Failure mode and effect analysis or cause and effect analysis

This technique involves selecting certain (usually critical) items and identifying all the possible modes of failure which could occur during its life cycle. The probability, causes and impact of such a failure are then assessed and the necessary controls and rectification processes put in place. Clearly, as with risk analysis, the earlier in the project this process is carried out, the more opportunity there is to anticipate a problem and, if necessary, change the design to 'engineer' it out.

Quality assurance approval

1121/DAR/QA Our ref: Your ref:

DATE

F.A.O: Quality Assurance Manager Dear Sirs,

QUALITY ASSURANCE APPROVAL

In order to meet the increasing Quality Assurance demands of our Clients, we are revising our Approved Vendor Lists. Should you wish to either remain on, or be added to these lists it will be necessary for you to complete the attached document and return it to us without delay.

It is of the utmost importance that the document is fully completed and gives all relevant information asked for regarding your existing Q.A. Approvals including the following details:-

Sub-Contract Quality Assurance - Form A

1) The level approved at.

2) The organisation or body who have awarded the approval.

3) Certificate Number

4) The date approved.

5) The period of validity of the approval.

6) Commodity and materials approved.

The completed form should be returned to:-(state address here)

Marked for the attention of Mr. John Brown - Procurement Manager

Figure 17.3 Confirmation of compliance request

The following example illustrates how this technique can be applied to find the main causes affecting the operability of a domestic vacuum cleaner.

The first step is to list all the main causes which are generally experienced when using such a machine. These causes (or quality shortcomings), which may require a brainstorming session to generate them, are:

• Electrical

• Physical (weight and size)

• Mechanical (brush wear)

• Suction (dust collection).

The second step is drawing a cause and effect diagram as shown in Figure 17.4 which is also known as an Ishikawa or fishbone diagram, from which it is possible to see clearly how these causes affect the operation of the vacuum cleaner.

The third step requires all the sub-causes (or reasons) of a main cause to be written against the tributary lines (or fishbones) of each cause. For example, the sub-causes of electrical failure

Figure 17.4 Cause and effect diagram

are the lead being too short, thus pulling the plug out of the socket, or hauling the cleaner by the lead and causing a break in the cable.

The last step involves an assessment of the number of times over a measured period each cause has resulted in a failure. However, it is highly advantageous to concentrate on those causes which are responsible for the most complaints and when this has been completed and assessed by applying the next technique, Pareto Analysis, appropriate action can be taken to resolve any problem or rectify any error.

Pareto analysis

In the nineteenth century, Vilfredo Pareto discovered that in Italy 90 per cent of income was earned by 10 per cent of the population. Further study showed that this distribution was also true for many other situations from political power to industrial problems. He therefore formulated Pareto's law, which states that 'In any series of elements to be controlled, a small fraction in terms of the number of elements always account for a large fraction in terms of effect'.

In the case of the vacuum cleaner, this is clearly shown in the Pareto chart in Figure 17.5 which plots the impact Y in terms of percentage of problems encountered against the number of causes X identified. The survey of faults show that of the four main causes examined, inadequate dust collection is responsible for 76 per cent (nearly 80 per cent) of the failures or complaints. This is why Pareto's law is sometimes called the 80/20 rule.

The percentage figure can be calculated by tabulating the causes and the number of times they resulted in a failure over a given period, say 1 year, and then converting these into a percentage of the total number of failures. This is shown in Figure 17.6. Clearly such ratios are only approximate and can vary widely, but in general only a relatively small number of causes are responsible for the most serious effects. Anyone who is involved in club committee activities will know that there are always a few keen members who have the greatest influence.

Cause : Figure 17.5 Pareto chart

Cause

No. of failures

% of failures

Electrical

e

12

Physical

2

4

Mechanical

4

s

Suction

as

76

Total

sc

100

Figure 17.6 Failure table

Figure 17.6 Failure table

Project Management Made Easy

Project Management Made Easy

What you need to know about… Project Management Made Easy! Project management consists of more than just a large building project and can encompass small projects as well. No matter what the size of your project, you need to have some sort of project management. How you manage your project has everything to do with its outcome.

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