Design for Die casting manufacturing
Design guideline
- Similar to injection moulding. Consider die casting when the inserted part does not have sufficient strength.
- Wall thickness function of alloy (typ 1.0 – 3mm). can go up to 10mm (will be permeable –a power not proportional to the wall)
- Ribs 80% wall thickness shrinkage less of an issue.
- Cooling time proportional to wall thickness (injection is t^2), so can have faster cycle times and thicker walls.
- Draft depends on alloy. Assume > 1.0 deg, esp. on cavity side.
- Tolerance is a function of alloy, part geometry and dies construction.
- Zinc alloy linear: + / − 0.025mm across up to 50mm.
- Zinc alloy hole: + / − 0.015mm up to 25mm diameter.
- need over flow wells and secondary ops − > $$
- No internal slides or snap fits.
The die casting option: broad range
- Agriculture machinery
- Auto motive vehicle
- Building hardware
- Electrical and electronic equipment
- Hand tools
- Home appliances
- Industrial product
- Instrumentation
- Lawn and garden equipment
- Office furniture
- Recreational equipment
- Portable power tools
Cold chamber
- Alloys: alu die casting, ZA-12 & 27, magnesium AM60, AS41, & large AZ91D.
- Advantages
- Large complex parts
- Higher pressure
- Many production layouts possible
Hot chamber Die casting
- Alloys: Zinc die casting, ZA-8 and small AZ91D Magnesium
- Advantages
- Metal temperature control.
- Automatic refill
- No cooling
- Less oxidation
Types of dies
- Single cavity die
- Multiple cavity die
- Family die
- Unit die
Injection sizing
- Critical variables
- Hydraulic pressure
- Cylinder size
- Dry shot speed
- Gate area
- Part volume
- Fill rate
Clamping tonnage
- Projected area of shot X metal pressure
- Metal pressure ͏͏͏͏̴ 10,000 psi (70 MPa)
- Example
- 100 ꭗ 10000/2000=500t (450mt) of clamping force required
Other process design concerns
- Filling pattern and plunger speed profile
- Venting and vacuum
- Thermal control
- Dimensional control
Thixocasting (semi – solid)
- Most casting processes use a fully liquid feed material
- Semi – solid casting uses as feed material that is 50% liquid and 50% solid
Semi – solid metal casting
Advantages
- Viscous flow (less air trapped)
- Shorter cycle time (colder material)
- Increased tool life (less shock)
- Reduced shrinkage (narrower cooling range)
- Reduced porosity (directional solidification)
- Improved mechanical properties
Example part
- Turbocharger impeller
Squeeze casting
- Fully liquid feel metal
- Inject slowly
- Avoid turbulence associated with conventional de casting
Processes
- Horizontal (HSC)
- Horizontal vertical (HVSC)
- Vertical (VSC)
Squeeze casting
- Process specific advantages
- Non – turbulent flow
- Reduced porosity (directional solidification)
- Improved mechanical properties
- Process specific disadvantages
- Casting wall thickness Min 4 to 5mm (0.150 to 0.200”)
- Large gates 6mm to 38mm (0.25 to 1.5”)
- Large runners
- Directional solidification (gate location)
- Limited cavity number (orientation in die, pressure opening die)
High integrity die casting processes
- Fully liquid feed
- Fast fill
- Vacuum level in the die cavity of 100 millibar or less
- Eliminates cavity gasses from the shot sleeve and die
- Used for crash resistant automotive castings