| Ishikawa diagram | |
|---|---|
| One of the Seven Basic Tools of Quality | |
| First described by | Kaoru Ishikawa |
| Purpose | To break down (in successive layers of detail) root causes that potentially contribute to a particular effect |
Ishikawa diagrams (also called fishbone diagrams, or herringbone diagrams , cause-and-effect diagrams, or Fishikawa) are causal diagrams that show the causes of a certain event -- created by Kaoru Ishikawa (1990).[1] Common uses of the Ishikawa diagram are product design and quality defect prevention, to identify potential factors causing an overall effect. Each cause or reason for imperfection is a source of variation. Causes are usually grouped into major categories to identify these sources of variation. The categories typically include:
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Ishikawa diagrams were proposed by Kaoru Ishikawa[2] in the 1960s, who pioneered quality management processes in the Kawasaki shipyards, and in the process became one of the founding fathers of modern management.
It was first used in the 1940s, and is considered one of the seven basic tools of quality control.[3] It is known as a fishbone diagram because of its shape, similar to the side view of a fish skeleton.
Mazda Motors famously used an Ishikawa diagram in the development of the Miata sports car, where the required result was "Jinba Ittai" (Horse and Rider as One — jap. 人馬一体). The main causes included such aspects as "touch" and "braking" with the lesser causes including highly granular factors such as "50/50 weight distribution" and "able to rest elbow on top of driver's door". Every factor identified in the diagram was included in the final design.
Causes in the diagram are often categorized, such as to the 8 M's, described below. Cause-and-effect diagrams can reveal key relationships among various variables, and the possible causes provide additional insight into process behavior.
Causes can be derived from brainstorming sessions. These groups can then be labeled as categories of the fishbone. They will typically be one of the traditional categories mentioned above but may be something unique to the application in a specific case. Causes can be traced back to root causes with the 5 Whys technique.
Typical categories are:
The original 6Ms used by the Toyoda Production System have been expanded by some to included the following and are referred to as the 8Ms. However, this is not Globally recognized. It has been suggested to return to the roots of the tools and to keep the teaching simple while recognizing the original intent, most programs do not address the 8Ms.
Man/Operator – Was the document properly interpreted? – Was the information properly circulated to all the functions? – Did the recipient understand the information? – Was the proper training to perform the task administered to the person? – Was too much judgment required to perform the task? – Were guidelines for judgment available? – Did the environment influence the actions of the individual? – Are there distractions in the workplace? – Is fatigue a mitigating factor? - Is his work efficiency acceptable? - Is he responsible/accountable? - Is he qualified? - Is he experienced? - Is he medically fit and healthy? – How much experience does the individual have in performing this task? - can he carry out the operation without error?
Machines – Was the correct tool/tooling used? - Does it meet production requirements? - Does it meet process capabilities? – Are files saved with the correct extension to the correct location? – Is the equipment affected by the environment? – Is the equipment being properly maintained (i.e., daily/weekly/monthly preventative maintenance schedule) – Does the software or hardware need to be updated? – Does the equipment or software have the features to support our needs/usage? - Was the machine properly maintained? – Was the machine properly programmed? – Is the tooling/fixturing adequate for the job? – Does the machine have an adequate guard? – Was the equipment used within its capabilities and limitations? – Are all controls including emergency stop button clearly labeled and/or color coded or size differentiated? – Is the equipment the right application for the given job?
Measurement – Does the gauge have a valid calibration date? – Was the proper gauge used to measure the part, process, chemical, compound, etc.? – Was a gauge capability study ever performed? - Do measurements vary significantly from operator to operator? - Do operators have a tough time using the prescribed gauge? - Is the gauge fixturing adequate? – Does the gauge have proper measurement resolution? – Did the environment influence the measurements taken?
Material (Includes Raw Material, Consumables and Information ) – Is all needed information available and accurate? – Can information be verified or cross-checked? – Has any information changed recently / do we have a way of keeping the information up to date? – What happens if we don't have all of the information we need? – Is a Material Safety Data Sheet (MSDS) readily available? – Was the material properly tested? – Was the material substituted? – Is the supplier’s process defined and controlled? - Was the raw material defective? - was the raw material the wrong type for the job? – Were quality requirements adequate for the part's function? – Was the material contaminated? – Was the material handled properly (stored, dispensed, used & disposed)?
Method – Was the canister, barrel, etc. labeled properly? – Were the workers trained properly in the procedure? – Was the testing performed statistically significant? – Was data tested for true root cause? – How many “if necessary” and “approximately” phrases are found in this process? – Was this a process generated by an Integrated Product Development (IPD) Team? – Did the IPD Team employ Design for Environmental (DFE) principles? – Has a capability study ever been performed for this process? – Is the process under Statistical Process Control (SPC)? – Are the work instructions clearly written? – Are mistake-proofing devices/techniques employed? – Are the work instructions complete? - Is the work standard upgraded and to current revision? – Is the tooling adequately designed and controlled? – Is handling/packaging adequately specified? – Was the process changed? – Was the design changed? - Are the lighting and ventilation adequate? – Was a process Failure Modes Effects Analysis (FMEA) ever performed? – Was adequate sampling done? – Are features of the process critical to safety clearly spelled out to the Operator?
Environment – Is the process affected by temperature changes over the course of a day? – Is the process affected by humidity, vibration, noise, lighting, etc.? – Does the process run in a controlled environment? – Are associates distracted by noise, uncomfortable temperatures, fluorescent lighting, etc.?
Management - Is management involvement seen? – Inattention to task – Task hazards not guarded properly – Other (horseplay, inattention....) – Stress demands – Lack of Process – Training or education lacking – Poor employee involvement – Poor recognition of hazard – Previously identified hazards were not eliminated
In a discussion of the nature of a cause it is customary to distinguish between necessary and sufficient conditions for the occurrence of an event. A necessary condition for the occurrence of a specified event is a circumstance in whose absence the event cannot occur. A sufficient condition for the occurrence of an event is a circumstance in whose presence the event must occur.[4] A sufficient condition naturally contains one or several necessary ones. Ishikawa diagrams are meant to use the necessary conditions and split the "sufficient" ones into the "necessary" parts. Some critics failing this simple logic have asked which conditions (necessary or sufficient) are addressed by the diagram in case[5]