Metrology Flashcards
What is metrology?
The science of measurement
Why are interchangeable parts so important?
Parts that were made at different times would fit into the same place
What is a dimension?
Linear or angular sizes of a component specified on the part drawing, containing the size and unit of a characteristic
What is a tolerance?
Allowable variations from the specified part dimensions that are permitted in manufacturing
Why are tolerances used?
To define limits of the allowed variation, as variations may occur in manufacturing.
Why are tolerances usually larger than smaller?
The more precise a piece is, the more costly it is to keep pieces to that exact level.
What is bilateral tolerance?
Permitted variation in both directions of the nominal dimension
What is unilateral tolerance?
Permitted variation in only one direction of the nominal dimension
What are limit dimensions?
Displays the maximum and minimum values allowed for a dimension instead of tolerances.
What is a geometric tolerance?
A tolerance that involves shape features of the part (e.g. radius, hole location)
what is allowance?
The difference in dimensions of mating parts
What is the basic size?
Dimension for which limits of size are derived; the nominal size
what is clearance?
The space between mating parts
what is clearance fit?
Fit that allows for rotation or sliding between mating parts
What is a datum?
A theoretically exact axis, point, line or plane
What is a feature?
A physically identifiable portion of a part
What is a fit?
The range of looseness or tightness
What is geometric tolerancing?
Tolerances that involve shape features of the part
What is interference fit?
A negative clearance; feature size is larger than hole size
What does MMC stand for?
Maximum Material Condition
What is 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?
The range of values for which a feature’s position can be placed at.
What is transition fit?
Fit with small clearance/interference that allows for accurate location of mating parts
What does surface technology cover?
The characteristics, texture, and integrity of a surface, as well as the relationship between manufacturing processes and the surface
What is the nominal surface?
The intended, ideal surface
What do surfaces do in relation to the part?
Surfaces can affect both how a part looks, and it’s behaviour in relation to other surfaces, such as wear or lubrication.
What is the surface texture?
The roughness, waviness, and flaws of the top surface
What is the substrate?
The majority of the part, further under the surface
What is the altered layer?
Between the surface texture and substrate, where energy affected (work hardened) area is
What can contaminations do to surfaces?
Affect appearance and inhibit joining of parts
What is the beilby layer?
An amorphous subsurface layer that appears in metals
What is roughness of a surface?
Finely spaced deviations from nominal surface; smaller dips and peaks of the surface
What is the waviness of a surface?
The larger spaced deviations from the nominal surface; the total deviation from minimum point to maximum point on a surface
What is lay?
The direction/pattern followed by a surface texture
What is a flaw for surfaces?
An irregularity that occurs near the surface, e.g. cracks, scratches, and inclusions
What kind of energy forms are included in surface integrity?
Mechanical, thermal, chemical, electrical
What are some surface changes due to mechanical energy?
Residual stresses in subsurface layer, cracks, voids/inclusions, and variations in hardness
What are some surface changes due to thermal energy?
Metallurgic changes (recrystallization, grain size variations, phase changes), metal being removed from surfaces while molten and reattached, resolidified material, and hardness changes
What are some surface changes due to chemical energy?
Corrosion/oxidation, contamination, absorption of elements on surface of metal, etching of surfaces
What are some surface changes due to electrical energy?
Conductivity/magnetism, craters from short circuiting
What basic quantities does metrology cover?
Length, mass, time, current, temperature, light intensity, and matter
What is the SI Unit for light intensity?
Candela
What is the SI Unit for temperature?
degree Kelvin
What is the SI unit for matter?
Mole
What is the SI unit for mass?
kilogram
What is accuracy?
How close the observed value is to the controlled value
What is precision?
How close observed values are to each other
What is resolution?
the smallest difference in dimensions that an instrument can detect or distinguish (smallest decimal value place)
What is repeatability/equipment variation?
Variation in multiple measurements by an individual using the same instrument
What is reproducability/operator variation?
Variation in the same measuring instrument used by different individuals
What is calibration?
Comparing a measurement/system to one having a known relationship national standards
What is a systematic error?
Positive or negative deviations from true value that are consistent from one measurement to the next
What is the other main system of units?
US Customary
What is inspection?
The usage of measurement and gaging techniques to determine whether a product its components, subassemblies, or materials conform to design specifications
What is inspection by variable?
Product or part dimensions are measured by the appropriate measuring instruments
What is inspection by attributes?
Product or part dimensions are gaged to determine whether or not they are within tolerance limits
What is the advantage of gaging over inspection?
Gaging is quicker
When should inspection be done?
During the manufacturing process, allowing for defects to be found earlier
What is acceptance sampling?
A whole lot is sent for inspection, and a sample of the batch is analyzed. If the batch is alright it is sent to production
What is contact inspection?
The usage of probes to measure/gauge the physical dimensions of a part.
What is non-contact inspection?
The usage of a sensor located at a distance from the object to measure or gauge the desired feature
What are some conventional measuring instruments and gauges?
Line graduated instruments, precision gage blocks, comparative instruments, fixed gages, angular measurement tools
What does graduated refer to?
The instrument is marked to indicate certain quantities
What is the resolution of most rules?
1mm or 1/64 in
What is the resolution of most vernier calipers?
25 micrometer or 0.001 in
What is the resolution of most micrometers?
2.5 micrometers, or 0.0001 in
What is the resolution of digital calipers?
2.5 micrometers or 0.0001 in
What are gage blocks?
Rectangular blocks with near nominal dimensions in various standard sizes
What are GO/NO-GO gages?
A double sided plug gage, GO side checks if a hole is large enough, NO-GO checks if hole isn’t too large
What are snap gages?
GO/NO-GO Gages for diameters
What are dial indicators?
Tools that convert linear measurements into rotational measurements
What is a sine bar?
Measures angle with gage blocks as height and length of bar
What do seagull shaped waves from optical flats mean?
Worn edges with hollow center
What do bracket shaped waves from optical flats mean?
Worn edges
What does a topological optical flat mean?
Hills and valleys
