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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