MANUFACTURING PROCESS – 01(CASTING)

BY SHIRAZ DEEP GUMBER

Introduction Manufacturing processes are the steps through

which raw materials are transformed into a final product. The  manufacturing process begins with the creation of the materials from which the design is made. These materials are then modified through manufacturing processes to become the required part.

There are four basis production process for producing desired shape of a product . These are

Casting MachiningJoining ( welding , mechanical fasteners etc)Deformation

Contents (Chapter -1)IntroductionDefinitionPattern Pattern Materials Types of PatternAllowances & its typesCore Prints & Core Boxes

Contents (Chapter -2)Types of Sand Its Main ConstituentsMoulding ProcessGating System Types of GatesSolidificationRisers & its TypesCores & its Types

ChapletsDefects in Casting

CASTING Casting is a manufacturing process by

which a liquid material is usually poured into a mould, which contains a hollow cavity of the desired shape, and then allowed to solidify. The solidified part is also known as a casting, which is ejected or broken out of the mould to complete the process.

Casting Methods

• Sand CastingHigh Temperature Alloy, Complex Geometry, Rough Surface Finish

• Investment CastingHigh Temperature Alloy, Complex Geometry, Moderately Smooth Surface Finish

• Die CastingHigh Temperature Alloy, Moderate Geometry, Smooth Surface

(c) Parting line - how to determine

(a)How do we make the pattern

[cut, carve, Machine]

Sand Casting Considerations..

(b) Why is the pattern not exactly identical to the part shape ?

-pattern outer surfaces; (inner surfaces: core)-shrinkage, post processing

Sand Casting Considerations..

(d) taper

- do we need it ?

Mold cavity

chaplet

Mold cavity

chaplet

(e) core prints, chaplets

- hold the core in position - chaplet is metal (why?)

(f) cut-off, finishing

Casting process can be divided into two basic categories:-

• 1. Those for which a new mould must be created for casting (the expandable-mould processes)

2. Those that employ a permanent , reusable mould ( the non-expandable-mould processes)

PATTERN :- A pattern is a replica of the object to be cast , used to prepare the cavity into which molten material is to poured during the casting process.Pattern used in the sand casting may be made up of wood ,metals , plastics or other materials

An exact copy or model

Functions of pattern

Types of PatternSingle piece pattern

Two piece Pattern Multi- piece Pattern

Match Plate PatternGated Pattern

Skeleton Pattern

Cope & Drag Pattern

Pattern with Loose Pieces

Segmental Pattern

Sweep PatternFollow Board Pattern

Types Of Pattern ….

2. Split or two Piece Pattern is most widely used pattern for intricate casting ,it is split along the parting surface into two parts.

1.One Piece or solid pattern is the simplest pattern and is made up of a one piece. It carries no joint, partition or loose pieces (used when job is simple).

3. Multi- piece Pattern is made up of more then two parts in order to facilitate an easy moulding and withdrawal of the pattern.

4. Match plate pattern are used where rapid production of small and accurate casting is desired on a large scale(construction cost is very high, but it is compensated by high rate of production ).

5. Gated pattern is used in mass production of small castings. For such multi cavity moulds are prepared (For small quantities wood is preferred and for large one metal is preferred).6. Skeleton Pattern is used when size of casting is very large, but easy to shape and only a few numbers are to be made (it is economical to make a large pattern of that size).

7.Cope and drag pattern is used when very large casting are to be made, the complete pattern become too heavy to be handled by a single operator(then two parts cope and drag).

8. Pattern with loose pieces is made to have loose species in order to enable their easy withdrawal for the mould (such pieces form an integral part of the pattern during moulding ).

9. Sweep Pattern can be used for preparing moulds of large symmetrical castings, particularly of circular cross section ( such effects saves time labor and material ).

10. Follow Board Pattern is a wooden board used to support a pattern during moulding ,it acts as seat for the pattern(pattern which have odd shape and very thin walled requires a follow board ).

11. Segmental pattern are used for preparing mould of large circular castings ,they work like a sweep but the difference is a sweep is given a continuous revolving motion to have a desired shape(mould is prepared by the parts of itself).

Watch video of pattern types

Allowances Shrinkage allowanceMachining allowanceDraft allowanceRapping or shake allowanceDistortion allowance

Dimension of pattern is larger than the casting produced. The extra dimension provided in the pattern is called pattern allowance.

Video watch for pattern allowances

Core & Core Prints A core is a device used in casting and

moulding processes to produce internal cavities and reentrant angles.

It is normally a disposable item that is destroyed to get it out of the piece.

The Core print is an added projection on the pattern and it forms a seat in the mould on which the sand core rests during pouring of the mould.

The core print must of the adequate shape and the size so that it can support the weight of the core during the casting operation.

Types of core… Horizontal coreVertical core

Balanced core

Hanging core

Wire core

Common type of core with its axis horizontal

axis being vertical

Core balanced in two parts

Core hangs in vertical position without any support provided from bottom.When a hole is made at such position where axis fall either above or below parting line

Types of Core PrintsHorizontal core Print

Vertical core Print

Balanced core Print

(It produces seats for horizontal core in the mould)

(It produces seats to support a vertical core in the mould )

(It produces single seat on one side of the mould and balances in the mould cavity)

Types of Moulding SandGreen SandDry Sand

Facing SandBacking SandSystem SandParting SandCore Sand

It is called green sand because of its water content. Its color is black. It is wet sand used for moulding and contains 20-30% clay and 8% water by part.If we dry the green sand mentioned above, then we get dry sand the physical composition remains same exact for the water content. This sand comes in contact with direct contact of molten metal. The basic composition is silica sand and clay.We can use old and repeatedly used sand for this purpose for purpose to support the mould.This sand is used in mechanical foundries where moulding is done with the help of machines

This is used so that green sand should not stick to pattern.This is also called oil sand. we can make this sand if we mix the normal silica sand with linseed oil etc. it is used to form the core

Types of moulding sand…

Green sand

Dry sand

Facing sand

Backing sand

Risers A riser is a passage made in the cope through which the molten metal rises after the mould is filled up.

Types of risers1. Blind riser2. Open riser

Blind riser is round cavity formed either on the top side of the casting and surrounded from all sides by the moulding sand,Open riser has top surface exposed to atmosphere and commonly employed on the topmost portion of the casting.

Chaplets Types of chaplets

•Chaplets are metal spacers used for supporting large and odd shaped cores which cannot be adequately supported by their own core prints.

•They are placed in a mould between mould face and core.

Stem chapletPipe chapletDoubled headed chapletRadiator chapletPerforated chaplet

Types of chaplets…….

Its use…

Pattern MaterialsWood is most common material used for pattern making…• cheap and available in abundance.• available in different forms and intricate designs.• Manipulation is easy.• lightness in weightMetals …(longer life than wooden patterns)• used when number of castings made is very high.• closer dimensional accuracy is required.• tendency to get rust.• heavy in weightPlastics..• lightness in weight.• high strength• fine surface finish• very reasonable cost

Gating systemThe term gating system involves the passages through which the molten metal enters the mould cavity. It includes risers, gates, pouring basin, runner etc.

Types of gates1.Parting line gates

2.Top gates3.Bottom gates4.Side gates

Chills…•A chill is an object used to promote solidification in a specific portion of a metal casting mould. Types of chills

1. Internal chills2. External chills

Internal chills are placed with in the mould cavity and they are usually in form of wiresExternal chills are embedded in the mould such that they are flush with the mould walls and form a part of it.

Casting defects During casting process several undesired irregularities creep into the final casting product. These irregularities are known as casting defects.

...Thanks