Lean Manufacturing – and by extension “lean” in all business activity – is a management philosophy which focuses on uninterrupted product flow through value-added processes, a pull system that cascades back from customer demand, and a culture of continuous improvement [1]. Although many of the precepts of lean thinking date back to manufacturing theorists and practitioners such as Taylor, Ford and Deming, the complete philosophy was developed largely by Toyota’s Taiichi Ohno. Although first publicly described as early as 1977 [2], it was not widely noted in the West until popularised by Womack in the early 1990s [3, 4]. Since then it has been heavily studied and implemented, to the point where “Any manufacturing manager or production engineer who has not engaged with these principles at some level (even if to reject them) can fairly be called an amateur” [5]. Although TPS remains the benchmark implementation of lean manufacturing, subsequent growth and westernisation of the philosophy, along with “continual improvement” in Toyota’s own interpretation of it, has resulted in popular concepts of lean thinking diverging from Toyota’s implementation of it.
In practice, lean (or TPS) is often viewed as a set of tools for the elimination of waste from production systems, and as an outgrowth of management practices such as TQM and JIT [see, for example, 6]. This approach is criticised by many lean proponents and is in marked contrast to the outlook of Ohno, whose publications on the subject concentrate upon the underlying philosophies, with only superficial attention paid to the tools [7].
Critics have referred to lean techniques as “management by stress” [8], and there is evidence within the writings of both Womack and Ohno to support this view [9]. The principles of kaizen and JIT require repeated stressing of the system (and therefore the people within it) to reveal and therefore eliminate problems. There is an internal inconsistency here in that this stress is itself a source of muri (overburden – pushing workers or machines beyond their capacity). It has also been noted that many lean implementations – including Toyota’s – rely heavily on shojinka (“the adjustment and scheduling of human resources”, exemplified in critics’ view by short-notice and unpaid overtime), which has the effect of providing an externalised labour buffer which makes the elimination of other buffers possible [10]. On the other hand, it can be argued that a “correct” implementation of lean principles results in the creation of labour “slack” through initial improvements, and relies on this to resource ongoing kaizen activities, therefore providing an internal rather than external labour buffer. Further, the principle of heijunka (workload levelling) aims to eliminate the need for both material and labour buffers. The application of lean thinking to NPD has been an area of significant interest in the past decade, although Smith & Reinertsen [11], among others, have previously advocated some of the underlying approaches Recent developments have been driven mainly by the aerospace and construction industries.
Some aspects of lean manufacturing have obvious analogues with NPD. On the whole, these align well with the focus of previous NPDM trends. For example, the principles of flow and transport minimisation which result in “cell” based manufacturing fit the thinking driving the CE staple of co-located cross-functional teams, while elimination of buffer stocks and batch-based operations are key tools of APD.
On the other hand, in other areas the analogy is less obvious. NPD is an information processing operation, and information differs from physical products in important ways:
- It can be in more than one place at a time
- Reprocessing (by iteration) can add value
- Its value is not always immediately visible or easily defined
- It is (by definition) impossible to fully define a process for processing it
These differences lead to difficulties in applying lean to NPD, and in their recent survey of lean NPD literature, Baines, Lightfoot, Williams, & Greenough [12] found that many of the key issues remain unresolved in the literature. Much of the recent work [e.g. 13, 14-16] focuses upon narrow areas such as definitions of value, it being apparent that without a clear understanding of what NPD work is value added, waste may go unnoticed. This is a particular problem in large complex projects, where value is often not readily defined. Of more system-focused work, a majority minimises the difficulties by focusing upon low-innovation environments [e.g. 17], or tools and process issues [e.g. 6, 18], where the lessons of lean manufacturing are more transferable. There appears to be no work to date focusing upon small-business applications of lean NPD.
It is notable that Toyota’s own NPD system, the Toyota Product Development System (TPDS), does not follow many of the precepts which western academics and practitioners espouse, and at first glance appears to conflict with lean first principles in several areas. The system, which has been described extensively by Liker [1, 7, 19, 20] among others, is based upon “set-based” design (i.e. pursuing multiple options simultaneously). This approach inherently produces a lot of “wasted” design work, although the value of having available options can be such as to make this economical [21]. TPDS is heavily functionally oriented, and does not cross-train engineers, which contrasts with principles of flexibility and cell-based operations (i.e. cross-functional project teams). The company also make limited use of value analysis tools, and have unremarkable CAE capability [14]. For all that, Toyota continues to move towards a dominant position in their industry: clearly they are doing something right.
