00193407-02 HWWS SIPLACE Machine Accuracy EN.pdf - 第12页
© Siemens AG . . Änderungen vorbehalten SIPLACE Placement Systems Machine capability indices Cmk Machine capability, e.g. min. C mk = 1,33 (4 Sigma specification)) Cmk: position of the mean value of the series of measure…
© Siemens AG . . Änderungen vorbehalten
SIPLACE
Placement Systems
Machine capability indices Cm
A machine suitability for the planned application is assessed with references to the indices Cm
(capability machine) and Cmk for the machine capability.
Outside disturbing influences have to be eliminated.
Cm: only dispersion in relation to the tolerance (4 sigma specification, Cm = min. 1,33)
USL = upper specification limit, e.g. + 50 um
LSL = lower specification limit, e.g. - 50 um
USL - LSL
6 x Sigma
Cm =
Machine Capability
© Siemens AG . . Änderungen vorbehalten
SIPLACE
Placement Systems
Machine capability indices Cmk
Machine capability, e.g. min. C
mk
= 1,33 (4 Sigma specification))
Cmk: position of the mean value of the series of measurements as well as the dispersion
¾ the machine capability is just a snap-shot and is performed with proper
measurement tools.
Cmk = Min (Cmk 1, Cmk 2) meaning the lowest value is only used for the Cmk
The centering index k is a measure of the deviation of the mean process value from the target value
(center of tolerance).
If the machine parameters are perfectly centered, k = equal to zero, and Cmk = equal to Cm.
Machine Capability
3 x Sigma
USG - Offset
Cmk 1 =
3 x Sigma
OSG - Offset
Cmk 2 =
© Siemens AG . . Änderungen vorbehalten
SIPLACE
Placement Systems
Quality Evaluation
For an evaluation of quality, a comparison with the specifications is necessary.
The specifications determine the upper and lower parameters, which during the process may not
be exceeded.
Each process has a determined set-point value which must be achieved. Each deviation from
this desired value includes additional risks .
centering and dispersion
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dispersion to
high
Cmk < 1.33
(4 sigma)
dispersion good,
centering not good
(offset high)
dispersion good,
centering good.
Cmk > 1.33
(4 sigma)
Cm value equal
the higher the Cm and Cmk, the better
Machine Capability
Machine Capability