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ME 350 Exam 1 material
Material from homeworks 1-4
85
Mechanical Engineering
Undergraduate 3
05/06/2012

Additional Mechanical Engineering Flashcards

 


 

Cards

Term
Design for manufacturability software are analytical tools designed to quantify:
Definition
Cost
Term
DFM software is supposed to optimize:
Definition
Quality
Term
Result of increasing strain hardening exponent (n)
Definition
Metal can be strained further before necking
Term
Design for manufacturability software are analytical tools designed to quantify:
Definition
Cost
Term
DFM software is supposed to optimize:
Definition
Quality
Term
Result of increasing strain hardening exponent (n)
Definition
Metal can be strained further before necking
Term
Types of Ceramics
Definition
Glasses: ceramics that melt
Traditional ceramics: clay, alumina, etc.
Term
3 processing operations
Definition
Shaping, property enhancing, surface processing
Term
2 types of assembly operations
Definition
joining processes, mechanical assembly
Term
Joining process
Definition
Creates permanent joint

Welding, brazing, soldering, adhesive bonding
Term
Mechanical assembly processes
Definition
fastening by mechanical methods

threaded fasteners, press fitting, expansion fitting, RIVETS
Term
Goal of Design for Manufacturability
Definition
reduce cost of production while acheiving optimal product quality
Term
Stress definition
Definition

σ=F/A

where F = applied force

A= initial (engineering stress/safety calcs) or instantaneous (true stress) cross sectional area

Term
Strain
Definition

ε=ln(L/L0)

Always use true strain

Term
Only 4 times to use engineering stress
Definition

Yield Strength (Y)

Tensile Strength (UTS)

Modulus of Elasticity (E)

 

Term
Flow Curve Equation
Definition

σ=Kεn

 

Only use true stress and strain

Term
Hooke's Law
Definition

σ=Eε

for elastic region

Term
Perfectly elastic behavior
Definition
only elastic region, fractures rather than yields, brittle
Term
elastic and perfectly plastic behavior
Definition

flow curve K=Y and n=0

metals above recrystallization temperature

Term
Elastic and strain hardening
Definition

K>Y and n>0

most metals

Term
shear stress
Definition

τ=F/A=T/2πr2t

 

F=applied force

A=deflection area

T=applied torque

r=tube radius

t=tube wall thickness

Term
shear strain
Definition

γ=δ/b=Rα/L

 

where δ=deflection

b=deflection distance

α=angular deflection

L=gauge length of tube

Term
Torsion stress-strain realtionship in elastic region
Definition

τ=Gγ

 

where G= Shear modulus

 

 

Term
Torsion stress-strain relationship in plastic region
Definition

τ=Sγn

 

where S=shear strength

n=strain hardening exponent

Term
Shear modulus approximation
Definition
G=0.4E
Term
Shear strength approximation
Definition

S=0.7TS

 

where TS is tensile strength

Term
Hardness
Definition
Resistance to permanent indentation
Term
Brinell Harndess equation
Definition

HB=2F/πDb(Db-√Db2-Di2)

 

where F=indentation load

Db=diameter of ball

Di=diameter of indentation

Term
Brinell Tensile Strength Approximation
Definition

TS=Kh(HB)

 

where Kh=3.45 for MPa or 500 for psi

Term
Effect of increasing temperature on metal properties (YS, Y, ductility)
Definition

TS decreases

Y decreases

ductility increases

Term
Recrystallization temperature
Definition

no longer strain hardens

new grains form free of strain

Tr=0.5T(IN KELVIN)

Term
Viscosity
Definition

Resitance to flow characteristic of given fluid

 

A meausure of the internal friction when velocity graidents are present in the fluid

Term
Shear rate
Definition
η=τ/γ
Term
Shear rate
Definition
γ=dv/dy
Term
1 mPa-s
Definition
Centipoise
Term
3 types of rapid prototyping
Definition

Liquid Based

Solid Based

Powder Based

Term
SLA part build time (layer)
Definition

Ti=Ai/(vD)+TD

 

where Ti = Time to complete layer i

Ai= area of layer i

v=average scanning speed of laser beam at surface

D=diameter of spot size

Td=delay time between layers

Term
SLA part build time (total)
Definition
Ttotal=Vpart/DtU+TdT
Term
SLA layer thickness
Definition
25-50 μm
Term
SLA pros
Definition

fewer support structures than other methods

highest resolution surface features

Term
SLA cons
Definition

must cut away support structures

messy to clean

Term
FDM volume solidification rate
Definition
Q=πD2U/4
Term
FDM pros
Definition

potential for high resolution

inexpensive

Term
FDM cons
Definition

overhanging features require many support structures

very slow at high resolution

difficult to achieve flat surface

Term
5 RP applications
Definition

Prototypes

Pattern for casting mold

Assembly testing

Parts with intricate internal geometries

Medical one of a kind parts

Term
Material Removal Rate
Definition

MRR=vfd

 

where v= cutting speed

f=feed

d=depth of cut

Term
Roughing vs Finishing
Definition

Roughing:remove large amounts of material

-large feeds and depths

-slow cutting speeds

 

Finishing:final dimenions, tolrances and finish

-small feeds and depths

-fast cutting speeds

Term
Chip thickness ratio
Definition

r=t0/tc

 

always less than 1

Term

Shear plane angle (chip formation)

 

Definition

tanφ=rcosα/(1-rsinα)

 

r=chip thickness raio

α=rake angle

Term
Properties of discontinuous chip
Definition

Work material: brittle

Cutting speed: slow

Feed and depth of cut: large

Tool-chip friction: large

Term
Continuous chip properties
Definition

Work material: ductile

Cutting speed: fast

Feed and depth of cut: small

Tool-chip friction: low

sharp cutting edge

Term
Continuous chip with Built up Edge Properties
Definition

Work material:ductile

Cutting speed:low-med

Tool-chip friction: large, causing portinos of chip to adhere to rake face

Term
Serrated chip properties
Definition

Semi-continuous sawtooth appearance

Alternating high shear strain and low shear strain

Difficult to machine metals at high cutting speeds

 

Term
Coefficient of friction between tool and chip
Definition

μ=F/N=tanβ

 

where β=friction angle

Term
Shear stress acting along shear plane of chip
Definition

S=Fs/As

 

where S=shear strength

 

As=t0w/sinφ

 

where t0=cut depth

w=cutting edge width

φ=shear plane angle

Term
The Merchant Equation
Definition

φ=45+α/2+β/2

 

in degrees

Term
How to increase shear plane angle (more effcient cutting)
Definition

increase rake angle α

decrease friction angle β

Term
Hottest point on cutting tool
Definition
Secondary shear zone
Term
Results of high cutting temp
Definition

Reduced tool life

Hazardous hot chips

Inaccuracies in part dimensions due to thermal expansion

Term
Cutting temperature equation
Definition

ΔT=(0.4U/ρC)(vt0/K)0.333=(0.4Fc/ρCfd)(vt0/K)0.333

 

where T=temperature at tool chip interface

U=specific energy

v=cutting speed

t0=chip thickness before cut

ρC=volumetric specific heat of work material

K=thermal diffusivity of work material

Term
Chamfering
Definition
cutting edge cuts an angle on the cylinder
Term
Cutoff (turning)
Definition
tool is fed radially into rotating work to cutoff end of part
Term
Facing
Definition
tool is fed radially inward
Term
Threading
Definition
pointed form too is fed at large feed rate, creating threads
Term
Contour Turning
Definition
tool follow contour that is other than straight
Term
Form Turning
Definition
tool has desired geometry and is fed directly into work piece
Term
Boring
Definition
Performed on inside diameter of existing hole
Term
Drilling material removal rate
Definition

MRR=πD2Nf/4

 

where D=drill diameter

N=spindle speed(rev/min)

f=feed (length/rev)

d=depth of cut

Term
Drilling time
Definition
Time = (d+A)/Nf
Term
Milling material removal rate
Definition

MRR=Wdv

 

where W=width of cut

d=depth of cut

v=feed rate

Term
Milling time
Definition
Time=(L+Lc)/v
Term
Three modes of tool failure
Definition

1.Excessive or dynamic cutting force, leading to brittle fracture (fracture failure)

2. Cutting temperature is too high for tool material (temperature failure)

3. Preferred wearing method (gradual wear)

Term
Taylor Tool Life Equation
Definition

vTn=C

 

where v=cutting speed

T=tool life

n is the slope of log-log plot

C is the intercept on the speed axis at 1 minute tool life

Term
Indications of tool nearing end of life
Definition

change in sound emitted

chips become ribbon like, stringy

degradation of surface finish

increased power required to cut

Term
Processes using single poin tools
Definition
turning, boring, shaping and planing
Term
Processes using miltiple point tools
Definition
drilling, reaping, tapping, milling, sawing, broaching
Term
Types and functions of cutting fluids
Definition

Improve cutting performance

-improve chip removal

-reduce cutting temp

-improve surface finish

 

Types:

Coolant (generally water-based)

-more effective at very high cutting speeds

Lubricant (generally oil based)

-more effective at low cutting speeds

Term
Lubricants
Definition
Term
Ideal surface roughness
Definition

Ri=f2/32NR

 

where f=feed

NR=nose radius

Term
How to avoid chatter
Definition

1. Add stiffness and or damping

2. Operate at speeds that avoud natural frequency of machine/tool system

3. Reduce feed (sometimes depth)

4. Change cutter design

5. Use Cutting fluid

 

Term
Do you select feed or speed first?
Definition
Feed
Term
total time per unit product for operation
Definition

Tc=Th+Tm+Tt/np

 

where Th=handling time per part

Tm=machining time per part

Tt/np=tool change time per part, where np=number of pieces cut in one tool life (round down)

Term
Total cost per unit product for operation
Definition

Cc=CoTh+CoTm+CoTt/np+Ct/np


where CoTh=Cost of part handling time (Co=cost rate for operator and machine)

CoTm=cost of machining time

CoTt/np=cost of tool change time

Ct/np=tooling cost (Ct=cost percutting edge)

Term
Cemented carbide/ceramic vs. HSS tool cutting speeds
Definition
Cemeted carbide/ceramic significantly higher
Term
How should cutting speed change as tool change time and/or tooling cost increase
Definition
Cutting speed should decrease
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