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Chapter 3 OverviewChapter 3 Overview
Several variations to die casting Several variations to die casting The variations depend on several factors:The variations depend on several factors:
• Temperature of the metal pumpTemperature of the metal pump• Consistency of the metal when it is injectedConsistency of the metal when it is injected• Metal velocityMetal velocity• Gating configurationGating configuration• Condition of die cavity at moment of injection Condition of die cavity at moment of injection
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Chapter 3 ObjectivesChapter 3 Objectives
Identify the two major methods of injecting Identify the two major methods of injecting metal into the diemetal into the die
List advantages of hot chamber die castingList advantages of hot chamber die casting Explain why cold chamber die casting is usedExplain why cold chamber die casting is used Explain how vacuum die casting can reduce Explain how vacuum die casting can reduce
defectsdefects List two emerging die casting technologiesList two emerging die casting technologies
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New TermsNew Terms
BilletBillet• A small metal barA small metal bar
Static metal pressureStatic metal pressure• The metal pressure in the die cavity at the instant The metal pressure in the die cavity at the instant
that the cavity is fullthat the cavity is full ThixotropyThixotropy
• The property of a fluid mixture to become more The property of a fluid mixture to become more fluid as the mixture is agitatedfluid as the mixture is agitated
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Two Major ProcessesTwo Major Processes
Hot chamber and cold chamber die castingHot chamber and cold chamber die casting Get name from temperature of metal pump Get name from temperature of metal pump
relative to temperature of the metalrelative to temperature of the metal• In hot chamber, the metal pump is submerged in In hot chamber, the metal pump is submerged in
the metal and is same temperature as the metalthe metal and is same temperature as the metal• In cold chamber, the metal pump is outside the In cold chamber, the metal pump is outside the
furnace and is cold relative to the metal ladled furnace and is cold relative to the metal ladled into itinto it
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Hot Chamber ComponentsHot Chamber Components A FrameA Frame
• Suspends shot Suspends shot components above components above and in the furnace; and in the furnace; mounted to mounted to stationary platenstationary platen
Shot cylinderShot cylinder• Actuates vertically; Actuates vertically;
metal is injected metal is injected with downward with downward stroke of the stroke of the shot cylindershot cylinder
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CouplingCoupling• Connects shot Connects shot
cylinder to plunger cylinder to plunger rod and tiprod and tip
Plunger rod and tipPlunger rod and tip• Pumps the metal; Pumps the metal;
piston tip has 2 piston tip has 2 or 3 grooves in it or 3 grooves in it for piston ringsfor piston rings
Hot Chamber ComponentsHot Chamber Components
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RingsRings• Prevents metal from Prevents metal from
bypassing tip; helps bypassing tip; helps maintain metal maintain metal pressure after die pressure after die cavity is filledcavity is filled
GooseneckGooseneck• Combination sleeve Combination sleeve
and metal path out and metal path out of the metal pumpof the metal pump
Hot Chamber ComponentsHot Chamber Components
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Hot Chamber ComponentsHot Chamber Components NozzleNozzle
• Tube connecting Tube connecting gooseneck to die cast gooseneck to die cast die; extends from die; extends from gooseneck, through gooseneck, through stationary platen, to die stationary platen, to die cast die; it’s heated to cast die; it’s heated to keep the metal liquid keep the metal liquid in the nozzlein the nozzle
Sprue bushingSprue bushing• What the nozzle seats What the nozzle seats
against; cooled to assure the metal in it freezesagainst; cooled to assure the metal in it freezes
Hot Chamber Machine Hot Chamber Machine CycleCycle
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Hot Chamber Process UsesHot Chamber Process Uses
For low melting point alloys and alloys with a For low melting point alloys and alloys with a small aluminum constituent small aluminum constituent
These alloys include those made from:These alloys include those made from:• LeadLead• TinTin• The Zamak family of zinc alloys, ZA8 zinc alloy The Zamak family of zinc alloys, ZA8 zinc alloy
and a small amount of AZ91D magnesium alloyand a small amount of AZ91D magnesium alloy
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Cold Chamber Cold Chamber ComponentsComponents
C-frameC-frame• Structural framework Structural framework
that supports the shot that supports the shot components; mounted components; mounted to stationary platento stationary platen
Shot cylinderShot cylinder• Mounted to theMounted to the
C-Frame; injects C-Frame; injects metal with its metal with its horizontal strokehorizontal stroke
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CouplingCoupling• Connects the shot Connects the shot
cylinder to the plunger cylinder to the plunger rod and tiprod and tip
Cold chamberCold chamber• Shot sleeve or tube Shot sleeve or tube
that the plunger slides that the plunger slides in to pump the metalin to pump the metal
Cold Chamber Cold Chamber ComponentsComponents
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Cold Chamber Cold Chamber ComponentsComponents
Plunger rod and tipPlunger rod and tip• Pumps the metal; Pumps the metal;
made from highly made from highly conductive material conductive material and is water-cooledand is water-cooled
• Conventional cold Conventional cold chamber plunger tips chamber plunger tips do not have rings; do not have rings; newest technology indicates that newest technology indicates that the tip may benefit from a design with ringsthe tip may benefit from a design with rings
Cold Chamber Machine Cold Chamber Machine CycleCycle
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Cold Chamber Process Cold Chamber Process UsesUses
Used for high melting point alloys and alloys Used for high melting point alloys and alloys with a significant aluminum constituent:with a significant aluminum constituent:• AluminumAluminum• CopperCopper• MagnesiumMagnesium• IronIron• TitaniumTitanium• Composite materialsComposite materials
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Hot Chamber AdvantagesHot Chamber Advantages
Metal temperature control is better Metal temperature control is better maintainedmaintained
Metal transfer not requiredMetal transfer not required Cooling of piston tip and sleeve not requiredCooling of piston tip and sleeve not required Fewer oxidation lossesFewer oxidation losses
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Process Process Limitations/VariationsLimitations/Variations
Conventional process limited by internal Conventional process limited by internal porosityporosity• Due to trapped gases or solidification shrinkageDue to trapped gases or solidification shrinkage
New technologies developed to provide New technologies developed to provide denser castings denser castings • Use vacuum, squeeze casting, or semi-solid and Use vacuum, squeeze casting, or semi-solid and
thixotropic melting/casting methodsthixotropic melting/casting methods
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Vacuum ProcessVacuum Process
Die cavity evacuated using a vacuum pumpDie cavity evacuated using a vacuum pump Several commercially available systemsSeveral commercially available systems Limitations to how complete a vacuum can Limitations to how complete a vacuum can
be achieved; 26-27 inches of mercury seems be achieved; 26-27 inches of mercury seems adequate for most applicationsadequate for most applications
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Squeeze CastingSqueeze Casting
Gate velocity is much lowerGate velocity is much lower Gate thickness is much higherGate thickness is much higher Metal pressures at the end of cavity filling are Metal pressures at the end of cavity filling are
much highermuch higher
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Semi-Solid CastingSemi-Solid Casting
Alloy cast is part liquid and part solidAlloy cast is part liquid and part solid• Premise: defects form during solidification; solids Premise: defects form during solidification; solids
therefore should be free of defects therefore should be free of defects Billet of material is preheated to casting temp. Billet of material is preheated to casting temp.
in a specially constructed induction heater in a specially constructed induction heater Billet placed in cold chamber, then injected Billet placed in cold chamber, then injected Uses low gate velocities and high metal Uses low gate velocities and high metal
pressures to make very dense castingspressures to make very dense castings
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Thixotropic CastingThixotropic Casting
Takes advantage of the thixotropy of alloyTakes advantage of the thixotropy of alloy• When injected and forced through the gate, literally When injected and forced through the gate, literally
sheared and agitated, it flows like a plastic materialsheared and agitated, it flows like a plastic material Injection system is a combination of the screw used Injection system is a combination of the screw used
in plastic injection and the plunger used in in plastic injection and the plunger used in conventional die castingconventional die casting
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SummarySummary
Two major processesTwo major processes• Components are similarComponents are similar• Process used is based on alloy’s melting point Process used is based on alloy’s melting point • Hot chamber process has several advantagesHot chamber process has several advantages
Process variations are based on new Process variations are based on new technologiestechnologies• Try to overcome conventional die casting’s Try to overcome conventional die casting’s
limitation of internal porositylimitation of internal porosity