Page 197 - Six Sigma for electronics design and manufacturing

Six Sigma for Electronics Design and Manufacturing
164
z 1 = 3 · Cpk = 2.45; f(–z 1 ) = 0.0071
z 2 = 3 · Cpk = 2.63; f(–z 2 ) = 0.0043
Total error = 0.0114; or 1.14% or 11,100 PPM
EV = 5.15 EV = 5.15 · 1.18133 = 6.08 or R double bar · K 1
= 2 · 3.05 = 6.10
AV = (1 .2 7 0 ) – ( E V / n r) = 7 .2 9 – 1 .1 8 1 3 3 / 3 = 2 .6 1
2
2

GR&R = E V* + A V = 6.63 2
2
G&GR% from specifications = 100(6.63/3) > 100%
Measurement system quality is unacceptable.
5.4 Determining Short- and Long-Term
Process Capability
An important part of new product development is the development of
process capabilities and specifications for new parts and products. De-
sign engineers work with the general specification of products that
are set by marketing or the customer, but these specifications do not
necessarily flow down to all of the parts and to all of their attributes.
It is necessary for design engineers to always question the relevance
of each part specification, and whether it is too tight for its proper use
in the customer’s hands. It is always desirable to use tools such as
quality function deployment or QFD, discussed in Chapter 1, to at-
tempt to relate each specification for every part to the customer’s
wishes.
For six sigma designs of new products, process capability should be
determined in the prototype stage of parts manufacturing. Some large
consumer and mass product companies normally plan for large proto-
type runs to fully simulate the variability of the production process.
This may not be feasible for many industries, due to the cost of parts
or the volume of expected sales, so that process capability has to be
derived from low volumes, using the techniques discussed in this
chapter.
Process capability for new products can follow one of the following
three scenarios:
1. The product represents an evolutionary increase in technology,
and engineers build the prototypes with tight control, in special
prototype shops. In this case, the process capability of the proto-
types might actually be of higher quality that the early production
runs.