Expanding Tolerance Analysis for a Robust Product Design Expanding Tolerance Analysis for a Robust Product | Page 5

Expanding Tolerance Analysis for a Robust Product Design

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But when the manufacturing variations are taken into
account for the thermal analysis, the results can be dramatic.
In the case of the oven below, the lower hinges were aligned at
the worst case for allowable variation and the flatness was
adjusted for its worst case variation.
The combined result is a leaking of heat from the oven and
a temperature increase on the handle of the oven door that is
beyond the acceptable range defined in the requirements.

Fig. 5. Visualization of equations of a locking mechanism

3.4. Understanding Impact of Sources of Variation
Each of the sources of variation may or may not have a
material impact on a particular product when that product is
used as designed. Thermal variation in an interior door lock is
certainly less of an issue than one for an external door lock in
freezing environments.
If we look at a simple example of an oven design, a basic
thermal analysis would look like this:
Heat is evenly distributed through the door with the highest
temperature centered on the glass viewing area.
A study of manufacturing variations turns into a review of
tolerances. Highly complex tolerance analysis software exists
to determine worst case and statistical results. Advanced
mathematics, or Monte Carlo experiments are employed
within these packages to determine the statistical probabilities
of the variations.

Fig. 7. Leaking heat distribution in an oven door

3.5. Iterate Changes in Design
Clearly the new situation with the temperatures of the
handle of the oven is unacceptable. To correct this, an
iterative process is required to look at how to change the
design. Through the use of the analysis software, contribution
and sensitivity plots can be provided to assist in understanding
which measurements to adjust and by how much in order to
increase the robustness of the design. Such a plot is shown
here:

Fig. 6. Normal heat distribution on an oven door
Fig. 8. Sensitivity Plot

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