posbul1a Drum –Buffer-Rope Based on : R. Holt, Ph.D., PE http://www.dbrmfg.co.nz/Production%20Implementation%20Details.htm TOC-fundamental knowledge and its applications * Thinking tool •CRT •Evaporating cloud •FRT •Transition tree •Prerequisite tree • * Simplicity * Bottlenecks * Cost world * Throughput world * Five focusing steps * Three questions CRITICAL CHAIN DRUM-BUFFER-ROPE P&Q (Product mix) DBR basics 7 9 5 8 Red numbers= parts/time unit 6 Components releasing See Excel file after few slides !!!!! 7 9 = non-constraints; 2=7-5 and 4=9-5 = protective capacities Throughput = finished goods DBR basics We must protect the constraint to make sure the correct material is always ready and waiting for processing in time. We can achieve this by ensuring that we release material by use of rope communication device in time prior to the scheduled consumption on the constraint. 7 9 & When there is work, complete it promptly !!! When there is no work, find something else to do !!! Non-constraints rules 9 DBR basics Fully on Fully off Slowing down Throughput creation Throughput protection Throughput destruction 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 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 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 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 !!! 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 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 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 Little´s law - definition (formula) * Fundamental relationships among : •WIP (Work In Process) •Cycle Time (CT) •Throughput (T or sometimes TH) * Formula * * Can be applied to : •Single machine station • Complex production line •Entire plant Relationships among these variables will serve to se clearly precise (quantitative) description of behaviour of the single production line . It helps user to use a given scale to benchmark actual production systems Definition of basic parameters * Throughput (Throughput rate, TH) : production per unit time that is sold (see TOC definition) * If TH is measured in cost dollars rather than in prices it is typically called : • • Cost of good sold (COGS) • * Upper limit of TH in production process is capacity * * If you release more raw material above capacity of the line (machine),system become unstable –> WIP goes up !! * * Definition of basic parameters * WIP (Work In Process) : inventory between start and end points of the product routing * * WIP can be used as one parameter to calculate (measure) an efficiency * * Efficiency can be defined as Turnover Ratio = TH/FGI for warehouses or TH/(FGI+WIP) for production plants where FGI=Finished goods inventory * * WIP : inventory still in line * * FGI : inventory waiting for dispatch (shipping) • * * Definition of basic parameters * CT (Cycle Time, Flow Time or Throughput Time) : average time from release of the job of the beginning of the routing until it reaches an inventory point at the end of the routing or time that part spends as a WIP. * * LT (Lead Time) : managerial constant used for planning of production * • Operation’s Dilemma Injection: Put a large inventory where its needed and low everywhere else! Manage production effectively Produce a lot Costs & delivery in control Increase work-in- process Decrease work-in-process Assumption: We can’t both increase WIP and decrease WIP at the same time. 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. •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 =Shipping buffer •Protects customer delivery from Constraint variation * Raw Material Buffer •Protects the Release of material from suppliers • Some resources http://www.dbrmfg.co.nz/Production%20Implementation%20Details.htm