First Edition Dated September, 2000 51
Combined parts
Assembly AB C
Key
A
4.5.5_4a
Part AB
Part AB Part C
Part C
+.015
A
A
+.015
+.030
Figure 4.5.5_4 depicts a design approach called monolithic design. In this
approach, the re-design creates fewer but more complex parts. With fewer
parts in the assembly, fewer features are involved in meeting the assembly
level requirement. Thus, tolerances are allocated across fewer features and
can be more relaxed.
In the above example, the only way to learn the optimal approach is to work
with one’s suppliers and ask the right questions. Involved suppliers must
know their process capabilities, be able to establish tooling costs, and provide
for economic and technical evaluation.
This section must be handled in concert with section 4.5.2 as customer
requirements from the factory are identified. However, the other customer
requirements of 4.5.2 (performance and service life) must also be addressed.
Efforts to allocate tolerances to match process capability should be pursued
to the greatest extent possible. In some rare cases, process capabilities will
not be available that match the tolerances necessary to meet the customer
requirements. When this happens the tolerances must still be driven by the
customer requirements and not process capabilities. Actions will have to be
undertaken to improve manufacturing processes or create new ones that
meet the customer requirements.
