Lean Manufacturing

What is Lean Manufacturing?

Image courtesy of Reliable PlantOpens in new window

Lean methodologies applied to manufacturing are a series of techniques where work time required to produce a product is built sequentially, one unit at a time, at a formulated rate, without wait time, queue time, or other delays.

The industry’s concern to provide a product or a service with excellence to clients has opened an innumerable list of action that needs to be directed to: reducing the wastes, improve the productivity, and create a culture of qualityOpens in new window.

Lean manufacturing can be defined as a combination of multiple tools to help eliminate activities that do not add value to the product, service and/or process by increasing the value of each activity, aimed to eliminate or reduce waste and improve operations.

The goal of Lean manufacturing is to establish and design a manufacturing line capable of producing multiple products using only the amount of time required to actually build the product.

Wait time, queue time, and other delays are considered waste and are greatly minimized or eliminated in Lean manufacturing.

Lean manufacturing defines waste as: “Anything other than the absolute minimum of time and resources to add value to the product and get the highest quality” (Martine, 2003a, b).

Lean manufacturing objectives include:

  • Specify the value for the customer
  • Identify all actions required to bring the product from being a concept to being launch, from an order to delivery, from raw material to the customer’s hands and even his life
  • Remove any action that does not add value and streaming align every action to add value as required by the customer
  • Analyze the results and start the evaluation process again.

Producing Products One at a Time versus Routing in Batches

Products can be produced in one of two different ways. They can be manufactured using a one-piece Lean methodology or in batch quantities routed through traditional work centers or departments.

Batch manufacturing methods group similar work types and machines together, creating departments or work centers. These departments and work centers are usually located in geographically separate areas of the facility, and work is moved from department to department until the product is completed. Batch manufacturing allows machines and people to appear more productive when large quantities of a product are built.

While departmentalization simplifies organizational control by facilitating the collection of performance, routing, and inventory data, lot sizing is based upon what would make machines or labor more productive and not necessarily what the market requires.

This sole focus on the productivity of machines and people has pitted manufacturing departments against marketing departments throughout industry when it comes to decisions about the best utilization of those resources.

The benefits of batch processing are offset by the problems created for manufacturing when responding to actual customer demand when trying to build a dynamic mix of products and volumes.

In addition, this grouping of work and machines usually provides little consideration for the equal distribution of capacity. This unequal distribution of capacity can create imbalances between manufacturing processes. These imbalances are often manifested in pools of excess inventory residing between imbalanced departments.

One-piece Lean manufacturing is a proven technique that allows work to be performed without bottlenecks or delays.

In the Lean environment, these activities do not add value to the product and are considered a waste. One-piece Lean processing causes the reasons for delays, bottlenecks, and stoppages to be eliminated.

The Lean manufacturing methodologies eliminate these wasteful activities by linking and balancing equal amounts of work steps together, enabling products to be consumed directly into the next step, one piece at a time until completed.

The sum of the work time minus the added queue and wait time required to progress through the manufacturing processes is always shorter than the time required to route products through a factory in batches.

Visualize the flowing of products in its actual work time as if it flowed through a tube with no interruptions. This ability to produce product approaching its actual work content time is the source of significant benefits in a facility layout so that all the processes necessary to produce a product are located adjacent to one another.

Only resources necessary to meet demand are located on the Lean line. Grouping of similar labor and machine resources into departments is no longer necessary.

Without the imbalance of capacity between departments, pools of work in process cannot accumulate, causing inventories to be greatly reduced. Physically locating manufacturing processes close together allows the completed output of one process to be directly consumed into the next, dramatically reducing inventories and cycle times.

This physical linkage allows the standard work tasks to be accomplished in a sequential and progressive manner at each workstation until the product is 100% completed. Wait and queue time normally associated with batches routed through the different manufacturing departments is greatly reduced or eliminated.

The Origins of Lean Thinking

Sakichi Toyoda and his son Kiichiro, the family that founded the Toyota Motor Corporation, began to produce weaving looms and then cars in the 1930s. The approach taken by the family was to engage in a variant of flow production that later matured to become known as the Toyota Production System (TPS) and has more recently become known as Lean manufacturing.

At the heart of the manufacturing system was an attention to using simple machinery that automatically stopped, and assembly lines that could be stopped by operators, when a defect was detected (a system known as Jidoka). In this manner, no defective products would be passed forward to internal customer operations (Shingo, 1981).

In the West, large batch sizes and the responsibility for quality inspection being the role of a specialist department meant that defects could move and be hidden in buffers only to generate interruptions downstream as defects were filtered.

Other factors conspired against the development of the mass production system at Toyota, not least the lack of natural resources and large amounts of capital to fund investments in large-scale and dedicated technology.

To counteract the lack of resources Toyota engaged a production system that did not rely upon forecasts for each department but used a pull system (Ohno, 1988b).

Under the pull system, parts actually needed by internal customer operations or customers are made (called Just-in-TimeOpens in new window). As such production strictly controlled and standardized inventory buffers deliberately disconnect operations. In this way the movement of production materials from a supplier to a customer operation created a replenishment order.

The basic system was later supplemented with a deliberate approach to level the workload of each production area (called Heijunka). It was not until after the Second World War that Taiichi Ohno (Toyota’s chief engineer) compiled these practices to form the lean Toyota Production System that exists today. (Womack and Jones, 1996).

    Research data for this work have been adapted from the manuals:
  1. Dennis P. Hobbs. Lean Manufacturing Implementation: A Complete Execution Manual for Any Size ...
  2. Jorge Luis García-Alcaraz, Aidé Aracely. Lean Manufacturing in the Developing World: Methodology, Case Studies and ...