EPEI (Every Part Every Interval) is used in the context of harmonising production and is a concept from Lean Management. It is the precursor to the well-known One Piece Flow. Users try to manufacture each product once in a defined time interval by keeping batch sizes as small as possible. In doing so, one must not produce less than the calculated smallest possible batch size, otherwise there will be a set-up collapse. With EPEI, in the best case, something is produced exactly when the client asks for a product.
EPEI, also known as 'Heijunka', which literally means "levelling" in Japanese, defines the time that elapses from manufacturing to production of a good. The targeted EPEI goal is to maximise flexibility, which in turn has implications for inventory levelling and production. The central goal is to bring demand, inventories and also production capacities into the greatest possible harmony and to reduce overcapacities and buffers that were needed for peak times in production. For this purpose, the EPEI divides production into lots of different sizes, according to capacity possibilities. The lots are produced in cycles, for example to meet a very sudden, unpredictable demand and to keep the stock from stagnating.
The production time required is usually referred to as an 'interval' and is defined in days, hours or even minutes, depending on the product. These EPEI intervals can be single or several short shifts in the factory or can extend over a whole quarter. It depends on the product and the existing demand. The point of EPEI is to avoid too much fluctuation or, if there is fluctuation, to spread it out cleverly over a period of time so that production is as smooth as possible.
But EPEI cannot be implemented with paper, pencil and paper. Rather, modern technologies ensure that all components are utilised: In the warehouse, for example, these are distributed IoT sensors in conjunction with advanced tracking methods that enable the inventory to be monitored with pinpoint accuracy. When developing EPEI intervals, several factors must always be taken into account in order to avoid waste: the changeover time of machines, the number of units, the number of models, and the cycle and interval lengths. When all these influences are accurately captured, measured and implemented, EPEI, in close connection with the networking and use of IoT sensors, RFID tags and digital twins, is essential for Industry 4.0.
Properly planned and executed, EPEI can generate the advantage of keeping up with all incoming orders and being able to react quickly and adequately even to last-minute orders. Machines are retooled at short notice and appropriately, expensive downtime is avoided while other machines continue to run as planned. At EPEI, the increase in efficiency lies both in production and in significantly shorter warehouse downtimes. To achieve this, data-driven forecasts are used to calculate precise demand forecasts.