Tools For the Toolbox

May 8, 1998
Helpful engineering software can turn statistics into goal-setting tools, find answers to tough physics problems, and illuminate equations more thoroughly than an ordinary spreadsheet program.

A Midwest manufacturer called in reliability expert James Mclinn to help design a new electric hand tool. One critical task was to predict its durability. Mclinn talked to marketing people, examined test results, and finally predicted that up to 10% of the product would require warranty service in the first year. Shocked at the high figure, the company redesigned the product. The changes resulted in a more acceptable first-year failure rate of 3.5%. The actual figure turned out to be 3.4%. Why was Mclinn so accurate? Because he used software that simplifies the tedious calculations required for Weibull plots, a statistical method that predicts results for large populations from small samples. It’s one of several engineering software tools that can help optimize design ideas before they are ready for production.

For instance, a package that might be characterized as pre-CAD software provides methods for stretching, trimming, and reshaping an idea many times over until it becomes usable geometry. Another pinpoints features that drive up costs in new products. And one program almost shows which physical principles you could team up to solve a sticky engineering problem. These and several others could be the solution to your next technical challenge.

Software from Dia-Soft Corp., Amherst, N.H., provides application data for designing diaphragms, a glossary of terms, and a few equations for calculating diaphragm qualities. The software takes longer to load than to learn; the one-page instruction sheet tells all.

Users can examine cross sections and see how a candidate diaphragm design seats and seals. They can also type in key dimensions, such as up and down stroke length or cylinder diameter, to check whether a design is workable by the software’s standard. There are also hundreds of stock designs to choose from.

Picks on terms in the glossary bring up an illustrative drawing and a discussion. The software computes nine equations. The user types in values to compute qualities such as burst pressure, safe working pressure, and fabric tensile strength. A material compatibility table includes hundreds of substances and chemicals, and details how different diaphragm materials perform.

Most traditional CAD packages work best when an idea is well formed. Imagineer Technical, on the other hand, might be called preCAD software, used before the design concept is ready for geometric modeling when it is likely to need a lot of changes.

Its GUI resembles that of 2D CAD screens. A smart cursor speeds the drawing process by giving users clues about nearby drawing elements such as line endpoints and angles that are perpendicular or parallel. A few mouse pick-and-drags add dimensions. Standard tools help create geometry, add holes and chamfers, and add details, while other features allow quickly reshaping ideas.

For instance, clicking on a dimension and the drawing element to which it refers links the two. Typing in a new dimension causes automatic resizing. The variable table is another big plus. It has only four columns for simplicity but lets any number of equations drive the drawing. A design load and minimum stress level, for example, could control the dimensions on a bracket design. CAD software packages, including Imagineer, sometimes allow spreadsheet calculations to drive drawing changes, but through a more involved process.

My 13-year-old son loaded the program and made a few elementary sketches without looking at the 170-page manual, which is clearly written and encourages experimentation. Costing $500 a copy, Imagineer has been priced by developer Intergraph Corp., Huntsville, Ala., so that it can be made easily accessible to designers in search of new ideas.

The electronic version of Marks’ Handbook for mechanical engineers is not as extensive as its 3-in.- thick hard-bound counterpart. But it contains hundreds of basic equations for disciplines such as heat transfer, mechanics, strength of materials, turbines, pumps, and compressors. The software runs with MathCAD, a number-crunching package from MathSoft Inc., Cambridge, Mass. What the electronic handbook does not include are specific details about sizing belt drives, clutches, or bearings.

The software takes no real training and works like this: Suppose you want to calculate the final temperature of two combined liquids, each initially at different temperatures. A few mouse clicks give access to the calculation for specific heat of mixtures. A tutorial briefly discusses the variables in the required equations. A nearby icon links to a MathCAD notebook which shows the equation with values assigned to the variables. Change the values and the equation updates. Other sections work the same way.

Users can also turn to MathCAD to write and save additional equations and ideas. The language of the math solver is straightforward and generally self evident from equations and examples in the handbook.

For more information:

Injection Molding software from Boothroyd-Dewhurst Inc., Wakefield, R.I., can spot factors that can dramatically boost costs well before a part hits production. The easy-to-use package comes with a brief but thorough 62-page manual.

Users familiar with mold making will find the software easy to use. Designers less familiar with molding may need help only because it can be tough to envision mold mechanisms, such as slides and cutouts, necessary for more complex parts.

Users generally start with a dimensioned design and enter information such as the life, volume, a batch size, envelope dimensions (length, width, height, and wall thickness), and the molding material. Selection of a material also brings up a cost/lb figure from an internal database.

Unfortunately, the package cannot import geometry from CAD files so the user must describe a part using a geometry calculator. The process consists of picking icons representing common geometry such as rectangular shapes or channels. Typing in dimensions and a flow direction gives the software a bit more to work with. Part details such as snap clips are icon picks as well. A generic cantilevered snap pops up ready for dimensions and a quantity count. Complex parts require more detailed inputs for posts, bosses, and ribs, but the process is the same.

Users describe molding qualities such as type of mold steel, cavity life, part tolerances, and mold mechanisms. Cost figures come out of this information. For example, one screen shows the molding machine selected for the job and estimates for fill time, cooling, mold-reset, and a total cycle time. Another window shows the process rate in dollars/hr, the batch size, set-up time, and set-up rate. One end result is an estimate of part cost with set-up costs excluded. Additional charts and graphs depict how costs change with the number of mold cavities per shot. The manual contains tips for using the geometry calculator, how to modify libraries, and how to graph results.

© 2010 Penton Media, Inc.

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