Understanding the Process Capability (Process Capability) and process performance

Statistically stable output (in control) from the manufacturing process can be identified by the distribution of the output. The characteristics of this distribution will be used for analysing through test run process

Thedistribution characteristics required shall be at the midpoint of the distribution. If the distribution is not in the correct position manufacturing process may produce products that do not meet the target value required.

In some cases, some products may be out of specification. Such distribution show the process can not meet customer requirement.Problem can occur if a large distribution involved, no matter where the distribution is located. Due to the characteristics of the distribution can not be known precisely,some data collectionand  action to analyze data is needed.

To define process capability, frequently use index as follows:
Index to only process variations, relative to specifications: Cp and Pp.
Index for the combined variant and the midpoint of the process, relative to the specification:
CPU, CPL, Cpk and School
A. Definition of Terms for Process
· Inherent Process Variation - Varaisi process of a common cause (Common Cause) only.
This variation can be estimated from the control charts from the R / d2
· Total Variation Process-variation resulting from common and special causes (common and special Causes).
This variation can be estimated from the S, the standard deviation values:
S = √ Σ (x ¹ - x) ² = ^ αs
n-1
where X: Value of individual readings
x: Average value of individual readings
n: Total number of individual data
· Capability Process (Process Capability)
- Variation of inherent processes for statistically stable prose where α is the estimated value of R / d2.
Performance Process (Process Performance) - The entire range of process variations for 6 α where α is S or the estimates of the standard deviation (^ αs).

B. Definition for Process Measurement
CP: index, which is defined as the ability of tolerant distributed degan wide process capability, tampa calculate the midpoint of the process.
Formula:
Cp = VSL - LSL
6 ^ α R / d2
Pp: Index performance where the width tolerant shared with the performance regardless of the midpoint of the process.
Here it is:
Pp = VSL - LSL
 ^ Αs
 CPU = Capability Index Up,
CPU = VSL - X
3 ^ α R / d2
CPL = Index Down capabilities,
 CPL = X - LSL
 3 ^ α R / d2
Cpk: Index that takes into account the ability of the central point and the minimum value is defined as the CPU or PKO
Ppk: performance index that takes into account the midpoint of the process and defined minimum value.



VSL - X or X-LSL
3 ^ 3 ^ αs αs
Cpk index or PPK useful for the following purposes:
· Measuring continuous improvement using the trend over time.
· Determine turukan priority to improving the process.

 Minimum requirements to be observed are as follows:
a - measured process data must be stable in statistical
b - measurement data must be approaching normality.
C - Specification based on customer requirements.
d - There is a willingness to accept the calculated index sebagia actual index. For example, ignoring the influence of sampling