The Funnel Model – a workload-oriented production control system

The funnel model is a widely used model in practice for mapping production processes. It was developed in 1981 by Bechte at Leibniz University Hannover.

By analogy with flow processes in process engineering, the funnel model aims to map the input variables (inventory and output variables).

The aim is to be able to represent every capacity unit that occurs in the manufacturing process. The prerequisite for this is that the capacity unit fully describes the manufacturing process.

For example, the following can be represented as ‘funnels’:

• individual workstations,
• the entire manufacturing process and
• cost centres.

To this end, the funnel model is categorised according to urgency levels. According to this approach, the order book determines the urgency with which an order passing through the funnel is processed.

• Urgent order: Production of 200 modified model helicopters, delivery date promised within 2 weeks, high profit margin
• Standard order: Production of 500 model helicopters (standard version), delivery date 3 months, medium profit margin
• Less important order: Production of 150 model helicopters (old version), delivery date 6 months, low profit margin
• Backlog orders: Production of 500 model helicopters (version no longer in active production but serving as a reserve), delivery date not specified!

Incoming: Order 1 (urgent order), Order 2 (standard order), Order 3 (less urgent order)

All incoming batches (e.g. modified model helicopters and older models) form the queue of pending orders together with the batches already present there (e.g. standard model helicopters).

Queue: Order 2 (standard order), Order 3 (less urgent order)

Each incoming batch first enters a queue and is only processed once Order 1 (urgent order) has been completed.

Orders 2 and 3 are used below to illustrate this. These are designated as a standard order and a less urgent order. Both orders have a confirmed delivery date. This means that, alongside Order 1, Orders 2 and 3 must also be processed urgently. As the orders converge in the funnel, a bottleneck forms at the narrowest point, where a decision is made as to which order must be processed next. This is where the so-called queue is formed.

Output: Order 1 (urgent order)

Once processed successfully, this batch of orders flows out of the funnel first and subsequently constitutes the output. As soon as the urgent order is fully completed, Order 2 and Order 3 follow.

The funnel model assumes that the throughput behaviour of any capacity unit in a production system is fully described by the variables receipts, stock and disposals. This allows each capacity unit to be represented as a funnel.

The batches arriving at the work system, together with those already present, represent a stock of pending orders. The funnel opening describes the throughput of the work system, which can be adjusted within the capacity limits.