Quality Management It costs a lot to produce a bad product. Norman Augustine
Cost of quality 1. Prevention costs 2. Appraisal costs 3. Internal failure costs 4. External failure costs 5. Opportunity costs
What is quality management all about? Try to manage all aspects of the organization in order to excel in all dimensions that are important to customers Two aspects of quality: features: more features that meet customer needs = higher quality freedom from trouble: fewer defects = higher quality
The Quality Gurus Edward Deming Quality is uniformity and dependability Focus on SPC and statistical tools 14 Points for management 1900-1993 1986 PDCA method
The Quality Gurus Joseph Juran Quality is fitness for use Pareto Principle Cost of Quality 1951 General management approach as well as statistics 1904-2008
History: how did we get here Deming and Juran outlined the principles of Quality Management. Tai-ichi Ohno applies them in Toyota Motors Corp. Japan has its National Quality Award (1951). U.S. and European firms begin to implement Quality Management programs (1980 s). U.S. establishes the Malcolm Baldridge National Quality Award (1987). Today, quality is an imperative for any business.
What does Total Quality Management encompass? TQM is a management philosophy: continuous improvement leadership development partnership development Cultural Alignment Customer Technical Tools (Process Analysis, SPC, QFD)
Developing quality specifications Design Design quality Input Process Output Dimensions of quality Conformance quality
Six Sigma Quality ± 6σ A philosophy and set of methods companies use to eliminate defects in their products and processes Seeks to reduce variation in the processes that lead to product defects The name six sigma refers to the variation that exists within plus or minus six standard deviations of the process outputs
Six Sigma Quality
Six Sigma Roadmap (DMAIC) Celebrate Project $ Next Project Control Document process (WIs, Std Work) Mistake proof, TT sheet, CI List Analyze change in metrics Value Stream Review Prepare final report Validate Project $ Define Customers, Value, Problem Statement Scope, Timeline, Team Primary/Secondary & OpEx Metrics Current Value Stream Map Voice Of Customer (QFD) Validate Project $ Measure Assess specification / Demand Measurement Capability (Gage R&R) Correct the measurement system Process map, Spaghetti, Time obs. Measure OVs & IVs / Queues Validate Project $ Improve Optimize KPOVs & test the KPIVs Redesign process, set pacemaker 5S, Cell design, MRS Visual controls Value Stream Plan Validate Project $ Analyze (and fix the obvious) Root Cause (Pareto, C&E, brainstorm) Find all KPOVs & KPIVs FMEA, DOE, critical Xs, VA/NVA Graphical Analysis, ANOVA Future Value Stream Map
Six Sigma Organization
Quality Improvement Quality Traditional Time
Continuous improvement philosophy 1. Kaizen: Japanese term for continuous improvement. A step-by-step improvement of business processes. 2. PDCA: Plan-do-check-act as defined by Deming. Plan Do Act Check 3. Benchmarking : what do top performers do?
Tools used for continuous improvement 1. Process flowchart
Tools used for continuous improvement 2. Run Chart Performance Time
Tools used for continuous improvement 3. Control Charts Performance Metric Time
Tools used for continuous improvement 4. Cause and effect diagram (fishbone) Machine Man Environment Method Material
Tools used for continuous improvement 5. Check sheet Item A B C D E F G ------- ------- -------
Tools used for continuous improvement 6. Histogram Frequency
Tools used for continuous improvement 7. Pareto Analysis Frequency 60 50 40 30 20 10 100% 75% 50% 25% Percentage 0% A B C D E F
Summary of Tools 1. Process flow chart 2. Run diagram 3. Control charts 4. Fishbone 5. Check sheet 6. Histogram 7. Pareto analysis
Case: shortening telephone waiting time A bank is employing a call answering service The main goal in terms of quality is zero waiting time - customers get a bad impression - company vision to be friendly and easy access The question is how to analyze the situation and improve quality
The current process Custome r A Operator Receiving Party Custome r B How can we reduce waiting time?
Fishbone diagram analysis Absent receiving party Working system of operators Absent Too many phone calls Out of office Lunchtime Not giving receiving party s coordinates Complaining Not at desk Lengthy talk Does not know organization well Absent Does not understand customer Makes custome r wait Leaving a message Takes too much time to explain Customer Operator
Reasons why customers have to wait (12-day analysis with check sheet) Daily average Total number A One operator (partner out of office) 14.3 172 B Receiving party not present 6.1 73 C No one present in the section receiving call 5.1 61 D Section and name of the party not given 1.6 19 E Inquiry about branch office locations 1.3 16 F Other reasons 0.8 10 29.2 351
Pareto Analysis: reasons why customers have to wait Frequency Percentage 300 87.1% 250 200 150 71.2% 49% 100 0% A B C D E F
Ideas for improvement 1. Taking lunches on three different shifts 2. Ask all employees to leave messages when leaving desks 3. Compiling a directory where next to personnel s name appears her/his title
Results of implementing the recommendations Before After Frequency Percentage Frequency Percentage 100% 300 87.1% 300 200 71.2% 49% 200 Improvement 100 100 100% 0% 0% A B C D E F B C A D E F
In general, how can we monitor quality? By observing variation in output measures! 1. Assignable variation: we can assess the cause 2. Common variation: variation that may not be possible to correct (random variation, random noise)
Statistical Process Control (SPC) Every output measure has a target value and a level of acceptable variation (upper and lower tolerance limits) SPC uses samples from output measures to estimate the mean and the variation (standard deviation) Example We want beer bottles to be filled with 12 FL OZ ± 0.05 FL OZ Question: How do we define the output measures?
In order to measure variation we need The average (mean) of the observations: X = 1 N N i= 1 x i The standard deviation of the observations: σ = N i= 1 ( x i N X ) 2
Average & Variation example Number of pepperoni s per pizza: 25, 25, 26, 25, 23, 24, 25, 27 Average: Standard Deviation: Number of pepperoni s per pizza: 25, 22, 28, 30, 27, 20, 25, 23 Average: Standard Deviation: Which pizza would you rather have?
When is a product good enough? High Incremental Cost of Variability Zero a.k.a Upper/Lower Design Limits (UDL, LDL) Upper/Lower Spec Limits (USL, LSL) Upper/Lower Tolerance Limits (UTL, LTL) Lower Tolerance Target Spec Upper Tolerance Traditional View The Goalpost Mentality
But are all good products equal? High Incremental Cost of Variability Zero Taguchi s View Quality Loss Function (QLF) Lower Spec Target Spec Upper Spec LESS VARIABILITY implies BETTER PERFORMANCE!
Capability Index (C pk ) It shows how well the performance measure fits the design specification based on a given tolerance level A process is kσ capable if X + kσ UTL and X kσ LTL UTL X X LTL 1 and 1 kσ kσ
Capability Index (C pk ) Another way of writing this is to calculate the capability index: X LTL UTL X C pk = min, kσ kσ C pk < 1 means process is not capable at the kσ level C pk >= 1 means process is capable at the kσ level
Accuracy and Consistency We say that a process is accurate if its mean is close to the target T. We say that a process is consistent if its standard deviation is low. X
Example 1: Capability Index (C pk ) X = 10 and σ = 0.5 LTL = 9 UTL = 11 LTL X UTL C pk = 10 9 11 10 min or = 3 0.5 3 0.5 0.667
Example 2: Capability Index (C pk ) X = 9.5 and σ = 0.5 LTL = 9 UTL = 11 LTL X UTL
Example 3: Capability Index (C pk ) X = 10 and σ = 2 LTL = 9 UTL = 11 LTL X UTL
Example Consider the capability of a process that puts pressurized grease in an aerosol can. The design specs call for an average of 60 pounds per square inch (psi) of pressure in each can with an upper tolerance limit of 65psi and a lower tolerance limit of 55psi. A sample is taken from production and it is found that the cans average 61psi with a standard deviation of 2psi. 1. Is the process capable at the 3σ level? 2. What is the probability of producing a defect?
Solution LTL = 55 UTL = 65 X =61 σ = 2 C C pk pk = = X LTL UTL X min(, ) 3σ 3σ 61 55 65 61 min(, ) = min(1,0.6667) 6 6 = 0.6667 No, the process is not capable at the 3σ level.
Solution P(defect) = P(X<55) + P(X>65) =P(X<55) + 1 P(X<65) =P(Z<(55-61)/2) + 1 P(Z<(65-61)/2) =P(Z<-3) + 1 P(Z<2) =G(-3)+1-G(2) =0.00135 + 1 0.97725 (from standard normal table) = 0.0241 2.4% of the cans are defective.
Example (contd) Suppose another process has a sample mean of 60.5 and a standard deviation of 3. Which process is more accurate? This one. Which process is more consistent? The other one.
Control Charts Upper Control Limit Central Line Lower Control Limit Control charts tell you when a process measure is exhibiting abnormal behavior.
Two Types of Control Charts X/R Chart This is a plot of averages and ranges over time (used for performance measures that are variables) p Chart This is a plot of proportions over time (used for performance measures that are yes/no attributes)
Statistical Process Control with p Charts When should we use p charts? 1. When decisions are simple yes or no by inspection 2. When the sample sizes are large enough (>50) Sample (day) Items Defective Percentage 1 200 10 0.050 2 200 8 0.040 3 200 9 0.045 4 200 13 0.065 5 200 15 0.075 6 200 25 0.125 7 200 16 0.080
Statistical Process Control with p Charts Let s assume that we take t samples of size n p = total number of (number of samples) "defects" (sample size) p( 1 p) s p = n UCL = p + zs p LCL = p zs p
Statistical Process Control with p Charts p= 80 6 200 = 1 15 = 0.066 s p = 0.066(1 0.066) 200 = 0.017 UCL= 0.066 LCL= 0.066 + 3 0.017 3 0.017 = = 0.117 0.015
Statistical Process Control with p Charts UCL = 0.117 p = 0.066 LCL = 0.015
Statistical Process Control with X/R Charts When should we use X/R charts? 1. It is not possible to label good or bad 2. If we have relatively smaller sample sizes (<20)
Statistical Process Control with X/R Charts Take t samples of size n (sample size should be 5 or more) X = 1 n n i= 1 x i X is the mean for each sample R = max { x i } min{ x i } R is the range between the highest and the lowest for each sample
Statistical Process Control with X/R Charts X = 1 t t j= 1 X j X is the average of the averages. R = 1 t t j= 1 R j R is the average of the ranges
Statistical Process Control with X/R Charts define the upper and lower control limits UCL X = X + A 2 R LCL X = X AR 2 UCL R = DR 4 Read A 2, D 3, D 4 from Table TN 8.7 LCL R = DR 3
Example: SPC for bottle filling Sample Observation (x i ) Average Range (R) 1 11.90 11.92 12.09 11.91 12.01 2 12.03 12.03 11.92 11.97 12.07 3 11.92 12.02 11.93 12.01 12.07 4 11.96 12.06 12.00 11.91 11.98 5 11.95 12.10 12.03 12.07 12.00 6 11.99 11.98 11.94 12.06 12.06 7 12.00 12.04 11.92 12.00 12.07 8 12.02 12.06 11.94 12.07 12.00 9 12.01 12.06 11.94 11.91 11.94 10 11.92 12.05 11.92 12.09 12.07
Example: SPC for bottle filling Calculate the average and the range for each sample Sample Observation (x i ) Average Range (R) 1 11.90 11.92 12.09 11.91 12.01 11.97 0.19 2 12.03 12.03 11.92 11.97 12.07 12.00 0.15 3 11.92 12.02 11.93 12.01 12.07 11.99 0.15 4 11.96 12.06 12.00 11.91 11.98 11.98 0.15 5 11.95 12.10 12.03 12.07 12.00 12.03 0.15 6 11.99 11.98 11.94 12.06 12.06 12.01 0.12 7 12.00 12.04 11.92 12.00 12.07 12.01 0.15 8 12.02 12.06 11.94 12.07 12.00 12.02 0.13 9 12.01 12.06 11.94 11.91 11.94 11.97 0.15 10 11.92 12.05 11.92 12.09 12.07 12.01 0.17
Then X =12.00 is the average of the averages R =0.15 is the average of the ranges
Finally Calculate the upper and lower control limits UCL LCL X X = 12.00+ 0.58 0.15= 12.09 = 12.00 0.58 0.15= 11.91 UCL LCL R R = = 2.11 0.15= 1.22 0 0.15= 0
The X Chart UCL = 12.10 X = 12.00 LCL = 11.90
The R Chart UCL = 0.32 R = 0.15 LCL = 0.00
The X/R Chart UCL X What can you conclude? LCL UCL R LCL