foundry ppt by vijayreddy.ravipati

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									METAL CASTING



                 By
           Anil Kumar S
        Assistant professor
       Mechanical department
History of casting :-
• Casting methods are adopted
  from 5000BC

• For knifes, tools, coins for non ferrous
  metals like bronze and copper

• Iron had been discovered and developed
  in the period around 2000BC
 Casting :-
• Material is heated to molten state in
  furnace

• Molten metal poured in a mould cavity
  (required shape)

• Product is taken out from mould cavity,
  trimmed and cleaned
   Some of the components
manufactured by different casting
           methods
Iron ore before converting into raw
              material
Furnace :-
• Device used for melting the material

• Iron obtained in the smelting furnaces

• First cast into ingots

• Re-melted in foundry for casting the
  required objects
Resources into raw materials :-
 For successful casting :-
• Preparation of mould

• Melting & pouring

• Solidification

• Defects & inspection
Pattern :-
• Pattern is the replica of the part to be cast

• Quality of the pattern is very important

• Either wood or metal
    Wooden pattern :-
•    Easily shaped
•    Joined to form any complex shape
•    Light in weight
•    Easily available
•    Cost is less
•    Suitable for small production only
Wooden pattern & casting :-
Wooden pattern & casting :-
Metal pattern :-
• Suitable for large production

• Prepared by casting from master pattern

• Double allowances have to made for
  contraction & machining
Pattern allowances :-
• Pattern allowance is vital feature in a pattern
  design.

Some of the allowances

•   Contraction allowance
•   Machining allowance
•   Draft allowance
•   Rapping and shake allowance
Single & split pattern
Moulding:-
• A mould is a primary cavity formed by one
  or more metal blocks, or a bonded
  refractory particles (sand) consisting of a
  primary cavity.

• It holds the liquid material and essentially
  act as a negative of the desired product
Mould cavities :-
Mould made in stone :-
Master mould with casting
 Types of casting process :-

• Sand mould casting process

• Shell-mould casting process

• Investment casting process

• Die casting (metal mould)
Moulding sand :-
• Principal moulding material material in the
  foundry shop

• It is used for all types of casting

• It posses important characteristics like
    1) refractoriness 2) chemical resistivity
               3) permeability
•   Principle ingredients of the moulding
    sand are

1) Silica sand grain

2) Clay

3) Moisture
Sand mould casting :-

 • Widely used process

 • Expendable mould

 • Process involves the use of furnace, raw
   material, pattern, moulding sand, cope &
   drag, tools for making mould
Equipment required for preparing the mould in sand casting :-
Process cycle for sand casting process :-


•   Mould making
•   Clamping
•   Pouring
•   Cooling
•   Removal
•   Trimming
Rammer
    Advantages
•   It can produce very large parts
•   Many material options
•   Scrap can be recycled
•   Low tooling & equipment cost
Limitations
•   Poor mould strength
•   Poor surface finish
•   Low production rate
•   High labour cost
•   Secondary machine is often required
             Applications
• Engine blocks, gears, pulleys, machine
  basis, & manifolds
Sand casting
Mould cavity with core and sprue
Shell mould casting :-
• This process uses organic binders like epoxy
  resin, phenolic resin.

• For production of high quality castings from
  small to medium size.

• Inspite of high involved, use in mould making.

• Because they produce superior quality of casting
• In this process mould material is a mixture
  of phenolic resin & fine sand.

• This process uses patterns of gray iron,
  aluminum, brass.

• First pattern is heated to 230oC -260oC.

• Then sand mixture is dumped over its
  surface.
Six stages involved in this process :-

•   Pattern creation
•   Mould creation
•   Mould assembly
•   Pouring
•   Cooling
•   Casting removal
Shell mould casting process
   Advantages :-
• Smoothness of the mould wall independent of
  the moulder’s skill.

• Good accuracy of dimensions & surface finish
  can be achieved.

• Process can used for all cast materials

• High rate of production is suitable with limited
  floor space.

• In most cases machining operation is required.
Limitations :-
• Cost of metal pattern is high.

• Cost of resin is high.

• Many equipment and control facilities are
  needed.

• Casting size and weight are limited.
Applications :-
• It is used for making fine castings of
  ferrous and non ferrous metals.
  Cylinder header, connecting rods
Investment casting process :-
• It produces excellent surface finish

• Molten metal is poured into the expendable
  mould.

• Suitable for wide range of shapes and
  contours.

• Here mould is made in a single piece.
• Mould is formed by a wax pattern
  (disposable piece )

• Pattern prepared by
  injecting a wax into a metal die which is
  given the shape of the pattern.

• If pattern is small in size
  several such patterns can be joined to the
  common wax sprue and ingates.
This process includes six stages :-

• Pattern creation

• Mould creation

• Pouring

• Cooling

• Casting removal

• Finishing
Injection moulding machine :-
    Advantages :-
•   Can form complex shapes
•   High strength parts
•   Very good surface finish & accuracy
•   Many material options
•   Little need for secondary machining
Limitations :-
• Time consuming process
• High labor cast
• High tooling cost
Applications :-
 • Turbine blades, armament parts, pipe
   fittings, lock parts, hand tools.
Metal mould casting :-
• Moulds are metallic are of permanent nature

• Superior surface characteristics than sand
  moulds

• Produce castings with close tolerances and with
  good surface finish

• Metal moulds have been remarkably
  mechanised

• High rate of production
• Metallic moulds are called dies

• Dies are usually pair

• Both halves are placed together to form
  cavity

• Equipped with mechanism for feeding the
  molten metal

• Equipped with mechanism for clamping &
  ejection
• Dies are provided with a generous taper
  allowance to facilitate extraction.

• Allowance for thermal expansion of the
  dies in addition to the usual contraction
  allowance.

• Taper allowance to facilitate extraction.

• Reducing the cycle time the dies may be
  air cooled or even water cooled.
Types of metal moulding process are :-

• Pressure die casting

• Centrifugal casting

• Continuous casting
Pressure die casting :-

• Fastest means of producing castings with
  high accuracy

• It can produce geometrically complex
  parts with reusable moulds

• Process involves the use of furnace, die
  casting machine, & metal die.
• Forcing the molten metal under high
  pressure into a mould.

• Die resembles the permanent mould

• Stationary die half called cover die

• The die which opens and close known as
  ejector die.
Process consist five stages :-
•   Clamping
•   Injection
•   Cooling
•   Ejection
•   Trimming
Clamping :-
• Clamping of two halves of the die by moving the
  ejector die.

• Each die half is cleaned & lubricated to facilitate
  the ejection of the next part.

• After lubrication , the two die halves are closed
  firmly together.

• So they do not separate due to the pressure of
  the molten metal injected.
Injection :-
 • Molten metal is at set temperature in the
   furnace.

 • Next it is transferred to the chamber, where it
   can be injected into the die.

 • Injected at high pressure (1000 psi to 2000 psi)

 • Amount of metal injected into the die is referred
   as “ shot”
Cooling :-
• Molten metal which is injected begins to cool &
  solidify once it enters the cavity.

• Die cannot be opened until the cooling time
  elapsed.

• Greater wall thickness require longer time.

• Cooling time also depend on the geometric
  complexity of the die.
Ejection :-
• After the predetermined time the die halves can
  be opened.

• An ejection mechanism can push the casting out
  of the die cavity.

• Must apply some force to eject the part.

• Because during cooling the part shrinks &
  adheres to the die.
Trimming :-
• During cooling the material in the channels will
  solidify attached to the casting.

• Excess material must be trimmed from the
  casting either manually via cutting or sawing.

• Scrap material can be reused
Hot chamber die casting machine :-
Hot chamber die casting machine :-
Cold chamber die casting machine :-
Cold chamber die casting machine :-
Die casting
Advantages :-

•   High production rate
•   Can form complex parts
•   Can produce large parts
•   Very good surface finish & accuracy
•   Low labour cost
 Disadvantages :-

• Trimming is required
• High tooling & equipment


Applications :-
• Engine components, pump components,

								
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