Lesson 5: Quality Management / Statistical Quality Control

Question 1

What is Quality?

Answer 1

Meeting or exceeding the expectations of customers

In several fronts such as:

• Conformance to specifications
• Perceived value
• Fitness for use
• Support/services
• Psychological impression

Question 2

What are the dimensions of quality?

Answer 2

Performance - main characteristics of the product or services.

Aesthetics - appearance, feel, smell, taste.

Special Features - some extra characteristics.

Conformance - how well the product or service conforms to customer’s expectations.

Reliability - consistency of performance.
Durability - useful life of the product.

Perceived quality - indirect evaluation of quality, such as (e.g. reputation).

Serviceability - service after sale.

Question 3

How is service quality evaluated?

Answer 3

Tangibles - the physical appearance of facility, equipment, personnel, and communication materials.

Convenience - the availability and accessibility of the service.

Reliability - the ability to perform a service dependably, consistently, and accurately for a certain length of time.

Responsiveness - the willingness of service providers to help customers in unusual situations and to deal with problems.

Time - the speed with which service is delivered.

Assurance - the knowledge exhibited by personnel and their ability to convey trust and confidence.

Courtesy - the way customers are treated by employees.

Consistency - the ability to provide the same level of good quality repeatedly.

Question 4

Benefits of Quality

Answer 4

Quality products fetch premium prices in the market and create a loyal customer base. In addition, costs related to warranty expenses are lowest for such companies.

Improved Quality of Design & Reputation; Premium Prices; Loyal Customer Base; Lower Warranty Expenses.

Quality Improves Perceived Value, without acceptable quality, products/services cannot qualify for order qualifiers.

Question 5

Costs of Quality

Answer 5

Failure Costs:
Internal Failure Costs - fixing problems during production. (Yield losses, Rework)

External Failure Costs - fixing problems after delivery to customer. (Warranty, Consequential losses (Additional costs), Litigation cost, Reputation/Future revenue)

Appraisal Costs:
Appraisal costs are associated with inspection and testing. The cost comes down as prevention matures.

Helps in identifying the quality problems; Cost incurred in inspection and quality checks at various levels; Quality test development; Screening of defective product.

Prevention Costs:
Prevention costs are associated with preventing the defects before they happen. This may involve quality training, planning, customer assessment, creating SOPs (this is standard operation processes) etc. Prevention increases expenditure of time and money and may delay the product.

Redesigning the process; redesigning the product; training of employees; suppliers involvement.

Question 6

Cost of detecting a defect

Answer 6

The cost of detecting a defect grows exponentially as the product moves from the conceptual stage to manufacturing, testing and finally to customer.

Identifying the flaws in the process and testing stages may result in delay, but identifying them at the customer stage may bring recalls, lawsuits, bad reputation, etc.

Question 7

Quality Gurus

Answer 7

W. Edwards Deming gave 14 steps to Quality and emphasized on reducing variations, using statistical process control, and involvement of top management.

Joseph M. Juran focuses on continuous improvement, which includes planning control and improvement. He believes that 80% of quality defects are controllable, thus management has the responsibility to correct these deficiencies.

Armand Feigenbaum introduced the concept of “quality at the source”. For example, defects should not be passed to the next workstation.

Philip B. Crosby emphasize that Quality is free – without Quality you have to pay at the customer level and the cost will be very high. But by improving the design and process, we can save the failure costs. The cost of adopting the good quality practices will cost less than the failure costs and hence quality is free. Moreover, he believed that any level of defects is too much and management should introduce programs to target zero defects.

Question 8

Certifications

Answer 8

• ISO 9001
• ISO 14000

(Check Formula Sheet for more)

Question 9

What is Total Quality Management (TQM)?

Answer 9

Total Quality Management is a philosophy that involves everyone in an organization in a continual effort to improve quality and achieve customer satisfaction.

TQM requires the participation of anyone who is related to Quality. For example, suppliers of raw material and store keepers who unload the material and store it.

Question 10

What is Continuous Improvement (TQM)?

Answer 10

The philosophy of continually seeking ways to improve process (Kaizen).

Ways of doing this are:

• Identify benchmarks of excellent practices
• Continually improve the operation/process
• Develop a sense of operator ownership
• Involve all employees

Question 11

What is employee involvement (TQM)?

Answer 11

Quality is everyone’s responsibility, which means that everyone who is related to creating or producing services and products should involve themselves in detecting and correcting the quality issues. In other words, all employees should participate and should be given authority to contribute.

Employee empowerment is one of the pivotal ideas common to all quality improvement philosophies.

Employees can participate and provide solutions in many ways. Some of the most common approaches are:

Quality circles: A group of workers in the same department who meet to discuss ways of improving the products or processes.

Brainstorming: brainstorming is a technique for generating a free flow of ideas on finding causes and solutions.

Affinity diagram: An affinity diagram shows the relationships among large number of ideas.

There are also special purpose teams, and self-managing teams.

Question 12

What is customer satisfaction (TQM)?

Answer 12

The third goal of TQM is customer satisfaction, which means meeting or exceeding customer expectations.

TQM looks at the quality differently.

In a traditional quality management setting, the focus is only to look at the final product or services.

In TQM, we look at every aspect related to the product, from purchasing processes to manufacturing processes and beyond.

Question 13

TQM Philosophy

Answer 13

In the center, our focus is customer satisfaction – which improves with superior quality and services. Superior quality and services is achieved through continuous innovation and improvements and with the participation of employees who create the products and services. Continuous improvement and employee involvement requires the setting of new goals, using new designs of making tools, designing and improving processes, involving up stream partners which improves the purchasing, etc.

Question 14

Deming Wheel (PDSA):

Answer 14

Plan: Studying the current problem, document the problem, collect data, specify measures for evaluation and develop the plan.

Do: Implement the plan, document any changes made during this phase, collect data systematically for evaluation.

Study/check: Evaluate the collected data and check how closely results match the original goals of the plan.

Act: If the results are successful, standardize the new solution or technique, document it. If not, revise the plan and repeat the cycle.

Question 15

Which of the following is not a dimension of service quality?

• Conformance
• Tangibles
• Responsiveness
• Convenience
• Assurance

Answer 15

Conformance

Question 16

Defective material from suppliers and lost production time are examples of:

• Internal failure costs
• External failure costs
• Replacement costs
• Prevention costs
• Appraisal costs

Answer 16

Internal failure costs

Question 17

Costs related to inspections, testing, test equipment, and labs are examples of:

• Replacement costs
• Internal failure costs
• Appraisal costs
• External failure costs
• Prevention costs

Answer 17

Appraisal costs

Question 18

Which of the following is not an example of an external failure cost?

• Scrap and rework during production
• Handling complaints
• Price discounts to offset inferior quality
• Warranty claims
• Loss of customer goodwill

Answer 18

Scrap and rework during production

Question 19

Monitoring, testing, and correcting quality problems after they occur is known as:

• Perceived quality
• Quality control
• Quality assurance
• Continuous improvement
• Conformance

Answer 19

Quality control

Question 20

The process of identifying other organizations that are best at some facet of your operations, and then modeling your organization after them is known as:

• Industrial espionage
• Employee empowerment
• Continuous improvement
• Parody
• Benchmarking

Answer 20

Benchmarking

Question 21

Groups of workers who meet informally to discuss ways to improve products or processes are called:

• Quality circles
• Quality teams
• Continuous improvement teams
• Benchmarking teams
• Brainstorming teams

Answer 21

Quality circles

Question 22

True or False:
Total quality management explicitly recognizes that management is primarily responsible for quality, not the workers with direct responsibility for completing work tasks.

Answer 22

False

Question 23

True or False:
A company that commits to TQM adopts a process-oriented focus rather than the product-oriented focus which traditional organizations typically have.

Answer 23

True

Question 24

True or False:

Cost of inspectors, testing, test equipment, and labs are examples of appraisal costs.

Answer 24

True

Question 25

True or False: Broadly defined, quality refers to the ability of a product or service to consistently meet or exceed customer expectations.

Answer 25

True

Question 26

Common Quality Tools

Answer 26

Checklists; Histograms/Bar Charts; Pareto Charts; Scatter Diagrams; Cause-and-effect Diagrams; Graphs; Control Charts.

Question 27

Checklists

Answer 27

Checklist are for data collection. To record frequency of occurrence of certain characteristic of service or product.

Question 28

Histograms/Bar Charts

Answer 28

In histograms and bar charts, we plot the frequency of desired information. It is useful for a comparative study. For example, we can plot number of defective products produced either every hour or every shift or machine etc. Similarly, we can plot average customer waiting time with respect to every customer service representative, every day of the week, etc.

Question 29

Pareto charts

Answer 29

Pareto charts help answer the question of which quality problem should be addressed first? Named after Vilfredo Pareto, these charts tend to show the 80-20 rule: that 80% of the activity is caused by 20% of the factors.

Question 30

Scatter diagrams

Answer 30

Scatter diagrams are useful in finding the correlation between two variables. For example, is there any relation between fatigue (continuous working hours) and number of defective products? Another correlation example is that the motor of newly produced blenders produces excessive vibration with rise of motor temperature.

Question 31

Cause-and-effect

Answer 31

Cause-and-effect diagrams are also known as fish-bone diagram. It helps us in finding the cause and effects. For example, if we see a low number of students show up to class in one given day, we can identify several causes. It could be due to transport problem, or some big public event or due to exam preparation, etc. Once we have effects, we can identify the causes.

Question 32

Graphs

Answer 32

Graphs or run charts are very similar to scatter diagrams or bar charts. We plot data points with respect to time to observe any trends. In fact, run charts are produced continuously and based on the observation. Other tools are used to investigate further.

Question 33

Control charts

Answer 33

Control charts are used to plot some attributes or dimensions of the products – very similar to graphs. However, in control charts, we also plot control limits and we observe if each data point is within the limits.

Question 34

Benchmarking

Answer 34

Benchmarking is one way of improving quality performance. It involves planning, analysis, integration and action. Planning involves identifying the process in your organization that needs an improvement, identifying a firm for bench marking, identifying performance measure and then data collection. Data collection will help in establishing the gap and identifying the causes of low performance. Integration involves setting up the goals and support, and in action, we develop a plan to improve the process, implement the improved process, monitor the progress, etc.

Question 35

Quality Engineering

Answer 35

An approach that involves combining engineering and statistical methods to reduce costs and improve quality by optimizing product design and manufacturing process.

Question 36

Quality Loss Function (Taguchi Loss Function)

Answer 36

Deviation of Quality characteristics from the target values. Taguchi was a pioneer in quantifying the quality in the form of function – mostly known as Quality loss function. Taguchi Concepts include: Quality robustness, Quality loss function, and Target-oriented quality.

Question 37

Six Sigma

Answer 37

Sigma is a Greek notation, commonly used to represent the standard deviation. Higher standard deviations mean there is more variability around the mean and hence, a higher chance of unacceptable Quality. Typically, the central area of normal curves can be represented in terms of sigma. It simply says that if the deviation in the process is so small, that is, sigma is so small, then the product’s specification limits can cover roughly all of the normal curve and we may not be making any defective products. For instance, 6 sigma quality level means we may be producing 3.4 defects per million, which means, whatever the variability we are producing, it is still within the specification limits.

Question 38

Quality Tools Problems Solve %

Answer 38

90% of the quality problems can be fixed by basic quality tools and philosophy. Improving the process further requires the Six Sigma quality philosophy. 90% - Basic tools of quality < 10% - Six Sigma < 1% Outside Specialists

Question 39

Six Sigma Improvement Model

Answer 39

Define - Measure - Analyze - Improve - Control

Question 40

Define (Six Sigma Improvement Model)

Answer 40

Determine the characteristics of the processes which are critical to customer satisfaction and identify any characteristics and the process capabilities.

Question 41

Measure (Six Sigma Improvement Model)

Answer 41

Quantify the work the process does that affect the gap. Decide what to measure, Identify data source, Data collection.

Question 42

Analyze (Six Sigma Improvement Model)

Answer 42

Perform process analysis—process improvement and redesign. Includes statistical process control, cause-effect diagram, scatter diagram, etc.

Question 43

Improve (Six Sigma Improvement Model)

Answer 43

Modify or redesign existing methods to meet the new performance objectives. Implement the changes.

Question 44

Control (Six Sigma Improvement Model)

Answer 44

Monitor the process to make sure that high performance levels are maintained. Again, data analysis, etc., will help with monitoring and evaluation of relative progress.

Question 45

A fishbone diagram would be used to:

Answer 45

Categorize potential causes of a problem.

Question 46

A quality improvement technique that involves the sharing of thoughts and ideas in a way that encourages unrestrained collective thinking is:

Answer 46

Brainstorming

Question 47

A chart showing the number of occurrences by category would be used in:

Answer 47

A Pareto analysis

Question 48

The tool that is useful to investigate the relationship between two variables is:

Answer 48

A scatter diagram

Question 49

True or False: Taguchi quality loss function is a graphical representation of how an increase in deviation from the target value leads to a faster rate of increase in customer dissatisfaction.

Answer 49

True

Question 50

True or False: The purpose of benchmarking is to establish a standard against which the organization's performance can be judged, and to identify a model for possible improvement.

Answer 50

True

Question 51

True or False: | Organizations committed to Six Sigma programs have very capable and precise processes.

Answer 51

True

Question 52

Statistical Quality Control

Answer 52

Uses statistical techniques and sampling to monitor and test the quality of goods and services, in order to avoid 100% inspection.

Question 53

Acceptance Sampling

Answer 53

Relies on the inspection of a sample from a batch to determine whether the batch is acceptable or not.

Question 54

Statistical Process Control

Answer 54

Determines if the process is operating within the acceptable limits during the production.

Question 55

Double Sample Plan

Answer 55

If the first sample failed the inspection, then we pick another sample. If the combined defectives in both samples are less than a predetermined number (c2), we keep the lot. Otherwise, we reject it.

Question 56

Sampling Errors

Answer 56

Since, we are accepting the lot based on the inspection of a very small number of items, our approach could give the wrong conclusion. We may pick a defective lot or we may reject a good lot based on our sampling. These errors are commonly known as type 1 and type 2 errors.

Question 57

Type 1 Error

Answer 57

When the part is good and our experiment says it is bad. This increases the probability of rejecting good parts as scrap.

Question 58

Type 2 Error

Answer 58

When part is bad but we accept it as a good. This increases the probability of a customer getting a bad lot represented as good.

Question 59

Sampling Plan Careful Design

Answer 59

Overall expected cost due to sampling (which includes costs of accepting defective items) is smaller than the costs of inspecting more or all items. It achieves the purpose of sampling- saving time, space, capital. To ensure the acceptable quality level (maximum percentage of defects that a company is willing to accept).

Question 60

True or False: | If a lot, or batch, is "rejected" during acceptance sampling, the lot will usually be thrown away.

Answer 60

False

Question 61

True or False: In a single-sampling plan, the entire lot, or batch of items, is accepted or rejected based upon only one specified sized sample.

Answer 61

True

Question 62

True or False: | Acceptance sampling is most useful when the cost consequences of passing defectives are low.

Answer 62

True

Question 63

True or False: | Acceptance sampling plans must specify the lot size, the sample size, and the acceptance/rejection criteria.

Answer 63

True

Question 64

True or False: | In a double-sampling plan, a second sample is taken if the results of the first sample are inconclusive.

Answer 64

True

Question 65

Acceptance sampling plans might call for selection of all of the following except: - 100% inspection plan - A single sample - Two samples - Multiple samples - Several samples

Answer 65

100% inspection plan

Question 66

A Type II (beta) error occurs when:

Answer 66

A bad lot is accepted

Question 67

A Type I (alpha) error occurs when:

Answer 67

A good lot is rejected

Question 68

Process Control Charts

Answer 68

Statistical techniques used to identify these variations and label them as random or assignable. Introduced by Walter A. Shewhart (1920), Bell Laboratories Around 100 years in existence Used as a tool to assist in controlling variation Japanese manufacturing became more competitive by using these tools

Question 69

Assignable Variations Identified

Answer 69

The process may not be capable and our intervention is required in order to investigate the cause of unnatural variations.

Question 70

Random variation

Answer 70

Natural variations in the output of process, created by countless minor factors.

Question 71

Assignable variation

Answer 71

A variation whose source can be identified

Question 72

Main task of SPC (Statistical Process Control)

Answer 72

Distinguish assignable from random variation

Question 73

Normal Distribution (Quick Info)

Answer 73

If some samples are outside the 3 sigma limit, the probability of such an event happening is very small or very rare. We conclude that it may not be due to random variation and an investigation is necessary.

Question 74

Type 1 and 2 Errors SPC

Answer 74

1: Concluding a process has changed when it has not 2: Concluding a process is in control when it is not

Question 75

Control Charts for Variables

Answer 75

Sample Mean Chart; Sample Range Chart;

Question 76

Sample Mean Chart

Answer 76

Sample mean control charts are popularly known as X bar chart. In this chart, we track our sample means and if the sample means deviate much i.e. falls outside the control limits, we mark the process out of control.

Question 77

Sample Range Chart

Answer 77

Sample range chart are popularly known as R charts. In this chart, we compute the range of a given sample and plot the range. These expressions provide the control limits for the Range chart. D3 and D4 values are provided in the same table. Typically, R charts always plot in association with X-bar charts because X chart tries to monitor the Mean of the process and R monitors dispersion of the sample. If any of the chart is out of control, we label the process out-of-control.

Question 78

Control Charts for Attributes

Answer 78

Control charts for attributes are used when the process characteristic is counted rather than measured. P-charts; C-charts.

Question 79

P-charts

Answer 79

P stands for proportion or probability. So, if the items can be easily categorized as good or bad, then it will be very easy to compute proportion defectives in a lot or compute the probability of defective items in a sample/lot. In p-charts, we pick samples and in each sample we find the number of defective items. The number of defective items divided by the sample size will give us the proportion of defectives or percentage of defectives. Based on that, we compute the control limits. The p-chart is used to monitor the fraction of defectives in samples. These expressions are used to compute the control limits. sigma limits are commonly used so we use z=3 Note: Because the formula for control limits is an approximation, sometimes LCL will be negative. In this case, zero should be used as the lower control limit.

Question 80

C-charts

Answer 80

The c-chart is used to monitor the number of defects per unit. These expressions are used to compute the control limits. 3 sigma limits are commonly used so we use z=3. If the value of c is unknown, as is generally the case, the sample estimate is used in place of c. When the lower control limit is negative, it is set to zero. C-charts are used when the number of occurrences of some attributes per unit is measured. Such as: Scratches, chips, dents, or errors per item; Cracks or faults per unit of distance; Breaks or tears per unit of area.

Question 81

Non-Random Patterns in Control Charts

Answer 81

In control charts, we see if the variations are randomly distributed around the central line. If they are not, then they must be forming some pattern – for example, three or more points on one side of the central line, or showing upward or down ward trend, etc. Remember, we say that if a point is outside the control limit, then the process needs attention – because the probability that a normal process shows such behavior is very small – or we call it a rare event. The control chart is used to identify such rare events. In other words, if the process is normal and points are forming some patterns, the probability of such event is very small and thus if such is happening, then the process requires attention. This chart shows commonly non-random patterns. In other words, even when all the points are within the control limits, these processes require attention.

Question 82

True or False: | Quality control efforts that occur during production are referred to as statistical process control.

Answer 82

True

Question 83

True or False: | The optimum level of inspection minimizes the sum of inspection costs and the cost of passing defectives.

Answer 83

True

Question 84

True or False: | Concluding that a process has not changed when it has is known as a Type I error.

Answer 84

False

Question 85

True or False: | Concluding that a process has changed when it has is known as a Type II error.

Answer 85

False

Question 86

True or False: | Statistical process control is based on comparing periodic samples from a process to predetermined limits.

Answer 86

True

Question 87

True or False: | Assignable variation is variation due to a specific cause, such as tool wear.

Answer 87

True

Question 88

True or False: | A sample statistic that falls outside the control limits suggests that the process mean has changed.

Answer 88

True

Question 89

True or False: | Sample range control charts are used to monitor process dispersion.

Answer 89

True

Question 90

True or False: If a point on a control chart falls outside one of the control limits, this suggests that the process output is non-random, assignable variation.

Answer 90

True

Question 91

True or False: | A p-chart is used to monitor the fraction of defectives in the output of a process.

Answer 91

True

Question 92

True or False: | A c-chart is used to monitor the number of defects per unit of a process output.

Answer 92

True

Question 93

True or False: | The number of defective parts in a sample is a process characteristic that is counted rather than measured.

Answer 93

True

Question 94

True or False: | A process is "capable" if the process output falls within the design specification.

Answer 94

True

Question 95

The purpose of control charts is to:

Answer 95

Distinguish between random variation and assignable variation in a process

Question 96

As the sample size increases, the distribution of sample averages approaches a Normal distribution regardless of the shape of the sampled population. This is identified in which of the following? - Assignable Variation - Random Variation - Central limit theorem - Type I errors - Mean charts

Answer 96

Central limit theorem

Question 97

A control chart used to monitor the process mean is the:

Answer 97

x-bar chart

Question 98

Using three sigma control limits (rather than two sigma limits) tends to have what impact on error probabilities?

Answer 98

Increase the Type II and decrease the Type I.

Question 99

A control chart used to monitor the fraction of defectives generated by a process is the:

Answer 99

p-chart

Question 100

The range chart (R-chart) is most likely to detect a change in:

Answer 100

Process variability

Question 101

A c-chart is used for:

Answer 101

Number of defects per unit

Question 102

You want to prepare an R-chart. ​ If the number of observations in a sample is 5, what is the appropriate “factor” used in the computation of the LCL?

Answer 102

The factor used in the computation of the UCL and LCL is 0 (from Table 10-3).

Question 103

You want to prepare a p-chart and you observe 200 samples with 10 in each and find 5 defective units. ​ What is the resulting “proportion defective”?

Answer 103

The resulting proportion defective is 0.0025 since 5/(200x10) = 0.0025.

Question 104

You want to prepare an x-bar chart. ​ If the number of observations in a “subgroup” is 10, what is the appropriate “factor” used in the computation of the UCL and LCL?

Answer 104

The factor used in the computation of the UCL and LCL is 0.31 (from Table 10-3).

Question 105

Process Capability

Answer 105

Ability of the process to meet the design specifications for a service or product.

Question 106

Capability Analysis

Answer 106

The determination of whether the variability of the process output falls within the acceptable range of variability allowed by the design specification.

Question 107

Capable (Capability Analysis)

Answer 107

Process output falls within specifications

Question 108

Incapable (Capability Analysis)

Answer 108

1. Redesign process or reduce variability 2. Use alternative process 3. Use 100% inspection 4. Examine/relax design specification

Question 109

Cookie Packages (Cpk)

Answer 109

An index that shows how well the units being produced fit within the specification limits. The process is considered capable if Cpk greater or equal to 1. This process will produce a relatively high number of defects. Many companies look for a Cpk of 1.3 or better. Six Sigma companies want 2.0.

Question 110

A methodology that is used to show how well parts being produced fit into a range specified by design limits is:

Answer 110

Capability Analysis

Question 111

True or False: | Control limits and process variability are directly related.

Answer 111

True

Question 112

True or False: | "Process capability" compares "process variability" to the "design specifications".

Answer 112

True

Question 113

True or False: The process capability index, indicated by Cp is calculated as the ratio of the design specification width to the process width.

Answer 113

True

Question 114

True or False: | The process capability index, indicated by Cpk is used only when the process is centred.

Answer 114

False

Question 115

True or False: | In order for a process to be capable, it must have a capability ratio of at least 1.00.

Answer 115

True