Kwek whether the process is within specification limits (SLs)

 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.

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Keywords. Processcapability indices; Machine capability.Introduction A process in the manufacturing industry is very special because the process needs the linkage of manpower, raw materials, machines, andmethods. In order to improve the quality level of products, the capability ofthe process plays an important role in the manufacturingindustry. Rezaie, K. 6. The process capabilityindices (PCIs) is also known as processcapability analysis which is widely used in manufacturing industry. ThePCIs is used to measure the ability of the process to meet the requirements ofthe customers which are also known as specification limits.

The analyst usedPCIs to evaluate 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.Montgomery, D. C. 5. The graphics can determine whether the process iswithin specification limits (SLs) or not. Steiner, S. et al.

9. Thehistogram is easy and clear method to determine the performance of the process. If the process is in control and the data isnormally distributed, the potential capability analysis can be used to improvethe quality of the process. Spano,A. 8. The PCIs is used to compare the output of in control process with theSLs by 6 sigmas. PCIs are quantitative measures based on the performanceand potential of the process. By doing so, the process can meet therequirements 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 measure form to ensure the performanceof the process. The cost spent in the process of rework and scrap will causethe loss of the industry. Hence, the high-qualityproduction should practice in industry and try to meet the requirements. JH, al. 3.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 under controlby the suppliers, we can try to improvethe 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 topredict the machining process that can meet the expectations and tolerancelimits 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.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  instead of  and .  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 process andthe 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 nonconforming items or not.

The quality of the product canbe maintained 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-sided process-capabilityratios 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       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 the of 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 becomenarrower. In the manufacturing industry, the quality of the products need moreuniform and 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.

 ConclusionThe processcapability indices can use in the manufacturing industry to ensure the processcapability. The process capability indices can ensure the products is withinthe specification limits. If the products donot meet the specification limits, the corrective actions can be taken.

Hence,the quality of the products can be maintainedin a uniform manner. Besides, the manufacturingindustry can use the process capability indices to monitor the process. Thequality of the products can be improved. The machine capability needed tocalculate in short term. The variation of the process should be eliminated. Theoverall process of the manufacturing industries can be maintained or evenimproved.

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.

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