A reducing the variation of the process. JH,

A process in the manufacturing industry is unique because the process needs the combinations of manpower, raw materials, machines, and methods. In order to improve the quality
level of products, the capability of the process plays an important role in the
manufacturing industry. Rezaie, K. 6. The process capability indices
(PCIs) is also known as process capability
analysis which is widely used in manufacturing industry. The PCIs is
used to measure the ability of the process to meet the requirements of the
customers which are also known as specification limits. The analyst used PCIs
to control and monitor the performance of the process in the manufacturing industry. Besides, the PCIs can use to improve the performance of the process by reducing the variation of the
process. JH, S. et al. 3.

The process capability analysis can be presented graphically by using
histogram and probability plot.
Montgomery, D. C. 5. The graphics can determine whether the process is
within specification limits (SLs) or not. Steiner, S. et al. 9. The
histogram is the easiest and clear method to determine the performance of the process. If the process is in
control and the data is normally distributed, the potential capability analysis
can be used to improve the quality of the process. Spano, A. 8. The PCIs is used to
compare the output of in control process with the SLs by 6 sigmas. PCIs are quantitative measures based on the performance and potential of the
process. By doing so, the process can meet the requirements of the customers.
Rezaie, K. et al. 6.

 

The process of the manufacturing
industry is considered as capable when the process is under control. Spano, A.
6. The automotive industry was applying the PCIs in Japan and United States
(US). The process capability with sampling properties and estimation procedures
is measured to determine the normality of the process and the process is in
statistical control or not. Kane, V.E. 4. The PCIs had been used in
manufacturing industry in quantitative measure form to ensure the performance
of the process. The cost spent in the process of rework and scrap will cause
the loss of the industry. Hence, the high-quality
production should practice in industry and try to meet the requirements. JH, S.
et al. 3.

According to the requirements of the
customers with the costs that needed to spend
by the suppliers, the suppliers still need to set the suitable cost for their
product and ensure that the products are under tolerance limits. If the process capability of the process is under
control by the suppliers, we can try to
improve the quality of products or the process by out of control action plan
(OCAP). The process capability indices
can help to analyze the capability and
try to predict the machining process that can meet the expectations and
tolerance limits of the customers. The process capability indices consist of

,

,

 and

. Abhijit S. et al., Montgomery, D. C. 1, 5. The

 value
will represent the performance of process. Table 1 summaries the six quality
condition with its

 value.
?hsan K.2.

Table 1: Quality conditions and

 value

Quality condition

 value

Super excellent

2.00 ?

Excellent

1.67 ?

 ? 2.00

Satisfactory

1.33 ?

 ? 1.67

Capable

1.00 ?

 ? 1.33

Inadequate

0.67 ?

 ? 1.00

Poor

 < 0.67      In manufacturing process,  value is used to identify the variation of the characteristics of the product within SLs that set by the engineers or the designer. Rupesh C. et al. 7. Although many manufacturing industry had use  value to determine the process capability of the process, but  value cannot used to determine whether the process is off-centering and we do not know the actual performance of the process. Thus, the  value is used to indicate that the process is in the SLs. The  and  always used in manufacturing industry in order to determine the number of the product that within the specification limits and ensure the process is well perform. ?hsan K.2.  and  have the same statistical properties. Since the  consists of the  and , most of the manufacturing industry will used  instead of  and .   The  value widely used in manufacturing industry. The  value can assume the normality and independency of the target value, T. If the sampling distribution had skewed slightly or off center slightly, the process can still considered as capable. Zhang, N. F. et al. 10. Since there are many manufacturing industry had uses the process capability, there are many study that try to use the capability indices to determine the performance of machining process. More undertakings have been given to utilizations and investigations of process capacity indices. Abhijit S. et al., JH, S. et al., Rezaie, K. et al. 1, 3, 6. In the future, the manufacturing industry might implement the capability indices to determine machining process performance.  

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