posbul1a Drum –Buffer-Rope Based on : R. Holt, Ph.D., PE Traditional Approach: Divide and Conquer * Division of Labor breaks down linkages complex systems into manageable chunks. * Which is harder to manage? Left or Right? Left Right We Measure Operational Efficiency * Work flows from left to right through processes with capacity shown. * Process A B C D E RM FG Capability Parts/Day 7 9 5 8 6 Excellent Efficiency--Near 100% Chronic Complainer Too Much Overtime Market Request 11 RM = raw material FG = finished goods Reward Based on Efficiency * Work flows from left to right. * Process A B C D E Capability Parts/Day 7 9 5 8 6 Both found ways to look busy and appear to have a capacity of 5 parts/day. RM FG In reality... Process A B C D E Potential P/D 7 9 5 8 6 Reality 5 5 5 5 5 * Processes A and B won’t produce more than Process C for long. RM FG P/D=parts/day Then Variability Sets In * Processing times are just AVERAGE Estimates Process A B C D E Reality 5±2 5±2 5±2 5±2 5±2 * RM FG 7 9 5 8 6 What’s an Average? 50% Process A B C D E Reality 5±2 5±2 5±2 5±2 5±2 Probability 0.5 0.5 0.5 0.5 0.5 * Half the time there are 5 or more per day at each process--Half the time less Two at a time: 0.25 0.25 Over all: 0,5*0,5*0,5*0,5*0,5=0,03125=3% Chance of 5 per day !!! RM FG 7 9 5 8 6 Previous Solution: Inventory WIP 5 5 5 5 5 Total 25 Process A B C D E Variable 5±2 5±2 5±2 5±2 5±2 Process * Put a day of inventory (WIP) at each process! RM FG 7 9 5 8 6 System Variability Takes Over--Chaos Variable 5±2 5±2 5±2 5±2 5±2 Process WIP 3 0 10 8 4 Total 25 RM FG Process A B C D E Inventory (WIP) quickly shifts position. Inventory manager/expediter tries to smooth it out. Distribution problems result. Costs go up !!! 7 9 5 8 6 System Variability Takes Over--Chaos WIP 3 0 10 8 4 Total 25 Variable 5±2 5±2 5±2 5±2 5±2 Process Shifting work-in-process creates large queues at some locations. This makes work wait longer to be processed. RM FG An Average of 5 means sometimes 3 and some times 7 Process A B C D E 7 9 5 8 6 System Variability Takes Over--Chaos WIP 3 0 10 8 4 Total 25 Variable 5±2 5±2 5±2 5±2 5±2 Process Shifting work-in-process creates large queues at some locations. This makes work wait longer to be processed. Other workstations are starving for work (B) The work they could do is delayed because they have no input material. They can’t take advantage of their extra capability. So....... ? RM FG 7 9 5 8 6 Process A B C D E System Variability Takes Over--Chaos WIP 3 5 10 8 4 Total 25 Variable 5±2 5±2 5±2 5±2 5±2 Process So… Management Helps! Management puts in more work (Inventory) (rate of RM) to give everyone something to do! Result: It takes longer and longer from time of release until final shipping. More and more delay!!!!!!!!!!! RM FG Process A B C D E ->X 30 7 9 5 8 6 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. Five Steps Applied to Flow Operations A B C D E 7 9 5 8 6 * WIP Total Step 3. Subordinate Everything Else (Rope) Step 4. Elevate the Constraint ($?) Step 5. If the Constraint Moves, Start Over Five Focusing Steps RM Step 1. Identify the Constraint (The Drum) FG Step 2. Exploit the Constraint (Buffer the Drum) 12 12 FG Understanding Buffers A B C D E 7 9 5 8 6 RM •The “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 buffer •If different items spend different time at the constraint, then number of items in the buffer changes •but Time in the buffer remains constant. WIP Total 12parts/5parts per day=2.5 Days We need more than one Buffer FG A B C D E 7 9 5 8 6 RM There is variability in the Constraint. To protect our delivery to our customer we need a finished goods buffer. Finished Goods Buffer There is variability in our suppliers. We need to protect ourselves from unreliable delivery. Raw Material Buffer Buffer Time is Constant-Predictable FG A B C D E 7 9 5 8 6 RM Finished Goods Buffer Constraint Buffer 2.5 Days Raw Material Buffer Finished Goods Buffer 1 Day Processing Lead Time is Constant Raw Material Buffer 2 Days=10/5 FG Buffer Management A B C D E 7 9 5 8 6 RM Constraint Buffer WIP Total 12/5=2.5 Days Time until Scheduled at Constraint 0 2.5 Days WO17 WO14 WO15 WO16 WO10 WO11 WO12 WO13 WO18 WO19 •The Constraint is scheduled very carefully •Buffer Managed by location •Individual activities in the buffer are not scheduled WO21 WO20 A B C D E FG Problem Identification 7 9 5 8 6 RM Time until Scheduled at Constraint 0 2.5 Days WO10 WO20 WO12 WO13 WO21 WO15 WO16 WO17 WO18 WO19 Delayed Parts WO11 WO14 WO19 WO19 OK (Green) Watch WO14 (Yellow) Constraint schedule is in jeopardy! (Red Zone Hole) Additional Buffers * Constraint Buffer (as we discussed) •Protects the Constraint from running out of work * Finished Goods Buffer •Protects customer delivery from Constraint variation * Raw Material Buffer •Protects the Release of material from suppliers * Assembly Buffer •Facilitates speedy flow of products