unit_i-manu tech-i

8/13/2019 unit_i-Manu Tech-I

1/38

UNIT I

CASTING


2/38

CASTING

Casting is a manufacturing process by which aliquid material is usually poured into a mold,which contains a hollow cavity of the desiredshape, and then allowed to solidify. Thesolidified part is also known as a casting


3/38

PROCEDURE TO MAKE SAND MOULD


4/38


5/38


6/38

Types of Core Boxes

half core box dump core box

split core box left and right core box gang core box strickle core box loose piece core box


7/38

Moulding Tools


8/38

1) Vent wire for sticking vent holes through the sand of the mould. (2) Pattern lifter. (3) Joint trowel (4) heart trowel for smoothing and finishing the parting and flat surfaces of the mould. (5) Gate cutter and pattern lifter. (6) Slick and oval spoon for finishing mould surfaces. (7) Sand lifters (8) slicks. (9) Yankee heel lifter and flat slick. (10) Flange and bead slick. (11) Corner slick. (12) Edge slick. (13) Bound corner slick. (14) Pipe slick. (15) Button slick. (16.) Oval Slick. (17) Hand rammer for ramming sand in flasks (not shown). (18) Spirit level for leveling open sand moulds (not shown).


9/38

Ceramic Moulding This process use a method very near to plaster mold

casting. Plaster, plastic, wood, metal or rubber is usedfor making the pattern.

A ceramic slurry comprising zircon, fused silica and abonding agent is first poured over the pattern. Likerubber it hardens quickly. It is then peeled of thepattern and reassembled as a mold. The volatilematerials are removed in a low temperature oven.

Ceramic mold, with high temperature pours is obtainedafter it is baked in a furnace at about 1000 C (1832 F).


10/38

Features of Ceramic Moulding

More accurate in dimension Surface finish is good

Wall thickness is small Weights is less Patterns are Reusable and cheap.


11/38


12/38

Pressure Die Casting Pressure Die casting is the process of forcing

molten metal under high pressure into moldcavities (which are machined into dies). Mostpressure die castings are made from non-ferrousmetals, specifically zinc, copper, aluminium,magnesium, lead, and tin based alloys, althoughferrous metal die castings are possible. The diecasting method is especially suited for

applications where a large quantity of small tomedium sized parts are needed with good detail,a fine surface quality and dimensionalconsistency.


13/38

Pressure Die Casting


14/38

Open Hearth Furnace


15/38

Electric Furnace


16/38

Special Casting Process


17/38

CO2 Moulding

CO2 Moulding Carbon dioxide molding is a sand casting process that employs a molding mixture of sand and liquid

silicate binder. The molding mixture is then hardened by blowing carbon dioxide gas through it. Thismethod offers a great deal of advantages over other forms of sand molding. It reduces productiontime as well as fuel costs and reduces the number of mould boxes required for making moulds. Thisprocess also offers a great deal of accuracy in production.

At VJP, we utilize these various advantages of carbon dioxide casting to the benefit of the customer.By speeding up the casting process and offering economical solutions, we improve the productivityand profitability of our customers' business.

Features High accuracy molding systems incorporating the gas carbon dioxide as a catalyst.

Advantages Provides good dimensional tolerances through strong core and mold Provides excellent casting surface finishes Generally used for high-production runs Accommodates a wide range of core and mold sizes. When used for making cores, the CO2 process can be automated for long durations & speedy

production runs.

Applications Ideal for casting applications where speed and flexibility is paramount.


18/38

Shell Moulding


19/38


20/38

Spruing. The wax copy is sprued with a treelike structure of wax that will eventually provide pathsfor molten casting material to flow and air to escape. The carefully planned spruing usually beginsat the top with a wax "cup," which is attached by wax cylinders to various points on the wax copy.This spruing doesn't have to be hollow, as it will be melted out later in the process.

Slurry. A sprued wax copy is dipped into a slurry of silica, then into a sand-like stucco , or drycrystalline silica of a controlled grain size. The slur ry and g rit combination is called ceramic shellmold material, although it is not literally made of ceramic . This shell is allowed to dry, and theprocess is repeated until at least a half-inch coating covers the entire piece. The bigger the piece,the thicker the shell needs to be. Only the inside of the cup is not coated, and the cup's flat topserves as the base upon which the piec e stands during this process. Prior to silica, a mixture ofplaster and fire-proof material such as chamotte was used.

Burnout. The ceramic shell-coated piece is placed cup-down in a kiln, whose heat hardens thesilica coatings into a shell, and the wax melts and runs out. The melted wax can be recovered andreused, although often it is simply burned up. Now all that remains of the original artwork is thenegative space, formerly occupied by the wax, inside the hardened ceramic shell. The feeder and

vent tubes and cup are also hollow. Testing. The ceramic shell is allowed to cool, then is tested to see if water will flow through the

feeder and vent tubes as necessary. Cracks or leaks can be patched with thick refractory paste. Totest the thickness, holes can be drilled into the shell, then patched.

Pouring. The shell is reheated in the kiln to harden the patches and remove all traces of moisture,then placed cup-upwards into a tub filled with sand. Metal is melted in a crucible in a furnace,then poured carefully into the shell. If the shell were not hot, the temperature difference wouldshatter it. The filled shells are allowed to cool.

Release. The shell is hammered or sand-blasted away, releasing the rough casting. The spruing,which are also faithfully recreated in metal, are cut off, to be reused in another casting. Metal-chasing. Just as the wax copies were chased, the casting is worked until the telltale signs of

the casting process are removed, and the casting now looks like the original model. Pits left by airbubbles in the casting, and the stubs of spruing are filed down and polished.
http://en.wikipedia.org/wiki/Sprue_(molding)http://en.wikipedia.org/wiki/Stuccohttp://en.wikipedia.org/wiki/Ceramichttp://en.wikipedia.org/wiki/Ceramichttp://en.wikipedia.org/wiki/Plasterhttp://en.wikipedia.org/wiki/Grog_(clay)http://en.wikipedia.org/wiki/Plasterhttp://en.wikipedia.org/wiki/Grog_(clay)http://en.wikipedia.org/wiki/Kilnhttp://en.wikipedia.org/wiki/Waterhttp://en.wikipedia.org/wiki/Waterhttp://en.wikipedia.org/wiki/Kilnhttp://en.wikipedia.org/wiki/Grog_(clay)http://en.wikipedia.org/wiki/Plasterhttp://en.wikipedia.org/wiki/Ceramichttp://en.wikipedia.org/wiki/Stuccohttp://en.wikipedia.org/wiki/Sprue_(molding)


21/38


22/38


23/38

Investment Casting Process Investment Casting Process PROCESS BENEFITS OF INVESTMENT CASTINGS (Lost wax) The process is capable of making parts

from prototypes to high volume. Investment Casting tooling is capable of making over 1 millionparts per tool.

Cast tolerance to +/- .005 or better, per inch Cast surface finish of 125 RMS or better Excellent cast details with regards to cast letter i.e. logo, names, part number, etc

Reduced machining due to castings designed to near net shape Investment castings can have undercuts, blind holes, thru holes .250 or greater and, almost any

geometric shape or sizeInvestment Casting. Often called lost wax casting, is regarded as a precision casting process tofabricate near-net shaped metal parts poured from almost any alloy including: stainless steel,aluminum, brass, bronze and copper. Casting by the investment process allows for parts to meet x-ray and non destructive testing specifications for: military, aerospace, semi conductor industry,valves, pumps and many other industrial applications. The investment casting process consistentlyprovides high integrity (sound) and dimensionally accurate castings. Cast part dimensions vary lessthan +-.001 from part to part. Investment casting uses a mold that has been produced bysurrounding an expendable pattern with a refractory slurry that sets at room temperature. Thepattern (usually of wax or plastic) is then melted or burned out, leaving the mold cavity. Investmentcasting is also known as the lost wax process? and as precision casting?


24/38

Process


25/38

Centrifugal Casting


26/38


27/38


28/38

Sand Casting Defects

1. Porosity2. Fins or Flash on Castings3. Inclusion(foreign material/sand) in Castings4. Rough castings

5. Bubbles or Nodules on castings6. Spalling (an area of the mold wall flakes into the mold

cavity)7. Non fill or Incomplete castings

8. Mould shift9. Blow Holes10. Pin Holes11. Shrinkage cavity


29/38

13. Shrinkage cavity14. Hot Tears (Cracks)

15. Cold shut and misrun16. Internal Air Pocket


30/38

POROSITY Pattern is improperly sprued. Sprues may be too thin, too

long or not attached in the proper location, causingshrinkage porosity.

Not enough metal reservoir to eliminate shrinkage porosity.

Metal contains gas. Mold is too hot. Too much moisture in the flux. Too much remelt being used. Always use at least 50% new

metal. Metal is overheated. Poor mold burnout.


31/38

FINS OR FLASH ON CASTINGS Flask was disturbed while investment was setting. Base was removed too soon. Flask was allowed to partially dry before de-waxing. Incorrect de-waxing or a furnace malfunction. Flask burned out and allowed to cool below (500oF (260oC) before casting

reheating, flask allowed to cool between de-wax and placement inpreheated oven. Flask was improperly handled or dropped. Speed was set too high on centrifugal casting machine. Patterns were placed on one plane. The should be staggered on top rack. Incorrect water powder ratio was used. Not enough investment was placed over the patterns. Flask was placed too close to heat source in burnout oven. Flasks were not held at low burnout temperature long enough

INCLUSIONS (FOREIGN PARTICLES) IN


32/38

INCLUSIONS (FOREIGN PARTICLES) INCASTINGS

Patterns were improperly sprued to wax base or tree or not filleted,causing investment to break at sharp corners during casting.

Flask was not sufficiently cured before placing into burnout oven. Improper de-waxing cycle was used. Flask was not cleaned from prior cast. Loose investment in sprue hole. Molten metal contains excess flux or foreign oxides. Crucible disintegrating or poorly fluxed. Improperly dried graphite crucible. Investment was not mixed properly or long enough. Contaminants in wax pattern. Flask was not held at low burnout temperature long enough. Flask was placed too close to heat source in burnout oven.


33/38


34/38

BUBBLES OR NODULES ON CASTINGS

Vacuum pump is leaking air. Vacuum pump has water in the oil. Vacuum pump is low on oil. Investment not mixed properly or long

enough.

Invested flasks were not vibrated duringvacuum cycle. Vacuum extended past working time.

SPALLING (an area of the mold wall


35/38

SPALLING (an area of the mold wallflakes into the mold cavity)

Flask was placed into a furnace at lowtemperature (below 300oF or 150oC) for anextended period.

Flask was placed too close to the source ofheat.

Sharp corners are struck by metal at highcentrifugal velocities.

Improper burnout cycle was used.


36/38

NON-FILL OR INCOMPLETE CASTINGS

Metal was too cold when cast. Mold was too cold when cast. The burnout was not complete. Pattern was improperly sprued, creating

tubulence when csting in a centrifugal castingmachine.

Centrifugal casting machine had too highrevolution per minute.


37/38

POROSITY

FLASH MOULD SHIFT


38/38

SHORT CASTING

INCLUSION

GAS

unit_i-manu tech-i

Documents