RCM Tools Histogram Pareto Chart Cause and Effect Diagram FMEA

Histogram 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 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 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 |||||| 6 3 9 – 12 |||||||||||| 12 4 13 – 16 |||| 4 5 17 – 20 ||||| 5 6 21 – 24 || 2 30

The graph of class versus frequency called Histogram 1 6 12 4 5 2 4.5 8.5 12.5 16.5 21.5 24 Range

Percentiles 1 6 12 4 5 2 20.5 24

Concept of Distribution

Histogram 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 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 Histogram After you have created a Histogram, it will take one of five shapes: Exponential : Failure is random

Use of Histogram Normal Distribution: The five shapes that a histogram could take include: normal distribution, positively skewed, negatively skewed, bi-modal distribution, and multi-modal distribution.

Use of Histogram Positively Skewed: Negatively Skewed: Preventive maintenance

Use of Histogram Bi-Modal Distribution: Multi-Modal Distribution:

Exercise in Class

Pareto Chart Prioritizing allocation of resources. 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 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 Chart 25 20 15 10 5 5 F A E L

Pareto 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 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 Diagram Materials Methods Equipment People Environment Cause Figure11-10 in text

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.

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.

FMEA: Failure Mode and Effects Analysis An important tool of RCM

FMEA 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 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 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

Prerequisites 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) One must be prevention oriented Continuous improvement is the force that drives FMEA

Good 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 the 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 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? 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

Figure 5

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

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.

Figure 8

Figure 9