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ThroughputFlowTimeAndLittlesLaw6x

ThroughputFlowTimeAndLittlesLaw6x - Industrial Data and...

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Unformatted text preview: 1/28/2007 Industrial Data and Systems Analysis 1 Throughput Concepts, Flow Time, and Little’s Law Peter L. Jackson Professor School of O.R. and I.E. 1/28/2007 Industrial Data and Systems Analysis 2 Overview • Throughput Concepts • What is it Worth to Increase Throughput? • Flow time and Lead time • Little’s Law • What is it Worth to Reduce Flow Time? 1/28/2007 Industrial Data and Systems Analysis 3 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. 1/28/2007 Industrial Data and Systems Analysis 4 What is Cycle Time? • Takt time • Inverse of throughput rate • Units of time per unit of output • Time between successive outputs • Toyota System • Flow time • Time spent in system by single unit (includes queue time) Definition of cycle time is not consistent: even within the same company! 1/28/2007 Industrial Data and Systems Analysis 5 Throughput Detractors • Unscheduled time • Starved / blocked by production control system • Speed loss • Quality loss • Scrap, rework • Breakdowns • Setup time • Planned downtime • partial shifts • maintenance • meetings, training 1/28/2007 Industrial Data and Systems Analysis 6 The M.F.D. THRUPUT Game 1/28/2007 Industrial Data and Systems Analysis 7 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 1/28/2007 Industrial Data and Systems Analysis 8 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 = unadjusted rate * y • Adjust for planned downtime 1/28/2007 Industrial Data and Systems Analysis 9 Adjust for Repair Cycles • 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 = Unadjusted rate * MTTF / (MTTR+MTTF) repair repair operational TTR TTF 1/28/2007 Industrial Data and Systems Analysis 10 Adjust for Setup Cycles • 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) • Throughput rate adjusted for setups =...
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ThroughputFlowTimeAndLittlesLaw6x - Industrial Data and...

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