品质管理精华理论SupplierSummit070504.ppt
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1、,Understand the difference between Inspection and Variation Reduction(SPC and Process Capability)Review New Process Capability 10-Steps and ScorecardWhat help do you need from Dell?Questions and Answers,Objectives,Process Capability Summit,Kirk ChiDell Inc.WWP BPI Business ChampionDell Black BeltASQ
2、 Certified Six Sigma Black BeltASQ Certified Quality Engineer7/05/04,Traditional Economic Model of Quality of Conformance,Total cost,Cost due to nonconformance,Cost of quality assurance,“optimal level”of quality,100%,Quality improvement based on Inspection,Modern Economic Model of Quality of Conform
3、ance,Total cost,Cost due to nonconformance,Cost of quality assurance,100%,Quality improvement based on Variation Reduction(SPC/Process Capability),Non-Value Added operations result in:Higher procurement cost of productsHigher probability of defects,Improve the Process To Reduce Non-Value-Added Opera
4、tions,Dell,VLRR/PID/CND,Hidden Costs,What is the difference between quality control based on Inspection and Variation Reduction?Inspection refers to the manufacturing operations based on Attribute Data(Pass/Fail).Current manufacturing operations are focused mainly on Pass/Fail inspections.Much of va
5、riable data is measured,but the data is converted to attribute data for Pass/Fail inspection.,If you inspect 100%,will your customer experience no failure?If you inspect 100%,and inspect again 100%,and inspect again 100%,will your customer experience no failure?Can you and Dell achieve the reduction
6、 of FIR(and VFIR)based on inspection quality control?,We will work together to understand the following points:Even if you inspect 100%,your customer will still experience failures Inspection does not detect the process and product mean shift 100%Inspection does not reduce the variation in your proc
7、ess(and product),Traditional Inspection View,Lower Spec,Upper Spec,no loss,nominal,tolerance,Traditional view:There is no failure as long as a parameter is within specification,New View(Taguchi Loss Function),nominal,tolerance,Failure rate,$,Lower Spec,Upper Spec,no loss,New View:Products still fail
8、 in time even if a parameter is within spec.The probability of failure increases as the parameter shifts away from the mean,nominal,tolerance,Failure rate,$,Lower Spec,Upper Spec,no loss,Where do we want to go?,Critical Process Parameters(x),Product Attribute(y(x),Metric(Y),VLRR,Sigma Level(Drive fo
9、r 5),PAPB,123,Yield,Cpk,Metric,What Measured,Metric(Y),Sigma Level(Drive for 5),VIFIR+90 D VFIR,Key Message:Only the reduction of process and product parameter variations will lead to the reduction of VFIR,High Cost of Quality,Lowest Cost of Quality,Approach to Process Capability,Identifying Cause a
10、nd Effect,What is Process Capability?,Process Capability is the“Voice of Process”to the“Voice of Customer”.Process Capability study provides valuable insight on how well an existing process is performing with regards to customer requirements(specifications)what needs to be done to improve performanc
11、eCapability studies enable manufacturers to improveproductivity,reduce costs,and enhance their strategicadvantage over competitors.,Process Stability Before Capability,Control of a process must be achieved first,before any attempt is made to measure capability or estimate the percentage of nonconfor
12、ming product.When a process is stable,it is repeatable,well-defined,and predictable.,You can predict the outcome only if the process is stable,time,PREDICTABLE,?,UNPREDECTIBLE,Process Stability:Statistical Process Control,Statistical Process Control(SPC),A process output is considered stable when it
13、 consists of only common-cause variation.,Sources of Variation in Production Processes,Materials,Tools,Operators,Methods,Measurement Instruments,HumanInspectionPerformance,Environment,Machines,INPUTS,PROCESS,OUTPUTS,Common Causes,Special Causes,Two Fundamental Management Mistakes,Treating as a speci
14、al cause any fault,complaint,mistake,breakdown,accident or shortage when it actually is due to common causesAttributing to common causes any fault,complaint,mistake,breakdown,accident or shortage when it actually is due to a special cause,Control Chart,Focuses attention on detecting and monitoring p
15、rocess variation over timeDistinguishes special from common causes of variationServes as a tool for on-going controlProvides a common language for discussion process performance,*,*,Commonly Used Control Charts,Variables datax-bar and R-chartsx-bar and s-chartsCharts for individuals(x-charts)Attribu
16、te dataFor“defectives”(p-chart,np-chart)For“defects”(c-chart,u-chart),Statistical Process Control(SPC),A methodology for monitoring a process to identify special causes of variation and signal the need to take corrective action when appropriate,Shift in Process Average,Identifying Potential Shifts,C
17、ycles,Trend,Quantitative Comparison ofTraditional Inspection vs.Control Chart,Review of Variable-Data Control Charts,+3,-3,+1,+2,-1,-2,+/-1=68%+/-2=95%+/-3=99.73%,Individual measurement distribution,SPC Control Limits,x-bar,x-bar+3X-bar,x-bar=/,UCL(Upper Control Limit)=X(double bar)+3X-barLCL(Lower
18、Control Limit)=X(double bar)-3X-bar,Sample mean distribution,Distribution of X vs.Distribution of Sample Means(X-bar),+3,-3,x-bar,x-bar+3X-bar,x-bar=/,Individual measurement distribution,Sample mean distribution,There is no relationship.Spec limits are determined by engineering based on customer req
19、uirements Control limits are determined by the common-cause variation in the process Spec limits are typically wider than control limits,Spec Limit vs.Control Limit,+3,-3,Control Chart:Example:Control chart is monitored by UCL and LCL.(Note:USL and UCL do not have any relation.),USL,LSL,x-bar,x-bar+
20、3X-bar,UCL,LCL,*If=2 for Inspection of individual parts,of subgroup size of 4 samples=1.,Why Control Charts Are Better Than Inspection?,+3,-3,Inspection:Example:One part is checked each hour.One part is checked every 20.Part passes the inspection if the part measurement is within spec.,USL,LSL,*Assu
21、mption:spec limit lis+/-3 sigma.,+3,-3,What happens to Inspection if process mean shifts 3 sigma?,USL,LSL,Anything above USL are rejected.,50%,Because half of the pieces are still within spec,there is 50%chance of selecting such a part and mistakenly deciding to continue running this modified proces
22、s.,What happens to Control Chart if process mean shifts 3sigma?,x-bar,UCL,LCL,*If=2 for Inspection of individual parts,of subgroup size of 4 samples=1.,99.865%,Only 0.135%of the subgroup averages would fall within the control limits.Conversely,99.865%will be above UCL.There is almost 100%chance this
23、 shift in the process mean will be detected.,+3 shift,Power of X-bar Chart to Detect Process Changes,Producers Risk(Alpha error):Rejecting a good partAlpha error measure the probability of rejecting good parts in the factory.Consumers Risk(Beta error):Shipping bad partsBeta error measures the probab
24、ility of shipping bad parts to customers,(1-),Probability of detecting a process shift is higher with larger n,i.e.Beta error(consumers risk)decreases as n increases.,Process Capability,Process Capability is defined as the ability of a process to satisfy customer expectations.Because the specificati
25、on limits are assumed to reflect customer desires,capability measures are said to relate the“Voice of the Process”to the“Voice of the Customer”,Process Capability,Process Capability Index,Cp=,USL-LSL 6s,Cpl,Cpu,USL-m 3s,Cpl=,m-LSL 3s,Cpk=min,Cpu=,Process Capability,Process Capability Index,CpCp 1.33
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