UNIT 10 CAUSE AND EFFECT ANALYSIS

Structure

10.1 Introduction

Objectives

10.2 Role of Analytical Tools

10.3 Cause-and-Effect Diagram

10.3.1 Cause Enumeration

10.3.2 Dispersion Analysis

10.3.3 Process Analysis

10.4 Pareto Analysis and Cause-and-Effect Diagram

10.5 Root Cause Analysis

10.6 Summary

10.7 Key Words

10.8 Answers to SAQs

10.1 INTRODUCTION

The philosophy that seek to improve all factors related to the process of converting inputs into output on an ongoing basis is called continuous improvement.

There is an increasing realisation that engineering changes after product launch are costly exercise. Consequently manufacturers have been compelled to adopt methods to detect problems at an early stage of the product design cycle. Failure mode and effect analysis (FMEA), concurrent engineering, multiple prototype builds and early supplier involvement are some of the means by which manufacturers try to surface problems early during the product development cycle. Detecting and addressing problems early makes penetration of product in the market a smooth and time bound activity. Other than addressing problems, improvement orientation is the most important parameter for competitiveness. The performance level of most enterprises tend to decrease over time unless effects are made to maintain the level which implies that barely to maintain the current level of performance, some degree of maintenance is necessary. For additional improvement, efforts beyond pure maintenance is required. If an organization does not improve, either competition or new entrant will capture and enter the market segment. As a result, customers today are more demanding. Quality of product offered are being improved rapidly. As a result expectations of customer are rising dramatically. There is however, no single solution to this dramatic customer expectation. But it can be said that continuous improvement combined with innovation will help organizations to stay competitive in the market place. Past experience have shown that organizations focusing on continuous improvement have been successful in occasional breakthrough in their improvement effort. On the other hand, neglecting continuous improvement is not conducive to create a breakthrough. Different improvement tools are suitable for different improvement activity.

A number of tools are used for analyzing date and problem solving. Among the most useful, cause-and-effect diagrams, offer & structured approach to problem solving. They are also referred to a fish bone diagrams because of their shape, or Ishikawa diagrams after Kaoru Ishikawa, the Japanese professional who developed the approach to help workers overwhelmed in problem solving by the number of factors that needed to be examined. The diagrams help organize problem solving efforts by providing several layers of categories that may be factors in causing problems. After cause-and-effect .

diagrams are used after brain storming sessions to organise the ideas generated.

Quality Tools - Others A cause-and-effect diagram shows the relationship between a quality characteristic and certain factors. It is a graphic tool which shows the relationship between causes and effects. Its principle purpose is to help identify the root cause of a problem.

Objectives

After studying this unit, you should be able to

know the role of analytical tool,

draw the cause-and-effect diagram,

describe how the pareto technique is used to analyze problems,

explain how the cause-and-effect (fish bone) diagrams are used in problem solving, and

understand the root cause analysis.

10.2 ROLE OF ANALYTICAL TOOLS

The main objective of the analytical tools can be problem identification or improvement. Some tools can contribute to more than one objective, but their category depends on the most prominent activity. Within the overall improvement model different stages appear as shown in Figure 10.1. As can be seen in the figure that the improvement effort has to be prioritized. This will indicate where to concentrate the improvement effort. This analysis is done through variaus tools l i b self assessment, trend analysis, QFD and spider chart etc.

5. lmprovement Generation Task Generation

1. Prioritizing 2. Process Improvement Understanding

Figure 10.1

After identifying the process which is to be improved, the next step is to understand the process in a detailed manner. This can be done through 'critical incident' technique for identifying problems within a process or 'relationship mapping'. It can also be accomplished by three of the deven basic problem-solving tools namely:

Efforts 1 -+

Check sheet (Tally Chart) are used to assist in the collection and classification of data to facilitate rapid information gathering.

3. Problem Analysis

Pareto analysis is an approach to pinpointing problems through the identification and separation of the vital few causes from the trivial many.

Flow charting is a systematic technique for describing the process to which the problem belongs. The main purpose for producing a flow chart is to establish a common understanding of all the stage9 under review.

To sustain an ongoing organizational development associated with 'improvement through teamwork', the improvement teams established need to be provided with appropriate tools. An inadequate approach with which to tackle the problem, will not be able to achieve the desired objective. To address these problems two sets of problem-solving tools are used. The first of these are the seven basic problem-solving tools, also called the 'Seven QC tools', which are normally used by quality improvement teams for problem solving. The second set of techniques are the seven advances tools,

referred to as the 'Seven management tools', which are used as advanced quality planning techniques. Since problem analysis is an important aspect of improvement work, it uses both these classes of tools. Some of the tools used for problem analysis are as follows:

Matrix diagram, one of the seven management tools, is a two-dimensional array similar to a spreadsheet. It graphically represents the relationship between factors. The most commonly used example of a matrix diagram is the 'House of Quality' diagram developed as a part of 'Quality function deployment'.

Relations diagram, one of the seven management tools, describes the logical links among the factors grouped together during a brainstorming session. By focusing upon a particular generated idea, the relations diagram brings logical structure and relationships to the creative activity.

Histograms, one of seven basic problem-solving tools, are used to display the data collected and often this form of ordered distribution i I lustrates fundamental properties of the problem.

Scatter diagram, another of the seven basic problem-solving tools, is used to establish or dispel a casual link between two factors. Quite often, after having established some correlation the solution to the problem becomes easier to identify.

Cause-and-Effect analysis, further one of the seven problem-solving tools, is used as a way of structuring the process of determining the root cause of a problem.

Root cause analysis helps in finding the true root cause of a problem.

SAQ 1

Why is improvement necessary in an organization?

10.3 CAUSE-AND-EFFECT DIAGRAM

Also known as fishbone (due to their shape) or lshikawa Charts (named after the person who developed this tool), cause and effect diagrams identify potential causes and help to direct problem-solving and data-collection efforts towards the most likely causes of observed defects.

These diagrams are built up from a problem statement through to detailed causes using the following steps :

Problem Statement

Analysis of the symptoms and causes yields the problem statement. In turn, this then becomes the label for the root effect arrow as shown in Figure 10.2.

Major Causes

The second step is to identify major categories of causes. These are then drawn at an angle to the root effect arrow as shown in Figure 10.2.

Cause and Effect Analy\i.

Quality l'ools - Cthers I Personnel (

Delays at check-in

Agents undertrained Aircraft

Agent's motivation

Late-heavy traffic

Delayed* Cancelled Late cabin cleaners

Wait baggage to aircraft

On-ground delays

Wait tug pushback Non-engine faults

Root Effect Arrow

Departure de l~ys

Heavy outbound

Other air traffic

I Other I

/ I Delays at check-in ( Confused sent allocation

/ Checkina oversize baaaaae --

Accepting late passengen

/ Cut-off too close to deoadure time*

Protecting late passengers

Desire to help maximize sales revenue

Gate locations (distance to travel) - Baggage handling L /-- Late baggage loading to aircraft*

Procedure errors at aircraft

Procedures rn Figure 10.2 : Cause and Effect Diagram used to Ascertain the Cause ormight Dela s

Detailed Causes + F ,,

The next step is to list all the detailed causes within each of the major categories. For example, 'whether' and 'other air traffic control delays' under the major cause 'other' as shown in Figure 10.2.

Principal Causes

The final step is to identify the principal causes within the list of detailed causes as a guide. For example, Figure 10.2 indicates these with an asterisk.

There are three types of cause-and-effect diagrams which are :

(i) Cause enumeration,

(ii) Dispersion analysis, and

(iii) Process analysis.

10.3.1 Cause Enumeration

The cause enumeration is closest to the idea generating technique-brain storming. The quality characteristic that has been identified for study is written on the right side of the diagram. Then a line drawn across the diagram to the characteristic. This is the spine. Finally, the event that might influence the process is recorded by drawing lines off the spine or other lines. All probable causes are simply brainstormed and listed in the order they are generated. This free thinking develops a complete picture of cause and effects. The diagram will contain the cause of the quality characteristic in question; however it may be difficult to single out any one cause from the many others. The general format for a cause and effect diagram is shown in Figure 10.3.

Material Man !

Quality Attribute

I I I I I I I

I Effect I I I

Machine Measurement Cause

Figure 10.3 : General Format for Cause-and-Effect Diagram

Example below describes a small cause enumeration for a very common problem - lost . .

luggage at airports. The quality characteristic under study, lost luggage is recorded on the right of the page and the spine is drawn pointing to causes as in Figure 10.4.

Changing Changing Missing Tag Flights Carrier

Handling and Ticketing Procedure

Handling

Similar Tags

I I Luggage Material Handling

Stolen Damaged LwiIgage

Figure 10.4 : Cause Enumeration, Cause-and-Effect Diagram for Lost Luggage from an Airline

The causes that are suggested are then drawn at the end of lines originating from spines. These are the bones of the diagram. One cause that has been identified, missing tag on luggage, is drawn at the end of a central bone. These causes are defined as far as possible. For the missing tag, it was decided by the group that either the ticketing agent forgot to place the appropriate tag on the luggage or the tag were ripped off during transportation to and from the airplane. If possible, these bones can be refined further to even more specific causes. In the present example, it could be that luggage tags all look the same, so ticket agents often commit mistake during rush to board passengers on the

Cause and Effect Analysis

Quality Tools - Others airplanes. Similarly, another cause attributes to lost luggage is the changing flights by the passengers. This again can be further attributed to improper information channels. This same procedure is followeduntil all ideas are exhausted.

10.3.2 Dispersion Analysis

The second type of diagram is the dispersion analysis. This is similar to the cause enumeration, except that causes are grouped under structured categories such as:

People

Machines and equipment

Materials

Methods

Measure

Environment

Similarly, for service processes, the traditional categories are :

People

Process

Frame conditions

Work environment

However, smaller causes that would have been listed in the cause enumeration diagram might not fit into any of the classified causes and could be missed out.

Material I C lncorrect

Product Assembled

Faulty I I

Computer Terminal I

I

\ \ 1 Incorrect I

I I I Prices I incorrect / I U !

S Price List I I

Incorrect Available I I

Key Punch Prices Used Order Charged I Errors \ but not I

1 / Informed I I

I People I

Figure 10.5 : Cause-and-Effect Diagram for Dispersion Analysis

The main steps for produc,ing a cause-and-effect diagram using dispersion analysis, which is the more common approach are :

(i) The diagram Can be done by an individual, but gives better result when created by a team. Therefore, group formation with members having necessary knowledge is required.

(ii) Mention cleafily the effect for which causes are sought.

(iii) Identify the niain categories of possible causes for the effect and place these at the end of booms emanating from the spine.

(iv) Brainstorm alil possible causes and place them in the suitable area of the diagram. Causes that belong to more than one category are placed in all

relevant positions. It is often required to draw the diagram after the first version has been completed.

(v) Analyze the identified causes to determine the most significant one.

Cause-and-effect diagram for dispersion analysis is illustrated in Figure 10.5. The effect being analyzed is the incorrect price quoted for a product launched.

10.3.3 Process Analysis

The final type of cause-and-effect diagram is the process analysis diagram. They are more directly aimed at improvement of business process. The diagram follows the product through the process, and the causes encountered at each step are recorded at step on diagram. This diagram helps to show the flow of the process and where problems occurs.

However, problems may occur repeatedly and causes that cannot be attributed to any particular step may be difficult to represent. Example below demonstrates the usage of a cause-and-effect diagram in process analysis.

Example 10.1

The component assembly manufacturer decides to prepare a cause-and-effect diagram in order to identify problems on the entire manufacturing floor. All of the manufacturing steps for the assembly are presented in Figure 10.5. Looking specifically at the assembly area, the improvement team identified several problems that were responsible for non-conforming units. First problem with the product (assembly) had been traced to the assembly area. The problem was traced to the incorrect handling method for the sub-component by the stores department prior to insertion in the assembly. Also the quality control program for the sub-components coming from vendors and other plants was found defective. A third source of damage during assembly was tools at the work stations, since operators were not trained to use the tools properly and the tools were not kept in proper operating condition. In addition, the operators were causing damage, since they were not trained and certified properly in the assembly procedure. Finally, the assembly, not being handled properly in the work stations was causing damage and resulting in non-conformities. Other areas of the process were analyzed similarly and the causes identified.

Customer Material Unit Exit Error Code Identification Handling

Cause and Effect ,\nalysis

\ Quality Control \ \ \ \

Stores On-line Test /

Maintenance

Training Material / Handling Test Station

Material Work Handling Station

racnlng Material

Test Station Box

Figure 10.6 : Process Analysis of an Assembly Line using Cause-and-effect Iliagram

Quality Tools - Others 10.4 PARETO ANALYSIS AND CAUSE-AND-EFFECT DIAGRAM

Pareto analysis is a technique for focusing attention on the most important problem areas. The Pareto concept, named after the 1 9 ' ~ century Italian economist Vilfredo Pareto, is that a relatively few factors generally account for a large percentage of the total cases (e.g. complaints, defects, problems). The idea is to classify the cases according to degree of importance, and focus on resolving the most important, leaving the less important. Often referred to as the 80-20 rule, the Pareto concept states that approxi~nately 80 per cent ol'the problems come from 20 per cent of the items. For instance, 8'. percent of machine breakdown come from 20 percent of the machines, and 80 percent of the product defects come from 20 percent of the causes of defects.

If the symptoms or causes of defective output or some other 'effect' are identified and recorded, it will be possible to determine what percentage can be attributed to any cause, and the probable results will be that the bulk (typically 80 percent) of the errors, waste, or 'effects', derive from a few for the cause (typically 20 percent). For example, figure 10.6 shows a ranked frequency distribution of a certain product. To improve the performance of the distribution process, therefore, the major incidents (broken bagsldrums, truck scheduling, and temperature problems) should be tackled first. An analysis of data to identify the major problems is known as Pareto analysis, after the Italian economist also realized the approximately 80 per cent of the wealth in his country was owned by approximately 20 percent of the people. Without an analysis for the set, it is far too easy to devote resources to addressing one symptom only because its cause seems immediately apparent.

Cause-and-effect diagrams are useful in identifying and isolating the cause, or the major causes, of a problem. This diagram, sometimes called a "fishbone diagram", lists the problem at one end of a horizontal line. Diagonal branches are drawn from this line for each major category of possible causes. More specific, contributory causes are added to the branch for each category. Example of a cause-and-effect diagram is shown in Figures 10.2-10.5. Cause-and-effect diagrams are useful in focusing the attention of an individual or improvement team on each specific possible cause of a problem and on possible solutions. Team often finds the technique of brainstorming useful as they deliberate and seek to uncover, the basic underlying cause of a problem and as they try to discover the most effective solution to identified problem.

A typical cause-and-effect diagram is often used in conjunction with Pareto analysis to identify and pinpoint causes to quality problem. This can be illustrated with the help of an example concerning the soldering process used in the manufacture of printed circuit boards (PCBs). A typical PCB has 1700 solder connections. Any defective solder connection can cause testing problem or performance and reliability problems for the customer.

In a particular organization, over 15 percent of observations exceeded control limits and a large number of solder connections required 'touch-up'. A project team was formed whose mission was to reduce the number of defective solder connections. A team of people, not from one department but from several cross-functional departments, was setup to guide the project and do the diagnosis. Figure 10.7 depicts the distribution of symptoms by type of solder defects. Data on the defects were analyzed and theories were offered on the cause of the defects. Figure 10.8 is a cause-and-effect diagram summarizing the theories. These theories were grouped into three categories, thereby allowing a checklist to be developed which was used by supervisors to evaluate the theories. After additional data collection and analysis, low solder temperature was found to be the main cause of the defect.

Figure 10.7 : Solder Defect Types. (Pareto Analysis)

Controller 1 Alloy t Amount

Maintenance

Temperature Control Error

Conveyor Speed

Movement -/ Interpretation

Specific Gravity

Storage \ I S o l d e r ) Defects

Cause and Effect Analysis

Specification ~ Z G ? p Z q

Figure 10.8 : Cause-and-effect Diagram for the Solder Defect

Further analysis revealed that, for ideal soldering conditions, either the temperature of the solder should be raised or the conveyor speed of the wave soldering machine should be reduced. These were remedies to remove the cause. A trial was conducted using a higher temperature. This resulted in an improvement in solder defects without any adverse effects.

SAQ 2

(a) Make a cause-and-effect diagram using dispersion analysis for the following problem. A compressor experience a frequent problem in the manufacturing process. The shaft for the compressor does not fit into the inner race of the bearing resulting in frequent rework. Make a dispersion analysis to solve the problem.

(b) Do cause-and-effect diagrams have any advantage over a simple list of possible cause of a problem? Why?

Quality Tools - Others 10.5 ROOT CAUSE ANALYSIS -

Cause-and-effect analysis can be further extrapolated to ensure that identified cause is the root cause of the problem and no? a symptom of a deep rooted cause. This technique is known as "Root cause analysis" or "Why-why chart". As the objective is to find the root cause of the problem, the starting point can be either a problem or a (high level) cause that should be further analyzed. Brainstorming is used to find the causes by the improvement team. Identified cause is questioned to find why this is a cause for the original problem. For each new answer to the question, further questions are asked till no new answer evolves. This can be one of the root causes for the problem. Often this requires five rounds of questions "Why".

SAQ 3

HOW cause-and-effect analysis is connected to FMEA?

10.6 SUMMARY --

To stay competitive in today's market place, it has become imperative for organizations to address problems early during product development cycle.

Number of analytical tools and techniques are used by quality improvement teams at different stages of improvement work. After the 'understanding stage', the next step is to work identifying specific causes for problems and solutions to them.

Cause-and-effect analysis, often called lshikawa Diagram or Fish Bone Diagram, is one of the most widely used tool for problem analysis.

The cause-and-effect diagram is helpful in categorizing the causes of a problem. Once the diagram has been developed, the various causes are considered (on this basis of priority) to determine root causes and separate studies. It may be necessary to crush out a second-level cause-and-effect diagram as a step in identifying root cause.

There are three types of cause-and-effect diagram: cause enumeration, dispersion analysis and process analysis! Cause-and-effect diagram can be used in conjunction with Pareto analysis to pinpoint quality problems or can be further extrapolated by using Root Cause analysis.

10.7 KEY WORDS

Cause-and-Effect Diagram : A tool that uses a graphical description of the process elements to analyse potential sources of

' process variation.

Pareto Analysis : A coordinated approach for identifying, ranking, and working to permeability eliminate defects, focuses on important error sources, 80120 rule : 80 percent of the proble~ns are due to 20 percent of the causes.

I 0.8 ANSWERS TO SAQS Cause and Effect Analysis

SAQ 1

Globalization has intensified competition because customers can compare products or problem solutions worldwide according to their cost-benefit ratio. Organizations today confront many icons both internal and external, unthinkable in the past. Accordingly, improvement has become a necessity for organizations today.

The basic reasons are as follows

If an organization does not focus on improvement, it can be taken for granted that rivals will not miss out. If such unusual thing happens that both the parties do not improve it can be certainly said that others will try to penetrate the market.

It has been observed that efficiency level of enterprises tend to reduce with the passage of time unless extra effort is made fo maintain the level. For additional improvement efforts more than pure maintenance is required.

Expectations of customers are rising significantly because of improvement in quality of supply. So expectations of customers are to be met not to lose the customer.

SAQ 2

(a) A close inspection reveals that most of the defects originate from the inaccurate dimension of the shaft. A cross functional grouping consisting of designers, the manufacturing engineer, the assembly department manager and some operations was formed. The objective is to eliminate the cause of the problem. The cause-and-effect diagram gives import clauses of the problem.

Dimension Error of the

Cutting Coolant Improper Maintenance

High Temperature and Dust /-

Sharpening Infrequent

Environment EquipmentIMachine

Figure 10.9

SAQ 3

Background information about the product, process or design, prior to the performance of a risk analysis such as FMEA are valuable. A key aspect of well executed FMEA is the identification of causes which lead to failure modes in a system or design. Once root cause is identified, the FMEA team will be well equated to recommend corrective measures. However, it is the 'effect' which is identified in most cases. For example, as air disaster is blamed on gyrocompass

Quality Tools - failure as opposed to why gyrocompass failed. Space shuttle disaster was attributed to the '0' ring failure, which was an effect, whereas the 'cause' was why the component became brittle at low temperature. Customers are primarily concerned with effects and will identify them but are rarely concerned with causes. A cause will lead to a failure mode which in turn will lead to an effect. An experienced FMEA heam will be able to identify causes very well.

Cause -, Failure Mode --+ Effect

The causes will reside within the 'fishbone'.