heat from the mold. Mold assemblies contain hundreds of components. Some parts are purchased from catalogs while the mold shop fabricates others.


Exploded view of a simple mold-base assembly.
Exploded view of a simple mold-base assembly.

Let’s compare the capabilities of SolidWorks’ standard mold-design aids with those of third-party tools.

Core and cavity design

SolidWorks 2004 primarily aids designers in designing core and cavity inserts. Draft analysis helps designers select parting lines and identify surfaces that have no draft angle or will lock in the mold. This capability enables designers to correct molded-part models before giving them to tool designers.

The first step in designing mold inserts is to make a scaled replica of the part model that compensates for shrinkage. SolidWorks, Imold, and SplitWorks all have this capability. However, SolidWorks requires the designer to look up and key the appropriate scaling factor, while the other products suggest values based on the type of material being molded. If your company uses relatively few materials that you know well, this difference might not be important. But professionals who design tools for a variety of customers and materials may appreciate having this function be more automated.

After scaling the part model, designers must separate the surfaces that will define the core (male) insert and the cavity (female) half. To do this, designers must first draw a parting line that separates the upper and lower halves of the mold. In many parts, the location of the parting line (actually a series of continuous lines and curves) is obvious. In such cases, both SolidWorks’ standard tools and those of Imold and SplitWorks are equally effective. However, when presented with more difficult geometry, Imold and SplitWorks are capable of finding better parting lines in a more automated fashion than SolidWorks.

To test parting-line capability, we asked Manusoft, R & B, and SolidWorks to create inserts for a mold of a car body. The best parting line passes through the center of the car door along the crown of the curved surface. Both third-party tools were able to find this line automatically in a few minutes. SolidWorks’ mold tools required more operator intervention. Before attempting to create the parting line, the designer had to employ SolidWorks’ split-line feature with the silhouette option to split the curved surfaces of the side panels. After that SolidWorks’ parting-line function was able to find the parting line automatically.


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