Originally published in the January 1995 issue of Advanced Systems.

First Impression

Parametric CAD with aplomb

By Alan D. Smith

Typically in the CAD market there are products that create lines, arcs, and circles. Combine these items with dimensions and notes, and out come drawings for civil, architectural, or mechanical design. Because traditional CAD tools are based on geometric objects, making a design change requires changing all appropriate components in order to make the drawing correct. But thanks to Parametric Technology Corp.'s (PTC) product, Pro/Engineer, this conventional process has become passˇ.

PTC bases Pro/Engineer on parametrics, a method of linking dimensions and variables to geometry in such a way that when the values change, the part changes as well. In this manner, design modifications and creation of a family of parts can be performed in remarkably quick time compared with the redrawing required by traditional CAD. In the past five years, PTC's success has prompted major CAD players to offer similar functions.

Pro/Engineer 13 runs on just about all workstations on the market, as well as PCs that sport Windows NT. A DEC 3000/500 with PXGTurbo graphics, 96 megabytes of RAM, and OSF/1 2.0, a 1-gigabyte hard drive, 400 megabytes of swap space, and a CD-ROM was used for this review. (Minimum requirements for DEC 3000s running Pro/Engineer include 200 megabytes of swap space, 64 megabytes of RAM, and 1 gigabyte of disk space.) The software is distributed on CD or tape. Pro/Engineer offers a painless install procedure and takes up a skimpy 40 megabytes of disk space.

Few surprises
Overall, Pro/Engineer springs few surprises. While its menu structure does not adhere to exact GUI standards, its layout and use is very good. The hierarchical menu scheme leads the user through the next required step for any given operation. Each subsequent menu has only the appropriately allowed submenu options available for any given function.

Pro/Engineer's power rests in its "features" -- design-intent definitions assigned to the geometry. Examples include a fillet along the edge of a part or the draft angle of an entire component. These features can be quickly assigned for designing, then quickly modified. With this technique, designers can create the base geometry and promptly transform their design into manufacturable components. By simply changing feature values, users can create alterations and a related family of parts.

Being all feature based, Pro/Engineer requires geometry to be created or imported and then dimensioned. For most parts, this is done in the Pro/Engineer Sketcher. The Sketcher performs automatic assumptions for constraints such as horizontal, vertical, and same-diameter size and perpendicularity.

Once the geometry is created it must be dimensioned. These dimensions are the basis of the constraints of the geometry required by the software. By using the Regeneration menu function, the system checks for over-constraint/under-constraint situations. It flags unconstrained elements by highlighting the geometry. Under-constrained sketches are not allowed. Therefore, all dimensions must be either provided with their automatic parametric name or modified with user-defined values.

For the use of geometry from other CAD programs as the basis for these profiles, Pro/Engineer supports a wealth of standard-file and model-import and -export formats, including the two most popular formats: IGES and DXF. Direct translation support is provided for CATIA (sold by Desault and IBM), ECAD, and CGM (Computer Graphics Metafile) formats from other CAD products. Conveniently, file-import functions appear as a submenu in places where the operator would logically be importing data. Note that importing IGES files into the Sketcher lets users assign parametric dimensioning to the geometry.

As with all Pro/Engineer geometry, surfaces also are controlled by parametric controls. All surfaces are created as features either by first creating the profiles or by importing file sections. Available surfaces include Extruded, Revolved, Sweep, Conic, Quilting, Blends, and Offset surfaces. Typical constraints and modification methods available for other features may also be added to surfaces. Users can replace and remove surfaces using operations similar to the common Boolean operations found in other products.

Pro/Engineer offers another function called Relations, which can enforce manufacturing restrictions or capture design decisions. Relations allow constraints to be based on equations or other constraints or variables. Family Tables, which allow spreadsheet-type editing of user-selectable/definable-dimensional parameters, provide further parametric functionality. The Instance command allows each instance of a particular family table to be displayed on the screen as a full part.

Unlike most other CAD products, Pro/Engineer actually lets users view a part in a dynamic full-shaded mode. Pro/Engineer allows for rendered images as a default viewing option. This dynamic rendered image provides a high level of visual feedback to the designer. Other solid modelers often offer a rendered image only in a static-shape form. Since Pro/Engineer is based on a nonfaceted geometry system, it can render an image before further commands -- like meshing the solid -- are performed on the image. With other CAD products, this meshing facets the solid and can take a long time to perform prior to the static render. Other display options include wireframe, hiddenline as a dashed line, and no hidden.

For drawing generation and documentation purposes, 2-D drawing files can be generated quickly from the solid model in another window on the screen. Associativity between the two formats allows the designer to make changes to the drawing that will update its related model or changes to the model that will change the drawing file.

The associativity of Pro/Engineer makes it stand out with these dimensions. In addition to driving the geometry, dimensions are used by the software for annotation in the Drawing mode. Pro/Engineer also supports driven dimensions that are more annotation-like in nature. These, too, are changed when the geometry is changed.

Bi-directional changes are supported from the drawing to the part and vice versa. In this manner, operators can make a change or update wherever they see the need. The associated modification holds true for other associated modules as well. A separate PTC application, Pro/PDM (Product Document Management), can be used to control the modification of associated files for security and release-control issues.

The $9,500-per-seat base Pro/Engineer package lets users create parts and assemblies sufficiently. Added features and specific applications require different modules (such as Sheet Metal, Assembly, Detail, Surface, Mesh, Cabling, and Manufacturing), which cost from $1,500 to $7,000 each. A bundled package that includes the Pro/Engineer core product plus eight modules costs $18,000 per seat.

Cool CAD
Pro/Engineer's modeling techniques and 2-D associativity are unequaled. With all design data based on features, quick modification of any feature of a part makes this a very productive design tool. The way parts can be created in Family Tables is valuable to companies that have a collection of part libraries. Changing data in these tables produces new parts almost instantly. Automatic annotation of 2-D drawings based on existing feature data as section and scale notes along with reusing dimensions makes the drawing generation extremely fast. All in all, this CAD product is one of the most impressive design tools on the market.

Parametric Technology Corp., 128 Technology Dr., Waltham, MA 02154, 617-398-5000, 617-398-6000 fax.

[Copyright 1995 Web Publishing Inc.]

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Last updated: 1 January 1995.