METAL CASTING NITC.

METAL CASTING 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 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 READY FOR SHIPMENT 3 1 2 3a 3c 3b 4b 5a 4a 5b 6 8&9 10

CASTING NITC 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
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

Outline of production steps in a typical sand casting operation
- pattern making - Core making - Gating system Moulding Mould Sand Melting Pouring casting Heat Treat Clean Inspect Furnaces Solidification Shakeout Addl. Heat Treatment Defects, pressure tightness, dimensions Outline of production steps in a typical sand casting operation NITC

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. NIT CALICUT NITC

Thin section limitations exist.
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. NIT CALICUT 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 TEMPERATURE TIME, log scale
Cooling of Liquid Latent heat of solidification given off during freezing- At constant temperature Freezing begins Freezing ends Liquid + Solid Cooling of solid Liquid Solid TIME, log scale

Freezing with drop in temperature
COOLING CURVE 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) (refresh dendritic growth- branches of tree, interlock, each dendrite develops uniform composition, etc) For Binary solid solutions TEMPERATURE Freezing with drop in temperature TIME, log scale

* * The ambient temperature is always in a state of transition
Minor variations in volumetric displacement are negligible, compared to the variations that occur from "A" to "B" and lastly to "C". A B 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

Solidified structures of metal - solidified in a square mould
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

LIKE A PRESSURISED SYSTEM
Atm.Pressure Pouring basin MOULD GATE SPRUE 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 b c d e 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

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. 1 3a 2 4a 3b 4b 5

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 * *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 mold-metal 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.

Some dimensioning ratio's from Chastain's Foundry Manual (no.2)
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 "Dead-End" 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 cross-sectional 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 cross-sectional area A2 (.75" by .75", sq") The passage expands to a cross-sectional area A3 (1" by 1", 1 sq"). Q= Rate of Flow (Constant - uncompressible) V=Velocity of flow A=Area (Cross-section) 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 is- Areas 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.

This example would resolve to a pressurized flow of 1 : 0.75 : 0.66
A1= Choke = 1 Sq Inch A2 = 1st Runner c/s Area = 0.75 Sq Inch A3 = 2nd Runner c/s Area = 0.66 Sq Inch A4 = 1st Gate = 0.33 Sq inch A5 = 2nd Gate = 0.33 Sq Inch Areas A2 & A3 do not get added as they are positioned in line with each other and flow is 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 METALS- Have clearly defined melting/freezing point, solidifies at a constant temperature. Eg: Al C, Fe C, and W C. NITC

Solidified structures of metal - solidified in a square mould
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

Alloys solidify over a range of temperatures
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 = 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
(2) CONTRACTION OF SOLIDIFYING METAL, LATENT HEAT OF FUSION (3) CONTRACTION OF SOLIDIFIED METAL DURING DROP TO AMBIENT TEMP 1 2 T 3 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 Grey cast Iron Expansion Carbon Steel to Copper Magnesium Zinc 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 ZONE- CASTING 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

Effect of microporosity on the ductility of quenched and tempered cast steel – Porosity affects the ‘pressure tightness’ of cast pressure vessel Ductility Elongation Reduction of area Porosity(%) 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
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 WOOD. 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

For durability, strength
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 1. SINGLE PIECE PATTERN. NIT CALICUT NITC

2. SPLIT PATTERN (TWO PIECE )
NIT CALICUT NITC

2. a, THREE PIECE SPLIT PATTERN
NIT CALICUT NITC

3. LOOSE PIECE PATTERN NIT CALICUT NITC

4. COPE AND DRAG PATTERN 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. NIT CALICUT NITC

5. MATCH PLATE PATTERN – Pattern generally of metal and plate making parting line metal/wood.
NIT CALICUT NITC

6. FOLLOW BOARD PATTERN. For thin sections.
THIN PATTERN NIT CALICUT NITC

7. GATED PATTERN - Gating system is a part of the pattern.
NIT CALICUT NITC

8. SWEEP PATTERN – For large size castings in small numbers
8. SWEEP PATTERN – For large size castings in small numbers. Template of wood attached to a sweep used. NIT CALICUT NITC

9. SEGMENTAL PATTERN – For rings, wheel rims, large size gears.
NIT CALICUT NITC

10. SKELETON PATTERN. - Stickle board used to scrape the excess sand
10. SKELETON PATTERN.- Stickle board used to scrape the excess sand. Eg. Oil pipes, water pipes, pipe bends, boxes, valve bodies etc. Stickle board NIT CALICUT NITC

11. SHELL PATTERN NIT CALICUT NITC

12. BUILT UP PATTERN – Also called lagged up patterns- For barrels, pipes, columns etc
NIT CALICUT NITC

13. LEFT AND RIGHT PATTERN – For parts to be made in pairs
13. LEFT AND RIGHT PATTERN – 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. NIT CALICUT NITC

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. NIT CALICUT NITC

CHARACTERISTICS OF PATTERN MATERIALS
CHARACTERISTIC RATING WOOD AL STEEL PLASTIC CAST IRON MACHINABILITY E G F G G WEAR RESISTANCE P G E F E STRENGTH E G E G G WEIGHT E G P G P REPAIRABILITY E P G F G RESISTANCE TO: CORROSION (by water) E E P E P SWELLING P E E E 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

bentonite and moisture 0.5 % each
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

about 10% to 15% of whole mould sand
DRY SAND- for moulding large castings. Moulds of green sand dried and baked with venting done. Add- cow 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

PARTING SAND- used for separating boxes from adhering, free from clay
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 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

Refractoriness- Ability of sand to withstand high temperature
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, pouring- Use of conveyors, automated handling, shakeout, cleaning, heat treatment, inspection, etc. NITC

CUPOLA. CHARGE PASSES DOWNWARDS UNDER GRAVITY
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 sections- charging 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

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 long-lasting 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: ductile iron. Process:Sand casting. Casting Supplier: Neenah Foundry Co., Neenah, Wisconsin. Originally manufactured as a stamping and weldment, this 25-lb 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: 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 8-10 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 NITC OR PERMANENT MOULD
COLD CHAMBER HOT CHAMBER (HEATING CHAMBER) OUTSIDE THE MACHINE INTEGRAL WITH THE MACHINE NITC

PERMANENT MOULD OR GRAVITY DIE CASTING
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
- VERY CLOSE TOLERANCE CASTINGS, MORE STRENGTH, LESS POROUS - BETTER SURFACE FINISH COMPARED TO SAND CASTING - SURFACE FREE FROM SAND - DENSITY HEAVY - MORE DIMENSIONAL ACCURACY 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 CHAMBER- HEATING CHAMBER OUTSIDE THE MACHINE - FOR Al, Mg, Cu, AND HIGH MELTING ALLOYS HOT CHAMBER- HEATING 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 POURING- SUBMERGED PLUNGE TYPE, DIRECT AIR DIE CASTING MACHINES NITC

CENTRIFUGAL CASTING TRUE- FOR 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 SURFACE- SHAPE BY MOULD AND CORE,
MAINLY NOT BY CENRTRIFUGAL ACTION- Eg:FLYWHEELS SPEED OF ROTATION- 60 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 ZINC, Al
CAST STEEL WITHOUT HEAT TREATMENT ZINC, Al HEAT TREATED LOW ALLOY STEEL COPPER BASE ALLOYS 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

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 kg 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

· 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

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

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 free-flowing 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 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
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 V-PROCESS 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

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

INVESTMENT CASTING INTRODUCTION
Investment casting, often called lost wax casting, is regarded as a precision casting process to fabricate near-net-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
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
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 computer-aided 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. fig 5 fig 4 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 high-strength qualities. To date, the customer has received 800 parts without encountering casting-related defects. NITC

An ice cutter used in an industrial ice machine
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
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 17-4PH 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
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 stress-corrosion 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

Basic economic factors relevant to casting operations to be studied.
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 flow- 3mm to 25 mm. Too large- volume large & rate of cooling less Location with largest circle inscribed critical. Cooling rate less shrinkage cavities & porosities result- Called 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 PLANE- GOOD 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

Tables shall be supplied
PROPERTIES AND TYPICAL APPLICATIONS OF CAST IRONS, NON FERROUS ALLOYS etc. Tables shall be supplied NITC

General Cost Characteristics of Casting Processes
PRODUCTION RATE (pc/hr) DIE EQUIPMENT LABOUR SAND L L-M <20 SHELL M-H <50 PLASTER M <10 INVESTMENT H <1000 PERMANENT MOULD <60 <200 CENTRIFUGAL 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 Injection moulding – required large quantities (15-30wt%) of entraining polymer and pressurized mould feeding Only traces (<1%) of binder are needed and no pressure needed for filling of moulds 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

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 C(about 20 hours) Mould sections assembled NITC

+ points - 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

Very accurate details obtained in intricate shapes
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 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

METALLIC PROJECTION (4)
CASTING DEFECTS SURFACE METALLIC PROJECTION (4) DEFECTIVE SURFACE (11) CHANGE IN DIMENSION- WARP INCOMPLETE CASTING MISRUN, RUNOUT CAVITY- BLOWHOLES, SHRINKAGE PINHOLES DISCONTINUITY HOT CRACK COLD SHUT, COLD CRACK SUBSURFACE SUBSURFACE CAVITY INCLUSIONS DISCONTINUITY NITC

NDTs Methods of testing Destructive- Non destructive- Radiagraphic
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

Inspection of Rails 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

Ultrasonic sizing of small flaws with
the distance-amplitude-correction (dac) curve NITC

METAL CASTING NITC.

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