Bài giảng môn Quản trị kinh doanh - Chapter 8a: Manufacturing planning and control

Manufacturing Planning and ControlMPC 6th EditionChapter 8aAdvanced SchedulingDetailed scheduling of individual jobs through work centers in a shop has been the focus of numerous researchers.Focusing on some basic concepts and results and relating them to some newer manufacturing approaches can show how to apply results in different operating situations.AgendaScheduling Research FrameworkA schedule is a plan for the sequence of time allotted for and operations necessary to complete an itemThe schedule has several inputsSequential constraintsTime estimates for each operationRequired resources for each operationScheduling ResearchThe One-Machine CaseProblem of how to best schedule a fixed set of jobs through a single machineAll jobs are available at the start of the periodSetup times are independent of the sequenceObjectivesMinimize total time–all sequences are equalMinimize average time–process shortest jobs firstMinimize average number of jobs in the system–process shortest jobs firstThe Two-Machine CaseMore complex than the one-machine caseMust consider job routingsMinimum total time (make span) depends upon sequencingTwo-machine case can be used as an approximation of the M-machine problem (where M > 2)Dispatching ApproachesDispatching approaches allow analysis of dynamic problems (where randomness in inter-arrival times and service times are considered)Uses logic rules to guide the prioritizing of jobs at a work center (sequencing rules)Often uses simulation methodology to study realistic problemsSequencing RulesSequencing rules provide guidelines to the wide range of possible sequencing optionsWith n jobs and m machines, there are (n!)m possible ways to schedule the systemSequencing RulesRandom–pick any job with equal probability. Used as a benchmark for other rules.First-come/first-served–jobs are processed in the order they arriveShortest processing time–reduces work-in-process, average completion time, and average latenessEarliest due date–often works well to reduce job latenessLeast work remaining–considers all remaining processing timeLeast setup–minimizes changeover time on the machine and maximizes capacity utilizationDue Date-Setting ProceduresEstablishing order release and due dates is critical in many firmsDue dates often must be set at the time of order entryEstimating manufacturing time is a key functionCalculating lead times on the basis of total work content is often bestDynamic Due DatesMaintaining valid due dates as system parameters change is also importantDynamic due dates allow updating of open order due datesMay lead to system “nervousness”Can cause shop floor employees to distrust the systemCan improve customer service and reduce total inventoryLabor-Limited SystemsUseful when labor is the bottleneck resourceThree major elements for controlling workflowDetermining which job to do next at the work centerDetermining when a person is available for transfer to another work centerDetermining the work center to which an available person is to be assignedResearch shows the importance of cross-training and labor assignment flexibilityBoth labor and job dispatching can have a major impact in controlling work flowGroup Scheduling and Transfer BatchesTheory of Constraints scheduling uses different batch sizes for bottleneck and non-bottleneck work centersRepetitive lots concept–original order quantities released to the floor can be split into smaller transfer batchesGives work centers the flexibility to start producing an order before the previous work center is completely done with the jobReduces flow times, improves utilization, cuts setup times, and smoothes work flowPrinciplesIt is important to determine the objective(s) of scheduling before selecting an approach.Shortest processing time sequencing rule can provide effective performance and should be considered a standard in designing shop-floor systems.Flexibility is introduced into scheduling through alternative routings, labor assignment adjustments, the use of transfer batches, and overlap scheduling. Flexibility can lead to great improvements.Setting and managing due dates is an important scheduling activity.Due date filtering procedures should be used to reduce shop-floor nervousness.Quiz – Chapter 8aIn the one-machine case, the order of job processing is not an important factor in performance? (True/False)The shortest processing time (SPT) sequencing rule performs well to minimize overall job lateness? (True/False)One means of evaluating the effectiveness of due date-setting is _________ __________ _____________.In TOC, original orders may be divided into smaller quantities called _____________ batches.