New 3-D CAD/CAM program simplifies, speeds parts design.

New 3-D CAD/CAM Program Simplifies, Speeds Parts Design

New to the United States, an advanced computer imaging program called DUCT (Design Using Computer Techniques) is a British system that lowers the cost and speeds the modeling and machining of complex surface shapes. Much like a computerized patternmaker, this system allows the rapid design and manufacture of tooling that can produce accurate parts at minimal cost.

The system can model the interior and exterior surfaces of the most complex shapes. Unlike the "wire frame" systems most often associated with CAD/CAM imaging, it uses 3-D model representations, basically using two-and three-dimensional sectional data, to produce 3-D surface shapes.

In operation, open or closed sections of the part to be modeled are positioned relative to each other within a 3-D space. This is done by placing the sections at an operator-defined curved or straight line in the space called a "spine" and defined by at least two points, each with x, y and z coordinates. Each section of the part must have the same number of points, where each point is fixed in relation to the coordinates.

When the number of sections equals the number of "spine" positioning points, the program takes over and automatically blends between the sections to create an optimally smooth surface. It utilizes a modified version of Bezier mathematics which assumes that the representative sections and surfaces are essentially plastic and able to be manipulated at will.

As the computer operator alters the contours of any part surface requiring modification, DUCT dynamically alters the model's surface. If a section does not exist in the area modified, the program creates one for the operator. In effect, the operator can freely design or modify the most complex surface shapes.

Blending Surfaces

Multiple geometry components, comprised of surfaces by the program, make up a part to be designed. The operator first models the various surfaces to their nominal dimensions and true position in the 3-D space, then, using the system's blending power, he molds the various surfaces into a completely modeled part.

Once modeled, he can use the system's visualization mode to call up a sophisticated, colored and shaded image of the complete part shape just as it will actually appear. With the model's exterior and interior surfaces shaded in different colors, critical aspects like blend quality, surface integrity, discontinuities and the like are quickly evident.

In addition, the system simulates multiple light sources, dynamic rotation, multiple simultaneous views and solid shading. These provide the necessary visual tools for a computer operator and the part's designer to completely analyze the design. The operator's VDT displays the part exactly as it will turn out after actual machining.

Foundry Application

The system has particular application in the foundry industry, where tooling is so critical and costly. Provisions for locating and validating gating, risers, surface area, volume, weight and cross sectioning at critical mold points are essential mold design considerations for the parts designer. This system eliminates much of the trial and error approach to mold design, and can reduce significantly the cost of producing patterns for manufacturing.

In addition, the system has an extensive data base to aid the foundry pattern department. Some examples include:

* parting lines: establishing parting lines with and without natural or radial draft;

* Shrink: determine uniform and anisotropic shrink allowances to produce a nominally dimensioned, uniform part;

* accuracy: precisely determine essentials like wall thickness and part weight, keys to producing interchangeable parts;

* checking/reverse engineering: the system's data base can interface with coordinate measuring machines (CMMs), digitizers, laser scanners;

* change orders: geometry changes from customer or production can be accommodated quickly;

* pattern repair: maintains tooling at set dimensions to reduce scrap;

* production estimates: the system's volume, surface area and cross section calculations aid in overall cost control and verification;

* analysis: provides interface with Finite Element Analysis (FEM) and simulation programs to predict part usability/manufacturability;

* customer communication: it supports effective neutral data graphic exchange specifications for easy communicating with other CAD systems;

* product lead time: lead times can be reduced as much as 33%.

The program offers a unique 3-D modeler for developing complex shapes, from initial concept to completed design, subsequently converting design geometry into precise sets of machining specifications.