Quality System

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Quality System

• System approach to quality concept

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What is Quality?

• Dictionary Definition a degree or level of
  excellence
• ANSI and ASQC the totality of futures and
  characteristics of a product or service that
  bears on its ability to satisfy given needs

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Quality System

• Involves the quality concept and quality cost
  through all phases of product, which are
• Idea Generation
• Concept Development
• Product and Process Design
• Full-scale Production
• Product Introduction
• Market Evaluation

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Product Development Process
Idea Generation
Concept development
Product process design
Full-scale production
Product introduction
Market evaluation
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A Typical Example

• From the standpoint of value received, the
  product quality is determined by the economic
  losses imposed upon society from the time a
  product is released for shipment.
• Loss caused by Functional VariationThe
  deviation of one of a products principle
  functional characteristics from the specified
  nominal (target) value of the product design
  specification.

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Quality System (2)

• If process design and quality control engineering
  are not capable of sufficiently reducing
  deviation by process adjustments, then inspection
  may be an economically useful alternative.

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Quality System (3)

• To minimize loss, one is faced with the task of
  producing the product at optimal levels with
  minimal variation in its functional
  characteristics.

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Input Output Diagram
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Signal Factors

• These are the parameters set by the user or
  operator of the product to express the intended
  value for the response of the product
• ExamplesThe spead setting on a table fanThe
  steering wheel angle
• The signal factors are selected by design
  engineer based on the engineering knowledge of
  the product being developed

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Controllable factors

• These are the parameters that can be specified by
  the desiner to determine the best values of these
  parameters
• Examples
• Dimensions of product
• Choice of material
• Cycle time or mould temperature in an injection
  moulding process

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Noise Factors

• Those nuisance variables which are either
  difficult, or impossible, or expansive to
  control.
• Essentially there are three types of noise
  factors
• Outher noise
• Inner noise
• Between product noise

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Noise Factors (cont.)

• Noise Factors, in general, are responsible for
  causing a products functional characteristicsto
  deviate from its target specified by the signal
  factor and lead to quality loss
• Is the goal then to identify the most guilty
  noise factors so that one may attempt to control
  them? No!

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Noise Factors (cont.)

• The levels of the noise factors change from one
  unit to another, from one environment to onother,
  and from time to time.
• Only the statistical characteristics (such as the
  mean and variance) of noise factors can be known
  or specified but the actual values in specific
  situations are not known.

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Purpose of Quality System

• The broad pupose of the overall Quality System is
  to produce a product that is robust with respect
  to all noise factors.
• Robustness implies that the products functional
  characteristics are not sensitive to variation
  caused by noise factors.

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Quality Control Activities

• In order to achieve robustness, quality control
  efforts must begin in the product design phase
  and be continued through production engineering
  and production operation phases.
• The following figure shows the three steps that
  are involved in the engineering optimization of a
  product or process
• System Design (conceptual design)
• Parameter Design
• Tolerance Design

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System Design

• In this step, the designer examines variaty of
  architectures and technologies for achieving the
  desired function of the product and selects the
  most suitable ones for the product
• Involves innovation and requires knowledge from
  the field of science and engineering

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System Design (cont.)

• It includes
• The development of a prototype design
• Determination of materials
• Parts
• Components (in the product design stage)
• The selection of production equipment
• Tentative values for process factors
• The determination of the manufacturing process.

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System Design (cont.)

• Can play an important role in reducing the
  sensitivity to noice factors as well as in
  reducing the manufacturing cost
• Quality Function Deployment is a technique that
  can improve the quality and productivity of the
  concept design step

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Parameter Desin

• In this step, the levels (values) of controllable
  factors (design parameters) are selected to
  minimize the effect of noise factors on the
  functional characteristics of the product
• We assume
• Wide tolerances on the noise factors
• That the low grade components and materials would
  be used

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Parameter Design (cont.)

• If at the end of parameter design the quality
  loss is within specifications, we have a design
  with the lowest cost and we need not go to the
  third step
• However in practice the quality loss must be
  further reduced therefore, we always have to go
  to the third step

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Tolerance Design

• It is employed if the reduced variation obtained
  through parameter design is not sufficent.
• It involves thighting tolerances on product
  parameters or process factors whose variations
  impart large influence on the output variation

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Tolerance Design (cont.)

• Tolerance design means spending money-buying
  better grade materials, components or machinary
• In USA, most engineers jump from system design to
  tolerance design
• Japanese do so well in parameter design

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• In 1987, during one of his consulting visits with
  ITT, Dr. Taguchi presented the figures shown
  below
• Time spent by engineers
• USA Japan
• System Design 88 20
• Parameter Design 2 50
• Tolerance Design 10 30

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Off-line and On-line Q.C.

• Quality control activities at the product
  planning, design and and production engineering
  phases will be referred to as off-line quality
  control or quality engineering
• Quality control activities during actual
  production will be referred to as on-line quality
  control

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• Don Clausing and T.B. Bakers jointly prepared
  figure given below illustrates the off-line and
  on-line process.

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Quality Engineering in Product Design

• System Design (example) The design of an
  electrical circuit for a TV set that converts an
  input of 100 V alternating current to 115 V DC
  current requires a search for the technically
  best circuit that is specifically relavent to
  this design. An automatic control system might be
  included in the design so that a target value of
  the desired voltage 115 is set.

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Quality Engineering in Product Design (cont.)

• Then continuous measurements of output power
  of the circuit are taken. If there are deviations
  between the measurements and the target value,
  the automatic control system should change the
  relevant parameter in the circuit. For instance,
  it may change the resistance value of a rheostat
  so that the difference between the target value
  and the measured output voltage is reduced to
  zero.

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Parameter Design

• Once the system design is established, the next
  step is to ascertain the optimal levels for the
  parameters of each element in the system so that
  the functional deviations of the product are
  minimized.
• As an illustration of parameter design, consider
  the design example of the electric power circuit
  for a television set with the capacity to convert
  an input of 100 V AC to an output of 115 V DC.

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Quality Engineering in Product Design (cont.)

• Parameter Design (example) Consider an example
  where 100 V is supplied to the prototype circuit
  but an output of only 80 V is obtained. To reduce
  the gap of 35 (115-80) V the parameter hFE
  (transistor gain) of a transistor used in the
  curcuit is set at a differntial level. The effect
  of transistor gain on the output voltage is shown
  in the following figure

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Evaluation of the graph

• Ao should be chosen
• This choice will reduce the difference to 20 V
  which must be eliminated
• Use resistor to reduce the difference 20 V to
  zero
• Increase of 1 kO in resistance decrease the
  voltage by 5 V
• Therefore choose a value of the resistor 4 O
  4520 V

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Quality Engineering in product design (cont.)

• Tolerance Design This step is to determine the
  tolerance of each individual parameter (factor)
  by trading off quality loss and cost.
• Example The effect of hFe on the output voltage
  A0 30 90 - 150

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Quality Engineering in Design of Production
Processes

• A. System Design
• The main objective of System Design is to
  determine the manufacturing processes that can
  produce the product within the specified limits
  and tolerances at the lowest cost
• For example, there are generally many
  manufacturing processes that can perform the same
  function on a workpiece
• Metal removal can be performed by using turning
  operation, milling operation, or shaping
  operations

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Quality Engineering in Design of Production
Processes (cont.)

• B. Parameter Design
• It determines the operating levels of the
  manufacturing processes so that variation in
  product parameter is minimized.
• Typical Examples
• Temparature variation
• Raw material variation
• Input-valtage variation
• Tool condition variation
• These variations, as well as several unidentified
  noise factors, can cause nonuniformity in the
  production processes, resulting in out of
  specification products
• Experimental design approach is used to determine
  the optimal levels of the parameters for the
  process.

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Quality Engineering in Design of production
Processes (cont.)

• C. Tolerance Design
• The objective in this step is to find
• optimal ranges of the operating
• conditions that minimize the sum of
• variation cost and the cost of the
• product
• This is the on-line feedback control system
• design problem

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Quality Engineering in production

• It is known that all processes will drift if
  control is not applied
• The purpose of on-line quality control is to
  produce uniform products by adjusting processes
  according to the information about the processes
  and/or the product produced

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Quality Engineering in production(cont.)

• Quality is a function of not only design, but of
  the control system
• Without controlling the process, it is not
  possible to control a products quality
• How often should we observe the process or
  product, and what are the optimal control limits?

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Quality Characteristics

• They are the elemental building block with which
  quality is constructed
• Determining appropriate quality characteristics
  it may be helpful to think of them as falling
  into one of the three categories
• Measurable characteritics
• Attribute characteristics
• Dynamic Charateristics

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Measurable Characteristics

• They are those end results or care-abouts that
  can be measured on a continous scale.
• They can be subdivided into three categories
• Nominal the best
• Smaller the better
• Larger the better

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Nominal the best

• Characteristics with a specific numerical goal or
  target value
• Dimensions typically fall within this category
• Specific examples include
• Heigth, length, witdh, tichness, diameter
• Area, volume, clearance, pressure
• mixture, moisture, PH, voltage

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Smaller-the-better

• A smaller-the-better characteristics is one in
  which the desired goal is to obtain a measure of
  zero
• A common example is shrinkage other examples
  include
• Machine wear, residue, contamination
• Lines of computer code, loudness
• Product deterioration, access time

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Larger-the-better

• The goal of larger-the-better characteristics is
  to achieve the highest value possible
• Infinity is the ultimate objective.
• Examples
• Strength, miles/gallon, ignition temperature,
  mean time between failures
• Melting point, corrosion resistance, vibration

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Attribute Characteristics

• Can not be measured on a continuous scale.
  Instead, they consist of classes into which the
  end results can be grouped.
• For example eggs are grouped into Grade A small,
  Grade A medium, Grade A large, Grade A extra
  large, Grade A Jumbo

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Attribute Characteristics (cont.)

• The simplest form of attribute data is Go/No Go,
  or pass/fail data
• Examples
• Reject rate, Scrap rate, Yield,
• Number of defects

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Attribute Characteristics (cont.)

• Classified attribute characteristics provide more
  information than No/No go
• No/No go determines whether the units are good or
  bad. Classified attribute characteristics
  evaluates the units interms of degree of goodness
  or badness.

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Attribute Characteristics (cont.)

• For example, in electronics assembly,
  bleedover is defined as the tendency of solder to
  run from one circuit bad to another.
• Rating Description
• 0 No bleedover
• 1 Bleedover up to 25 to adjacent pad
• 2 Bleedover between 25 and 50
• 3 Bleedover between 50 and 75
• 4 Over 75 to adjacent pad

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Elements of Cost

• Quality at what cost?
• Delivering a high-quality product at low cost is
  an interdisciplinary problem involving
  engineering, economics, statistics, and
  management.
• The three main categories of cost one must
  consider in delivering a product are
• Operating Cost
• Manufacturing Cost
• RD Cost

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Operating Cost

• It consist of the cost of energy needed to
  operate the product, environmental control,
  maintenence, inventory of spare parts and units,
  etc.
• A manufacturer can greately reduce the operating
  cost by designing the products sensitivity to
  environmental and usage conditions, manufacturing
  variation, and deterioration of parts.

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Manufacturing Cost

• Important elements of manufacturing cost are
  equipment, machinery, raw materials, labor,
  scrap, rework, etc.
• It is important to keep the unit manufacturing
  cost (umc) low by using low-grade material,
  employing less skilled workers, and using
  less-expensive equipment,and at the same time
  maintain an appropriate level of quality.
• This is possible by designing the product and the
  manufacturing process robust

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RD Cost

• The time taken to develop a new product plus the
  amount of engineering and laboratory resources
  needed are the major elements of RD cost.
• The goal of RD activity is to keep the umc and
  operating cost low.
• Robust Design play an important role in achieving
  this goal.

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Dynamic Characteristics

• A dynamic characteristic is a functional
  representation of the process being studied. The
  process is viewed as a dynamic system described
  by a signal or input and by the resulting output
  or end result that is a result of this signal.
• A basic example is the temperature control for a
  room. The thermostat (system) can be adjusted to
  a range of temperatures (input signal), and the
  number of people in the room.

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Dynamic Characteristic Examples

• System/Subsystem M Input Signal y Output
• Measurement system True value Measured value
• Sensing system True state Signal sent out
• Photographic system True image Photographic
  image
• Control system Control given Resulting control
• Adjustment system Adjustment made Resulting
  change
• Communication system Signal to be sent Signal
  transmitted
• Radar True position Measured position
• Radar True image Received image
• Microscope True image Received image
• Copying function Original contrast Copied
  contrast
• Paper feeder Roller rotation Paper travel
  distance
• Automatic transmission Engine RPM Change of gear
• Molding Die dimension Molded dimension
• Shower water temperature Adjustment Resulting
  temperature
• Steering function Steering wheel angle Vehicle
  turning radius
• Digital communication Zero/one Zero/one
• Thermostat Temperature On/off
• From Dynamic System Optimization An
  Introduction to Dynamic Characteristics