Metrology Flashcards
slay the midterm
Metrology is…
a science of measurement
Metrology includes…
all theoretical and practical aspect of measurement
what factors determine performance of product (other than mechanical and physical properties)
dimensions and tolerances
Definition of Dimensions
linear or angular sizes of components
Definition of Tolerances
allowable variation with NO effect on performance
dimensions on part drawings represent…
nominal or basic sizes of the part
when do variations occur?
occur in any manufacturing process (manifested as variations in part size)
what are tolerances used for?
used to define limits of allowed variation
If tolerance is too small what does it cost?
it costs ALOT, cost is high
how much does tolerence shrink every 10 years
shrinks by a factor of 3
Can parts from the same machine be different?
Yes.
1. speed of operation *
2. temperature *
3. lubrication
4. difference of incoming material *
What is bilateral tolerance
Two, variation in both positive and negative direction from nominal
Unilateral Tolerance?
One, either positive OR negative
Limit dimention?
Max dimension and min dimension, tolerance is the difference.
interference fit
you have to force it (shaft bigger than hole)
Transition fit
fit with small clearance or
interference that allows for accurate location of
mating parts
(shaft and hole are practically the same)
clearance fit
smaller than hole (fits easily and allows for rotation)
what are the 3 types of tolerance
- Bilateral (balanced and unbalanced)
- Unilateral (only one)
- limit dimension (max and min dimension)
Allowance
the specific difference in
dimensions between mating parts
Basic size
dimension from which limits of
size are derived
Clearance
the space between mating parts
Datum
theoretically exact axis, point, line or
plane
Fit
the range of looseness or tightness
Interference
negative clearance
Geometric tolerancing
tolerances that involve
shape features of the part
Feature
Physically identifiable portion of a
part, e.g. hole, slot, pin, chamfer
MMC (maximum material condition)
condition where a feature of size contains the maximum
amount of material within the stated limits of size
what is Positional tolerancing system
A system of specifying the
true 1.position, 2.size, and 3.form of the feature of a
part, including allowable variation
What are the three parts of a metallic part surface
- surface texture
- altered layer (sub surface layer)
- substrate (bulk)
which part from metallic part surface is most important and why
Altered layer/ subsurface layer… because it affects the functioning of the product
Surface roughness equations
- Ra = roughness average = (a+b+c..)/n
- Rq = root mean square = sqrt[(a^2+b^2…)/n]
Surface texture
repetitive/ random deviations from the nominal surface of an object
- Lay
predominant direction or pattern of the surface texture
- roughness
zoomed in variations (determined by material characteristics and process)
the 7 types of Lay
= parallel
⊥ perpendicular
x both direction in an angle
M Multi directional
C circular to center
R radial relative to center
P particulate, nondirectional or protuberant
Equation for surface-roughness measurement
- Ra = roughness average = (a+b+c+…)/n
- Rq = rooughness root mean square = sqroot[(a^2+b^2)/n]
- Flaws
irregularities that occasionally occur on surface. includes; cracks, scratches inclusions. (relate to surface texture but can affect surface integrity)
- waviness
zoomed out variations (deviations due to work deflection, vibration, heat treatment, and similar factors)
What are the 4 elements of surface texture
- roughness
- waviness
- lay
- flaws
- Lay
predominant direction or pattern of the surface texture
surface roughness
measurable characteristic based on roughness deviations
the 7 lay symbols
= parallel
⊥ perpendicular
X angular in both directions
M multidirectional
C circular relative to center
R radial relative to center
P particulate, nondirectional or protuberant
Surface finish
subjective term denoting smoothness and general quality of surface
- Flaws
irregularities that occur occasionally on the surface, relate to surface texture but also effect surface integrity. (cracks, scratches, inclusions, and defects in surface)
What are 4 elements of surface texture
- Roughness
- Waviness
- Lay
- Flaws
Cut off length
used as a filter between waviness roughness and waviness (cut off length is shorter than the waviness)
Surface Integrity
study of subsurface (altered) layer and changes
that occur during processing which may influence performance of finished product
4 types of energy that cause surface changes
- mechanical energy
- thermal energy
- chemical energy
- electrical energy
surface changes caused by mechanical energy
- residual stresses (causes week points
- hardness variations (after applying mechanical force it becomes much harder)
- cracks (micro & macroscopic)
- voids or inclusions
surface changes caused by thermal energy
- metallurgical changes
- redeposited
- resolidified material
- heat affected zone in welding
- hardness changes
surface changes caused by Chemical energy (fast production, commonly used)
- intergranular attach (corrosion and oxidation)
- chemical contamination
- absorption of certain elements such as h and CI in metal surface
- slective Etch
- alloy depletion and resulting hardness changes
surface changes caused by electrical energy
- change in conductivity/magnetism
- craters (rough surface depression left in the surface)
a better surface finish requires..
more money because it requires more operations and time. processes include horning, lapping, polishing and superfinishing.
Measurement
Procedure in which an unknown quantity is
compared to a known standard, using an
accepted and consistent system of units
In manufacturing what quantity is most focused on
Length quantity
Accuracy
closeness of agreement between an observed value and standard (systematic error)
Precision
closeness of agreement between randomly selected individual measurements (random error)
Magnification
amplification
Sensitivity
resolution (smallest difference in dimension)
Rule of 10
measuring tool is 10 times accurate than the tolerance ur measuring
Stability (drift)
ability to maintain calibrated status
what is the standard measuring temperature?
20 degrees Celsius
Repeatability is the
equipment variation (same person using the same instrument)
Reproducibility
operation variation (different people using the same instrument)
Calibration
comparing a measuring device to one having a known relationship to national standards
What are the 2 types of inspection
- inspection by variables
- inspection by attributes
1.Inspection by variable
product dimensions are measured by appropriate measuring instruments
- Inspection by attributes
pass or fail but we don’t know specifics (yes or no to a standard)
Contact vs. Non-Contact
contact is cheaper and non contact is expensive (lasers and light; x-rays, ultrasounds)
non contact is used for when u cant touch the product
Inspection/ testing points
- receiving inspection
- in-process inspection
- final inspection
100% manual inspection is…
100% manual inspection is not 100% good quality product
Automated 100% inspection gives ________ feedback
continuous
Acceptance Sampling
choosing a sample and deciding if the whole thing is valid or not
What is the economic model, breakeven analysis
p*c2 = C1
c1=cost of inspection
c2=cost of repair
p=true fraction nonconforminf
when do you use 100 % inspection
if p> c1/c2
when do you do nothing
if p < c1/c2
What are the 2 types of measuring instruments?
- Graduated measuring (inspection by variable)
- Nongraduated measuring (inspection by attribute)
what is a nongraduated tool
a simple caliper (just compares)
what are graduated tools
gauge blocks, vernier caliper, micro meter, and ruler
What does a dial gauge measure?
parallelism, straightness, roundness
what is the equation for variation in parallelism, perpendicularity and angularity
V=dR/D
d = distance in question (actual)
R = dial guage value
D = distance dial gauge traveled
(doesnt exceed tolerence)
3 tool used to measure angles
- squares
- sine bars
- protractors
Sine bar equation and use
sin A = Height/Length
stack gauge blocks (heights) till sine bar makes perfect contact with angle being measured
Optical flats, determining fringe spacing and angles equation
Fringe spacing = λ/2sinθ
Coordinate Measuring Machines (CCM) measures 5 and etc
- length
- angles
- dimensions
- flatness
- roundness
(highly accurate and sensitive)
what are the 3 styles of CMM
- Gantry style CMM (most accurate)
- Horizontal Atm CMM
- Articulate Arm CMM (least accurate)
CMM - touch probes (end effector); 3 main configurations
- fixed (solid material)
- touch triggered (on contact measures by sending electrical signal)
- optical (least accurate, use active light to measure distance)
What do u have to do whenever u change a probe?
CALIBRATE!!!
CMM - part datums
is the principle axis of the part (defined on machine)
What does laser stand for
Light
Amplification by
Stimulated
Emission of
Radiation
the 4 machine vision applications
- inspection
- part identification
- visual guidance and control
- safety monitoring
Machine vision inspection is
90% of all industrial machine vision applications
