quality improvement of a grinding operation … · quality improvement of a grinding operation...

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Int. J. Mech. Eng. & Rob. Res. 2012 J Praveen Kumar et al., 2012

QUALITY IMPROVEMENT OF A GRINDINGOPERATION USING PROCESS CAPABILITY

STUDIES

J Praveen Kumar1*, B Indhirajith1 and K Thiruppathi1

*Corresponding Author: J Praveen Kumar, [email protected]

Quality is a state of a finished product, being free from defects, deficiencies and significantvariations. This measure of an excellence can be brought about by the strict and consistentadherence to measureable and verifiable standards to achieve uniformity of output that satisfiesspecific customer or user requirements. This paper gives a proposed methodology for to increasethe quality of a product manufactured in a grinding machine, using the various quality improvementtools like Process monitoring techniques, Cause and Effect diagram, Why-Why analysis andStatistical Process Control Charts. The key note in using these tools is because of ease way todetect the problems and solutions for the same. The quality improvement is accompanied bythe changes in machining parameters of a grinding machine and the optimisation of those changesreflects as an increase in the acceptance level of the product in the world market.

Keywords: Quality improvement techniques, Process capability studies, Statistical processcontrol, Process monitoring chart, Process capability index

INTRODUCTIONManufacturing processes are often met withlot of variations in a product from the customerspecified limits during the machining processand it is characterised by the strong effect onthe quality of a product. The variations in aproduct are an inevitable one. No two productsare identical in nature. The variations on amachine are due to either special (assignable)causes or chance (natural) causes (Mahajan,

ISSN 2278 – 0149 www.ijmerr.comVol. 1, No. 1, April 2012

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Int. J. Mech. Eng. & Rob. Res. 2012

1 School of Mechanical Engineering, SASTRA University, Tanjore 613401, India.

2004). Sometimes, the variation occurs dueto both of these causes, which affects thequality of a product severely. In a grindingoperation, variations which arise as a result ofthese causes play a vital role in acceptancelevel of a product. These causes are detectedusing various quality improvement tools andfinding remedies in a simply way. ProcessMonitoring Charts and Statistical ProcessControl techniques find to be a simplest

Research Paper

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method among various quality improvementtools for detecting the variations in a product.

The Process Monitoring charts are used forthe purpose of identifying the chance andassignable causes. It gives a well-definedwarning signal, if the process is going out ofcontrol. By using this technique, thereoccurrence of the defects or variations in aproduct can be rectified. The StatisticalProcess Control are the charts, where theaverage, range, standard deviations, processcapability values can be determined bystatistical approach.

These tools use the Process Capabilityindex value as a major technique to verifywhether any variations occurred on thegrinding operation or not (Gijo, 2005).

Process Capability Calculation

Process Capability index value (Cpk) iscalculated statistically using StatisticalProcess Control sheet and it is validatedagainst the Sigma value to determine therejection level of a product. The Cpk calculationis done with the use of Upper SpecificationLimit (USL), Lower Specification Limit (LSL)of a product, given from the customer side. Byusing these specification limits, USL and LSL,the Cpu and Cpl are calculated. Cpu is nothingbut a statistic, which related the differencebetween USL and the centre line to theStandard deviation () (Gijo, 2005). Cpl is alsoa statistic which relates the difference betweenthe centre line and LSL to the Standarddeviation (). The formula for calculating Cpuand Cpl is given below:

SigmaXUSLCpu *3 (http://www..quality-control-plan.com/spc-definitions.html)and

SigmaLSLXCpl *3 (http://www..quality-control-plan.com/spc-definitions.html)

Sigma is the standard deviation value ()and X is the average of the sum of all thevalues, i.e., mean of all observed values. Fromthe calculated Cpu and Cpl values, one candetermine the Cpk value from the formula,shown below:

Cpk = Minimum(Cpu, Cpl) (http://www.qua l i t y -con t ro l -p lan .com/spc -definitions.html)

The minimum value is taken for the Cpkcalculation because, it indicates whether or notthe process being analysed is capable ofproducing little or no defects. The higher thenumber, the less likely it will be defectives areproduced.

Each company is focusing to implement SixSigma (6) quality on a product for to achievenil (0.05 PPM) rejection level. Based on theProcess Capability Index value, the rejectionpercentage is determined. As the variationsis high, due to any one of those causes, affectsthe Cpk value and hence results in decline ofthe Sigma level. So, the Six Sigma quality levelcan be achieved in a grinding operation onlywhen the variations on the grinding processare eliminated. This methodology not only suitsgrinding operations, but it is meant for all kindof machining processes like turning, milling,shearing, etc.

ANALYSISIn grinding operations, the variation takesplace during the machining process is majorlydue to the parameters with in the machine andthese parameters can be acknowledged bybrainstorming method. By brainstorming, the

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motives for the causes occurred on a grindingmachine are thoroughly analysed from variousangles, to determine the significant andinsignificant causes. From this method, therecognised possible causes for the variationsare Tail stock clamping insufficient, Grindingwheel unbalance, Wheel head grinding speed,Work head rpm, Dressing frequency, Grindingwheel grade, Coolant flush ineffective, Coolanttemperature, Coolant filtration, Improperchecking method, Centre wear andmisalignment, radius formation, Feed rate,Outer Diameter stock for grinding, Machinerepeatability, Burr in centre, Hardness of thematerial, Dressing parameters and its norms,Wrong offset settings, Loading and unloadingerror and last but not least the cutting tool.

The above described possible causes arethe main reasons for the occurrence of thevariations in a product during grindingoperation. Hence, these possible causes arescrutinised to find the significant andinsignificant causes. From the abovementioned various possible causes, some

may be eliminated by proper training to thepersonnel and by experience. This can be doneby using Cause and effect diagram, a majorquality tool, which differentiates the causes into4M categories, namely Man; Materials;Machine; Methods (http://www. isixsigma.com/tools-templates/capability-indices-process-capability/process-capability-cp-cpk-and-process-per fo rmance-pp-ppk-what -difference/).

Cause and Effect Diagram

The cause and effect diagram clearly denotesthe causes in 4 M s for a single effect of Sizevariation (Figure 1). These causes are labelledin green and red colors, where green colorcauses can be eliminated by proper trainingand experience and red color causes playsan important role in size variations of aproduct. By eliminating the green color labelledcauses from the Cause and Effect diagram,we get both significant and insignificantcauses, for the variations to occur in a grindingmachine.

Figure 1: Cause and Effect Diagram for the Size Variation by Considering the 4M’s

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From the mentioned causes in the Causeand Effect diagram, the Significant andInsignificant causes has to be determined. TheSignificant causes are the main reason for thevariations in a grinding operation to happen.The Significant causes are taken into accountfor total elimination.

Possible Causes

When examine the possible causes after theremoval of green marks from the Cause and

Effect diagram (Figure 2), some causes areseems to be insignificant for the effect on agrinding machine to occur. The causes likeCoolant temperature, Tailstock clampinginsufficient, Wheel head grinding speed,Coolant temperature, Machine repeatability,Coolant flush ineffective, Centre misalignmentand Burr in centre are termed to be insignificantbecause nowadays the CNC grinding machineare made to eliminate these causes before it

Figure 2: Cause and Effect Diagram for the Size Variation by ConsideringBoth Significant and Insignificant Causes as Possible Causes

Figure 3: Cause and Effect Diagram Showing the Significant Causes for the Size Variation

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comes to existence. By using varioustechniques like Poke Yoke, building of Servomotors with an encoder, the minor causes aretotally eliminated to avoid the variations of aproduct. Hence, apart from these causes, restof them are considered to be Significant andresponsible for the variations in a grindingprocess to happen. The Significant causes areclearly demonstrated in by Cause and Effectdiagram (Figure 3).

So, “a systematic analysis on these fourcauses, namely Work head speed, Feed rate,Dressing frequency, Cutting tool, mayeliminate the variations occur on the productduring grinding operations”. The analysedresults needed to be optimized for thecontinuous improvement in a grindingmachine, if not; the outcome products will havedefects and leads to rejection. To prove thisstatement a detailed analysis should be madeon a grinding machine.

EXPERIMENTATIONThe four major causes, Work head rpm,Dressing frequency, Feed rate and Cutting toolare responsible for the variations to occur ona product during the grinding operation. So,an Industrial experimentation is carried out ona grinding machine to eliminate the variationsoccurring on a product by making somechanges on these causes. These four causesare the key parameters in a grinding machine.Hence, an effect can be surely achieved, oncea change is made on these causes.

The experimentation is carried out in a firm,where a numerous products are beingmanufactured. In that firm, a product ismanufactured with more variations in size andthey are facing lots of rejection. This situation

in that firm is merely due to a single operationout of various operations at various stages onthe product. The variation occurs only duringmachining of the same product, after the heattreatment process. The operation is grindingand it is performed in a grinding machine.Hence, this can be taken as an experimentalapproach to prove the statement.

OBSERVATION

Initial Condition

The Worm shaft is the product beingmanufactured in the firm as a part of HydraulicPower Steering. In that product, an operationof seal groove making is done in the grindingmachine. The grinding machine is a FANUCprogramming one.

Initially, when observation is made on thegrinding machine (HMT K130 U2), the processcapability index (Cpk) was found to be 0.49by using Process Monitoring Chart (PMC) andStatistical Process Control (SPC) with workhead rpm of 170, feed rate of 1.1 mm/minthroughout the depth, dressing frequency isdone once in 10 components, cutting tool ofopen grain 19A 80 L8 VS. The Cpk value of0.49 in that machine is due to the assignablecauses.

The assignable causes can be eliminatedby making changes in the four main significantcauses in a grinding machine. So, acomprehensive analysis is done on themachine for to improve the Cpk value andreduce the rejection level in the grindingmachine, using only the four main significantcauses.

The PMC for the initial observation takenin the machine clearly shows the variations

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of the product (Figure 4). The SPC analysisfor the initial observation, which uses thestatistical approach, is used to find theStandard deviation (Sigma) value. The SPCanalysis for the value of Cpk 0.4911 isexplained in detail using the SPC chart. Thechart uses the formula for the calculation of Xbar, Standard deviation and ProcessCapability index, generates as the valueenters in the column. The SPC analysis clearlyshows the values for 30 observations takencontinuously on the product in the grindingmachine (Figure 5).

The Cpk improvement in the machine willbe carried out using showed ProcessMonitoring Chart (Figure 4), to find the pointof occurrence of the variation and StatisticalProcess Control (Figure 5) for statisticalapproach to determine the process capabilityindex (Cpk) value.

Figure 4: PMC Shows the Observations atthe Initial Condition of the Machine

Figure 5: SPC Chart Analysis for theObservations Made in PMC at the Initial

Condition of the Machine

ACTIONThe four significant causes are to be modifiedin the grinding machine for the sake ofimprovement in the Cpk value.

Work Head Speed

The initial action on a machine is taken tomodify the work head speed from 170 rpm to184 rpm. By using the quality tools such asProcess Monitoring chart (PMC), theobservation is monitored in the form of graphand it is validated in Statistical Process Control(SPC) analysis charts for to find the Cpk value.The result for the monitored observations canbe attained, only after the observations are fedinto the SPC analysis chart. The PMC for themonitored observations are clearlydemonstrating the variations are occurred onlydue to chance causes (Figure 6).

The SPC analysis briefly explains the X bar,Standard deviation and Cpk values for the Cpk

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Figure 6: PMC for the Increased WorkHead Speed of 184 rpm from the Initial

Condition of 170 rpm

improvement from the initial condition of themachine (Figure 7). The result becomespositive as the work head speed increasesand Cpk value increases from 0.4911 to

Figure 7: SPC Chart Analysis for theObservation Made in PMC at a Work Head

Speed of 184 rpm

0.8179. Hence the modification has a positiveapproach towards the Cpk value. Therefore,as there is a sign of increase in Cpk value asthe work head rpm increases, because as thework speed increases the ‘arc of contact’between the cutting tool and the work piecedecreases. This decrease in arc of contact,leads to creation of less variations in size(Pankaj and Arunesh, 2009).

The graph shows the improvement in the Cpkvalue from the initial condition, i.e.,170 rpm, to the increase in the work headspeed, i.e., 184 rpm, of the machine (Figure 8).

As there is a positive approach towards theCpk value, as work head speed increases,further improvement in Cpk value, can be doneby still increasing the work head rpm. So, thework speed is further increased from 184 rpmto 200 rpm, to see the effect of variation of theproduct.

The observations of the product at workhead speed of 200 rpm are monitored usingPMC and the variations are observed (Figure9). The variations of the products falls on the

Figure 8: The Comparison of Cpk Valuesfrom the Previously Operating Condition

Work Head rpm

170 184

Cp

k V

alu

e

1.0

0.5

0

Cpk Improvement

0.4911

0.8179

83


green zone, from PMC, means as the workspeed increases, the variations are beingcontrolled within the limits and also results incontinuous improvement. As the variations arecontrolled, gives rise to the Cpk values as well.

The SPC chart shows the Sigma values andthe corresponding result in Cp and Cpk values(Figure 10). As the work speed increases, theCpk value again increases from 0.8179 to1.0454. This also shows a positive attitudetowards the Six sigma quality.

The Cpk improvement after the change inwork head speed from 184 rpm to 200 rpmis clearly demonstrated using the graph(Figure 11).

The Cp and Cpk value are increased as thework speed increases and this also favour theobjectives. Hence, the speed can be furtherincreased to see the changes on the productvariations and as well as in the Cp and Cpkvalues.

Figure 10: SPC Chart Analysis for theObserved Values Under the Work Head

Speed of 200 rpm

So, the work head rpm is increased to 225rpm from 200 rpm and notice the changes. Asthe speed increases, as mentioned earlier, thecontact point between the work piece and thecutting tool decreases, results in the declineof the range in variations. This can be seenfrom the monitored observations in PMC, at

Figure 11: The Chart Showing theImprovement in Cpk Value from the

Previous Operating Condition

Work Head rpm

184 200

Cp

k V

alu

e

1.5

0.5

0

Cpk Improvement

0.8179

1.04541.0

Figure 9: The PMC for the Increased WorkHead Speed from 184 rpm to 200 rpm

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the work head speed of 225 rpm (Figure 12).The PMC shows the variations falls on thegreen zone, which denotes 100% acceptanceof the product. The recording of data of eachproduct on PMC is an easy process to findthe deviations from the recommendedspecification limits of the product. By knowingthis, the employer can make some changesto bring back the component into the greenzone only if the deviation reaches yellow or redzone of PMC. Otherwise, the processes neednot to be disturbed.

The SPC chart analysis shows an increasein the Cpk value from 1.0454 to 1.1806, whenthe machine is operated under the work headspeed of 225 rpm (Figure 13). So, the workhead speed works well for the improvement inquality of the product by reducing thevariations. The Cpk improvement from thepreviously operating condition is shown

Figure 12: The PMC for the Increased WorkHead Speed of 225 rpm from 200 rpm

Figure 13: The SPC Chart Analysis for theObserved Values Under the Condition of

Work Head Speed 225 rpm

through graph (Figure 14). The increase inwork head speed results in the improvementof both Cp and Cpk values. Hence, the speedhas been decided to increase further tovisualize the changes in the variation of theproduct.

Figure 14: The Graph Shows the CpkImprovement from the Previously

Operating Condition

Work Head rpm

200 225

Cp

k V

alu

e

1.20

1.05

0.05

Cpk Improvement

1.0454

1.1806

1.15

1.00

1.10

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Therefore the work head speed is increasesfrom 225 rpm to 250 rpm, and monitored thechanges of the machine in PMC (Figure 15).

the changes are visualized. The next action isto take any of those remaining significantcauses for alteration and see the changesreflect on the product.

Dressing Frequency

The dressing frequency is taken for furtherdiscussion and changes on the dressingfrequency is done by keeping the optimisedwork head speed, i.e., 225 rpm in the machine.From the PMC of the product at various workspeed, the variation of the component is highonly after the 7th component in a dressing cycleof 10 components. Hence, the 8th, 9th and 10th

component of the dressing cycle shows a highvariation from the target value. So, the dressingfrequency is made to change from 10components to 7 components. As the dressingfrequency is decreases, the dressing depth ofcut needs to be decrease (Linke, 2008). So,the depth of cut is changed from 0.15 mm to0.1 mm radially.

By implementing the above specifiedchanges in that machine and data arecollected. The PMC for the monitoredobservations at a dressing frequency of 7components is demonstrated clearly(Figure 16).

The PMC shows the variations are fall onthe green zone and denotes 0% rejection. Butat the same, the cycle time of the processincreases due to the reduction in the dressingfrequency

The SPC chart analysis for the variationsof the product under the condition of dressingfrequency 7 components is shown in Figure17, with the Cp and Cpk values and standarddeviations. The change in dressing frequencyshows an improvement in Cpk value from

Figure 15: The PMC for the Condition ofChange is Dressing Frequency

from 10 to 7 Components

As the speed increases to 250 rpm from225 rpm, the variation in the product is incontrol, but the vibration of the machinebegins to increase and this ends in theformation of chatters on the product whichleads to rejection of the component (http://www.nortonindustrial.com/uploadedFiles/SGindnortonabrasives/Documents/Toolroom%20Selection%20 Chart%207505.pdf). Thischattering formation is noticed on the firstproduct after the change of speed from225 rpm to 250 rpm. So, further process onthis speed is stopped and the work head rpmof 225 is optimised in that machine.

From the four significant causes, one cause,i.e., the work head rpm has been altered and

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But, due to increase in the cycle time of thewhole process, further changes on thedressing frequency is stopped by optimisingthe changes in that machine and look forchanging any of the remaining two significantcauses.

Feed Rate

We take the feed rate concept for the furtherimprovement in Cpk value. When the workpiece is examined, the hardness of the materialchanges as the depth of the componentincreases due to the heat treatment processon it. The hardness of the component is about1.1 mm along the depth in the total depth of2.9 mm. Hence, the single feed rate of 1.5 mm/min is not sufficient for the removal of materialof the whole depth of the component. So,stepped feed needs to be implement for theefficient removal of material.

Stepped feed in 3 stage as 1.7, 1.6, 1.4mm/min is to be implement by keeping all other

Figure 16: SPC Analysis Observed Valuesof Dressing Frequency of 7 Components

Figure 17: The Cpk Comparison of Effectsof Both Dressing Frequencies

Dressing Frequency

10 7

Cp

k V

alu

e

2.0

1.0

0

Cpk Improvement

1.1806

1.45191.5

0.5

1.1806 to 1.4519 and the value of Cpk is verynearer to the objective of Six sigma quality,i.e., Cpk of 1.67.

The Cpk improvement for the change in thedressing frequency from 10 components to 7components on the machine is shown by graph(Figure 17).

Figure 18: The PMC for the Variationsat Stepped Feed Rate Condition

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changed process constant and theobservations are carried out using the PMC(Figure 18). The PMC shows the values areinside the green zone and there are nopossibilities of rejection of the component.Hence, the feed rate change gives a positiveresult for the objective.

take the final significant cause, i.e., cutting tool.The feed rate of stepped feed is optimised inthe machine and looks for any making anychange in the cutting tool.

Cutting Tool

Cutting tool in grinding machine is an abrasiveand it is an important significant cause thanothers. The analysis on the cutting tool is atedious process, since lot of parameters areinvolved in this such as abrasives, grid size,grade, structure and bond type. In all theprevious process, the grinding wheel used isA 80 L8 VS.

This grinding wheel A 80 L8 VS has variousexplanations for each letters and numbers. The‘A’ denotes the Aluminium oxide abrasive; ‘80’denotes the fine grain size; ‘L’ denoted theMedium grade; ‘8’ denotes the Open structure;‘V’ for the vitrified bond; ‘S’ for bondmodification (http://metalwebnews.com/machine-tools/ch5.pdf).

In the above mentioned grindingspecification, the structure is an open structureand during removal of huge depth more wear

Figure 19: SPC Analysis on the ObservedValues Under the Condition

of Stepped Feed Rate

The SPC chart for the changed feed rateprocess reveals an improvement in the Cpkvalue from 1.4519 to 1.5013. The SPC chartshows an improvement in the Cp and Cpkvalues from the previous process and thechange enhances the process further.

The increase in Cpk value is clearly shownthrough graph by comparing the previouschanges with the change in the feed rate(Figure 20).

Further change in the feed rate cannot bedone, because the supplementary change infeed rate affects the surface finish andoptimise the change on the machine. Hence

Figure 20: The Cpk Comparison of theEffects of Both Feed Rates

Dressing Frequency

Single Feed Stepped Feed

Cp

k V

alu

e

1.52

1.48

1.42

Cpk Improvement

1.4519

1.50131.50

1.44

1.46

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occurs, results in minimum life of the wheel.So, the structure is taken as a defectiveparameter in that grinding wheel and it is tobe replaced with a dense structure (http://www.grindwellnorton.co.in/GrindingTech/pdfs/FactorsAffectSelection.pdf).

As per the analysis, the dense structurewheel available in the inventory of the companyis taken to replace this wheel for to examineany change is occurring in the variation of thecomponent.

So, the dense structure wheel ofspecifications DA 80 K5 V10 is made toreplace the previous cutting tool. The newwheel has a dense structure, ‘5’ . Other thanthat, no other parameters are changed. Bykeeping the previously changed significantcauses as optimised one and changing thenew grinding wheel for the examination.

The observations are monitored and thedata are noted in the PMC (Figure 21). Thevariations of the product fall within the greenzone and hence the probability of rejectionis 0%. Some process shows nil variationsin the product and it falls exactly at the targetvalue.

The product variations are very nearer tothe target value. This may give raise to bothCp and Cpk value from the previous process.This can attained from the SPC chartanalysis.

The SPC chart analysis (Figure 22) showsthe Cpk value of 1.9359, which exceeds theobjective of 1.67. This Cpk value denotes thatthe rejection of the product beingmanufactured in this machine is about 0.5PPM. Hence, Six Sigma quality isimplemented in HMT machine by improving

Figure 22: The SPC Analysis for theObserved Values on the Operating

Condition of Dense Structure Cutting Tool

Figure 21: The PMC for the Variations in aProduct at Dense Structure Cutting Tool

Operating Condition

the four major significant causes in a grindingmachine.

The increase in the Cpk value from thepreviously operated condition to the change

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in the cutting tool is clearly demonstrated usingthe line graph (Figure 23).

Finally, the work head speed of 225 rpm;dressing frequency of 7; stepped feed rate of1.7, 1.6, 1.4 mm/min; dense structure cuttingtool of specification DA 80 K5 V10 areoptimised in the machine for the defects lessand variations less product output. The totalresult of the project is shown with differentstages of action of the corresponding Cpkvalue (Figure 24).

CONCLUSIONThis improvement in the quality not only givescustomer satisfaction, it also gains more profitto the organisation. The back tracking of thefinished product is minimum hence this makesa way for reducing the time constraints.

The available time increases as a result ofreduction in the re-work and backtracking ofthe products, the productivity increases rapidly.If all these are achieved in the machine, thecost of a product will play a major role. Theorganisation can give a product at acompetitive price, than other firms and at thesame time, deliver at a world class products.

This methodology is applicable for any kindof grinding machine for to improve the qualityof the product. The four significant causes canbe made into insignificant, if the analysis andapproach to the existing problem in a right way.This method has to be done with carefulpremeasures and with the knowledge of theemployer.

ACKNOWLEDGMENTThe authors sincerely thank RANE TRW Steering

Limited, Viralimalai, Trichy, India, for their support

and encouragement to perform a risky task without

caring about their production and cost of the product.

The authors would also like to thank K Sudhakar, V

Figure 23: The Cpk Comparison of CuttingTool from the Previously Operated

Condition

Cutting Tool

19A 80 L8 VS DA 80 K5 V10

Cp

k V

alu

e

2.5

1.5

0

Cpk Improvement

1.5013

1.93592.0

0.5

1.0

RESULTS AND DISCUSSIONThe Process Monitoring Chart and StatisticalProcess Control are the helping tools forperforming such a huge process. The everyimprovement in the process cycle is noticedand implemented for the permanentachievement in the quality of the product.

Figure 24: The Cpk Improvementon Every Actions and Optimization

of the Each Completed Action

IC

Cp

k V

alu

e

2.5

1.0

Cpk Improvement in Stages

0.4

911

2.0

0

0.5Cpk

1.5

Note: IC – Initial Condition; WHS – Work Head Speed in rpm;DF – Dressing Frequency; FR – Feed Rate in mm/min;CT – Cutiing Tool (abrasive).

184 200 225

DF FR CTWHS

0.8

17

9

1.0

45

4

1.1

80

6

1.4

51

9

1.5

01

3

1.9

35

9

90


Rajarajan, S Krishnadevarajan, G Rajkumar of

RANE TRW unit.

REFERENCES1. ASM Handbook, Machining Process,

Vol. 16, pp. 424-435.

2. Factors for Selecting Right GrindingWheel [online], available at http://www.grindwellnorton.co.in/GrindingTech/pdfs/FactorsAffectSelection.pdf

3. Gijo E V (2005), “Improving ProcessCapability of Manufacturing Process byApplication of Statistical Techniques”,Quality Engineering, Vol. 17, No. 2,pp. 309-315.

4. Grinding Machine Details [online],available at http://metalwebnews.com/machine-tools/ch5.pdf

5. Grinding Troubleshooting [online], availableat http://www.nortonindustrial.com/uploadedFiles/SGindnortonabrasives/

Documents/Toolroom%20Selection%20Chart%207505.pdf

6. Linke B (2008), “Dressing Process Modelfor Vitrified Grinding Wheels”, Vol. 57,pp. 345-348.

7. Mahajan M (2004), Statistical QualityControl, 2nd Edition, Dhanpat Rai & Co.

8. Pankaj Chandnal and Arunesh Chandra(2009), “Quality Tools to Reduce CrankShaft Forging Defects: An Industrial CaseStudy”, Journal of Industrial and SystemEngineering, Vol. 3, No. 1, pp. 27-37.

9. Technical Definitions [online], available athttp://www.quality-control-plan.com/spc-definitions.html

10. Quality Formula [online], available at http://www.isixsigma.com/tools-templates/capability-indices-process-capability/process-capability-cp-cpk-and-process-performance-pp-ppk-what-difference/