Lean principles have been applied since the 19th Century. In 1880, Eli Whitney, the inventor of the Cotton Gin, a machine to remove the seeds from cotton, popularized the use of interchangeable parts. This was important as identical parts could be produced and inserted into an assembly without custom fitting or relying on craft manufacturing processes. Then in the 1900’s Frederick Taylor, a mechanical engineer who sought to improve industrial efficiency published a book called The Principles of Scientific Management. In this he discussed efficiency techniques and performed time studies which developed the concept of standardized work. In 1909, Frank and Lilian Gilbreth expanded on Taylor’s work, they focused on time and motions studies and the elimination of the non-value added portion of work to increase employee efficiencies.
In 1913, Henry Ford, an American industrialist and the founder of the Ford Motor Company developed the assembly line technique of Mass production, which combined the concepts of interchangeable parts, standard work and flow. Ford focused on four basic elements of manufacturing – people, machines, tooling and materials or products. In Ford’s assembly line, a semi-finished assembly moved from workstation to workstation and interchangeable parts were added in sequence until the final assembly was produced. This resulted in less labor and faster assembly of a finished product and made the sale of affordable automobiles available to the general public.
In 1945, Taichii Ohno a mechanical engineer from Toyota, continued development of Henry Ford’s assembly line concept. He developed the Toyota Production System (TPS), a novel manufacturing approach, that disrupted the entire automobile market. It allowed Toyota to rapidly manufacture low cost and high quality automobiles quickly and by 1972 Toyota had produced 10 million vehicles. At the crux of it, Ohno believed that reducing inventory would make the business stronger and more agile. He developed the concept of Just in Time production, eliminating or reducing inventory, creating a pull system that aligned the incoming raw materials from suppliers with the production process and customer demand forecast. In conjunction, he developed Kanban, a sign-based scheduling method that shows goods in, goods in process and goods out and avoids overcapacity of inventory and work in-process. In contrast to the assembly line, they adopted assembly cells. Machines were lined up in process sequences with quick setups that contained all the required materials and tools. Raw material flowed to the cell and a subassembly or fully assembled product leaves the cell. Workers were cross-trained to do some or all assembly tasks and had other extended responsibilities such as production scheduling or preventative maintenance. Workers were encouraged to stop the production line if they noticed any problems in the production process. This helped to reduce errors and improve quality in a culture of continuous improvement called Kaizen. Ohno was focused on the flow of the product through the total process and elimination of any waste in the process, He described this as Muda, Mura, Muri. Muda refers to waste in the process such as inventory, transportation, motion, waiting, over-processing, overproduction and defects. Mura refers to unevenness in the process, also known as workload volatility. Muri is overburdon, the over loading of people or equipment. Through TPS, it was possible to rapidly produce high quality products at low cost to the customer.
In 1990, James P. Womack, Daniel Roos and Daniel T. Jones, provided a comprehensive description of the entire lean system. They documented its advantages over mass production and articulated the principles and advantages of lean production. The key concepts outlined were:
- Specify the value
- Identify the value stream for each product
- Remove any non-value added activities
- Make the product flow
- Introduce pull between all steps
- Manage toward perfection ensuring the number of steps and the amount of time and information needed to serve the customer continually falls
With the success of Toyota, other industries successfully followed suit such as Boeing, Intel and Motorola. Nowadays, lean thinking continues to spread across diverse industries such as non-profits, services, retail, healthcare, construction and even start-ups and across every country in the world. Industries are adopting and adapting lean tools and principles beyond manufacturing and to great success.