posbul1a Drum –Buffer-Rope Based on : R. Holt, Ph.D., PE Principy Resource : http://www.allaboutlean.com/drum-buffer-rope/ imaginace Simplified Drum Buffer Rope (S-DBR) Principy Most importantly, it does try to constrain the work-in-progress (WIP) and aims to prevent an overloading of the system. As such it can be considered sort of a pull system like Kanban or CONWIP (Constant Work in Progress), and hence Drum-Buffer-Rope is superior to the traditional push systems. Push –MRP-II Pull –JIT- kanban= WIP WIP WIP=0 DBR disadvantage : no Consideration for Shifting Bottlenecks System is not controlled Based on pictures taken from CH.Hohman show System not controlled and DBR modification Based on pictures taken from CH.Hohman show ROPE= feedback Rope opened raw material valve Based on pictures taken from CH.Hohman show We Measure Operational Efficiency * Work flows from left to right through processes with capacity shown. * Process A B C D E RM FG Capability (Throughput Rate) 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 Bottleneck Reward Based on Efficiency * Work flows from left to right. * Process A B C D E Capability(Throughput Rate) Parts/Day 7 9 5 8 6 Both (D and E) found ways to look busy and appear to have a capacity of 5 parts/day. RM FG „upper stream“ „down stream“ In reality... Process A B C D E Potential Part/Day 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 (not a good one !): Inventory WIP 5 5 5 5 5 Total 25 in WIP 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 WIP= Work in Progress System Variability Takes OveràChaos 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 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 RM FG An Average of 5 means sometimes 3 and sometime 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 input RM) to give everyone something to do (Cost World Approach)! 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) – feadback Step 4. Elevate the Constraint ($?->related to additional cost) Step 5. If the Constraint Moves, Start Over Five Focusing Steps RM Step 1. Identify the Constraint (The Drum) – CRT FG Step 2. Exploit the Constraint (Buffer the Drum) – time reserve 12 12 12parts/5parts per day=2.5 Days reserve in buffer 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 alters (see below) •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 12=2,5 days 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 WO21 WO20 WO = Work Order Each part during processing is associated with a different work order, which has different delivery (termination) parameters, etc. 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 WO11 Delayed Parts WO11 WO14 WO19 WO19 OK (Green) Watch WO14 (Yellow) Constraint schedule is in jeopardy! (Red Zone Hole WO11) Buffer 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 https://www.youtube.com/watch?v=8yehd2ZsKH0 DBR additional information * https://www.dbrmfg.co.nz/Production%20DBR.htm DBF postulates * Drum-Buffer-Rope (DBR) is a theory-based resource planning and scheduling solution * restriction (TOC). * The basic assumption of DBR is that there is one or a limited number of capacities in each company * limited resources that are key to the performance (efficiency) of the company. * We call this limited resource the "drum" (DRUM) because it sets the pace for everyone * other resources. * To achieve the maximum output of the system, we must first manage our limited (limited) system * source = DRUM), i.e. its use, planning which orders will be realized on it. * Ensuring that the DRUM operates continuously (see steps 2-3 of the five TOC corks) is necessary. * Failure of any source inputs (material or loss of sources before our limitation) is * provided by time reserve (bumper, BUFFER). * A feedback element ensure synchronization with other sources called a rope (ROPE) * Scheduling * Each source must be in terms of its load, and available capacity must be assessed individually * For example, let's have 1000 hours available and demand 880 hours for that capacity. * However, this demand does not describe the indicated situation with sufficient precision. * In the picture, we see that most work centers (WC) still have sufficient capacity while WC3 is fully loaded, and it is not possible to use it for a possible next job (time requirement) * The actual situation is that the capacity of the company is limited because we can not increase the number of orders because we are already determined by the filling capacity of WC3 C1 C2 C4 C4 +C1+C2=1000-880=120 What we have at our disposal and what are the requirements We need to consider the time frame in which demand occurs. A monthly or weekly demand plan may not be enough to take action to meet the requirements over time. Requirement : what we need Capacity: what is available TOC Approach * To improve the system, we must optimize the weakest link; restriction (DRUM). All other sources are subject to this decision. The scheduling is as follows : * 1.Develop a detailed drum work assignment plan (DRUM) * 2. BUFFER is added to protect performance our limited resource * 3. The work schedule of other resources is synchronized according to the schedule drum (DRUM) Resource utilization (drum) to the maximum 40 hours/week P1 requirement 51 pcs per day 5 50 pcs per day 3 P2 requirement 10 pcs per days 1-5 Requirement : what we need Capacity: what is available Scheduling on CCR (drum) Day Productk Qty Minutes 1 P2 10 240 1 P2 10 240 2 P2 10 240 2 P1 20 240 3 P1 30 360 3 P2 5 120 4 P2 15 360 4 P2 5 120 5 P1 40 480 6 P1 11 132 P1 51 pcs day 5 (production time 1pc/12 minutes) P1 50 pcs day 3 P2 10 pcs day 1-5 (prodution time 1pc//24 minutes) CCR =Capacity-Constrained Resource, Qty=Quantity Day 1 Day 2 Day 3 Day 4 Day 5 Day 6 480 40 hours/week P1 requirement 51 pcs per day 5 50 pcs per day 3 P2 requirement 10 pcs per days 1-5