Cadalyst MCAD Tech News #133

19 Nov, 2004 By: Joe Greco

Cadalyst MCAD Tech News

Upfront Tolerance Analysis

GEOMATE Products are Low-Cost but Effective

If you follow the CAE (computer-aided engineering) and CAA (computer-aided analysis) industries, you probably have been hearing a lot about up-front FEA (finite element analysis), up-front CFD (computational fluid dynamics), up-front this and up-front that. In this issue I will introduce you to a new "up-front," maybe the most important one — up-front tolerance analysis.

Current Solutions
Today the market offers many tools for tolerance analysis. Some of the most popular are SigmundStacks from Varatech (Holland, Michigan), CETOL 6 Sigma from Sigmetrix (McKinney, Texas), and TASys from Labein Tecnalia (Derio, Spain). These are all fine products, but they can be quite costly. For instance, Labein Tecnalia's most basic package, Pre-TASysWorks, costs $995, and its high-end program, TASysWorks-INTOL, goes for $4,995.

Although tolerance analysis is important enough to justify this type of purchase, it really works properly only when every designer, engineer, and manufacturer involved in the product development cycle uses it. At these prices, implementing it across the board could get very expensive. Add to that the fact that many tolerance analysis systems only work with one MCAD program, yet many companies employ several MCAD products, and you're looking at needing two or more licenses of the same tolerance analysis product per user.

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To combat this high entry cost, GEOMATE of San Jose, California, has offered low-cost tolerance analysis solutions for years. ToleranceCalc v1 was competitively priced at $395 a few years ago, but its price has been falling even further and now stands at only $95. In addition, ToleranceCalc works with any CAD program that can produce a DXF file. The company recently added the ability to perform linear stack-up and Six Sigma analysis concurrently. I had a chance to work with these new features in ToleranceCalc v3.

Figure 1. ToleranceCalc is a simple-looking program, but it holds a lot of power beneath the surface.
Once you acquire a license code, ToleranceCalc installs in seconds, literally — the entire program is only 224K. Although the ToleranceCalc user interface is very powerful, it's been kept to the bare minimum. On opening the program, all you see is a dialog box with four tabs — that's the entire program (figure 1).

This figure also shows a DXF file that was imported later. It's just two lines, which is all that's needed to represent the problem that we wish to evaluate. By analyzing parts and assemblies as a simple abstraction, ToleranceCalc can solve tolerance problems before the user commits to thinking about actual components and other details.

Figure 2. The 2D vectors from this 3D model were imported into ToleranceCalc.
The two lines in the image represent the x- and y- tolerance vectors that determine the distance from the center of a circular fitting to the center of a hole placed on its perimeter (figure 2). Looking at figure 1 again, you'll see that you just enter the plus and minus values of manufacturing tolerances for the first vector, highlighted in red. Then press the Next button and the system highlights the second vector and adds its tolerances. In addition to the number of iterations and the total number of parts to be produced (batch size), the only other required input is the acceptable deviation in the part's dimensions, entered in the OK Delta-L field.

In this example, that's the radial distance from the center of the ring to the center of the hole. After this value is added, press the Calculate button and the program performs the standard Monte Carlo analysis. By clicking on the new tab called Sigma, you can determine the Sigma quality level and, more importantly, how many parts in the entire batch will be defective.

Figure 3. A tolerance stack-up analysis.
The Stack-Up panel (figure 3) shows the maximum, minimum, and worst-case values of the distance of the hole from the center of the part.

Unlike other tolerance analysis applications that might require weeks of training, says GEOMATE founder Shyamal Roy, ToleranceCalc does almost everything a designer, engineer, or manufacturer needs with a learning curve in the minutes. I haven't done a full analysis of competing products and therefore can't discuss their usability issues, but I can say that after using ToleranceCalc, I can't see how tolerance analysis could be much easier.

Other GEOMATE Applications
Many CAD programs can return properties of a 2D section such as area, perimeter, centroid, and even moments of inertia. However, another GEOMATE program called SectionCalc can also handle product of inertia, polar moments of inertia, the distance of neutral axis from extremes, radius of gyration, and section modulus. It has recently been updated and can now calculate sections with cutouts (islands) and built-in structural members.

For instance, let's assume you need to support a machine with a beam that is made up of two L-shaped members with a C-channel welded to the bottom. With other software, you may be able to get some properties of the individual components; SectionCalc evaluates the entire built-up section.

The company's oldest product is GrafiCalc, and it rounds out a fine trio of applications. GrafiCalc is a design calculation and analysis package for helping engineers perform what-if analysis. It has also been updated by simplifying the constraining of entities.

People tend to be skeptical of products that seem to be priced extremely low. You probably wouldn't buy a new car if it were advertised at $500, figuring something had to be wrong. However, software is a different animal. And although GEOMATE products, especially ToleranceCalc, may not look like much or even manage everything that would be possible using a much more expensive competitor, they are worth investigating. You can install and learn the products in minutes, and you might even find that you can achieve your return on investment that quickly, as well.

Closing on a Light Note
A young engineer was leaving work one evening when he found the CEO standing in front of the paper shredder with a piece of paper in his hand.

"Listen," said the CEO, "this is important, and my secretary has left. Can you make this thing work?"

"Certainly," said the young engineer. He turned the machine on, inserted the paper, and pressed the start button.

"Excellent, excellent!" said the CEO, as his paper disappeared inside the machine. "I just need one copy."

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