Design for Die casting manufacturing

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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

  1. Advantages
  2. Large complex parts
  3. Higher pressure
  4. Many production layouts possible

Hot chamber Die casting

  1. Advantages
  2. Metal temperature control.
  3. Automatic refill
  4. No cooling
  5. 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

Vacuum Die casting

  • 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