FEA - A Real-Time Case History From Industry

Finite Element Analysis (FEA) and cooperation between machine manufacturers, fixture construction companies and end-user companies shortens the time of art-to-part and reduces costs.

When it comes to avoiding problems and getting production moving as quickly as possible, the magic word among manufacturing project managers today is simulation.

A wide variety of simulation software packages exist today for desktop computers. Engineers can anticipate the performance of components and mechanisms with easy-to-learn and easy-to-use engineering software with graphical user interfaces on fast, inexpensive computers. Ten years ago, only Top-500 companies using large mainframe computers, awkward keypunch cards and cryptic texts could come close to today's desktop power. Capitalizing on the ever-increasing power of the PC, simulation software packages for performing Finite Element Analysis (FEA) provide a very powerful engineering design tool that enables engineers to simulate structural behavior, make design changes and see the effects of those changes on the computer.

Algor, Inc. (Pittsburgh, PA) is one company that has been developing FEA software for the desktop. With its InCAD family of products, these FEA tools work with CAD solid modelers to capture exact memory of the CAD geometry without file translation. The InCAD products also offer a feature suppression utility within CAD, which engineers can use to eliminate any CAD solid model details that are unnecessary to include in the FEA analysis. This way, fewer elements are included in the FEA model, since only the areas of interest are captured and less time is needed for the analysis.

A recent invention - Mechanical Event Simulation (MES) software - realistically simulates motion in mechanical parts or assemblies, eliminating the need to input estimated loads. It also computes and shows resulting stresses on the computer model at each instant in time. MES often replaces physical prototype testing with virtual prototype testing because it per-forms linear and nonlinear static and dynamic finite element stress analysis with physics-based motion. Algor also offers other FEA capabilities including linear and nonlinear static stress, vibration and natural frequencies, heat transfer, fluid flow, electrostatics, piping design and analysis and composite materials. The entire software product line works with any CAD system and offers a wide range of FEA meshing tools.

Mathias Landgraf of Speedy Engineering (Lake Constance, Germany) says that he is pleased with Algor's FEA software because of its capability to work directly with CAD solid geometry. In this article, he presents an example of a project he recently undertook with a manufacturer. Before choosing Algor, he took time to look at several software packages, but thought Algor was easier to use as well as learn. Why?

"We chose Algor because there is no sense in having software that you need a week or two to synchronize or program before tackling the real problem," says Landgraf.

Landgraf worked with a company that had contracted him to interface its 3-D CAD solid model of a fixture geometry with Algor FEA software to predict the behavior of the fixture design in advance. The analysis work was to take place before the first fixture prototype was produced in order to assure a smooth operation. The model was a fixture that would eventually hold automobile parts in place during drilling and high precision milling.

The company provided Speedy Engineering a rough draft of the geometry in IGES format, a universal file for exchanging geometry between certain CAD systems and FEA. Reviewing the company's first IGES file revealed that different export parameters needed to be employed. FEA analysis results confirmed that the fixture was stiff enough to fulfill all of the requirements and the casting process could begin.

"To avoid costly prototypes prior to the casting process, linear static and dynamic analysis of the motor component fixture geometry was performed within a few days of its design to determine displacements and frequencies of the geometry," Landgraf says. "I used Algor because of its ease in working directly with CAD solid geometry."

To shorten the operation start-up time, Landgraf suggested to the company that he first analyze the dynamic behavior of the fixture component. Dynamic analysis determines the destructive frequencies and typical displacements for each mode. If a vibrating tool causes resonance, the machined part's surface may be unacceptably rough. If the machined part, the fixture, the machine or a combination of these items has resonance frequencies, the surface is destroyed and the part is unusable. Usually the weight and stiffness of the parts have to be taken into consideration, as well.

In this case, the fixture needed to be fully constrained at the six mounting points on the palette - so no rigid body modes were expected - and the first 30 frequencies were computed. When looking at the displacement produced by each frequency, two factors needed to be taken into consideration, Landgraf says:

1. Whether displacement is occurring in an area of the model that might cause damage to the surface of the component being milled; and,

2. How much energy the mode has - base and low frequencies have more energy than higher frequencies.

By considering the factors for each mode, Landgraf eventually determined which frequencies caused undesirable vibration. The results of the dynamic analysis enabled Speedy Engineering to specify maximum working loads for production, which guaranteed success with the first use of the fixture design.

"The process demonstrated in this example represents an advance in construction techniques that opens new possibilities in the future of machine and fixture development. FEA along with cooperation among machine manufacturers, fixture construction companies and end-user companies shortens the time of art-to-part and reduces costs," Landgraf says.

Algor has been a pioneer in the mechanical engineering software industry since it introduced FEA for PCs in 1984 and began interfacing with CAD systems in 1985. The company's FEA software has enabled 20,000 engineers in 60 countries to create cost-effective designs, according to Algor officials.

For engineers getting started with FEA, Algor introduced InCAD DesignPak to work from within CAD, providing access to powerful FEA tools. InCAD DesignPak features a solid tetrahedral mesh engine for faster, solid, FEA meshes, enhanced plate-shell modeling, static stress analysis and an HTML Report Wizard.