Operations Management MGMT 3165
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This 21 page Class Notes was uploaded by Berenice Rutherford V on Monday October 12, 2015. The Class Notes belongs to MGMT 3165 at Georgia College & State University taught by Jiaqin Yang in Fall. Since its upload, it has received 155 views. For similar materials see /class/221960/mgmt-3165-georgia-college-state-university in Business, management at Georgia College & State University.
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Date Created: 10/12/15
Topic 14 Production Activity Control Production Activity Control PAC Objectives of PAC 1 Meeting Job DueDates Customer Service Level 2 Controlling WorkInProcess Inventory level a Reducing shop Congestion Level and Job leadtimes J Controlling the queues at each work center U Preventing quotbottleneckquot machines in advance Ox Increasing shop utilization Five Major Data Files in PAC 1 Item Master File Item NoDescriptionBOM 2 Job Routing File OperationsTimeSequencel 3 Work Center Master File CapacityMachinel 4 Shop Order Master File Release DateDue Date 5 Shop Order Status File Current LocationRem Ope Topic 14 1 Data Requirements The les generally required for a PAC system are ITEM MASTER DATE RELATED TO AN ITEM NUMBER SHOP ORDER MASTER DATA RELATED TO A SHOP ORDER DATA RELATED TO AN OPERATION ON AN MANUFACTURING SHOP ORDER DETAIL DATA RELATED TO AN OPERATION ON A SHOP ORDER WORK CENTER MASTER DATA RELATED TO A WORK CENTER Planning Files Control Files Topic 14 2 Scheduling and Shop Floor Decisions in Process Focused Operations aster Production Engineeringthe Prgduct Designs 1 Schedule MPS an Processing Plans I Material gt Capacity lt OrderProcessing Requirements Requirements or Plan MRP Plan CRP lgt Routing Plans i l i Planned Work Center Assignment of Order ReleaSes Loading and r ers to Report Overtime Plan Work Centers l i l DaytoDay Scheduling and Shop Floor Decisions 1 Setting the priorities of orders at each work center In other words determining the sequence in which orders will be processed at each work center 2 Given that orders can be assigned to several machines within each work center determining to which machine each order should be assigned 3 Shop floor controldispatching or releasing orders to work centers expediting orders if necessary coordinating work center schedules and revising schedules as conditions change Topic 14 3 Functions of Production Activity Control The major functions of an efficient production activity control system consist of the following Releasing order to the production on schedule having verified material tool equipment and personnel availability Preparing shop packet shop order drawing pick list route sheet tool request form labor ticket move ticket etc Establishing scheduled start and completion dates so steps in the production process as well as the schedules completion date of the order as milestones to measure progress Comparing future workload with planned capacity to allow for a determination of appropriate action for balancing work Ranking orders in designed priority sequence by work center and issuing a dispatch list Tracking the current status of each order in process Providing timely and accurate feedback on activities not proceeding according to plan Revising order priorities on the basis of performance and changing conditions Monitoring and controlling lead time work center queue and work in process Providing exception and performance evaluation reports scrap rework late order and work center ef ciency analysis reports Topic 14 4 Production Control Overview The functions of production control are c Releasing orders 0 Control shop workload 0 Meet job s duedate 0 Maintain shop workin process level 0 Dispatching 0 Determine job processing priority for jobs waiting at each work center 0 Tracking the status 0 Monitor job processing progress 0 Examine job order completion status 0 Collecting performance data 0 For every job order I Actual cost vs planned cost I Actual leadtime vs planned leadtime o For each work center I Utilization level I Average job waiting time Topic 14 5 Job Dispatching Sequencing Rules Dispatching Rule determine which job will be processed next among the jobs waiting in queue Common Dispatching Rules FCFS FirstCome FirstServed SPT Shortest Processing Time Job First LPT Longest Processing Time Job First EDD Earliest DueDate Job First MRO Most Remaining Operations Job First CR Critical Ratio Smallest CR Job First aynmwn DueDate 7 Current Time Total Remaining Operation Time If CR 1 this order is in critical If CR lt 1 this order is late already If CR gt 1 this order has some slack time Most Dispatching Rules are Heuristic in nature Different Rules perform differently under different measures Topic 14 6 06 Examples of Evaluation Criteria for Production Scheduling Minimize average lateness for completed jobs Minimize average ow time for completed jobs Minimize maximum lateness for completed jobs Minimize maximum ow time for completed jobs Maximize machine utilization in facility Minimize average value of workinprocess Maximize worker utilization Balance workload assigned to each workermachine Maximize volume of work completed in each time period Topic 14 7 Job Dispatching Example There are three jobs waiting for processing Their processing time requirement and duedates are given below b Time 7 15 11 Dispatching jobs by SPT LPT and EDD Comparing the Average Job Flow Time and the Number of Jobs Late a SPT b LPT c EDD Topic 14 8 Exercise Job Dispatching Problem There are eight jobs waiting in the queue for processing on machinel The jobs are arranged in the order of their arrival with ABCGH Jobs ABCDEFGH ProcessingTimes days 27 14 7 31 9 27 3 21 DueDatedays from now 32 33 17 40 28 52 9 44 A Use FCFS firstcomefirst serve dispatching rule Compute total job completion time average job ow time and average job lateness B Use SPT shortest processing time dispatching rule Compute total job completion time average job ow time and average job lateness Topic 14 9 Supplement Scheduling Example a By Rule Processing Flow Time DueDate Lateness Time Total Average Flow Time Total FlowTimeNumber of Jobs Average Lateness Total LatenessNumber of Jobs Topic 14 10 B By Rule Processing Flow Time DueDate Lateness Time Total Average Flow Time Total FlowTimeNumber of Jobs Average Lateness Total LatenessNumber of Jobs Topic 14 11 JobSequencing Problem 0 We want to determine the sequence in which we will process a group of waiting orders at a work center 0 Many different sequencing rules can be followed in setting the priorities among orders 0 There are numerous criteria for evaluating the effectiveness of the sequencing rules Ordersequencing rules 0 O O O O O Firstcomefirst served FCFS Shortest processing time SPT Earliest due date EDD Least slack LS Critical Ratio CR Least Changeover Cost LCC General Performance 0 O O Firstcome firstserved o Performs poorly on most evaluation criteria 0 Does give customers a sense of fair play Shortest processing time 0 Perform well on most evaluation criteria 0 But have to watch out for longprocessingtime orders getting continuously pushed back Critical ratio 0 Works well on average job lateness criterion 0 May focus too much on jobs that cannot be completed in time causing other to be late too Topic 14 12 Scheduling in Service Operations Major Characteristics of Scheduling in Service Operations 1 Large demand fluctuation due to customer involvement 2 Intangible output can not be inventoried capacity exibility is critical customers will not wait in a long line 3 Capacity is laborintensive in customercontact operations Two Major Scheduling Issues 1 Worker Shift Construction How many shifts per working day 2 Staf ng for Each Shift How many workers will be assigned to each shift Major Scheduling Technigues in Service Operations 0 Optimization Analytical Models eg LP ILP o PracticalOriented Scheduling Heuristics o Queuing WaitingLine Models 0 Computer Simulation Search Algorithms Topic 14 13 Service Operations Planning and Scheduling Services are operations With o Intangible outputs that ordinarily cannot be inventoried Close customer contact and short lead times High labor costs relative to capital costs Sub jectively determined quality Need better planning controlling and management to stay competitive Positioning strategies contain two elements 0 Type of service design 0 Standard of custom 0 Amount of customer contact 0 Mix of physical goods and intangible services 0 Types of production process 0 Quasimanufacturing production occurs much as manufacturing physical goods dominant over tangible services 0 Customerasparticipant high degree of customer involvement physical goods may or may not be significant service either standard or custom o Customerasproduct service performed on customer usually custom Scheduling Challenges in Services Planning and controlling daytoday activities difficult due to 0 Services produced and delivered by people 0 Pattern of demand for services is nonuniform Topic 14 l4 Scheduling for NonUniform Demand 0 As firms cannot inventory services in advance of highdemand periods so businesses use following tactics o Preemptive actions to make demand more uniform Offpeak incentivesdiscounts Appointment schedules Fixed schedules Make operations more exible so it is easier to vary capacity 0 Parttime personnel 0 Subcontractors o Inhouse standby resources 0 O O 0 Additional tactics used by business 0 anticipated demand and schedule employees during each time period to meet demand 0 allow waiting lines to form Scheduling quasimanufacturing services 0 Productfocused operations customer demand is forecast and capacity decisions made just as in manufacturing 0 high volumes of standardized products 0 management focused on controlling production costs product quality and delivery of physical goods 0 Processfocused operations inputoutput control important to balance capacity between operations 0 Gantt charts used to coordinate flows between departments 0 Sequence of jobs consider sequencing rules changeover costs and flow times Topic 14 15 Work Shift Scheduling in Service Operations 0 Three dif culties in scheduling services 0 Demand variability 0 Service time variability 0 Availability of personnel when needed 0 Managers use two tactics 0 Use fulltime employees exclusively 0 Use some fulltime employees as base and fill in peak demand with parttime employees Scheduling CustomerasParticipant Services 0 Must provide customer ease of useaccess features lighting walkways etc 0 Layouts must focus on merchandising and attractive display of products Employee performance crucial to customer satisfaction Waiting lines queuing models used extensively to level demand because 0 Demand patterns are irregular or random 0 Service times vary among customers 0 Managers try to strike a balance between efficiently utilizing resources and keeping customer satisfaction high Topic 14 l6 Waiting Line in Services Examples Computer printing jobs waiting for printing Workers waiting to punch a time clock Customers in line at a drivenup window Drivers waiting to pay a highway toll Skiers waiting for chair lift Airplanes waiting to take off Waiting line analysis assists managers in determining How many servers to use Likelihood a customer will have to wait Average time a customer will wait Average number of customer will wait Waiting line space needed Percentage of time all servers are idle Scheduling customer as product services Wide range of complexity Every facet designed around the customer Highly trained motivated and effective workforce critical to success Waitingline analysis can be helpful in determining staffing levels In more complex operations simulation is a helpful tool in scheduling resources Reasons for simulating operations Experimentation with the real system is impossible impractical or uneconomical System is so complex that mathematical formulas cannot be developed Values of the system s variables are not known with certainty Topic 14 l7 Exercise Operations Scheduling 1 Six jobs are waiting to be processed at a workstation Their job code numbers estimated production times and promised delivery times are given in the following table t0 Determine the sequence of producing the jobs using the following rule a Shortest processing time rule Longest Processing Time rule and Critical ratio rule b Calculate the Average Job FlowTime and Average Job Lateness for each of the three dispatching rules above 2 Seven jobs are waiting to be processed at a workstation Their job code number estimated production times and promised delivery times are given below A 24 310 Determine the sequence of producing the jobs using the following rule a Shortest processing time rule Longest Processing Time rule Critical ratio rule b Calculate the Average Job FlowTime and Average Job Lateness for each of the three dispatching rules above Topic 14 18 3 A company does heattreating for industrial customers on a rstcome rstserved basis but wonders if shortest processing time would be better The jobs that are now waiting to be produced are listed in the order in which they arrived with their estimated production times time to promised delivery and the necessary computations Job Estimated Job Sequence Flow Time Job Sequence Flow Time Production FCFS days SPT days Time hours A l 6 4 16 B 3 2 9 2 5 C 2 3 l l l D 5 4 l6 3 10 a Rank the two sequencing rules on two evaluation criteria average ow time and average job lateness b Which sequencing rule would you recommend Why 4 A production planner must decide the sequence in which to produce four customer orders Customer Estimated Time to FirstCome Flow Time Lateness Order Production Promised FirstServed days days Time days Delivery Order days Sequence A 10 15 l 10 0 B 21 3 0 2 3 l l C 26 60 3 57 0 D 19 77 4 76 l Rank the rstcome rstserved shortest processing time and critical ratio sequencing rule on two evaluation criteria average ow time and average job lateness Topic 14 l9 Review Questions for Topic 14 lt PRODUCTION OPERATIONS SCHEDULINGgt 1 In class we discussed the implementation of a scheduling system and general management information system for a job shop production facility Identify several dispatching rules which might be used in such a system How should the choice of a dispatching rule depend on the firm39s strategy 2 De ne dispatching and expediting Where does each fit in the general production control cycle 3 Be prepared to sequence several jobs on one machine by the SPT rule the EDD rule the FCFS rule and the LPT rule Be prepared to evaluate the resulting schedules on the basis of average ow time and average lateness In addition what is the impact of these rules on workinprocess 4 What is the critical ratio scheduling rule Be prepared to apply this rule for sequencing several jobs on a machine 5 Identify several scheduling evaluation criteria for production shops ie given two different schedules for a production shop for the same day how would one determine which one is best 6 Why is the job release an important function for a shop manager What are the impacts of releasing jobs too early or too late to the shop oor 7 Describe draw a job scheduling GANTT chart For what purpose is it used 8 Based on class discussions and the text presentation what job shop scheduling performance results in terms of minimizing job ow time and lateness would be expected from the use of the SPT LPT FCFC and EDD heuristic rules 9 Based on our inclass discussions what is the objective function in scheduling telephone information operators or airline reservationists What are the constraints Topic 14 20
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