Once the core and cavity have been finalized, work can begin on the remainder of the mold assembly.

Since most mold components are made up from fairly simple, prismatic geometry, solid modeling is the most appropriate method for their design and their assembly into the overall mold. Catalogs of standard mold components are required to complete the mold design efficiently as the user does not want to spend time creating these components over and over again. These catalogs are now available in a number of mold design systems, although the range of catalogs varies between the different systems. The software also needs to allow the moldmaker to design—quickly and easily—any non-standard components that might be required since few molds can be completed simply from standard components. Once completed, the designs can be added to the user’s personal catalog for future use.

As well as offering different catalogs, mold design systems differ in the degree of automation they incorporate. Some software includes a special option that allows parametric components to react automatically as they are placed within an assembly, adding all of the necessary fit-features to the connecting components. The software even adds the tolerances needed between the components.

For example, if the designer adds an ejector pin to the mold assembly, the software will automatically create the corresponding hole features in the plates through which it passes. Then the tolerances between the various components also are defined automatically. Thus, a sealing-fit hole is placed in the die block and the necessary clearance allowance added to the holes in all the other plates through which the pin passes. This automatic creation of relationships makes the development of the overall design much quicker than other 3-D mold design systems and also makes errors in the design process far less likely.

Of course, this software option maintains relationships in a similar way to linked objects in other CAD systems so that, for example, if the ejector pin is moved subsequently, all the associated holes move with it. However, the degree of associativity is more flexible, such that all component dimensions, tolerances and positions can be modified either individually or as part of a group of similar parts, or by using a global edit for multiple groups of components. To further increase design speed, all identical parts within an assembly are automatically recognized as instances of the same component so preventing unnecessary duplication of data. This reduces overall model sizes and makes regeneration of the model after design changes much faster.

However, the use of parametrics for the automatic adjustment of dimensions can produce problems. Making changes based purely on mathematical relationships will often generate non-standard sizes. This means that the components have to be specially made, which is both more expensive and takes longer than using standard components. To overcome this problem, software should use intelligent parametrics. Instead of using the exact mathematical result, the software recommends the nearest standard size to the designer. He can then choose whether this is close enough for his needs or whether a non-standard component is required.