Lean Thinking

Womack and Jones generalise the Toyota Production System into five principles applicable beyond automotive manufacturing, following their earlier study The Machine That Changed the World.

The five principles are: specify value from the end customer's perspective, since value defined by the producer is usually the producer's convenience; identify the value stream, meaning every step from raw material to customer, and classify each step as creating value, creating no value but currently unavoidable, or creating no value and immediately removable; make value flow continuously by eliminating the batching, queuing and departmental handoffs that create waiting; let the customer pull value rather than producing to a forecast and pushing inventory downstream; and pursue perfection through repeated cycles, since each improvement reveals the next constraint.

Their empirical claim is that mapping a complete value stream in most organisations reveals that the large majority of elapsed time adds no value, with the actual work occupying a small fraction of the total. The case studies cover manufacturers in several countries including Pratt and Whitney, Porsche, Lantech and Wiremold, with before and after figures for inventory, lead time, space and productivity. The book also covers the organisational difficulty, including that value streams cross departmental boundaries and that departmental optimisation is what produces the waste.

The examples are manufacturing and the translation to service and knowledge work, which the authors attempted later, is harder than they present it. Lean has been widely implemented as a cost-cutting programme rather than as the system described, which the authors have criticised. The value stream mapping method is the tool practitioners use.