posbul1a Drum –Buffer-Rope Based on : R. Holt, Ph.D., PE Principles Resource : http://www.allaboutlean.com/drum-buffer-rope/ imagination Feedback - if the amount of materials in the buffer drops below a certain limit, the input of components to the line is released Simplified Drum Buffer Rope (S-DBR) Principles 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 The line is not controlled by the source with the lowest flow (throughput), but by the requirements of the Customers DBR disadvantage : No Consideration for Shifting Bottlenecks This system is not controlled Based on pictures taken from CH.Hohman show valve valve First part is not controlled ->so it has to be modified (DBR) Based on pictures taken from CH.Hohman show ROPE= feedback Rope opened raw material valve R1 Based on pictures taken from CH.Hohman show DBR example * Imagine a hospital waiting room. If the time the doctor takes to see each patient is the Drum, then the Buffer can be the receptionist scheduling appointments so there are always two or three patients in the waiting room. The Rope is the nurse calling in each patient once the doctor is ready to see them. We Measure Operational Efficiency * Workflow 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 * Workflow 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 RM = raw material FG = finished goods 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 It can be a value between 3 and 7 (3,4,5,6 or 7) 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 and 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 One solution -not a good attempt! 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 * At the beginning of the process you put a day of inventory (WIP) before each process RM FG 7 9 5 8 6 WIP= Work in Progress System Variability Takes Over à 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. The Inventory manager tries to smooth it out. Distribution problems result. And 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 what to do? 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-see TOC) ! 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 Days 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 The order of priority for processing parts assigned to different Work Orders is determined by color (as in traffic lights) 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 (home study) * Drum-Buffer-Rope (DBR) is a theory-based resource planning and scheduling solution restriction. * * 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 every other resource. * To achieve the maximum output of the system, we must first manage our limited system • source (so called DRUM), meaning its use and priority planning which work orders will be realized on it * Ensuring that the DRUM operates continuously (see steps 2-3 of the five TOC steps) is a must * Failure of any source inputs (material or failure of sources before our limitation) is • provided by time reserve (BUFFER). * A feedback element ensure synchronization with other sources before DRUM is called ROPE. * DBF postulates (home study) * Drum-Buffer-Rope (DBR) is a theory-based resource planning and scheduling solution restriction. * * 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 every other resource. * To achieve the maximum output of the system, we must first manage our limited system • source (so called DRUM), meaning its use and priority planning which work orders will be realized on it * Ensuring that the DRUM operates continuously (see steps 2-3 of the five TOC steps) is a must * Failure of any source inputs (material or failure of sources before our limitation) is • provided by time reserve (BUFFER). * A feedback element ensure synchronization with other sources befire |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 work order specified by 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 fully used capacity of WC3 C1 C2 C4 C4 +C1+C2=1000-880=120 à our time reserve Reserve capacity remaining 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 Days TOC Approach * To improve the system, we must optimize the weakest link (restriction) called 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 of our limited resource * 3. The work schedule of other resources is synchronized according to the schedule drum (DRUM) * •Scheduling means that we determine what will be done by which resource at given times. • 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 P1 and P2 are the products we will produce in the company. Requirements Requirements (every day 10 pcs of P2) Scheduling on CCR (drum) – home study 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 minutes 40 hours/week P1 requirement 51 pcs per day 5 50 pcs per day 3 P2 requirement 10 pcs per days 1-5 480/20 = 24 10 pcs per 240 minutes Thank you for your attention