Design News for Mechanical and Design Engineers

FEA, in particular, has gone from an esoteric tool to one used by mainstream engineers, largely due to the efforts of developers such as MSC.Software, ANSYS, SDRC, SRAC, and Algor. In fact, a recent Design News survey shows that 79% of engineers use FEA. That same survey revealed that 15 people per engineering department, on average, use computer-aided engineering (CAE), including FEA.

Here are some examples of engineers using FEA to generate profits:

The right stuff. NASA engineers incorporated a combination of physical testing and computer simulation—the FEMAP FEA software from SDRC (Milford, OH), and MSC.Nastran—to design the Geoscience Laser Altimeter System (GLAS). NASA expects to launch the 600-lb. satellite in December 2001 aboard the ICESat spacecraft to measure the thickness of the polar ice caps.

Engineers used FEA modeling on each individual component as well as on the entire system to reduce the amount of physical testing, minimize post-testing design changes, reduce weight of individual components, and ensure the satellite met necessary requirements of space flight, says Ryan Simmons, lead mechanical analyst for GLAS.

After the FEMAP analysis, engineers exported the model to MSC.Nastran from MSC.Software (Los Angeles, CA), the primary solver for this project.

MSC.Nastran results pointed out a potential problem, so engineers used FEMAP's model interrogation functionality to search for an explanation. This allowed engineers to instantly view each part's constraints and bordering elements. Using this method, analysts quickly found an artificial grounding condition, where free-moving parts had been mistakenly constrained.

In addition to quick trouble shooting, NASA saw a reduced turnaround time. "Analyses that formerly took weeks are now done in a few days," says Simmons.

Complexity matters. Matthew Stein, president of Stein Design, a small design shop, holds a BSME from MIT and has considerable experience with traditional handbook thermal and stress analysis. But Stein used DesignSpace from ANSYS to develop the design of a plastic flow meter housing for Renau Electronic Laboratories (Chatsworth, CA). Their modular flow meters, installed in commercial coffee makers, vending machines, and water filtration devices must hold up to long-term pressures at near-boiling temperatures.

For a good high temperature performance at a reasonable price, Stein chose an NSF approved 20% glass-filled polypropylene from RTP with a tensile strength of 7,200 PSI and a 264-PSI heat deflection temperature of 285F. Stein modeled and assembled parts using SolidWorks (Concord, MA) 3D CAD software. He used split lines to cut the interior surfaces so he could load only the wetted surfaces with 200 psi, twice the expected maximum pressure. Target stress was 1,800 psi maximum (25% of tensile strength) when loaded at 200 psi.

On the first FEA run, the flow module housing had a maximum equivalent stress of 3,152 psi around the boss in the bottom center of the housing. Burst tests on an earlier version of the flow module resulted in failures at the sharp inside corner of an identical boss. To strengthen the parts without the increased cost of thicker walls, Stein added ribs around the bottom central boss in the housing and increased the inside cap radius from 0.015 to 0.093 inch. On the next FEA run, the flow module housing maximum equivalent stress decreased to 1,403 psi and the cap maximum equivalent stress decreased as well. Mold construction proceeded with the modified design.

"To speed the analysis, I added a feature to my 3D model to cut away the rest of the model except for the area immediately surrounding the snap," Stein says. "This cut is easily suppressed or deleted to return the model to its previous state."

Another testimonial for software use comes from Kevin Woolsey of ELDEC Corporation (Lynnwood, WA), designer and manufacturer of electronic sensors and systems for aerospace and defense applications. "The bottom line is that the manufacturer gains a higher profit margin while the customer gains a high quality product and a reasonable time to market," he says. "I don't see any other way that is as cost effective or more accurate." ELDEC engineers use Maxwell FEA software from Ansoft (Pittsburgh, PA).

FEA has made a big difference at West Coast Engineering (British Columbia, Canada), an engineering firm that designs freestanding structures such as antennas or transmission towers. Five years ago, says Ioan Giosan, senior design engineer, "no one here was familiar with FEA software. But when I showed company principals how powerful this tool was and how it could help the design team, they realized it would be a good investment."

The company no longer has to perform load tests. "The structures we build are very large," says Giosan. They often measure 40 meters tall, and weigh around 20 tons. To build such a tower costs around $100,000. "If we perform a load test, we essentially waste $100,000 because we build a tower only to destroy it," he says. "FEA allows us to see what is happening on the computer without building a prototype."

The company received a contract recently to design an appliance to mount a helicopter searchlight for Aeromation Design & Repair Inc. (British Columbia). The job was expected to take a month, but because of the FEA it took only two weeks, he says. "Time translates into money in our business." West Coast Engineering uses mechanical event simulation from Algor.

• In the conceptual design stage, simulation enables the concept designers to validate their basic design.
• If it's used in the detailed design stage, engineers can verify that the design will perform as intended and that it is producible.
• In the test stage, simulation can reduce the number of prototypes by reproducing the test on the computer. If a test article fails the simulated test, a redesign is very inexpensive. If used to optimize the manufacturing processes, it can help reduce scrap material and reduce forming steps. Simulation also improves the product's productibility and reduces warranty costs by identifying and eliminating design features that lead to defects during the manufacturing process.
• Simulation makes it easier to market a product by allowing a customer to visualize how it will perform in his/her environment.
• Field technicians can use simulation in the support stage to guide their repairs and modifications, ensuring that they correct the problem while maintaining the original design's functionality.
• Once a product's useful life is over, simulation can help select manufacturing processes and packaging that make recycling possible and cost-effective for various materials.
• When a company purchases simulation software, services, and computers, it is making an investment.

For a FREE white paper on "How to Grow Your Sales and Profits by Using Simulation," contact MSC.Software at (800) 642-7437.