Fishbone Diagram, Pareto Diagram, Cp

Fishbone Diagram, Pareto Diagram, Cp and CPk values

Fishbone diagram

The Fishbone diagram is a highly used tool of analysis since it clearly identifies and reveals the relationship between various inputs and variables to the final cause. Specifically, the diagram strives to identify and present the causes of a given problem, and the effect of given variables.

In the situation assessed, the effect is that of breakdown, and the cause is a multifold one, represented by numerous reasons for breakdown, at each of the ten machineries operating at the respective level. The diagram below indicates this:

In other words, there are ten machines at the sewing company and each of them suffers malfunctions and creates errors that lead to the subsequent breakdowns and delays in apparel manufacturing. The malfunctions are referred to only by their code, as a means of increasing the structural efficiency and the clarity in creating and reading the Fishbone diagram. For machinery 1 for instance, the malfunctions include:

Dull knife (217)

Skip stick (145)

Stuck pedal (193)

Skip stick (187)

Breaking needles (192).

Some of these causes arise as a result of malfunctions, whereas others are created by man made mistakes, or are generated by natural processes of machine usage. In either case however, they all create breakdowns and lead to a slowing down of the apparel production.

2. Pareto analysis

As the fishbone analysis has revealed, the causes leading to breakdowns are multiple, and in order for the management at the sewing company to be able to make the best informed decision, it is necessary for them to identify which of the causes are the most common ones. By identifying this, they would be able to develop and implement targeted solutions addressing the specific issues which are of the most interest.

In this order of ideas, it is important to construct a Pareto diagram by which to assess the recurrence of all breakdown causes.

Error

Recurrence of error

Dull knife

2

Skip stitch

14

Stuck pedal

4

Breaking needles

15

Air pressure low

6

Thread breaks

3

Other

4

As it can be seen from both the collection of the data in the table, as well as the graphical representation in the Pareto diagram, the more common problem encountered at the sewing company is represented by the breaking of the needles, followed closely by the skipping of stitches. These are the two most important causes of breakdowns and they are the ones that should be addressed first by the management. Specifically, the priority in addressing the issues is revealed as follows:

1 -- Breaking of the needles

2 -- Skipping the stitches

3 -- the low air pressure

4 -- the stuck of the pedal

4 -- Other causes

5 -- the breaking of the thread, and last

6 -- the dull knife.

3. CP and CPK values

A recent article in Quality Engineering revealed the various figures associated with the compactibility of sand; according to the author of the article, the values varied between 38 and 46, meaning otherwise that the lowest value of sand compactibility was of 38 and its highest value was of 46.

In this context, it is useful to calculate the Cp and the Cpk for the sand compactibility. Both Cp and Cpk are concepts pertaining to the Six Sigma principles and they are used in correlation to the capability of processes. When used in correlation to each other, the Cp and the Cpk can help the researcher form an objective and informed opinion regarding the capability of the process assessed. More importantly, they also help identify any potential issue that might exist throughout the process and as such, constitute grounds for future improvement endeavors.