ThroughputFlowTimeAndLittlesLaw v2

ThroughputFlowTimeAndLittlesLaw v2 - Throughput Concepts,...

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Unformatted text preview: Throughput Concepts, Flow Time, and Littles Law Peter L. Jackson Professor School of O.R. and I.E. 1/31/2011 Industrial Data and Systems Analysis 1 Overview Throughput Concepts What is it Worth to Increase Throughput? g p Flow time and Lead time Littles Law What is it Worth to Reduce Flow Time? 1/31/2011 Industrial Data and Systems Analysis 2 What is Throughput? Activity of a repetitive process Output = input ( throughput), unless... Measure of interest: throughput rate Flights per hour, out-patients per day, gallons per second, messages per hour, etc. 1/31/2011 Industrial Data and Systems Analysis 3 What is Cycle Time? Takt time Inverse o Flow time ime spent in Definition of cycle time is not consistent: even within the same company! throughput rate Units of time per unit of output Time spent in system by single unit (includes queue time) Time between successive outputs 1/31/2011 Industrial Data and Systems Analysis 4 Toyota System Throughput Detractors Unscheduled time Starved / blocked by production control system Speed loss Quality loss Scrap, rework Breakdowns Setup time Planned downtime partial shifts maintenance 1/31/2011 Industrial Data and Systems Analysis 5 meetings, training The M.F.D. THRUPUT Game 1/31/2011 Industrial Data and Systems Analysis 6 Throughput Targets DGR (daily going rate): units per day required to support final assembly schedule (level schedule) Cycle time (Takt time): time allowed between successive units of output to achieve DGR Takt time = effective daily operating time / DGR Stated as requirement: process must be designed and operated to achieve these targets 1/31/2011 Industrial Data and Systems Analysis 7 g p g Will the Process Achieve Target? Begin with throughput rate achievable under ideal operating conditions Adjust for breakdowns, setups, quality loss, speed loss Ex. Adjust for speed loss: Equipment runs at 100y% speed Throughput rate adjusted for efficiency = g p j y unadjusted rate * y Adjust for planned downtime 1/31/2011 Industrial Data and Systems Analysis 8 Adjust for Repair Cycles repair repair operational TTR TTF MTTF: mean time to fail (when running) MTTR: mean time to repair Mean repair cycle length = MTTR+MTTF Fraction of time equipment is operational = MTTF / (MTTR+MTTF) Throughput rate adjusted for repair = * + 1/31/2011 Industrial Data and Systems Analysis 9 Unadjusted rate MTTF / (MTTR MTTF) Adjust for Setup Cycles etup etup n setup setup run Setup time Run time Run time = average lot size / production rate Setup cycle length = Setup time + run time Fraction of time equipment is running = Run time / (Setup cycle length) ( p y g ) Throughput rate adjusted for setups = unadjusted rate * run time / cycle length 1/31/2011 Industrial Data and Systems Analysis 10 Adjust for Scrap 100x% 100(1-x)% I O Output rate is 100(1-x)% of input rate...
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ThroughputFlowTimeAndLittlesLaw v2 - Throughput Concepts,...

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