Sources of Waste: Defects

by Jan 5, 2021Continuous improvement

The goal of any continuous improvement action is generally to tackle one or more sources of waste which are commonly known as Muda (無駄), a Japanese word meaning “wastefulness; uselessness”.

In the literature, we can find several sets of sources of waste, but the set with the optimal number of sources of waste is made up of seven elements, namely:

  • Defects
  • Inventory
  • Overproduction
  • Overprocessing
  • Transport
  • Waiting
  • Motion

These elements are considered sources of waste because they often represent actions or situations that do not add value, and very likely, cause other problems in particular related to the safety and well-being of workers.

This blog will be the first in a series of 7 blogs addressing each source of waste individually.

In this here blog, we will start with defects/rejects since it is one of the most significant sources of waste, because it is responsible, not only of not adding value, but it also often causes the loss of value that would be brought about by other stages of the process.

It is also the most obvious source of waste, yet the most difficult to detect before it reaches the client (internal or external).

In terms of loss, defects/rejects generate very significant costs because the loss is not limited only to the value of the units rejected since each unit that fails or does not meet the specifications and requirements targeted during the design will require re-processing or replacement which generates addition loss of resources and material. This usually comes with an inevitable impact on client confidence and satisfaction which can be lost in an irreversible manner.

Like any other problem, the principle of “prevention is better than cure” applies perfectly to waste due to defects/rejects. It is therefore necessary to act proactively on the factors that can lead to these situations, such as lack of control of oversight of the process, problematic design of products or processes, lack or insufficiency in the level of maintenance planning and inadequate training or lack of operator competence, etc.

Among the tools that are generally applicable to the prevention or correction of problems related to waste caused by defects/rejects are, among others, intelligent automation also known as, autonomation (from the Japanese principle of jidoka or 自働化) and mistake-proofing, also known as, Poka-yoke (from the Japanese: ポカヨケ).

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