NITC
Some basics - you had in Foundry
Sand casting.
Steps:
»
»
»
»
»
»
»
»
»
»
1.Mechanical Drawing of the part
2. Making pattern- about pattern material.
3.Making cores- if needed
4.Preparing drag and cope. (Setting the core, positioning etc.)
5.Removal of pattern
6Assembling cope and drag
7.Pouring- factors, method, etc.
8.Casting removed
9.Trimming etc.
10. READY FOR SHIPMENT
NITC
Some basics you had
in Foundry
1.Mechanical Drawing of the part
2. Making pattern- about pattern
material.
3.Making cores- if needed
1
3
2
3a
4.Preparing drag and cope.
(Setting the core, positioning etc.)
5.Removal of pattern
3c
3b
6Assembling cope and drag
4b
7.Pouring- factors, method, etc.
5a
4a
8.Casting removed
9.Trimming etc.
5b
6
8&9
10
10. READY FOR SHIPMENT
CASTING
FUNDAMENTALS
Basically involves
i. Pouring molten metal into a mould patterned after the part to be made
WITHOUT TURBULANCE , SERIES OF EVENTS TAKES PLACE
INFLUENCE SIZE, SHAPE, UNIFORMITY OF THE GRAINS FORMED,
AND THUS THE OVERALL PROPERTIES.
•
ii. Allow it to cool
HEAT TRANSFER DURING SOLIDIFICATION
•
iii. Remove from the mold
INFLUENCE OF THE TYPE OF MOULD MATERIAL
•
SIMILARITY WITH POURING CAKE MIX INTO A PAN
NITC
POURING CAKE MIX INTO A PAN (MOULD) & BAKING IT
*SELECT THE KIND AND SIZE OF PAN,
*CONTROL THE COMPOSITION OF THE MIX,
* CAREFULLY POUR THE MIX,
* SET THE PROPER BAKING TEMPERATURE,
* SET THE TIMER FOR PROPER BAKING TIME,
* LEAVE THE CAKE IN THE MOULD FOR A CERTAIN
AMOUNT OF TIME BEFORE REMOVING.
(CASTING OF PLASTICS & CERAMICS - DIFFERENT)
NITC
Knowledge of certain fundamental relationships
is essential to produce good quality economic
castings
This knowledge helps in establishing proper
techniques for mould design and casting practice.
Castings must be free from defects, must meet the
required strength, dimensional accuracy, surface
finish
NITC
Moulding
Sand
- pattern making
- Core making
- Gating system
Mould
Melting Pouring
casting Heat Treat
Furnaces Solidification
Shakeout
Clean
Inspect
Addl. Heat Treatment
Defects, pressure tightness, dimensions
Outline of production steps in a typical sand casting operation NITC
NIT CALICUT
ADVANTAGES OF CASTING PROCESS
• Process is cheap
• More suitable for mass production
• Most suitable for manufacturing
complex/complicated/intricate shaped products.
• Large parts weighing several tonnes and also small
components weighing a few grams can be cast.
• No limitation on the size of component.
• Directional properties absent in castings. Components with
uniform properties as well as with varying properties at
different locations can be cast.
• By use of cores, saving in machining of holes achieved.
• Internal stresses are relieved during solidification in many
types of castings.
• Even some materials which cannot be made by other
processes made by casting: eg. Phosphor-Bronze.
NITC
NIT CALICUT
DISADVANTAGES
• Cast product properties inferior in many
cases when compared with other
manufacturing processes.
• Elevated temperature working in
castings, as material has to be melted.
• Thin section limitations exist.
• For number of components very small,
casting not preferred.
NITC
SIGNIFICANT FACTORS•TYPE OF METAL,
•THERMAL PROPERTIES OF BOTH THE METAL
AND MOULD,
• GEOMETRIC RELATIONSHIP BETWEEN THE
VOLUME AND SURFACE AREA ,AND
•SHAPE OF MOULD.
NITC
• SOLIDIFICATION OF METALS
• AFTER POURING MOLTEN METAL INTO
MOULD, SERIES OF EVENTS TAKES
PLACE DURING SOLIDIFICATION AND
COOLING TO AMBIENT TEMPERATURE.
• THESE EVENTS GREATLY INFLUENCE
THE SIZE, SHAPE, UNIFORMITY OF THE
GRAINS FORMED, AND THUS THE
OVERALLL PROPERTIES.
NITC
Three Stages of Contraction (Shrinkage)
The liquid Metal has a Volume
"A”
It solidifies to solid with a new
volume "B"
The solidified casting further
contracts (shrinks) through
the cooling process to Volume
"C"
COOLING CURVE
For pure metal or compound
T
E
M
P
E
R
A
T
U
R
E
Cooling
of Liquid
Freezing begins
Freezing ends
At constant
temperature
Cooling of solid
Liquid
Liquid
+
Solid
Solid
TIME, log scale
Latent heat of
solidification
given off
during
freezing-
COOLING CURVE
For Binary solid solutions
T
E
M
P
E
R
A
T
U
R
E
Freezing with drop in
temperature
And FOR ALLOYS:
Alloys solidify over a range of
temperatures
Begins when temp. drops below
liquidous, completed when it
reaches solidous.
Within this temperature range,
mushy or pasty state.
Inner zone can be extended
throughout by adding a catalyst.sodium, bismuth, tellurium, Mg
(or by eliminating thermal
gradient, i.e. eliminating
convection. (Expts in space to
see the effect of lack of gravity in
eliminating convection)
TIME, log scale
(refresh dendritic growthbranches of tree, interlock, each
dendrite develops uniform
composition, etc)
The ambient
temperature is
always in a state of
transition
*
A
B
C
Minor variations in
volumetric
displacement are
negligible,
compared to the
variations that occur
from "A" to "B" and
lastly to "C".
*
A
B
C
STRUCTURE
FOR PURE METALS:
At the mould walls, metal cools rapidly. Produces
solidified skin or shell (thickness depends on
composition, mould temperature, mould size and
shape etc)
• These of equiaxed structure.
• Grains grow opposite to heat transfer through the mould
• These are columnar grains
• Driving force of the heat transfer is reduced away from
the mould walls and blocking at the axis prevents further
growth
NITC
Development of a preferred texture
- for pure metal at a cool mould wall.
A chill zone close to the wall and
then a columnar zone away from
the mould.
Solidified structures of metal solidified in a square mould
(a). Pure metal
(b). Solid solution
(c). When thermal gradient is absent
within solidifying metal
Three basic types of cast structures(a). Columnar dendritic;
(b). equiaxed dendritic;
(c). equiaxed nondendritic
Size and distribution of the overall grain structure throughout
a casting depends on rate & direction of heat flow
(Grain size influences strength, ductility, properties along
different directions etc.)
CONVECTION- TEMPERATURE GRADIENTS DUE TO
DIFFERNCES IN THE DENSITY OF MOLTEN METAL AT DIFFERENT
TEMPERATURES WITHIN THE FLUID - STRONGLY EFFECTS
THE GRAIN SIZE.
Outer chill zones do not occur in the absence of convection
NITC
Atm.Pressure
Pouring basin
MOULD
SPRUE
GATE
LIKE A PRESSURISED SYSTEM
MOULDERS’
TOOLS
AND
EQUIPMENT
MOULDING BOARD
FLASK
SHOWEL
DRAW SPIKE
RIDDLE
SLICK
RAMMER
LIFTER
STRIKE-OFF BAR
TROWELS
GATE CUTTER
BELLOWS
SPRUE PINS
VENT ROD …..
a
c
b
d
Making a Core; (a). Ramming Core Sand. (b). Drawing the core box
(c). Baking in an oven (d) Pasting the core halves
(e). Washing the core with refractory slurry
e
1.
1
2.
3a
3.
2
4a
3b
4.
5.
4b
5
Make the pattern in
pieces, prepare the core.
Position the drag half of
pattern on mould board
in the drag half of flask
Prepare the drag half of
mould, roll drag over,
apply parting sand, place
the cope half of pattern
and flask, ram and strike
off excess sand
Separate flasks, remove
patterns, cut sprue, set
core in place, close flask
Now after clamping,
ready fro pouring.
THREE BOX MOULDING
PROCEDURE
LOAM MOULDING USING
LOAM SAND
Design of Risers and Feeding of Castings
•
A simplified diagram by putting in
references to the equations (1, 2 & 4)
there is no Equation 3, diagram not changed
•
EQ(1) - Freeze Point Ratio (FPR)
FPR=X
X = (Casting Surface/Casting Volume) /
(Riser Surface/Riser Volume)
•
EQ(2) - Volume Ratio (VR) (Y Axis)
VR=Y=Riser Vol/Casting Vol*
Note: The riser volume is the actual poured
volume
• EQ(4) - (Freeze Point Ratio) Steel
X=0.12/y-0.05 + 1.0*
*The constants are from experiments and
are empirical
References - AFS Text Chapter 16; Chastain's Foundry manual Vol 2, Google
Volumes, Surface Areas, Castings and
Risers...
There are relationships between all these
items and values that will help in designing
a complete mold that controls progressive
solidification, and influences directional
solidification to produce castings with
minimal porosity and shrinkage defects.
This is by ensuring that the riser(s) are the
last to solidify.
4 points about the Riser/Casting
Relationship
• 1 - Risers are attached to the
heaviest sections of the casting
• 2 - Risers are the last to solidify
• 3 - A casting that has more than
one heavy section requires at
least one riser per heavy section
• 4 - Occasionally the thermal
gradient is modified at the moldmetal interface by the introduction
of a "Chill" that can better conduct
the heat away from the casting
and lower the solidification time
for that section.
Gating / Runner Design
•
Now a look at the flow characteristics of the
metal as it enters the mold and how it fills the
casting.
Of the flow characteristics
fluidity/viscosity plays a role. Also,
velocity,
gravitational acceleration & vortex,
pressure zones,
molten alloy aspiration from the mold and
the momentum or kinetic energy of a fluid.
The demarcation point is
Re < 2000 is considered a Laminar Flow
Re > 2000 is considered a Turbulent Flow
Objective is to maintain Re below 2000.
Basic Components of a Gating System
• The basic components of a gating system are:
 Pouring Basin,
 Sprue,
 Runners and
 Gates that feed the casting.
The metal flows through the system in this order.
Some simple diagrams to be familiar with are:
Pouring Basin - This is the "Crucible -Mold Interface", A pouring cup and
pouring basin are not equivalents, The pouring cup is simply a larger target
when pouring out of the crucible, a Pouring Basin has several components
that aid in creating a laminar flow of clean metal into the sprue.
The basin acts as a point for the liquid metal to enter the gating system in a
laminar fashion.
"Crucible-Mold Interface" is where the metal
from the crucible first contacts the mold
surface. This area is lower than where the
Mouth of the Sprue is located, by having a pool
of metal from the flow will be less chaotic than
pouring from the crucible down into the sprue.
"Dross-Dam" - to skim or hold back any dross
from the crucible or what accumulated through
the act of pouring.
As the lower portion fills and the metal is
skimmed, the clean(er) metal will rise up to
meet the opening of the sprue in a more
controlled fashion.
Sprue Placement and Parts
The sprue is the extension of the sprue
mouth into the mold
The choke or narrowest point in the taper
is the point that would sustain a "Head" or
pressure of molten metal.
To reduce turbulence and promote Laminar
Flow, from the Pouring Basin, the flow
begins a near vertical incline that is acted
upon by gravity and with an accelerative
gravity force that is 32ft/Sec/Sec
So a mass falling has a velocity of 384
inches/sec after a free fall duration of 1
entire second. Fluids in free fall tend to
distort from a columnar shape at their start
into an intertwined series of flow lines that
have a rotational vector or vortex effect
(Clockwise in the northern hemi-sphere,
and counter clockwise in the southern
hemi-sphere)...
• The rotational effect, though not a strong
force, is causing the cork-screwing effect
of the falling fluid. If allowed to act on the
fluid over a great enough duration or free
fall the centrifugal force will separate the
flow into droplets.
• None of the above promotes Laminar flow,
plus it aids the formation of dross and gas
pick-up in the stream that is going to feed
the casting.
•By creating a sprue with a taper, the fluid is constrained to
retain it's shape, reducing excessive surface area development
(dross-forming property) and gas pick-up.
•The area below the sprue is the "Well". The well reduces the
velocity of the fluid flow and acts as a reservoir for the runners
and gates as they fill.
Some dimensioning ratio's from
Chastain's Foundry Manual (no.2)
• 1- Choke or sprue base area is 1/5th the area of the well.
• 2- The well depth is twice the runner depth.
• 3- the Runner is positioned above the midpoint of the
well's depth
The Runner System
•
•
•
•
The runner system is fed by the well
and is the path that the gates are fed
from.
This path should be "Balanced" with the
model of heating or AC ductwork
serving as a good illustration. The
Runner path should promote smooth
laminar flow by a balanced volumetric
flow, and avoiding sharp or abrupt
changes in direction.
The "Runner Extension" is a "DeadEnd" that is placed after the last gate.
The R-Ext acts as a cushion to absorb
the forward momentum or kinetic
energy of the fluid flow. The R-Ext also
acts as a "Dross/Gas Trap" for any
materials generated and picked-up
along the flow of the runner.
An Ideal Runner is also proportioned
such that it maintains a constant
volumetric flow through virtually any
cross-sectional area. In the illustration,
notice that the runner becomes
proportionally shallower at the point
where an in-gate creates an alternate
path for the liquid flow.
The Gating System
• The Gates (in this case)
accommodate a directional
change in the fluid flow and
deliver the metal to the
Casting cavity.
• Again, the design objective
is to promote laminar flow,
the primary causes of
turbulence are sharp
corners, or un-proportioned
gate/runner sizes.
• The 2 (two) dashed blue
areas when added together
form a relationship to the
dashed blue area of the
Runner, which forms a
relationship to the Choke or
base of the Sprue Area.
• The issue of sharp corners (both inner
and outer) create turbulence, low & high
pressure zones that promote aspiration of
mold gases into the flow, and can draw
mold material (sand) into the flow. None
of this is good... By providing curved
radius changes in direction the above
effects are still at play but at a reduced
level. Sharp angles impact the
solidification process and may inhibit
"Directional Solidification" with crosssectional freezing...
• The image to the right is just too good a
representation to pass-up..
• By proportioning the gating system, a
more uniform flow is promoted with near
equal volumes of metal entering the mold
from all points. In an un-proportioned
system the furthest gates would feed the
most metal, while the gates closest to the
sprue would feed the least.
(this is counter to what one initially thinks).
Formulae, Ratios and Design Equations
• What is covered so far is comprehensive, and intuitive on a
conceptual level, but the math below hopefully offers some insight
into quick approximations for simple designs, and more in-depth
calculations for complex systems.
• Computerized Flow Analysis programs are used extensively in large
Foundry operations.
• From basic concepts, designing on a state of the art system shall be
attempted:
• Continuity Equation –
• This formula allows calculation of cross-sectional areas, relative to
flow Velocity and Volumetric flow over unit time. This is with the
assumption that the fluid flow is a liquid that does NOT
compress (that applies to all molten metals).
Here, a flow passes through A1
(1" by 1", 1 sq")
The passage narrows to a crosssectional area A2
Q= Rate of Flow
(Constant - uncompressible)
V=Velocity of flow
A=Area (Cross-section)
(.75" by .75", 0.5625 sq")
The passage expands to a crosssectional area A3
(1" by 1", 1 sq").
If A1 and A2 are considered, the Area A2 is almost half of
A1, thus the velocity at A2 has to be almost double of A1.
GATING RATIO isAreas of Choke : Runner : Gate(s)
• The base of the Sprue and Choke are the
same.
• The ratios between the cross-sectional Area
can be grouped into either Pressurized or
Unpressurized.
• Pressurized: A system where the gate
and runner cross-sectional areas are either
equal or less than the choke cross-sectional
area.
A1= Choke = 1 Sq Inch
• Areas A2 & A3 do not get A2 = 1st Runner c/s Area = 0.75 Sq Inch
added as they are
A3 = 2nd Runner c/s Area = 0.66 Sq Inch
positioned in line with
A4 = 1st Gate = 0.33 Sq inch
each other and flow is
A5 = 2nd Gate = 0.33 Sq Inch
successive between the
points and not
simultaneous.
• While Areas A4 & A5 are
added together as flow
does pass through these
points simultaneously.
• This example would
resolve to a pressurized
flow of 1 : 0.75 : 0.66
Unpressurized:
• The key distinction is that the Runner must have
a cross sectional area greater than the Choke,
and it would appear that the Gate(s) would equal
or be larger than the Runner(s).
• Common Ratio's noted in Chastian's Vol 2 are:
• 1:2:4
• 1:3:3
• 1:4:4
• 1:4:6
• An exception is noted in Chastain with a 1 : 8 : 6
ratio to promote dross capture in the runner
system of Aero-Space castings.
• The Continuity Equation is simplified with the
use of ratios as the velocity is inversely
proportional between any 2 adjacent ratio
values. ie H : L equates to an increase in
velocity while a L : H equates to a drop in
velocity.
• Laminar Flow is harder to control at a high
velocity than a relatively lower velocity.
• Chastain's Vol 2 has much more mathematical
expressions and calculations.
PURE METALSHave clearly defined melting/freezing point,
solidifies at a constant temperature.
Eg: Al - 6600C,
Fe - 15370C,
and W- 34100C.
NITC
Development of a preferred texture
- at a cool mould wall.
A chill zone close to the wall and
then a columnar zone away from
the mould.
Solidified structures of metal solidified in a square mould
(a). Pure metal
(b). Solid solution
(c). When thermal gradient is absent
within solidifying metal
Three basic types of cast structures(a). Columnar dendritic;
(b). equiaxed dendritic;
(c). equiaxed nondendritic
STRUCTURE
FOR PURE METALS:
At the mould walls, metal cools rapidly. Produces
solidified skin or shell (thickness depends on composition,
mould temperature, mould size and shape etc)
• These are of equiaxed structure.
• Grains grow opposite to heat transfer through the
mould
• These are columnar grains
• Driving force of the heat transfer is reduced away
from the mould walls and blocking at the axis
prevents further growth
NITC
Size and distribution of the overall grain structure throughout
a casting depends on rate & direction of heat flow
(Grain size influences strength, ductility, properties along
different directions etc.)
CONVECTION- TEMPERATURE GRADIENTS DUE TO
DIFFERNCES IN THE DENSITY OF MOLTEN METAL AT DIFFERENT
TEMPERATURES WITHIN THE FLUID - STRONGLY EFFECTS
THE GRAIN SIZE.
Outer chill zones do not occur in the absence of convection
NITC
FOR ALLOYS:
• Alloys solidify over a range of temperatures
• Begins when temp. drops below liquidous,
completed when it reaches solidous.
• Within this temperature range, mushy or pasty
state
(Structure as in figure)
• Inner zone can be extended throughout by adding
a catalyst.- sodium, bismuth, tellurium, Mg
(or by eliminating thermal gradient, i.e. eliminating
convection. (Expts in space to see the effect of lack of
gravity in eliminating convection)
(refresh dendritic growth- branches of tree, interlock, each
dendrite develops uniform composition, etc)
NITC
SOLIDIFICATION TIME
During solidification, thin solidified
skin begins to form at the cool mould
walls.
Thickness increases with time.
For flat mould walls
thickness  time
(time doubled, thickness by 1.414)
NITC
CHVORINOV’S RULE
solidification time (t) is a function of volume of
the casting and its surface area
t = C ( volume/ surface area )2
C is a constant [depends on mould material, metal
properties including latent heat, temperature]
A large sphere solidifies and cools at a much slower rate
than a small diameter sphere. (Eg- potatoes, one big and
other small)
Volume  cube of diameter of sphere,
surface area  square of diameter
NITC
Solidification time for various shapes:
Eg: Three pieces cast with the SAME volume, but different shapes.
(i)Sphere, (ii)Cube, (iii)Cylinder with height = diameter.
Which piece solidifies the fastest?
Solution: Solidification time = C (volume/surface area)2
Let volume = unity. As volume is same, t = C/ surface area2.
Sphere: V= 4/3 (π r3); i.e. r = (3/4 π)1/3
A= 4 π r2 = 4 π (3/4 π)1/3 = 4.84
Cube: V = a3; ie a = 1; A = 6 a2 = 6.
Cylinder: V = πr2h = 2 π r3; ie, r = (1/2 π) 1/3
A = 2 πr2 + 2πrh = 6 πr2 = 5.54.
Then, t cube = 0.028C ; t cylinder = 0.033C ; t sphere= 0.043C
Metal poured to cube shaped mould solidifies the fastest.
NITC
SHRINKAGE AND POROSITY
METALS SHRINK(CONTRACT) DURING
SOLIDIFICATION
- CAUSES DIMENSIONAL CHANGES
LEADING TO CENTRE LINE SHRINKAGE, POROSITY,
CRACKING TOO
NITC
SHRINKAGE DUE TO:
(1).CONTRACTION OF
MOLTEN METAL AS IT
COOLS PRIOR TO
SOLIDIFICATION
1
(2) CONTRACTION OF
SOLIDIFYING METAL,
LATENT HEAT OF
FUSION
2
T
3
(3) CONTRACTION OF
SOLIDIFIED METAL
DURING DROP TO
AMBIENT TEMP
Time
OUT OF THESE, LARGEST SHRINKAGE DURING COOLING
OF CASTING (ITEM 3) eg:pure metal
NITC
SOLIDIFICATION CONTRACTION FOR VARIOUS METALS
METAL Volumetric Solidification Contraction
Al
6.6
Grey cast Iron
Expansion 2.5
Carbon Steel
2.5 to 3
Copper
4.9
Magnesium
4.2
Zinc
6.5
NITC
• POROSITY DUE TO SHRINKAGE OF GASES
AND METAL TOO.
RELATED TO DUCTILITY
AND SURFACE FINISH
(DUCTILITY V/S POROSITY CURVES FOR
DIFFERENT METALS)
- ELIMINATION BY VARIOUS MEANS
(ADEQUATE SUPPLY OF LIQUID METAL, USE
OF CHILLS, NARROWING MUSHY ZONECASTING SUBJECTED TO ISOSTATIC PRESSING
NITC
POROSITY BY GASES
LIQUID METALS HAVE HIGH SOLUBILITY FOR
GASES
DISSOLVED GASES EXPELLED FROM
SOLUTION DURING SOLIDIFICATION
(Hydrogen, Nitrogen mainly)
ACCUMULATE IN REGIONS OF EXISTING
POROSITY OR
CAUSE MICROPOROSITY IN CASTING
- TO BE CONTROLLED
NITC
Ductility
Effect of microporosity on the ductility of quenched and
tempered cast steel – Porosity affects the ‘pressure tightness’ of
cast pressure vessel
Elongation
Reduction of area
0
5
10
Porosity(%)
15
NITC
FLOW OF MOLTEN METAL IN MOULDS
Important: pouring basin, mould cavity & riser
GATING SYSTEM Design -fluid flow, heat transfer, influence
of temperature gradient,
FLUID FLOW
Without turbulence
or with minimized turbulence
HEAT FLOW INFLUENCED BY MANY FACTORS
FLUIDITY-A characteristic related to viscosity.
TEST OF FLUIDITY - USING A SPIRAL MOULD.Fluidity Index
NITC
TEST FOR
FLUIDITY
USING A SPIRAL
MOULD.
FLUIDITY INDEX IS
THE LENGTH OF
THE SOLIDIFIED
METAL IN THE
SPIRAL PASSAGE.
GREATER THE
LENGTH, GREATER
THE FLUIDITY
INDEX.
PATTERN
• Model of a casting constructed such that it
forms an impression in moulding sand
NITC
PATTERN
• 1st step- Prepare model (pattern)
Differs from the casting
Differences
Pattern Allowances.
• To compensate for metal shrinkage,
• Provide sufficient metal for machining
• Easiness in moulding
• As Shrinkage allowance, Draft allowance, Finishing
allowance, Distortion or camber allowance,
Shaking or rapping allowance
NITC
MATERIAL
1. WOOD.
2. METAL
Al, CI, Brass,
3. For special casting processes,
Polystyrene which leaves mould as gas
when heated also used.
Types- many
Simple-Identical patterns;
Complex, intricate- with number of pieces.
Single or loose piece; Split; gated; Match Plate;
Sweep; Segmental; Skeleton(frame, ribbed), skell;
Boxed Up; Odd shaped etc. Sketches--
NITC
Material
1. WOOD.
(+) Cheap, easily available, light, easiness in surfacing,
preserving (by shellac coating), workable, ease in
joining, fabrication
(-) Moisture effects, wear by sand abrasion, warp during
forming, not for rough use.
Must be properly dried/ seasoned,
free from knots, straight grained
Egs. Burma teak, pine wood, mahogany, Sal, Deodar,
Shisham, Walnut, Apple tree
NITC
2. METAL:
For durability, strength
Egs: Al alloys, Brass, Mg alloys, Steel, cast Iron for
mass production
(first, wooden pattern is made, then cast in the metal)
Type of material depends on shape, size, number of
castings required, method of moulding etc.
NITC
TYPES OF PATTERNS
NIT CALICUT
1. SINGLE PIECE PATTERN.
NITC
NIT CALICUT
2. SPLIT PATTERN (TWO PIECE )
NITC
NIT CALICUT
2. a, THREE PIECE SPLIT PATTERN
NITC
NIT CALICUT
3. LOOSE PIECE PATTERN
NITC
4. COPE AND DRAG PATTERN
•
•
•
NIT CALICUT
•
COPE AND DRAG PARTS OF THE PATTERN
MOUNTED ON SEPARATE PLATES.
COPE HALF AND DRAG HALF MADE BY
WORKING ON DIFFERENT MOULDING
MACHINES.
THIS REDUCES THE SEPARATE COPE AND DRAG
PLATE PREPARATION.
GENERALLY FOR HIGH SPEED MECHANISED
MOULDING.
NITC
5. MATCH PLATE PATTERN –
Pattern generally of metal and plate making
NIT CALICUT
parting line metal/wood.
NITC
6. FOLLOW BOARD PATTERN.
For thin sections.
NIT CALICUT
THIN PATTERN
NITC
7. GATED PATTERN
-
NIT CALICUT
Gating system is a part of the pattern.
NITC
8. SWEEP PATTERN
–
For large size castings in small numbers. Template of
NIT CALICUT
wood attached to a sweep used.
NITC
9. SEGMENTAL PATTERN
–
NIT CALICUT
For rings, wheel rims, large size gears.
NITC
10. SKELETON PATTERN.Stickle board used to scrape the excess sand.
Eg. Oil pipes, water pipes, pipe bends, boxes, valve bodies etc.
NIT CALICUT
Stickle board
NITC
NIT CALICUT
11. SHELL PATTERN
NITC
12. BUILT UP PATTERN
–
Also called lagged up patterns- For barrels, pipes,
NIT CALICUT
columns etc
NITC
13. LEFT AND RIGHT PATTERN
–
NIT CALICUT
For parts to be made in pairs.
Eg: legs of sewing machine, wood working lathe,
garden benches, J hangers for shafts, brackets for
luggage racks etc.
NITC
•
•
•
•
•
NIT CALICUT
Type of pattern depends on:
Shape and size of casting,
number of castings required,
method of moulding employed,
easiness or difficulties of the moulding
operations,
• other factors peculiar to the casting.
NITC
CHARACTERISTICS OF
PATTERN MATERIALS
CHARACTERISTIC
RATING
WOOD
MACHINABILITY
WEAR RESISTANCE
STRENGTH
WEIGHT
REPAIRABILITY
RESISTANCE TO:
•
•
AL
STEEL
PLASTIC
CAST IRON
E
P
E
E
E
G
G
G
G
P
F
E
E
P
G
G
F
G
G
F
G
E
G
P
G
CORROSION (by water) E
SWELLING
P
E
E
P
E
E
E
P
E
E- Excellent; G- Good; F-fair, P- Poor
NITC
Functions of pattern
•
•
•
•
•
•
Moulding the Gating system;
Establishing a parting Line,
Making Cores,
Minimising casting Defects,
Providing Economy in moulding
Others, as needed
MOULDING SAND
• Granular particles from the breakdown of rocks by frost,
wind, heat and water currents
• Complex Composition in different places
• At bottom and banks of rivers
• - mainly silica (86 to 90%); Alumina (4% to 8 %);
Iron oxide (2 to 5%) with oxides of Ti, Mn, Ca. etc.
NITC
NATURAL SAND , called Green sand. Only water as
binder; can maintain water for long time
SYNTHETIC SAND.- (1)GREEN and (2)DRY types
(1) Artificial sand by mixing clay free sand,
binder(water and bentonite)
Contains New silica sand 25%; Old sand 70%;
bentonite 1.5%;moisture 3% to 3.5%
(2) New 15%; Old 84%;
bentonite and moisture 0.5 % each
NITC
DRY SAND- for moulding large castings. Moulds of
green sand dried and baked with venting done. Addcow dung, horse manure etc.
LOAM SAND- mixture of clay and sand milled with
water to thin plastic paste. Mould made on soft bricks.
The mould dried very slowly before cast. For large
regular shapes- drums, chemical pans etc.
FACING SAND- used directly with surface of pattern;
comes in contact with molten metal; must have high
strength, refractoriness.
Silica sand and clay without used sand- plumbago
powder, Ceylon lead, or graphite used. Layer of 20 to
30 mm thick--about 10% to 15% of whole mould sand
NITC
BACKING SAND- old used moulding sand called floor
sand black in colour. Used to fill mould at back of
facing layer. Weak in bonding strength
SYSTEM SAND- used in machine moulding to fill whole
of flask. Strength, premealibility and refractoriness
high
PARTING SAND- used for separating boxes from
adhering, free from clay
CORE SAND- for making cores. Silica sand with core oil
(linseed oil, rosin, light mineral oil, binders etc)
SPECIALISED SANDS - like CO2 sand, Shell sand, etc
for special applications
Mould washers- slurry of fine ceramic grains applied on
mould surface to minimize fusing
NITC
About MOULDING SAND
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
NATURAL SAND
SYNTHETIC SAND.- GREEN and DRY
DRY SAND
LOAM SAND
FACING SAND
BACKING SAND
SYSTEM SAND
PARTING SAND
CORE SAND
SPECIALISED SANDS
Mould washers
NITC
MOULDING SAND- PROPERTIES
• Green Strength- Adequate strength after mixing, and plasticity
for handling
• Dry Strength- After pouring molten metal, adjacent surface
loses water content. Dries. Dry sand must have enough
strength to resist erosion
• Hot Strength- Strength at elevated temperature after
evaporation of moisture
• Permeability- Permeable or porous to permit gases to escape.
Ability of sand moulds to allow the escape of gases
NITC
• Thermal stability- Rapid expansion of sand surface at
mould-metal interface. May crack. Results in defect called
SCAB
• Refractoriness- Ability of sand to withstand high
temperature
• Flowability- Ability to flow & fill narrow portions around
pattern
• Surface finish- Ability to produce good surface finish in
casting
• Collapsibility- Allow easy removal of casting from mould
• Reclamation- Should be reusable and reclaimable
NITC
FURNACES
•
•
•
•
•
•
Proper selection depends on:
Composition and melting point of alloy to be cast
Control of atmospheric contamination
Capacity and rate of melting required
Environmental considerations- noise, pollution
Power supply, availability, cost of fuels
Economic considerations-initial cost, operating cost,
maintenance cost etc.
CUPOLAS (> 50 T, VERTICAL, HIGH RATES)
ELECTRIC FURNACES
INDUCTION FURNACES
NITC
FOUNDRIES
• From Latin word- fundere (meaning melting & pouring)
• Pattern & Mould making- automated, computer integrated
facilities- CAD/CAM
• Melting, controlling composition & impurities, pouringUse of conveyors, automated handling, shakeout,
cleaning, heat treatment, inspection, etc.
NITC
CUPOLA
* CHARGE PASSES DOWNWARDS
UNDER GRAVITY
* MEETS FLOW OF HOT GASES
MOVING UPWARDS
* CONTINUOUS IN OPERATION
.Vertical steel shell, lined with fire
bricks.
.Base on four steel columns
.Hinged doors in the base plate to
remove residue at the end of melt.
.Air blast through tuyeres (number on
size)
.Through charging door, coke, pig
iron, scrap & lime stone charged.
.Cold & Hot blast cupolas.
TOWER FURNACE
TO MELT ALUMINIUM
& alloys
3 main sectionscharging elevator,
melting unit, holding
furnace (Cylindrical
rotary unit).
Automatic controls
Grate above burners
supports solid charge
Molten charge runs
down
REVERBERATORY FURNACE
Small units (50kg) for melting non ferrous metals, large (about 25T)
10 T capacity to melt iron
AIR FURNACE:
One type of RB- to melt cast iron for roll mill rolls, malleable castings,
15 T capacity – Charge out of contact with fuel, less sulphur absorbed,
long melting time enables control of composition, large size scrap
handled.
Lump coal, pulverised fuel, oil used to fire. Solid coal burnt in a grate
The Sand Casting Process
The most commonly used Casting Process, in the entire
Casting Industry.
• Concept: The top and the bottom of the mold form the flask.
"holds the whole thing together." The cope and the drag.
• An impression device, in the middle of the flask assembly,
called the pattern.
• The sand around the pattern is called the, holding medium.
• These are the basic, universal casting components, which can
be applied to all Casting and Molding Processes.
• The mold maker uses the pattern to make the impression in
the holding medium, the sand, then sets the pattern aside,
closes the cope and drag, to complete the flask, and forms
the mold, fills that void with a molten material; which could
be almost anything.
NITC
NITC
Casting a component
NITC
Middle support for a bike rack on public trains.
•
•
•
•
•
•
•
Material:535 aluminum.
Process: Sand casting.
Casting Supplier: Dent
Manufacturing, Inc.,
Northampton, Pennsylvania.
This 2-lb casting replaced four
stainless steel fittings, eliminating
the need for several nut and bolt
assemblies.
The 8.5 x 7.5 x 3.5-in. component
is designed to hold 1.25-in. steel
pipe handrails on a bike rack.
The foundry polishes and clear
anodizes the casting for a longlasting finish, which provides a
cleaner appearance when
compared to the previous
assembly.
The casting eliminates the need
for multiple parts, reducing
manufacturing time and overall
cost.
NITC
Air scoop that directs air flow for an agricultural
combine.
•
•
•
•
Material:80-55-06 ductile iron.
Process:Sand casting.
Casting Supplier: Neenah
Foundry Co., Neenah, Wisconsin.
Originally manufactured as a
stamping and weldment, this 25lb component was converted to a
ductile iron casting at a 40% cost
reduction. Pictured is the casting
(r) and the previous
stamping/weldment (l).
The cast component, which
measures 210 x 60 x 620 mm,
afforded the customer a simpler
design, eliminating the need for
capital resources and manpower
for extensive stamping and
welding equipment.
NITC
Torque arm bracket for the after-market automotive
industry.
•
•
•
•
•
•
Material:80-55-06 ductile iron.
Process: Sand casting.
Casting Supplier: Farrar Corp.,
Norwich, Kansas.
Converted from a fabricated steel
assembly, the casting saved the
customer $49/part due to reduced
grinding and no assembly time
for the component (previously 810 hours per bracket).
Fully machined by the foundry,
the casting achieves tighter
dimensional tolerances than the
fabrication and has experienced
zero returns due to failure in the
field.
Using rapid prototyping, the
foundry was able to deliver
sample parts for approval within
one week from design delivery.
NITC
DIE CASTING
GRAVITY
SEMI PERMANENT MOULD
OR PERMANENT MOULD
COLD CHAMBER
HOT CHAMBER
(HEATING CHAMBER)
OUTSIDE THE MACHINE
INTEGRAL WITH THE MACHINE
NITC
PERMANENT MOULD
OR GRAVITY DIE CASTING
*METALLIC MOULDS USED - MOULD TO
WITHSTAND TEMPERATURE
*NO EXTERNAL PRESSURE APPLIED,
*HYDROSTATIC PRESSURE BY RISERING
*LAMP BLACK/CORE OIL APPLIED TO DIE SURFACES
FOR EASY REMOVAL
*FAST CONDUCTION, RAPID COOLING
*TWO HALVES OF DIES- ONE FIXED, ONE MOVABLE NITC
• +POINTS
• •
•
•
•
•
•
•
•
•
•
•
-
VERY CLOSE TOLERANCE CASTINGS,
MORE STRENGTH, LESS POROUS
BETTER SURFACE FINISH COMPARED TO
SAND CASTING
SURFACE FREE FROM SAND
DENSITY HEAVY
MORE DIMENSIONAL ACCURACY - 0.06 TO 0.3 MM
DIES LESS COSTLY THAN PRESSURE DIE CASTING DIES
GOOD FOR PRESSURE TIGHT VESSELS
LESS COOLING CRACKS
LESS SKILL
GOOD FOR LARGE QUANTITIES
NITC
- POINTS
§
§
§
§
§
§
ONLY FOR SMALL AND
MEDIUM SIZE CASTINGS
FOR NON FERROUS, MAINLY
LARGE QUANTITY,
BUT IDENTICAL PIECES ONLY
POOR ELONGATION
STRESS AND SURFACE HARDNESS DEFECTS
OBSERVED
CASTING TO BE WITHDRAWN CAREFULLY
FROM DIES
NITC
SEMIPERMANENT DIECASTING
• DIE PRESSURE AT 20 TO 20,000 ATM
• PRESSURE FILL SOLIDIFICATION
• FOR NONFERROUS METALS
• FOR INTRICATE SHAPES
• CLOSE TOLERANCES POSSIBLE
• FOR MASS PRODUCTION, >10,000
NITC
FOR SEMI AND PRESSURE DIE CASTING SET UPS,
THE FOLLOWING FACTORS A MUST
1.
A GOOD DIE SET MECHANISM
2.
MEANS FOR FORCING METAL
3.
DEVICE TO KEEP DIE HALFS PRESSED
4.
ARRANGEMENT FOR
AUTOMATIC REMOVAL OF CORES- IF ANY
5.
EJECTOR PINS
NITC
TWO TYPES OF PRESSURE DIE CASTING
COLD CHAMBERHEATING CHAMBER OUTSIDE THE MACHINE
- FOR Al, Mg, Cu, AND HIGH MELTING ALLOYS
HOT CHAMBERHEATING INTEGRAL WITH THE HANDLING
GOOSE NECK MECHANISMS WIDELY USED
FOR LOW MELTING ALLOYS- Zn, Pb, Etc.
ALSO VACUUM DIE CASTING MACHINES- SPACE
BETWEEN THE DIES AND PASSAGE VACUUMISED
BEFOR POURINGSUBMERGED PLUNGE TYPE, DIRECT AIR DIE
CASTING MACHINES
NITC
CENTRIFUGAL CASTING
TRUEFOR HOLLOW CIRCULAR- PIPES- SHAPE
BY CENTRIFUGAL ACTION- SPEED OF
ROTATION IMPORTANT
CAN BE HORIZONTAL, VERTICAL OR
INCLINED
C.I. PIPES, LINERS, BUSHES, CYLINDER
BARRELS ETC.
NITC
• SEMI• CENTRE CORE FOR INNER SURFACESHAPE BY MOULD AND CORE,
MAINLY NOT BY CENRTRIFUGAL ACTIONEg:FLYWHEELS
• SPEED OF ROTATION60 TO 70 TIMES GRAVITY FOR HORIZONTAL
AND INCLINED TYPES
ABOVE 100 FOR VERTICAL TYPES.
NITC
VACUUM DIE CASTING MACHINES
•
•
•
•
•
SOME AIR ENTRAPPED IN ORDINARY DIE CASTING MACHINES
THIS PRODUCES BLOW HOLES
IN VACUUM DIE CASTING TYPE, VACUUM PUMP CREATES
VACUUM IN DIE CAVITY, A SEAL CUTS OFF THE PIPE CONNECTION
AFTER EVACUATING
THIS PREVENTS FLOW OF METAL FROM DIE TO VACUUM PIPE
FLOW OF MOLTEN QUICK AND AUTOMATIC
• FINISHES:
•
ALL DIE CASTINGS SUSCEPTIBLE TO CORROSION, HENCE
SUBJECTED TO FINISHING OPERATIONS OR PLATING
NITC
DESIGN CONSIDERATIONS
• USE OF RIBS, HUBS, BOSSES MUST BE TO REDUCE WEIGHT,
STRENGTHEN THE PART, IMPROVE THE APPEARANCE
• THICK SECTIONS MAKE DIE HOTTER AND THUS LESSEN
DIE LIFE
• LARGE SECTIONS TO BE COOLED MAY CAUSE POROSITY
• EXCESSIVE SECTIONAL CHANGES TO BE AVOIDED
• AVOID UNDERCUTS
• FILLETS DESIRABLE OVER SHARP EDGES
• DRAFTS NEEDED ON ALL CASTINGS
• EJECTOR PINS AT BACK TO AVOID VISIBILITY OF MARKS
• FLASH NECESSARY , TO BE REMOVED LATER BY
TRIMMING
NITC
DIE MATERIALS
CASTING ALLOYS
DIE MATERIAL
TIN, LEAD ALLOY CAST STEEL WITHOUT HEAT
TREATMENT
ZINC, Al
COPPER BASE
ALLOYS
HEAT TREATED LOW ALLOY STEEL
HEAT TREATED SPECIAL ALLOY STEEL
NITC
DIE CASTING ALLOYS
• MAINLY NON-FERROUS CASTINGS WITH
PROPERTIES COMPARABLE WITH FORGINGS
ZINC ALLOYS:- WIDELY USED (  70%)- Al 4.1%; Cu
•
•
•
•
MAX 1%, Mg 0.4%; BALANCE ZINC
-- PERMITS LONGER DIE LIFE, SINCE TEMP. IS LOW
GOOD STRENGTH, Tensile Strength: 300 Kg/cm2
VERY GOOD FLUIDITY, THUS THIN SECTIONS POSSIBLE
USES: AUTOMOBILES, OIL BURNERS, FRIDGES, RADIO, TV
COMPONENTS, MACHINE TOOLS, OFFICE MACHINERIES
NITC
ALUMINIUM ALLOYS:
• BY COLD CHAMBER PROCESS• Cu 3 to 3.5%, Si 5 to 11 %, BALANCE Al.
• LIGHTEST ALLOYS, GOOD CORROSION
RESISTANCE, FINE GRAINED STRUCTURE
DUE TO CHILLING EFFECT
• Tensile Strength: 1250 to 2500 Kg/cm2
• GOOD MACHINABILITY, SURFACE FINISH
• USES: MACHINE PARTS, AUTOMOTIVE,
HOUSE HOLD APPLIANCES ETC.
NITC
COPPER BASED ALLOYS:
• Cu 57 to 81%;Zn 15 to 40%; SMALL QUANTITIES
OF Si, Pb, Sn
• VERY HIGH TENSILE STRENGTH: 3700 to
6700Kg/cm2;
• GOOD CORROSION RESISTANCE; WEAR
RESISTANCE
• LOW FLUIDITY, HENCE REDUCED DIE LIFE
• USES; ELECTRICAL MACHINERY PARTS,
SMALLGEARS, MARINE, AUTOMOTIVE AND
AIR CRAFT FITTINGS, HARDWARES
NITC
MAGNESIUM BASED ALLOYS:
• LIGHTEST IN DIE CASTING, PRODUCTION COST
SLIGHTLY HIGH, Al: 9%; Zn: 0.5%; Mn: 0.5%; Si:
0.5%, Cu:0.3%; REMAINING Mg.
• USES: IN AIRCRAFT INDUSTRY, MOTOR &
ISTRUMENT PARTS, PORTABLE TOOLS, HOUSE
HOLD APPLIANCES
LEAD & TIN BASED ALLOYS;
• Lead base: 80% Pb
& ; Tin base 75% tin,
antimony, copper
• LIMITED APPLICATIONS. LIGHT DUTY
BEARINGS, BATTERY PARTS, X-RAY SHIELDS,
LOW COST JEWELLERY, NON-CORROSIVE
APPLICATIONS
NITC
• PRODUCTION OF ALLOY WHEELS
• METHOD OF PRODUCTION; COUNTER
PRESSURE DIE CASTING
•
• The manufacturing process commences
with the smelting of pure aluminium
ingots in a 5-ton basin type furnace.
NITC
NITC
• The furnace is a dry sole type furnace whose
function is to smelt the primary raw
material, and reprocess alloy scraps
consisting of:- wheels used in destructive
testing by the quality control department,
and the risers and gates removed from the
wheels following the casting process. From
the dry sole furnace, the molten aluminium
is transferred to the alloy induction furnaces
via a feed channel to enable the mixing and
smelting of the elements required in the
preparation of the alloy – AlSi 7.
NITC
• A spectrometer equipped quality control laboratory is
used during the process of alloy preparation to ensure
the composition of the alloy meets the required
specification during this stage of the preparation
process. Spectrometer analysis sampling is also applied
randomly to finished wheels.
NITC
• Molten alloy is transferred to holding furnaces for
eventual transfer to the casting machines. After the
molten alloy has been tested for conformance to
specifications, it is transported to the alloy treatment
station where the alloy is submitted to three procedures
performed by an automatic process control system. The
treatment unit introduces salts into the molten alloy
using a high-speed spinner, where the alloy purification
is assisted by the use of nitrogen gas jets. The three
procedures to which the molten alloy is submitted are: 
Degassing
 
Refining
 
Modifying
NITC
These processes are intrinsic to the removal of all
undesirable impurities in the molten alloy. The automation
of these processes improves the product quality control,
production rates and importantly minimizes wastage by
reducing the possibilities of rejection of the finished
product. Following the procedures to ensure that the
molten alloy conforms to precise specification, it is
transported in holding furnaces to the low pressure casting
machines. These furnaces are designed to produce casting
by employing pressurised air within a range of 0.3 – 1.0
atm., the pressurization being monitored and varied by a
computerized process control system according to flow
requirements
NITC
Computerized process technology automatically controls the casting process, and then,
at the end of the 4.5 minute casting cycle, cools and ejects the wheel onto a catcher arm
designed for this purpose.
Holding furnaces contain between 500-750kg of molten alloy - sufficient for up to
approx. 4 hours of casting operations. When the holding furnace is exhausted it is
exchanged for a full replacement furnace using the transfer shuttle - illustrated above without interruption to the casting process.
Hydraulic systems control many of the unit’s operating movements, and, due to high
operating temperatures many measures have to be taken to enable minimization of risk
and reduction of maintenance of these systems. For example, it is necessary for all
hydraulic systems to employ fire resistant fluids thereby eliminating fire risk. Likewise,
all hydraulic hoses have to be metal covered and insulated against accidental splashes
of molten metal.
The operators of the Counter Pressure Casting Machines perform an initial visual
quality control as the wheels are ejected from each unit and palleted ready for transport
to the Riser cutting department.
At this first stage in the machining process following casting, the removal of the gates
and risers is carried out by automated machines designed for this purpose – with a cycle
time of 50 seconds per wheel. The CNC riser-cutting unit performs the following
operations
NITC
NITC
 
•
•
•
•
Pre-boring of the central hole of the wheel
·
Removal of the channel burrs corresponding to the surface joints on the Die’s
moving parts
·
Trimming upper and lower edges of the wheel
The working cycle of the Riser cutting unit is completely automated to improve both
quality control and production rate per machine. All waste products are collected for
recycling at the foundry. The machine operations are performed under a suction hood to
remove aluminium dust and particulates from the environment in proximity to this unit.
Customarily, after the machining processes have been completed on the newly cast
wheels, the wheels are passed to the quality control unit for examination under a variety
of non-destructive and destructive tests. Batch sampling of the wheels may involve
taking a 1-2mm scrape taken using a lathe, and running a spectrometer analysis of the
resulting alloy sample.
NITC
•
•
•
•
X-Ray analysis machine in Quality control department
Non-destructive testing is undertaken using radiography processes. It is common
practice for the VM customers to include within their contractual requirements testing
volumes and timescales (i.e. before or after machining). The X-ray control equipment
can be pre-set with information from up to 1000 wheel designs, and wheels can be
inspected on a wide variety of positions / angles (normally 20 position variants).
The wheel manipulator for handling the wheels during the inspection cycle has 5 fully
computerized axes and a roller conveyor automatically provides loading/unloading of
the machine with the wheels for inspection.
The X-Ray unit takes 2 wheels at a time - one in process of inspection cycle, and a
second wheel in a ‘holding’ position. As the testing machine completes the automated
inspection cycle, it simultaneously ejects the inspected wheel, puts the second wheel
into position for inspection and draws another wheel into the ‘holding’ position. Thus
the performance inspection cycle is enhanced to its maximum possibility. During an
inspection, the operator monitors the x-ray image on a viewing console and has the
possibility of magnifying the image or ‘replaying’ the process to precisely identify any
casting defect exposed by this machine.
NITC
• The next stage of the quality control process is undertaken on Geometrical
control benches where the physical dimensions of the wheels are compared
with the specification standard using pantographs and micrometers.
• The semi- finished product, having been submitted to various machining
and quality control procedures are passed to the finishing dept. which dependent upon client specification - either submits the wheels through an
automated paint shop - or polishing line where a bright lacquer finish has
been specified.
• The finished wheels are then palleted and wrapped in polyethylene film ready for transfer to a wheel/tyre assembly plant - prior to final shipment
to the production lines of the VM customer
NITC
• The pallet/box wrapping equipment consists of a motorized wrapping
machine – allowing pallets to be placed on a rotating turntable, and
providing film wrapping through this rotation with a fixed unit holding
the polyethylene roll.
• The finished wheels are stored on pallets/boxes until shipping.
• COUNTER PRESSURE DIE CASTING MACHINES
• The casting machines have evolved over 25 years of development and
manufacturing experience of counter-pressure & low pressure casting
machines.
• Simplicity of design, operating convenience and ease of maintenance are
the core attributes that produce highest levels of egonomics and safety.
• The above principles are well emphasised by the rugged vertical tie-bar
construction incorporating an integral holding furnace.
• The well tried and proven technical solutions provide stability, accuracy in
guiding and controlling the precision of the moving parts, and include
essential rigidity, operational dependability and longevity of the machines.
• All machines are designed to withstand heavy-duty service in foundries
operating continuous 24 hour cycles.
NITC
NITC
V-Process
1. Pattern (with vent holes) is placed on hollow carrier
plate.
2. A heater softens the .003" to .007" plastic film.
Plastic has good elasticity and high plastic deformation
ratio.
3. Softened film drapes over the pattern with 300 to
600 mm Hg vacuum acting through the pattern vents
to draw it tightly around pattern.
4. Flask is placed on the film-coated pattern. Flask
walls are also a vacuum chamber with outlet shown.
5. Flask is filled with fine, dry unbonded sand. Slight
vibration compacts sand to maximum bulk density.
6. Sprue cup is formed and the mold surface leveled.
The back of the mold is covered with unheated plastic
film.
7. Vacuum is applied to flask. Atmospheric pressure
then hardens the sand. When the vacuum is released
on the pattern carrier plate, the mold strips easily.
8. Cope and drag assembly form a plastic-lined cavity.
During pouring, molds are kept under vacuum.
9. After cooling, the vacuum is released and freeflowing sand drops away leaving a clean casting, with
no sand lumps. Sand is cooled for reuse.
NITC
Benefits Of Using The V-Process:
•
•
•
•
•
•
•
•
•
•
Very Smooth Surface Finish
125-150 RMS is the norm. Cast surface of 200 or better, based on The Aluminum
Association of America STD AA-C5-E18.
Excellent Dimensional Accuracy
Typically +/-.010 up to 1 inch plus +/-.002 per additional inch. Certain details can
be held closer.
+/-.010 across the parting line.
Cored areas may require additional tolerances.
Zero Draft
Eliminates the need for machining off draft to provide clearance for mating parts
and assembly.
Provides consistent wall thickness for weight reduction and aesthetic appeal.
Allows for simple fixturing for machining and inspection.
NITC
•
•
•
•
•
•
•
•
•
•
•
•
•
Pattern construction becomes more accurate and efficient.
Total tolerance range becomes more accurate and efficient.
Geometry/tolerance of part is at its simplest form. Draft does not use up
tolerance.
Design/drafting is less complex. Calculations and depictions related to draft are
eliminated.
Thin Wall Sections
Walls as low as .100 in some applications are possible.
Excellent Reproduction Of Details
Very small features and lettering are possible.
Consistent Quality
All molding is semi-automatic. Variable "human factor" has been reduced.
Superior Machining
Sound metal and no hidden sand in the castings means fewer setups, reduced
scrap and longer tool life.
Low Tooling Costs
NITC
•
•
All patterns are made from epoxy, machined plastics, SLA or LDM. There
is no need to retool for production quantities.
Unlimited Pattern Life
Patterns are protected by plastic film during each sand molding cycle.
Easy Revisions To Patterns
No metal tooling to weld or mill. Great for prototypes.
Short-Run Production Capability
Excellent for short-run production while waiting for hard tooling. The VPROCESS method can outproduce traditional prototype methods such as
plaster or investment castings.
Fast Turnaround
•
From placement of order to sample casting in as little as two to four weeks.
•
•
•
•
•
•
NITC
CENTRIFUGAL CASTING
• + points:
• Denser structure, cleaner, foreign elements
segregated (inner surface)
• Mass production with less rejection
• Runners, risers, cores avoided
• Improved mechanical properties
• Closer dimensions possible, less machining
• Thinner sections possible
• Any metal can be cast
NITC
- points:
- Only for cylindrical and annular parts with limited
range of sizes
- High initial cost
- Skilled labour needed
- Too high speed leads to surface cracks- (high
stresses in the mould )
NITC
CENTRIFUGAL CASTING
AN OVERVIEW
• Known for several hundred years.
• But its evolution into a sophisticated production method for other
than simple shapes has taken place only in this century.
• Today, very high quality castings of considerable complexity are
produced using this technique.
NITC
• To make a centrifugal casting, molten metal is poured into a
spinning mold.
• The mold may be oriented horizontally or vertically, depending on
the casting's aspect ratio.
• Short, square products are cast vertically while long tubular
shapes are cast horizontally. In either case, centrifugal force holds
the molten metal against the mold wall until it solidifies.
• Carefully weighed charges ensure that just enough metal freezes in
the mold to yield the desired wall thickness.
• In some cases, dissimilar alloys can be cast sequentially to produce
a composite structure.
NITC
• For copper alloy castings, moulds are usually made from carbon
steel coated with a suitable refractory mold wash.
• Molds can be costly if ordered to custom dimensions, but the
larger centrifugal foundries maintain sizeable stocks of molds in
diameters ranging from a few centimetres to several metres.
• The inherent quality of centrifugal castings is based on the fact
that most nonmetallic impurities in castings are less dense than
the metal itself. Centrifugal force causes impurities (dross, oxides)
to concentrate at the casting's inner surface. This is usually
machined away, leaving only clean metal in the finished product.
• Because freezing is rapid and completely directional, centrifugal
castings are inherently sound and pressure tight.
• Mechanical properties can be somewhat higher than those of
statically cast products.
NITC
• Centrifugal castings are made in sizes ranging from
approximately 50 mm to 4 m in diameter and from a few
inches to many yards in length.
• Size limitations, if any, are likely as not based on the
foundry's melt shop capacity.
• Simple-shaped centrifugal castings are used for items such
as pipe flanges and valve components, while complex
shapes can be cast by using cores and shaped molds.
• Pressure-retaining centrifugal castings have been found to
be mechanically equivalent to more costly forgings and
extrusions.
NITC
CENTRIFUGAL CASTING - ANIMATION
NITC
NITC
PRODUCTS
Brake drum for commercial highway Class 8 trucks and trailers.
•
•
•
•
•
Material:Gray iron.
Process: Centrifugal casting.
This 84-lb brake drum is produced by casting
gray iron centrifugally into a steel shell. This
shell acts as a protective jacket, resulting in
superior drum strength and allowing for the
removal of iron in the drum band and
mounting areas normally required in a full
cast brake drum.
Through concerted efforts between the
foundry, machine shop and engineering/testing
resources, 6 lb were removed from the brake
drum while providing the same performance,
balance and reliability as the standard drum.
With the weight optimized at 84 lb, the drums
are ideal for weight sensitive applications such
as refrigerated trailers, tankers and bulk
haulers.
Utilizing these drums on an 18-wheel
tractor/trailer application can provide up to
224 lb of weight savings.
NITC
Commercial products made by centrifugal casting
• Belt buckles, battery lug nuts, lock parts, "pot
metal" gears and machine parts, bushings,
medallions, figurines, souvenirs, memorial coins
and plaques, toy and model parts, concrete
expansion fasteners, hardware such as drawer
pulls and knobs, handles, decorative wall switch
plates etc. etc.
NITC
INTRODUCTION
• Investment casting, often called lost wax casting, is
regarded as a precision casting process to fabricate nearnet-shaped metal parts from almost any alloy. Although its
history lies to a great extent in the production of art, the
most common use of investment casting in more recent
history has been the production of components requiring
complex, often thin-wall castings. A complete description of
the process is complex. But, the sequential steps of the
investment casting process are as below, with emphasis on
casting from rapid prototyping patterns.
NITC
Fig: 1- Investment casting process
NITC
• The investment casting process begins with fabrication of a
sacrificial pattern with the same basic geometrical shape as
the finished cast part
• Patterns are normally made of investment casting wax that
is injected into a metal wax injection die. Fabricating the
injection die is a costlier process and can require several
months of lead time.
• Once a wax pattern is produced, it is assembled with other
wax components to form a metal delivery system, called
the gate and runner system. The entire wax assembly is
then dipped in a ceramic slurry, covered with a sand
stucco, and allowed to dry. The dipping and stuccoing
process is repeated until a shell of ~6-8 mm (1/4-3/8 in) is
applied.
NITC
Fig. 2- Investment casting process - dewaxing
NITC
• Once the ceramic has dried, the entire assembly is placed in a
steam autoclave to remove most of the wax.
• After autoclaving, the remaining amount of wax that soaked
into the ceramic shell is burned out in a furnace. At this point,
all of the residual pattern and gating material is removed, and
the ceramic mold remains.
• The mold is then preheated to a specific temperature and filled
with molten metal, creating the metal casting. Once the casting
has cooled sufficiently, the mold shell is chipped away from the
casting.
• Next, the gates and runners are cut from the casting, and final
post-processing (sandblasting, machining) is done to finish the
casting.
(The CAD solid model, the shell, and the pattern produced in the QuickCast
process is schematically shown)
NITC
Fig. 3. Investment casting process –Preheating and pouring
NITC
•
•
•
•
The major impact rapid prototyping processes have had on investment casting is
their ability to make high-quality patterns (Fig. 5) without the cost and lead times
associated with fabricating injection mold dies.
In addition, a pattern can be fabricated directly from a design engineer's computeraided design (CAD) solid model. Now it is possible to fabricate a complex pattern in
a matter of hours and provide a casting in a matter of days.
Investment casting is usually required for fabricating complex shapes where other
manufacturing processes are too costly and time-consuming.
Another advantage of rapid prototyping casting is the low cost of producing
castings in small lot sizes.
NITC
Vacuum Vessel for the power generation industry
Material:Inconel 625
•
•
•
•
Process: Investment Casting
The 5-lb casting is one-tenth scale of the vacuum vessel
for the National Compact Stellarator Experiment
(NCSX) being developed by the Princeton Plasma
Laboratory and the Oak Ridge National Laboratory as
the next generation of fusion experiment. The scale
model was investment cast to determine the feasibility
of using a casting for a vacuum vessel with complex
geometry.
To meet the rush timeline (with the help of
buycastings.com), SLS rapid prototyping techniques
were employed to make the complicated wax patterns
from a CAD/STL file in 2 weeks. Solidification modeling
predicted the potential “hot spots” and ways to optimize
the pour parameters.
The foundry employed a vacuum-assist casting method
to cast the Inconel 625 air melt alloy with a consistent
wall thickness of 0.1 in. The entire vessel is assembled
by welding three equal segments cast by the foundry.
NITC
Cam clamp used to secure ambulance gurnees.
Material:Stainless steel.
•
Process: Investment casting.
•
The casting design requires intricate angles
and surface profiles—the dimensional
integrity of the profile angles have to be
held to ±0.005 in./linear in. tolerances while
helix and spiracle angles move both
horizontally and vertically.
The foundry redesigned the component to
remove material from the rear casting
section for weight reduction. In addition,
the founry designed in a tapered bore for
mounting a bearing during assembly.
The casting requires slotting at the top and
bottom to align mating components. Holes
at the top and bottom are cast-in and sized
as ready-to-tap.
•
•
NITC
Mounting bracket for medical centrifuge.
Material:CF3M stainless steel.
Process: Investment casting.
•
•
•
This casting provides balanced,
vibration-free support to a centrifuge
that turns at more than 1000 RPM.
Originally designed as a machined
weldment, investment casting
reduced costs by 450% and provided
this precision component with
dimensional repeatability and highstrength qualities.
To date, the customer has received
800 parts without encountering
casting-related defects.
NITC
An ice cutter used in an industrial ice machine.
Material:316 stainless steel.
•
Process: Investment casting.
•
Converted from a stainless steel fabrication
consisting of 4 stampings, bar stack and a
form rolled base, this one-piece casting has
an enhanced overall efficiency and
performance.
The conversion to casting reduced the
customer's annual cost by more than
$100,000, eliminated extensive straightening
operations due to warping in the welding
process, and reduced the component's high
scrap.
The finished cast component is supplied by
the foundry after being completely machined
to print specifications and solution-annealed.
•
•
NITC
Duck bill for White Cap, L.L.C. to seal caps on food jars.
Material:316L stainless steel.
•
Process: Investment casting.
•
Casting Supplier: Northern Precision
Casting Co., Lake Geneva, Wisconsin.
Originally constructed as a three-piece
stamping/weldment, the 3.9-oz, 3.44 x 3.15 x
1.49-in. new casting design offers lighter
weight (29% reduction), a one-piece
construction, increased strength and a
smooth sanitary finish (an important
requirement for the food service industry).
The conversion to casting from a multi-piece
weldment resulted in a 70% cost savings for
the customer.
To accommodate the thin sections of the
component, the foundry designed a unique
gating and tooling system that uses wedge
gates and gating into the top of the
component to ensure against porosity.
•
•
•
NITC
A fan frame hub for General Electric’s CF-6-80C engine
for Boeing’s 747, 767 and MD-11 aircraft.
Material:Titanium.
•
Process: Investment casting.
•
This single 52-in. titanium investment
casting replaced 88 stainless steel parts
(from five vendors) that were
previously machined and welded
together.
The casting, which supports the front
fan section of the engine and ties it to
the compressor section, provides
improved strength and dimensional
control in addition to a 55% weight
reduction.
Conversion to a metal casting allowed
GE to include several unique details
including bosses, flanges and a 2-in.
larger overall diameter.
•
•
NITC
Racing car upright for Minardi Formula 1.
Material:Titanium 6246.
•
Process: Investment casting.
•
Normally manufactured via machining or
welding, four of these one-piece cast
components were manufactured via rapid
prototyping and investment casting from
design to delivery in 8 weeks.
Using rapid prototyping with the
investment casting process eliminated an
up-to-$50,000 tooling cost for these
components.
The cast titanium provided the same
strength—but at a reduced weight—as 174PH steel (the other material considered).
In addition, with no welds required to
manufacture the components, they don’t
require any rework during use.
•
•
NITC
Housing actuator for an engine for Hamilton
Sundstrand.
Material:A203 aluminum alloy.
•
Process: Investment casting.
•
With wall thickness to 0.12 in., this
casting requires moderate strength,
good stability and resistance to stresscorrosion cracking to 600F (316C).
This casting exhibits mechanical
properties at room temperature of
32-ksi tensile strength, 24-ksi yield
strength and 1.5% elongation, while
maintaining a 16-ksi tensile strength
and 4% elongation at 600F.
The component's as-cast surface
finish meets the customer's
requirements, and the invest casting
process reduced the customer's
finishing and machining costs.
•
•
NITC
Spacer component for an aerospace radar system.
Material:17-4PH steel.
• Process: Investment casting.
• Converted from a
weldment, the cast design
reduced component weight
and machining time
required.
• The 1-lb component is cast
near-net-shape with zero
draft and webbed walls.
NITC
A laser chassis (housing) for an Israeli Aircraft
Industries night targeting system.
Material:A357 aluminum alloy.
•
Process: Investment (lost wax) casting.
•
Previously machined from A6061
aluminum wrought alloy, the
component was redesigned for
investment casting at a cost savings of
$25,000/part.
The casting achieves mechanical
properties of 41 ksi tensile strength, 31
ksi yield strength and 3% elongation
in areas up to 2.5 mm thick and 38 ksi
tensile strength, 28 ksi yield strength
and 5% elongation in areas over 2.5
mm thick.
•
NITC
CARBON-DI OXIDE PROCESS
(SILICATE BONDED SAND PROCESS)
• FIRST IN 1950s
• MIXTURE OF SAND AND 1.5% TO 6 %
SODIUM SILICATE (AS BINDER)
• MIXTURE PACKED AROUND THE
PATTERN, HARDENED BY BLOWING CO2
• DEVELOPED FURTHER BY ADDDING
OTHER CHEMICALS AS BINDERS
• MAINLY TO MAKE CORES-AS USE IS IN
ELEVATED TEMPERATURE APPLICATION
NITC
Na2O SiO2 + H2O +CO2
Na2CO3 + (SiO2 +H2O)
(Silica Gel)
Formation of Silica Gel gives strength to the moulds
+ Points:
• Drying not necessary
• Immediately ready for pouring
• Very high strength achieved
• Dimensional accuracy very good
- Points
- Collapsibility poor, can be improved by additives
- Na2O SiO2 attacks and spoils wooden pattern
NITC
Funnel
Mould
CO2
CO2 Moulding
NITC
DESIGN CONSIDERATIONS
CAREFUL CONTROL OF LARGE NUMBER OF
VARIABLES NEEDED•
CHARACTERISTICS OF METALS &
ALLOYS CAST
•
METHOD OF CASTING
•
MOULD AND DIE MATERIALS
•
MOULD DESIGN
•
PROCESS PARAMETERS- POURING,
TEMPERATURE,
•
GATING SYSTEM
•
RATE OF COOLING Etc.Etc.
NITC
• Poor casting practices, lack of control of process
variables- DEFECTIVE CASTINGS
• TO AVOID DEFECTS• Basic economic factors relevant to casting
operations to be studied.
• General guidelines applied for all types of castings
to be studied.
NITC
CORNERS, ANGLES AND SECTION THICKNESS
• Sharp corners, angles, fillets to be avoided
Cause cracking and tearing during solidification
• Fillet radii selection to ensure proper liquid metal flow3mm to 25 mm.
Too large- volume large & rate of cooling less
• Location with largest circle inscribed critical.
Cooling rate less
shrinkage cavities & porosities resultCalled HOT SPOTS
NITC
• LARGE FLAT AREAS TO BE AVOIDED•
•
•
•
•
•
WARPING DUE TO TEMPERATURE GRADIENTS
ALLOWANCES FOR SHRINKAGE TO BE PROVIDED
PARTING LINE TO BE ALONG A FLAT PLANEGOOD AT CORNERS OR EDGES OF CASTING
DRAFT TO BE PROVIDED
PERMISSIBLE TOLERANCES TO BE USED
MACHINING ALLOWANCES TO BE MADE
RESIDUAL STRESSES TO BE AVOIDED
ALL THESE FOR EXPENDABLE MOULD CASTINGS.
NITC
• DESIGN MODIFICATIONS TO AVOID DEFECTS•
•
•
•
•
AVOID SHARP CORNERS
MAINTAIN UNIFORM CROSS SECTIONS
AVOID SHRINKAGE CAVITIES
USE CHILLS TO INCREASE THE RATE OF COOLING
STAGGER INTERSECTING REGIONS FOR
UNIFORM CROSS SECTIONS
• REDESIGN BY MAKING PARTING LINE STRAIGHT
• AVOID THE USE OF CORES, IF POSSIBLE
• MAINTAIN SECTION THICKNESS UNIFORMITY
BY REDESIGNING (in die cast products)
NITC
PROPERTIES AND TYPICAL APPLICATIONS OF
CAST IRONS, NON FERROUS ALLOYS etc.
Tables shall be supplied
NITC
General Cost Characteristics of
Casting Processes
PROCESS
COST
DIE
SAND
SHELL
PLASTER
INVESTMENT
PERMANENT
MOULD
DIE
CENTRIFUGAL
EQUIPMENT
LABOUR
PRODUCTION
RATE (pc/hr)
L
L-M
L
M-H
L-M
L-M
<20
<50
L-M
M-H
M
M
L-M
M
M-H
H
L-M
<10
<1000
<60
H
M
H
H
L-M
L-M
<200
<50
NITC
THIXOTROPIC DIE CASTING
Some of the die-cast joints used in the Insight's aluminum
body are made using a newly developed casting technology
invented by Honda engineers, called Thixotropic Die
Casting.
Thixotropic Die Casting uses aluminum alloy that has been
heated to a semi-solid condition, instead of the molten, liquid
state normally used in die casting.
Pieces made with molten aluminum must be more highly
processed and refined before casting.
NITC
However, Thixotropic Die Casting requires less energy for
smelting (an important consideration since aluminum is more
expensive than steel), and owes much of its strength to the
controlled formation of discrete aluminum crystals within the
metal casting.
Thixotropic casting involves vibratory casting of highly
thixotropic slips of very high solids loadings that are fluid only
under vibration, using porous or nonporous molds.
It is quite different from other conventional and new methods
for solid casting ceramics, including vibroforming,
vibraforming, in situ flocculation, direct coagulation casting,
and gel casting.
This is demonstrated in Table 1.
NITC
Table 1. Thixotropic casting in comparison with the alternatives.
Casting Method and Major Features
Differentiating Properties of Thixotropic
Casting
Vibroforming – Requires a cement for
setting
Cement is not required for setting
Vibraforming – Requires excess counter
ions and centrifugation for settling
Addition of organic deflocculant/binder
and vibration are the only necessary
steps
In situ flocculation – requires the
addition of urea and heating to control
the pH to the isoelectric point
No urea additions, heating, control of
pH, or attainment of the isoelectric point
are required
Only traces (<1%) of binder are needed
and no pressure needed for filling of
moulds
Injection moulding – required large
quantities (15-30wt%) of entraining
polymer and pressurized mould feeding
Direct coagulation casting – requires
control of the pH through an enzyme
catalysed decomposition reaction
No enzyme additions or control of pH
are required
Gel casting – requires use of a
neurotoxin to cause polymeric gelling
No polymer additive or polymerization
are required
NITC
Thixotropic casting is a little-known derivative of solid slip
casting, having reportedly been used in the refractories industry
in the early 1970's.
Since then, the refractories industry has since largely embraced
low-cement and ultra-low-cement castables.
It is also a suitable process for forming ceramic matrix
composites and metal-ceramic functionally gradient materials.
Thixotropic casting involves vibratory casting of highly
thixotropic slips of very high solids loadings that are fluid only
under vibration, using porous or nonporous molds.
It is quite different from other conventional and new methods
for solid casting ceramics, including vibroforming,
vibraforming, in situ flocculation, direct coagulation casting,
and gel casting.
(This is demonstrated in Table 1)
NITC
NITC
NITC
NITC
NITC
NITC
Ejector Pump
The ejector pump is a type
of vacuum pump. Gas is
removed from a container
by passing steam or water
at a high velocity through a
chamber that is connected
to the container. The mixing
chamber contains both the
gas from the container and
the steam or water. At the
inlet port, the ejector pump
is connected to the container
that is being evacuated.
NITC
• Melting
NITC
PLASTER MOULD CASTING
• For casting silver, gold, Al, Mg, Cu, and alloys of brass and
bronze.
• Plaster of Paris (Gypsum) (CaSo4.nH2O) used for cope and drag
moulding
• A Slurry of 100 parts metal casting plaster and 160 parts water
used.
• Plaster added to water and not water to plaster. To prevent cracks,
20-30% talc added to plaster. Lime and cement to control expansion
• Stirred slowly to form cream Poured carefully over a match plate
pattern (of metal)
• Mould vibrated to allow plaster to fill all cavities.
• Initial setting at room temperature(setting time reduced by either
heating or by use of terra-alba/ magnesium oxide)
• Pattern removed
• Cope and drag dried in ovens at 200- 425 C(about 20 hours)
NITC
• Mould sections assembled
+ points
• Dimensional accuracy 0.008 t0 0.01 mm per mm
• Excellent surface finish as no sand used.. No further
machining or grinding
• Non ferrous thin sectioned intricate castings made.
- points
• Limited to non ferrous castings.(sulphur in gypsum
reacts with ferrous metals at high temperatures)
• Very low permeability as metal moulds used. Moulds
not permanent, destroyed when castings removed.
NITC
FROZEN MERCURY MOULDING
(MERCAST PROCESS)
•
•
•
•
•
•
•
•
•
Frozen Mercury used for producing precision castings
Metal mould prepared to the shape with gates and sprue holes
Placed in cold bath and filled with acetone (to act as lubricant)
Mercury poured into it, freezes at –20 C, after a few minutes
(10mins)
Mercury Pattern removed and dipped in cold ceramic slurry
bath.
A shell of 3 mm is built up. Mercury is melted and removed at
room temperature.
Shell dried and heated at high temperature to form hard
permeable shape.
Shell placed in flask- surrounded by sand-, preheated and
filled with metal.
Solidified castings removed.
NITC
• For both ferrous and non ferrous castings.(melting
temperature upto 16500C)
• Very accurate details obtained in intricate shapes
• Excellent surface finish, machining and cleaning
costs minimum.
• Accuracy of 0.002 mm per mm obtained.
• But, casting process costly.
• Casting cost high.
NITC
INSPECTION OF CASTINGS
•
•
•
•
•
SEVERAL METHODS
VISUAL
OPTICAL
- FOR SURFACE DEFECTS
SUBSURFACE AND INTERNAL DEFECTS
THROUGH NDTs & DTs
• PRESSURE TIGHTNESS OF VALVES BY
SEALING THE OPENING AND
PRESSURISING WITH WATER
NITC
CASTING DEFECTS
SURFACE
METALLIC PROJECTION (4)
DEFECTIVE SURFACE (11)
CHANGE IN DIMENSION- WARP
INCOMPLETE CASTING
MISRUN, RUNOUT
CAVITYBLOWHOLES, SHRINKAGE
PINHOLES
DISCONTINUITY
HOT CRACK
COLD SHUT, COLD CRACK
SUBSURFACE
SUBSURFACE CAVITY
INCLUSIONS
DISCONTINUITY
NITC
NDTs
Methods of testing
DestructiveNon destructiveRadiagraphic
Ultrasonic
NITC
Non Destructive Testing
with Ultrasonics
for flaw Detection in Castings,
Weldments, Rails, Forged Components etc.
NITC
ULTRASONIC TESTING
NITC
Why Ultrasonics ?
………
Flaw detection in metals and nonmetals
Flaw measurement in very thick materials
Internal and surface flaws can be detected
Inspection costs are relatively low.
Rapid testing capabilities and portability.
NITC
Ultrasonic waves are simply vibrational waves
having a frequency higher than the hearing range
of the normal human ear, which is typically
considered to be 20,000 cycles per second (Hz).
The upper end of the range is not well defined.
Frequencies higher than 10 GHz have been
generated. However, most practical ultrasonic
flaw detection is accomplished with frequencies
from 200 kHz to 20 MHz, with 50 MHz used in
material property investigations. Ultrasonic
energy can be used in materials and structures
for flaw detection and material property
determinations.
NITC
• Ultrasonic waves are mechanical
waves (in contrast to, for example, light
or x-rays, which are electromagnetic
waves) that consist of oscillations or
vibrations of the atomic or molecular
particles of a substance about the
equilibrium positions of these particles.
Ultrasonic waves behave essentially
the same as audible sound waves. They
can propagate in an elastic medium,
which can be solid, liquid, or gaseous,
but not in a vacuum.
NITC
In solids, the particles can (a) oscillate along the direction of sound
propagation as longitudinal waves, or (b) the oscillations can be
perpendicular to the direction of sound waves as transverse
waves. At surfaces and interfaces, various types of elliptical or
complex vibrations of the particles occur.
NITC
THEORY OF TESTING
NITC
MACHINE SPECIFICATIONS
Make:
Weight:
Calibration range upto 9999 mm.
Choice of Frequency range
Provision for adjusting gain.
Documentation possibility via printer
Limitation:…………….
NITC
Probe
NITC
SCANNING TECHNIQUES
• Pulse Echo method
• Straight beam method
• Angle beam method
NITC
PULSE ECHO METHOD
NITC
Inspection of:
• Gas porosity
• Slag Entrapment
• Cracks
NITC
With the exception of single gas pores all the
defects listed are usually well detectable by
ultrasonics.
Ultrasonic flaw detection has long been the
preferred method for nondestructive testing ,
mainly in welding applications.
This safe, accurate and simple technique has
pushed ultrasonics to the forefront of inspection
technology.
NITC
The proper scanning area for the weld:
First calculate the location of the sound
beam in the test material.
Using the refracted angle, beam index point
and material thickness, the V-path and skip
distance of the sound beam is found.
Then identify the transducer locations on the
surface of the material corresponding to the
crown, sidewall, and root of the weld.
NITC
NITC
NITC
Inspection of Rails
NITC
NITC
• New trend:
Ultrasonic Simulation - UTSIM
UTSIM is a user interface integrating a
CAD model representing a part under
inspection and an ultrasound beam
model.
NITC
NITC
NITC
Ultrasonic sizing of small flaws with
the distance-amplitude-correction (dac) curve
NITC