Lecture : Variatio Ris Maagemet Quality Types Total Quality Huma resources Maufacturig Orgaizig ad operatig Product ad Services Desig
What is variatio? Variatio = Deviatio from omial variatio: the etet to which or the rage i which a thig varies vary: to mae differeces betwee items All processes itroduce variatio ito part dimesios Variatio impacts performace Variatio impacts cost 3 Nomial vs. Variatio Nomial Defiitio the target value that the desig tried to achieve Quality of omial desig Feature set Loo/feel Variatio Defiitio Variatio is the small deviatio from omial itroduced by the eviromet maufacturig process degradatio Quality of desig for variatio Robust to iteral variatio Robust to eteral variatio 4
Comple Product 5 Why is this a iterestig problem? There are thousads of articles o variatio ad robust desig but. Compaies cotiue to struggle with variatio ad its effects why? 6 3
Did t Taguchi solved this problem already? Desig of Eperimets is oe tool of may used i the variatio ris maagemet process Tolerace desig ad parameter desig methods are limited to sigle cause/effect methods Robust desig methods ca be used for sigle subsystems Other researchers Simulatio tools to predict variatio for particular problems Robust cocept desig 7 What problems have ot bee solved Compleity It is ot eough to loo at sigle cause ad effect, the product (sub-assembly) must be evaluated as a system Prioritizatio There are ot eough resources to improve ad cotrol all processes Data supported processes The data sources are limited 8 4
Source of Compleity Compleity Prioritizatio Data Sources Process Variatio Part Dimesio Variatio Subassembly dimesioal variatio Fuctioal Variatio Customer Dissatisfactio Stampig variatio Door pael shape Gap betwee the door ad frame Ecess wid oise ad lea Customer Dissatisfactio Locatig system for - holes Mis-located part Need for a custom shim Ecess weight Customer Dissatisfactio 9 Compleity Methods of Maagig Data Compleity Prioritizatio Data Sources Key characteristics: The set of small set of product features whose variatio will create sigificat loss 0 5
Key Characteristics Flowdow Compleity Prioritizatio Data Sources Characteristics of flowdow May layers deep May cotributors Cotour Cross coupled Cotour of the Mai Torque Bo Drag Gap betwee the sis System Assembly Feature Fiture Height Spar Agle of Frot Spar Distace Betwee Spars Etrusio Agle of Rear Spar Process Eample from a medical product Compleity Prioritizatio Data Sources 6
Mathematical Model Compleity Prioritizatio Data Sources y y y i y f Product-KCs (= j Subsystem- KCs j l l jl l l Part-KCs (=l- Process- KCs (=l) ij = i f ( ( i, ( i,..., ( ) 3 y i y σ i Variatio Model Compleity Prioritizatio Data Sources = f (, i y = = i y i,..., y σ i ) y i y... σ i y... i σ yi determied usig VSA (variatio systems aalysis) Desig of Eperimets Product/process models 4 7
8 5 Matri Represetatio = ( ( ( ( ( ( ( ( ( K M M M M K K ô K ( 3 = l Kô ô ô ô T = ( ( ( ( ( ( ( ( ( K M M M M K K ä K ( 3 = l Kä ä ä ä D l Tó l ó Db b f f = = ad y y y i j j l l jl Compleity Prioritizatio Data Sources 6 Debate Demig: Zero Defects are best Ay attempt to reduce variatio ad its impact will have a positive retur $0K $00K $00K $300K $400K $500K $600K Desired variatio Cost for Reductio Cost for Rewor Net cost Jura: Need to balace the cost of variatio agaist the cost of etra precisio Compleity Prioritizatio Data Sources
Problem defiitio Compleity Prioritizatio Data Sources Quality is Free, but Quality requires a ivestmet of resources ad there are limited resources i a compay. 7 Why is prioritizatio o-trivial? Compleity Prioritizatio Data Sources Variatio is assessed at the system The user sees the paper jam ot the roller diameter Variatio is cotrolled at the feature level There are t eough resources to cotrol every dimesio or process Importat thig is to fid the critical few 8 9
Data sources Compleity Prioritizatio Data Sources Kowledge of the system is scattered throughout the orgaizatio Process capability data is available but ot used Cost data is scattered 9 Process capability data Compleity Prioritizatio Data Sources Measuremets tae o eistig products i productio Surrogate data used to predict variatio i future products 90% of all compaies we iterviewed had capability data 0% of them used the data durig desig 0 0
Process Capability Databases Dimesioal measuremets tae from part Dimesioal target values oted Process parameters etered ito PCDB Data values etered ito PCDB The Purpose of PCDBs Maufacturig improvemet Process cotrol/diagostics Historical referece Maufacturability aalysis Desig improvemet Part redesig New part desig Maufacturability aalysis PCDB creatio Maufacturig process results are measured, etered ito PCDB Process target values are documeted Data Materi may be orgaized Dateby: al Machi Proces e s Operat Featur or The Problem Missig Data i PCDBs Hiders Desig Missig data is caused by No data collectio from process Occurrece OR New process: o precedet Tolerace query for process X NO DATA µ =? σ =? mi =? ma =? Missig data results i Ureliable predictio of process capabilities Less efficiet desig processes ad maufacturig plas Project Goal Develop methods to reliably predict values for missig data Mea Variace Tolerace
Variatio Ris Maagemet Defiitio Systematic idetificatio, assessmet ad mitigatio of variatio ris through the desig process to most effectively reduce the impact of variatio give limited resources Assumptio Variatio will always cause degradatio i quality. Desig/maufacturig/quality eped resources to reduce the magitude ad/or impact of variatio Problem is where do you put resources to most effectively reduce the cost of variatio. 3 Ris Two parts to ris Chace of failure (P) Cost of failure (C) Mea cost of variatio C*P Chace of Failure low high Cost of Failure low high Miimal ris?? High Ris 4
VRM Stages Idetificatio Idetify variatio sesitive system requiremets Idetify system, sub-system, feature ad process characteristics that may cotribute to the system variatio Assessmet Quatify the probability of variatio (P) Quatify the cost of variatio (C) Mitigatio Select mitigatio strategy based o costs, schedule ad strategic impact Eecute the strategy 5 Variatio Sesitive Customer Requiremets What requiremets are liely to be sesitive to variatio? Eamples Steps ad gaps Flaes i pritig Ueve i depositio What are the toleraces/latitudes Idetificatio Assessmet Mitigatio 6 3
Two methods of Assessmet Aggregated Usig a models of variatio to tae process capability ad flow it up to chec quality RSS, VSA Desegregated Usig models of variatio to allocate variatio dow the tree Tolerace allocatio Used i cojuctio Idetificatio Assessmet Mitigatio 7 Assessmet Three parts to assessmet Sesitivity to variatio Process variatio Cost of system variatio Ris System Variatio Cost of Variatio Sesitivity Process Variatio 8 4
Failure rate LL i y i m i UL i UL U L P C p = failure = pdf ( y) 6σ LL µ LL UL C p = mi, 3σ 3σ Idetificatio Assessmet Mitigatio µ 9 Relatioship betwee Tolerace ad s For a Cp =.33 (ormal accept levels) UL LL.33 = 6σ UL LL = 8σ Idetificatio Assessmet Mitigatio 30 5
Cost of Variatio: Taguchi Loss fuctio $ Prob. Deviatio from Mea L = (y m) Cost of adefectiveproduct = (Tolerace) A = Ä ó L = meavalue of (y m) mea = (b ó ) Idetificatio Assessmet Mitigatio 3 Variatio ris mitigatio strategies Desig Chage Desig Quality cotrol Ispect Chage Process Advaced maufacturig Moitor process Improve Process Factory Idetificatio Assessmet Mitigatio Variatio reductio 3 6
Mitigatio durig desig Desig chage Chage the geometry, features, parts to mae the product less sesitive to variatio Robust desig Process chage Specify a more precise process to reduce variatio Idetificatio Assessmet Mitigatio 33 Mitigatio durig productio Variatio Reductio Focused efforts to reduce variatio i processes Stadard operatios, maiteace schedules, etc.. Statistical Process cotrol Ogoig cotrol to prevet process degradatio Ispectio Each part is looed at idividually If it fails ispectio it is either scrapped or rewored. Idetificatio Assessmet Mitigatio 34 7
Compariso of strategies Yield Improvemet Recurrig Costs Norecurrig Costs High- Medium High - Medium Strategic Impact Desig Chage High Noe - Low High Process High-Medium Medium - High Chage Low Variatio Medium Low Medium Medium reductio Process Medium-low Medium - Low Medium Moitorig Low Ispectio Low Low Low Low Idetificatio Assessmet Mitigatio 35 How to select Resource availability Cost of effort Beefit of effort Calculated by baselie without cotrol cost with cotrol 36 8
Documetatio system Documetatio of variatio riss Several commo idustry methods IPPD data sheets Tailored databases Keys o drawigs Weaess No commo approach to documetatio No commercial systems Every team ivets a ew system 37 Summary Most compaies address variatio late i the desig process deped o SPC/ispectio rather tha desig chages prioritize efforts based o qualitative assessmets Barriers Lac of good models usable i the early stages of desig Lac of good documetatio systems Lac of good process capability databases 38 9