1 Of 8 Part Machining Die Casting Characteristics Quality

PartHD headcontrol arm1 of 8QualitycharacteristicsDie castingDimension: height,width, wallthicknessMechanicalproperties ofmaterials: hardness,brittleness, andporosity.MachiningDimension: holes,grooves, and cutsProcessesControl variablesDie casting produces the complicated geometrieswith high dimensional accuracy (in near netshape). It involves forcing molten metal (in thiscase, probably aluminum) into a steel die cavity atpressures ranging from 0.1-100 ksi. Thegeometry of the control arm after the die castingprocess is determined by the geometry of the dietooling. Surface finish and geometry will also bedetermined by molten temperature, castingpressure. Machine states: casting pressure,machine temperature (“oven temperature”),clamping force, and tooling temperature.Machine properties: thermal conductivity of tool,surface finish of tooling, and geometry of tooling(sharp edges, thin walls, etc.). Material states:material temperature, molten flow rate, moltenmetal pressure, solidification front, and materialstresses. Material properties: melting temperatureof material, stress-strain properties, thermalexpansion characteristics, viscosity, and heatconductivity.Machining performs the finishing operationssuch as drilling holes, making cuts, surfacefinishing, and shaving to proper dimension. Thiscan be done on a manual mill or a CNC machine.Here the determinants of part geometry will bethe tool path of the mill combined with feed,spindle speed, cutting tool material, etc.Equipment states: feedrate, spindle speed, spindletorque, workpiece temperature, coolanttemperature, coolant flow rate, tool holderposition, and “clamping” force. Equipmentproperties: tool geometry, tool material, structuralstiffness, damping, natural frequency, andstructural geometry. Material states: stresses andDie casting oventemperature,casting pressure,clamping force, andtoolingtemperature.Machining feed,spindle speed, toolholder position, andcoolant flowrate/temperature (ifnecessary).EnergyinteractionsDie casting: heattransfer andsolidification occursthroughout the partand the interfacebetween the part andthe tool (mold). Theenergy transfer isthermal. The modeof transfer isparallel.Machining:material removaloccurs “locally.”The tool “plows”through theworkpiece to removematerial. The areaof interactionbetween the tool andthe workpiece ismuch smaller thanthe characteristicarea of theworkpiece itself.The energy transferis mechanical. Themode of transfer isserial.Sources of variationDie casting Die wearalters the surface finishcharacteristics, the heattransfer from the metalto the mold, and theflow of molten metalthat also affect the heattransfer characteristicsof molten metal.Impurities in the alloyaffect viscosity and,hence, the flow andheat transfercharacteristics ofmolten metal.Machining machinetool vibration/chatter,cutting tool wear,build-up edge oncutting tool.

2 of 8Die castingDimension, surfacefinishMechanicalproperties ofmaterials: hardness,brittleness, andporosity.MachiningDimensions, surfacefinishGeometry: beamlength andwidth/height (crosssectional area) toachieve desireddeflection foraccelerationmeasure. Clearancefor unobstructedbeam deflection isalso critical.workpiece temperature. Material properties:stress-strain properties, porosity, and heatconductivity.SEE ABOVEThe part is made through a series of depositionand etch cycles using photolithography and wetchemical etching, respectively. A blank substrateis taken as the base. A deposition step continuesto build up a sacrificial layer. This layer is thencoated with a mask that is subsequently patterned(photolithography). The beam material is thendeposited. An etching/release step “eats away”the exposed mask as well as part of the sacrificiallayer along directed crystalline planes (wetchemical etching). Geometry is determinedthrough control of deposition/etch rates bycontrolling the chemical concentration of theagents as well as the duration of deposition/etch.Accuracy and resolution of the exposed mask isalso very important as it determines which partsof the materials are exposed to etch steps. Properselection of base materials also plays a large partas it partially determines the controllability of theetch reaction (speed and direction).Photolithography. Equipment states: flow ofmasking agents, chemical potential for maskexposure, proper temperature. EquipmentSEE ABOVEDeposition/etchingmaterialconcentration andtemperature.SEE ABOVESEE ABOVEImproper masktolerances createwrong size parts.Unexposed/underexposed regions causewrong geometry.Local variations inchemical concentrationwill cause unevenreaction rates.Temperature variationswill change reactionrates (local and globaleffects). Wrongcrystalline structurewill cause chemicaletching in undesireddirections. Operatorswill cause variationsby changingconcentrations andreaction times.

Disk brakerotor3 of 8Sand casting:Dimension:diameters accordingto specifications.Material properties:bubbles/porosity,residual imensions(roundness, length,width, height, etc.)according tospecifications.Surface finish,flatness. Materialproperties:properties: clean environment, geometric sizingof dispensing nozzles and pattern creation.Material states: chemical potential and extent ofreaction. Material properties: mask thickness andviscosity.Wet Chemical Etching. Equipment states:pressure and flow of reactive agents(deposition/etch reactants supplied into reactionchamber), proper reaction temperature.Equipment properties: chamber size and nonreactivity with process materials, dispersion ofchemical materials, cleanliness. Material states:chemical potential and extent of reaction, properreaction temperature. Material properties: propermaterial composition/structure and beamstiffness.Sand casting: (process principle determinants ofpart geometry): (i) Produce master pattern dimensional accuracy of pattern, draft angle; (ii)Create the sand mold (2 part) of pattern densityof sand pack, sand grain size & composition; (iii)Create the flask, risers, sprue diameter of sprue,flow rate of pour; (iv) Remove the pattern andclose & clamp the mold clamp force,dimensional accuracy of mold; (v) Pour moltenmaterial material properties, temperature; (vi)Cool the part time, ambient temperature,material properties; (vii) Open the mold andremove part speed of opening; and (viii)Remove the sprue and runners clean removal.Equipment states: ambient temperature (if thefactory is climate controlled), mold temperature,and clamp force of mold. Equipment properties:draft angle, geometry of mold, grainsize/composition, permeability, pattern geometry,heat expansion coefficient of sand and heattransfer coefficient of sand. Material states:Sand casting:(initial) moldtemperature,molten alloy(initial)temperature,pouring flow rate,clamping pressure,and cooling time(An indication ofprocess completion,cycle time is alsorate-depending.)Machining: SEEABOVESand casting:variations in materialproperties: minorchanges in the materialviscosity can result inmajor changes in howwell the mold fills,variation in the heattransfer properties ofthe mold alters thetemperature in moltenmetal that causeschanges in its viscosityand the way the moldfills. Changes in heattransfer property effectcooling rate that cancause porosity. Wearon the mold wall affectthe flow of moltenmetal and the heat

Tape driveHeadBeamAssemnly4 of 8Surface finish,weight, properlocation of datumsurfacestemperature profile, flow rate during filling,pressure of molten metal during filling, andsolidification front (crystallization of alloy).Material properties: viscosity, heat transfercoefficient, impurities, density of chosenmaterial, and heat expansion coefficient of alloy.Machining (process principle determinants ofpart geometry): (i) Position location feature in amill equipment fixture accuracy; (ii) Bore centerhub & screw holes depth of tool, spindle speed,tool diameter, equipment properties, tool bitproperties; (iii) Remove part & fix on lathe equipment properties; (iv) Turn the part spindlespeed, feed speed, traverse speed, tool bitproperties & position; and (v) Remove part.Equipment states: feedrate, spindle speed, spindletorque, tool temperature, coolant temperature,coolant flow rate, tool holder position, and“clamping” force. Equipment properties: toolgeometry, tool material, structural stiffness,damping, natural frequency, and structuralgeometry. Material states: stresses. Materialproperties: stress-strain properties, porosity, andheat conductivity.Injection Molding: The primary determinant ofthe injection molding process is the shape of themold cavity. Secondary determinants include theresin state and composition, design of the gatingand mold flow paths, injection pressures andtemperatures and the mold coolingcharacteristics. Equipment states: temperature(preheat chamber), control force, screw velocity.Equipment properties: Mold cavity geometry,thermal mass and coefficient through flow path,cleanliness and surface conditions. Materialstates: temperature, injection pressure, flow rate.Material properties: viscosity, thermaltransfer properties ofthe mold.Machining: SEEABOVEInjectionMolding: moldshape, temperature,pressure, fillvolume.Machining:toolpath, velocity.See aboveSee above

coefficient, composition of material.Machining: The primary determinant for themachining operation is the shape, sharpness,rotational velocity, and trajectory of the endmillwith respect to the fixture datum. Also importantis the consistency of HBA position with respectto the fixture datums (and by extension to the toollocation). Equipment states: rotational velocity,force, temperature, heat flux. Equipmentproperties: mill and fixture geometry, stiffness,damping, endmill geometry. Material states:bending stress, strain in workpiece. Materialproperties: initial geometry, materialcomposition.5 of 8

In the following table, we will discuss the control techniques for the above processes.ProcessDie castingMachiningPhotolithography & wetchemical etchingSand castingProcess taxonomy:ProcessMachiningControl techniquesMachine control for injection, machine control to regulate mold temperature,machine control to regulate temperature of molten metal. Statistical processcontrol to monitor any variations in the raw material quality and the effect ofany other common causes on the output. We also need standard operatingprocedures.Machine control for tool trajectory, machine control for cooling, SPC tomonitor variations in the raw material quality, the effect of tool wear, and theeffect of other common causes on the output. We need standard operatingprocedures.Statistical Process Control and Run by Run control. SPC detects variations inmaterial and equipment properties. We also need standard operatingprocedures.Machine control to regulate the melt temperature. Machine control toregulate the filling process. If filling is done manually, then we need standardoperating procedures to provide guidelines for consistency in the process.SPC is used to detect variations in the material properties as well as in themachine properties (e.g., mold wear) and other common causes that influencethe outputs.TaxonomySerial removalSpatial ResolutionHighSand castingParallel solidificationformingLowPhotolithographyParallel photochemicalremovalParallel chemicalremovalParallel solidificationformingLowCharacteristic timeHigh; however, cycletime can be lowdepending oncomplicated geometryMedium to Low, cycletime is approximatelyequal to characteristicprocess timeLow to mediumLowLow to mediumLowLow to mediumWet chemical etchingDie casting6 of 8

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viscosity can result in major changes in how well the mold fills, variation in the heat transfer properties of the mold alters the temperature in molten metal that causes changes in its viscosity and the way the mold fills. Changes in heat transfer property effect cooling rate that can cause porosity. Wear on the mold wall affect the flow of molten