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Shop Floor Planning & Control

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In this presentation, we will discuss shop floor planning and operation pipeline, objectives of production activity, operations planning various stages of scheduling, Gantt chart preparation, its …

In this presentation, we will discuss shop floor planning and operation pipeline, objectives of production activity, operations planning various stages of scheduling, Gantt chart preparation, its importance, Johnson’s rule of algorithm, flow shop, batch scheduling. We will also talk about scheduling and controlling production for delivery schedules – line of balance method.
To know more about Welingkar School’s Distance Learning Program and courses offered, visit: http://www.welingkaronline.org/distance-learning/online-mba.html

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  • 1. Production Planning & ControlChapter 4 Shop Floor Planning & Control Chapter4 1
  • 2. Shop Floor Planning & ControlOnce the Broadest Strategic decisions concerningmanufacturing company viz.,a)What business it is in &b)What territory it will serveAre made the operations managers use the forecasts ofexpected demand to select most appropriate type of factoryThe choice may be one of following types1.Job Shop2.Flow Shop3.Continuous production4.Project organization for manufacturing or service Chapter4 2
  • 3. Shop Floor Planning & Control The Production EnvironmentIn f o r m a tio n E x c h a n g e B e t w e e n L e v e l 3 & 4 Chapter4 3
  • 4. Shop Floor Planning & ControlB u s in e s s F u n c tio n s ( S 9 5 ) Business Functions E n t e r p r is e P e r fo r m a n c e R e p o r tin g Level 4 D em and C ost H u m a n R e s o u rce P la n n in g S u p p ly C h a i n P la n n in g A c c o u n t in g M anagem ent B u s in e s s P la n n in g & S a le s & M a te r ia l P ro d u c tio n W a re h o u s e M a in t e n a n c e D is t r ib u ti o n M anagem ent P la n n in g M anagem ent M anagem ent L o g is t ic s D e t a il P ro c e ss R e c ip e P e r fo rm a n c e P ro c e ss S c h e d u l in g O p t im iz a tio n M anagem ent M anagem ent A n a ly s is Level 3 M a n u f a c tu r in g R e s o u rce P ro d u c tio n W IP M a t e r ia l P ro d u c tio n Q u a lit y M anagem ent E x e c u tio n M anagem ent H is to r y M anagem ent O p e r a tio n s R e a l- T im e R e a l- T im e E x e c u tio n SPC Level 2 P la n t F lo o r R e a l- T im e R e a l- T im e C o n tro l C o n tro l M o n it o r in g Chapter4 4
  • 5. Shop Floor Planning & Control Several generic tasks characterize production, the processthrough which parts and materials are transformed into finalproducts. These tasks include, among others, the receipt andacknowledgment of orders, the acquisition of materials, theperformance of shop floor operations, and the generation ofinformation needed to support continuous improvement. Together, these tasks (when properly done) constitute aqualified production process. Qualifying a production process is a demanding and importanttask that requires people trained and physically qualified for agiven job, machines and Chapter4 5
  • 6. Shop Floor Planning & Control process instruments that can be guaranteed to operatewithin specifications, production capacity that can matchthe order demand, and the availability of productioncapacity in the desired time frames. The information-processing view of a production facilityis in essence the same as that for an individual work cellwithin the facility. Both factories and work cells processorders and turn out products. For a factory, the order usually comes from a customeroutside the factory; for a work cell, the order comes frominside the factory. Chapter4 6
  • 7. Production/shop floor Activity Control The MRP System specifies what products or componentsare needed &When they are required.The productionactivity control(PAC)directs how,when,where theproduct/components should be made in order to ensuredelivery of goods as per schedule. Priority Production activity Capacity Control Control Control Priority Control ensures that production activities are carried out as per plan Chapter4 7
  • 8. Objectives of Production Activity Control To know The current status of job To determine what should be next job to beprocessed & which work center To ensure correct quantity of materials are inright place To minimize work in process inventory To minimize setup costs To maintain control of operations by monitoringjob status To maximize operational efficiency Chapter4 8
  • 9. Operations Planning & Scheduling In this context the scheduling processcenters around:1. Time to do the work,2. The department which will perform thework,3. The resources to be applied,4. Statusing work progress versus workscheduled, and5. Monitoring and reporting Chapter4 9
  • 10. Operations Planning & Scheduling Scheduling is an important tool for manufacturing andengineering, where it can have a major impact on theproductivity of a process. In manufacturing, the purpose of scheduling is tominimize the production time and costs, by telling aproduction facility what to make, when, with which staff,and on which equipment. Production scheduling aims tomaximize the efficiency of the operation and reduce costs. Production scheduling tools greatly outperform oldermanual scheduling methods. This provides the productionscheduler with powerful graphical interfaces which can beused to visually optimize real-time work loads in variousstages of the production, Chapter4 10
  • 11. Operations Planning & Scheduling and pattern recognition allows the software toautomatically create scheduling opportunities which mightnot be apparent without this view into the data. For example, an airline might wish to minimize thenumber of airport gates required for its aircraft, in order toreduce costs, and scheduling software can allow theplanners to see how this can be done, by analyzing timetables, aircraft usage, or the flow of passengers .Companies use backward and forward scheduling toallocate plant and machinery resources, plan humanresources, plan production processes and purchasematerials. Chapter4 11
  • 12. Operations Planning & Scheduling Forward scheduling is planning the tasks from the dateresources become available to determine the shipping dateor the due date. Forward scheduling is also done if no product isavailable on the material availability date calculated bybackward scheduling. The system does an availabilitycheck to determine the first possible date when productwill be available. This new material availability dateforms the starting point for scheduling the remainingactivities. The loading time, pick/pack time, transit time,and transportation lead time are added to the new materialavailability date to calculate the confirmed delivery Chapter4 12
  • 13. Operations Planning & Scheduling Backward scheduling is planning the tasks from thedue date or required-by date to determine the start dateand/or any changes in capacity required.Backward scheduling is the calculation of deadlinedates: the arrival time at the customer site is calculated asthe earliest possible goods receipt time at the customersunloading point on the requested delivery date.All four of the delivery and transportation scheduling leadtimes are subtracted from the customer’s requesteddelivery date to determine if this date can be met. The transit time, loading time, and pick/pack time aresubtracted from the customer’s requested delivery date tocalculate the required Chapter4 material availability date. 13
  • 14. Operations Planning & Scheduling The system calculates backward scheduling as follows: Requested delivery date minus transit time = Goods issuedateGoods issue date minus loading time = Loading dateLoading date minus transportation lead time =Transportation scheduling dateLoading date minus pick/pack time = Material availabilitydate By default, the system will calculate delivery dates theclosest day, taking into consideration the working days ofthe shipping point and a rounding profile. In this case thesystem assumes a 24 hour work day and lead times can beentered in days up to 2 decimal points. This is referred to as Chapter4 14daily scheduling.
  • 15. Operations Planning & Scheduling Precise scheduling calculated down to the day,hour and minute is supported. This allows thescheduling of a delivery within a single day. It isactivated by maintaining the working hours for aparticular shipping point. Backward scheduling is always carried outfirst. If the material availability date ortransportation scheduling date is calculated to be inthe past, the system must then use forwardscheduling. Chapter4 15
  • 16. Operations Planning & Scheduling Forward scheduling is also done if no product isavailable on the material availability date calculated bybackward scheduling. The system does an availability check to determine thefirst possible date when product will be available. This newmaterial availability date forms the starting point forscheduling the remaining activities. The loading time, pick/pack time, transit time, andtransportation lead time are added to the new materialavailability date to calculate the confirmed deliverydate. Chapter4 16
  • 17. Operations Planning & SchedulingOrderRelease Dept.X Dept.Y Dept.ZDate L.T =4WK L.T =5WK L.T =3WK Operation A Operation B Operation C Start Finish Start Finish Start Finish Completion Date Total manufacturing lead time Example of forward scheduling Chapter4 17
  • 18. Operations Planning & Scheduling Dept.X Dept.Y Dept.Z L.T =4WK L.T =5WK L.T =3WK Operation A Operation B Operation CToday’s Start Finish Start Finish Start Finish CompletionDate Date Total manufacturing lead time Example of backward scheduling Chapter4 18
  • 19. Stages in Scheduling Scheduling is performed in two stages1.Loading: is the process of determine whichwork center receives which job.It involvesassessing a jog or task,machine/worker, rawmaterial availability2.Dispatching:is sequencing and selecting thejobs waiting at work center(determining whichjob to be done next).It lists all jobs waiting atwork center & arrange as per priority Chapter4 19
  • 20. Stages in Scheduling Finite loading :Start with specific Capacity for each work centers and a list of jobs processed at the work centers(sequencing) The work center capacity is allocated to job s by simulating job starting times and completion times 100Hr/WeekLoad inStandard 50Hours 0 2 4 Chapter4 6 8 10 20 Period Weeks
  • 21. Stages in Scheduling Infinite loading :The process of loading work centers with all jobs without regard to the actual capacity available at he work center 200 Work center Capacity 100Hr/Week 100Load inStandardHours 50 0 2 4 Chapter4 6 8 10 21 Period Weeks
  • 22. Operations Planning & Scheduling The benefits of production scheduling include: Process change-over reduction Inventory reduction, leveling Reduced scheduling effort Increased production efficiency ,Labor loadleveling Accurate delivery date quotes ,Real timeinformation Chapter4 22
  • 23. Gantt ChartPlanning and scheduling complex projectsGantt Charts are useful tools for analyzing andplanning complex projects. They:•Help you to plan out the tasks that need to becompleted•Give you a basis for scheduling when these taskswill be carried out•Allow you to plan the allocation of resourcesneeded to complete the project, andHelp you to work out the critical path for a projectwhere you must complete it by a particular date. Chapter4 23
  • 24. Gantt ChartWhen a project is under way, Gantt Charts help you tomonitor whether the project is on schedule. If it is not, itallows you to pinpoint the remedial action necessary to put itback on schedule.Sequential and parallel activities:An essential concept behind project planning (and CriticalPath Analysis) is that some activities are dependent on otheractivities being completed first. As a shallow example, it isnot a good idea to start building a bridge before you havedesigned it! These dependent activities need to be completed in asequence, with each stage being more-or-less completedbefore the next activity can begin. We can call dependentactivities sequential or linear. Chapter4 24
  • 25. Gantt ChartOther activities are not dependent on completion of any other tasks. These may be done at any time before or after a particular stage is reached. These are nondependent or parallel tasks.Drawing a Gantt ChartTo draw up a Gantt diagram (Gant diagram), follow these steps:1. List all activities in the plan For each task, show the earliest start date, estimated length of time it will take and whether it is parallel or sequential. If tasks are sequential, show which stages they depend on. Chapter4 25
  • 26. Gantt ChartGantt Chart Chapter4 26
  • 27. Gantt ChartGantt Chart Chapter4 27
  • 28. What Is Sequencing?•Predictable, consistent ordering and delivery oflearning activities, in an instructionally meaningfulmanner, regardless of delivery environment•Designers/authors specify sequencing behaviorsat design/authoring time.•Activities are sequenced at time of deliverydepending on specified behaviors and the learner’sactions.•Sequencing behaviors are external from thecontent to enable greater degree of granularity andreuse Chapter4 28
  • 29. Priority SequencingPriority sequencing in a real world job shop An engineering industry job shop thatmanufactures 19 types of products against orders isdescribed, with the objective of evaluating a newsequencing rule based on the monetary value of thejob and its processing time, the highest value timeratio rule. Analysis of this rule has not appeared inliterature on job shop scheduling. For purposes ofcomparison, based on the performances in paststudies, the following four sequencing rules areincluded: Chapter4 29
  • 30. Priority Sequencing (These rules were evaluated on the followingcriteria: work-in- process inventory in monetaryterms, and delivery performance, and acombination of the two measures. Results of the study show that the highest valuetime ratio rule results in minimum work-in-processinventory. The shortest processing time rule resultsin maximum delivery performance; the same ruleis superior on combined measure of performance. Chapter4 30
  • 31. Priority Sequencing(Rules)1) Shortest processing time (SPT) :The jobs are having the shortest processing time isgiven the highest priority.2) Least Slack per operation (LS): the highestpriority given to job which has least slack3) First-Cone, first-Served (FCFS):Jobs are selectedin the same sequence as they come4) Earliest Due date (EDD):Jobs are processedaccording to due dates Chapter4 31
  • 32. Priority Sequencing(Rules)5) Longest Processing Time(LPT):the highest priority givento job which has longest processing time6) Shortest Processing Time(LPT) :Jobs are selected as perShortest Processing Time .7) Random Selection: Jobs are selected randomly8) Cost over time(COVERT):Uses the ratio of expecteddelay cost over the processing cost9) Preferred Customer order(PCO):As per customer order10 Least Change Over cost ((LCOC):The sequencing ofjobs is done by analyzing the total cost of makingall the machine changeover between jobs Chapter4 32
  • 33. Illustration for Sequencing(Rules)XYZ company has received the following jobs at awork center to be processed.The processing time (in days),arrival date and duedate are given Determine the sequence in which jobsshould be processed according to priority rulesFCFS,SPT,LPT,EDD,TSPT,LS & COVERTAssume today is is day 100 & jobs can not bedelayed more than 60 daysAssume expected cost of delay is Rs 10/day Chapter4 33
  • 34. Illustration for Sequencing(Rules)Job Processing Arrival Due Date Time(Days) DateA 15 95 185B 20 110 200C 10 112 175D 30 125 235E 25 125 180F 18 130 220 Chapter4 34
  • 35. Illustration for Sequencing(Rules)Priority Rules: FCFS Sequence A B C D E FPriority Rules: SPT Sequence C A FB E DPriority Rules: LPT Sequence D E B F C APriority Rules: EDD Sequence C E A B F DFor TSTP rule ,it is specified that the jobs can notbe delayed by more than 60 days if we apply SPTRule .If none of the jobs violets the constraints ,thesequence will be identical for SPT and TSPTrule.To examine this ,we should know the wait timefor the jobs as per SPT rule ,which is determined asper next slide Chapter4 35
  • 36. Illustration for Sequencing(Rules) SPT RuleJob Processing Arrival Start Date Wait Time Time(Days) Date Days Days daysC 10 112 112 NilA 15 95 122 27F 18 130 135 7B 20 110 155 45E 25 125 175 50D 30 125 200 75 Chapter4 36
  • 37. Illustration for Sequencing(Rules)Least Slack RuleJob Processing Available Slack Days Sequence (Rank) Time(Days) time DaysA 15 90(185-95) 75 5B 20 90 70 3C 10 63 53 2D 30 110 80 6E 25 55 30 1F 18 90 72 4 JOB sequence E C B F A D Chapter4 37
  • 38. Dynamic Sequencing Rules Dynamic slack(DS) rule:When the least slack rule isused repeatedly at each machine/work center forsequencing the jobs ,it is known as dynamic slack rule. Dynamic slack per remaining operation(DS/RO) rule:In this rule ,the ratio of total slack time available for thejob to the number of operations remaining including thecurrent operation is obtained. Total Slack time DS/RO ratio = Total number of operations remaining (including the current operation is obtained.) Job with Smallest DS/RO ratio is scheduled first Chapter4 38
  • 39. Dynamic Sequencing Rules Critical Ratio rule: The critical ratio rule is designed to give priority tojobs that have most urgently needed work to meet theshipping schedule. Due date-Date now C/R ratio = Days required to complete the = D.D-D.N L.T.R Chapter4 39
  • 40. Dynamic Sequencing Rules Illustration ABC Company has 6 jobs arriving at random at several work stations & passing through them,requiring different processing time.For particular work station the data is given below.Job Arrival Processi Due No of Time for Due Time ng Time subsequent subsequent time Time operations operations Hrs Hrs Hrs1 12 2 4,00PM 2 12 202 2 PM 2 5PM Nil Nil 123 3,30PM 4 8PM 4 30 504 3,30PM 3 7PM 3 10 255 4,30PM 6 12PM 2 20 456 6PM 4 8Am 4 25 38 Next day Chapter4 40
  • 41. Dynamic Sequencing Rules Illustration Ds /Ro RuleJob Arrival Processing Due Time Dynamic Slack Time Time Hrs Available time-Total Hrs operation time (Hrs) 1 12 2+12 20 20-14=6 2 14 2+nil 12 12-2=10 3 15.5 4+30 50 50-35=16 4 15.5 3=10 25 25-13=12 5 16.5 6+20 45 45-2619 6 18 4+25 38 38-29=9 Chapter4 41
  • 42. Dynamic Sequencing Rules Illustration Calculation of Ds /Ro RatioJob Dynamic Remaining Operations(RO) DS/RO Ratio Slack(DS) 1 6 2+1=3 6/3=2 2 10 Nil+1=1 10/1=10 3 16 4+1=5 16/5=3.33 4 12 3+1=4 12/4=3 5 19 2+1=3 19/3=6.33 6 9 4+1=5 9/5=1.8 Sequence As per Ds/Ro rule: 6,1,4,3,5,2 Chapter4 42
  • 43. Dynamic Sequencing Rules Illustration Critical Ratio RuleJob Processing Time Available time Critical ratio Hrs (Hrs.) 1 2 4 4/2=2 2 2 3 3/2=1.5 3 4 4.5 4.5/4=1.125 4 3 3.5 3.5/3=1.166 5 6 7.5 7.5/6=1.25 6 4 14 14/4=3.5 Sequence As per CR rule: 3,4,5,2,1,6 Chapter4 43
  • 44. Johnson’s Rule or algorithm FLOW SHOP SCHEDULING n JOBS (n JOBS, m MACHINES) BANK OF m MACHINES (SERIES) 31 2 M1 M2 Mm 4 n Chapter4 44
  • 45. FLOW SHOPS PRODUCTION SYSTEMS FOR WHICH: A NUMBER OF OPERATIONS HAVE TO BE DONE ON EVERY JOB.THESE OPERATIONS HAVE TO BE DONE ON ALL JOBS IN THE SAME ORDER, i.e., THE JOBS HAVE TO FOLLOW THESAME ROUTE.THE MACHINES ARE ASSUMED TO BE SET UP IN SERIES. COMMON ASSUMPTIONS: UNLIMITED STORAGE OR BUFFER CAPACITIES IN BETWEEN SUCCESIVE MACHINES (NO BLOCKING). A JOB HAS TO BE PROCCESSED AT EACH STAGE ON ONLY ONE OF THE MACHINES (NO PARALLEL MACHINES). Chapter4 45
  • 46. PERMUTATION FLOW SHOPS FLOW SHOPS IN WHICH THE SAME SEQUENCE ORPERMUTATION OF JOBS IS MAINTAINED THROUGHOUT:THEY DO NOT ALLOW SEQUENCE CHANGES BETWEEN MACHINES. PRINCIPLE FOR Fm||Cmax: THERE ALWAYS EXISTS AN OPTIMAL SCHEDULE WITHOUT SEQUENCE CHANGES BETWEEN THE FIRST TWO MACHINES AND BETWEEN THE LAST TWO MACHINES. THERE ARE OPTIMAL SCHEDULES FOR F2||Cmax ANDF3||Cmax THAT DO NOT REQUIRE SEQUENCE CHANGES BETWEEN MACHINES. Chapter4 46
  • 47. JOHNSON’S F2||Cmax PROBLEM FLOW SHOP WITH TWO MACHINES IN SERIES WITH UNLIMITED STORAGE IN BETWEEN THE TWO MACHINES.THERE ARE n JOBS AND THE PROCESSING TIME OF JOB j ON MACHINE 1 IS p1j AND THE PROCESSING TIME ON MACHINE 2 IS p2j. THE RULE THAT MINIMIZES THE MAKESPAN IS COMMONLY REFERRED TO AS JOHNSON’S RULE. Chapter4 47
  • 48. JOHNSON’S PRINCIPLE ANY SPT(1)-LPT(2) SCHEDULE IS OPTIMAL FOR Fm||Cmax.(THE SPT(1)-LPT(2) SCHEDULES ARE NOT THE ONLY SCHEDULES THAT ARE OPTIMAL. THE CLASS OF OPTIMAL SCHEDULES APPEARS TO BE HARD TO CHARACTERIZE AND DATA DEPENDENT). Chapter4 48
  • 49. DESCRIPTION OF JOHNSON’S ALGORITHM1. IDENTIFY THE JOB WITH THE SMALLEST PROCESSING TIME (ON EITHER MACHINE).2. IF THE SMALLEST PROCESSING TIME INVOLVES:• MACHINE 1, SCHEDULE THE JOB AT THE BEGINNING OF THE SCHEDULE.• MACHINE 2, SCHEDULE THE JOB TOWARD THE END OF THE SCHEDULE.3. IF THERE IS SOME UNSCHEDULED JOB, GO TO 1. OTHERWISE STOP. Chapter4 49
  • 50. EXAMPLE CONSIDER THE FOLLOWING INSTANCE OF THE JOHNSON’S (Fm||Cmax) PROBLEM: JOB 1 2 3 4 5 p1j 4 4 10 6 2 p2j 5 1 4 10 3SEQUENCE: Chapter4 50
  • 51. SEQUENCE: EXAMPLE: SCHEDULE 51432 JOB 1 2 3 4 5 p1j 4 4 10 6 2 p2j 5 1 4 10 3M1M2 t Chapter4 51
  • 52. A BOUND ON THE MAKESPAN FOR JOHNSON’S PROBLEM: ⎧⎛ n ⎞⎛ n ⎞⎫ ⎪⎜ ⎟⎜ ⎟⎪Cmax (OPT ) ≥ max ⎨⎜ min p 2 j + ∑ p1 j ⎟, ⎜ min p1 j + ∑ p 2 j ⎟ ⎬ ⎪⎜ j=1,..,n ⎩⎝ j=1 ⎟ ⎜ j=1,..,n ⎠⎝ j=1 ⎟⎪ ⎠⎭ Chapter4 52
  • 53. JOHNSON’S ALGORITHMLET U = {1, 2,..., n} BE THE SET OF UNSCHEDULEDJOBS.k =1,l = n,Ji = 0, i IDENTIFICATION OF SMALLEST PROCESSING TIMESTEP 1: = 1, 2, ..., n.IF U = ∅, GO TO STEP 4.LET ⎧ ⎫ p i* j* = min ⎨ min p1 j, min p 2 j ⎬ ⎩ j=1,..,n j=1,..,n ⎭IF i* = 1 GO TO STEP 2; OTHERWISE GO TO STEP 3. Chapter4 53
  • 54. JOHNSON’S ALGORITHM (CONTINUED)STEP 2: SCHEDULING A JOB ON EARLIEST POSITION• SCHEDULE JOB j* IN THE EARLIEST AVAILABLE POSITION: Jk = j*.• UPDATE k: k = k + 1.• REMOVE THE JOB FROM THE SCHEDULABLE SET, U = U – {j*}.• GO TO STEP 1.STEP 3: SCHEDULING A JOB ON LATEST POSITION• SCHEDULE JOB j* IN THE EARLIEST AVAILABLE POSITION: Jl = j*.• UPDATE l: l = l - 1.• REMOVE THE JOB FROM THE SCHEDULABLE SET, U = U – {j*}.• GO TO STEP 1. Chapter4 54
  • 55. JOHNSON’S ALGORITHM (CONTINUED)STEP 4: SEQUENCE OF JOBSTHE SEQUENCE OF JOBS IS GIVEN BY Ji,WITH J1 THE FIRST JOB, AND SO FORTH. Chapter4 55
  • 56. Fm||Cmax Fm||Cmax IS A STRONGLY NP-HARD PROBLEM.AN EXTENSION OF JOHNSON’S ALGORITHM YIELDS AN OPTIMAL SOLUTION FOR THE F3||Cmax PROBLEM WHEN THE MIDDLE MACHINE IS DOMINATED BY EITHER THE FIRST OR THIRD MACHINE. Chapter4 56
  • 57. MACHINE DOMINANCE: F3||Cmax A MACHINE IS DOMINATED WHEN ITS LARGEST PROCESSING TIME IS NO LARGER THAN THE SMALLEST PROCESSING TIME ON ANOTHER MACHINE. FOR F3||Cmax PROBLEM: ⎧ ⎫ p 2 j ≤ max ⎨min p1 j , min p 3 j ⎬ ⎩ j ⎭WHICH IMPLIES THAT MACHINE 2 (DOMINATED MACHINE) CAN NEVER CAUSE A DELAY IN THE SCHEDULE. Chapter4 57
  • 58. JOHNSON’S ALGORITHM FOR 3 MACHINESFOR F3||Cmax, WHENEVER MACHINE 2 IS DOMINATED, i.e., min{p1 j } ≥ max{p 2 j } OR min{p 3 j } ≥ max{p 2 j } j j j jSOLVING AN EQUIVALENT TWO-MACHINE PROBLEM WITH PROCESSING TIMES: p’1j = p1j + p2j AND p’2j = p2j + p3j GIVES THE OPTIMAL MAKESPAN SEQUENCE TO THE DOMINATED THREE-MACHINE PROBLEM. Chapter4 58
  • 59. EXAMPLE: F3||Cmax CONSIDER F3||ΣCmax WITH THE FOLLOWING JOBS: JOB 1 2 3 4 5 p1j 4 9 8 6 5 p2j 5 6 2 3 4 p3j 8 10 6 7 11min{p1 j } = max{p 2 j } = min{p 3 j } = j j j Chapter4 59
  • 60. EXAMPLE: PROCESSING TIMES, DUMMY MACHINES JOB 1 2 3 4 5 p1j 4 9 8 6 5 p2j 5 6 2 3 4 p3j 8 10 6 7 11 p1j p2jSEQUENCE: Chapter4 60
  • 61. SEQUENCE: EXAMPLE: SCHEDULE 1 4 5 2 3 JOB 1 2 3 4 5 p1j 4 9 8 6 5 p2j 5 6 2 3 4 p3j 8 10 6 7 11M1M2M3 t Chapter4 61
  • 62. Illustration for Johnsons ruleEstimated processing time (Hours)Job Work Center Work Center WC1 WC2A 2 1B 4 2.25C 0.75 2.5D 1.5 3E 2 4F 2 3.5 Chapter4 62
  • 63. Illustration for Johnsons rule Applying Johnsons rule Job C has the shortestprocessing time in either work center (I.e.75hour),assign job C as as the first job in the sequence. Next Job A has Shortest time (I.e 1 Hr) assignJob A as last job in sequence and cross out timefor Job The Next smallest time is 1.5 hours for job D onWC1 The next smallest time is 2 hr for job E and F onWC1,Since there is tie in between jobs E,F choosethe job with smaller subscript I.e job E Chapter4 63
  • 64. Illustration for Johnsons rule Assign the job E as the next job after job Dfrom beginning of the sequence. The next Job after job E is job F The last job Bhas to be accommodated in the gap between job Fand the last job in the sequence i.e Job A Hence the sequence is C,D,E,F,B,A Chapter4 64
  • 65. Batch Scheduling Batch production falls between job shopproduction and continuous. In batch production system, the output is can bestored as inventory for further processing or asfinished products and can be produced insubstantial volume, even-though the volume maynot justify continuous production. In these situations, it is necessary to determinethe lot-size for a batch to be produced at one timein addition to scheduling the batch on the facilities. Chapter4 65
  • 66. Batch Scheduling Examples of such production are production ofpharmaceutical products, paints etc., Decision to be takenby Operations manager are (i)the lot size; and(ii)The scheduling decision regarding when to begin theprocessing of the batch. A key-off in the determination of the lot size for an itemis between set-up costs and inventory carrying costs. Another important consideration is the requirement toproduce a feasible schedule that meets the demand for allitems. Chapter4 66
  • 67. Batch Scheduling For example, if set-up costs are low ascompared to inventory carrying costs, it may beadvantageous to go for small lot sizes But it may not be possible to produce therequired quantities of all items within thespecified time period if these small lot sizes areemployed. This will happen if much of the time isconsumed for machine set-ups thereby reducingthe available production time. To overcome thisproblem, larger lot sizes may have to be employedwhich will result in higher inventory carryingcosts. Chapter4 67
  • 68. Batch Scheduling Hence, it is necessary to compute economic lotsizes while maintaining feasibility in schedulingbatches of such lot sizes for the items to beproduced. Two types of costs associated with lotmanufacture are: (a)Set up costs i.e. costs/unit which decreasewith batch size.(b)Inventory carrying cost which increases withbatch size. Chapter4 68
  • 69. Batch Scheduling Set up cost includes: (i)Cost of releasing work orders, shop orders,stores requisitions, tool requisitions etc. (ii)Cost of first off inspection, cost of rejectionstill machine set up is ready for production run. (iii)Machine set-up cost for mountingaccessories, tools, jigs and fixtures on themachine. Chapter4 69
  • 70. Batch Scheduling Inventory carrying costs include: (i)Cost of working capital tied up in averageinventory. (ii)Cost of handling and storing materials (i.e.parts produced) (iii)Insurance charges and taxes. (iv)Cost of spoilage and obsolescence etc. Chapter4 70
  • 71. Case1 Batch SchedulingInstantaneous Supply with no simultaneous consumption Let A= Annual demand for an Item S= Set up cost per setup I =Inventory Carrying cost C=Cost per unit of item produced Q=Economical batch Quantity The Solution: No of batches per year =A/Q Setup cost per year =A/Q* S Average inventory held=Q/2 Chapter4 71
  • 72. Batch SchedulingInstantaneous Supply with no simultaneous consumption Inventory carrying cost per year=Q/2*C*I Total Cost per year =Set up cost per year + inventory carrying cost per year. T.C=A/Q*S+Q/2CI For minimizing the total cost d T.C = -(AS/Q*Q)+(CI/2) dQ For T.C to be minimum d T.C =0 dQ Or –AS/Q8Q+CI/2=0 Or CI/2=AS/Q*Q, Hence Q= 2AS Chapter4 ٧ CI 72
  • 73. Batch Scheduling Instantaneous Supply with no simultaneous consumption Maximum InventoryQuantity Average InventoryERQ Q Time Chapter4 73
  • 74. Case 2 Batch SchedulingInstantaneous Supply with simultaneous consumption Let A= Annual demand for an Item S= Set up cost per setup I =Inventory Carrying cost C=Cost per unit of item produced Q1=Economical batch Quantity d=demand or consumption rate p=Production rate The Solution: No of Set ups per year =A/Q1 Setup cost per year =A/Q1* S Average inventory held = Maximum inventory/2 Chapter4 74
  • 75. Case 2 Batch SchedulingInstantaneous Supply with simultaneous consumptionTo calculate the inventory built up let us assumethat production period is t1( weeks )andconsumption only period is t2 (say weeks)Quantity produced in time t1=Q1(at the rate of“p”per week)Q1=p*t or t1=Q1/pConsumption during period t1=dt1(at the rate of “d”per week)=d*Q1/p or =Q1*d/p Chapter4 75
  • 76. Case 2 Batch SchedulingInstantaneous Supply with simultaneous consumption(Maximum inventory built up =Qty produced-Qty Consumed During period t1) =Q1-Q1*d/P =Q1(1-d/P) Average inventory = Q1/2(1-d/P) Inventory carrying cost per year= Q1/2(1-d/P)*CITotal cost per year = Set cost per year+Inventory carrying cost per year Tc=A/q1*s+Q1/2(1-d/P)*CI Chapter4 76
  • 77. Case 2 Batch SchedulingInstantaneous Supply with simultaneous consumptionFor the total cost Tc to be minimum dTc =0 dQ1 I.e –A.S/Q1*Q1+ (1-d/P)*CI = 0 22 Solving for Q1 2As Q1= CI(1-d/p) Chapter4 77
  • 78. Batch Scheduling Instantaneous Supply with simultaneous consumption Consumption onlyProduction period (t1) period (t2) Maximum Inventory Quantity Average Inventory ERQ Q Time Chapter4 78
  • 79. Run out or Run out time method This method attempts to use the total productioncapacity available in each time period to produce justenough of each product variety so that if production isstopped ,the finished goods inventory for each productwould be depleted or would run out at the same pointof time. The run out time is expressed as the ratio of thecurrent inventory to demand forecast for the period. Run out Time = Current inventory of Item X Demand per period for item X Chapter4 79
  • 80. Aggregate Run out or Run out time method In case of above , run out time method,it is observed that ,there is shortage of required capacity .If it is necessary to produce all items required for a product ,shortage of any single item should not occur In such case s the aggregate run out method is used. (Machine hours inventory +(Total Available for all items) Machine hours)AROT = Machine Hours requirements forecasted for all the items Chapter4 80
  • 81. Scheduling & Controlling Production ForDelivery Schedules - Line of Balance method Line of balance technique has been used inproduction scheduling and control to determine ,at aview date,not only how many( quantity )of itemshould have been completed by that date,but also howmany should have passed through previous operationstages by that time so as to ensure the completion ofthe required delivery schedule. LOB is a charting and computational technique formonitoring and controlling products and services thatare made to meet specific delivery schedule Chapter4 81
  • 82. Line of Balance method -Example XYZ company has received orders to deliver a aproduct for which the operations program anddelivery schedule s are given below Week No Qty of end product to be delivered1 52 103 104 105 15 Chapter4 82
  • 83. Line of Balance method -Example Purchased part Fabrication Assembly Delivery of End product Develop a LOB chart & determine the Quantities that should have passed through the upstream processing steps during the review point at the end of 2nd week 1 2 3 Item A 5 Item B 410 9 8 7 6 5Chapter4 4 3 2 1 83
  • 84. Line of Balance method SolutionMethod: the five steps required to be followed in LOBtechniques: Preparation of operation program or assembly chart Preparation of Cumulative completion/deliveryschedule Construction of LOB chart Construction of program progress Analysis of progress and corrective action Chapter4 84
  • 85. Line of Balance method -SolutionPreparation of operation program or assembly chart The operation program shows the “lead time”for eachoperation.The lead time is shown as length of time prior tocompletion of final Completion operation. Assembly Delivery of End product Fabrication Purchased part 1 2 3 Item A 5 Item B 410 9 8 7 6 5Chapter4 4 3 2 1 85
  • 86. Line of Balance method SolutionPreparation of operation program or assembly chart The delivery date for the finished product (enditem) is zero & the time scale indicating “leadtime”runs from left to right. The operation program indicates that Purchased partA must be combined with B in operation stage 4 threedays before completion of end item. Item B ,prior to combination has undergone aconversion operation which has to be completed fivedays before the completion of end item,The purchasedpart for item B must be available ten days prior todelivery date for end item which means longest leadtime is ten days Chapter4 86
  • 87. Line of Balance method SolutionStage 2 : Preparation of Cumulative completion/delivery scheduleThe quantities of end item to be completed week byweek and cumulatively indicated in table as shownbelow Week No Qty of end item to be Cumulative Qty to be completed Nos. completed Nos. 1 5 5 2 10 15 3 10 25 4 10 35 5 15 50 Chapter4 87
  • 88. Line of Balance method SolutionStage 3 : Construction of line of balance chart The line of balance shows the quantity of itemthat should have completed at each operationstage in a particular week at which progress willbe reviewed.So as to meet the delivery schedule The line of balance chart can be constructed asshown in next slide Chapter4 88
  • 89. Line of Balance method Solution5045 Line of Balance4035 35 Nos.30 25 Nos.25 21 Nos.20 5 Nos.15105 1 2 3 4 5 1 2 3 4 5 Chapter4 89
  • 90. Line of Balance method Solution Stage 4 : Construction of progress chart50 The progress chart for review week is shown45 below.40 Excess production35 35 Nos.30 Shortage production25 21 Nos. Exact production20 15 Nos.15105 1 2 3Chapter4 4 5 90
  • 91. Line of Balance method SolutionStage 5 : Analysis of progress & corrective actiondelivery schedule By referring to programme process chart which isprepared every week the difference between thedesired production (as indicated by line ofbalance)for the review week can be compared withthe actual production achieved at the end of thereview week. The excess production or shortage production canbe found out & appropriate actions taken to bringproduction in line Chapter4 91
  • 92. Line of Balancing Methods The various Line balancing methods are: Heuristic method Linear programming Dynamic programming Computer based sampling techniqueA heuristic is a method for helping in solving of a problem,commonly informal. It is particularly used for a method thatoften rapidly leads to a solution that is usually reasonablyclose to the best possible answer. Heuristics are "rules ofthumb, educated guesses, intuitive judgments or simplycommon sense. In more precise terms, heuristics stand forstrategies using readily accessible though loosely applicableinformation to control problem-solving in human beings andmachine Chapter4 92
  • 93. Line of Balancing MethodsHeuristic method (Illustration)The table below shows the number of work stations(N),Cycle time( C) & daily production for a product No of Cycle Time Daily production Workstations N C Sec (8 Hrs shift) 1 120 240 2 60 480 3 40 720 4 30 960 5 24 1200 6 20 1440 Chapter4 93
  • 94. Line of Balancing MethodsHeuristic method (Illustration) It is desired to have two assembly lines eachproducing 720 units per day,the cycle time will be40 seconds & there will be 3 work stations in eachassembly line The precedence diagram is shown in next slide. The activity time in seconds are given in bracketfor each of twenty operations involved Assuming that activities may be combined withingiven zone ,without violating the precedencerelationship ,assign the activities into threeworkstations.This can be done by trial & error basisby adding activity time Chapter4 94
  • 95. Line of Balancing Methods 12 4 3 10 5 10 8 1 5 18 5 2 6 11 3 13 15 19 2 7 12 7 5 14 4 4 5 8 2 13 16 20 9 76 6 17 9 14 3 Chapter4 95
  • 96. Line of Balancing MethodsHeuristic method (Illustration) Activities Total time SecWork station 1 1,7,2,8,9,11 5+5+2+14+5+7+2=40Work station 2 4,5,10,12,13,3 3+8+12+7+4+6=40Work station 3 14,15,16,17,18, 6+3+4+9+10+3+5=40 19,20A perfect balance is obtained since all work stations haveexact the same workload of 40 sec. Chapter4 96
  • 97. Scheduling ServicesServices are those economic activities in which theprimary product is nether a product nor aconstruction.Some of the examples of services are Transportation Utilities Communication Wholesale trade Retail trade Real estate Hotel & restaurant Hospital services Chapter4 97
  • 98. Scheduling ServicesFour approaches that are usually used are Use of waiting lines Use of appointment schedules Personal schedules Emergency services Chapter4 98
  • 99. Shop Floor Planning & ControlEnd OfChapter 4 Chapter4 99
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