RCM ToolsRCM Tools

Histogram Pareto Chart Cause and Effect Diagram FMEA

HistogramHistogram

A histogram is a of a bar chart representing the frequency of an entire data grouped into evenly spaced category. It can be viewed as a graph of class versus frequency. It used for the following:– Organizing data.– Spotting variation in data.– Identifying data distribution.

Frequency DistributionFrequency Distribution

Let us examine the following data for the demand in weeks for the last 30 orders of computers/drug.

15 6 21 15 12 9 18 6 9 9 18 6 12 15 3 21 6 18 12 9 15 9 6 18 12 12 6 18 12 12 n = 30

Frequency DistributionFrequency Distribution

The Frequency Dist. Is Table that provide classes and frequency (number of occurrences in the class). For the demand data it is No. Class Frequency 1 1 – 4 | 1

2 5 – 8 |||||| 63 9 – 12 |||||||||||| 124 13 – 16 |||| 4

5 17 – 20 ||||| 5 6 21 – 24 || 2

30

1 6 12 4 5 2 4.5 8.5 12.5 16.5 21.5 24 Range

The graph of class versus frequency called The graph of class versus frequency called HistogramHistogram

Frequency

1 6 12 4 5 2 20.5 24

PercentilesPercentiles

Concept of DistributionConcept of Distribution

Histogram ShapesHistogram Shapes• While the number of shapes that a histogram ca

take is unlimited, certain shapes appear often then others.

• Drawing a line that connects the edges of the bars in a Histogram forms a curve. We can make certain inferences about the data from the shape of the curve.

Distribution

Histogram QuestionHistogram Question

Does the shape of the histogram tells something?

If the answer is yes how? How do we assess variability from

the histogram?

Use of HistogramUse of Histogram After you have created a Histogram, it will

take one of five shapes:

Exponential : Failure is random

Use of HistogramUse of Histogram

Normal Distribution:

Use of HistogramUse of Histogram

Positively Skewed:

Negatively Skewed: Preventive maintenance

Use of HistogramUse of Histogram

Bi-Modal Distribution:

Multi-Modal Distribution:

1, ½, ¾, 2, ½, ½, 1, 1, ¾, 3, 1, ¾ 1, ¾, 2, 8, 3, ¾, ½, 8, 4, 7, 10, ¾ 2, ½, 1, ½, 30, 1, 2, 1, 50, 6, 3, 3 5, 4, 6, 5, 72, 2, 4, 2, 3

Table 1 : Grinder downtime in hours for the last three months (rounded to the nearest half hour)

Exercise in Class

Pareto ChartPareto Chart

Pareto chart/diagram is a bar chart that categories possible causes of problem areas and organize them in order of decreasing frequency/cost/impact. It is a problem solving tool used to separate the “Major” few from the trivial “many”. It can be used for:

– Identify important causes for bad quality

– Prioritizing allocation of resources.

Example on Pareto ChartExample on Pareto Chart

Below is a check sheet that lists type of injury in a factor

Type of injury Tally Frequency Fingers (F) 1111 1111 1111 1111 111 23

Eyes (E) 1111 1111 9

Arms (A) 1111 1111 111 13

Leg (L) 1111 5

Total 50

Pareto ChartPareto Chart

5

5

10

15

20

25

F A E L

Pareto Chart UsesPareto Chart Uses

Identifying major quality problems Identifying major unsafe acts Identify major causes of budget over run Identify major costs factors in a process Identify major reasons for not meeting

targets.. Many others.

Cause and Effect DiagramCause and Effect Diagram

It is a chart that relates the problem to its causes.

It’s objective is to identify causes of a problem

It is useful in sorting, interrelating and visualizing the causal factors influencing a particular problem

Cause-and-Effect DiagramCause-and-Effect Diagram

Figure11-10 in text

Effect

MaterialsMethods

EquipmentPeople

Environment

Cause

Cause

Cause

Cause

Cause

CauseCause

Cause

CauseCause

Cause

Cause

The steps of the CED are:

Decide the quality characteristic, and effect needed to be studied. This is usually a phenomena (effect) we need to improve and control. As an example not meeting production targets. (next Figure)

Write the effect on the right side. Draw a broad arrow from the left side to the right side

Write the main factors which may be causing the target miss, directing a branch arrow to the main arrow (Figure 7). Group the major possible causes into categories such as materials, equipment, methods of work, and measuring methods. Each category will form a branch as in the next Figure.

Missing Target

Equipment People Methods

Procedures Materials

Write on each of the side branches the detailed factors which may be regarded as the causes. These will be like twigs and on these write more detailed factors and so on. (see next figure)

Check to make sure that all causes are included in the diagram and the relationships are properly illustrated.

Mis

sin

g

Ta

rg

et

Procedure Methods

Lo

ng

Repair

Job Preparation

Transportation

Documentation

No

t cle

ar

Hard

to

use

Delay in reporting

Inspection Materials

Not structured

Temperature Fatique

Coolant

Ordering policy

Preparation

Lack of material

Equipment

Rotation

Str

uc

k

Un

ev

en

Does not tell situation

FMEA:FMEA: Failure Mode and Effects AnalysisFailure Mode and Effects Analysis

An important tool of RCM

FMEA DefinitionFMEA Definition

A procedure and tools that help to identify every possible failure mode of a process or product, to determine its effect on other sub-items and on the required function of the product or process. The FMEA is also used to rank & prioritize the possible causes of failures as well as develop and implement preventative actions, with responsible persons assigned to carry out these actions.

Failure modes and effects analysis (FMEA) is a disciplined approach used to identify possible failures of a product or service and then determine the frequency and impact of the failure.

FMEA definedFMEA defined

FMEA is a specific methodology to evaluate a system, design, process, or service for possible ways in which failures (problems, errors, risks, concerns) can occur

For each failure identified (known or potential), an estimate is made of its occurrence, severity and detection.

An evaluation is made of the necessary action to be taken

ASQC DefinitionASQC Definition

FMEA is an engineering technique used to define, identify, and eliminate known and/or potential failures, problems errors, and so on from the system, design, process, and or service before they reach the customer

ASQC 1983

PrerequisitesPrerequisites

All problems are not the same

The vital few as opposed to the trivial many The customer must be known

end user or downstream operation

The function must be known

The function, purpose, and objective of what is to be accomplished must be known

Prerequisites (cont’d)Prerequisites (cont’d)

One must be prevention oriented

Continuous improvement is the force that drives FMEA

Good FMEAGood FMEA

Identify known and potential failure modes Identifies the causes and effects of each

failure mode Prioritizes the identified failure modes

according to the risk priority number

(RPN = frequency x severity x detection) Provides for problem follow-up and corrective

action

Components that that help define Components that that help define the priority of failuresthe priority of failures

Occurrence

Severity

Detection

..

Occurrence is the frequency of the failure

Severity is the seriousness (effects) of the failure

Detection is the ability to detect the failure before it reaches the customer

FMEA and RCMFMEA and RCM

Specifying PM tasks without a good understanding of of failure mode and cause information is, at best, nothing more than a guessing game

FMEA play a vital role in the RCM process

How is FMEA performed?How is FMEA performed?

A good understanding of the equipment design and operation is an essential starting point

The FMEA process proceeds in an orderly fashion to qualitatively consider the ways in which the individual parts or assemblies in the equipment can fail. These are the failure modes that we wish to list.

......

Each Failure mode is then evaluated for each effect on

- the component itself (local effect)

- next higher level of assembly

- the top level of assembly or system

Fig 3.6 and Fig 3.8

....

When a well-executed FMEA is accomplished, a wealth of useful information is generated to assist

in achieving the expected product reliability

Breakdown

Duration Frequency Relative

Frequency 0 < t 1 1< t 2 2< t 3 3< t 4 4< t 5 5< t 6 6< t 7

t 8

20 6 5 3 2 2 1 6

44.44 13.33 11.11 6.67 4.45 4.45 2.22

13.33

Total 45 100.00

Table 2 : Frequency distribution for the downtime data in table 8.1

Downtime intervals

1 2 3 4 5 6 7 8

Figure 7

f

5

10

15

20

25

Frequency

Figure 5

GrinderTime

Figure 6

The steps of the CED are:

Decide the quality characteristic, and effect needed to be studied. This is usually a phenomena (effect) we need to improve and control. In our case it is the grinder downtime. (Figure 6)

Write the effect on the right side. Draw a broad arrow from the left side to the right side

Write the main factors which may be causing the grinder downtime, directing a branch arrow to the main arrow (Figure 7). Group the major possible causes into categories such as materials, equipment, methods of work, and measuring methods. Each category will form a branch as in Figure 7.

Figure 7

GrinderTime

Equipment Procedure Methods

Inspection Materials

Write on each of the side branches the detailed factors which may be regarded as the causes. These will be like twigs and on these write more detailed factors and so on. (Figure 8)

Check to make sure that all causes are included in the diagram and the relationships are properly illustrated.

Gri

nde

r

dow

ntim

e

Procedure Methods Long

Repair

Not slanded

Job Preparation

trasnsportation

Documentation

Not clear Hard to use

Delay in reporting

Inspection Materials

Not structured

Rise in temperature

Coolant

Leakage

Does not come out

Wet

Polishing grinder

Equipment

Rotation

Struck

Uneven

Does not tell situation

Figure 8

23

12

5

3

a b c d e

10

20

30

40

Number ofBreak downs

Figure 9