Using Material requirements planning for Scheduling
A lot has been written about the problems of using material requirements planning (MRP) for scheduling. The primary problems that arise are usually:
- That MRP ignores capacity availability when determining start and due dates of planned orders.
- That MRP uses fixed lead times.
- That the MRP output does not dictate sequence of activities required in a day.
- And more
More explanations can be found on the Internet.
In this article I would like to explore an additional misapplication of MRP in the world of scheduling viz. thinking that MRP can be used for short term scheduling viz. scheduling daily activities.
The first problem is that most MRP programs work with daily calendars and any output therefore requires that outputs be manually reworked to create sequences by shift or hour.
Let us consider environments with very short reaction lead times e.g. the packing of salads and other “fresh” foods.
In this environment the customer demand changes daily and is only advised in the morning the shipment is required. Shelf life of packed products is very short, preventing the build-up of finished stocks to buffer demand fluctuations.
Daily activities, the fundamental focus of the business, need to be determined as actual demand is received. These activities are dependent on any prepared or semi-prepared materials that exist in the system.
The final schedule must advise in what sequence activities must take place at all levels, to maximise available capacity and customer service as it does not have the capability of fine sequencing.
It is clear that implementing MRP functionality will provide no benefit to scheduling daily activities.
An overall observation related to using MRP for scheduling is that it produces incorrect outputs and requires substantial manual effort to “panel beat” the result to become an executable schedule.