SCHEDULING STRATEGIES

Scheduling strategies vary widely among firms and rage from “no scheduling” to very sophisticated approaches.

The strategies are grouped into four classes: (i) Detailed scheduling.

(ii) Cumulative

(iii) Cumulative detailed (iv) Priority decision rules.

1. Detailed scheduling for specific jobs that are arrived from customers is impracticable in actual manufacturing situation. Changes in orders, equipment breakdown, unforeseen events deviate the plans.

2. Cumulative scheduling of total work load is useful especially for long range planning of capacity needs. This may load the current period excessively and under load future periods. It has some means to control the jobs.

3. Cumulative detailed combination is both feasible and practical approach. If master schedule has fixed and flexible portions.

Capacities are planned on a broad basis first in terms of total labour and machine hour requirements per week at key work centres. As changes occur during the weeks prior to manufacturing, the computer updates material and capacity requirements automatically. Capacity may then be allocated to specific jobs later a few days before the commencement of job. The shortest scheduling unit for job shop is one day.

4. Priority decision rules are scheduling guides that are used independently and in conjunction with one of the above strategies, e.g., First Come First Serve. These are useful in reducing work-in-process (WIP) inventory.

17. Explain Forward Scheduling and Backward Scheduling. FORWARD SCHEDULING AND BACKWARD SCHEDULING Forward Scheduling

(Set forward) is commonly used in job shops where customers place their orders on “needed as soon as possible” basis. Forward scheduling determines start and finish times of next priority job by assigning it the earliest available time slot and from that time, determines when the job will be finished in that work centre. Since the job and its components start as early as possible, they will typically be completed before they are due at the subsequent work centres in the routing. The set forward method generates in process inventory that are needed at subsequent work centres and higher inventory cost.

Forward scheduling is simple to use and it gets jobs done in shorter lead times, compared to backward scheduling.

Backward Scheduling

(Set backward) is often used in assembly type industries and commit in advance to specific delivery dates. Backward scheduling determines the start and finish times for waiting jobs by assigning them to the latest available time slot that will enable each job to be completed just when it is due, but not before. By assigning jobs as late as possible, backward scheduling minimizes inventories since a job is not completed until it must go directly to the next work centre on its routing.

Bill of materials (BOM) and lead time estimates are maintained for all work centres otherwise the system breaks down and due dates are violated. Figure shows forward and backward scheduling.

Figure – Forward and backward scheduling 18. What is Progressing? Explain various types of progressing.

PROGRESSING

Progressing is that part of the production control function which is responsible for making routine comparisons between production performance and production plans and for reporting exceptional variances to the line staff so that they can be corrected. Progressing in the production control completes the loop and which by giving early warning when actual production deviates from planned production makes it possible for corrective action to be taken in order to regain the desired course.

Progressing can be divided into four main tasks: 1. Recording of actual production.

2. Comparison of actual production with planned production. 3. Measurement of deviation.

4. Reporting of all excessive deviations to the authorities responsible for executing the plans.

Types of Progressing

1. Programme control: It is the job of comparing the actual production output with the

production programme and reporting deviations from plan to the line management for consideration and correction. There are different ways in which product output can be recorded and compared with a programme control. Gantt charts, tabulated records and Z- charts are used for recording. The Z-chart is a programme control method which shows the actual outputs at the end of each chosen interval and also show cumulative output since the beginning of the financial year and the moving annual totals at the same intervals. The Z- chart can be used to show both the plan and the performance and deviation from the plan can be easily indicated by knowing the gap between two curves.

2. Order progressing: It is concerned with the control of internal orders and purchase

requisitions. There are four main progress record systems in use for this purpose.

(a) Due date filing: It is simplest of all order progressing systems. It involves the filing of copies of all orders in a box file in due date sequence. Order copies are removed from the file only

when they are completed. Feedback is though orders overdue list normally prepared once in a week and circulated to all the concerned.

(b) Order delivery records: The typical order delivery record shows the deliveries and schedules requirements for purchased part.

(c) Operation progress records: It is a record concerned with the type of order normally completed and delivered all at the same time as one complete batch. It is a record used to show the state of completion of a batch.

The advantages include the following:

(i) It shows the position of all work in the shop. (ii) It shows operations which are behind schedule.

(iii) It shows how much work has been scrapped at each operation.

(d) List order progress: It is a type of order processing associated with standard batch control and occasionally with base stock control, job loading and period batch control. A measure of the progress achieved is given by the number of items on the list which still await completion and for full control of the orders it is necessary to maintain records showing which items still have to be finalized.

3. Shortage chasing: It is job of comparing the actual availability of materials and parts with

the quantities required for production and of reporting any shortages so that they can be produced quickly.

4. Daily plan progressing: It is the control used at the third level of production control to see

that the daily plans made during dispatching are achieved.

The most effective and general method used is to have a departmental meeting every morning to review the progress during the previous day. A weekly reporting by the departmental manager to his superior is usually sufficient to maintain the efficiency of progressing.

5. Departmental progress control: It is a method used to assess the efficiency of the different

production departments in a factory by recording number of failures to complete orders by due-date in each department at regular intervals and by comparing these quantities with the prescribed limits of performance. Feedback system determines the efficiency of the control systems.

UNIT – V