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Introduction%20to%20SPC

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Title: 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
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