Chapter 3 Overview
 Several
variations to die casting
 The variations depend on several factors:
•
•
•
•
•
Temperature of the metal pump
Consistency of the metal when it is injected
Metal velocity
Gating configuration
Condition of die cavity at moment of injection
3-1
Chapter 3 Objectives
 Identify the
two major methods of injecting
metal into the die
 List advantages of hot chamber die casting
 Explain why cold chamber die casting is used
 Explain how vacuum die casting can reduce
defects
 List two emerging die casting technologies
3-2
New Terms
 Billet
• A small metal bar
 Static metal
pressure
• The metal pressure in the die cavity at the instant
that the cavity is full
 Thixotropy
• The property of a fluid mixture to become more
fluid as the mixture is agitated
3-3
Two Major Processes
 Hot
chamber and cold chamber die casting
 Get name from temperature of metal pump
relative to temperature of the metal
• In hot chamber, the metal pump is submerged in
the metal and is same temperature as the metal
• In cold chamber, the metal pump is outside the
furnace and is cold relative to the metal ladled
into it
3-4
Hot Chamber Components

A Frame
• Suspends shot
components above
and in the furnace;
mounted to
stationary platen

Shot cylinder
• Actuates vertically;
metal is injected
with downward
stroke of the
shot cylinder
3-5
Hot Chamber Components

Coupling
• Connects shot
cylinder to plunger
rod and tip

Plunger rod and tip
• Pumps the metal;
piston tip has 2
or 3 grooves in it
for piston rings
3-6
Hot Chamber Components

Rings
• Prevents metal from
bypassing tip; helps
maintain metal
pressure after die
cavity is filled

Gooseneck
• Combination sleeve
and metal path out
of the metal pump
3-7
Hot Chamber Components

Nozzle
• Tube connecting
gooseneck to die cast
die; extends from
gooseneck, through
stationary platen, to die
cast die; it’s heated to
keep the metal liquid
in the nozzle

Sprue bushing
• What the nozzle seats
against; cooled to assure the metal in it freezes
3-8
Hot Chamber Machine Cycle
3-8
Hot Chamber Process Uses
 For low melting point alloys and alloys with a
small aluminum constituent
 These alloys include those made from:
• Lead
• Tin
• The Zamak family of zinc alloys, ZA8 zinc alloy
and a small amount of AZ91D magnesium alloy
3-10
Cold Chamber Components

C-frame
• Structural framework
that supports the shot
components; mounted
to stationary platen

Shot cylinder
• Mounted to the
C-Frame; injects
metal with its
horizontal stroke
3-11
Cold Chamber Components

Coupling
• Connects the shot
cylinder to the plunger
rod and tip

Cold chamber
• Shot sleeve or tube
that the plunger slides
in to pump the metal
3-12
Cold Chamber Components

Plunger rod and tip
• Pumps the metal;
made from highly
conductive material
and is water-cooled
• Conventional cold
chamber plunger tips
do not have rings;
newest technology indicates that
the tip may benefit from a design with rings
3-13
Cold Chamber Machine Cycle
3-14
Cold Chamber Process Uses
 Used
for high melting point alloys and alloys
with a significant aluminum constituent:
•
•
•
•
•
•
Aluminum
Copper
Magnesium
Iron
Titanium
Composite materials
3-15
Hot Chamber Advantages
 Metal
temperature control is better
maintained
 Metal transfer not required
 Cooling of piston tip and sleeve not required
 Fewer oxidation losses
3-16
Process Limitations/Variations
 Conventional process limited by
internal
porosity
• Due to trapped gases or solidification shrinkage
 New technologies developed to
provide
denser castings
• Use vacuum, squeeze casting, or semi-solid and
thixotropic melting/casting methods
3-17
Vacuum Process
 Die
cavity evacuated using a vacuum pump
 Several commercially available systems
 Limitations to how complete a vacuum can
be achieved; 26-27 inches of mercury seems
adequate for most applications
3-18
Squeeze Casting
 Gate
velocity is much lower
 Gate thickness is much higher
 Metal pressures at the end of cavity filling are
much higher
3-19
Semi-Solid Casting
 Alloy cast
is part liquid and part solid
• Premise: defects form during solidification; solids
therefore should be free of defects
 Billet of material is
preheated to casting temp.
in a specially constructed induction heater
 Billet placed in cold chamber, then injected
 Uses low gate velocities and high metal
pressures to make very dense castings
3-20
Thixotropic Casting

Takes advantage of the thixotropy of alloy
• When injected and forced through the gate, literally
sheared and agitated, it flows like a plastic material

Injection system is a combination of the screw used
in plastic injection and the plunger used in
conventional die casting
3-21
Summary
 Two major processes
• Components are similar
• Process used is based on alloy’s melting point
• Hot chamber process has several advantages
 Process variations are
based on new
technologies
• Try to overcome conventional die casting’s
limitation of internal porosity
3-22