Manufacturing Technologies Flashcards
1
Q
Define UTS
A
Ultimate tensile strenght (maximum strenght)
2
Q
Define true strain
A
dε = dl/l => έ = Ln(l/l°)
3
Q
Définie engineering strain
A
e = Δl/lº
έ = Ln(1+e)
4
Q
What hypothesis can be made about the volume of a deformed material?
A
It’s constant
5
Q
What are the additivity specificities of the strain?
A
e1+ e2 ≠ e(tot)
ε1 + ε2 = ε(tot)
6
Q
What are the two basics model for elastic and plastic strenght? In cold conditions
A
σ=Ε*σ (elastic behavior)
σ= Κε^n (plastic behavior) Holmon’s eq.
7
Q
How to read the toughness on the σ/ε diagram?
A
It’s the area under the curve
8
Q
In the Holmon equation, for metals, n is between ____ and ____
A
0.05 & 0.6 Øunit
0 -> rigid perfectly plastic
1 -> Elastic
9
Q
In the Holmon equation, for metals, K is between ____ and ____ unit?
A
180 MPa (Al) - 2070 MPa (Co)
10
Q
What is the effect of a temperature increase on the strain and the strenght?
A
A% increase,
σe and UTS decrease
11
Q
Define the engineering and the true strain rate
A
ė = ν/l° engineering strain
dε/dt = ν/l
12
Q
What is the basic model for the strenght in hot condition?
A
σ=C(dε/dt)^m
m: strain rate exponent coefficient (0.2-1.0)
C: strength coefficient (10-1000 MPa)
13
Q
What are the name of the two phenomena (in tensile and compressive state)of shape changes?
A
Barreling
Necking
14
Q
What are the specificities of the torsion test?
A
No friction
High level of strain
Strength gradient
15
Q
What is the effect of the increase of the strain rate on the strength?
(No effect on strain)
A
UTS increase with the strain rate
16
Q
What are the 3 eq. Of the generalized Hook’s law?
A
ε1 = 1/Ε [σ1 - ν(σ2+σ3)]
ε2 = 1/Ε [σ2 - ν(σ1+σ3)]
ε3 = 1/Ε [σ3 - ν(σ2+σ1)]
17
Q
What are the generalized Mises-Levy flow rules?
A
dεi = dέ/σ [σj - 1/2(σj +σk)]
18
Q
What is the tresca criteria?
A
It’s a value above the one we observe yielding.
In mohr circle Y=σmin-σmax
k= Y/2
Y: uniaxial yield stress of the material
k: shear yield strenght of the material
19
Q
Define the VM criteria
A
Yielding the following equality is satisfied:
(σ1-σ2)^2 + (σ2-σ3)^2 + (σ1-σ3)^2 = 2Υ^2
20
Q
What become the VM & tresca criteria under plan deformation?
ε2 = 0
A
σ2 = (σ1 + σ3)/2
σ1 - σ3 = 2/ vΓ(3) * Υ
21
Q
How is calculated the deformation work?
A
u= Yf * e1
Where Yf is the average yield stress
or
u = K e1^(n+1)/(n+1)
Work = u * volume
22
Q
Efficiency of a deformation?
A
uideal/utotal
Extrusion 30%-60%
Rolling 75%-95%
23
Q
What is the multiplicative factor between the projected area and the real contact area ?
A
4-5 order of magnitude lesser
24
Q
Is the friction model of coulomb usable with any τ and σ? Remind the formula
A
σ = μ.τ
Only valuable for small τ and σ. After the tresca model is better.
25
What is the tresca friction model ?
τ = m.k
m = τi/k
k: shear yield stress of the softer material
τi: shear strenght
26
Is the coef of friction μ increasing or decreasing with the temperature? Why?
It increase a lot (0.05 -> 0.2)
Because of the oxides broken
The higher chemical attractively
The elastic limit less high
27
What the Archard wear law describes?
It estime the amount of material removed by wear from a surface
V = k.L.W/(3p)
28
What are the different forms of lubrication?
Thick film
Liquid
Mixed
29
What are the function of the lubricant ?
Reduce friction
Reduce tool wear
Thermal barrier
30
What are the characteristics of the lubricant?
Easiness to apply
Non-toxic and non-inflammable
Odorless
Non-reactive
Adaptable to different process conditions
31
How is selected a lubricant?
In function of:
• The process
• Compatibility with the WP/tool
• Preparation of the surface
• Methods to apply it and remove it
• Treatment of exhausted lubricant
• storage and conservation
• environmental and biological hazards
32
What's the tolerance on forging process?
0,5% to 1%
33
What are the advantages of the forging process (comparing to casting)
Metal flow and grain structure can be controlled
– Results in good strength and toughness
– Near net shape
– Design reasonably complex
* Landing gear
* Connecting rods
* Complex shafts
34
What are the disadvantage of the forging process (comparing to casting)
– Dies are expensive, particularly for hot forging
– Highly skilled labor required
35
What is the main problem of the open die forging?
Barreling
36
Describe the repartition of the stress in open die forging (plain strain)
pav = Yf' (1+μa/h)
Maximal at the center:
exp(2μa/h)
a: rayon
h: height of the billet
37
What is called fullfering?
moves material away from center
38
What is called Edging?
moves material away from edges
39
What is called flashing?
Part of the matter outside the functional zone c(exceed of matter)
40
How is defined forgeability
It's the capability of a metal to undergo deformation
without cracking
41
What test can be carried out to measure the forgeability?
upset test (compressive test)
hot torsion test (nb of twist before break)
42
What are the main defect of forging?
* Surface cracks (forgeability limits)
* Buckling
* Laps
* Internal cracks
43
What is the name of the process used to make coin?
What are its characteristics
coining, high pressure, die's cavities totally closed
44
What's is called heading?
Forging the end of a tip (bolt, screws)
45
What is piercing?
Punch inside a closed die to make a cavity
46
What is the name of the process:
* Uses rolls to shape parts
(ball bearings)
* Similar to shape rolling
but makes discrete parts
* Makes axis-symetrical parts
Rolling
47
What is called orbital forging?
- Forms the part incrementally
– Small forging forces
because the die contact is
concentrated on a small part
of the workpiece at anyone
time
– Applicable to mostly
cylindrical shapes
48
What is Isothermal forging?
– Dies at same
temperature of workpiece
– No workpiece cooling
– Low flow stresses
– Better material flow
– More close tolerances
and finer details can be
achieved
49
What is called cogging?
– Cylindrical parts subjected to radial impact forces by reciprocating dies
– Used to reduce tube diameter and introduce rifling into gun barrels
50
What are the 4 differnts types of press and their advantages?
* Hydrolic press (Limited load)
* Mechanical press (energy limited)
* Screw press (energy limited)
* Hamer press (energy limited)
51
what are the variable for hot rolling process?
Depedent variables :
* Roll speed
* Draft (amount of thickness reduction) or roll gap
* Billet thickness
* Billet width
* Billet material
* Billet temperature
* Lubricant
indepedent variables :
* Roll force
* Power
* Speed of exiting strip
* Final strip temperature
* Maximum draft
* Roll strip contact length
* Sheet or plate shape
52
What are the advantages and disadvantages of Hot rolling process (quote 3 of each)
6
Hot rolling
Advantages
– Stresses lower
– Forces smaller
– Power requirements less
– No work hardening
– Large deformations possible
– Breaks up the cast structure into preferable forms
– Closes porosity
– Sometimes the only way to create sheet
Disadvantages
– Higher friction
– Rolls need to be cooled
– Material handling difficult
– Personnel must be protected from heat
53
What are the advantages and disadvantages of cold rolling process (quote 2 of each)
Advantages
– Deformations of ~ 50 to 80%
– Work hardening increases strength
– Excellent surface finish
– Excellent tolerances on thickness and shape
Disadvantages
– High forces
– Small reductions give rise to surface stresses and non-
uniform stress distributions
54
What is called neutral
Point in the arc of
contact where the roll
velocity and the strip
velocity are the same
55
How looks like the stress distribution in hot rolling along the roling direction?
As an idian tepee,
More the friction coef is high, more the stress is high and centered.
The less the friction, the closer of the output is the maximium.
56
What can be done to reduce the force needed for rolling?
Back/forward tension
57
What is the general friction coeff. for hot rolling?
Between 0,2 and 0,7
58
What are the effect of a two high rolling force? What are the solution to prevent it?
The rollers bend and flattern.
We can reduce the bending by adding back-up rollers
59
What can we control on the final product by using hot rolling?
* Thickness
– Roll gap which impacts roll force and hence the dimensions
of the mill frame
* Width (due to spreading of slab)
– Edge rollers (push material back)
– Edge shears (cut material off)
* Length
– End shears
* Mechanical Properties
– Controlled by the microstructures which is controlled by the
rolling parameters
60
What is called Sendzimir rolling mill?
A lot of back-up roller on hot rolling (pyramde 3-based+driving wheels)
61
What can be produced using shape rolling?
– I-Beams
– H-sections
– Rails (trains)
– Angle iron
62
How is called the process permiting to forge thorical axis-symetrical parts?
Ring rolling
63
What is Thread rolling?
It's a process involving flat dies, moving parrally to their surface. Threads can be forged at high speed with high mechanical resistance.
64
What is called process Mannesmann?
A process for tubes-making using a defect (cavity) in the center of bar. The defect is opened by using a mandrel.
65
What is called trimming?
Removal of the flashing
66
What is called extrusion process?
2D geometry extruded:
* Push an ingot through an orifice
with the desired shape
* Both hot and cold extrusion are
possible
67
What are the different type of extrusion?
* Direct
* Indirect
* Impact (mix btw indirect + forging)
* Hydrostatic
* Lateral extrusion
68
What are the mains parameters of direct extrusion process?
The die angle, reduction in cross-section, extrusion speed,
billet temperature, and lubrication all affect the extrusion pressure
69
What are the components of the force needed to carry out direct extrusion process?
Friction
Plastic deformation
their is an optimum die angle
70
What are the advantages of cold extrusion?
– Improved mechanical properties
– Work hardening
– Good control of tolerances
– Improved surface finish
– Elimination of heating costs
– High production rates
71
Describe the cold extrusion process
Two punch in front of each other in a closed matrix
72
What are the advantages of the hot extrusion?
Lower stress
Only way for certain materials.
73
To what are due the cracks in extrusion process?
high speed
high friction
high temperature
74
What is called chevron
defect?
It's a cavity in extrusion process at the center of the part. it's due to the material flow.
75
What is called drawing process?
Like extrusion but material pulled out the orifice.
Used to make rod & wires
76
what is called the "land" on extrusion and drawing process?
The zone of contact btw the WP and the die where the WP move parrallely to the die.
77
What is the main limitation of the drawing process?
We can reduce the size of max 63% by pass => need multiple pass.
78
In drawing process, what are the effect of the back tension on the stress in the WP and in the die?
It increasethe stress in the WP but reduce the stress in the die
79
What material is used to make the die of drawing process?
WC
80
What are the 3 basics processes of sheet forming?
Cutting
forming (bending, deep drawing, stretching)
finishing
81
What is called Lueders bands?
Name of the parallele bands inclined in tensile state.
82
What is "normal anysotropy"?
It's a difference of A% in two direction of a plane.
83
What is called bending process and what are its advantages/disadvantages?
Bending of a sheet
—
Advantages
– Easy to perform
– Simple, low cost tooling
– Fairly precise
—
Disadvantages
– Limited in the shapes it can produce
– Spring back difficult to estimate
– Some materials difficult to bend without tearing or
necking
84
What is called MBR in bending process?
Minimum Bend Radius (MBR) is defined to
occur when a crack appears at the outer fibers
85
What are the hypothesis made to calcul the MBR?
Hypotheses: the material is
homogeneous and isotropic;
the sheet is bent in a state
of plane stress
The strenght on the outer skin is equal to the elastic limit of the material.
86
How is exprimed the MBR?
In function of the thickness of the material, (0,5T, 2T, ..., 6T)
87
How bendability of a material can be increased?
It can be increased through heating or by application of
hydrostatic pressure
88
what are the variables influent on the MBR?
Edge condition of sheet
* Rough edges decrease bendability
– Amount and shape of inclusions
– Amount of cold work on edges due to shearing
– Anisotropy
– Elastic modulus - the springback phenomenon
89
What is called springback?
It is caused by the elastic behavior of workpiece
material – elastic recovery
90
How is called the springback factor?
Ks
Ks=1 no springback
Ks=0 complete elastic recovry
91
How is compensed the springback effect?
– Overbending
– Applying compressive stresses to the bend zone
– Stretch bending/forming
– Raising temperature
92
How can we prevent the collapse of the tube on itself during bending process?
By using a mandrel inside, sand or other to counteract the pressure.
93
What is called stretching of a sheet?
* The sheet metal is clamped around its edges and
stretched over a die or form block, which moves upward,
downward, or sideways
* The shape is developed entirely at the expense of the
sheet thickness
94
What is called deep drawing process?
[Cans process]
– Place a round blank over the die
– Clamp in place by means of the blankholder
– Punch travels downward into die
* metal deforms by stretching into the die
95
What are the main disadvantages of the deep drawing process?
– Limited shapes
– Material quality critical to obtain high-quality parts
– Dies are expensive
96
Quote some of the main variables of deep drawing process
Blankholder force
– Too high - workpiece tears
– Too low - cup gets wrinkles
* Radius/diameter of the punch
* Diameter of the blank
* Thickness of the blank
* Clearance between the punch and die
– Clearances usually 1.07 to 1.14 thickness
– Too low - blank pierced
* Friction/lubrication
* Radius of entry into the die
* Radius on end of the punch
– too small - cracking at corners
– too large - wrinkling
* Punch force (dependent variable)
97
What are the stress state under the blankholder and in the wall in deep drawing process?
Under the blankholder:
* Compressive through the thickness
* Tensile along the radius
* Compressive along the circumference due to decreasing blank circumference
In the die:
* Mostly tensile in the punch direction
* Also tensile at right angles to the punch
direction because of the cup contraction
under tensile stresses in the cup wall
* Stresses cause material to thin in
punch direction and shrink around the
die in the circumferential direction
98
How is define drawability?
By the Limiting Drawing Ratio (LDR)
* In an ordinary deep-drawing process, failure
occurs by thinning in the cup wall under high longitudinal tensile stresses
* When LDR is reached, the draw force just exceeds the force that the cup wall can support
99
What is called earing?
It's a defect occuring in deep drawing process when the sheet is not anysotropic. => wavy top of the walls.
100
How is measured the sheet formability?
Tensile test:
total elongation at fracture, strain hardening
exponent, the planar and the normal anisotropy
—
Cupping test:
Erichsen and Olson tests (stretching) and
Swift and Fukui tests (drawing); to measure the capability of
the material to be stretched before fracturing
—
Bulge test:
a circular blank is clamped at its periphery and is
bulged by hydraulic pressure; to obtain effective stress-
effective strain curves for biaxial loading under frictionless
conditions
101
What is the Erichsen test?
spherical punch pass through a sheet clamped by blankholders.
102
What's the swift test?
Determine the LDR (Dmax/d)
Cylindric punch goes deeper a possible.
103
What is called Nakajima test?
Spherical punch hit the more or less width sheet.
From simple tensile to biaxial tensile.
104
Describe the Forming limit diagram (FLD).
On the left side: Compressive stress state.
On the right side: Tensile stress state.
y-axis: major strain
A curve decreasing until the plane strain and then increasing.
105
How to plot the FLD?
The swift test give a point on the compressive curve.
The nakajima test give the maximal strain in tensile state.
The plane strain point.
106
Where is the safe zone on the FLD?
Between the two virtual lines passing by 0,0 and nakajima ppoint on a side and swift test by the other.
107
Quote X other sheet process?
Hydroforming
Spining
Incremental sheet forming
Super elastic forming
Pen forming
Hot stamping
108
What is called rake angle?
In chips formation process, the rake angle is the angle btw the tool face and the perpendicular to the machined surface.
109
What is called the shear angle?
In chips formation mechanism, It's the angle btw the machined surface and the shear plan (plan of dislocation)
110
What is called clearence angle of a cutting tool?
It's the angle between the flank of the tool and the machined surface.
111
What are the hypothesis of the orthogonal cutting condition?
* Process adequately represented by two-dimensional geometry
* Tool is perfectly sharp
* Tool only contacts workpiece on its front (rake) face
* Primary deformation occurs in a very thin zone adjacent to the
shear plane
* Cutting edge is perpendicular to cutting direction
* The chip does not flow to the side
112
What is called BUE?
The built-up edge, it's a accumulation of matter btw the tool and the WP.
113
How to reduce the size of the BUE?
* decrease the depth of cut
* increase the rake angle
* use a tool with a small tip radius
* use an effective cutting fluid
* Increase the cutting speed
114
What are the different sort of chipsin orthognal cutting?
Segmented chips:
* Zones characterised by low and high shear strain
* Metals with low thermal conductivity and strength that
decreases sharply with temperature (like titanium)
—
Discontinuous chips:
* Brittle materials
* Materials containing hard inclusions and impurities
* When the cutting speed is too high or too low
* When the depth of cut is very large
* Without a proper cutting fluid
* When the machine is not sufficiently stiff
115
What are the two componement of the force exerced by the tool on the WP? In the tool
Ft: Thrust force (perp. to machined surface)
—
Fc: Cutting force (// to machined surface)
116
How is discomposed the force inside of the WP in orthogonal cutting?
Fs: Shearplan- //
Fn: Shearplan- _I_
117
How is called the circle where all the forces in chip mechanism can be drawn?
(Force circle diagram)
Merchant's circle
118
The friction in milling operation lead to imortant increase of temperature. What are the main effects?
* Cause dimensional changes in the workpiece
* Induce thermal damage in the machine surface
* Affect strength, hardness and wear resistance of the cutting tool
* Eventually distort the machine tool itself
Dull tools also generate heat through rubbing of the workpiece surface
119
What are the parameters influents on the temperature of the WP?
Average chip-tool interface temperature rise
(ΔT) is a function of:
* specific cutting energy (u)
* cutting speed (V)
* depth of cut (t0 )
* workpiece thermal conductivity (k)
* workpiece density (ρ)
* workpiece specific heat (c)
120
Where is the hotspot on the cutting tool?
On the tool face
121
What is the difference between blanking and punching? (cutting process)
Punching: remove matter inside a sheet.
Blanking: remove the border arround
121
What is the difference between blanking and punching? (cutting process)
Punching: remove matter inside a sheet.
Blanking: remove the border arround
122
what are the different design of the punch in cutting operation?
Bevel (guillotine)
Double bevel
convex shear
123
What are the different influent factors in cutting operation?
* Punch and Die
– Shape
– Material
* Clearance between punch and die
– Increased clearance
* Workpiece ductility and thickness
– Increased ductility
– Decreased thickness
* Dulled tools
* Speed of punch/shear
– Decreased speed
* Increased Lubrication
124
One what depend the size of the clearence in cutting process?
* Workpiece material
* Thickness
* Size of hole
* Proximity of hole to sheet edge
– Small holes required larger clearances
than large holes
– Typically range form 2-10% of sheet
thickness
– Can range from 1%(Fine Blanking) to 30%
125
What is called Fine blanking?
a lower pressure cushion follow the movement (back pushing) and avoid the bending of the sheet.
The crack is much more shiny.
126
What is called tool wear?
Matter removed from the tool on flank and rake(tool) face
127
How is characterized the wear?
Taylor's equation express the life time of the tool in function of the matter and the cutting speed.
128
What cause the wear crater?
*Chemical affinity
*High temperature (=friction)
129
What is called tool chipping?
Breaking away of a piece from the cutting edge of the tool. It's caused by mechanical shock or thermal fatigue.
130
what are the different way to estimate the usure of a tool?
Direct method (look, measure)
Indirect method (transducer, accoustic emmision)
131
what is called surface finish
geometric features of the surface
132
what is called surface integrity?
Pertains to properties as fatigue life and corrosion resistance
133
What is the feed?
The depth of the WP eaten by the tool by revolution unit.
134
Define feed rate
speed at which the tool travels along the
feed direction [mm/min]
135
What is the depth of cut in turning operation?
The depth the tool remove direction perpendicular to the axis.
136
What are the parameters defining the machinability?
* Force and power requirements
* Tool life obtained
* Surface finish and integrity of the machined part
* Chip control
137
How is called the removable cutting part of the tool?
Insert
138
What are the different materials used for making cutting tools?
Carbon tool steels
High speed steels
Cast alloys
Carbides
Ceramics
139
What are the function of the cutting fluid?
Reduce friction
Cooling
Wash chips away
prevent corrosion
Reduce force energy consumtion
140
How to reduce vibration in milling process?
Stiffer machine
Tuned dumper
active control
Support WP rigidly
Increase cutting speed
Minimize cutter overhang
Modify tool geometry
change process parameters(speed,feed,lubricant, depth of cut)
141
What is called MRR
Material removal rate: Volume of material machined in
the time unit [mm 3 /min]
142
What is the difference between climb milling and conventionnal milling?
In climb milling, the tooth goes perpendiculary in the matter while in conventionnal milling, the tooth goes // to the matter.
143
What is the advantage of climb milling?
Less vibration (if the installation is very stiff)
144
When the grinding process is used?
Too hard materials,
Too high accuracy asked
145
What are the superabrasive materials?
cubic boron nitride,
Diamond
146
what are the conventionnal abrasive
Silicon carbide
Alumine
147
What are the different type of ligent used in the griniding wheels?
Vitrified
Resinoïd
Rubber
Metal bond
148
What is measured by the wheel grade?
the bond’s strength and thus measure of the hardness of a bonded abrasive (from A-soft to Z-hard)
149
What is measured by the "structure wheels factor"
The porosity of the bonded abrasive (1-dense to 16-open)
150
What is the specificity of the rake angle in grinding?
The average rake angle of the grains is highly negative: consequently the shear
angle is very low and the shear strain can become very large
151
Why the specific energy is so high in grinding?
Size effect:
The smaller the grinding chips, the higher the strenght extremely high density of dislocation in the shear
—
Wear flat:
The size of the wear flat is much larger than the grinding chips
—
Chip morphology:
shear strins are very large,
Plowingconsume energy without contributing to chip formation.
152
What are the effects of the increase of temperature at the surface of the worpiece in grinding?
* Tempering
* Burning
* Residual stress
153
What is called wear flat in grinding operation?
The contact zone btw the grain and the machined WP.
Also called usure plan.
This plan depends on the chemical affinity.
154
What are the 3 main defect attributed to the grinding
Attritous wear
Grain fracture
Bond fracture
155
What can be done when the grinding wheel is worn?
We can dress the surface again with a diamond tip.
156
What can be done when the grinding wheel is used?
We can dress the surface again with a diamond tip.
157
What is the difference between conventionnal and unconventionnal machining?
The unconventional machining use other sort of energy than the classical one.
158
What are the 4 sort of energy used in unconventional machining?
Electrical
Chemical
Termal
Mechanical
159
What is the chemical machining?
Chemical attacks metals and etch them by removing small amounts
of material from the surface using reagents or etchants
160
How is called the hole formed under the mask in chemical machining?
Undercut
161
When using the unconventionnal machining can be economicaly advantagous?
* Hard, Strong alloys
* Material to flexible
* Complex geometries
* Very high surface finish
* Temperature raise or residual stress undesirables
162
What are the advantages/disadvantages of the Ch. Machining?
Advantages:
Low capital cost once basic
equipment is installed
*Many work surfaces can be
“machined” simultaneously
*No cutting forces: no distortion or thermal stress problems
*Good for delicate parts
*No edge burring
—
Disadvantages:
Undercutting of masked areas represents a problem
*Sharp corners not possible
*Work piece material must be homogeneous
*Disposal of chemical etchant expensive
*Operators require special protection against possible chemical spillage
163
What is chemical blanking?
A process similar to the chemical machining but to clean part. (electronic, decorative)
164
What is the Electro chemical machining?
An electrode is the tool. The WP is inside electrolyte. The metal is remover by is own ionization. (5A to 40 000A)
165
What is the die-sinking?
A kind of electro-chemical machining where the electrode scan a whole surface.
166
What part is made by using electrochemical machining?
compressor blade: the part who link the turnig wheel.
The electrode can have any geometry.
167
What are the advanages/disadvantage of the electrochemichal machining?
Advantages:
*Any hardness of material can be cut
*No physical contact with work piece so
no cutting or thermal stresses generated
making it good for delicate parts
*Long tool life
*No edge burrs
*Holes complete in one “pass”
—
Disadvantages:
*Work piece must be electrically
conductive
*Capital equipment expensive,
particularly the electrolyte pumping
and cleaning systems
*Form tooling cost can be high,
particularly where 360 degree cutting
is required
168
What is the advantage of electromechancal grinding?
only a small part of the matter is removed because of the friction, less residual stress
169
What is the other name of electroerosion?
Elecro discharge machining
170
What is the principle of the EDM?
The WP is in dielectric fluid,
a localized spark between the electrode (tool) and the WP melt the metal
171
What are the advantages/disadvantages of EDM?
Advantages:
*Material of any hardness can be cut
*High accuracy and good surface finish
are possible
*No cutting forces involved
*Intricate-shaped cavities can be cut with
modest tooling costs
*Holes completed in one “pass”
—
Disadvantages:
*Limited to electrically conductive
materials
*Slow process, particularly if good
surface finish and high accuracy are
required (2-400 mm3 /min)
*Dielectric vapor can be dangerous
*Heat Affected Zone (HAZ) near cutting
edges
*Die sinking tool life is limited
172
What is the material generally used as electrode in EDM?
Classical EDM : Graphite
Wire EDM: Brass, Copper or tungstene alloys.
173
What are the advantages/Disadvantages of the laser machining?
Advantages:
* Virtually any material can be cut
* 2D and 3D shapes can be cut
* Holes having length/diameter ratio of
up to 100:1 is possible
* High speed cutting possible with thin
material
* No consumable tooling needed
* Work area need not be under vacuum
as required with EBM
—
Disadvantages:
* Holes bigger than 1mm (1/32”) diameter
difficult to drill
* HAZ formed around cut surface edges
* Reflective surfaces difficult to machine
174
What are the advantages/disadvantages of the electron-beam machining?
Advantages:
*Any material can be cut
*No cutting forces are involved so no
stresses imposed on part
*Exceptional drilling speeds possible
with high position accuracy and form
*Extremely small kerf width when
profiling so little material is wasted
—
Disadvantages:
*Skilled labor is required
*A suitable backing material must be used
*Maximum thickness that can be cut about
10mm (3/8”)
*Drilling length/diameter ratio up to 15:1
*Work area must be under a vacuum
*Capital equipment cost is high
175
what are the water jet advantage and disadvantages?
Advantages:
*Materials of any hardness can be cut;
even food
*Cutting can be in any direction
*3D cutting possible with CNC nozzle
control
*No deburring is required
*No thermal stresses in the work piece
Disadvantages:
*Limited nozzle life, particularly when
abrasive is used
*High capital cost of equipment
*Very noisy process because of
supersonic nozzle velocities
176
What is the limit value of µ above the one we consider the friction as high?
0.3
177
[Deep drawing] What happen if ΔR is lower than 0?
Occurrence of ears defect
178
How can be measure the machinability in turning?
By comparing the speed of the tool in the material with the one of a reference material
179
Define boring & internal grooving
milling of a pocket from a drilled hole.
180
What is called facing?
In turning operation the tool move _l_ to the axis.
181
What is face grooving?
Milling the face in turning
182
What is straight turning?
In turning operation the tool move // to the axis.
183
What are the components of the grinding specific energy in grinding?
u = u(chip)+u(plowing)+u(sliding)
