fundamentals of manufacturing processes-casting technology
TRANSCRIPT
Course Material on
Fundamentals of Manufacturing Processes
Faculty: Dr. B.Venkateshwarlu, Associate Professor,
School of Mechanical Engineering
VIT University, Vellore
Fundamentals of Manufacturing Processes (MEE 205)
MEE 205
Terminology:
Cast Product is also called as “ CASTING”
https://www.youtube.com/watch?v=l638qR0Y6YE
Step1: Preparation of Drag Box
Sprinkle dry facing Sand after placing the pattern
Step2: Preparation of Cope Box
Lecture 4
Fluidity: The physical property of a substance that enables it to flow.
Moulding Sand Composition
Ingredients of Moulding Sand:
• Silica grains (SiO2)
• Clay (as binder)
• Moisture (to activate clay and provide plasticity)
Refractory: Resistance to heat
Ex: Silica is a very good refractory material (1,713 °C)
It is the ability of the moulding material to resist the temperature of the liquid metal to be poured so that it does not get fused with the metal. The refractoriness of the Silica sand is highest.
Permeability tells us how well the generated gases can pass through the moulding sand
The moulding sand must be sufficiently porous to allow the dissolved gases, which are evolved when the metal freezes or moisture present or generated within the moulds to be removed freely when the moulds are poured. This property of sand is called porosity or permeability.
It is the important property of the moulding sand and it is defined as the sand particles must be capable of adhering to another body, then only the sand should be easily attach itself with the sides of the moulding box and give easy of lifting and turning the box when filled with the sand.
Green strength is the strength of sand in the wet state and is required for making possible to prepare and handle the mould.
• If the metal is poured into a green mould the sand adjacent to the metal dries and in the dry state it should have strength to resist erosion and the pressure of metal.
• The strength of the sand that has been dried is called dry strength
At the time of pouring the molten metal the mould must be able to withstand flow and pressure of the metal at high temperature otherwise the mould may enlarge, crack, get washed or break
Hot Strength
The sand adjacent to the metal is suddenly heated and undergoes expansion. If the mould wall is not dimensionally stable under rapid heating, cracks, buckling and flacking off sand may occur.
Thermal stability
3-D View
Ferrous (Cast Iron, steel)or non-ferrous like aluminium
Thermosetting resin binder
2.5-4.0%
175-370 0C
Coated with a heat resistant lubricant (Silicone) to facilitate removal
The heated pattern partially cures the mixture
Curing of shell for 1 - 3 min at 250 0C – 450 0C
(Backing material)
Figure: Shell Moulding Process
Figure: Shell Moulding Process
Advantages :
-High precision and accurate castings with smooth surface finish can be produced economically.
-complex parts having intricate shapes, and cleaning of casting is reduced or completely eliminated.
-size of casting is 10 - 13.5 kg and minimum wall thickness 2 - 2.5mm is possible.
Examples: Brake drum, bushing, cam/cam shaft, piston, piston rings, pinions, pipe bends, air compressor crank cases, etc.,
https://www.youtube.com/watch?v=Xar5r9Jm04g
https://www.youtube.com/watch?v=UrUsaGussfc
Animated Movie of Investment Casting Process
WAX or Plastic (polystyrene)
Binder: Water, Ethyl Silicate, etc.
WAX drains off
Temperature of 90-175 0C
Temperature of 650-1050 0C
Ex: Aluminium, Magnesium, Zinc and copper based alloys
Patterns also can be made of aluminium alloys, thermosetting plastics, Zinc alloys, etc.
Plaster of Paris + Water + Silica flour
Temperature of 120-2600C
Gears, Valves, Fittings, tools and Ornaments, etc.
(ZrSiO4)
(Al2O3)
Die Casting Process
Hot Chamber Die Casting process
Cold Chamber Die Casting Process
Centrifugal Casting Process
Rotational speed: 1000 rpm (250-3600 rpm)
• Core may or may not be used
• Mostly used for making hollow objects like pipes, tubes and bushes
The forces generated by the rotation of the mould ensure the distribution of molten material to all the regions of the casting
Semi centrifugal casting manufacture is a variation of true centrifugal casting and uses vertical axis with less rotational speeds.
The main difference is that in semi centrifugal casting the mold is filled completely with molten metal, which is supplied to the casting through a central sprue.
Castings manufactured by this process will possess rotational symmetry.
If a central bore is required in the casting, a dry sand core is best suited.