RESEARCH – The author reflects on several highly-ranked academic publications to paint a picture of salient lean knowledge, both past and present, and suggests several avenues for future lean research.

Words: Daryl Powell, Chief Scientist, SINTEF

"If you come to a fork in the road, take it" is a famous quote ascribed to Yogi Berra, a late American baseball catcher, manager, and coach. After more than three decades of lean research, it certainly seems as if we have reached one such fork.

First introduced in John Krafcik's 1988 paper The Triumph of the Lean Production System and later popularized by the book The Machine that Changed the World by Jim Womack, Dan Jones, and Daniel Roos, Lean Production has arguably become the most successful approach to business improvement of our time. It has outlasted many other improvement approaches and it has been adopted by organisations in all kinds of industries, the world over.

At the same time, it seems to have become one of the most misunderstood business phenomena – one that causes very heated debate both online and offline in a variety of fora. But what does academic research say about the lean phenomenon? Where has this research come from and where is it going? In this article, I’d like to reflect on a selection of journal publications from the Journal of Operations Management (JOM) and the International Journal of Operations and Production Management (IJOPM), the most highly ranked academic journals in the field of Operations and Technology Management (see the Chartered Association of Business Schools Academic Journal Guide, 2021). These publication channels have also produced some of the most frequently cited works about lean production.

THE PAST

With more than 3,600 citations, Rachna Shah and Peter Ward's Lean manufacturing: context, practice bundles, and performance (published in JOM in 2003) is the most highly cited lean research article and clearly demonstrates that the implementation of lean practices (or rather practice bundles – just-in-time, total productive maintenance, total quality management, and human resource management) has a positive impact on operational performance. From the perspective of running factory operations, this article provides sound advice for manufacturers seeking operational excellence. But let's not forget that Lean Production was originally presented as an organization-wide endeavor. What then, does previous lean research say about this?

Both Christer Karlsson and Pär Åhlström's Assessing changes towards lean production (published in IJOPM in 1996) and Matthias Holweg's The genealogy of lean production (published in JOM in 2007) present the scope of lean production as it was first described in The Machine that Changed the World:

• Designing the car (lean product development);

• Coordinating the supply chain (lean procurement);

• Running the factory (lean manufacturing);

• Dealing with the customer (lean distribution);

• Managing the enterprise (lean enterprise).

The genealogy of lean production provides a detailed account and history of the Toyota Production System (TPS), the International Motor Vehicle Program (IMVP), and the development of the assembly plant benchmarking study. It also describes the developments from just-in-time manufacturing to lean production. Holweg states that, although the publication of the “Machine” sparked a wealth of research into the adoption of lean manufacturing best practices, it also provided a much larger remit than operational improvement in the factory.

However, though Karlsson and Åhlström fully accept the stance of Machine to conceptualize lean production, recognizing at first its true scope, they proceed to take a much more operational view of the changes required when moving towards lean production – adopting an elimination of waste perspective (waste elimination was also presented in the 2003 Shah and Ward work as a core construct of the lean production philosophy). As such, the authors provide a model that operationalizes the different principles in lean production, albeit with a focus on those that concern the work organization in the manufacturing part of a company only.

THE PRESENT

Given that efficient operations are a primary focus of operations management research, it is perhaps no surprise that most lean research has been tainted with a blinkered view of operations. However, to realize the true promise of lean production requires the adoption of a much wider scope. And here lies the dilemma. Contemporary lean research presents us with a choice – a fork in the road, if you like.

On the one hand, lean research is set to continue cruising down "highway operational excellence" – with an unhealthy focus on best practices for the purpose of waste elimination and efficient operations only. For example, Wallace Hopp and Mark Spearman's recent paper The lenses of lean: visioning the science and practice of efficiency (published in JOM in 2021) equates lean with efficiency management, where the authors regard anything that increases the efficiency of delivering products as a lean practice and suggest that although the pursuit of efficiency is a never-ending journey, lean as a title may have an expiration date. Such a reductionist view of lean is very unfortunate and offers little for the future of lean research.

Likewise, in the 2021 paper A lean view of lean (also in JOM), Tyson Browning and Suzanne de Treville explore operational attributes that underlie lean and operational excellence, themselves presenting lean through several different lenses, including efficiency, less waste and more value, and the TPS. They ask the question What is lean? Is it a phenomenon? An ideal? A philosophy? A way of thinking? A collection of practices? A strategy? Widespread agreement is lacking – and in that respect I agree. However, to “sharpen our concepts and definitions”, Browning and de Treville conclude that lean has evolved from its original conception in the 1980s as “what Toyota did” towards general operational excellence. At the risk of “outgrowing its name”, they suggest that lean can be given a longer life if we limit its scope to a list of best practices from 1994, including JIT, small-lot production, production levelling, and work standardization (see Cusumano, M.A. (1994) The limits of lean. Sloan Management Review, 35(4) pages 27-32 for a more comprehensive overview). In my opinion, if this is the future of lean research, there is a risk that lean research is already dead.

But there is hope. The alternative direction for lean research, the one that takes the road less traveled, presents lean as a holistic socio-technical system. It talks about it as an education system, with organizational learning and continuous improvement at its core. For example, in the 2021 IJOPM paper Is lean a theory? Viewpoints and outlook, Pär Åhlström, Pamela Danese, Peter Hines, Torbjørn Netland, Rachna Shah, Matthias Thürer, Desiree van Dun and I discuss the role of theory in lean production. We agree, disagree, and sometimes agree to disagree, but in doing so, provide a much brighter outlook for lean research (in my rather unbiased opinion).

Åhlström presents lean as a practice-based umbrella concept with flow efficiency at its core, while Thürer suggests that just as the theory of swift and even flow seeks to explain the law of variability, lean can be considered as a theory to explain the law of just-in-time. Hines acknowledges that it is rather difficult to establish a theory of lean when there is little agreement about what the term really means, while Netland draws lean not as theory, but a business phenomenon – capturing all previous attempts to define lean under one roof (e.g., waste reduction, bundles of practices, a cultural transformation, and a learning system). Danese presents lean as a socio-technical system that has advanced from a focus on the adoption of lean tools to the managerial approach that underlies lean organizations – based on systematic routines that foster scientific reasoning. Van Dun also discusses several contextual factors for successful lean adoption, including organizational learning, customer-orientation, closely engaging with suppliers, and adopting transformational leadership behaviors.

And this leads me, a lean pracademic who has studied and led lean transformations for the past 15 years, to my current research. My most recent work with Paul Coughlan, the 2020 paper Rethinking Lean Supplier Development as a Learning System (in IJOPM), highlights the development of a learning-to-learn capability as a critical success factor for a sustainable lean transformation. For me, lean is neither TPS nor the Toyota Way. Rather, it is an attempt to generalize and replicate the performance lessons from Toyota – outside the company, the industry, and the country. As such, I like to think of lean as an education system, and as Dr W. Edwards Deming said, “without theory, there can be no learning”. That’s why I present lean as a meta-theory, or a theory of theories, consisting of:

• a better production theory with the TPS to teach better thinking to everyone, everywhere, every day.

• a better product development theory with the chief engineer (shusa) system to develop reliable products at affordable cost.

• a better management theory with Toyota total quality control (TQC) to involve staff and back-office operations in the continuous development of people – fostering greater levels of teamwork for increased global effectiveness.

• a better economic theory with Hoshin Kanri – starting from product-planning all the way to policy deployment – to better understand the business problem(s) and scope the true potential for regular product renewal in every segment, supporting the vision of “one-time customer, lifetime customer”.

• an underlying psychology theory with kaizen, which recognizes that a person’s sense of achievement stems from contributing towards the development of better products by practicing continuous improvement (this rests on a shared understanding of problems, supporting teamwork, and encouraging kaizen mindset).

As the saying at Toyota goes: monozukuri wa hitozukuri (making things is about making people).

THE FUTURE

So, what about the future of lean research?

I, for one, believe that as lean researchers, we must expand our focus from realizing efficient delivery systems to creating effective discovery systems. By embracing lean as an education system rather than a production system, we can turn the lean tools into frames for learning – promoting growth through personal mastery and organizational learning.

Operational excellence research will for sure continue, to some extent examining the combination of digital technologies with analogue lean practices in what has been coined the era of digital lean manufacturing, or lean 4.0. But the real challenge lies in discovering how such technologies can help operators, engineers, and managers to gain improved insight to better create value by solving more customer problems – while simultaneously reducing waste by consuming less resources. This also requires lean researchers to explore the role of Lean Thinking in sustainability initiatives, for example in achieving the United Nations' Sustainable Development Goals.

Does Lean Thinking hold the key to a waste-free society? Time will tell!

_{THE AUTHOR}