DFMA as Applied to the Swingline 747 Desktop ... - University of Utah

2.5 Assembly Paradigms
DFMA as Applied to the Swingline ® 747 Desktop Stapler
When designing for assembly, there are many varied considerations. As has been
the precedent, a brief discussion of the DFMA paradigms will be followed by application
of relevant paradigms to the Swingline ® 747 classic stapler. The object of design for
assembly is to provide the designers a tool for effective assembly considerations, to guide
the designers to simplicity, to provide information from experienced engineers early in
the process that will help less experienced designers, and to establish a database of
assembly times and cost factors. Most of the following information is taken from Product
DFMA, 2 nd ed., hereafter referred to as PDFMA, by Boothroyd, Dewhurst, and Knight.
While there are tools and equations to be used for both manual and automated (robotic,
high-speed) assembly, the focus will remain on manual assembly since it is most
pertinent to the case at hand. Briefly, the main advantage for automation is the reduced
errors in assembly that lead to quality issues. The authors state, “…it is becoming widely
accepted that faulty assembly steps, rather than defective components, are more often the
reason for production quality problems.” For more information on automated assembly,
the interested reader is referred to the text. For manual assembly, there are several issues
to be considered.
2.5a Assembly Times and Efficiency
Assembly efficiency, also known as the DFA index, is vital to proper assembly
design. Two main factors that influence efficiency are the number of parts and the ease
of handling, inserting, and fastening those parts. To calculate the efficiency, Ema, the
following equation is given:
Ema = Nminta/tma
where Nmin is the theoretical minimum number of parts, ta is the basic assembly time for
one part, which is about 3 s, and tma is the estimated time to complete the assembly of the
entire product.
There are three time systems that can be used to estimate assembly times. One of
these, MOST, is used for very large parts which cannot be carried by workers. A lifting
device must be employed. Since this is beyond the scope of the example, it is not
discussed here. The other two systems, methods time measurement (MTM) and work
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