1. 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

2. 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
Review course objectives.
Tell participants that all testing will be based on the course and chapter level objectives.

3. New Terms Billet Static metal pressure Thixotropy A small metal bar
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
Discuss sand, investment, and lost foam casting.
Use gravity to fill the mold. The mold is destroyed to remove the casting. Mold making is as important part as is making the casting.
Metal flow is slow.
Walls are much thicker than in die casting.
Cycle time longer because of inability of mold material to remove heat.
Discuss permanent mold casting.
A cousin to die casting. The mold is reused, not destroyed. The process uses gravity to fill the casting.
Mold is steel with comparatively good thermal conductivity, hence the release agents used in this process are also insulators. This keeps the casting from freezing periodically and prevents filling.
Machines for this process are smaller than machines used to die cast for similar sized castings.
Discuss centrifugal casting.
Frequently made by jewelers. The choice for low volume castings with a small amount of pressure.
The molds are placed around the circumference of a centrifuge. As the centrifuge spins, metal is poured in at the center and centrifugal force distributes the metal to the molds.

4. 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
Discuss sand, investment, and lost foam casting.
Use gravity to fill the mold. The mold is destroyed to remove the casting. Mold making is as important part as is making the casting.
Metal flow is slow.
Walls are much thicker than in die casting.
Cycle time longer because of inability of mold material to remove heat.
Discuss permanent mold casting.
A cousin to die casting. The mold is reused, not destroyed. The process uses gravity to fill the casting.
Mold is steel with comparatively good thermal conductivity, hence the release agents used in this process are also insulators. This keeps the casting from freezing periodically and prevents filling.
Machines for this process are smaller than machines used to die cast for similar sized castings.
Discuss centrifugal casting.
Frequently made by jewelers. The choice for low volume castings with a small amount of pressure.
The molds are placed around the circumference of a centrifuge. As the centrifuge spins, metal is poured in at the center and centrifugal force distributes the metal to the molds.

5. 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

6. 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

7. 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

8. 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

9. Hot Chamber Machine Cycle
3-8

10. 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

11. 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

12. 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

13. 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

14. Cold Chamber Machine Cycle
3-14

15. Cold Chamber Process Uses
Used for high melting point alloys and alloys with a significant aluminum constituent:
Aluminum
Copper
Magnesium
Iron
Titanium
Composite materials

16. Hot Chamber Advantages
Metal temperature control is better maintained
Metal transfer not required
Cooling of piston tip and sleeve not required
Fewer oxidation losses

17. 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

18. Vacuum Process Die cavity evacuated using a vacuum pump
Several commercially available systems
Limitations to how complete a vacuum can be achieved; inches of mercury seems adequate for most applications

19. Squeeze Casting Gate velocity is much lower
Gate thickness is much higher
Metal pressures at the end of cavity filling are much higher

20. 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

21. 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

22. 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