Metrology Flashcards
Midterm Review
what is metrology
the study of measurement
What is interchangeable part
Every part has to be made of specific dimensions, and specific tolerance
what is a dimension and tolerance
linear or angular sizes of a component specified on a part or drawing. Tolerance is the allowable variation permitted in the manufacturing process
Micro x10^-6
Nano x10^-9
what 5 things impact tolerance
- speed of operation
-temp - Lubrication
- Variation of Incoming Material
- other factors
What is Bilateral Tolerance
a tolerance in both the positive and negative direction
What is the tolerance of/what kind of tolerance is it:
+0.005
-0.005
Bilateral Tolerance: 0.010
Remember: Tolerance is the a DIFFERENCE btwn the max and minimum
what is a balanced tolerance
a bilateral tolerance with the same max and min.
i.e +0.005
-0.005
what is a unilateral Tolerance
a tolerance only in 1 direction
+0.005
-0.000
What is a Limit Dimensions
A tolerance of a maximum dimension and a minimum dimension.
i.e : 2.505
2.495
what is a clearance fit
a fit where the shaft can fit easily into the whole
what are the 3 kinds of fits
clearance: slides in easily
interference: force it through as the shaft is slightly bigger than the whole
Transition fit: the hole and shaft have very close tolerance
what is Allowance
The specific difference in dimensions between mating parts
what is basic size?
the dimension from which limits of size are derived
what is a datum
theoretically exact axis, point, line or plane
what is interference
negative clearance
what is clearance
the space between mating parts
what is another way to say normal surface?
Nominal Surface:
appear as absolutely straight lines, ideal circles, round holes, and anything else deemed as “geometrically perfect”
what is actual surfaces
determined by the manufacturing process used to design a part. i.e nominal is what we want, actual is what we are going to get.
why are surfaces important?
- aesthetics
- safety
- friction and wear
- assembly
- operation(i.e painting coating welding)
- smooth surfaces make better electrical contacts
what are the 4 elements of surface texture
- roughness
- waviness
- lay
- flaws
what is roughness
variation of tiny specific section(zoomed in)
waviness
the shape on a larger scale (zoomed out)
how to calculate roughness average
r= (a+b+c…..)/n
what is lay
the direction in which the pattern of surface is in
what are flaws
irregularities that occur occasionally on the surface
what is the cutoff length
distinguishes between the roughness and waviness by being less than the waviness length/width
Surface integrity is…..
surface integrity is a crucial aspect of manufacturing that involves understanding and managing the properties of the surface and subsurface layers of materials to ensure the desired performance and functionality of the final product.
residual stress in…
subsurface layer i.e bending of sheet metal
cracks are…
microscopic and macroscopic breaks. i.e tearing of ductile metals in machining
what are hardness variations
work/strain hardening. happens in plastic deformation when the material becomes much harder than it originally were
the two main surface changes caused by mechanical energy are….
residual stress and hardness variations(work hardening)
what are surface changes caused by?
caused by forms of energy during processing
what are the surface changes by thermal energy
- metallurgical changes: recrystallization, grain size changes, phase changes as surface
- redeposited: melted metal is removed, then added back before it solidifies
- resolidified: same as redeposited except it is not detached
- heat affected zone in welding: heated but not melted area to undergo changes
- Hardness changes (usually heat causes things to become less hard)
what are the surface changes by chemical energy
- intergranular attack: corrosion/oxidation
- chemical contamination
- absorption of elements(H and CI) in metal surface: leads to a property change
- Selective Etch : removing a material through chemical reaction: concentrate on certain components in base metal
- alloy depletion and resulting hardness changes
surface changes by electrical energy
1.Changes in conductivity and/or magnetism:
- Craters: These are rough surface depressions left behind due to short circuits during certain electrical processing techniques such as arc welding, Electro Discharge Machining, and Electro Chemical Machining.
what is the difference between accuracy and precision?
Accuracy: degree to which the measured value agrees to the true value
Precision: degree of repeatability
What is repeatability of an instrument
variation of equipment/the ability for an instrument to provide similiar results
what is reproducibility?
variation of operator on the same equipment
what does calibration mean
comparing a measurement device to one having a known relationship to national standards
what is resolution?
the smallest increment on a measurement device.
why does product quality matter in manufacturing?
- for interchangeable manufacturing
- standardization and mass production
- the product components must assemble properly and be replaceable
- prevention of defects
what makes a high quality product?
reliability in performance and a higher cost
what makes a low quality product?
less reliable/fails after a short time, hard to use and low cost
what is inspection?
using measurement and gaging techniques to determine whether a product, and its specific components align with a design specification
what is inspection by variable?
actually measuring a product or part using necessary instruments
what is inspection by attribute?
indirectly measuring something using gages to determine if they fit into the tolerance limits.
inspection by variable or attribute?
Measuring the diameter of a cylindrical part
variable
inspection by variable or attribute?
Measuring the temperature of an oven
variable
inspection by variable or attribute?
Measuring the electrical resistance on electrical components
variable
inspection by variable or attribute?
Gaging a cylindrical part with a GO/NO=GO gage to determine if it is within tolerance
attribute
inspection by variable or attribute?
Determining the defect rate of sample of production parts
attribute
inspection by variable or attribute?
Counting the number of defects in an automobile as it leaves the final assembly
attribute
what is gaging and what is it good for?
it determines if the characteristics of the part meets the requirements. It is faster but does not tell you a lot about the feature
what are pros and cons of Manual Inspection
its boring and takes a time. theres a high risk of error, but for small batches of data is is often used.
what con does sampling inspection cause?
it may lead to inaccuracy because it only takes a small portion of a large data set.
what two categories make up how automated inspection is used ?
- to sort parts into quality levels. I.e acceptable and unacceptable
- to have inspection feedback to reduce variability and improve quality
when is the best time to do inspection?
the earlier the better, when the product is being made.
what are the three testing points in inspection?
- Receiving inspection
–> sample inspection of raw materials - In process “
–> inspecting any amount of quality related costs and customer requirements - Final “
What is acceptance sample, give pros and cons
sample inspection- analyze materials and either accept or reject it.
pro: it provides risk assessement, feasible, less time and energy
Cons: does not work for stable processes,, only detects poor qualit things, it does not add any benefit/improvement/prevention (tells you whats wrong but not how to fix it)
What is the economic model equation
Break even analysis: p*C2 = C1
C1= cost of inspection
C2 = Cost of repair
p= number of failing parts
p>C1/C2, use 100% inspection
P< C1/C2, do nothing
Give examples of/ state the uses of Contact and Non-contact inspection
Contact: inexpensive, accurate and practical
- Coordinate measuring machine (measures mechanical dimensions)
- stylus type surface texture “ (measures roughness and waviness)
- Electrical contact probe( testing circuits and circuit boards.
Non contact: fast, feasible 100% inspection, can access things some contact inspections can’s, avoiding damages.
- optical light : machine vision, laser scanning, roughness/profile measurement etc
- non optical : use of energy forms besides light such as radiation, electric fields X-RAY etc.
what kind of measuring devices include a set of markings on a linear/angular scale
Graduated measuring devices
what kind of measuring devices have no scale and are used to compare dimensions
non graduated measuring devices
What is a GO/NOGO Gages?
One gage limit can be inserted whilst the other can not.
GO Limit: measures dimension at maximum material condition, i.e min size for internal and max size for external feature
NOGO: measures dimension at minimum material condition
what is Dial Gage amplification?
amplifies a linear motion into a circular motion
what are the disadvantages of optical flats
fragile
thin sample, could bend
if the optical flat is not flat enough, it could alter the accuracy
what is an alternative to optical flats?
interferometers: uses the same principles hower provide more accuracy and does not damage the sample
interfermometry does not look beneath the surface
what is a better way to measure surface roughness instead of interferometry
interferometry is a great way to measure surface roughness but a stylus is cheaper
what is a disadvantage of a stylus
it is a contact measurement and the radius of the stylus can impact the accuracy and resolution
what does CMM stand for
coordinate measuring machine: measuring x-y-z measurements
what are the 4 componenets of CMM
bridge - made out of granite
ram
probe - can move in xyz direction
reference
styles of CMM
gantry style- most accurate
Horizontal arm- not stable
articulate arm- portable but the least accurate
what are the 3 kinds of touch probes for CMM
- Fixed - contact and easily breakable
- Touch triggered - contact
- optical -
what 2 things impact what kind of probe you use
effective working length_ length of probe
diameter of probe
what are some benefits of CMM
- Versatile
- great accuracy and precision
- higher productivity
