Batch Production – Problems and Prospects

Material requirement planning (MRP):

The master schedule gives us the end products (final products) per period and the work force levels. Given this, MRP calculates the timing of all sub-assembly component and raw material production and purchasing activities necessary to satisfy the master schedule. MRP is done with a view to minimizing WIP inventory. Because of voluminous data, most MRP systems are computerized.

The process of determining component and sub-assemblies from the master schedule of end products is called Parts explosion requirements.

Line of Balance (LoB) for control of batch production:

Batches are split to study the progress of jobs periodically, and with reference to delivery schedule. We begin with the delivery schedule, and construct an operations program. While reviewing a program progress chart is drawn. Above this chart is drawn a line (LoB) which shows the requisite number of items which should have been completed at each operation at the review time. Analysis of progress is then done. Shortage and non-conformance to schedule are identified. LoB is management by exception.

Here, WIP and the lead times are large. Requirement planning is a tool to overcome this. MRP, however, needs computerization. Kanbaan system of Japan emphasizes the reduction in production lead times and WIP by using shorter production runs of a particular product.

FMS: Flexible Manufacturing system is also a tool to overcome problems of batch production. FMS machines though general purpose are versatile enough to perform different operations which are linked by material handling system. The machines and material handling are controlled by a computer system. FMS makes possible machining of desired mix of parts in a given time period. It reduces WIP and increases machine utilization in small batch manufacturing.

Batch scheduling:

There are basically three batching methods:

1. Individual batch size fixed for each part.
2. Aggregation of parts which are treated as one batch.
3. Fixed batch quantity for a product rather than of parts.

Irrespective of the batching method used, we have to decide the order of processing the batches at the various stages of production. Suppose a certain machine has to take four batches for processing. It means this can be done in 24 ways. The more the number of batches the greater are the ways of ordering the batches. e.g. 8 batches give over 40,000 ways. It is difficult to choose the particular scheduling sequence. We have to keep in mind the objectives of a schedule and its significance. Are we aiming to reduce the idle machine time or work-in-progress (WIP) or production costs? These may be desirable objectives, but in practice, they come in conflict. In a particular situation, we have to make assessment of their costs. The problems should be kept simple by scrutinizing the product range and parts made for which a simple manufacturing process can be designed. Jobs which are troublesome are contracted out. Scheduling problems are eased by excess capacity. However, loading a plant fully increases the scheduling problems.