Page 103 - Six Sigma for electronics design and manufacturing

Six Sigma for Electronics Design and Manufacturing
72
trol charting be independent from each other and directly related to
the overall performance of the product.
When introducing control charts to a manufacturing operation, it is
beneficial to use elements that are universally recognized, such as
temperature and relative humidity, or take readings from a process
display monitor. In addition, the production operators have to be di-
rectly active in the charting process to increase their awareness and
get them involved in the quality output of their jobs. Several short-
comings have been observed when initially introducing control charts.
Some of these to avoid are:
Improper training of production operators. Collecting a daily sam-
ple and calculating the average and range of the sample data set
might seem to be a simple task. Unfortunately, because of the poor
skill set of operators in many manufacturing plants, extensive
training has to be provided to make sure the manufacturing opera-
tor can perform the required data collection and calculation.
Using a software program for plotting data removes the focus from
the data collection and interpretation of control charting. The is-
sues of training and operating the software tools become the pri-
mary factors. Automatic means of plotting control charting should
be introduced later in the quality improvement plan for production.
Selecting variables that are outside of the production group’s di-
rect sphere of influence, or are difficult or impossible to control,
could result in a negative perception of the quality effort. An ex-
ample would be to plot the temperature and humidity of the pro-
duction floor when there are no adequate environmental controls.
The change in seasons will always bring an “out-of-control” condi-
tion.
In the latter stage of six sigma implementation, the low defect rate
impacts the use of these charts. In many cases, successful implemen-
tation of six sigma may have rendered control charts obsolete, and the
factory might switch over to TQM tools for keeping the quality level at
the 3.4 PPM rate. The reason is that the defect rate is so low that only
few defects occur in the production day, and the engineers can pay at-
tention to individual defects rather than the sampling plan of the con-
trol charts.

3.2 Control of Variable Processes and Its
Relationship with Six Sigma
Variable processes are those in which direct measurements can be
made of the quality characteristic in a periodic or daily sample. The