Limits and fits Flashcards
What are some of the results of guilding parts
Minimises number of parts
Design for ease of assembly
Design to be fool proof during assembly
What are the benefits for DMforA
Shorter time to market Smoother transition to production Fewer components is production Easier Assembly Lower production costs Higher production quality Greater customer satisfaction
What is another name for simultaneous engineering
Concurrent Engineering
What has the to be the same between to parts for interchangabilitity
The size and tolerance
Closer tolerance leads to better performance but it is….
More expensive
What Tolerance should you choose
The largest possible tolerance without reducing the function of the part
What is tolerance
an undesirable but permissible deviation from a desired dimension
What errors cause tolerance
Material behaviour, temperature during process, wear of tools, human error
What is an allowance
Intentional desired difference between dimensions of two meeting parts
What percentage of parts of lie within 3 standard deviations of the nominal size
99.76%
Describe clearance, interference and transition fit
Clearance- shaft is smaller than hole
Interference- hole is smaller than shaft
Transition- a fit that may provide either clearance or interference
What British Standard table do we use for shaft and hole sizes
BS4500
What is the fundamental deviation
The closest deviation to the 0 line, gives the tolerance with respect to 0
What is a shaft based system
When the fundamental deviation of the shaft is always 0, i.e shaft always lies on the dotted line.
What is a hole based system
When the fundamental deviation of the hole is always 0, i.e the hole always lies on the dotten line.
What are the fundamental deviations denoted by for both holes and shafts
Holes use Capital letters
Shafts use lower case letters
What letter is used for a shaft based system
h
What letter is used for a hole based system
H
What is the basic size of 25 H11-c11
25
Is 25 H11-c11 a shaft or hole based system
Hole
What is the hole tolerance grade of 25 H11-c11
11
What is the shaft tolerance grade of 25 H11-c11
11
When does Maximum Material condition occur
When hole diameter is a minimum and shaft diameter is at a maximum
When does least material condition occur
when hole diameter is at a maximum and shaft diameter is at a minimum
What is more commonly used hole based system or shaft based system and why
Hole based system because holes are usually only made to standard sizes
When might a shaft based system be used
When fitting several parts to one shaft
What are allowance and Tolerance functions of
Basic size
How many grades do tolerances come in
18
The tolerance grades are IT01, 1T0 and….
IT1-IT16
Tolerances are made depending on if the part is to
Mate with another part and how they are to made
What are functional and non functional parts
Functional parts are essential to the operation of the part so use close tolerances. Non-Functional parts are not as important and use more generous tolerances
What is the equation for process capability index
PCI=T(tolerance)/6*standard deviation
Does a hole make a difference to thermal expansion
No
How is increase in allowance related to original allowance
Linearly
What are shrink fits useful for
High torque and large axial loads
What is the equation for allowance at maximum material condition for thermal expansion
Allowance at max material condition=Min hole-Max shaft+ Shaft expansion
What is the equation for allowance at maximum material condition for thermal contraction
Allowance at Max material condition= Min Hole -Max shaft + Shaft contraction - Hole contraction
What is the equation for allowance and thermal change and what are the sign convention
Allowance at Max material condition=Min hole-max shaft-shaft change +hole change
Expansion is positive
Contraction is negative
What do the symbols stand for in the equation for shrink fitted parts
1=Length
alpha = linear coefficient pf temperature
T= temperature
What are the symbols in the interference pressure
P= interference pressure Sigma= total diameter interference a=outer radius of inner b=outer radius of inner Eo= youngs modulus of outer Ei= youngs modulus of inner v= poisons ratio
What is the equation for the torque carried by the shrink fitted
T=2muppia^2*l
What do the symbols in the torque equation mean
T=torque mu= co of friction p= pressure a=interference radius L=length of inference fit
What percentage of parts would you expect to find within + or - 1 standard deviation of nominal size
68.26%
What percentage of parts would you expect to find with + or - 2 standard deviations nominal size
95,46%
What percentage of parts would you expect to find within + or - 3 standard deviations of nominal size
99.73%
What is the upper deviation of the shaft.
Distance between max diameter and the zero line (basic size)
What is the lower deviation of the shaft
Distance between min diameter and zero line (basic size)
What is the upper deviation of the hole
Distance between max diameter and zero line (basic size)
What is the lower deviation of hole
Distance between min diameter zero line ( basic size)
What is the Equation for PCI
PCI= Tolerance/ (6x standard deviation)
