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CAD/CAM systems and their integration in mold design.

Wire frame, surfacing, solids, and parametrics are among the capabilities offered by different systems at various stages of the design process.

We have seen an evolution of the computer technology used within the molding industry. Currently, all types of CAD/CAM systems - from the very basic two-dimensional systems to the most advanced parametric feature-based solids - are used in the mold design process.

CAD/CAM resources vary widely because of the diverse sizes and needs of companies performing product design, mold design, and mold building. This wide variation in CAD/CAM resources is also a consequence of mold designers' servicing multiple product designers and mold builders. The need exists, therefore, to integrate many types of CAD/CAM systems.

This article does not identify the best brand of CAD/CAM software or the type of CAD/CAM system that should be used. Instead, it reviews the various types of CAD/CAM systems available and then describes techniques of integrating them.

CAD/CAM Types

For purposes of this discussion, we may segregate CAD/CAM systems by the following capabilities or types: two-dimensional (2-D), wire frame, surfacing, solids, parametrics, and features. Specific CAD/CAM systems may contain one or more CAD/CAM types.

When evaluating brands of CAD/CAM systems that contain multiple types, one should know that each type may consist of separate modules or options. Often, the options can be bundled into complete packages that appear seamless to the operator.

An example of a multiple-type CAD/CAM system may be a 2-D system that has parametric and feature capabilities, but no 3-D capabilities. Many CAD/CAM systems may have multiple types. Typically, however, they excel in only a few areas.

2-D

The two-dimensional type resembles the drafting board and has only two axes in which data are defined. It is often the foundation of a CAD/CAM system. The primary characteristic of the 2-D type, shown in Fig. 1, is a flat appearance that lacks depth.

Associated with 2-D are all the detailing and annotation methods. Cross hatching, dimensioning, notes, and labels were essential on drafting boards of the past. Today, despite efforts to achieve a "paperless" society, a need still exists for detailers' skills.

To possess powerful plotting capabilities, a CAD/CAM system must have a robust 2-D module. This includes not just the ability to plot an object, but all supporting information that describes the object on paper.

Wire Frame

The wire frame type has three axes and defines only edges of an object. As Fig. 2 shows, wire frame has an openness. Often, its appearance lacks definition. Wire frame produces an optical illusion that challenges the operator to determine if the object is coming out of - or going into - the screen.

Surfacing

One step further than wire frame, surfacing defines the shape bounded by the edges. Surfacing lacks volume. It may start with 2-D or wire frame as a foundation. It extends beyond the wire frame by defining mathematically what happens between the edges.

As Fig. 3 shows, surfacing can be used to define shapes ranging from very simple to very complex. When creating a surface in mold design, the designer must create both cavity and core surfaces to define the mold. Surfaces may be offset to generate wall thickness.

Solids

A region that is bounded, defining a volume, is indicative of the solids type of CAD/CAM system. Solids may be created from primitive shapes or complex surfaces. Some systems permit creation of solids from 2-D or wire frame.

An excellent application of solids in mold design is the creation of section views, shown in Fig. 4. However, once the section views are generated, a 2-D system is required for detailing.

Solids capabilities also include calculation of volume, weight, and center of gravity. All this information could be valuable in the mold design process.

Parametrics

Parametrics may be seen in 2-D, wire frame, surfacing, and solids systems. They permit variable dimensions and are commonly used in defining objects that may vary in size, as seen in Fig. 5.

Some systems permit the operator to first sketch in a shape and define dimension later. The technique also permits designers to incorporate changes quickly.

Features

Features can be seen in any of the prior types. Features comprise an association of CAD/CAM geometry that represents a component or an assembly. They give rise to automated capabilities, such as bill of materials, installation instructions, and typical applications when gathering subassemblies. Shown in Fig. 6, features can automate the design process and increase the efficiency of the mold designer.

The Design Process

For purposes of this discussion, we can segregate the design process into the stages of product design, cavity and core design, mold base assembly design, cavity and core manufacturing, and mold base assembly manufacturing.

Product Design

Surfacing, solids, and parametrics are often used in the product design stage. As the product shape becomes more complex, we find a shift toward complex solids with parametrics.

Solids systems provide the product designer with valuable information, including volume and fit with mating parts. Both solids and surfacing can interface with finite element analysis for analysis of the part (and application of the product) during and after the molding process. Solids can also interface to various rapid prototyping methods, including SLA modeling.

Parametrics permit product designers to begin with a conceptual shape and fine tune the dimensions to meet design requirements. This can often parallel the designer's thought process.

Cavity and Core Design

Typically, cavity and core design contains surfacing. The surfaces may have originated from prior solids or surface product data, but must include shrinkage calculations. Creation of uneven parting lines would be included in the cavity and core design.

Mold Base Assembly Design

In most cases, mold base assembly design is performed in a 2-D environment. A view of the mold base assembly shows that rectangular plates and inserts with square and round pockets and holes are abundant. With the exception of the cavity and core, surfaces are not typically found in mold base assembly design.

Cavity and Core Manufacturing

Manufacturing of cavities and cores, as well as their design, typically requires surfacing. With most manufacturing equipment, one would machine the surface of the cavity and core. Solids would be used in the manufacturing of cavities and cores if one were using a computer-generated 3-D modeling system, such as stereolithography or selective laser sintering.

Mold Base Assembly Manufacturing

When manufacturing the mold assembly, it is common to stay within 2-D or wire frame. With respect to geometric shapes, mold bases are fundamentally the same today as in the past. The mold base assembly consists primarily of rectangles and circle.

Integration

The integration process must be established and maintained by all participants. A company that is attempting to provide quality products and services to another company may find that the type of CAD/CAM system used affects communications between them. Various stages of the design process have specific needs, and companies having varying resources, but communication problems can be overcome.

Often, the data transmitter controls what is sent. The receiver must accept the data "as is." Tools are available to massage the data, but they may introduce another step that results in propagation of error. Both parties - the sender and receiver of data - must work together to ensure optimum communications, which are a benefit to all.

Conclusion

Purchasers must identify their needs and resources before selecting a CAD/CAM system type and brand. The higher-end systems are typically more costly and require more skills to operate. Lower-end systems are typically inexpensive and limited. Resources of both supplier and customer must be identified and included in the CAD/CAM selection process. Selection must be an ongoing process that continually evaluates the changing environment.

A wide variety of CAD/CAM system types exists for the mold design process. Integration of the various types is necessary, and must be structured as a cooperative effort by all participants.
COPYRIGHT 1996 Society of Plastics Engineers, Inc.
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Copyright 1996 Gale, Cengage Learning. All rights reserved.

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Author:Padalino, Anthony F.
Publication:Plastics Engineering
Date:Oct 1, 1996
Words:1321
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