PRODUCTION PLANNING AND CONTROL IN DIFFERENT PRODUCTION SYSTEMS
PPC in Job Production
Job production involves manufacture of products to meet specific customer requirements of special orders. The quantity involved is usually small. Examples of job production are manufacture of large turbo generators, boilers, steam engines, processing equipments, material handling equipments, ship building etc.
Under job production, we may have three types according to the regularity of manufacture namely :
1. A small number of products produced only once.
2. A small number of products produced intermittently when, the need arises.
3. A small number of products produced periodically at known intervals of time.
When the order is to be executed only once, there is either scope for improvement of production techniques by introducing intricate method studies, special tools or jigs and fixtures unless the technical requirement justifies it. But if the order is to be repeated, jigs and fixtures, tools as well as specially designed inspection gauges should be carefully considered to reduce the manufacturing cycle time.
PPC function is relatively difficult in job production because of the following reasons
1. Every job order is of a different nature and have different sequences of operations. There is no standardized routing for job orders.
2. Specific job orders are assigned to different work stations as per the availability of capacity.
3. Production schedules drawn depend on the relative priority assigned to various job orders.
4. Scheduling is dependent on the assessment of production times and estimating is based on judgment.
PPC in Batch Production or Intermittent Production
Batch production is the manufacture of a number of identical articles either to meet a specific order or to satisfy the continuous demand. The decisions regarding tooling and jigs and fixtures are dependent on the quantities involves in the production batch.
In batch production too, there can be three types namely:
(a) A batch produced only once.
(b) A batch produced repeatedly at irregular intervals, when the need arises.
(c) A batch produced periodically at known intervals, to satisfy continuous demand.
Here again, planning and control become more simplified as quantities increase and as manufacture becomes more regular. Two problems that may arise in batch production are due to the size of the batch and due to scheduling of production.
The solution to these problems depends on whether the production is governed by—
(a) External customer orders only
(b) Whether the plant is producing for internal consumption i.e. a sub-assembly used in the final product.
If it is the case of external customer orders, the customer order size usually determines the batch size. The timing will also depend on the delivery dates specified by the customers. If it is for internal consumption, both batch size and production scheduling problems are matters for internal management decisions.
The problem of optimal batch size has to take into account the set-up costs which are involved, before each production runs and the inventory carrying costs incurred, when the finished product is held in stock. The batch size determines the length of the production run and affects both the production schedule and batch size considerations of other products.