Quality Control Tools

Quality Control (QC) is a procedure which intends to ensure that, a manufactured product or performed service adheres to a defined set of quality principles or meets the demands of the customer. The QC tools are used to achieve quality.

The following are considered as the basic tools for achieving quality control:

Flow Chart Check sheet Histogram Pareto Analysis Scatter Diagram Control Chart

Cause and Effect Diagram

Now let us consider each tool listed above and analyse how it helps to improve the quality of a system.

Flow Chart: It is a visual representation of process, showing the various steps. It helps in locating the points at which a problem exists or an improvement is possible. Detailed data can be

collected, analysed, and methods for correction can be developed. A sample is shown below.

1. List the various steps or activities in a particular job.

2. Classify them as a procedure or a decision.

3. Each decision point generates alternatives.

4. Criteria and Consequences that go with decision are amenable to evaluation for purposes of assessing quality.

The flow chart helps in pin-pointing the exact point at which errors have crept in. A simple chart is shown below.

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Opn Insp Opn Insp Pack Rej Rej

Figure 11.1: Process Flow Chart 1

Check Sheet: These are used to record the number of defects, types of defects, locations at which they occur, times at which they occur, and the workmen responsible for its occurrence. These sheets make a record of the frequencies of occurrence with reference to possible defect causing

parameter. It helps to implement a corrective procedure at the point where the frequencies are more, so that the benefit of correction will be maximum.

A sample sheet is shown below.

Table 11.1: Check Sheet DEFECT DAY 1 2 3 4 5 1 // /// /// ///// //

2 / //// /// //// ///

3 // ////// //// // //

4 // //// /// // //

5 /// ////// /// / ///

6 // //// /// /// //

The above table depicts that the number of defects in 1 and 5 are not many as compared to defect no 2, which increased over the days and appears to be stabilising at the higher side. Therefore these defects in 2 have to be attended immediately. The column representing days can be changed to represent observed by the hour, if required.

Histogram . Histograms are pictorial representations of distribution of data.

They are used to record big volumes of data about a process. They reveal whether the pattern of distribution has a single peak or many peaks and also

the extent of variation around the peak value. This helps in identifying whether the problem is serious. When used in conjunction with parameters Operations Management Unit 11

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that are comparable, the visual patterns help us to identify the problem which must be attended to.

14 27 32 50 29 20 0 10 20 30 40 50 60 70 80 90 100

A B C D E F FREQUENCY

Figure 11.2: Histogram

The values shown in the above figure are the number of observations made regarding a parameter. Sometimes, percentages are shown to demonstrate the relative contribution of each of the parameters.

Pareto Analysis . Pareto Analysis is a tool for dividing problem areas according to the degree of importance and attending to the most important.

Pareto principle, also called 80-20 rule, states that 80 percent of the

problems that we encounter arise out of 20 percent of items. If you find that, in a day, you have as many as 184 assemblies having problems and there are 11 possible causes. It is observed that 80 per cent of them, that is, 147 of them have been caused by just two or three of them. It will be easy to focus on these two or three and reduce the number of defects to a great extent. When the cause of these defects has been attended, we will observe that some other defect becomes predominantly observed. It is observed that if the process is continued, we will march towards zero defects.

Scatter Diagram . These are used when we have two variables and want to know the degree of relationship between them. We can determine if there is any cause and effect relationship existing between and its extent over a range of values. Sometimes, we assume that there is no relationship, in Operations Management Unit 11

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which we can change one parameter making sure that it does not affect the variable.

Figure 11.3: Scatter Diagram

We can see that the change in Variable 2 does not have much effect on Variable1. The other interpretation can be that for a small change in Variable 1, the effect on Variable 2 is more.

Control Charts . These are used to verify whether a process is under control. When variables remain within a range, they will render the product and maintain the specifications. This is the quality of conformance. The design parameters determine the range of permitted deviations. Samples

are taken and the mean and range of the variable of each sample

(subgroup) is recorded. The mean of the means, of the samples gives the control lines. Assuming normal distribution, we expect 99.97 per cent of all values to lie within the Upper Control Limit (UCL) and Lower Control Limit (LCL). Corresponding to + 3.. The graphical representation of data helps in changing settings to bring back the process closer to the target.

Consider The Following Data:

A shaft is to be made with a diameter of 25mm. They area required to be ground to be between +0.01 and -0.02mm, by a process of centre less grinding. A sample of five nos. is taken every hour and the observations are recorded as shown below:

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9 A.M

24.98 24.99 25.0 25.04 25.01 10 A.M.

25.01 25.02 25.0 25.01 25.0 11 A.M.

24.99 24.98 25.02 25.02 24.97 12 Noon

24.97 24.99 25.01 25.04 25.03 2 P.M.

25.01 25.02 25.0 25.03 25.01 3 P.M.

24.99 24.98 25.02 24.97 25.00 4 P.M.

24.97 24.99 25.01 25.04 25.03 5 P.M.

25.01 25.02 25.0 25.03 25.01

1. Draw A Line Diagram Taking The Means Of Every Hour 2. Draw The R Chart And X Charts And

Determine Whether The Process Is Under Control.

The steps to be followed to find the range for the sample readings of each hour are:

Find the mean of the readings of each hour that is, x

Add all the means calculated above and take the mean of the means . you will get the mean for all samples.

The UCL is x . 3. where . is the standard deviation of the means of dimensions obtained on the dimensions of samples obtained every hour.

However, in drawing the control charts, it is customary to range a constant that depends on the size of the sample, to calculate the UCL and LCL. The formulas are as under.

d n R UCL x 2 3 . .

d n R UCL x 2 3 . .

d2 - values depend on the sample size.

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On a graph sheet, y axis represents the dimension. The mean value is drawn as a horizontal line, near the middle of the y-axis while the horizontal axis represents the serial number, of the

samples. Variations of the dimensions get marked on both sides of the mean line.

Cause and Effect Diagram: In this diagram all possible causes are classified on quality

characteristics that lead to a defect. These are arranged in such a way that, different branches representing causes connect the stem, in the direction of the discovery of the problem. When each of them is investigated thoroughly, we will be able to pinpoint some factors that cause the problem. We will also observe that a few of them will have cumulative effect or even a cascading effect.

Figure 11.4: Cause and Effect Diagram

When we observe that we have excessive defects from a machine, we try to identify all possible sources of the causes of defects. We make a study of each of them and try to correct it.

Acceptance Sampling . In this method of quality control, the supplier and customer agree upon accepting a lot, by inspecting a small number taken randomly from the bulk supply. Out of the sample, if a small number is determined and accepted by both parties are defective, the lot is accepted. If the number of defectives is more than the agreed size, the entire lot is rejected.

Obviously, risks for the producer and buyer exist. As the sample Operations Management Unit 11

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size increases and the number of acceptable defectives decreases, the risk for the buyer decreases. And the converse is also true. That is the reason these numbers cannot be fixed, as they depend on the customer.s requirements. Sometimes parties go for a doubling sampling plan.

In this case, a range of defectives is fixed. If defectives are less, the lot is accepted. If it is more than the higher number, the lot is rejected. If the no of defectives falls between the above two numbers, another sample of a higher size is taken for inspection. If the total number of defectives is less than another determined number, the lot is accepted.

11.4 Quality Based Strategy

Strategy means planning and supplementing a series of activities based on the evaluation of both internal and external environment, so as to maximise the yield. Essentially short term and long term objectives are in the horizon. The available resources, both present and future are evaluated. Within the restraints they place on the system, the most beneficial activities are planned. Most importantly, an assessment of the competitors in all these aspects is made to either confront it or bypass it, for reaching the goals. Unless these are not based on the quality of the product or service, the effort is meaningless. Quality in design, manufacture, packing,

delivery, pricing, and after sales service acts as an advantage and plays an important role is ensuring customer satisfaction. So the foundation of any strategy should be quality. Nowadays price is also a component of quality. To achieve quality at low prices, efficiencies in all processes have to be realised. This is where we have Lean Manufacturing, Just in time, Flexible

Manufacturing Systems, and so on that play a vital role in controlling costs. Working for quality awards like Deming, Malcolm Baldrige Awards increases efficiencies in the organisation and builds customer confidence.

11.5 Total Quality Management (TQM)

TQM is viewed from many angles . as a philosophy, as an approach and journey towards excellence. The main motive is to satisfy customer by involving everybody in the organisation, in various functions with constant improvement driving all activities. TQM systems are designed to prevent poor quality in products/services. The steps listed below have to be implemented to achieve Total Quality:

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1. Take all measures to know what the customer wants that is, voice of the customer. Develop methods that generate facts, which can be used for decision making. Do not ignore the internal customer that is, the next person in the process.

2. Transform the demands into design specifications that meet or exceed customer expectations.

3. Processes are to be designed, so that they facilitate doing the job right from the first time.

Include elements that make it impossible to commit mistakes. It is known as fail-saving or fool proofing. The Japanese call it Pokayoke.

4. Maintain record of all procedures followed, occurrences, and consequences. They help in formulising the processes, so that constant improvement becomes possible. More particularly, any gaps can be seen and corrected immediately.

One of the basic tenets of TQM is ¡°just because something is working well, improvement is not necessary¡±. The search must be continuous, to find ways and means to improve every aspect of the business process like finance, operations, and management. Complacency must never be allowed to creep in at any time. In this aspect, culture plays an important role. All these require top management commitment

11.5.1 Approaches to TQM

Being practiced worldwide by different organisations, TQM has different approaches towards its achievement. The basic thrust of each of these is realising excellence. All the approaches have many features in common, but the emphasis shifts from one to the other. Needless to say, each organisation will use any of these or even a combination to suit its structure, culture, and need.

Some emphasise on the philosophy of TQM and the role of management and employees in being aware, committed and act. Some expect us to use statistics more intensely. Some give us an .integrated approach.. The following are some of the approaches used to determine the quality of product/services:

Deming Wheel

Juran.s Quality Triology Crosby.s Absolutes of Quality Taguchi.s Quality Loss Function Operations Management Unit 11 .: 222

Deming Wheel

Deming wheel or PDSA Cycle, as it is called is a constant quality enhancing model; it consists of a logical sequence of four repetitive steps for constant enhancement and learning

Deming¡¯s approach is summarised in his 14 points.

Constancy of purpose for continuous improvement.

Adopt the TQM philosophy for economic purposes.

Do not depend on inspection to deliver quality.

Do not award any business based on price alone.

Improve the system of production and service constantly.

Conduct meaningful training on the job.

Adopt modern methods of supervision and leadership.

Eliminate fear from the minds of every individual, connected with the organisation.

Remove barriers between departments and people.

Do not exhort, repeat slogans, and put up posters.

Do not set up numerical quotas and work standards.

Give pride of workmanship to the workmen.

Education and training to be given vigorously.

State and show top management.s commitment, for better quality and productivity.

Deming with the help of the above principles gave a four step approach to ensure a purposeful journey of TQM. The slope illustrated in figure 11.5 is used to indicate that, if efforts are let up, the programme will roll back.

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Act Plan

Check Do

Deming Cycle -Plan -Do -Check- Act Figure 11.5: Deming Wheel

The explanation for every quarter of the Deming Wheel, shown in the above figure is as follows:

Plan . means that a problem is detected, processes are stated and relevant theories are checked out.

Do . means that the plan is implemented on a trial basis. All inputs are correctly measured and recorded.

Check . means that the trials taken according to the plan are in accordance with the expected results.

Act . means that regular production is started, so that quality outcomes are assured when the above steps are satisfying.

Juran¡¯s Quality Triology

Juran utilised his well-known Universal Breakthrough Sequence to implement quality programmes. He suggested the following quality programs:

Proof of need: This means that there should be a compelling need to make changes.

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Project Identification: in this, what is to be changed is defined and determined. Projects with certain time frames and the resource allocation are determined.

Organisation with top management.s commitment is made by assigning people and fixing their responsibilities.

Diagnostic journey: Every team will determine the systematically or randomly or deliberately arising problems. Root causes are ascertained with utmost certainty.

Remedial Action: This is the stage when changes are introduced. Validation, testing, and inspection, are also included at this point.

Holding on to the gains: The above steps result in beneficiary results. Maintaining records of all actions and consequences assists in further improvements. The actions that resulted in the benefits derived must be the norm for establishing standards.

Juran has classified cost of quality into four categories, they are:

Failure costs . Internal: These are costs of rejections, repairs, and so on in terms of materials, labour, machine time, and loss of morale.

Failure costs . External: These are costs of replacement, on-site rework including spare parts, and expenses of the personnel, warranty costs, and loss of goodwill.

Appraisal Costs: This consists of costs of inspection, including maintenance of records, certification, segregation costs, and so on.

Prevention costs: This consists of the sequence of three sets of activities that is, Quality Planning, Quality Control, and Quality Improvement from the trio logy, to achieve Total Quality

Management.

Juran argues that:

Good planning considering the needs of both internal and external customers and developing processes to meet them, results in good quality. The processes are also planned to meet them.

Quality is built into the system of manufacture, inputs, and processes that are on stream like raw material, spare parts, labour, machine maintenance, training, warehousing, inspection

procedures, packaging, and so on. They Operations Management Unit 11

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should be prepared to follow certain standards and control exercised, to make sure that mistakes do not repeat often and if they occur they are corrected at the source.

Quality Improvement measures are very important to preserve the quality culture. Newer methods will be found, some operations can be eliminated, and improved technology will be available. In short, as experience is gained, things can always be done better. It is for the management to take

the responsibility and encourage the employees to be on the look out for opportunities for improvement.

Crosby¡¯s Absolutes of Quality

Like Deming, Crosby also lays emphasis on top management commitment and responsibility for designing the system so that, defects are not inevitable. He requested that there should be no restriction on spending for achieving the best quality. In the long run, maintaining quality is easier and cheaper or economical rather than compromising on its achievement.

Crosby.s absolutes are listed below:

Quality is conformance to requirements, not .goodness..

Prevention, not appraisal, is the path to quality.

Quality is measured as the price paid for non-conformance and as indexes.

Quality originates in all factions. There are no quality problems. It is the people, design, and process who create problems.

Crosby has also given 14 points similar to those of Deming. His approach stresses on, increasing awareness, measurement of quality, error cause removal, corrective action, and continuously reinforcing the system, so that advantages derived are not lost over time. He intends that the quality management regimen must improve the overall health of the firm or organisation and prescribed a vaccine.The ingredients of the vaccine are:

Commitment . Integrity and honesty to produce everything right first time and every time.

Communication . Flow of information between suppliers, departments, customers helps in recognising opportunities.

Systems and operations . These must bring in a quality environment so that everybody is uncomfortable with anything less than the best.

Taguchi¡¯s Quality Loss Function

His contention is that quality comes from design. He propagated a wide use of Design of Experiments, for experimentation on variables and obtains specifications those results in the highest quality of the product. It assists in bringing price effective improvements in quality. He beliefs that designers must prepare effective designs, so that product can withstand the

variability.s that tend to be consistent and give quality for longer periods. His objective in transferring the loss function is, to make producers realise that it is the target value of the specification that must be achieved and not the permissible deviations. The loss caused is the double of the deviation multiplied by a cost constant that is represented as shown below:

2 L . C(X .T)

Where L = Total Loss C = Cost constant

X = average value of the quality characteristic T = target value of the characteristic.

Taguchi also explains about losses to society because of a dent in quality.

That is, both the manufacturers and users in society, who will have to endure the consequences of, reduced performance, as long as the product

That is, both the manufacturers and users in society, who will have to endure the consequences of, reduced performance, as long as the product

In document Operations Management (Page 117-125)