1. CHAPTER 3 :
METAL WORKS, CASTING
PROCESS AND HEAT
TREATMENT ON STEEL

2. COLD WORK

3. INTRODUCTION OF COLD
WORK
• Definition : Cold work is a process of plastic deformation
which carried out below recrystallization temperature at room
temperature.
• Grains become deformed and elongated.

4. COLD WORK PROCESS
ROLLING
WIRE AND
TUBE
DRAWING

5. ROLLING
• Definition :
- Process of reducing the thickness (or changing the cross-
section) of a long workpiece by compressive forces applied
through a set of rolls and carried out at room temperature.
• Produce :
- Plates, Sheets and Foils.
• Advantages :
- Better surface finish.
- Good dimensional accuracy.
- Increase tensile strength and toughness.

6. • Diagram :

7. WIRE AND TUBE DRAWING
• Definition :
- Process of reducing or changing the shape/cross section of a
round rod or wire by pulling it through a die.
• Produce :
- Wire, rod and tube.
• Advantages :
- Good surface quality.
- Good dimensional accuracy.

8. • Diagram :

9. ADVANTAGES AND DISADVANTAGES OF
COLD WORK
Advantages Disadvantages
1. Better 1. High cost
surface finish.
2. Has to be
2. Good annealed to
dimensional remove
accuracy brittleness.

10. HOT WORK

11. INTRODUCTION OF HOT
WORK
• Definition : Hot work is a process of plastic deformation which
carried out above recrystallization temperature.
• Grain recrystallization.

12. GRAIN RECRYSTALLIZATION
• Process by which deformed grains are replaced by a new set
of undeformed grains that nucleate and grow until the original
grains have been entirely consumed.

13. TYPES OF HOT WORK
FORGING
HOT ROLLING
EXTRUSION

14. FORGING
• Definition :
- Process which the workpiece is shaped by compressive
forces applied through various dies and tools.
• Produce :
Discrete parts
• Advantages :
- Good strength and toughness.

15. • Diagram :

16. HOT ROLLING
• Definition :
- Process of reducing the thickness (or changing the cross-
section) of a long workpiece by compressive forces applied
through a set of rolls and carried out above recrystallization
temperature.
• Produce :
- Wire, rod and tube.
• Advantages :

17. • Diagram :

18. EXTRUSION
• Definition :
- Process when hot billet is forced through an opening die by
hydraulic force.
• Types :
- Direct/Forward : billet forced by ram through die.
- Indirect/Inverted : die moves toward the billet.
• Produce :
- Cylindrical bars or hollow tubes.
• Advantages :
- Able to produce complex shape.
- Have high dimensional accuracy.
- Have a good surface finish.

19. • Diagram :

20. ADVANTAGES AND DISADVANTAGES OF
HOT WORK
Advantages Disadvantages
Porosity of
Poor surface
the metal is
finish
minimised
Increase in Less precise
ductility tolerances

21. CASTING

22. INTRODUCTION
• Definition of Casting :
Is a process of pouring molten metal into a mould, allowing it
to cool and removing the metal from the mould after solidify.

23. CASTING PROCESS
1. SAND
2. LOST
CASTING
WAX/INVESTMENT
CASTING
3. PRESSURE
DIE CASTING

24. SAND CASTING
• Is a method of casting metals in sand mould.
• Consist of :
1. Filling the 2. Allowing the
resulting cavity with molten metal to
molten metal. solidify.
4. Removing the 3. Breaking away
casting. the sand mould.

25. SAND CASTING MOULD

26. • Flask :
- A mould frame which consists of two parts:
Cope (the upper part)
Drag (the lower part).

27. • Gating System :
- Channels which a molten metal flows through to the mould
cavity.
- Consists of :
i) Pouring cup – which the molten metal is poured.
ii) Sprue – which the molten metal flows downward.

28. iii) Runner – a channel which the melt is supplied to the gates.
iv) Gates – inlets to the mould cavity.
v) Riser – which supply additional metal to the casting as it
shrinks during solidification.

29. • Vent :
Remove air within the mould cavity and gases formed when a
molten metal contacts the mould surface.
• Cores :
A separate insert made from sand which are placed in the
mould to form the interior surface of casting.

30. SANDS FACTORS
Properties Factors
Casting surface Fine and round grain sand which can
finish be closely packed
Gas permeability Fine grain sands allow gases and steam
evolved during casting to escape
easily.
Mould strength Fine grain sands.
Collapsibility Allow for the casting to shrink while
cooling in order to avoid defects in the
casting.

31. TYPES OF SAND MOULD
• Sand moulds are characterized by ;
- The types of sand that comprise
- The methods used to produce
• 3 Types of sand:
Green sand - The green sand is prepared from silica sand,
water and a certain quantity of a clay (bentonite, kaolin).
Resin bonded sand - a mixture of silica sand with a polymeric
resin as the bonding agent.
Sodium silicate bonded sand - a mixture of silica sand with 3-
4% of sodium silicate.

32. PROCESS OF SAND CASTING
• Mould-making
- A sand mould is formed by packing sand into each half of the
mould.
- The sand is packed around the pattern, which is a replica of
the external shape of the casting.
- When the pattern is removed, the cavity that will form the
casting remains.

33. • Clamping
- The surface of the mould cavity is first lubricated to facilitate
the removal of the casting.
- Then, the cores are positioned and the mould halves are
closed and securely clamped together.

34. • Pouring
- The molten metal is ladled from its holding container in the
furnace and poured into the mould.
- Enough molten metal must be poured to fill the entire cavity
and all channels in the mould.

35. • Cooling
- The molten metal that is poured into the mould will begin to
cool and solidify once it enters the cavity.
- When the entire cavity is filled and the molten metal
solidifies, the final shape of the casting is formed.

36. • Removal
- After the predetermined solidification time has passed, the
sand mould can simply be broken, and the casting removed.
- This step, sometimes called shakeout, is typically performed
by a vibrating machine that shakes the sand and casting out of
the flask.

37. • Trimming
- During cooling, the material from the channels in the mould
solidifies attached to the part.
- This excess material must be trimmed from the casting either
manually via cutting or sawing, or using a trimming press.

38. ADVANTAGES & DISADVANTAGES OF
SAND CASTING
ADVANTAGES DISADVANTAGES
Low cost of mould
Rough surface.
materials and equipment
Large casting dimensions Poor dimensional
may be obtained. accuracy.
Wide variety of metals Limited wall thickness:
and alloys may be cast. not higher than 2.5-5
mm.

39. LOST /WAX INVESTMENT
CASTING
• Is a casting process where molten metal is poured into an
expendable ceramic mould.

40. PROCESS OF INVESTMENT
CASTING
• Pattern creation
- A central wax gating system (sprue, runners, and risers), form
a tree-like assembly.
- The gating system forms the channels through which the
molten metal will flow to the mould cavity.

41. • Mould creation
- This "pattern tree" is dipped into a slurry of fine ceramic
particles, coated with more coarse particles, and then dried to
form a ceramic shell around the patterns and gating system.
- This process is repeated until the shell is thick enough to
withstand the molten metal it will encounter.
- The shell is then placed into an oven and the wax is melted
out leaving a hollow ceramic shell.

42. • Pouring
- The mould is preheated in a furnace and the molten metal is
poured from a ladle into the gating system of the mould, filling
the mould cavity.

43. • Cooling
- After the mould has been filled, the molten metal is allowed
to cool and solidify into the shape of the final casting.
- Cooling time depends on the thickness of the part, thickness
of the mould, and the material used.

44. • Casting removal
- After the molten metal has cooled, the mould can be broken
and the casting removed.
- Once removed, the parts are separated from the gating
system by either sawing or cold breaking (using liquid
nitrogen).

45. • Finishing
- Often times, finishing operations such as grinding or
sandblasting are used to smooth the part at the gates.
- Heat treatment is also sometimes used to harden the final
part.

46. ADVANTAGES & DISADVANTAGES
OF INVESTMENT CASTING
ADVANTAGES DISADVANTAGES
- Can form complex shapes - Time-consuming process.
and fine details. - High labour cost.
- Many material options. - High tooling cost.
- High strength parts. - Long lead time.
- Very good surface finish
and accuracy.

47. PRESSURE DIE CASTING
• The molten metal is forced into the die cavity at high pressure.

48. PROCESS OF PRESSURE DIE
CASTING
• Clamping
- The first step is the preparation and clamping of the two
halves of the die.
- Each die half is first cleaned from the previous injection and
then lubricated to facilitate the ejection of the next part.
- After lubrication, the two die halves, which are attached
inside the die casting machine, are closed and securely
clamped together.

49. • Injection
- The molten metal, which is maintained at a set temperature
in the furnace, is next transferred into a chamber where it can
be injected into the die.
- The method of transferring the molten metal is dependent
upon the type of die casting machine, whether a hot chamber
or cold chamber machine is being used.
- Once transferred, the molten metal is injected at high
pressures into the die.

50. • Cooling
- The molten metal that is injected into the die will begin to
cool and solidify once it enters the die cavity.
- When the entire cavity is filled and the molten metal
solidifies, the final shape of the casting is formed.

51. • Ejection
- After the predetermined cooling time has passed, the die
halves can be opened and an ejection mechanism can push
the casting out of the die cavity.
- The ejection mechanism must apply some force to eject the
part because during cooling the part shrinks and adheres to
the die.

52. • Trimming
- During cooling, the material in the channels of the die will
solidify attached to the casting.
- This excess material, along with any flash that has occurred,
must be trimmed from the casting either manually via cutting
or sawing, or using a trimming press.

53. ADVANTAGES & DISADVANTAGES
OF PRESSURE DIE CASTING
ADVANTAGES DISADVANTAGES
- Can produce large - Trimming is required.
parts. - High tooling and
- Can form complex equipment cost.
shapes. - Long lead time
- Very good surface
finish and accuracy.
- High production rate
- Low labor cost