FULL MOULD CASTING

Presented by:

PRADEEP KUMAR.T.P.III Sem. M.Tech (PT) in ME

CASTING PROCESS

IntroductionCasting is one of the most versatile form of

mechanical processes for producing components.

It offers one of the cheapest methods and gives high strength and rigidity even to intricate parts.

Principle of casting consists of introducing the molten metal into a cavity or mould of the desired shape and allowing it to solidify.

Casting is the cheapest and most direct way of producing a shape with certain desired mechanical properties.

Casting is best suited where components are desired in low quantities.

Certain metals and alloys can't be worked mechanically and can be cast only.

Intricate shapes can be produced cheaply and quickly by casting.

Full-mould casting

Full mould casting process is also known as Lost Foam Process/ Evaporative Pattern Casting Process.

The full mold process was originally known as the lost foam process.

However, current patents have required that the generic term for the process be full mould.

Full-mould castingFull-mould casting is an evaporative-pattern casting

process which is a combination of sand casting and lost-foam casting.

It is used to make primarily large, one-of-a kind castings.

It uses an expanded polystyrene foam pattern which is then surrounded by sand, much like sand casting.

The metal is then poured directly into the mould, which vaporizes the foam upon contact.

In full mold casting, thermally decomposable materials like polystyrene is used for making pattern instead of wood or wax.

The process is similar to lost wax process, here the foam disappears when the molten metal is poured into the mold, therefore the process in expendable.

The polystyrene pattern can be designed with the aid of a computer, that helps in making alteration to the design before the actual process is done.

The ProcessFirst, a pattern is made from polystyrene foam, which

can be done in many different ways.

For small volume runs, the pattern can be hand cut or machined from a solid block of foam.

If the geometry is simple enough, it can even be cut using a hot-wire foam cutter.

If the volume is large, then the pattern can be mass-produced by a process similar to injection moulding.

Pre-expanded beads of polystyrene are injected into a preheated aluminium mould at low pressure.

Steam is then applied to the polystyrene which causes it to expand more to fill the die.

The final pattern is approximately 97.5% air and 2.5% polystyrene.

Once the pattern is made pre-made pouring basins, runners, and risers can be hot glued to form the final pattern.

The EPC procedure starts with the pre-expansion of beads, usually polystyrene. After the pre-expanded beads are stabilized, they are blown into a mold to form pattern sections. When the beads are in the mold, a steam cycle causes them to fully expand and fuse together.

The pattern sections are assembled with glue, forming a cluster.  The gating system is also attached in a similar manner.

The foam cluster is covered with a ceramic coating.  The coating forms a barrier so that the molten metal does not penetrate or cause sand erosion during pouring. 

After the coating dries, the cluster is placed into a flask and backed up with bonded sand.

Mold compaction is then achieved by using a vibration table to ensure uniform and proper compaction.  Once this procedure is complete, the cluster is packed in the flask and the mold is ready to be poured .

Finally, the molten metal is poured into the mold, which vaporizes the foam allowing the metal to fill the entire mold.

The casting is allowed to cool and then dumped out of the flask ready to use.

The sand does not need to be reprocessed so it can be directly reused.

The EPC process is an economical method for producing complex, close-tolerance castings using an expandable polystyrene pattern and unbonded sand.

Expandable polystyrene is a thermoplastic material that can be molded into a variety of complex, rigid shapes.

The EPC process involves attaching expandable polystyrene patterns to an expandable polystyrene gating system and applying a refractory coating to the entire assembly.

After the coating has dried, the foam pattern assembly is positioned on loose dry sand in a vented flask.

Additional sand is then added while the flask is vibrated until the pattern assembly is completely embedded in sand.

Molten metal is poured into the sprue, vaporizing the foam polystyrene, perfectly reproducing the pattern.

The minimum wall thickness for a full-mold casting is 2.5 mm (0.10 in).

Typical dimensional tolerances are 0.3% and typical surface finishes are from 2.5 to 25 µm (100 to 1000 µin) RMS.

The size range is from 400 g (0.88 lb) to several tonnes.

Full-mold casting is often used to produce Cylinder heads, Engine blocks, Pump housings, Automotive brake components and Manifolds.

Commonly employed materials include Aluminium, iron, steel, nickel alloys and copper alloys.

Advantages and disadvantages

This process is advantageous for complex castings that is usually done using cores and drafts

It is also dimensionally accurate, requires no draft, and has no parting lines so no flash is formed.

As compared to investment casting, it is cheaper because it is a simpler process and the foam is cheaper than the wax.

Risers are not usually required due to the nature of the process; because the molten metal vaporizes the foam.

The first metal into the mold cools more quickly than the rest, which results in natural directional solidification.

It is an effective method for both small and large mould production

A time saving and cost saving method, since the pattern need not be shaped as in wood patterns

Patterns are not be stored unlike other casting techniques where metal, wood and plaster pattern are kept for future use.

Pattern correction can be easily done in the computer before the actual casting process begins

Casting weight is reduced

No draft allowance is required since foam is used

Simpler process and the foam is cheaper than wax.

The two main disadvantages are: Pattern costs can be high for low volume

applications and the patterns are easily damaged or distorted due to their low strength.

If a die is used to create the patterns, there is a large initial cost.

History

The The use of foam patterns for metal casting was patented by H.F. Shroyer on April 15, 1958.

In Shroyer's patent, a pattern was machined from a block of expanded polystyrene (EPS) and supported by bonded sand during pouring.

In 1964, M.C. Flemmings used unbounded sand with the process. This is known today as lost foam casting (LFC).

With LFC, the foam pattern is molded from polystyrene beads.

LFC is differentiated from full mold by the use of unbounded sand (LFC) as opposed to bonded sand (full mold process).

Foam casting techniques have Foam casting techniques have been referred to by a variety of been referred to by a variety of generic and proprietary names. generic and proprietary names.

Among these are: lost foam casting,

evaporative pattern casting,

cavity less casting,

evaporative foam casting, and

full mold casting.

ReferencesReferences(1) nptel.iitm.ac.in/courses/Web-course

contents/IIT-ROORKEE/MANUFACTURING- PROCESS/metalcasting.

(2) en.wikipedia.org

(3) R K Jain: “Production Technology”, Khanna Publishers, New Delhi.

(4) Richard W Heine, Carl R Loper, Philip C Rosenthal, “Principles of Metal Casting”, TMH, New Delhi.