Operation engine ii session iv operations scheduling
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1) The document discusses various production planning and scheduling techniques used in job shop and process-focused manufacturing environments. 2) Key topics covered include master production scheduling, capacity requirements planning, input-output control, sequencing rules to determine job order, controlling changeover costs, and techniques for batch scheduling and delivery schedules. 3) The document provides details on several scheduling and sequencing methods including finite loading, earliest due date, economic order quantity, and line of balance.
Operation engine ii session iv operations scheduling
- 1. Operation Engine II Session IV Operations Scheduling Fatima Aliza Assistant Professor IILMAHL
- 2. Process Focused Manufacturing These types of factories are called Job- Shops. A job shop in an organization in which the work centers or departments are organized around similar types of functions or departmental specialties , such as forging, milling, turning, heat treating, drilling and assembly. Jobs are usually processed in batches, with the batch size based either on the customer order size or some economical quantity.
- 3. Master production schedule(MPS) Material requirements plan(MRP) Capacity requirements plan(CRP) Planned order releases report Work center loading and overtime plan Engineering the product designs & processing plans Order processing or routing plans Assignment of orders to work centers
- 4. Shop Floor Planning and Control Assigning a priority to each order. Issuing dispatching lists to each work centers. Keeping the WIP inventory updated. Providing input- output control on all work centers. Measuring the efficiency , utilization and productivity of workers and machines at each work center.
- 5. Input- Output Control This is a key activity that allows operations managers to identify such problems as insufficient capacity, excessive capacity and production difficulties among a group of connected workstations. From such reports operations managers can determine if the amount of work flowing to a work center is the planned amount and if the capacity of the work center is according to plan.
- 6. Gantt Charts Gantt Charts can be used to visually display the workloads in each work center in a department. It is used to compare the weekly schedule for five work centers in a model shop. The jobs scheduled to be worked on during the week are displayed with their code names or numbers ( A,B,C, etc.) , beginning times , and ending times, which are represented by an open bar. As work progresses on a job, a solid bar shows how the work center is performing to the schedule. Machine changeovers , maintenance and other planned nonproduction work are indicated by an X. Blank spaces indicate planned idle time at the work center. Gantt charts are very useful for coordinating a diversity of schedules of work teams, work centers and activities of projects.
- 7. Finite & Infinite Loading Infinite approach is used when jobs are assigned to work centers without considering the capacities of the work centers. This approach abandons CRP & its loading schedules. Unless a company has excessive production capacity, unacceptable queues of waiting jobs occur at work centers. Finite approach is used when the capacities of work centers are allocated among a list of jobs. By using a computer simulation model or other means each work center’s capacity is allocated to jobs hour by hour by varying the start and completion times of the jobs. The end result of this approach is scheduled to a work center during any hour than the capacity of the work center. This approach is integral to CRP and is used by many companies today.
- 8. Forward & Backward Scheduling There are two ways to determine to which time slots jobs are assigned within work centers. In forward scheduling , jobs are assigned to the earliest unassigned time slots in work centers. This approach assumes that customers want their jobs delivered as soon as possible. Although simple to use , excessive in process inventories usually result because jobs tend to sit and wait for their next work center assignments.
- 9. Order Sequencing Problems In order sequencing problems we want to determine the sequence in which we will produce a group of waiting orders at a work center. We analyze these problems by discussing the various sequencing rules , the criteria for evaluating the sequencing rules, a comparison of sequencing rules , the control of changeover costs , and the minimization of production costs.
- 10. Sequencing rules First come first serve (FCFS): The next job to be produced is the one that arrived first among the waiting jobs. Shortest Processing time(SPT): The next job to be produced is the one with the shortest processing time among the waiting jobs. Earliest Due Date(EDD): the next job to be produced is the one with the earliest due date among the waiting jobs. Least slack(LS): The next job to be produced is the one with the least slack ( time to due date minus total remaining production time) among the waiting jobs. Critical Ratio(CR): The next job to be produced is the one with the least critical ratio ( time to due date divided by total remaining production time) among the waiting jobs. Least changeover cost(LCC): Since some jobs logically follow each other because of ease of changeovers, the sequence of waiting jobs is determined by analyzing the total cost of making all of the machine changeovers between jobs.
- 11. Criteria for evaluating sequencing rules Average flow time: the average amount of time jobs spend in the shop. Average number of jobs in the system: The average number of jobs in the shop. Average job lateness: The average amount of time that a job’s completion date exceeds its promised delivery date. Changeover cost: The total cost of making all the machine changeovers in a group of jobs.
- 12. Controlling changeover costs Changeover costs are the costs of changing a processing step in a production system over from one job to another. They include costs for such things as changing machine settings, getting job instructions, and changing materials and tools. Usually , jobs should be produced in the sequence that minimizes the cost of these changeovers.
- 13. Scheduling product – focused manufacturing There are two general types of product focused production : Batch & Continuous Batch production is often called a Flow shop because products follow along direct linear routes. Large batches of several standardized products are produced in the same production products are produced in batches , the production system must be changed over when a different product is to be produced. In Continuous production, a few highly standardized products are produced continuously in very large volumes and changeovers are rare. The products may be discrete such as plastic molded products , or they may be continuous , such as gasoline.
- 14. Batch Scheduling In product focused systems that produce products in batches, a key issue is the size of batches. Two approaches to this issue will be discussed here: EOQ for production lots Run out method
- 15. EOQ for production lots The production lot size problem is solved using the following formula: EOQ=√ (2DS/C) (p/(p-d)
- 16. Run – Out method Various deficiencies of the EOQ in planning production lot sizes have led to the development of the run–out method. This method attempts to use the total production capacity available in each time period to produce just enough of each product so that if all production stops, the finished goods inventory for each product runs out at the same time.
- 17. Delivery schedules : Line of Balance method Some production systems often commit to delivery schedules for their products that stipulate how many products must be delivered to customers in each future week. If it is important that actual product deliveries match with the planned delivery schedule, a system must be devised to schedule and control all the production steps. To avoid any delays and corrective actions line of balance (LOB) has been used to schedule and control upstream production steps.