Page 166 - Design for Environment A Guide to Sustainable Product Development

Design Rules and Guidelines 145

with disassembly. If adhesives are required, try to use adhe-
sives that are compatible with the joined materials.
• Use snap fits to join components where possible. Snap fits
involve an undercut on one part, engaging a molded lip on
a mating part to retain an assembly. Snap fits are relatively
inexpensive to manufacture and have attractive mechanical
properties.
• Avoid threaded fasteners (screws), if possible, because they
increase assembly and disassembly costs.
• Use alternative bonding methods, such as solvent bonding
or ultrasonic bonding. Such methods may be acceptable for
bonding parts made from the same material and which will
not be separated at end-of-life.
• Spring clips or speed clips can be an inexpensive and effective
way of joining parts and materials. They permit easy assem-
bly and disassembly, and do not introduce contaminants.
Example: The End-of-Life Vehicle Directive, enacted by the European
Union in 2000, imposed requirements on automotive manufacturers
to design for disassembly and recycling (see Chapter 3). However,
German companies such as BMW and Volkswagen had already de -
veloped disassembly methods at least 10 years earlier. For example,
Volkswagen has oper ated a recycling plant since 1990, at which cars
are dismantled, liquids are drained, wastes are separated for repro-
cess ing, and some of the plastics are recycled into new automobile
bumpers. Through design changes, such as elimination of threaded
fasteners and part count reduction, they were able to significantly
reduce dis assembly time.

C.3 Design for Recyclability
A high priority in any DFE effort is to minimize waste by assuring
that all by-products, materials, components, and packaging can be
recovered and reused or recycled at the end of their useful life. While
some companies have established “zero waste” as a goal, this is dif-
ficult to achieve in practice for both economic and pragmatic reasons.
Therefore, design teams should make realistic assumptions about the
proportions of end-of-life products that can be reused or recovered,
and ensure that any residual wastes can be readily and safely recy-
cled or disposed of.
To be recoverable with positive economic value, materials need to
be as close as possible to the state of desired manufacturing feedstock.
An important consideration in end-of-life material recovery is the ease
of disassembly, which determines the residual economic value (see Sec-
tion C.2, Design for Product Disassembly). Product materials or compo-
nents that cannot be recovered economically become potential wastes
but can still be recycled and thus converted into useful by-products.