Manufacturing Processes for Engineering Materials (5th

1
Manufacturing Processes for Engineering
Materials (5th Edition in SI Units)

• Chapter 4
• - Surfaces oxide layer, contaminants, roughness
• - Tribology friction, wear, lubrication
• Dimensional Characteristics tolerance
• Inspection
• - Product Quality Assurance SQC, SPC

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Surface Structure and Properties

• Thickness of individual layers depends on
  processing conditions and environment.
• During processing residual stresses may develop
  due to
• Non-uniform surface deformation
• Severe temperature gradients

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Surface Structure and Properties

• Surface integrity
• Surface integrity describes the geometric
  features, mechanical and metallurgical properties
  of surfaces.
• Defects can be caused by
• defects in the original material
• method by which the surface is produced
• lack of proper control of process parameters

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Surface Texture and Roughness

• All surfaces have their own set of
  characteristics (surface texture).
• Some guidelines for identifying surface texture
• Flaws, or defects,
• Lay, or directionality
• Waviness
• Roughness

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Surface Texture and Roughness

• Surface roughness
• Described by 2 factors
• Arithmetic mean value
• Root-mean-square average
• Maximum roughness height, Rt, used as a measure
  of surface roughness.

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Surface Texture and Roughness

• Symbols for surface roughness
• Symbols used to specify only the roughness,
  waviness, and lay, not flaw.
• Measuring surface roughness
• Surface profilometers used to measure and record
  surface roughness.

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Tribology Friction, Wear and Lubrication -
Friction

• Friction is defined as the resistance to relative
  sliding between two contact bodies under load.
• Adhesion theory of friction
• Based on the observation that two clean, dry
  surfaces, in contact at only small area of
  contact.
• This bond involves atomic interactions, mutual
  solubility, and diffusion.

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Tribology Friction, Wear and Lubrication -
Friction

• Coefficient of friction
• Coefficient of friction at the interface is
• Relationship of F and N is as the follow graph.

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Tribology Friction, Wear and Lubrication -
Friction

• Coefficient of friction
• Friction factor, or shear factor, m, is defined
  as
• Different processes need different coefficient
  friction factor.

where ti shear strength of the interface
k shear yield stress of the softer
material in a sliding pair
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Tribology Friction, Wear and Lubrication -
Friction

• Abrasion theory of friction
• Plowing is when hard body slide over soft body
  where it will scratch and produce grooves on the
  lower surface.
• Involves 2 mechanisms
• surface is deformed plastically.
• generates a chip or sliver from the softer body.

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Tribology Friction, Wear and Lubrication -
Friction

• Measuring friction
• Ring compression test
• Good lubrication, both the inner and outer
  diameters increase as the specimen is compressed.
  
• Poor lubrication, friction is high and inner
  diameter decreases.

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Example 4.1Determining the coefficient of
friction
In a ring compression test, a specimen 10 mm in
height with outside diameter of 30 mm and inside
diameter of 15 mm is reduced in thickness by 50.
Determine the coefficient of friction and the
friction factor if the outer diameter (OD) after
deformation is 39 mm. Solution From constant
volume constancy, Thus, For a 50 reduction in
height and a 13 reduction in ID,
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Wear

• Wear is the undesired removal of material from a
  surface.
• Affects the manufacturing process, size and
  quality of the parts produced.
• It will change the surface topography and result
  in severe surface damage.

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Wear

• Adhesive wear
• Define as when applying tangential force,
  shearing of the junctions take place at the
  original interface of the two bodies or along a
  path at the interface.
• Archard wear law states that

where V vol of material remove k
wear coefficient L length of travel
W normal load p
indentation hardness of soft body
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Example 4.2Adhesive wear in sliding
The end of a rod made of 60-40 brass is sliding
over the unlubricated surface of hardened tool
steel with a load of 90.72 kg. The hardness of
brass is 120 HB. What is the distance travelled
to produce a wear volume of 1.64e-8 m3 by
adhesive wear of the brass rod? Solution The
distance travelled is
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Wear

• Abrasive wear
• Abrasive wear is caused by a hard and rough
  surface sliding against another.
• Removes particles by producing slivers resulting
  in grooves on the softer surface.
• Abrasive wear resistance of pure metals and
  ceramics is directly proportional to their
  hardness.

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Wear

• Corrosive wear
• Corrosive wear or oxidation is caused by chemical
  reactions between surfaces and environment.
• Fatigue wear
• Fatigue wear is caused by surfaces subjected to
  cyclic loading.
• Reduced by (a) lowering contact stresses, (b)
  reducing thermal cycling and (c) improving the
  quality of materials.

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Lubrication

• The interface is subjected to a wide range of
  variables
• Contact pressure
• Speed
• Temperature
• When two surfaces slide each other under high
  pressure, speed, and/or temperature, friction and
  wear will be high.

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Lubrication

• Lubrication regimes
• 4 regimes of lubrication
• Thick film
• Thin film
• Mixed
• Boundary lubrication
• (Film Teflon, DLC-Gillet)

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Metalworking fluids

• Functions of metalworking fluids
• Reduce friction
• Reduce wear, seizure, and galling
• Improve material flow
• Act as a thermal barrier
• Act as a release or parting agent
• Metalworking fluids includes Oils, emulsion,
  Synthetic solutions, Soaps, Greases and Waxes.

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Surface Treatments, Coatingsand Cleaning

• Surface treatments are necessary to
• Improve resistance to wear, erosion, and
  indentation
• Control friction
• Reduce adhesion
• Improve lubrication
• Improve resistance to corrosion and oxidation
• Improve fatigue resistance
• Rebuild surfaces on components
• Improve surface roughness

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Surface treatment processes

• Some examples (Modification by mechanical
  thermal methods)
• Shot peening, water-jet peening, and laser shot
  peening
• Roller burnishing (surface rolling)
• Thermal spraying

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Cleaning of surfaces

• Cleaning involves the removal of solid,
  semisolid, or liquid contaminants from a surface.
• Depends on the type of contaminants to be
  removed.
• Some of the cleaning methods
• Mechanical cleaning methods physically
  disturbing the contaminants.
• Electrolytic cleaning a charge is applied to be
  cleaned in an acqueous solution.
• Chemical cleaning methods removing oil and
  grease from surfaces.

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Engineering Metrology and Instrumentation

• Engineering metrology is the measurement of
  dimensions.
• Quality of an instrument involves
• Accuracy agreement between the measured and true
  magnitude
• Precision degree of repeated measurements
• Resolution smallest dimension read
• Sensitivity smallest difference in dimensions
  distinguished

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Dimensional Tolerances

• Defined as the acceptable variation in the
  dimensions (height, width, depth, diameter,
  angles) of a part.
• Tolerances are unavoidable.
• Certain terminology is used to define geometric
  tolerances.

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Dimensional Tolerances

• There is a general relationship between
  tolerances and surface finish of parts
  manufactured by different processes.
• Be careful when defining
• the tolerance

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Testing and Inspection- Nondestructive testing
techniques

• Carried out in such a manner that part integrity
  and surface texture are preserved.
• Commonly used techniques
• liquid-penetrants- fluids penetrate into
  openings
• magnetic-particle inspection- placing fine
  ferromagnetic particles on the surface
• ultrasonic inspection- ultrasonic beam trave
• X-ray inspection (short wavelength penetrates
  deeper)

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Automated inspection

• Uses sensors that monitor the relevant parameters
  during the manufacturing process (on-line
  inspection).
• Flexible, high responsive, less operator skill is
  required, productivity is increased, higher
  quality, reliability and dimensional accuracy.

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Quality Assurance

• Quality assurance is to ensure that the products
  conform to specifications and standards.
• Responsibility of everyone involved.
• Control materials and processes that the products
  are made correctly in the first place.
• Inspections must be continued throughout
  production for
• - dimensions and properties- performance of
  tools, dies, and machines - human error-
  assembly errors

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Statistical methods of quality control

• Essential as a large number of material and
  process variables are involved in manufacturing
  operations.
• Random events are called chance variations while
  events with specific causes are called assignable
  variations.
• Terms commonly used in statistical quality
  control (SQC)
• - Sample size- Random sampling- Population-
  Lot size

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Statistical methods of quality control

• The method of variables is the quantitative
  measurement of characteristics such as dimensions
  and tolerances.
• Data from manufacturing operations is represented
  by the normal distribution curve.

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Statistical methods of quality control

• Average value (arithmetic mean) is defined as
• Difference between the largest value and smallest
  value is called the range.
• Dispersion is estimated by the standard deviation.

n number of measurements
x measured value for each part.
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Statistical methods of quality control

• Six sigma
• A set of statistical tools, based total quality
  management principles.
• Measure the quality of products and services in
  selected projects.
• Includes considerations such as - ensuring
  customer satisfaction- delivering defect-free
  products - understanding process capabilities

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Statistical process control

• Advises operator of the appropriate measures to
  avoid producing further defective parts.
• Known as statistical process control (SPC).
• Consists of
• control charts and setting control limits
• capabilities of the particular manufacturing
  process
• characteristics of the machinery involved

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Statistical process control

• Control charts
• Represent the variations of a process over a
  period of time.
• Consist of data plotted during production.

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Statistical process control

• Control charts
• Control limits are set to statistical-control
  formulas within acceptable range.
• Control limits for R are obtained from
• We estimate standard deviation from