Thixomolding Of Magnesium - Het Aluminium Centrum

Basic Features of MagnesiumASTM Mg alloy designation system- Alloys-Major alloyingingredient,aluminumSecondary alloyingingredient,zincFourth composition ofthis alloy registered withASTM A-E, X1A:aluminumE:rare earthsM:manganeseS:siliconZ:zincH:thoriumK:zirconiumQ:silverW: YttriumAZ91DNominal percentageof major ingredientNominal percentageof secondary ingredient

Basic Features of Magnesium- Alloys-Table Nominal compositions of typical magnesium alloys.Al Mn Zn Zr Other Fe Ni CuAZ91D 9.0 0.13 0.7 … … 50 20 300AM60B 6.0 0.13 … … … 50 20 100AM50A 4.9 0.26 … … …AS41B 4.2 0.20 … … 1.0Si 35 20 20AE42F 4.0 0.1 … … 2.5REWE54A … … … 0.7WE43A … … … 0.75.2Y3.0RE5.2Y3.0RE50 300100 50 300AZ31B 3.0 0.20 1.0 … … 50 50 500Compositions are in %, impurities are in ppm.

Basic Features of MagnesiumAdvantages of magnesium over plastic- Material property-• Stronger (Tensile strength : 28 MPa)• Stiffer (Young’s modulus : 45 GPa)• Higher heat resistance (No deformation at 100 ? )• EMI & RFI Shielding (No plating is required)• Better heat transfer and electrical conductivity characteristics• Less warp• Better recyclability

Principle of Thixomolding- Molding technology-CastingLow pressurecastingInvestiment castingSand or plaster castingPermanent mold castingMgnesiumMoldingHigh pressurecastingDie castingHot chamber DCCold chamber DCSqueeze castingExtrusionSemi-solidformingThixomoldingRheocastingThixocastingForgingPress formingForgingFigureDifferent molding processes utilized formagnesium products.

Principle of ThixomoldingDie casting- Molding technology-(a) Cold chamber machine(b) Hot chamber machineFigureDie cast machines for magnesium.

Principle of Thixomolding- Semi-solid forming-SolidphaseLiquidphaseSolid phaseLiquidphaseStationary state(without shear force)ViscosityHighFluidityLowLowHighThixotropic state(with shear force)FigureSchematic illustration of evolution of structure duringsolidification with vigorous agitation.

Principle of Thixomolding- Semi-solid forming-L (liquid phase)ConventionalcastingTemperatureSemi-solidstateaa + LSemi-solidforminga + bPressformingL + bFigure Concept ofsemi-solid forming.ACompositionB

Principle of Thixomolding- Semi-solid forming-Advantages of semi-solid forming– Less casting shrinkage– Fine grain structure– Increased dimensional accuracy– Higher material efficiency– Improved mold filling - solid front -

Principle of Thixomolding- Thixomolding-Chipped raw materialsProductsArgon atmosphereBand heaterHopperVolumetric feederRotary driveMoldScrewBarrelSlurry temperature (560-630? )High speed shotsystemFigureThixomolding machine for magnesium.

Principles of Thixomolding- Thixomolding-FigureThixomolding machine (JLM220-MG).

Principle of Thixomolding- Thixomolding-SlurryTemp.SolidphaseFigure605? 595? 585? 575? 565?

Application of Thixomolded Products- Magnesium market -Mini-DiskplayerOthersCameraVideoCameraMg alloysPCFigureApplication for magnesium products.

Application of Thixomolded Products- Automobile applications -FigureExamples of magnesium productsfor automobile parts

Thixomolding vs. Die castingParameterMelt temp.(?)(AZ91D)- Machine -Table Machine specification.Die castingThixomoldingHot chamber Cold chamber580 - 610 630 - 650 680 – 700Inj. speed (m/s) 1 - 4 1 - 4 1 - 8Inj. press.( kgf/cm 2 ) 500 - 1200 250 - 350 400 - 700Intensifi. press. (Holding pressure) No YesInternal defect Few Medium ManyMachine size

Thixomolding vs. Die castingTable Product quality.- Product-Parameter ThixomoldingDie castingHot chamber Cold chamberFlow marks Few Few MediumShrinkage Small Medium MediumSurface Excellent MediumGood(high-speed inj.)ShrinkageDim. precision3.5 – 4.5 / 1000Good5 – 5.5 / 1000Medium7 – 8 / 1000Not goodDistortion Small Medium LargeMech. property Good Medium GoodCorr. resistance Good Medium Not good

Thixomolding vs. Die castingCorrosion rate (mg/cm 2 /day)0.150.100.05- Corrosion -0TM DC(1) DC(2) DC( Lit.)Figure Weight loss corrosion rates of thixomolded (TM)and die cast(DC) AZ91D specimens.

Thixomolding vs. Die casting- Strength -Y.S. and T.S. (MPa)350300250200150100500Die cast (T.S.)Die cast (Y.S.)Barrel temp.:898KInjection velocity:1.4m/sDie cas t(El.)0 10 20 30 40 50Shot No.100806040200Elongation (%)FigureStability of mechanical properties (AM50A).

Thixomolding vs. Die casting-Microstructure-FigureMicrostructure close to thixomolded anddie cast surface.50µm

Thixomolding vs. Die casting- Accuracy -Deviation from the mean value (mm)0.80.60.40.20ThixomoldedDiecastA B C D E FPositionDEACFBFigure Dimensional accuracy of die cast and thixomolded PC housings.

Requirements for Thixomolding- Product design -Draft:Zero Draft is possible, Normal draft .5 to 3 degrees.Pattern shrinkage: 4 - 4.5/1000Ribs:Radii and Fillets:Uniform Cross Sections:Ejector Pin Marks:Die Steel Sections:Reduce Assembly:use ribs for strength and thin down the wallsavoid sharp corners…too large a fillet cause shrinkavoid rapid change in sections..shrink and flow problemsidentify areas where pin marks are prohibited or allowedavoid designs that produce thin die steel sections..die lifedesign several components into one thixomolding

Requirements for Thixomolding- Product design -Factors influencing the production of thin wallMg housingsProduct design-thickness variation-slide & core-othersMolding condition-melt temperature-mold temperature-injection speed-othersOptimum thickness(0.6-1 mm)Surface treatmentProduction yieldTool design- gate design- overflow location- hot runner- othersMaterials- alloy- lubricant- others

Structure of Long NozzleSealingIH HeaterInsulating ringHeaterAdvantages· Improving material yield· Reducing shot cycletime(10%)· Making quality of moldedpartshigh (For cosmetic parts)· Reduce Runner Weight (30-50%)PlugNozzleStructure of Long Nozzle

ComparisonCold Runner Hot Sprue Long NozzleSealingPressure Touch Pressure Tough+Thermal expanding sealThermal expanding sealSeal face Seal face Seal faceTool costLow(1.0)High(1.2)Low(1.0)Material Yield bad (1.0)Good (0.5~ 0.8)Good(0.5~ 0.8)Shot CycleLong(1.0)Short(0.9)Short (0.9)Life time Fair(1.0) Short (0.8) Long (1.2)Operation Easy (1.0) Bad (0.8) Fair ? (0.8) (1.0)

Shot Sample· Cell phone parts: Key Pad FrontShot weight: 41gShot weight: 30g· Cell phone parts: LCDShot weight: 115gShot weight: 61g

Concluding Remarks• Magnesium is steadily recognized as a structural materialin automotive and electronic industries.• Thixomolding process offers high quality magnesiumproducts with the environmentally-friendly process.• New process technology such as a hot runner system or apowder lubricant, is expected to bring higher yields withfurther cost down.