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MEC322 - Manufacturing fundamentals > Week 1 - Eng. Metrology > Flashcards

Week 1 - Eng. Metrology Flashcards

1
Q

Metrology term meaning

A

(From greek ‘metron’ (Measure, and –logy) is a science of measurement

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2
Q

Metrology definition

A

Metrology include all theoretical and practical aspect of measurement

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3
Q

Metrology Importance

A
  • Modern manufacturing development (concept of interchangeable parts)
  • Ex: Ford rear axles same dimensions, easy to fit
  • Ex: Royal Royce, parts hand fitted, takes 30min to fit
  • Science of measurement
  • Modern design, each part has certain dimension and tolerance to function together
  • Metrology used by manufacturing engineer to measure parts within tolerance
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4
Q

Car manufacturing example

A
  • Car assembly line worker only get 15 secs @station

- If part doesn’t fit, worker stops line

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5
Q

Dimensions and tolerances

A

Factors that determine performance of products, other than mechanical and physical properties:

  • Dimensions: Linear or angular sizes of a component specified on the part drawing. (# value)
  • Tolerances: Allowable variations from the specified part dimensions that are permitted
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6
Q

Dimensions (ANSI Y14.5M-1982)

A
  • Represent nominal or basic sizes of the part and its features.
  • Indicates the part size desired by the designer if it could be made w/ errors
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7
Q

Tolerances (ANSI Y14.5M-1982)

A
  • Total amount by which a dimension is permitted to vary. Difference between max and min limits.
  • Variations occur in any manufacturing process
  • Tolerances used to define limits of allowed variation
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8
Q

Tolerance

A
  • Tolerare, put up with, endure
  • Impossible to make perfect parts
  • Too small tolerance, high cost
  • NIST tolerance shrink by a factor of 3 every 10 year . 001mium
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9
Q

Tolerance importance

A
  • Parts from the same machine can be different:
  • Speed of operation
  • Temperature
  • Lubrication
  • Variation of incoming material
  • other
  • ISO system; definitions
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10
Q

Bilateral Tolerance

A
  • Variation permitted in positive and negative directions from the nominal dimension
  • Possible to be unbalanced. Ex: 2.500 +0.010, -.005
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11
Q

Unilateral Tolerance

A

-Variation from the specified dimension only permitted in one direction
-Either positive or negative
Ex: 2.500 +0.010 -0.000

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12
Q

Limit dimensions

A

-Permissible variation in a part feature size consist of the max and min dimensions allowed.
Ex: 2.505, 2.495

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13
Q

Ways to specify limits for dimensions

A
  • Bilateral
  • Unilateral
  • Limit dimensions
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14
Q

Tolerance control (slide 17)

A

slide 17

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15
Q

Engineering drawing symbols

A

slide 20

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16
Q

Geometric tolerance

A

Tolerances that involve shape features of the part

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17
Q

Allowance

A

Specific difference in dimensions between mating parts

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18
Q

Basic size

A

Dimension from which limits of size are derived

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19
Q

Bilateral tolerance

A

Deviation from the basic size (+ or -)

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20
Q

Clearence

A

Space between mating parts

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21
Q

Clearance fit

A

Fit that allows rotation or sliding b/ mating parts

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22
Q

Datum

A

Theoretically exact axis, point, line or plane

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23
Q

Feature

A

Physically identifiable portion of a part, eg hole, slot pin, chamfer

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24
Q

Fit

A

Range of looseness or tightness

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25
Q

Interference

A

Negative clearence

26
Q

Interference fit

A

The external dimension of one part slightly exceeds the internal dimension of the part into which it has to fit

27
Q

Limit dimension

A

Max and min dimension of a part

28
Q

MMC (Maximum material condition)

A

Condition where a feature of size contains the max amount of material within the stated limits of size

29
Q

Positional tolerancing

A

A system of specifying the true position, size, and form of the feature of a part including allowable variation

30
Q

Transition fit

A

Fit with small clearance or interference that allows for accurate location of mating parts

31
Q

Surface technology

A

Concerns with:

  • Defining the characteristic of a surface
  • Surface texture
  • Surface integrity
  • Relationship b/ manufacturing processes and characteristics of resulting surface
32
Q

Nominal surface

A

Designer’s intended surface contour of part, defined by lines in the eng. drawing

  • Nominal surfaces appear as absolutely straight lines, ideal circles, round holes, and other edges and surfaces that are geometrically perfect
  • Actual surfaces of a part are determined by the manufacturing processes used to make it
33
Q

Surfaces

A
  • Surfaces have properties and behaviour that is different from the bulk of the part
  • Surfaces affect function, appearance of the manufactured parts
34
Q

Surface appearance

A
  • How the surface feels
  • How it looks
  • How it behaves for coating or sealing
35
Q

Surface function

A
  • How it behaves in contact with another surface
  • How the surface will wear
  • How well will it retain lubricant
  • How well will it hold a load
36
Q

Why surfaces are important?

A
  • Aesthetic reason (smooth surface, favorable impression to customer)
  • Surfaces affect safety
  • Friction and wear depend on surface characteristics
  • Surfaces affect mechanical and physical properties (surface flaws-stress concentration point)
  • Assembly of part is affected by their surfaces (strength of adhesively bonded joint-increases when surface is slightly rough)
  • Subsequent operation (painting, coating, welding, soldering)
  • Smooth surfaces make better electrical contacts (good electrical and thermal conductivity)
37
Q

Metallic part surface

A

OUT-IN

  • Surface texture
  • Altered layer
  • Substrate
38
Q

Surface characteristics

A
  • Microscopic scale reveals irregularities
  • Substrate: bulk of the part, under the surface
  • Surface texture: roughness, waviness, flaws
  • Altered layer: Work hardening (Mech E), Heat (thermal E), chemicals, electrical E.
  • Surface integrity (definition, specification, and control of surface layer, includes surface texture and altered layer
39
Q

Contamination

A 
-Oxide film:
  Rust(Iron), Aluminum
-Other
  Dirt, oil, cutting fluids, lubricants, absorbed gases.
-Affects appearance
-Inhibits joining
  Soldering, plating, adhesives
40
Q

Surface structure of metals

A
  • Contaminant
  • Absorbed gas
  • Oxide layer
  • Amorphous (beilby) layer
  • Work-hardened layer
  • Metal substrate
41
Q

Surface texture

A

Repetitive and/or random deviations from the nominal surface of an object

  • Lay direction
  • Crack
  • Waviness spacing
  • Waviness height
  • Roughness height
  • Roughness width
42
Q

Surface texture

A

The topography and geometric features of the surface:

  • When highly magnified, the surface is anything but straight and smooth
  • Has patterns and/or direction resulting from the mech process that produced it
43
Q

4 Elements of surface texture

A
  1. Roughness:
    small, finely-spaced deviations from nominal surface
    -Determined by material characteristics and processes that formed the surface
  2. Waviness:
    Deviations of much larger spacing
    -Occurs due to work deflection, vibration, heat treatment, etc
    -Roughness is superimposed on waviness
  3. Lay:
    Predominant direction or pattern of the surface texture
  4. Flaws:
    Irregularities that occur occasionally on the surface
    Cracks, scratches, inclusions
    Although some flaws relate to surface texture, they also affect surface integrity
44
Q

Surface roughness

A

A measurable characteristic based on roughness deviations

Within surface texture

45
Q

Surface finish

A

More subjective term denoting smoothness and general quality of a surface
Surface finish=surface roughness
Surface texture

46
Q

Surface roughness

A

Average of vertical deviations from nominal surface over a specified

47
Q

Surface roughness equation

A

slide 45

48
Q

Surface roughness specification

A

slide49

49
Q

Cutoff length

A

-Problem of Ra computation is that waviness may get included
-To deal with it a parameter called cutoff length is used as a filter to separate waviness from roughness deviations
-Cutoff length is a sampling distance along the surface
Shorter than the waviness eliminates waviness deviations and only includes roughness deviations

50
Q

Surface integrity

A
  • Metallurgical changes in the altered layer beneath the surface that can have a significant effect on a material’s mechanical properties
  • Study and control of this subsurface layer and the changes in it that occur during processing which may influence the performance of the finished part
51
Q

Energy forms in surface integrity

A
  • Mechanical (forging, extrusion,machining)
  • Thermal
  • Chemical
  • Electrical
52
Q

Surface changes by Mechanical energy

A
  • Residual stresses in subsurface layer
  • Cracks micro and macro
  • Voids or inclusions
  • Hardness variations
53
Q

Surface changes by thermal energy

A

-Metallurgical changes
(re-crystallization, grain size changes, phase changes)
-Redeposited
Metal is removed from the surface in molten state, reattached prior to solidification
-Resolidified material
Portion of the metal which was melted and then solidified without detaching from the surface
-Heat affected zone in welding
Region not melted but heated to undergo metallurgical changes
-Hardness changes

54
Q

Surface changes by Chemical energy

A
  • Intergranular attack (corrosion and oxidation)
  • Chemical contamination
  • Absorption of certain elements such as H and Cl in metal surface (lead to property change)
  • Selective Etch: concentrate on certain components in the base metal
  • Alloy depletion and resulting hardness changes
55
Q

Surface changes by electrical energy

A
  • Changes in conductivity and/or magnetism
  • Craters, rough surface depression left in the surface, resulting from short circuits during certain electrical processing techniques such arc welding, electro dischange machining, electro chemical machining
56
Q

Sawed surface

A

slide 57 pic

57
Q

Turned surface

A

SLIDE 58 PIC

58
Q

Dimensional tolerances as a function of part size

A

slide 60 graph

59
Q

Dimensional tolerance range and surface roughness in various processes

A

slide 61 graph

60
Q

Tolerance and manufacturing processes

A
  • some processes more accurate than others
  • Examples:
    • Most machining accurate tolerances +/-0.05mm(0.002in) or better
    • Sand casting inaccurate, tolerances of 10 to 20 times the machined parts
61
Q

Surfaces and manufacturing processes

A
  • Some processes produce better surfaces than others
    • Processing cost higher with higher surface finish bc additional operations and more time are used
  • Processes for superior finishes: honing, lapping, polishing and superfinishing

MEC322 - Manufacturing fundamentals (2 decks)

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