Introduction%20to%20SPC

1
Introduction to SPC

• 2WS02 Industrial Statistics
• A. Di Bucchianico

2
What is Statistical Process Control (SPC )?

• The set of operational and managerial activities
  that a company uses to ensure that the quality
  characteristics of a product are at the required
  level??
• A series of control charts??

3
Statistical methods

• acceptance sampling (AS)
• statistical process control (SPC)
• design of experiments (DOE)

4
Dimensions of Quality

• Performance
• Reliability
• Durability
• Serviceability
• Aesthetics
• Features
• Perceived Quality
• Conformance to standards

5
Definitions of Quality

• Fitness for use
• design
• conformance
• Inversely proportional to variability

6
Why study history of quality control?

• understand and foresee trends and future
  developments
• companies may still be working with concepts
  from the past

7
History of Quality control

• craftsmen quality is what producer and consumer
  agree about
• start of mass-production
• parts should be exchangeable
• all the same
• no variability

8
History in the beginning

• Quality really became an issue during the
  Industrial revolution (19th century).
• Inspection-oriented quality was adopted in the
  emerging factories (usually through inspection
  department)
• F.W. Taylor started research on quality and
  management in the 1890s (for more information,
  read the introduction to the Taylor collection at
  the Stevens Institute of Technology)

9
History part I inspection

• inspection just before shipping of product
• related definition of quality
• conformance to specifications

10
Problems with total inspection

• mistakes have already been made
• one cannot inspect quality into a product
• does not yield insight in production process
• very expensive
• inspection is not water-tight

11
How many times does the letter f occur ?

• Finished files are the result of years of
  scientific study combined with the experience of
  many years.

12
How many times does the letter f occur ?

• Finished files are the result of years of
  scientific study combined with the experience of
  many years.

13
Example of acceptance sampling

• simplest form
• lot size N
• sample size n
• acceptance number c (lot is accepted if number of
  defectives in sample is ? c)
• OC (Operating characteristic)-curve gives
• P(acceptance of lot percentage defectives)

14
History part II Acceptance sampling
15
History W.A. Shewhart

• Shewhart developed at Bell Labs in the 1920s a
  process oriented control approach.
• Instead of inspection, production process is
  monitored
• Sampling plans were used to achieve acceptable
  quality levels (AQL)
• Techniques employed in quality control were
  statistical, basically sampling methods and
  control charts

16
History part III Monitoring process output
OCAP
control charts
limits
single process
output
input
17
SPC Statistical process control

• new important tool control chart
• measurements of production process during
  production
• prevention instead of detection afterwards
• monitoring variance behaviour of production
• corresponding definition of quality
• variation of process fits within tolerances

18
History World War II

• Increase of production during World War II caused
  a large expansion of quality control activities
  in both the U.S.A. and Britain.
• Statistical techniques were so effective that
  they were classified as military secrets during
  World War II!
• After World War II, the U.S.A. only had major
  production facility left.
• Lack of competition and enormous post-war demand
  caused disinterest in quality control.

19
History Japan

• Before World War II, Japanese products were cheap
  but of low quality.
• After World War II, Japan had to rebuild its
  factories (including the management structure).
• American consultants (in particular Deming and
  Juran) were brought in to teach quality.
• A national centre for quality control was
  established (JUSE) and many national activities
  were organized.
• Japanese companies have extensive training
  programme for everyone in the company.

20
History W.E. Deming

• Deming applied Shewharts principles of quality
  control at various places
• From 1950 on, he often visited Japan as lecturer
  and consultant (the Japanese honoured him by
  naming the highest Japanese quality award after
  him)
• In spite of this, his fame in the US did not
  really start until 1980.
• Deming puts much emphasis on management rather
  than production floor.

21
History J.M. Juran

• Early Japanese efforts in quality control
  overemphasised statistical methods under the
  influence of Deming.
• Jurans 1954 visit to Japan initiated a change of
  focus on technology to a focus on management
  (especially involvement of top-management).
• Juran also emphasised the importance of education
  and the cost of quality.

22
History part IV Problem solving tools

• 7 problem solving tools (Magnificent Seven)
• fishbone/Ishikawa diagram
• Pareto chart
• run chart
• defect concentration diagram
• Box-and Whisker plot
• ...

23
History K. Ishikawa

• Ishikawa was very important to the quality
  revolution in Japan because of his many
  activities (consulting, member of various
  committees, ...).
• Ishikawa stressed that quality control must try
  to meet the requirements of customers.
• Technical contribution the cause-and-effect (or
  fishbone) diagram.

24
Process thinking

• all deviations from product specifications have
  causes in production process
• outcome production process is caused by many
  process factors

25
Design of Experiments

• preferably design phase (cf. EVOP)
• off-line
• team
• detect causes of variation
• optimise process

26
History G.E.P. Box

• Introduced DOE in industrial environment since
  early 1950s
• Developed response surface methods at Imperial
  Chemical Industries
• Moved to US in 1960 and initiated Center for
  Quality and Productivity Improvement in
  Wisconsin
• ASQC history http//www.asq.org/join/about/histor
  y/box.html
• George Box award http//www.enbis.org/barcelonaco
  nference/gepbox.html

27
History Taguchi

• Systematic experimentation is necessary for
  product development that leads to high quality
  products
• Taguchi developed a system of statistical
  experimentation that meet the needs of the
  engineer working in industry and is easier to
  understand than the classical statistical methods
• Taguchi introduced the concept of loss function
  (i.e., how much do I conform to
  specifications?) and robust design.

28
Conformance to specifications

• why is product just outside specifications worse
  than product just inside specifications?

29
Conformance to specifications II
specifications of characteristic 2
specifications of characteristic 1
30
History US rediscovers quality control

• In the 1970s and 1980s Japan established itself
  as world leader in quality and became an economic
  superpower
• Several American industries could not compete
  with Japanese industries, because of their
  neglect of quality control
• Quality control starts to prosper again in the
  1980s in the US under the guidance of Deming,
  Juran and new names like Feigenbaum and Crosby.
• Examples of successful American companies include
  Ford (QS9000) and Motorola (Six Sigma).
• ASQ American Society for Quality

31
History Europe

• Interest in quality control in Europe did not
  start until the 1990s.
• Much emphasis in Europe on ISO 9000
  certification.
• European quality control initiatives like EFQM
  focus mainly on management issues.
• In 2000, ENBIS (European Network for Business and
  Industrial Statistics) was founded. Initiative by
  Bisgaard, then successor of Box in Wisconsin.

32
History part V Monitoring process input

• Control of process factors
• Prevention of disturbances
• Tools SPC, TPM, Poka Yoke, ...
• corresponding definition of quality
• variation of process fits within tolerances

33
History new developments

• An important new development is the Six Sigma
  approach developed by Motorola (one of the first
  winner of the Baldrige Award)
• Six Sigma approach uses known statistical and
  management concepts to come to an overall
  approach to quality
• use statistical tools (DOE, regression analysis)
  to understand relations between input and output
  parameters of processes
• use control charts on inputs instead of outputs
• direct link of efforts with reduction of costs

34
History part VI Quality by design

• Actions in design phase
• prevent quality problems in production phase
• prevent quality problems when customer uses
  product
• Typical tools Design of Experiments, Robust
  Design
• Corresponding definition of quality
• quality is conformance to customer requirements
  and expectations

35
Summary of historical development

• The main line of history to be remembered is
• total inspection
• acceptance sampling
• control charts on output
• control charts on input
• technical solutions/ TPM / ...
• quality by design