Bài giảng môn Quản trị kinh doanh - Chapter 13: Lean systems: eliminating waste throughout the supply chain

Chapter 13Lean Systems: Eliminating Waste Throughout the Supply Chain1Learning ObjectivesDescribe the overriding objective of just-in-time management (JIT).State the wastes that were the focus of Toyota’s original version of JIT.Describe the enterprise wide JIT techniques and explain how each affects wastes in the business.Describe the inventory-focused JIT techniques and explain how each reduces inventory waste.Describe the workforce-focused JIT techniques and explain how each reduces workforce waste.Describe the capacity-focused JIT techniques and explain how each reduces capacity waste.Describe the facility-focused JIT techniques and explain how each reduces facility waste.Describe the competitive benefits of lean systems.Determine the takt time for production.Calculate the appropriate number of kanbans.Determine the batch size to minimize inventory.2The overriding objective of lean thinking is to reduce waste. It does this by:Improving process productivityReducing inventoryImproving qualityIncreasing worker involvementLean practices were imported in an attempt to copy the success of the Japanese just-in-time (JIT) approach to automobile production. Lean originated in manufacturing, but has begun to influence services as well.Introduction: A Management Framework for Waste Elimination3Toyota’s original version of lean focused on reducing various kinds of waste.Eliminate Waste: The Focus of Lean4Overproduction waste: The waste caused by producing in excess of demand.Creates excess inventoryWastes capacity on products that have no demandProducing too early has similar effects to producing too muchWaiting time waste: Waste that results from customer orders, inventory, or completed products waiting in queue for a process to begin.Reduces value for customersIncreases delay to obtain financial return on the productThe cost associated with cars waiting to be shipped to dealerships, for example, has been estimated to be as much as $10 per vehicle per dayEliminate Waste: The Focus of Lean5Transportation waste: Results from excessive materials handling and movement.May be caused by ineffective facility layoutsMay also be caused by ineffective choice of locations for suppliers or warehousesMoving materials around is not only expensive in itself, but also wastes timeProcessing waste: Results from steps in production processes that do not contribute value or create too much cost.One of the most popular ways of improving a business is to reduce this by identifying and removing the non-value-adding stepsEliminate Waste: The Focus of Lean6Inventory waste: Waste that consists of excess inventory over and above that which is necessary.Excess inventory increases costs and lead timesExcess inventory reduces quality and flexibility One of the most important benefits of inventory reduction is not having inventory that covers up other problems. When inventory is reduced, problems are exposed, making it possible to improve systems by solving the problems that inventory hid.Eliminate Waste: The Focus of Lean7Unnecessary motion waste: The waste of human resources caused by unnecessary labor due to ineffective job design.Wasting labor resources increases product and service costProduct defect waste: The waste of capacity, inventory, and labor resulting from products that do not meet customer specifications.Eliminate Waste: The Focus of Lean8Lean practices attempt to increase employee involvement in decision-making.Lean values “local” knowledge: Waste elimination typically results from the expertise of employees most familiar with the processes.Involvement is frequently implemented through process improvement teams.Eliminate Waste:Operation Resources and Waste9Tools for eliminating waste range from techniques that are very narrow in focus to those that are broad-based.Exhibit 13.2 JIT Techniques and Their Impact on Operations resourcesEliminate Waste:Waste Reduction Techniques10Quality ManagementQuality management is a prerequisite to lean systemsIt has a positive impact on all the areas that lean targets for waste reduction.KaizenTranslates to “continuous improvement”.Implies that business should strive to make everything betterNothing should ever be considered “good enough”A kaizen blitz is a two or three day marathon of tearing down an entire department and completely redesigning its processes.Enterprisewide Lean Techniques11Inventory-Focused Techniques: Matching Production to DemandLean production strives to match the rate of production to the rate of demand at very small time increments.This is done on a daily or even hourly basis12Takt time: How often you must produce a product in order to meet demand.Producing faster than takt time results in a buildup of inventoryTakt Time = Havail/DWhereHavail is hours of available capacityD is demandFor example, if demand is 90,000 and capacity is 38 hours (136,800 seconds). . .Takt time = 136,800/90,000 = 1.52 seconds. A product must exit the system every 1.52 seconds to meet demand.Inventory-Focused Techniques:Matching Production to Demand13KanbanA system used to link production rate to demand.Kanban is Japanese for “visible record” or “signal”.The traditional approach is to forecast demand and produce in a batch to meet that forecast. Products are “pushed” through the system and then sold.In kanban systems, the demand “pulls” products through the system.Inventory-Focused Techniques:Kanban Systems14Kanban systems use small buffers of inventory between work centers, departments, and manufacturing plants.Management determines the maximum size of these buffers. When a buffer is at its maximum (full), the process that feeds that buffer is not authorized to produce.The signal to start producing again is when the buffer drops below its maximum size. In this scenario, the kanban or “signal” is the buffer being less than full.In other kanban systems, particularly when the buffer is not within sight of the feeding process, a card or message or even a container can be used as a kanban. When inventory is consumed, a card is sent to the supplying work center. Or, if a container is emptied, the empty container is sent back.Inventory-Focused Techniques:Kanban Systems15Assume seven work centers, with containers between them that hold six items each. The full container prevents production. If the container has room, it authorizes replenishment.The rightmost buffer is full of finished product, and the rest are full of WIP inventory.Exhibit 13.4 Kanban SystemInventory-Focused Techniques:Kanban SystemsBuffer is full, so preceding WC is not authorized to produce 16What happens if one item of finished product is taken out of the buffer after WC7?Exhibit 13.4 Kanban SystemWC1WC2WC3WC4WC5WC6WC7Inventory-Focused Techniques:Kanban Systems17The empty space in the buffer after WC7 is the signal for WC7 to start producingWC7 will pull one item out of the buffer preceding itThat empty space is the signal for WC6 to start productionWC6 will pull one item out of the buffer preceding it...and so on, all the way up the chain.Each work center produces to replenish the bufferand all buffers are full againExhibit 12.4 Kanban SystemInventory-Focused Techniques:Kanban SystemsExhibit 13.4 Kanban SystemWC1WC2WC3WC4WC5WC6WC718What is the total amount of WIP inventory that can be in the system?Each buffer holds 6 items, and there are 7 buffers, so the maximum WIP inventory level is 42Management controls this numberExhibit 13.5 Inventory Levels in Kanban SystemInventory-Focused Techniques:Kanban Systems19Kanban Simulation (a)FinishedProductsRawMaterialsWork Center#1Work Center#2WIPInventoryAs soon as demand consumes a finished product, work center 2 begins processing by removing an item from WIP inventory, which authorizes work center 1 to process, which requires a unit of raw materials. The supplier immediately replenishes raw materials . . . . .CustomerSupplierFinished Goods20Kanban Simulation (b)FinishedProductsRawMaterialsWork Center#1Work Center#2WIPInventoryAs soon as work center 2 completes its unit, it is transferred to finished products. Work center 1 completes its unit, and WIP inventory is replenished. All buffers are now at their maximum quantity, so production stops, until demand consumes another finished product. . .CustomerSupplierFinished Goods21Kanban Simulation (c)FinishedProductsRawMaterialsWork Center#1Work Center#2WIPInventoryOnce again, as soon as demand consumes a finished product, work center 2 removes a unit from WIP inventory, which authorizes work center 1 to process, which requires a unit of raw materials. Again, the supplier replenishes raw materials.CustomerSupplierFinished Goods22Kanban Simulation (d)FinishedProductsRawMaterialsWork Center#1Work Center#2WIPInventoryOnce again, as work center 2 completes its unit, it is transferred to finished products. Work center 1 finishes its unit, and replenishes the WIP inventory buffer. All buffers are now at their maximum quantity, so production stops. CustomerSupplierFinished GoodsSimulation over23Work centers don’t have to be next to each other to be linked using kanban systemsThe kanban (visible signal) doesn’t have to be an empty container. It can be anything, as long as it clearly sends the signal to make moreExhibit 13.6 Kanban System Extending to SuppliersInventory-Focused Techniques:Kanban Systems24Management must decide how much inventory to have in the system, and this is done by computing the appropriate number of kanbans, which dictate the maximum size of the buffer.SDkLT+=CWherek = Number of kanbans or containersDLT = Average Demand during the replenishment lead timeLT = Replenishment lead timeS = Safety stockC = Number of units per containerInventory-Focused Techniques:Kanban Systems25Step-by-step: Determining the Appropriate Number of Kanbans.Determine the average lead time for a container of partsSum of production time, transit time, and wait timeDetermine the demand for parts during that lead timeFrom the hourly production rate of the downstream work center that receives them. Multiply the lead time by the production rateAdd a safety stockDetermine the number of containers neededDivide demand for parts during the lead time, plus the safety stock, by the number of parts that fit in the containerInventory-Focused Techniques:Kanban Systems26Example: Determining the number of kanbansSuppose a golf club manufacturer wishes to determine the appropriate number of kanbans for inventory that flows between the shaft/head assembly area and the final step, which is the handle grip station. The “kanban” used is a rack that holds a maximum of 20 clubs. Use the values below to determine the number of racks (containers) that should be used.Average production time for shaft/head assembly of 36 clubs:0.7 hourAverage transit time:0.5 hourAverage wait time of container at shaft/head assembly:1.9 hoursAverage output of grip wrapping station:35 clubs/hourDesired safety stock:10%Inventory-Focused Techniques:Kanban Systems27Example: Determining the number of kanbansAvg. total lead time = Production time + transit time + wait time = 0.7 + 0.5 + 1.9 = 3.1 hoursAvg. demand during lead time = lead time x production rate of downstream work center = 3.1 hrs. x 35 clubs/hr. = 108.5 clubsAdd 10% safety stock: 108.5 + 10.85 = 119.35 clubsNumber of racks = (demand + safety stock)/container size = 119.35/20 = 5.975 = round up to 6 racksInventory-Focused Techniques:Kanban Systems28Standardizing components of a product line lowers total inventory cost. In some industries, such as the automotive industry, component standardization can reduce inventory investment by at least 50%.Inventory-Focused Techniques: Component Standardization29Small-batch production is an important approach for matching production rate to demand rate.Producing in more frequent, smaller batches drives the average inventory level down.But it also increases the number of times equipment must be changed over, which can cut into available capacity.Small-batch production becomes economical only when changeover times can be reduced sufficiently.Inventory-Focused Techniques:Small-batch Production30One approach in small-batch production is to identify the amount of capacity that is not needed for production and use all of it for changeovers:D(Hreq – Havail)/TWhereD = Demand during the planning horizonHreq = Hours of required capacityHavail = Hours of available capacityT = Time it takes to perform a changeoverInventory-Focused Techniques:Small-batch Production31Step-by-step: Batch size determinationDetermine the hours of required capacityDetermine the hours of available capacitySubtract required capacity from total available capacity to yield the capacity that could be dedicated to changeovers, in hoursDivide the hours that could be dedicated to changeovers by the changeover time to yield the number of changeovers feasible without utilizing production capacityDivide the total demand for the planning horizon by the number of changeovers feasible to yield the smallest possible batch sizeInventory-Focused Techniques:Matching Production to Demand32Example: Batch size determinationA company that stamps small parts out of sheet metal has one particular stamping press that is scheduled to stamp out 144,000 parts, taking a total of 200 hours during the next month. There are 235 hours available for production during the time period. Changeover time for the die on that press is 20 minutes (0.333 hours). Determine the number of batches that can be run on the press during the next month and the minimum size of each batch.Capacity that could be dedicated to changeovers = 235 – 200 = 35 hoursNumber of changeovers feasible = 35/0.333 = 105.105 changeoversMinimum batch size = 144,000/105.105 = 1,370.0585 = (round) 1,371Inventory-Focused Techniques:Matching Production to Demand33Changeover time reduction is an integral aspect of lean production.U.S. manufacturers who adopted JIT, with modest effort, reduced changeover times from hours to minutesThe result was shorter production runs, smoother flow of materials, and reduced inventoryFrequent deliveries from suppliers has an effect similar to that of small batch production.Raw materials and component parts are “pulled” from suppliers just like they are within a plant.The result is that inventory is “pulled” from the supplier and the supplier’s production more closely matches the rate of demand.Inventory-Focused Techniques:Reduced Changeover Times34Frequent deliveries from suppliers accomplishes nearly the same thing as small batch productionRaw materials and component parts are “pulled” from suppliers just like they are within a plantInventory-Focused Techniques:Frequent Deliveries35There are fixed costs associated with deliveries from suppliers. Reducing these “order” costs makes it possible to take more frequent (smaller) deliveries. How are these costs reduced?Much of the administrative cost can be eliminated by using electronic data interchange (EDI) instead of paper transactionsInventory-Focused Techniques:Paperless Transactions36Relationships with suppliers must improve with lean.Good communication is essential for frequent deliveriesRelationship must be long lasting and more exclusive, because the supplier must invest in a changeThe supplier must become a lean manufacturer. Lean practices must be incorporated upstream in the supply chain in order to provide true benefitsInventory-Focused Techniques:Improved Supplier Relationships37Process Focus: Lean focuses on process expertise, not product expertise.Build expertise in processes instead of trying to do a large variety of different processes. Eliminate Non-Value-Adding Steps: Reduce one of the most common forms of waste in business by reexamining how things are done. Just because things have been done in a certain way historically doesn’t mean it’s the right way to do them.Capacity-Focused Techniques:Process Focus38Eliminate Non-Value-Adding Steps: Reduce one of the most common forms of waste in business by reexamining how things are done. Just because things have been done in a certain way historically doesn’t mean it’s the right way to do them.Capacity-Focused Techniques:Eliminate Non-Value-Adding Steps39AutomationNot exclusive to lean, many lean firms use it for repetitive or dangerous jobs.Capacity-Focused Techniques: Automation40Small-Scale EquipmentProduction using many small machines can be preferable to production using one big one.Small machines provide flexibility to turn some of them on or off and adjust the output rate to more closely match a variable rate of demand. With a single large machine, output is typically either running at maximum output or not at all. These extreme rates do not match the rate of demand.Capacity-Focused Techniques:Small Scale Equipment41Protective CapacityMaintain a small amount of excess capacity instead of inventory.It is equally effective at satisfying unexpected demand, but extra capacity doesn’t have the negative impact on flexibility and quality that inventory has.Capacity-Focused Techniques:Protective Capacity42Level Loading Capacity: Lean manufacturers can’t have level production as their aggregate planning strategy because it requires large buildups of inventoryNor can they chase demand, because constant hiring and firing ruins workforce qualityThe alternative is to create a somewhat level demand for production. One option is to manufacture complementary products (motorcycles in summer and snowmobiles in winter)Another option is to level the load for a period of time, then adjust it to another level for a period of timeCapacity-Focused Techniques:Level Loading of Capacity43Increased Preventive Maintenance: Decoupling between work centers is eliminated in lean manufacturingMachine breakdown can quickly bring an entire production line to a haltOne approach to reducing the potential for a production line stoppage is to reduce machine breakdowns by increasing the amount of preventive maintenanceCapacity-Focused Techniques:Increased Preventive Maintenance44Cellular Layouts and Group Technology: Cellular layouts are attractive in lean environments for several reasons.It virtually eliminate material movementIt utilizes small-scale equipmentWorkers are responsible for broad rather than narrow tasksCross-trained employees improve the reliability of cellsThe number of workers in a cell can be reduced in the event of a downturnFacility-Focused Techniques:Cellular Layouts and Group Technology45U-shaped production lines eliminate transportation waste and reduce the potential for damage.Exhibit 13.7 Comparison of U-Shaped and Traditional Production LinesFacility-Focused Techniques:U-shaped Production Lines46Workforce-Focused Techniques:Employee InvolvementEmployee InvolvementKnowledge and talent of employees should not be wastedThe impact of decisions on customer interactions and specific processes is needed and can be obtained from employees.47Workforce-Focused Techniques:Employee Cross TrainingEmployee Cross-TrainingIn a pull system, things are not produced unless they are needed.It is difficult to pay employees to do nothingIf a particular work center has no demand, a cross-trained employee can go work elsewhere in the facility.48Workforce-Focused Techniques:Improvement TeamsImprovement TeamsUtilize employee knowledge and talent to achieve the continuous improvement attitude that forms a foundation for JIT.49Competitive Benefits of LeanInventory Reductions:Enhance qualityIncrease flexibilityReduce response TimesProcess Expertise:Eliminates non-value-adding stepsIncreases use of automationFlexibility from protective capacityStability from level loading50Competitive Benefits of LeanManufacturing AdvantagesCellular layouts, GT, and U-shaped lines improves flows, reduces costs and adds flexibilityEmployee involvement, cross-training and improvement teams make better use of employee knowledge and talent.51