EPEI describes a concept in the context of Heijunka to level and smooth mixed model production. EPEI reduces the batch size and distributes the model mix evenly throughout the day by splitting big volumes down so that Every Part is produced in Every Intervall. Its target is to manufacture products in the smallest batch size possible to achieve maximum robustness and flexibility. To use EPEI, manufacturers need to be advanced in lean techniques and certainly have implement line balancing and SMED concepts first to meet the prerequisites for EPEI.
A demand forecast consists of the total number of products and their mix for a certain timeframe. The demand is then broken down into weekly/daily and hourly schedules. The weekly forecast for a volume of 100 products in figure 1 is broken down into daily forecasts of 20 products per day. In traditional systems, models/variants are cumulated into large batches to reduce setup times from one product to another. Therefore on Monday and Tuesday, only product A is manufactured, followed by product B on Wednesday and Thursday. Product C and D are manufactured only on Friday.
If a customer order contains products A and D, the order can be shipped on Friday at the earliest. At the same time product A needs to be stored within the warehouse until it gets shipped leading to the buildup of additional storage capacity and longer due dates.
In the first step, EPEI distributes the product volume per week equally onto each day (see figure 2). Instead of storing products in the warehouse, they can now be sent to the customer at the end of the day.
Depending on the setup time these daily schedules can be broken down into even smaller sequences. To break these batches further down, setup times need to be reduced using the SMED concept. If it is possible to sufficiently optimize setup times a one-piece flow can be introduced. Sufficiently in this context means, that the available operating time is bigger the processing and setup time combined for the daily schedule. By searching for the biggest divider (weekly:10, daily: 2) the products per sequence are calculated:
Figure 3 displays the EPEI sequence derived from the forecast.
The EPEI concept is one of the most controversial concepts within the lean toolbox. Correctly implemented EPEI enables production to directly follow the customer’s demand. Products don´t need to be stored in big warehouses, but can directly be transported from production to packaging and sent to the customers. This reduces work in progress inventory, reduces motion in internal logistics, lowers storage costs, and increases delivery reliability. On the other hand, EPEI can cause hiccups on the shop floor, when the organization has not implemented other lean principles first.
The breakdown of the demand into recurring EPEI sequences is only possible if operations on the shop floor run smoothly. Rush orders, cancellations, changes in demand forecasts, supplier shortages and defect materials may negatively impact operations. In traditional manufacturing environments, these events often cause further hiccups and result in daily fire fighting.
Digital tools such as the WORKERBASE platform distribute information to the involved operators to enable them to react to fluctuations in real-time. By pushing an unscheduled rush order into the sequence, parts, processes, and routines need to be adapted to the change. In a digitized and agile manufacturing environment, operators, logistics, quality, and all other involved parties receive a notification on a mobile device, telling them how to react to the change. The changeover app suite automatically loads the right workinstructions to set up and operate the machines based on the underlying updated sequence. The material management app suite automatically initiates the transport order and notifies the logistics operator about additional material supply at the stations. Quality controls are automatically updated for the rush order and stored within the quality databases using the quality control app suite.
Through the combined power of these app-suites rush orders and other causes of production of hiccups can be managed, although EPEI is used to split batches into small sequences.
Author: Marius Maier, Digital Transformation Consultant, WORKERBASE