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How 300,000 parts make a perfect fit

How 300,000 parts make a perfect fit

Toulouse, France-Piecing together a large aircraft is an engineering feat like no other. The ability to bring these thousands of parts together with a fit that is neither too tight nor too loose depends on the design of the individual parts, as well as assembly order and effectiveness. The best assembly sequence and assembly process will minimize the effect of variances in the subassemblies. However, the assembly sequences have to be defined very early on, prior to the heavy investment in tooling and materials. Current applications available to calculate tolerances require a fully defined product and assembly process and therefore can only be used much later in the development cycle.

To avoid costly refitting, or the redesign of parts during final assembly of an Airbus, Aerospatiale Matra's Common Research Center-which develops strategic tools common for all Aerospatiale Matra groups-created an assembly simulation tool named Anatole, for ANAlysis of TOLErance software. Anatole analyzes tolerances and assembly order much earlier in the development, prior to the validation of the build process.

"Assembly is very important, since there are five or six levels in the hierarchy for joining the thousands of parts that make up a vehicle. This level of complexity is very difficult to manage, and requires a view that can start global, and follow down to the smallest piece," says Nicolas Chevassus, senior project manager at Aerospatiale Matra. "Our goal was to control the tolerances as early as possible in the development cycle in order to optimize the assembly process."

Anatole, developed with the help of Open CASCADE (see box), only requires the form and the thickness of each part. Assembly simulation in Anatole includes sequence analysis, variation analysis and over-constraint resolution. These calculations allow the designer and assembly specialist to work together to try a number of solutions, either by modifying the design or changing the assembly order. This ability to modify the assembly sequence can enlarge the part tolerance values, which lowers manufacturing costs.

The Anatole application functions as a geometric preprocessor between the CAD modeling and assembly data and Aerospatiale Matra's proprietary calculation code. Its software analyzes a variety of aspects needed to validate an assembly process. For example, Anatole has a modeler for assemblies and solvers for both over-constraint loops and tolerances. The application will not only perform the calculations necessary, but also has assembly knowledge integrated into its functions, so different types of attachments are automatically done in a specific order.

Because of Open CASCADE's open source environment, Anatole is compatible with a variety of CAD systems. Geometric data is transferred though a STEP AP203 interface, or can be more tightly integrated into a specific CAD system. This feature was particularly important since the Common Research Center of Aerospatiale Matra develops strategic tools for all the Aerospatiale Matra groups. In addition, the Center needed to develop a dedicated, specialized tool adapted to the assembly specialists who are not regular CAD application users.

Anatole is seen as a strategic tool to improve product quality while shortening assembly times and reducing costs through fewer errors and enlarged tolerances in manufacturing. "The simulation of construction and assembly also allows us to better identify the inspection points needed," Chevassus adds. The application is currently under final evaluation by Aerospatiale Matra Airbus, with a goal to offering Anatole to other Aerospatiale Matra subsidiaries and partners in the future.

Open code CAD

What if your company decided one day that it would start giving away its main product?

You might be a little concerned about where your next paycheck would come from, or how your office would pay the rent. But on December 7, 1999, that is exactly what the French software company, Matra Datavision, announced it would do, when it took its biggest program "Open Source" and made it available online.

In the past, Matra Datavision was best known for supplying process engineering solutions based on EUCLID. But today the company's main software development focus is Open CASCADE, a platform of components for the development of trade-specific modeling applications, ranging from CAD/CAM/CAE, biomedical software, and optical simulation, to CFD and product design. It was previously known as the "CAS.CADE object libraries," which had an installed base of 130 active customers using 250 development licenses worldwide.

But instead of selling the software based on the platform, Matra Datavision now sells its expertise in training, consulting, and support. An additional offering is its "turnkey" service in which the company creates specific applications for a client. Since Open CASCADE is not an end-user CAD program, it does not compete with software programs like AutoCAD and Pro/ENGINEER, but rather, helps customers develop their own niche applications.

As with all open source software, the philosophy is that all these developers will share their creations, so the program will benefit from the efforts of thousands of minds, not just a single company. Located on the web at and (a developer's site), Open CASCADE gives developers free access to the source code of dozens of 3D geometry data structures and hundreds of modeling algorithms. The C++ code makes it legible to the major flavors of Linux, Sun Solaris, Silicon Graphics IRIX, IBM AIX, and Windows. It reads and provides output to standard IGES and STEP data formats, supporting interoperability. And it allows companies to rapidly develop personalized applications, by providing model parameterization and the power to attach non-geometric data to geometric objects.

Says Marketing and Business Development Manager Sana Abou-Haidar: "Open CASCADE greatly facilitates developing, because it provides a ready-to-use architecture. It's like a mold, or a template of data structures which users can then specialize for their particular application."

And how is the strategy going? Matra Datavision reports 125,000 visitors to its sites between the Dec. 20 "open source" announcement and the end of July, including 5,500 visitors who downloaded Open CASCADE. Compared to the 130 customers who paid to use the program in all of 1999, that is one trend that makes Abou-Haidar very happy.

TAGS: Aerospace
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