STandard for the Exchange of Product Model Data - STEP - weapon systems research

Program Manager, Nov, 2000 by Gerald Moeller

Why DoD Should Have an Iso 10303 (STEP) Migration Plan

The DoD needs to implement a plan for assuring that the engineering data associated with procurement, distribution, and repair of its weapons systems will support interoperability and data reuse. The STandard for the Exchange of Product model data (STEP) structure is an emerging international standard that enables interoperability resulting in large cost savings. [1] This article provides some history on engineering data, reports on STEP development progress, and provides recommendations on implementing STEP within the DoD.

Evolution of the Engineering Environment And Associated Data

In the late 80s, DoD undertook an effort to convert engineering data into an electronic media to not only physically preserve this data, but also make it universally available. The approach taken by DoD was that of basically scanning existing drawings into electronic pictures called raster images. [2] While this approach is acceptable for preserving legacy data, it is not sufficient for helping create new or reengineering weapons systems using the computer-aided design/computer-aided manufacturing (CAD/CAM) tools available today

CAD/CAM systems have experienced a tremendous growth in capability. Many of these systems initially started out as computer-aided drafting tools, offering essentially automated line and curve manipulation capabilities, which facilitated producing the conventional three-view (front, top, side) orthogonal parts drawings used by machinists.

Today's CAD/CAM systems provide many capabilities that speed up the parts design process. The biggest speed contributor is the ability to build solid models of parts as a composite of other solids like cubes, cylinders, or cones. Composite solid model structuring is accomplished by pick-and-place operations; the CAD/CAM user picks a basic solid shape out of a library of shapes, dimensions it to match the size of the feature on the new part being created, and then appropriately places it on the other composite features already structured for the new part. Solid modeling also provides a capability to freely roll the part around on the computer screen so it can be viewed from any angle. This facilitates adding new part features and checking part integrity.

Parts'designing is an iterative "trial-and-error process." The engineer is usually trying to minimize weight to enable meeting airlift constraints. In the typical partsdesign scenario, engineers develop an initial design, which they then test using simulation, stress, and fatigue analysis. These tests typically indicate a need to change some key feature, which often requires other modifications on the part, plus modifications of mating parts.

To aid the modification process, most CAD/CAM systems offer a capability to set up parametric relationships among key design parameters such as a constant hole size or a constant ratio between two or more dimensions on a part or among parts on mating assemblies. A change in a dimension on a part then automatically drives changes on mating parts within an assembly of parts. Additionally, design constraints can be applied so when the bumping effect of a change in a dimension occurs, the CAD/CAM user will be notified if a spatial constraint has been violated.

Today's CAD/CAM systems are rich in capability to support manufacturing operations. The most supportive manufacturing role is that of providing the input file required to drive automated Numerical Controlled (NC) processes. Additionally, most of these systems provide a capability to simulate conventional cutting operations to assure part manufacturability, i.e., some part surfaces may not be accessible for some cutting tools. These CAD/CAM capabilities, coupled with automated manufacturing layouts, have in many applications eliminated the need for a machinist.

CAD/CAM systems store their data in a variety of formats, collectively known as vector formats. Vector data are often referred to as intelligent data because they embody all the CAD/CAM background structure needed to rapidly change a design. Raster data unlike vector data are essentially a bit map picture of the part generally shown in the conventional 3-view format. They essentially require the engineer to start from ground zero and develop the solid models needed to change the design or do the changes by hand. For these reasons, raster data are often referred to as dumb data.

All the CAD/CAM vendors offering products in the marketplace today have their own proprietary format for creating and storing vector data. These proprietary formats make it very difficult to move the engineering data associated with the design of a part or assembly from one CAD/CAM vendor's system to another. Complex DoD weapons system designs today are frequently done in a collaborative distributive environment among a team of designers using heterogeneous CAD/CAM systems. [3] As design complexities increase and designers are becoming increasingly distributed throughout an expanding virtual enterprise, the quantity and quality of collaborative vector data exchanges become critical elements for effective, efficient design and manufacturing.