Bài giảng môn Quản trị kinh doanh - Chapter 11: Manufacturing planning and control

Manufacturing Planning and ControlMPC 6th EditionChapter 11Order Point Inventory Control MethodsOrder point methods are used to determine appropriate order quantities and timing for individual independent-demand product items that are characterized by random customer demand.Performed well, these inventory management functions can provide appropriate levels of customer service without excess levels of inventory and/or cost.Agenda–Order Point Inventory Control MethodsBasic ConceptsInventory supports both independent- and dependent-demand itemsIndependent-demand inventories–primarily influenced by factors outside of company decisions (e.g. random variation)Demand forecasts estimate the average usage rate and pattern of variationDependent-demand inventories–influenced mainly by internal factors within the firm’s controlInventory Management IssuesRoutine inventory decisions–how much to order and when to orderInventory control decision rules can simplify these decisionsInventory Management IssuesDetermining Inventory System PerformanceInventory turnover (annual sales divided by average inventory investment)Fill rate (percentage of units available when requested by customers)Allows comparison of different systems and evaluation of system changesInventory Management IssuesImplementing Changes in Managing Inventory–making the appropriate changes at the right time is criticalMore formalized change management system is required as the scope of the business increasesInventory-Related CostsIncremental costs–does the cost represent an actual expenditure or lost profit? Does the cost actually vary with the decision being made?Economic Order Quantity (EOQ) ModelDescribes the relationship between cost of ordering, cost of carrying inventory, and the order quantityTotal CostsOrdering CostsInventory Holding CostsDetermining the EOQ–Graphical MethodA = 1,250Cp = 6.25CH = 25TAC=(1,250/Q)6.25+(Q/2)25TAC curve shows clear minimum value at Q=25Determining the EOQ–Deriving the EOQ FormulaDerivative of TAC with respect to QSet derivative equal to zero and solve for QEconomic time between orders (TBO)Order Timing DecisionsQ,R ruleWhen stock reaches predetermined inventory level (R), a fixed quantity (Q) is orderedOrder point is influenced by demand rate, replenishment lead time, uncertainty of demand rate and replenishment lead time, and acceptable level of customer serviceSafety stock is the difference between average demand during lead time and the reorder pointSafety Stock in a Q,R systemSRInventory levelTimeLead timeOrder quantity (Q)Reorder pointSafety stockDetermining the Safety Stock in a Q,R systemStockout probability–specify an acceptable risk of stocking out during any given replenishment cycleCarry stock sufficient to satisfy expected demand with this probabilityCustomer service level–define an acceptable level of customer service (percent of demand met from inventory)Stockout ProbabilityWith a lead time of one day, 95% of cycles will experience demand for 7 or fewer unitsSum of demand probability is 0.05 (5%)Safety stock of 7 units will provide 5% chance of stockout during a one day lead timeCustomer Service Level Sum = 0.35A reorder point of 5 units has a 35% chance of stockout, with an average of 0.56 units short each cycleSafety Stock with Continuous DistributionsReorder pointProbability of at least one stockout during cycleExpected number of stockouts per cycleProbability of Stocking OutSafety stock = ZσdReorder point = mean demand during replenishment lead time + ZσdZ = appropriate value from standard normal tableσd = standard deviation of demand during replenishment lead timeProbability of demand between 3.5 and 6.5 units is 0.6827. Probability of stockout when safety stock is 1 unit is 0.3173 (1 – 0.6827)Customer Service CriterionFind the calculated E(Z) in the chart to determine the Z valueCalculate E(Z) using the desired service level (SL) and reorder quantity (Q)Safety stock = ZσdTime Period Correction FactorVariations in demand and lead time complicate the calculationsWhen standard deviation of demand is measured over a different time period than the lead time, correction is requiredWhen both demand and lead time vary, additional adjustments are requiredForecast Error DistributionSafety stock can be based on forecast error rather than historical demand variationStandard deviation = 1.25 MADMAD – mean absolution deviationMulti-Item ManagementManagement attention should be focused on the most important itemsABC analysis segments the inventoried items according to annual cost volume usage(unit cost x annual usage)A items are the most importantThis small percentage of items usually makes up a majority of annual cost volume usageB and C items are progressively less criticalPrinciplesThe difference between dependent and independent demand must serve as the first basis for determining appropriate inventory management procedures.Organizational criteria must be clearly established before we set safety stock levels and measure performance.A sound basic independent demand system must be in place before attempting to implement advanced techniques.Savings in inventory-related costs can be achieved by a joint determination of the order point and order quantity parameters.All criteria should be taken into account in classifying inventory items for management priorities.The functions of inventory are useful principles to apply in determining whether or not inventory reductions can be made.PrinciplesQuiz – Chapter 11Order point methods are generally used for _____________ demand items.Cycle stock is are a result of manufacturing lot sizes? (True/False)Stock produced for upcoming promotional events would be considered _______________ stock.The two main decisions when managing independent demand items are _______________ and ______________.A measurement that relates inventory levels to product sales volume is ___________ _____________.The three types of costs associated with holding inventory are ____________, ______________, and ____________.