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Application of Process Capability Indices toMeasure Performance of Manufacturing Process Kwek Yan PingFacultyApplied Science and Technology, University Tun Hussien Onn Malaysia, Malaysia [email protected] process capability indices (PCIs) are used to evaluate and monitorthe process of manufacturing industry. The PCIs that used in the manufacturing industry are , ,  and .

The machine capability is calculated by  and  which is in short period. The PCIs areimportant in manufacturing industry.Keywords. Processcapability indices; Machine capability.Introduction A process in the manufacturing industry is very unique because the process needs the linkages of manpower, raw materials, machines, andmethods.

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The linkages are the variationof the process that are hard to control. In order to improve the quality levelof 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 capabilityanalysis which is widely used in manufacturing industry. The PCIs isused to measure the ability of the process to meet the requirements of thecustomers which are also known as specification limits.

The analyst used PCIsto 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 theprocess. JH, S. et al. 3.The process capability analysis can be presented graphically by usinghistogram and probability plot.

The histogram and probability can show theresult of PCIs visually.Montgomery, D. C.

5. The graphics can determine whether the process iswithin specification limits (SLs) or not. Steiner, S. et al.

9. Thehistogram is the easiest and clear method to determine the performance of the process. If the process is incontrol and the data is normally distributed, the potential capability analysiscan be used to improve the quality of the process. Spano, A.

8. By referring to thehistogram, we can determine whether the process is off centering or not. ThePCIs 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 theprocess. By doing so, the process can meet the requirements of the customers.

Rezaie, K. et al. 6. The process of the manufacturingindustry 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 proceduresis measured to determine the normality of the process and the process is instatistical control or not. Kane, V.E. 4.

The PCIs had been used inmanufacturing industry in quantitative form to ensure the performance of theprocess. The numerical data will help the person in charge can modify theprocess by using more efficient methods. The cost spent in the process ofrework and scrap will cause the loss of the industry. Hence, the high-quality production should practice inindustry and try to meet the requirements.

JH, S. et al. 3. The PCIs is thebest method to maintain the quality of the product. According to the requirements of thecustomers with the costs that needed to spendby the suppliers, the suppliers still need to set the suitable cost for theirproduct and ensure that the products are under tolerance limits. If the process capability of the process is undercontrol by the suppliers, we can try toimprove the quality of products or the process by out of control action plan(OCAP).

The process capability indicescan help to analyze the capability andtry to predict the machining process that can meet the expectations andtolerance limits of the customers. The process capability indices consist of , ,  and . Abhijit S. et al., Montgomery, D.

C. 1, 5. The  valuewill represent the performance of process. Table 1 summaries the six qualitycondition with its  value.?hsan K.2. The different  valuewill represent different quality condition.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 thecharacteristics of the product within SLs that set by the engineers or thedesigner. Rupesh C. et al. 7. Although many manufacturing industry had use  value to determine the process capability ofthe process, but  value cannot used to determine whether theprocess is off-centering and we do not know the actual performance of theprocess.

Thus, the  value is used to indicate that the process isin the SLs. The  and  always used in manufacturing industry in orderto determine the number of the product that within the specification limits andensure the process is well perform. ?hsan K.2.  and  have the same statistical properties. Sincethe  consists of the  and , most of the manufacturingindustry will used  only. The  value widely used in manufacturing industry.The  value can assume the normality and independencyof the target value, T.

If the sampling distribution had skewed slightly or offcenter slightly, the process can still considered as capable. Zhang, N. F. et al.

10. Since thereare many manufacturing industry had uses the process capability, there are manystudy that try to use the capability indices to determine the performance ofmachining process. More undertakings have been given to utilizations andinvestigations 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 capabilityindices to determine machining process performance.MethodsProcess Capability Indices Inthe manufacturing industry, the PCIs areused to monitor the capability of the process. The , ,  and  will relate with the process parameter thatset by the industry. The PCIs always used in assessing and predicting theprocess performance. The PCIs provide the measurements in numerical value whichcan help to improve the quality of products and process easily.1.       The estimated standard deviationThetrue standard deviation in a production process is always unknown.

The  value is always replaced by the  value from the sample measurement. The  value is calculated by using the equationbelow:   = Average of range                                                                            = Factors of center line Thefunction of  is depend on the sample size of the processand the value of  can determine by referring the Appendix VI. Montgomery, D.

C. 5. The  value is used when calculating the  and  value. 2.      The  value Themain reason for using  value to assess the process ability to produceproducts with small amount of variation. The 6? is the natural tolerance of theprocess. The  value can determine whether the manufacturingindustry produce the defect items or not. The quality of the product can bemaintained by industry as long as the process is statistically in control.

Ifthe process is out of control, the OCAP can be taken by manufacturing industry.The higher the value of  , the higher the quality conditionof the process. The estimate of the  value is calculated by using the equationbelow:  3.      The  valueThemain reason for using  value to assess the process ability to produceproducts that within the SLs. The  is calculated by setting the 3? between theaverage of the process and the closest SLs. The  is determined by the minimum value of  and .The  value can determine the whether the industryproduce the products within SLs or not. The  value should closer with  value because the process should not far fromthe target value.

The  value is calculated by using the equationbelow:   One-sidedprocess-capability ratios for upper specification limit  One-sidedprocess-capability ratios for lower specification limit µ    =Mean Results and Discussion   Bad     Good                            Bad                                                                            Good Process not capable change tool or adjust for good accuracy. The process is capable but average need to be adjusted. Not possible.

The process capable and well adjusted. Figure 1: Therelation between  and   There are many manufacturing industries inMalaysia. Hence, the manufacturing industries are keep trying to improve thequality level of their products.

The industries try to produce the productsthat can surpass the expectation of the customers. Hence, the PCIs are veryimportant in order to improve the performannce of the process and products.     Figure 1 is about the relation between  and . JH, S. et al., Rezaie, K.

et al. 3, 6. The processin manufacturing industry is considered capable if the  value is equal to 1. The  value should as high as possible. This isbecause the higher  value means the variation of the process islower.

In manufacturing process, the variation of the process must be reducedin order to produce the products with constant quality level. If the  value for a process is greater than 2, we canconsidered the process that undergo by the manufacturing industry is qualifiedas six sigma process. The  value can only determine the variation of the process but  value cannot ensurethe production of the process is within the SLs. If the process is notcentering, the process is considered faultily.      In order to ensure the process of themanufacturing industry is in good condition, the  value is calculated. The process is consideras capable as the process is within the SLs and  value must larger than 1 in manufacturingsector. If the  value is equal to 1, the manufacturingindustry will accept 99.

73% of the product. The higher  value, the process distribution become narrower.In the manufacturing industry, the quality of the products need more uniformand within the SLs. Hence, the  value is considered a good measurement inmanufacturing industry because it can ensure the quality of products are alwayswithin the expectation of industry. If the  value is greater than 3, most of themanufacturing industry will do nothing because the process is very capable.

        If the  value is equal to  value, the process will consideredcentralized. In most of the manufacturing industry, the  value will not exactly equal to  value. Some of the manufacturing industry willset minimum value for  and  as 1. Actually,  and  value should be more than 1.33 which means theprocess of the manufacturing industry is satisfied.

The  value will never higher than  value. If the  value is slightly lower than  value, the process is still acceptable formanufacturing industry. The  and  value is important to determine the processcapability in the manufacturing industry.

 MachineCapability Process Variation Machine Method Manpower Measurement Environment Material                                 Figure 2: Ishikawadiagram     The environment of manufacturing sector will affect the capabilities of the process in a longperiod. The machine capability will not consider whether the machine is incontrol or not as the problems of the machine can determine by the controlchart. However, the machine capability cannot use to predict the status of theprocess in long-term by short-term sampling plan. Thus, the capability of the machineis not suitable calculated in a long period.    Generally, the machinecapability is used plus and minus three standard deviations (± 3 ). This is the baseline for the manufacturing process. Byusing the machine capability,the manufacturing industry can determine the condition of every single machine.The machine capability is similar with PCIs.

The machine capaility incides arevariation of the machine itself. The calculation for  is represent  while  represent . Hence,the  value is used to determine the capability ofthe process while the  value is used to determine the capability ofthe machine.    There are some elements whichwill cause the variation of the process which is shown in Figure 2. All of thevariation that mentioned in Figure 2 might influence the outcome. The machinecapability we only determine the dependency and the centering of the machineparameters.

JH,S. et al., Rezaie, K. et al. 3, 6. Conclusion     The process capability indices can use in the manufacturingindustry to ensure the process capability.

The process capabilityindices can ensure the products is within the specification limits. If theproducts do not meet the specificationlimits, the corrective actions can be taken. Hence, the quality of the productscan be maintained in a uniform manner.Besides, the manufacturing industry can use theprocess capability indices to monitor the process. The quality of the productscan be improved.

The machine capability needed to calculate in short term. Thevariation of the process should be eliminated. The overall process of themanufacturing industries can be maintained or even improved with the help ofthe PCIs.

If all of the manufactruing industry in Malaysia practice to use thePCIs, the products that produce in Malaysia will have good reputation.AcknowledgementsThe author very appreciates the referees because the informationand knowledge they gave are very useful in orderto accomplish this paper. References1.

 Abhijit S., & Himadri M. (2016). Process analysis andoptimization in turning of ATSM A36 through process capability index, Journal of King Saud University -Engineering Sciences.2. ?hsan K.

& Cengiz K. (2011). Process capability analyses basedon fuzzy measurements and fuzzy control charts.

Expert Systems with Applications, Vol. 38, Issue 4, 3172-3184.3.  JH, S., & Katikar, R. S.

IMPORTANCE OFPROCESS CAPABILITY AND PROCESS PERFORMANCE INDICES IN MACHINE TOOL.4.  Kane, V. E. (1986). Processcapability indices. Journal of quality technology, 18(1),41-52.5.

  Montgomery, D. C.(2007). Introduction to statistical quality control. John Wiley& Sons.6.  Rezaie, K.

, Ostadi, B., & Taghizadeh,M. R. (2006). Applications of process capability and process performanceindices. Journal of applied sciences, 6(5), 1186-1191.

7.  Rupesh C.,& Jatinder K.

(2014). Process Capability Analysis and Optimization inWEDM of Commercially Pure Titanium,Procedia Engineering, Vol. 97, 758-766.8.  Spano, A.

(2012). Process CapabilityAnalysis.9.  Steiner, S., Abraham, B.,& MacKay, J. (1997).

Understandingprocess capability indices. Institute for Improvement of Quality andProductivity, Department of Statistics and Actuarial Science, University ofWaterloo, Waterloo, Ontario N2L 3G1.10.  Zhang, N. F., Stenback, G.

A., & Wardrop, D. M. (1990). Interval estimation of process capabilityindex Cpk.

 Communications in Statistics-Theory and Methods, 19(12),4455-4470.   

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