Mold requirement check tools

It is essential to understand the characteristics of a given mold used for designing plastic parts, which are produced using molds. If engineers lack sufficient understanding, they may be unable to make molds, attain satisfactory dimensional accuracy, or prevent such molding defects as warpage and sink marks. Should such problems occur, the designs of parts must be changed to address those problems, resulting in retrogression of the development process. Fuji Xerox thus developed mold requirement check tools to prevent changes in parts design after the related drawings are issued, as well as uneven molding quality. These problems are all related to varying skill levels of engineers (levels of understanding mold characteristics). We therefore aim to improve product design quality by utilizing these tools.

As shown in Fig. 1, the tools are used to check 3D models that are created during the design of a product, thereby allowing us to verify the quality of parts design from the standpoint of mass production. The tools have functions to check the following mold requirements: mold technical standards and product design specifications determined through in-house mold standardization activities, production requirements including the feasibility of mold structures, and accumulated design know-how (e.g. past trouble, supplier information). 3D models are checked automatically to determine whether they satisfy the mold requirements. Then the tools are used to detect and specify any nonconformance. In case of nonconformance, measures for improvement are selected from the standpoint of mass production, with feedback being provided to the designers in charge of designing the part in question.

Fig. 1: Overview of mold requirements check

We developed check tools (more than ten items) for such common features of plastic parts as undercuts and sharp edges, as well as check tools (more than ten items) for such uniquely shaped parts as developer housing parts. These tools are incorporated into the mold requirement check tools. Some of the check tools are described below. Check tool for undercuts Undercut refers to an indentation or protrusion in a shape that prevents a molded part from being directly ejected from its mold. The circled area in Fig. 2 is an undercut. In the case of this shape, there is an object in the mold-cutting direction (indicated by a white arrow).
Consequently, a simple one-piece mold cannot be used. Instead, a mold must have sliding cores that can slide in both the left and right directions (indicated by blue arrows). And given the complex structures of molds necessary for shapes with undercuts, molding may not be possible in some cases. The check tool is used to detect undercuts automatically at the parts design stage, so that we can prevent highly complex mold structures and not have to change part shapes at the mold design stage. We developed a special algorithm to detect undercuts based on analyses of undercuts in various parts. Undercuts can be detected with high precision by simply specifying a mold-cutting direction.

Fig. 2: Undercut

Check tool for bosses:
As shown in Fig. 3, we set eight items for bosses to prevent inadequate mold strength and poor molding. Based on the analyses of various bosses, we developed an algorithm to find bosses automatically from 3D models, and incorporated it into the check tool. By simply selecting a mold-cutting direction and an outer surface, detected bosses are checked according to pre-defined values (for eight items), followed by the display of check results.

Fig. 3: Boss specifications (eight items)