In my previous post on structured problem solving, I discussed the “5 Whys” technique.  Although it is a very useful method, it can potentially lead you astray as a problem becomes increasingly complex and an intuitive answer (often guided by experience) is not apparent.

In these cases, it may be more beneficial to use a Cause and Effect, or Ishikawa Fishbone Diagram.   Karou Ishikawa (1915-1990) was a Japanese industrialist and statistician, whom we will meet again later when discussing other problem solving tools.  He was a contemporary and disciple of Dr. Deming (1900-1993.) He also shared great friendships with other North American quality notables such as Joseph Juran (1904-2008.)

A Fishbone Diagram can help us to identify possible root causes, sort and relate possible root cause interactions, and present them in an organized manner.  It works under the premise that all problems can be attributed to one of the following six causitive factors (or to a combination of these factors):

Manpower

Methods

Materials

Machinery

Measurements

Environment

Originally, only the first five factors were considered and were called the “Five Ms”, but environment was soon added to the list.  Many variations of this “5 Ms and an E” list exist, including: 8 Ps, 8 Ms and 4 Ss.  At the top of article is an example of a Fishbone Diagram using a short shot/small dimensional reject as the problem:

The above is a simplified Fishbone Diagram, but it shows how the main causes and subsequent sub-causes lead to the effect: in this case, a rejected shipment due to short shots and dimensionally small parts. This is why it is also known as a Cause and Effect Diagram.  It is a visual analytical tool that is especially useful to the injection molder in solving complicated problems.

Brainstorming, the technique we used out on the floor to quickly and informally solve molding problems, is also key when constructing a Fishbone Diagram.  Cross-functional problem solvers representing tooling, design, quality, maintenance, and molding gather around the conference table.  Everybody offers their ideas, and if the group agrees that they are valid, the ideas are posted as “bones” or spines on the diagram as possible causes or factors.  Later, the group decides which causes are critical factors and which are minor.  In the above diagram, they may decide that a cold molding room is a minor factor not worthy of further investigation.

There are 3 main rules for Brainstorming:

Everybody contributes ideas.

There are no “crazy” ideas; even those that are seemingly “off-the-wall” can lead to other relevant concepts.

Do not criticize others’ ideas or get personal.  This is the quickest way to shut off the flow of creativity and bring the brainstorming session to a screeching halt.  The idea is to generate as many ideas as possible to write on the board and then to decide which ones to include on the Fishbone Diagram.

In subsequent blogs, I will examine other structured problem solving methods that should be in every molder’s toolbox.

 

Brent Borgerson
Senior Process Engineer (Older Molder) 
Matrix Tooling Inc. /Matrix Plastic Products