Title: Introduction%20to%20SPC
1Introduction to SPC
- 2WS02 Industrial Statistics
- A. Di Bucchianico
2What 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??
3Statistical methods
- acceptance sampling (AS)
- statistical process control (SPC)
- design of experiments (DOE)
4Dimensions of Quality
- Performance
- Reliability
- Durability
- Serviceability
- Aesthetics
- Features
- Perceived Quality
- Conformance to standards
5Definitions of Quality
- Fitness for use
- design
- conformance
- Inversely proportional to variability
6Why study history of quality control?
- understand and foresee trends and future
developments - companies may still be working with concepts
from the past
7History 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
8History 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)
9History part I inspection
- inspection just before shipping of product
- related definition of quality
- conformance to specifications
10Problems 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
11How many times does the letter f occur ?
- Finished files are the result of years of
scientific study combined with the experience of
many years.
12How many times does the letter f occur ?
- Finished files are the result of years of
scientific study combined with the experience of
many years.
13Example 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)
14History part II Acceptance sampling
15History 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
16History part III Monitoring process output
OCAP
control charts
limits
single process
output
input
17SPC 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
18History 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.
19History 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.
20History 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.
21History 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.
22History 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
- ...
23History 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.
24Process thinking
- all deviations from product specifications have
causes in production process - outcome production process is caused by many
process factors
25Design of Experiments
- preferably design phase (cf. EVOP)
- off-line
- team
- detect causes of variation
- optimise process
26History 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
27History 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.
28Conformance to specifications
- why is product just outside specifications worse
than product just inside specifications?
29Conformance to specifications II
specifications of characteristic 2
specifications of characteristic 1
30History 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
31History 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.
32History 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
33History 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
34History 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
35Summary 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