Introduction to Die Casting Alloys and Fundamentals Introduction to Die Casting Series Part 3 of 4 February 2017
Die Casting Alloys Mechanical and Physical Properties Aluminum Alloy Magnesium Alloy Zinc Alloy ZA Alloy Alloy Selection
Mechanical and Physical Properties Material Density: Mg =.066 lb/in 3 (1.81 g/cm 3 ) Zn = 0.24 lb/in 3 (6.65 g/cm 3 ) Ultimate Tensile: Mg = 31 ksi (210 MPa) ZA-27 = 60 ksi (414 MPa) Modulus of Elasticity Mg = 6,500 psi (45 GPa) Al = 11,800 psi (81.3 GPa)
Aluminum Alloys
Aluminum Product Application 380 383 360 413 390 518
Aluminum Heat Treatment & Welding
Silicon in Aluminum As silicon content approaches 12.6%: 1. Fluidity increases 2. Solidification shrinkage decreases 3. Pressure tightness improves 4. Hot shortness reduces 5. Stiffness increases 6. Specific gravity decreases 7. Thermal expansion decreases 8. Corrosion resistance improves
Copper in Aluminum 2-3% copper: Increases tensile strength Increases hardness Improves mechanical properties at elevated temperatures Copper content inversely effects corrosion resistance
Magnesium in Aluminum Advantages: Enhance chip formation and removal in machining operations Improves strength and hardness Disadvantages: Reduce ductility Embrittlement
Iron in Aluminum 0.6-1.2% iron content: Reduce erosion Reduce soldering
Manganese & Zinc in Aluminum Modify iron-aluminum inter-metallic phase to more benign state Provide solutionstrengthening effects Improve machinability Excessive amounts can cause cracking
Zinc Alloys Zinc 3 Zinc 5 Zinc 7
ZA-8
ZA-12
ZA-27
Magnesium Alloys Primary Alloy Element Secondary Alloy Element Primary Alloy Content Variation Secondary Alloy Content
Magnesium elements: A Aluminum E Rare Earth M Manganese S Silicon Z - Zinc Alloy Designation
Alloy Cost
Process Cost 1. Hot chamber = smaller machines that run at faster rates 2. Die maintenance and replacement costs: Zinc <= Lowest Magnesium ZA Aluminum <= Highest 3. Magnesium, zinc and ZA may reduce or eliminate machining 4. Zinc and ZA-8 for very small die castings
Structural Properties
Dent Resistance Dent resistance = Ys 2 /(2E) Ys = yield stress E = modulus of elasticity Design guide for comparative purposes only: Tabulated stress data are generated at low strain rates All other factors are rarely equal
Alloy Selection Magnesium: Minimum weight Aluminum: Weight considerations Cost Mechanical properties Zinc: Impact strength [reduced below 32 F (0 C)] Dent resistance ZA: Dent resistance
Surface Finish Typical As-Cast Surface Roughness Guide Typical Surface Roughness [μ-inches (microns)] Alloy Family / Alloy Expected in a New Die Over the Life of a Die Aluminum, ZA-12, ZA-27 63 (1.6) or better 100-125 (2.5-3.2) Magnesium 63 (1.6) or better 63 (1.6) should be maintainable Zinc, ZA-8 32 (0.8) or better 63 (1.6) should be maintainable
Corrosion Resistance
Bearing Properties & Wear Resistance Shaft Spinning
Machinability
Die Casting Fundamentals Standard equipment Die Casting Machine or DCM Holding furnace Die sprayer Ladle (cold chamber) Plunger tip lubricator (cold chamber) Optional equipment An extractor/robot A quench Conveyors Die heaters A trim press/die
Holding Furnace Provides liquid metal to process Maintains metal at a preselected temperature Keeps the alloy free of contamination Receives metal For cold chamber or hot chamber processes Located adjacent to the DCM May be used to melt the metal
Holding Furnace: Cold Chamber Has 3 distinct chambers: Charge well - metal enters Bath - holds bulk of metal Dip well - metal ladled from here to cold chamber Chambers are connected below the metal level with an arched passage
Holding Furnace: Hot Chamber Located adjacent to the stationary platen Simpler than a cold chamber furnace Typically are open crucibles, or pots Can be fossil fuel-fired or electrically-heated Temperature control thermocouple is located near the gooseneck
Die Spray Applies a protective coating of release material on the die face Provides cooling in areas that cannot be cooled internally Can be applied through different appliances Variables Spray pattern Spray time Spray applied
Types of Die Sprayers Manual Fixed: mounted to the die or machine platens Reciprocator
Ladling Manual ladling or auto ladling Ensure dross is not allowed in ladle Advantages and disadvantages to both Ladling time is important due to temperature loss resulting in filling defects
Hand Ladling
Automatic Ladling
Plunger Lubricator Some older methods of application include: Brushing heavy petroleum lubes into grooves in the plunger tip. Dripping the lube on the tip every cycle. Mounting a fixed nozzle above the cold chamber pour hole and spraying a water-based lube into the cold chamber. Drilling the plunger rod with spray holes behind the tip, connecting this line to a spray nozzle, and spraying lube into the sleeve during the return stroke. Some newer methods include Dropping dry lubricants into the pour hole. Spraying powdered lubricant inside the sleeve.
Manual removal Mechanized removal Drop-through Casting Removal
Quenching Forced cooling of the die casting Achieves rapid cooling/dimensional stability Cold water quenching Forced air quenching
Material Handling Conveyors, chutes, and slides Move the castings to the next operation, or to move scrap back to the reverb furnaces Baskets or pallets Stack castings for subsequent operations Other containers Accumulating scrap
Die Heaters Preheat the casting die prior to startup Maintain the die temperature during production Goal: to get die to minimum temperature of 350 F (175 C) before subjecting it to the thermal shock of first shot Some used exclusively to preheat the die prior to production Hand-held Gas Heater Hot Oil Die Heater
Trim Press Usable Casting
Trim Press
Workcell Environment Utilities Hoses and wires must be damagefree Housekeeping Area must be maintained to assure safety Workstation set-up
Fundamental Machine Cycle Elements Die spray/die inspection Die closing Ladling (cold chamber) Injection Dwell/casting inspection Die opening Ejection Casting removal/inspection
Step 1: Inspection After casting is removed, it is quickly inspected for completeness and obvious visual defects Kept short in order to maintain the rhythm of the casting cycle
An opportunity to inspect the die for: Flash on parting line, in vents, in slide pockets Soldering and lube buildup Puts protective barrier on die Removes heat from areas After spraying: Blow off die with highpressure air Cleaned die parting line to remove any flash Step 2: Die Spray
Step 3: Machine Closing Several acceptable methods Double palm buttons (most common cycle start mechanism) Safety door closure Combination of door closures and palm buttons Safety conditions must be satisfied After all conditions are satisfied, the safety pawl is withdrawn and the machine can begin closing
Step 4: Ladling/Injection Before injection can occur, process and safety conditions must be met The injection sequence begins when metal is poured into the cold chamber 7-48
Step 5: Machine Dwell/Hold After the shot made, the metal must be allowed to freeze and gain strength During dwell, casting is cooling in the die Internal stress occurs
Step 6: Machine Opening Requires high pressure to relieve tie bars Needs to open slowly initially Plunger must push out biscuit and keep it in contact with ejector die until it is fully out of the shot sleeve Casting needs to be in ejector half cavity of the die
Step 7: Ejection Several methods Bump method Fixed plate Hydraulically-operated bump plate
Step 8: Casting Removal After ejection, casting is removed Must be done with care, otherwise the die and casting can be damaged Use of a tool is recommended Must be pulled straight off ejector pins Follow safety precautions
Summary Designers consider range of issues when creating a die casting Each alloy has different mechanical properties: tensile strength, yield strength, elongation, and MOE The alloy chosen must be appropriate to the die casting s application Alloy selection is based on characteristics and properties of the alloys in 9 categories
Summary Fundamental steps include: Die spray/die inspection Die closing Ladling (cold chamber) Injection Dwell/casting inspection Die opening Ejection Casting removal/inspection
Questions Name: Beau Glim Phone: 847-808-3164 E-mail: glim@diecasting.org