Quality Crimp Handbook
Two operators may measure the same part differently,
or the same operator may measure the part differently
when using two types of gauges. Molex recommends a
gauge capability study to identify what part of the
variability is coming from measurement error. Micro-
terminals crimped to small wire sizes need a tight crimp
height range to maintain pull force. The variability from
measurement error can keep C pk values low.
The capability of the crimping tools needs to be re-
confirmed if the production data is significantly different
changes, or setup adjustments. Record the data point
on the chart before making a crimp height adjustment.
If data is recorded after each adjustment, the process is
likely to assume control and provide little data for
improving the process. The operator needs to make as
many notes as possible on the chart. The only truly
effective and economically sensible way to manage a
manufacturing process is to understand, monitor and
reduce sources of variability that are inherent to the
process itself. Every minute required for setup or
adjustments is unproductive.
from the capability study.
What does this sample chart tell us?
Production
Before the tool is ready for production, the level of
capability needs to be established. Many harness
manufacturers run only a few hundred or few thousand
wires at one time. In this case, it is not practical or
economical to run a twenty-five-piece capability with
every set-up.
Visual Inspection
X and R Chart
It needs to be standard operating procedure for the
operator to manually fan each bundle of crimped wires
and visually check bell mouth, conductor brush,
insulation position, cut-off tab length, and insulation
crimp.
Control Charting
Crimp height is typically control charted because it is a
quick nondestructive measurement and is critical for the
termination's electrical and mechanical reliability.
There are three primary purposes for control charting.
One, the number of setup samples is usually small, with
limited statistical value. Two, since special cause
effects on a process are irregular and unpredictable; it
is necessary to be able to catch changes in the process
as soon as they occur. This prevents thousands of
terminations from being scrapped after the run is over.
Three, and most important, this data is necessary to
assess and improve the crimp process.
Control limit for sample of 5 = Avg
(Avg of 5 readings) + .577 x Avg (Ranges)
It indicates that a process shift occurred between
measurement 12 and 13. This type of shift could occur
due to a change in wire, a change in terminal lots, a
jam in the machine that damaged the tooling, a change
in operators, or an adjustment to the insulation crimp.
Since the measurements are still within specification,
would you stop production to adjust crimp height?
A shift in the process due to a change in material may
warrant a crimp height adjustment. A shift after a jam
would not indicate an adjustment, but a close
evaluation of the tooling. A shift in the process
between operators would not indicate an adjustment,
but an evaluation of measurement capability. The
purpose of a control chart is to identify what caused the
shift in process to determine if an adjustment to the
process is needed.
Once the tooling process is setup and the wire size
does not change, keep one control chart for wire color
changes, wire length changes, terminal material
Order No: TM-638000029
Revision: D
Release Date: 09-04-03
Revision Date: 12-23-09
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