Die Casting Parts Review

Pinless tag clip- zinc die casting parts

  • Zinc: ZA-8
  • Weight: 0.35 oz
  • Miniature  zinc
  • 100,000 parts in 4 weeks

Power conditioning module chases – aluminum die casting parts

  • Aluminum: 380
  • Weight: 2..3lbs
  • ̴12”ꭗ12” (30ꭗ30 cm)
  • Die built in 8 weeks
  • Replace machined component
  • Significant cost savings

Steering knuckles

Performance

  • Passed 1.4g cornering load at 130,000 min and 280,000 cycle’s max (4 to 8ꭗ req.)
  • UTS > 2ꭗ customer requirements in all tests
  • Lower control arm test: unbreakable (fixture failure)
  • Outperformed all previous AI knuckles
  • 10% weight reduction
  • 5% cost reduction

Thrust rods

Performance

  • ̴50% weight reduction
  • Ribs allowed stiffness needed
  • Three parts consolidated into one
  • Replaced stamped steel parts

Engine base bracket

Performance

  • 43.6% weight reduction over stamped steel fabrication
  • Met strength and ductility requirements
  • 16 parts to 1
  • 4 different brackets now one common bracket
  • Cost reduction confidential per customer
  • Up to 1M per year

Engine subframe

Performance

  • Welded to hydro/bulge formed and squeeze cast parts
  • 46% weld length reduction  ̴40% lighter
  • Down to 16 parts from 48 (66% less)
  • Cost reduction realized, but confidential

Shock tower

Performance

  • 40% weight savings
  • Eliminated 5 part steel assembly
  • Exceeded requirements
  • Elongation allowed self-piercing riveting
  • Allowed thin wall heat treatment

Porosity – background

  • Common in many die castings
  • Common in metal casting
  • All defects are characteristics of the process
  • Considered a defect when porosity level exceed requirements

Outline

  • Sources of casting defects
  • Process control of defects
  • Design control of defects
  • Measuring defects

The cause of defects

Background

  • Two sources of porosity
  • Solidification
  • Gas (various sources)
  • Smooth pores formed at high liquid fractions
  • Jagged pores formed at a lower liquid fraction
  • Many aluminum alloys shrink  ̴6%
  • Common casting pore fraction < 3%

Shrinkage porosity – summary

  • Shrinkage can account for all the porosity
  • To reduce shrinkage porosity
  • Feeding, feeding, feeding
  • Bigger gates
  • High pressure
  • Etc
  • Alloy design
  • Interacts with gas porosity

Dissolved gas porosity

Three major causes of gas

  • Hydrogen gas
  • Entrained air
  • Evaporation of lubes, water, etc…

cannot be separated from shrinkage easily

gas will fill shrinkage pores

Hydrogen porosity

hydrogen solubility

  • high in liquid
  • low in solid

during solidification

  • hydrogen gas rejection
  • forms porosity

typically

  • microspores
  • combine with larger pores

Entrained air porosity

air caught during filling

  • in short sleeve
  • during injection
  • poor venting

difficult to predict quantitatively

process variables and design affects air entrainment

The vacuum can be effective

Other gas porosity

typical other sources of porosity include:

  • die lube
  • plunger tip lube
  • water
  • hydraulic oil/heating oil leaks

color of porosity can help identify sources

  • dark = lubes
  • light/shiny = water

Reduce leaking

  • impregnation
  • reduce porosity
  • avoid removing skin
  • avoid soldering
  • move knit lines

practically

  • process control
  • gating
  • design

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

  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