High Pressure Die Casting of Magnesium Engine Block

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High Pressure Die Casting of Magnesium Engine
Block
A literature survey by Ola Heien
Solem Brynjar Hoff Helgetun Linda Karlsen Hege
Lien
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High Pressure Die Casting of Magnesium Engine
Block
Contents

• Function and requirements to geometrical
  tolerances
• Mechanical requirements
• Thermal requirements
• Chemical exposure
• Alloy information
• Alternative alloys and fabrication methods
• Prototyping
• Casting method and gating system
• Design (Die and part)
• Post casting
• Casting defects

A Literature Survey in TMM 4180 Casting Technology
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High Pressure Die Casting of Magnesium Engine
Block
Introduction

• High Strength / Low Weight
• Transportation Industry
• Sports equipment
• Audioapplications

• HPDC (High Pressure Die Casting)
• Fully automatic
• Well established method
• Large volume
• High productivity process
• Complex, thin walled shape castings
• Traditionally utilised in production of
  housings etc.

A Literature Survey in TMM 4180 Casting Technology
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High Pressure Die Casting of Magnesium Engine
Block
Function and requirements to geometrical
tolerances

• Function
• Contain cylinder bores, crankshaft etc.
• The engines core component
• Requirements to geometrical tolerances
• Requires a high degree of accuracy
• Requires extensive post-casting machining

A Literature Survey in TMM 4180 Casting Technology
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High Pressure Die Casting of Magnesium Engine
Block
Mechanical requirements

• Must withstand/ absorb vibrations
• Must withstand various mechanical stresses
• Material must be free of pores
• Especially around the gasket areas

A Literature Survey in TMM 4180 Casting Technology
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High Pressure Die Casting of Magnesium Engine
Block
Thermal requirements

• Typical thermal environment in an Engine Block
• Liquid cooled
• Temperatures range from approx. -40 C to 120
  C
• Temperatures rarely exceed 120 C.

A Literature Survey in TMM 4180 Casting Technology
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High Pressure Die Casting of Magnesium Engine
Block
Chemical exposure

• Oil
• Cooling liquid
• Air

A Literature Survey in TMM 4180 Casting Technology
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High Pressure Die Casting of Magnesium Engine
Block
Alloy information
A Literature Survey in TMM 4180 Casting Technology
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High Pressure Die Casting of Magnesium Engine
Block
Alloy information

• The current commercial magnesium die casting
  alloys all contain aluminium as the main alloying
  element
• Al improves the strength, corrosion properties
  and castability.
• Zinc and Manganese are also added in some alloys.

A Literature Survey in TMM 4180 Casting Technology
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High Pressure Die Casting of Magnesium Engine
Block
Alternative alloys and fabrication methods
A Literature Survey in TMM 4180 Casting Technology
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High Pressure Die Casting of Magnesium Engine
Block
Prototyping

• The high cooling rate obtained in the die (100
  1000 s) leads to formation of fine grained
  structure with well dispersed intermetallic
  constintuents. Altough some porosity will be
  invetiable, the mechanical properties as well as
  corrosion properties of die cast parts are better
  than those of parts made by other casting
  processes with slower solidification rates. This
  means that if prototypes with the properties of a
  cast component are required, the approach is to
  make an alternative tool that can be used in the
  die casting process
• P20 Steel
• Sand castin if wall thickness gt 3-4 mm
• Plastic mould if wall thickness lt 3-4 mm
• Other die cast parts
• Rapid prototyping
• Stereolithography of layered manufacturing
• Produces 3-D patterns from CAD-files
• Can readily be used in prototyping by sand or
  plaster casting

A Literature Survey in TMM 4180 Casting Technology
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High Pressure Die Casting of Magnesium Engine
Block
Casting method

• Extremely narrow dimentional, shape and position
  tolerances.
• Shot-like die filling
• Microporosity
• Local shrinkage-cavity can hardly be eliminated
• No re-feeding possibility, but reaches
  appreciable strength in thin-wall areas
• Extremely fast heat dissipation

A Literature Survey in TMM 4180 Casting Technology
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High Pressure Die Casting of Magnesium Engine
Block
Method and gating system

• Equipment
• Both cold chamber and hot chamber die casting
  machines are used.
• But in the production of motor blocks cold
  chamber is mostly used.
• The level of automation varies.

Left Cold chamber process (die temp
200-300) Right Hot chamber process (die temp
700-800)
A Literature Survey in TMM 4180 Casting Technology
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High Pressure Die Casting of Magnesium Engine
Block
Method and gating system
Die for cold chamber machine

• Metal metered into the shot sleeve
• Plunger movement
• The die is filled (fast)
• During solidification the casting is pressurized
  hydraulically to feed the shrinkage.

A Literature Survey in TMM 4180 Casting Technology
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High Pressure Die Casting of Magnesium Engine
Block
Method and gating system

• Feeding system
• The gates may be of different geometry
• Metal flow from the gates should be parallel or
  divergent, and designed for minimum flow
  distance, to reduce turbulence
• Opposing metal flows should not meet in thin
  walled areas
• Parts filled from different gates should be
  filled simultaneously
• Overflows should be applied to wash out oxides
  and remains of the lubricant, as well as adding
  heat to cold parts of the die.

A Literature Survey in TMM 4180 Casting Technology
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High Pressure Die Casting of Magnesium Engine
Block
Die design

• Complex tool
• Must fulfill several tasks
• Defines a general geometry
• Strong influence on the dimensional variation
  from shot to shot
• Use of fixed or moveable cores adds to the
  flexibility to cast complex near net shapes
• Determine the die filling characteristics
• The thermal conditions of the die determines the
  solidifications of the part and therefore the
  microstructure and quality
• Attainable cycle time
• Eject the part after solidification

A Literature Survey in TMM 4180 Casting Technology
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High Pressure Die Casting of Magnesium Engine
Block
Die materials

• H13 - premium steel
• Direct contact with molten metal
• Partially annealed hardened 46 - 48 HRC
• 25 wt of the die
• Mild steel
• Medium carbon steel
• Standard unit dies
• Smaller castings and relatively simple
  geometries
• Main frame and ejector system
• Die cavity inserts can be exchanged
• Same unit die is used for a number of different
  castings

A Literature Survey in TMM 4180 Casting Technology
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High Pressure Die Casting of Magnesium Engine
Block
Part design

• Section thickness
• Excellent die filling characteristics
• Wall thickness gt 1 mm
• Uniform wall thickness
• Non-uniform wall thickness can lead to local
  hot-spots
• Porostity or voids
• Easy die filling
• A shot-like die filling (10-100 ms)
• Round corners/edges to avoid turbulence
• Ribs for strengthening
• Avoid local overheating
• Can lead to thermal fatigue

A Literature Survey in TMM 4180 Casting Technology
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High Pressure Die Casting of Magnesium Engine
Block
Design

• Surface finish
• Texture the surface for an even apperance
• Lettering and shallow features should be raised
  rather than sunk into the surface
• Changes in section thickness
• Gradual to avoid stress concentration
• Draft
• Recommended 2-5 degrees
• Common 1-3 degrees (and even zero draft)

A Literature Survey in TMM 4180 Casting Technology
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High Pressure Die Casting of Magnesium Engine
Block
Post Casting

• Trimming
• Machining
• Not necessary when die casting are produced to
  net shaped
• Surface treatment
• Vibratory finishing in ceramic media
• Usually applied to removeremaining flash and
  sharpedges
• Grinding, buffing
• When needed
• Blast cleaning
• Be careful and don't introduceimpurities
• Heat treatment
• None
• Joining
• Bolting

A Literature Survey in TMM 4180 Casting Technology
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High Pressure Die Casting of Magnesium Engine
Block
Casting defects

• Incomplete filling
• Inedequate injection speed
• Cold dies
• Low metal temperature
• Impoper gating or insufficient die venting
• Cold flows of cold shuts
• Low temperature of eighter die or metal
• Gas porosity
• Entrapping of air/ gas or due to precipitation
  of dissolved hydrogen
• Shrinkage porosity
• Restricted metal feeding local hot spots

A Literature Survey in TMM 4180 Casting Technology
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High Pressure Die Casting of Magnesium Engine
Block
Casting defects

• Flow marks
• Splashing and turbulent flow
• Poor gating
• Sharp corners
• Excessive lubricants
• Hot cracking
• May occur when metal is partly solidified
• Constraints in die cause buildup of stresses
• Sharp corners and delayed ejection of the cast
  part hot cracking
• Deformation / distorion / fractures
• May be caused during ejection of the part due to
  shrinkage stresses

A Literature Survey in TMM 4180 Casting Technology
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High Pressure Die Casting of Magnesium Engine
Block
Casting defects
A Literature Survey in TMM 4180 Casting Technology
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High Pressure Die Casting of Magnesium Engine
Block
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