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Paul Hamilton Paul Hamilton
Director CAD Segment

3D Technologies for Stamping Die Design

August 1, 2014
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Understand the differences between parametric and direct modeling to find the right method, or combination of methods, for the die-design job at hand.

3D technologies for Stamping Die DesignMetal stampers have a variety of software tools available to them: design tools (CAD), simulation and analysis tools (CAE), and manufacturing tools (CAM). On the design side, the most often used design tool is referred to as parametric or history-based modeling. Another technology quickly gaining acceptance: direct modeling.

A Brief History Lesson

In the early days of mechanical CAD, software developers selected one of two techniques for developing geometry at the accuracy levels required to support mechanical design: construct solid geometry (CSG), and boundary representation (b-rep). The CSG technique to create and modify geometry uses primitives such as cylinders, blocks and cones with Boolean operations such as union, intersection and combines. The primitives and Booleans were organized in a structured tree. To modify the model, an existing primitive or Boolean, or both, could be edited or replaced. The designer could replay or regenerate the tree structure, resulting in a different 3D object.

The b-rep technique of representing 3D shapes describes the connectivity (topology) of vertices, edges and surface boundaries to form faces, which connect to form solid bodies. It provided flexibility in the types of geometry described, but proved somewhat rigid when it came to editing the geometry. On the other hand, CSG traditionally has proved somewhat limited in the types of geometry that could be represented, while providing editing flexibility.

In the early to mid-1980s, work by Sam Geisberg (a Russian immigrant and mathematics genius) and others sought to combine the CSG tree structure with b-rep primitives, so that the b-rep primitives could be created with sketches. Any primitive shape could be defined and used in the model creation. These sketches were parametrically controlled and managed as elements of the feature tree. As such, the resulting b-rep primitives (features) were parametrically controlled. This combined the robustness of b-rep with the editability of CSG and created parametric modeling, also called history-based or feature-based modeling.

direct geometry editing and parametric modeling
 Fig. 1
As parametric modeling became the industry standard for 3D mechanical CAD, Hewlett Packard worked to develop a different to make b-rep more flexible. It sought to remove the need to understand design intent before beginning the modeling process. Staying with pure b-rep, HP developers found s to make the software more flexible, and their development work led to the creation of dynamic (or direct) modeling. (The organization responsible for mechanical CAD at HP separated from HP in 2000 and became CoCreate Software, purchased by PTC in 2007).

With direct modeling, any 3D geometry can be fully manipulated and integrated regardless of how it was created, or the CAD tool used. This reduces the need for modeling standards, improves interoperability and reduces the amount of model recreation.

The Parent/Child (Part/Die) Relationship

We describe parametric modeling as being a history-based process, and direct modeling as being history-free. And while designers now can directly edit geometry in a history-based environment, these geometry edits must be captured and maintained in the history tree. Designers also now can control geometry parametrically in a history-free environment. So, both methods provide direct geometry editing and parametric modeling and control (Fig. 1). The fundamental difference: history-based methods record every modeling operation.

Aligning technology to real business value in die design
 Fig. 2
How do these differing capabilities impact die design? To the right of the value pyramid (Fig. 2) we provide examples of how business objectives and process drivers apply to die design. Dies typically are “children” to the actual stamped part (the parent). As a result, the natural parent/child relationship of a history-based CAD system can be very useful for die design. If dies are tightly connected to the native master part (using the same CAD system for part design as for die design), then the designer can gain significant value from this parent/child relationship to drive automation into the design process. In this case, direct-editing capabilities in the history-based tool may prove useful for making minor refinements as the die design matures.

Handling Design Changes

Pros and Cons of History-Based and History-Free Modeling

History-Based Modeling Benefits

• Mature CAD products with many die-design-specific extensions

• Excellent for design optimization and automation

• Develop reconfigurable intelligent platforms, and reuse

• Inherent feature-to-feature associativity (part > strip > die)

• Many designers with experience in one or more of these tools

• Growing direct-editing capabilities for improved flexibility

Challenges

• Long learning curve, can be complex

• Data exchange at the history or feature level

• Must plan ahead and follow good modeling practices

• Complex dies can be overwhelming to the system

• Large file size and potential slow performance

History-Free Modeling Benefits

• Relatively short learning curve, easy to learn

• Many s to create and edit geometry

• Work with geometry from any source

• Independent from how geometry is created

• Can work with STEP and IGES data as native data

• Flexibility in capturing design intent

• 70- to 90-percent smaller files

Challenges

• Many immature representations of direct modeling on the market

• Few die-design-specific extensions

• Less optimized for design optimization and automation

• No parent/child relationship, i.e. no inherent feature-to-feature associativity
If on the other hand the designer works with non-native data and the business demands excessive data exchange between varieties of CAD tools, then direct modeling can become a significant tool in the CAD toolbox. A quick and easy metric to consider: the amount of geometry being recreated, either manually or automatically, as a result of design changes or next-generation designs. Direct modeling provides an opportunity to greatly reduce the amount of geometry that gets recreated, allowing the designer to leverage and reuse geometry in s that previously were not possible.

While some may consider history-free direct modeling as a lower-level design tool suited only for quick and dirty geometry creation, some mature direct-modeling systems will create geometry at a very high level of accuracy and quality. After all, in direct modeling, geometry is the master rather than a feature tree. To work effectively, the geometry must be robust and accurate. Also, mature history-free direct modeling can allow designers to add parameters, relationships and constraints to geometry, even STEP and IGES geometry.

Here are seven factors driving the growing use of history-free direct modeling:

1) One-off design, where front loading a design with robust design intent and structure does not yield long-term value;

2) Where speed is more critical than highly parameterized and structured models;

3) When designers must work with non-native CAD data and interoperability;

4) Where unpredictable late-stage changes occur often;

5) Where product lifecycles are short, i.e.; little payoff for the investment in the structured/ordered model;

6) Where many iterations are needed to make critical design decisions; and

7) When stampers need to get parts out the door as quickly as possible. MF
Industry-Related Terms: CAD, Case, Die, Feature-to-Feature, Form, IGES, Model, Surface
View Glossary of Metalforming Terms

 

See also: PTC Inc.

Technologies: Software, Tooling

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