What is Scheduling ?
Scheduling may be defined as the process of arranging the work associated with the manufacturing process with a view to (i) having the optimum output, and (ii) keeping a control over the entire process. As part of this process, the work is assigned to the plant with appropriate time-frame for each operation and the sequence in which they need be carried out. Backward as well as forward scheduling is used by the manufacturers to (i) allocate plant and machinery resources, (ii) plan human resources, and (ii) plan production processes and purchase material.
Scheduling provides short-term production planning, which may be as short as on daily basis or weekly basis. Such short-term planning is not warranted in the continuous production system or the mass production system (assembly lines) or large batch production.
Scheduling consists of the following steps :
- Assignment of the quality and rate of output, specific to a plant or a department.
- Stipulation of time-frame in respect of each operation and the sequence thereof. Beginning and completion of each operation is prescribed along with the order in which they have to take place.
Scheduling would emerge as following from the above definition :
- Stipulation in respect of place, time and the order in which each operation necessary to manufacture a product needs to be performed.
- Prescribing the timings of the beginning and completion of each operation involved in the process.
Definition of Scheduling
According to Kimball and Kimball :
"The determination of time that is required to perform each operation and also the time required to perform the entire series as routed is scheduling".
According to James L. Lundy :
"Work schedulibg consists of the assignment of starting and completion time for the various operations to be performed".
According to Spriegal and Lansburgh :
"Scheduling involves establishing the amount of work to be done and the time when each element of work will start or order of work".
Functions of Scheduling
The functions of scheduling basically include dealing with the problems related to the production process. They may be summarized as follows :
1) Assignment :
Allocation of orders or jobs amongst various work centres.
2) Sequencing :
Stipulating the specific sequencing of various operations, which are required to be. performed at a specific work-centre.
3) Dispatching :
Ensuring the beginning of the work at various work centres.
4) Monitoring and Controlling :
The progress of the work assigned to various work-centres needs to be monitored on an ongoing basis, and wherever required, necessary adjustments in the schedules are made.
Objectives of Scheduling
The objectives of scheduling may be summarized as follows :
1) Customer Satisfaction :
The prime objective of the scheduling is customer service. The date of completion of a job is determined through the scheduling, which in turn put pressure on all the operative heads ensure adherence with the pre-decided time-frame in respect of each step involved in the process. The result is timely finished product in hand, ready for delivery to the customer. Elevation in the customer satisfaction level leads to an improvement in the manufacturer's image, followed by a series of orders from the old as well as new customers.
2) Optimization of Cost :
Pre-mature or delayed completion of any job by a manufacturer may prove to be costly for it, in view of the following :
- If a job is completed by a manufacture before the scheduled date (pre-mature completion), the inventory of finished goods or work-in-progress (WIP) stands at a higher level. The result is obvious more wastage and higher cost.
- Any delay in completion of a job by a manufacturer is likely to lead, idling of machines, which are required to wait for next activity in the transformation process. This waiting period acts against the optimum utilization men and machines, and as such proves to be costly for the organization.
3) Increase in Efficiency :
It is a well-established fact that a remarkable improvement is brought about the shop-floor people in the schedule finalized by the planning department of any organization. This comes naturally as a result of the expertise, knowledge and experience of the shop-floor people. Therefore, the overall efficiency of the shop-floor, credit also needs to be given to the scheduling (in addition to the people). The efficiency may further be enhanced by grouping together the orders with identical components, requirements, activities and set-ups.
4) Reduced Variances in the Transformation Process:
During operation of plant, the transformation process is subjected to a number of variations. However, this is smoothed through the process of scheduling of operations and activities, especially if one work centre is overloaded and congested due to disproportionate work. Scheduling acts as an equalizer, by raising the levels of orders allocated to comparatively idle work centres to keep them busy while decreasing the workflow: to the overloaded work centres. Detailed scheduling is the solution for both the extreme cases, viz. problems of heavy workload at one work-centre, and insufficient workload at other work centre, due to idle machines.
5) Employee Focus in Scheduling :
In scheduling. the role played by the company's employees is a significant one. Their competence and expertise can ensure the timely completion of any job. At times, specific scheduling is required to be chalked out in respect of individual employees; the extent of this may be gauged from the fact that non-availability of a key employee, having an expertise in a particular field, may lead to the re-schedule of the job by the scheduler. In this regard, experience of an employee is of paramount importance, as the availability an out of experienced employee may ensure sorting out any unforeseen problem. In view of the above, it would not be an exaggeration if a statement is made that the success or failure of a schedule largely depends on the skills and experience of the manufacturer's employees.
Types of Scheduling
The scheduling pattern is not uniform in all the cases, it is job specific. In other words, it varies from job to job, as is evident from the following facts :
1) Production Schedule :
Production scheduling is chalked out with a view to ensuring that the amount of work is conveniently carried out by the plants, machinery, equipment, etc. without any outside intervention. While taking decision in this regard, following points need to be taken into consideration :
- Type of the available facilities in the plant, which are necessary for the processing of the scheduling material.
- Individuals or workers with requisite expertise and experience for undertaking the work involved, which includes operating the machinery, equipment etc.
- Various required materials & purchased parts.
2) Master Schedule :
Preparation of the master schedule is the first step in the scheduling exercise. Master schedule involves breaking down of the weekly or monthly requirement in respect of each product for a certain time-frame. This running record of the total production requirements enables the manufacturer to change the production exercise from one product to another according to the changed production requirements. Master schedule is the basis of a all the successive scheduling activities. Master schedule is invariably followed by what is referred to as the operator schedule, which (i) stipulates the requirement of the total time for performing a job using a particular machine or (ii) shows the requirement of the total time for carrying out each operation of a specific job with a specific machine or process.
3) Manufacturing Schedule :
Preparation of manufacturing schedule depends upon the nature /pattern of manufacturing process Manufacturing schedule is of extreme use in the cases, where the production of a single or few products takes place in a repetitive manner on a regular basis. It shows the necessary quality of order and each product in which the same needs to be operated.
4) Parts Scheduling :
Parts scheduling provides the information with regard to the number of units required to be produced in respect of various parts of a product. It is prepared on the basis of master schedule every month giving the details i of production for every week.
5) Machine Loading Schedule :
Machine loading schedule is associated with the earmarking of work load for different machines. It acts as a time-schedule to be followed by different machines. It is prepared on the basis of parts schedule every week giving the details of production for every day.
6) Scheduling of Job Order Manufacturing :
Scheduling of job order manufacturing is of paramount significance. It facilitates prompt accomplishment of the work at all the individual centre points.
Techniques of Scheduling
Techniques used for scheduling are as follows :
Job Sequencing Rules
Sequencing may be defined as the arrangement of a series of activities in a particular order. It is a process, which establishes the priorities to be given to various job orders in the manufacturing process. The priorities are decided in terms of 'priority rules' for job orders. However, in a scenario of availability of multiple choices in the job sequencing, a real challenge is faced by the operations manager. Under such circumstances. 'effectiveness' is the factor, on the basis of which a decision is taken with regard to the order or sequence of the tasks are required to be performed.
Gantt Charts
The Gantt chart is an improvised kind of bar chart, wherein horizontal bars are used to show each activity in ratio of the time required for its completion. For the monitoring purpose, a cursor is attached to the chart, which can be used to compare the actual performance as at a particular point of time vis-a-vis the planned one, by moving it cross the chart. Gantt charts are good monitoring tool, but they have their limitations, as they are not of any help to the management for deciding the priorities to the job orders.
Queuing Analysis
Queuing analysis is associated with the study of queuing systems and waiting lines. A queue may be defined as a line or sequence of customers or units waiting for their turn to be attended to or to be serviced. The length of a queue depends upon the rate of arrival of customers and the rate of service provided to them. When rate of customers' or units' arrival is more than the rate of providing services to them, a queue is formed, and the customers or units are compelled to wait for their turn to receive the service. For the service provider, it is necessary to keep this waiting period at the bare minimum, as it has some cost for them. The length of may be reduced by the service provider queue may through an increase in the rate of providing the services by improving the capacity of service facilities.
However, if the customer or unit arrival rate reduces, the service facilities are rendered idle. Therefore, striking a balance between the rate of customers' or units' arrival on one hand and the rate of service provided to them on the other is of paramount importance.
Queuing analysis may be effectively used by the operation's managers to strike necessary balance between the costs of waiting period and the costs of providing additional service facilities. Determination of the optimum number of service centres becomes easy through the queuing analysis.
Critical Ratio Method
This method is a job sequencing technique popular amongst the operations managers, who use it to ensure timeliness with regard to the operation of a job, i.e. to verify whether a job is being carried out as per the schedule or is lagging behind. The critical ratio of a job is computed by operation's managers with the help of the following formula :
Actual Time Remaining
Critical Ratio = ----------------------------------
Scheduling Time Remaining
Critical ratio of an operation below one is indicative of the fact that the operation is lagging behind the schedule, whereas if the value of the critical ratio is more than unity, it indicates that the operation is ahead of the schedule. Once it becomes clear that the operation is lagging behind or ahead of the schedule, appropriate measures can be taken by the operation's manager, and re-prioritization may be accorded by him.
Factors Affecting Scheduling
There are certain factors, which play a crucial role in the implementation of the scheduling, and as such need to be taken into consideration at the time of finalizing the scheduling plan. These factors may be within the control of a company's management (internal) or beyond that (external), they are discussed in the following points :
1) External Factors :
The external factors are beyond the control of the management. They are governed by the outside forces, on which the company's management has no control whatsoever. The management makes an effort to make necessary adjustments with those forces, so that the company's interests are kept protected. Some of the external factors are as under :
i) Customer's Demand :
The assessment of customers' demand is done through the sales forecasting. In the case of manufacturers engaged in continuous production, scheduling is done on the basis of forecast of sales level pertaining to the specific items. However, in the case of manufacturers not engaged in continuous production the forecast is based on the expected volume of business in rupee terms.
ii) Customer's Delivery Dates :
The scheduling in the cases of continuous production of goods, having cyclical demand, is planned such a manner that a balanced level of production is maintained throughout the entire year, and the inventory of finished goods continues to be sufficient to meet the demand at any period of time. In the cases of intermittent production, the cyclical demand is met by delivering the products on the due date as per the customers' order. Additional t orders are normally accepted only if they accommodate into the planned production.
iii) Stock of Goods Already Lying with Dealers and Retailers :
In the cases of continuous production of standardized items, there is a possibility of a scenario, wherein dealers and retailers are having the stock of goods. Normally they maintain adequate level of stock with them. It is necessary to plan the scheduling, keeping in view the stock position of the dealers and retailers.
2) Internal Factors :
Internal factors are those, which can be monitored and controlled by the company's management. There is a need to manage such factors in an appropriate manner during the scheduling, so that the objectives of the production function are achieved in an efficient and cost-effective manner. Some of the important internal factors are listed in the following points :
i) Stock of Finished Goods with the Firm :
In the cases of continuous production, where the production is continued with the objective of stock-piling, scheduling is required to be planned, keeping in view the level of goods in stock with the dealers / retailers Normally, the stock is kept at a level, which is considered sufficient for certain duration supply on hand. The forecasting in respect of new sales as well as the scheduling needs to be made on the basis of the variations in the stock holding.
ii) Time Interval to Process Finished Goods from Raw-Material :
The time taken for the processing of raw-materials into the finished good, i.e. the time required to manufacture each component, sub-assembly and assembly (i.e., the finished good), is one of the most important internal factors.
iii) Availability of Machines :
The production various machines and capacities of various equipment's are variable. It is advisable to take the help of "machine-load charts" for arriving at their occupancy scheduling.
iv) Availability of Manpower :
Significance of the manpower cannot be undermined under any circumstances, and as such the scheduling should be finalized keeping in view their availability. In cases of urgency, the production may be rushed through by resorting to overtime working, extra shift working or hiring of the temporary labour. Inefficiency in this regard needs to be dealt with in a strict manner. If need be, the shirkers may be adjusted through transfers. The layoffs should be kept at the lowest level. Induction and adequate training to the new employees should be given priority.
v) Availability of Materials :
Availability of the raw materials is of paramount importance for an uninterrupted production flow. Adequate stock level is a basic requirement for a successful scheduling. In the cases of possible stock-outs of crucial items, additional efforts are required to be made for their procurement at the earliest. In the meantime, limited stock should be used in a judicious manner, by issuing them for the sustenance of the critical operations. In such scenarios, the scheduling is also required to be changed in order to be in sync. with the critical situation.
In the cases of intermittent production, "the bill of materials" (enlisting the need of specific order) should form the basis for the procurement of the materials. Scheduling would be leveled by such process.
vi) Manufacturing Facilities :
Provision and availability of manufacturing facilities like power requirements, material handling services, store-keeping, work-bench area and such other facilities should be adequate. which would ensure the smooth flow of the production without any interruption. Scheduling function would also be facilitated by appropriate manufacturing facilities.
vii) Feasibility of Economic Production Runs :
Normally, two costs are subjected to comparison under the economic lot production; they are set-up cost and the carrying cost. These two costs are equated under these production systems.