Bài giảng Operations Management for Competitive Advantage - Chapter 18 Synchronous Manufacturing and Theory of Constraints

Chapter 18Synchronous Manufacturing and Theory of ConstraintsGoldratt’s RulesGoldratt’s Goal of the FirmPerformance MeasurementCapacity and Flow issuesSynchronous ManufacturingOBJECTIVES Goldratt’s Rules of Production SchedulingDo not balance capacity balance the flowThe level utilization of a nonbottleneck resource is not determined by its own potential but by some other constraint in the systemUtilization and activation of a resource are not the sameAn hour lost at a bottleneck is an hour lost for the entire systemAn hour saved at a nonbottleneck is a mirage Goldratt’s Rules of Production Scheduling (Continued)Bottlenecks govern both throughput and inventory in the systemTransfer batch may not and many times should not be equal to the process batchA process batch should be variable both along its route and in timePriorities can be set only by examining the system’s constraints and lead time is a derivative of the scheduleGoldratt’s Theory of Constraints (TOC)Identify the system constraintsDecide how to exploit the system constraintsSubordinate everything else to that decisionElevate the system constraintsIf, in the previous steps, the constraints have been broken, go back to Step 1, but do not let inertia become the system constraintGoldratt’s Goal of the FirmThe goal of a firm is to make moneyPerformance Measurement:FinancialNet profitan absolute measurement in dollarsReturn on investmenta relative measure based on investmentCash flowa survival measurement Performance Measurement:Operational1. Throughputthe rate at which money is generated by the system through sales2. Inventoryall the money that the system has invested in purchasing things it intends to sell3. Operating expensesall the money that the system spends to turn inventory into throughput ProductivityDoes not guarantee profitabilityHas throughput increased?Has inventory decreased?Have operational expenses decreased? Unbalanced CapacityIn earlier chapters, we discussed balancing assembly linesThe goal was a constant cycle time across all stationsSynchronous manufacturing views constant workstation capacity as a bad decisionThe Statistics of Dependent EventsRather than balancing capacities, the flow of product through the system should be balanced Process Time (B)Process Time (A)106 8 10 12 14Process Time (B)Process Time (A)106 8 10 12 14(Constant)(Constant)(Variable)(Variable)When one process takes longer than the average, the time can not be made upCapacity Related TerminologyCapacity is the available time for productionBottleneck is what happens if capacity is less than demand placed on resourceNonbottleneck is what happens when capacity is greater than demand placed on resourceCapacity-constrained resource (CCR) is a resource where the capacity is close to demand placed on the resource Capacity Example Situation 1XYMarketCase AThere is some idle production in this set up. How much?25% in YCapacity Example Situation 2YXMarketCase BIs there is going to be a build up of unnecessary production in Y?Yes, 25% in YCapacity Example Situation 3XYAssemblyMarketCase CIs there going to be a build up in unnecessary production in Y?Yes, 25% in YCapacity Example Situation 4XYMarketMarketCase DIf we run both X and Y for the same time, will we produce any unneeded production?Yes, 25% in YTime Components of Production CycleSetup time is the time that a part spends waiting for a resource to be set up to work on this same partProcess time is the time that the part is being processedQueue time is the time that a part waits for a resource while the resource is busy with something else Time Components of Production Cycle (Continued)Wait time is the time that a part waits not for a resource but for another part so that they can be assembled togetherIdle time is the unused time that represents the cycle time less the sum of the setup time, processing time, queue time, and wait timeSaving TimeBottleneckNonbottleneckWhat are the consequences of saving time at each process? Rule: Bottlenecks govern both throughput and inventory in the system. Rule: An hour lost at a bottleneck is an hour lost for the entire system. Rule: An hour saved at a nonbottleneck is a mirage. Drum, Buffer, RopeABCDEFBottleneck (Drum)Inventorybuffer(time buffer)Communication(rope)MarketExhibit 18.9Quality ImplicationsMore tolerant than JIT systemsExcess capacity throughout systemExcept for the bottleneckQuality control needed before bottleneck Batch SizesWhat is the batch size?One? Infinity? Bottlenecks and CCRs:Flow-Control SituationsA bottleneck (1) with no setup required when changing from one product to another(2) with setup times required to change from one product to anotherA capacity constrained resource (CCR)(3) with no setup required to change from one product to another(4) with setup time required when changing from one product to another Inventory Cost Measurement:Dollar DaysDollar Days is a measurement of the value of inventory and the time it stays within an area Benefits from Dollar Day MeasurementMarketingDiscourages holding large amounts of finished goods inventory PurchasingDiscourages placing large purchase orders that on the surface appear to take advantage of quantity discounts ManufacturingDiscourage large work in process and producing earlier than needed Comparing Synchronous Manufacturing to MRPMRP uses backward schedulingSynchronous manufacturing uses forward scheduling Comparing Synchronous Manufacturing to JITJIT is limited to repetitive manufacturingJIT requires a stable production levelJIT does not allow very much flexibility in the products produced Comparing Synchronous Manufacturing to JIT (Continued)JIT still requires work in process when used with kanban so that there is “something to pull”Vendors need to be located nearby because the system depends on smaller, more frequent deliveries Relationship with Other Functional AreasAccounting’s influenceMarketing and productionEnd of Chapter 18