Mura (斑)

Mura means unevenness, non-uniformity, and irregularity. Mura is the reason for the existence of any of the seven wastes. In other words, Mura drives and leads to Muda. For example, in a manufacturing line, products need to pass through several workstations during the assembly process. When the capacity of one station is greater than the other stations, you will see an accumulation of waste in the form of overproduction, waiting, etc. The goal of a Lean production system is to level out the workload so that there is no unevenness or waste accumulation.

Mura can be avoided through the Just-In-Time ‘Kanban’ systems and other pull-based strategies that limits overproduction and excess inventory. The key concept of a Just-In-Time system is delivering and producing the right part, at the right amount, and at the right time.

Just in Time

Just-in-time (JIT) was developed in the 1960s and 1970s in Japan and is commonly known as the Toyota Production Systems (TPS).   Japan's was rebuilding during the post-World War II era and needed to solve problems they faced due to the lack of natural resources, space and cash flow.   The Japanese also suffered from high unemployment.   As the factories in Japan were being rebuilt they did not have the captial, or the space, for large warehouse and as a result they built smaller, lean, factories.

JIT has several objectives.   Companies can prioritize these objectives based on their needs.

• Labor cost reduction
• Space reduction
• Inventory reduction
• Work in Process (WIP) reduction
• Quality improvement

Typically companies embrace JIT as a way to better control raw materials through reduction of inventory levels.

There are some risks to JIT that should be considered.   The biggest risk is geography.   While Japan is a relatively small country, with all suppliers located within just a few miles of a factory, the U.S. is much larger geographically.   Maintianing a robust logistics over thousands of miles presents a large barrier to effective JIT.   Additionally, natural disasters and most recently COVID-19 have caused disruptions in the flow of goods that can have a significant impact on JIT deliveries.   Increased demand for products during these disasters are at odds with smaller inventories and can lead to shortages.

Kanban

Kanban is the Japanese word for signboard, or billboard.   In simple terms it means to display (visually) the work being performed.   The intent of kanban is to level the demand with the capcity and reduce or eliminate bottleneck.

By creating visual tools workers can see the entire process start-to-finish. Work is pulled rather than pushed reducing the amount of excess WIP.

The most common way kanban is implemented in a manufacturing environment is in controlling raw materials flow.   A "2-bin" kanban system relies on two bins of materials.   When the first bin is used up the materials group knows to replenish the products stocked at that location. Kanban cards are another method of this visualization. When the worker places the card in a specified location, the materials handlers know it is time to restock.   Kanban cards typically display the part number, description and a stock quanitity.

Kanban is not limited to only inventory within manufacturing.   Software development teams have adopted kanban as a workflow tool.   Kanban allows development teams to avoid bottlenecks in the development cycle as it creates the discipline of a limit to how much WIP can be in any one part of the development cycle at a time.   As one each task in development, the work moves to the next step, freeing up space for more work to move into the previous step.   The following image is an example of a development kanban board.   Each project (or Epic) is represented by a color and the location of that project on the board is understood by all.   A policy (not shown) sets the limit on the number of projects that can be in a given step at the same time and also the rules around what must be accomplished in order for a project to move to the next step.   By limiting the number of projects that can be in a step at one time bottlenecks can be avoided as resources can be shifted to help the step that has the most items.   Backlog items cannot be started until there is room in the design step.