Shell and Investment Casting

1. Dr. Jayanta Kr. Mahato
Assistant Professor
Mechanical Engineering Dept.
Shobhit Deemed to-be University

2. Introduction: Shell Casting
 Shell molding, also known as shell-mold casting.
It is an expendable mold casting process that
uses a resin covered sand to form the mold.
It is used for small to medium parts that require
high precision.
Shell mold casting is a metal casting process
similar to sand casting, in that molten metal is
poured into an expendable mold.
In shell mold casting, the mold is a thin-walled
shell created from applying a sand-resin mixture
around a pattern.
Dr. Jayanta Kr. Mahato, Asst. Prof., Mechanical Engineering

3. Introduction: Shell Casting (Contd..)
It requires the use of a metal pattern,
oven, sand-resin mixture, dump box, and
molten metal.
It allows the use of both ferrous and non-
ferrous metals, most commonly using cast
iron, carbon steel, alloy steel, stainless
steel, aluminum alloys, and copper alloys.
Typical parts are small-to-medium in size
and require high accuracy, such as gear
housings, cylinder heads, connecting rods,
and lever arms.
Dr. Jayanta Kr. Mahato, Asst. Prof., Mechanical Engineering

4. Shell Casting Processes
Pattern
creation
Pouring
Cooling
Mold
Assembly
Casting
Removal
Mold
creation
Final
Product
Dr. Jayanta Kr. Mahato, Asst. Prof., Mechanical Engineering

5. Shell Casting Processes
Dr. Jayanta Kr. Mahato, Asst. Prof., Mechanical Engineering

6. 1. Pattern creation: A two-piece metal pattern is created in
the shape of the desired part, typically from iron or steel. Other
materials are sometimes used, such as aluminum for low volume
production .
2. Mold creation: A First, each pattern half is heated to 175 -
370°C (350-700°F) and coated with a lubricant to facilitate
removal.
 Next, the heated pattern is clamped to a dump box, which
contains a mixture of sand and a resin binder.
 Each pattern half and surrounding shell is cured to
completion in an oven and then the shell is ejected from the
pattern.
3. Mold Assembly: The two shell halves are joined together
and securely clamped to form the complete shell mold. If any
cores are required, they are inserted prior to closing the mold.
The shell mold is then placed into a flask and supported by a
backing material.
Dr. Jayanta Kr. Mahato, Asst. Prof., Mechanical Engineering
Shell Casting Processes

7. 4. Pouring: The mold is securely clamped together while
the molten metal is poured from a ladle into the gating
system and fills the mold cavity.
5. Cooling: After the mold has been filled, the molten metal
is allowed to cool and solidify into the shape of the final
casting.
6. Casing Removal: The After the molten metal has
cooled, the mold can be broken and the casting removed.
Trimming and cleaning processes are required to remove
any excess metal from the feed system and any sand from
the mold.
 Examples: Gear housings, cylinder heads and connecting
rods.
 It is also used to make high-precision molding cores.
Dr. Jayanta Kr. Mahato, Asst. Prof., Mechanical Engineering
Shell Casting Processes

8. Shell Casting Processes: Advantages
 Can form complex shapes.
 Very good surface finish.
 High production rate.
 Low labor cost, Low tooling cost.
 Low tooling and equipment cost
 Little scrap generated Can produce very large
parts & Scrap can be recycled
 Short lead time possible
Dr. Jayanta Kr. Mahato, Asst. Prof., Mechanical Engineering

9. Shell Casting Processes: Disadvantages
 High equipment cost Poor material strength
 High porosity possible
 This process is usefull for casting that may rang
in weight from 200gm to as high 200kg in both
ferrous and non ferrous metal
 Another is the resin for the sand is expensive,
however not much is required because only a
shell is being formed.
Dr. Jayanta Kr. Mahato, Asst. Prof., Mechanical Engineering

10. Introduction: Investment Casting
Investment casting process also known as lost wax
process or ceramic shell investment casting.
Wax is coated with refractory material to make a
mould after which the wax is melted away prior to
pouring the molten metal.
Dr. Jayanta Kr. Mahato, Asst. Prof., Mechanical Engineering

11. Investment casting: Processes
Step 1: Wax patterns are produced; with a help of
special steel dies. Wax is injected at 1500F at a
pressure range of 7 – 70 kg/cm2.
Dr. Jayanta Kr. Mahato, Asst. Prof., Mechanical Engineering

12. Investment casting: Processes
Step 2: Several patterns are attached to a sprue to
form a pattern tree.
Dr. Jayanta Kr. Mahato, Asst. Prof., Mechanical Engineering

13. Investment casting: Processes
Step 3: The pattern tree is coated with a thin layer
of ceramic slurry material.
Ceramic
slurry
Fine grained
refractory
powders of
Zircon (ZrSiO4),
Alumina (Al2O3),
Fused Silica
(SiO2) and a
liquid chemical
binder (Alcohol
based Silicon
Ester).
Dr. Jayanta Kr. Mahato, Asst. Prof., Mechanical Engineering

14. Investment casting: Processes
Step 4: The full mould is formed by covering the
coated tree with sufficient thickness.
• To strengthen it is coated with a fine zircon powder.
Step 5: The mould is held in an inverted position and
heated to melt the wax and permit it to drip out of the
cavity.
Dr. Jayanta Kr. Mahato, Asst. Prof., Mechanical Engineering

15. Investment casting: Processes
 Step 6:
Dr. Jayanta Kr. Mahato, Asst. Prof., Mechanical Engineering
The mould is preheated to a high
temperature, which ensures that all contaminants are
eliminated from the mould; it also permits the liquid
metal to flow more easily into the detailed cavity; the
molten metal is poured; it solidifies.

16. Investment casting: Processes
Step 7: The ceramic mold is then broken by vibration
and parts (final products) are separated from sprue.
Dr. Jayanta Kr. Mahato, Asst. Prof., Mechanical Engineering

17.  Complex shape can be made.
 Good surface finish.
 Unmachinable alloys can be cast.
 NO of castings can be made at a
time.
 Can obtain directional solidification
components. (high strength)
Dr. Jayanta Kr. Mahato, Asst. Prof., Mechanical Engineering
Investment casting: Advantages

18.  Only small size is possible.
 More expensive.
 Location of hole is impossible.
Dr. Jayanta Kr. Mahato, Asst. Prof., Mechanical Engineering
 Applications:
 Nozzles, vanes, gas turbines
 Aerospace industry parts
 Scientific instruments
Investment casting process has wide application in industry
Investment casting: Disadvantages

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