Automating Engineering Calculations
Software for predictive
engineering cuts costs in product design
08/03/2009
by Sandy Joung of PTC CAD software has evolved to make the
basic mathematics of product design transparent to users. But design
also requires frequent adhoc calculations for everything from
converting units to testing probability models. These vital
calculations were  and often still are  done with calculators or
manually on paper.
Bidirectional integration between Mathcad and Pro/Engineer lets
dimensions and parameters from the CAD model drive a Mathcad
analysis. Here, results from these calculations have returned to
Pro/Engineer to update the model geometry.
This manual approach suits organizations with simple
productdevelopment processes and relatively obvious market demands.
But today’s typical company faces evermore challenging competitors,
increasing product complexity and the number of globally dispersed
teams even while budgets tighten. Spreadsheets or manual engineering
calculations cannot scale to meet these demands.
A moreefficient approach is to automate and capture adhoc
calculations with engineering calculation software such as Mathcad,
which simultaneously performs and documents calculations using
standard math notation. The program has been around for over 20
years. Its direct competitors are Matlab and Mathematica, however
these programs use their own syntax (programming language) to
compute results. Also, the math, text, and graphics are not
integrated into one worksheet.
Mathcad users can easily insert equations into the user
interface, via typing or selecting functions in the UI, as they
would appear in a textbook, and the software dynamically calculates
the result. Engineers can combine live math, text, graphs, and
images to comprehensively document their design assumptions and
calculations. This practice documents the original designer’s
specific intent in a form that’s traceable, testable, and — most
important — reusable.
For example, users can easily share calculations, which are
readily understood by anyone who can read and understand
mathematical equations. Compare this to spreadsheets and their
complex web of cells and abbreviations for calculation functions, or
to other math applications that require special programming
languages. If you don’t know the programming language, you can’t see
the basic assumptions and equations used to calculate results.
Mathcad also lets users cutandpaste equations from one
worksheet to another. This cuts time recreating calculations and
makes it easier for companies to develop standardized templates of
approved calculations and share best practices. The software
generates annotations explaining where equations were copied from
(or users can add notes). In addition, the integration between
Mathcad and Windchill lets users easily capture, search, and reuse
engineering calculations and design knowledge on an enterprisewide
scale.
The software performs complex calculations in a fraction of the
time it takes traditional methods such as calculators, which often
require complex programming for advanced functions. Users can also
set up matrices, arrays, and programs to perform iterative
calculations much faster. These capabilities reduce or prevent
designer error and helps companies deliver betterquality products
in shorter time frames.
A worksheet in Mathcad combines natural math notation and
diagrams, letting engineers fully document analyses and
calculations.
For example, consider the case of a designer building a new shock
absorber. First, an existing product model is opened from a CAD file
repository such as Windchill. The original designer’s detailed
assumptions and decisions are readily available in a Mathcad
worksheet, which resembles a Word document if the worksheet is
stored and associated with the CAD model. Calculations and notes
documented in the worksheet might show, for instance, that a shock
absorber was originally intended for a certain axle size and later
changed to fit a different size. The designer can thereby determine
where the original engineer’s design compromises might affect the
new design — for example, in axle clearance or vibration threshold.
This information can help avoid a lot of wheelspinning.
Automating the capture of engineering calculations also helps
ensure that design requirements are met. The software handles
calculations involving factors such as weight, volume, strength, and
stress that are too difficult or time consuming to do manually, to
predict the behavior of a component or material before it goes for a
complete analysis.
Mathcad has a direct, bidirectional integration with Pro/Engineer
that lets users make calculations on the exact geometries of a CAD
model. The software then updates the results in the CAD model. This
lets designers tighten assumptions passed to analysis software,
saving the costs of unnecessary testing. (Examples of assumptions
include dimensions, tolerances, range of testing loads, and range of
testing temperature.)
In fact, engineering calculation software proves useful in all
stages of product design:
In concept design and planning, the software lets users
perform calculations to test functional performance, instead of just
drawing geometries and hoping the design will meet the requirements.
In the building of a refrigeration unit, for instance, a designer
can use the software to see if the piping will fit inside the
refrigerator casing. Likewise, a cellphone designer might check the
basic fit of the printedcircuit board, speaker, or microphone. This
is different from CAD, which lets users draw the dimensions and
geometries but doesn’t tell how the design will perform unless users
run analysis or calculations via some other method.
Requirements definition typically involves the whole
design team including the design engineer, project manager,
marketing, as well as the customer via video conference. Engineers
can use Mathcad here for “scratch pad math” and preliminary design
optimization to explore alternatives that might arise in the
meeting. For example, a design engineer might calculate the impact
of changing the material or part thickness on the amount of material
needed, cost of the part, and other physical properties such as
strength. The software lets users easily change the design input
parameters and see the results or impact instantly. This helps
designers fully exploit the spontaneity of the meeting to raise and
resolve important issues.
Design modeling often begins with a search for previous
parts or assemblies for reuse. In the shockabsorber example,
designers might retrieve the currentgeneration model from the CAD
library along with the axle or other assemblies that makes use of
the shock absorber. If the files contain engineering calculations,
designers are likely to gain a precise knowledge of the conditions
surrounding the original designer’s work because they can see and
understand the initial analysis.
Analysis can benefit from the use of
engineeringcalculation software because it supports pre and
postprocessing tasks for FEA and other tools. As a preprocessor,
the software helps with basic sizing and the testing of toplevel
assumptions by giving firstorder approximations of performance
using simplified geometries, surface areas, volumes, and the like.
The insight gained helps engineers avoid wasting time on a
misdirected analysis project. A full FEA simulation can take several
hours, so it’s helpful to make it as meaningful as possible.
As a tool for postprocessing, the software helps designers
sanitycheck analysis results by running simplified tests that will
deliver numbers in the same range as the FEA outputs. For instance,
to sanitycheck the shock absorber’s stress test, the designer can
use Mathcad to place a virtual box around the shock and then put a
load on the box. The software can’t perform the same detailed,
computationally intensive deformation testing as a fullblown FEA
tool, but it does deliver results within range of the FEA tests.
Finally, the software supports quality assurance by
helping users check that the product will meet manufacturing
specifications. Again, the software can’t perform extensive testing,
but in a matter of seconds it can answer and clearly document simple
conditional statements: Does the model meet a certain safety
requirement for maximum load or weight, load before failure, or
adequate insulation for electrical parts? The software even tells
whether a design meets certain Six Sigma requirements. Tests that
raise a flag help catch quality problems early in the cycle before
the model had been passed directly to manufacturing, where solving
even a small problem can quickly become quite costly.
Mathcad offers a broad range of over 700 functions. Other useful
capabilities include support for matrices, differential equations,
IEEEadherent math, which ensures that designs conform to standards
for math definitions and formulas (for example, the definition of
the operation 0/0), and other commonly used engineering equations.
The software also provides extensions for data analysis, signal
processing, and other disciplines. The use of a file format based on
XML and support for standardsbased dataexchange interfaces lets
the software work with a range of CAD and CAE applications, as well
as other engineering calculation software and Open DataBase
Connectivity (ODBC)compliant databases.
Article edited by Leslie Gordon,
Sr Editor, Machine Design

Article reprinted by permission of Penton Media,
publisher of Machine Design 
