Presentation on theme: "Drum –Buffer-Rope Skorkovský Based on : R. Holt, Ph.D., PE."— Presentation transcript:
1 Drum –Buffer-RopeSkorkovskýBased on : R. Holt, Ph.D., PE
2 Traditional Approach: Divide and Conquer Division of Labor breaks down linkages complex systems into manageable chunks.Which is harder to manage? Left or Right?LeftRight
3 We Measure Operational Efficiency Work flows from left to right through processes with capacity shown.Market Request 11Process A B C D ERMFGCapabilityParts per DayExcellent Efficiency--Near 100%Chronic ComplainerToo Much Overtime
4 Reward Based on Efficiency Work flows from left to right.Process A B C D ERMFGCapabilityP/DBoth found ways to look busy and appear to have a capacity of 5 parts/day.
5 In reality...Processes A and B won’t produce more than Process C for long.Process A B C D ERMFGPotentialP/DReality
6 Then Variability Sets In Processing times are just AVERAGE EstimatesProcess A B C D ERMFGReality ± ± ± ± ±2=35, 7=35/5=7 (average)
7 Over all: 3% Chance of 5 per day !!! What’s an Average? 50%Half the time there are 5 or more per day at each process--Half the time lessProcess A B C D ERMFGReality ± ± ± ± ±2Probability0.25Two at a time:Over all: 3% Chance of 5 per day !!!
8 Previous Solution: Inventory Put a day of inventory at each process!WIP Total 25Process A B C D ERMFGVariable 5± ± ± ± ±2ProcessWIP=throughput in bottleneck
9 System Variability Takes Over--Chaos Inventory (WIP) quickly shifts position.Inventory manager/expediter tries to smooth it out.Distribution problems result. Costs go up.WIP Total 25RMFGProcess A B C D EVariable ± ± ± ± ±2Process25=
10 System Variability Takes Over--Chaos An Average of 5 means sometimes 3 and some times 7Process A B C D EWIP Total 25RMFGVariable ± ± ± ± ±2ProcessShifting work-in-process creates large queues at some locations. This makes work wait longer to be processed.
11 System Variability Takes Over--Chaos Process A B C D EWIP Total 25RMFGVariable ± ± ± ± ±2ProcessShifting work-in-process creates large queues at some locations. This makes work wait longer to be processed. Other workstations can be starved for work. The work they could be doing is delayed because it is not there (B). Theycan’t take advantage of their extra capability. So...
12 System Variability Takes Over--Chaos Process A B C D E->X 30WIP Total 2530=25+5RMFGVariable ± ± ± ± ±2ProcessSo… Management Helps! Management puts in more work(Inventory) to give everyone something to do!Result: It takes longer and longer from time of releaseuntil final shipping. More and more delay!!!!!!!!!!!
13 Attempts to Control WIP Use Kanban Cards-JITWIP Total 25Process A B C D ERMFGVariable 5± ± ± ± ±2ProcessJust-In-Time uses Kanban Cards to limit the queuesbuilding in the system.No more than 5 parts are allowed at any station.Looks good, but is it?
14 Effects of Inventory Limits on Production What does a Kanban card of 5 Mean?WIP Total 25Process A B C D ERMFGVariable 5± ± ± ± ±2Process5+/-2 Average = 5BeforeKanban7Average = 3,5 = (3*5+5*0,5)/5Can’t exceed5After Kanban25,53
15 Operation’s Dilemma Increase work-in- process Produce a lot Assumption:We can’t both increase WIP and decrease WIP at the same time.Manage productioneffectivelyCosts & delivery in controlDecrease work-in-processInjection: Put a large inventory where its needed and low everywhere else!
16 TOC Steps to Continuous Improvement Step 1. Identify the system’s constraint.Step 2. Exploit the system’s constraint.Step 3. Subordinate everything else to the above decision.Step 4. Elevate the system’s constraint.Step 5. If a constraint is broken (that is, relieved or improved), go back to Step 1. But don’t allow inertia to become a constraint.
17 Five Steps Applied to Flow Operations Step 3. Subordinate Everything Else (Rope)Step 2. Exploit the Constraint (Buffer the Drum)12WIP TotalA B C D EStep 1. Identify the Constraint (The Drum)RMFGStep 4. Elevate the Constraint ($?)(5,5) 8 6Step 5. If the Constraint Moves, Start Over7Five Focusing Steps
18 Understanding Buffers WIP Total 12parts/5parts per day=2.5 DaysA B C D EFGRMThe “Buffer” is Time!In general, the buffer is the total time from work release until the work arrives at the constraint.Contents of the buffer ebb and flow within the bufferIf different items spend different time at the constraint, then number of items in the buffer changesbut Time in the buffer remains constant.
19 We need more than one Buffer There is variability in our suppliers. We need to protect ourselves from unreliable delivery.Raw Material BufferThere is variability in the Constraint. To protect our delivery to our customer we need a finished goods buffer.Finished Goods BufferA B C D ERMFG
20 Buffer Time is Constant-Predictable Raw Material BufferFinished Goods BufferA B C D ERMFGRaw MaterialBuffer2 DaysConstraint Buffer 2.5 DaysFinished Goods Buffer 1 DayProcessing Lead Time is Constant
21 Buffer Management FG Constraint Buffer WIP Total 12/5=2.5 Days A B C D EFGRMWO21WO17WO13The Constraint is scheduled very carefullyBuffer Managed by locationIndividual activities in the buffer are not scheduledWO20WO16WO12WO19WO15WO11WO18WO14WO102.5 DaysTime until Scheduled at Constraint
22 Problem Identification RMWatch WO14 (Yellow)A B C D EConstraint schedule is in jeopardy! (Red Zone Hole)WO19 OK (Green)FGRMWO19 Delayed PartsWO21WO17WO13WO20WO16WO12WO19WO15WO11WO18WO14WO102.5 DaysTime until Scheduled at Constraint
23 Additional Buffers Constraint Buffer (as we discussed) Protects the Constraint from running out of workFinished Goods BufferProtects customer delivery from Constraint variationRaw Material BufferProtects the Release of material from suppliersAssembly BufferFacilitates speedy flow of products
24 Additional Buffers Ropes Buffer Types: Constraint FG RM Assembly WIP Finished goodsA B C D ERaw MaterialRMFGF G HAssemblyRM8 7 6
25 Manufacturing is an integrating discipline TOC ThinkingProcesses Physical SystemsBehaviorOperations OptimizationSimulation Decisions Reliability Supply ChainPeople Organizations PerformanceMeasurement Assignments QualityFinance Capital ProjectsUncertainty Investment MeasuresProjects Full TheoryScheduling Manage Quality Design for ExperimentsStrategy CorporateDepartmental Subordination Focus
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