PRODUCTION SCHEDULING PART-A

Transcription

1 PRODUCTION SCHEDULING PART-A 1. List out any five priority sequencing rules. (Nov-2017) First come, first served (FCFS) Last come, first served (LCFS) Earliest due date (EDD) Shortest processing time (SPT) Longest processing time (LPT) 2. What is MRP? List the various inputs required for it. (Nov-2017) It is a computational technique that converts the master schedule for final product into a detailed schedule for the raw material and parts used in the final product. Various Inputs 1. MPS 2. Bill of materials 3. Inventory record file 3. What is master scheduling? (Apr-2017, Apr-2016, Apr-2012) It is a detailed plan that states how many end items will be available for sale (Or) distribution during specific periods 4. What is meant by Kanban system? (Apr-2017, Apr-2015) A Kanban is a card that is attached to a storage and transport container. It identifies the part number and container capacity, along with other information. 5. Differentiate between product sequencing or sequencing and scheduling. (Nov-2016, Nov-2015, Nov-2014) Scheduling refers to the setting of operation start dates so that jobs will be completed by their due date. Product Sequencing- It is a systematic procedure for determining the optimum sequence (order) of jobs that minimizes the total completion time. 6. Cite the meaning of the term line of balance. (Nov-2016, Nov-2015) Line-of-balance (LOB) is a charting technique that uses lead times and assembling sequencing to compare planned component completions with actual component completions. SRI VIDYA COLLEGE OF ENGG&TECH Page 1

2 7. Write a note on perpetual loading. (Nov-2014) In perpetual loading, a copy of every order is placed in an open file which moves with the job going to different facilities. During the processing, the progress is reported with the help of tickets such as inspection ticket, material requisition ticket, move ticket, etc. 8. What is Gantt chart and how it is constructed? (Apr-2014, Apr-2015) Gantt charts are usual (bar chart) aids to depict the sequencing, load on facilities, or progress associated with work effort over a well-defined time period. 9. With reference to line balancing, define the terms (a) line efficiency; (ii) balance delay. (Apr-2014) Line efficiency- is the ratio between the time needed and the time allocated in an assembly line. Balance delay-is the percentage of wasted time. 10. What is manufacturing lead time. MLT is the total length of time used to process raw materials and components through all upper levels in the bill of material into an end item. 11. Write down the advantages and disadvantages of master scheduling` Advantages 1. It translates aggregate plans into specific end items. 2. It evaluates alternative schedules. 3. It generates material requirements. Disadvantages 1. The complete information is available in gross, and thus it can sometimes mislead. 12. List the key functions of the production scheduling and control. (i) (ii) (iii) (iv) Release orders; Assign jobs; Sequencing priorities; MLT by expediting and tracking. 13. What is dispatching. It is the routine of setting productive activities in motion through the release of orders and instructions in accordance with previously planned times and sequences embodied in route sheets and schedule charts. SRI VIDYA COLLEGE OF ENGG&TECH Page 2

3 14. What are the advantages, disadvantages of Gantt load chart? Advantages i) This system is quite simple. ii) ii) This could be maintained even by electrical staff after some training. iii) iii) Overall cost of operation is small. Disadvantages From the load chart it is not possible to learn the exact time of a work. It tells only the total load ahead of a department or a facility. 15. What are the main objectives of loading? (i) (ii) (iii) (iv) To check the feasibility of production programs To assist in the efficient planning of new work To assist in balancing the plant to the existing load To assist in fixing of reliable delivery promises. 16. List the function of expediting (Or) Follow up (Or) Progressing. (Apr-2012) It is a control function that keeps track of the progress of work in accordance with planned schedule. PART-B 1. Explain the process flow involved in Master scheduling. (Nov-2017) or Explain the scheduling procedure with suitable example. Discuss in detail about the scheduling rules. (Apr-2012, Apr-2017) SRI VIDYA COLLEGE OF ENGG&TECH Page 3

4 Basic scheduling techniques depend on the type of production type and frequency of jobs, demand patterns and flexibility offered by available processing time. Basic scheduling problems include: Job shop scheduling (also known as unit scheduling) Batch production scheduling Flow production scheduling Production scheduling Major inputs of MPS Forecast of demand of end items Customer orders Inventory on-hand from the previous period functions of MPS To translate aggregate plans in to specific end times To evaluate alternative schedules To generate material requirements. To generate capacity requirements To facilitate information processing To maintain valid priorities To utilize capacity effectively Advantages of master scheduling The overall cost of operating is minimum than any other loading and scheduling systems This method is very simple to understand This could be even maintained by clerical staff. It could be easily kept current. dis-advantages of master scheduling The detailed information cannot be obtained. It is efficient for small units only Scheduling Rules or Priority Rules When many jobs are waiting before an operational facility, there are some rules to decide the priority while sequencing. FCFS First Come First Served SOT Shortest Opening Time SPT Shortest Processing Time SRI VIDYA COLLEGE OF ENGG&TECH Page 4

5 Due Date Earliest due date first Start Date [Due Date Normal lead time] STR Slack time remaining (Due date - Processing time) STR/OR Slack Time Remaining Per Operation CR Critical Ratio [difference b/w due date and current date and the no. of days remaining] QR Queue Ratio LCFS Last Come First Serve Random Order or Whim. 2. Discuss in detail the method of obtaining the MPS for a system with example. Suitable assumptions can be made. (Nov-2015, Nov-2016) The Master Production Schedule (MPS) formalizes the production plan and translates it into specificend-item requirements over a short to intermediate planning horizon. The end items are then explodedcapacity Requirements Planning (CRP) systems. Thus, the MPS essentially drives the entire production and inventory system. The major inputs to the master production schedule are: 1. Forecasts of demand, e.g., of end items and service parts. 2. Customer orders, i.e., including any warehouse and interplant needs. 3. Inventory on-hand from the previous period. Forecasts of demand are the major input for make-to-stock items. However, to be competitive,many make-to-order firms must anticipate orders by using forecasts for long lead-time items and by matching the forecasts with customer orders as the orders become available. Master Scheduling Planning Horizon The time horizon of master scheduling depends upon the type of product, volume of production, andcomponent lead times. It can be weeks, months, or some combination, but the schedule must normally extend far enough into the future so that the lead times for all purchased and assembled components are adequately encompassed, schedules frequently have both firm and flexible (or tentative) portions. Table illustrates an MPS for a furniture company that has one such schedule-where the firm and flexible portions have not open to change. SRI VIDYA COLLEGE OF ENGG&TECH Page 5

6 Two-time fence can be identified in MPS: A demand and a planning time fence. (a) A demand time fence is the firm or frozen portion of the master schedule (beginning with the current period) during which no changes can be made to the schedule without managementapproval. (b) A planning time fence is the portion of the master schedule (also beginning with the current period) during which changes will not automatically be made (i.e., via computer) to accommodate demand. This gives the master scheduler a manageable base to work from and stillallows some discretion in overriding the constraint. Question: How does master scheduling differ under manufacturing strategies of (a) make-tostock, (b) assemble-to-order, and (c) make-to-order? See Figure where the shorter line segments represent fewer items. In (a) make-to-stock operations, the (fewer) end items are stocked, to support customer service, and the master productionschedule (MPS) is structured around those end items. In (b) assemble-to-order plants, such as inautomobile manufacturing, the master scheduling is done for the major sub-assembly-level items. In(c) make-to-order products, such as customized furniture, there are fewer raw materials than enditems; the end items may even be one of a kind. Here, the master schedule is typically structuredaround the raw material usage. SRI VIDYA COLLEGE OF ENGG&TECH Page 6

7 3. (i) What is perpetual loading? Describe. (Apr-2015) In perpetual loading, a copy of every order is placed in an open file which moves with the job going to different facilities. During the processing, the progress is reported with the help of tickets such as inspection ticket, material requisition ticket, move ticket, etc. Steps in making Perpetual Schedule a. Preparation of load analysis sheet. Load analysis can be prepared by posting the load information on the form. b. Presentation in Gantt chart The total load against each department is added up and knowing the weekly capacity of a department, the number of weeks load against each department is calculated. These informations can be transferred in the form of chart, usually on a Gantt load chart. Advantages 1. It is very simple and understandable. 2. It requires less overall cost. 3. These charts can be used for various type of work. (ii) Describe Gantts chart. What are their used? (Nov-2014) Gantt chart is simple bar graphs that can be used to schedule any type of operation. Two basic types of Gantt charts Work Load Charts Scheduling Charts SRI VIDYA COLLEGE OF ENGG&TECH Page 7

8 A Gantt work load chart is usually used to depict work load levels for equipment work station or departments. A Gantt scheduling chart is used to depict workload levels for equipment, workstations (Or) departments. Advantages iv) This system is quite simple. v) ii) This could be maintained even by electrical staff after some training. vi) iii) Overall cost of operation is small. Disadvantages From the load chart it is not possible to learn the exact time of a work. It tells only the total load ahead of a department or a facility. (iii) Explain any one of techniques for aligning completion times and due dates. (Apr- 2015, Nov-2014) MLT is the total length of time used to process raw materials and components through all upper levels in the bill of material into an end item. MLT = no (Tsu + Q Tc+Tno) Tno= non operation time (min), Tsu= setup time to prepare for the batch (min), Q = batch quantity (pc), and Tc= operation cycle time per work unit (min/cycle). Example: A certain part is produced in a batch size of 100 units. The batch must be routed through five operations to complete the processing of the parts. Average setup time is 3 hr/operation, and average operation time is 6 min (0.1 hr). Average nonoperation time due to handling, delays, inspections, etc., is 7 hours for each operation. Determine how many days it will take to complete the batch, assuming the plant runs one 8-hr shift/day Given data: Number of operation, no = 5 Tsu= setup time to prepare for the batch (min)= 3 quantity, Q= 100 SRI VIDYA COLLEGE OF ENGG&TECH Page 8

9 Tc= operation cycle time per work unit (min/cycle) = 0.1 hr Tno= Average non operation time =7 hr Solution: The manufacturing lead time, MLT = no (Tsu + Q Tc +Tno) = 5 X (3+ 100X ) = 100 hours At 8 hr/day, this amounts to 100/8 = 12.5 days 4. Discuss the following: (Nov-2014, Apr-2015) (a) Flow production scheduling; In flow shop scheduling problem, there are n jobs; each require processing on m different machines.the order in which the machines are required to process a job is called process sequence of that job. The process sequences of all the jobs are the same. But the processing times for various jobs on a machine may differ. If an operation is absent in a job, then the processing time of the operation of that job is assumed as zero. The flow-shop scheduling problem can be characterized as given below: 1. A set of multiple-operation jobs is available for processing at time zero (Each job requires moperations and each operation requires a different machine). 2. Set-up times for the operations are sequence independent, and are included in processing times. 3. Job descriptors are known in advance. 4. m different machines are continuously available. 5. Each individual operation of jobs is processed till its completion without break. The main difference of the flow shop scheduling from the basic single machine scheduling is that the inserted idle time may be advantageous in flow shop scheduling. Though the current machineis free, if the job from the previous machine is not released to the current machine, we cannot startprocessing on that job. So, the current machine has to be idle for some time. Hence, inserted idletime on some machines would lead to optimality. (b) Periodic batch control Batch Production a. many planning steps i. Aggregate planning ii. master scheduling SRI VIDYA COLLEGE OF ENGG&TECH Page 9

10 iii. material requirements planning (MRP) iv. capacity requirements planning (CRP) (c) Kanban. A Kanban is a card that is attached to a storage and transport container. It identifies the part number and container capacity, along with other information. Production or (In-Process)-Kanban Provides production instructions for the work center Tells the workers exactly the quantity and the type of part to produce Used for work centers that produce only one-part number or have minimal setups in spite of multiple part number production Rectangular one-piece flow production Triangular for small lot production Withdrawal-Kanban Inter-Process Kanban Delivers order for parts from a preceding process Specifies quantity and type of parts to deliver from Location A to Location B Later replenishment system kanban are filled from suppliers finished goods shelf Sequenced withdrawal supplier sequences parts in reverse order for truck loading Supplier Kanban Same as an inter-process Kanban, except it signals conveyance of part from an outside supplier Job Order-Kanban Issued for each job order Through-Kanban When two processes are very close, it doesn t make sense to issue two Kanbans. Used where one process directly feeds (conveyor) the next process. Common-Kanban Where a withdrawal kanban is used as a production ordering kanban if the distance between two processes is very short and share the same supervisor. Emergency-Kanban Temporary, when there is a defect or problem, can be withdrawal or production SRI VIDYA COLLEGE OF ENGG&TECH Page 10

11 (d) Dispatching It is the routine of setting productive activities in motion through the release orders and instructions, in accordance with previously planned times and sequences embodied in route sheets and scheduled charts. Activities of Dispatching Movement of material from stores Issue of tool orders Issue of job order Issue of time tickets Issue of inspection orders Issue of move orders Functions of dispatching To prepare manufacturing orders (shop order, move order, tool order) Issue of material from stores Issue of instructions to tool room Issue of orders authorising the commencement of operations in accordance with the predicted dates Issue of time, time instruction cards, drawings Issue of order to the inspection department Ordering finished products to the stock room Time recording Issue of time tickets to finance department Recording of the idle time of machines and operations Common Forms Used in Dispatching Material requisitions form Job card / job ticket Labour card / Tickets Move Card / Ticket Inspection Card / Tickets Tool and Gauge Tickets SRI VIDYA COLLEGE OF ENGG&TECH Page 11

12 (e) Discuss in detail the various steps involved in Line of balance Technique. (Apr- 2016) Line of balance (LOB) is a charging technique that uses lead times and assembly sequencing to compare planned component completions with actual component completions Uses of LOB Source of each component element (purchase, manufacture, assemble, test) Sequence of assembly, including sub-assembly, testing and inspection, packaging, shipping and related activities. Comparison of scheduled versus actual finished product deliveries Comparison of scheduled versus actual component (element completion showing present and shortages) Input to LOB Schedule of Delivery. Key operations in making the product which needs to be controlled. The sequence in which the key events are controlled. Lead times of the above events. Various charts used in LOB Operation programme chart/ or assembly chart Objective chart Progress chart Line or balance chart. 5. Discuss the concepts, inputs, characteristics, working, output and benefits of MRP. Also Explain in detail the various components of MRP (Nov-2017, Apr-2017, Nov- 2016, Nov-2015, Apr-2012) Material Requirement planning Material requirements planning (MRP) is a computational technique that converts the master schedule for end products into a detailed schedule for the raw materials and components used in the end products. The distinction between independent demand and dependent demand is important in MRP. Independent demand means that demand for a product is unrelated to demand for other items. Final products and spare parts are examples of items whose demand is independent. Independent demand patterns must usually be forecasted. SRI VIDYA COLLEGE OF ENGG&TECH Page 12

13 Dependent demand means that demand for the item is directly related to the demand for some other item, usually a final product. The dependency usually derives from the fact that the item is a component of the other product. Inputs to the MRP System To function, the MRP program must operate on data contained in several files. These files serve as inputs to the MRP processor. They are: (1) MPS, (2) Bill of materials file and other engineering and manufacturing data, and (3) Inventory record file. Figure illustrates the flow of data into the MRP processor and its conversion into useful output reports. In a properly implemented MRP system, capacity planning also provides input to ensure that the MRP schedule does not exceed the production capacity of the firm. (1) MPS The MPS lists what end product, and how many of each are to be produced and when they are to be ready for shipment. Manufacturing firms generally work toward monthly delivery schedules, but the master schedule in our figure uses weeks as the time periods. 'Whatever the duration, these time periods are called time buckets in MRP. Instead of treating time as a continuous variable (which of course, it is). MRP makes its computations of materials and parts requirements in terms of time buckets (2) Bill of materials file The bill of materials (BOM) file is used to compute the raw material and component requirements for end products listed in the master schedule. It provides information on the product structure by listing the component parts and subassemblies that make up each product. The structure of an assembled product can be illustrated as in Figure. This is much SRI VIDYA COLLEGE OF ENGG&TECH Page 13

14 simpler than most commercial products. but its simplicity will serve for illustration purposes. Product PI is composed of two subassemblies, S1 and S2, each of which is made up of components C1, C2, and C3, and C4, C5, and C6, respectively. Finally, at the bottom level are the Jaw materials that go into each component. The items at each successively higher level are called the parents of the items feeding into it from below. For example, S1 is the parent of C1, C2, and C3. The product structure must also specify the number of each subassembly, component, and raw material that go into its respective parent. These numbers are shown in parentheses in our figure. (3) Inventory record file The inventory record file is referred to as the item master file in a computerized inventory system. The types of data contained in the inventory record are divided into three segments: 1. Item master data This provides the item's identification (part number) and other data about the part such as order quantity and lead times. 2. Inventory status This gives a time-phased record of inventory status. In MRP, it is important to know not only the current level of inventory, but also any future changes that will occur against the inventory. Therefore, the inventory status segment lists the gross requirements for the item, scheduled receipts, on-hand status, and planned order releases. 3. Subsidiary data The third file segment provides subsidiary data such as purchase orders, scrap or rejects, and engineering changes. SRI VIDYA COLLEGE OF ENGG&TECH Page 14

15 MRP Outputs and Benefits Outputs include: (1) Planned order releases, which provide the authority to place orders that have been planned by the MRP system: (2) Report of planned order releases in future periods (3) Rescheduling notices, indicating changes in due dates for open orders (4) Cancelation notices, indicating that certain open orders have been canceled because of changes in the MPS; (5) reports on inventory status (6) Performance reports of various types, indicating costs, item usage, actual versus planned lead times (7) Exception reports, showing deviations from the schedule, orders that are overdue, scrap, and so on: and (8) Inventory forecasts, indicating projected inventory levels in future periods. Benefits (1) Reduction in inventory (2) Quicker response to changes in demand than is possible with a manual requirements planning system. (3) Reduced setup and product changeover costs, (4) Better machine utilization, (5) Improved capacity to respond to changes in the master Schedule, and (6) As an aid in developing the master schedule. 6. Sequence the following jobs to minimize the processing times on the two machines. Also compute the idle times of the machines. (Apr-2015) Job Machine Machine This sequencing problems can be solved using Johnson s rule. The sequence of job can be obtained as below. J4 J2 J4 SRI VIDYA COLLEGE OF ENGG&TECH Page 15

16 J3 J2 J4 J3 J1 J2 J4 J3 J1 J6 J2 J4 J3 J1 J5 J6 J2 J4 Machine 1 Machine 2 Optimal sequence of job is The final schedule for the above job sequence can be drawn as shown below. From the above figure, we can write Total elapsed time = 42 time units Idle time for M1= 3 time units Idle time for M2 = = 6 time units 7. An assembly line is to be designed to operate 7.5 hours per day and supply a steady demand of 300 units per day. The following table shows the tasks and their performance times. (i) Draw the precedence diagram, (ii) What is the cycle time? (iii) Assign tasks to work stations stating your logical rules, and (iv) What is the efficiency of your line balance? (Apr-2014) Task a b c d e f g h i j k l Preceding a b c d e f g h,i j,k Performance time (sec) SRI VIDYA COLLEGE OF ENGG&TECH Page 16

17 Given data Working time = 7.5 hours per day Demand = 300 units per day (i) Precedence diagram (ii) Cycle time (CT) CT = Operating time per day Desired output per day (iii) Assigning tasks to workstations = 7.5 X 60 X = 90 seconds = 1.5 min Workstation Assign task Idle time (in seconds) 1 a, d c, f, i g, j b, h e, k, l = 40 (iv) Efficiency of line balance Percentage of idle time (balance decay) for the line = Idle time per cycle No.of workstations X Cycle time X 100 = 40 5 X 90 X 100 = 8. 9 % Efficiency of the line = 100 Percentage of idle line=1 8.9 = 91.1% 8. There are seven jobs which are to be processed first on Machine I and then on Machine II. Process time in hours is given below. Find the optimal sequence and total elapsed time. (Apr-2014) Task a b c d e f g Machine I Machine II This sequencing problems can be solved using Johnson s rule. The sequence of job can be obtained as below. SRI VIDYA COLLEGE OF ENGG&TECH Page 17

18 f a f a g f a d g f a d b c g f a d e b c g f Machine 1 Machine 2 Optimal sequence of job is a--- d----e---b---c---g----f The final schedule for the above job sequence can be drawn as shown below. From the above figure, we can write Total elapsed time = 132 time units Idle time for M1= 2 hours Idle time for M2 = = 33 hours SRI VIDYA COLLEGE OF ENGG&TECH Page 18