Forming and Shaping ISAT 430 Module 7 Spring 2001ISAT 430 Dr. Ken Lewis 2 Forming and Shaping Meanings blend Forming means changing the shape of an existing

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  • Forming and ShapingISAT 430Module 7

    ISAT 430 Dr. Ken Lewis

    Module 7

    Forming and ShapingMeanings blendForming means changing the shape of an existing solid body.Shaping usually involves molding or castingThe resulting product is usually near net shape.

    ISAT 430 Dr. Ken Lewis

    Module 7

    Forming and Shaping ProcessesRolling -- FlatProduction of flat plate, sheet and foilLong lengths, high speedsGood surface finishRequiresHigh capital investmentIncurs low to moderate labor cost.

    ISAT 430 Dr. Ken Lewis

    Module 7

    Forming and Shaping Processes2Rolling ShapedProduction of various structural shapesBarsI-beamsHigh speedsRequires shaped rolls, expensive equipmentLow to moderate labor costsModerate operator skill

    ISAT 430 Dr. Ken Lewis

    Module 7

    Forming and Shaping Processes3ForgingProduction of discrete parts with a set of dies.Some finishing operations usually necessaryUsually performed at elevated temperaturesDie and equipment costs are highRequiresModerate to high labor costModerate to high operator skillSimilar parts can be made by casting and powder-metallurgy techniques

    ISAT 430 Dr. Ken Lewis

    Module 7

    Forming and Shaping Processes4ExtrusionProduction of long lengths of solid or hollow products with constant cross sectionProduct is cut into desired lengthsCold extrusion has similarities to forging and is used to make discrete products.RequiresModerate to high die and equipment costsLow to moderate labor costsLow to moderate labor skill

    ISAT 430 Dr. Ken Lewis

    Module 7

    Forming and Shaping Processes5DrawingProduction of long rod and wire with round or various cross sections.Smaller cross section than extrusionGood surface finishRequiresLow to Moderate die and equipment costsLow to moderate labor costsLow to moderate labor skill

    ISAT 430 Dr. Ken Lewis

    Module 7

    Forming and Shaping Processes6Sheet metal formingProduction of a wide variety of shapes with thin wallsSimple or complex geometriesRequiresModerate to high die and equipment costsLow to moderate labor costsLow to moderate labor skill

    ISAT 430 Dr. Ken Lewis

    Module 7

    Forming and Shaping Processes7Powder MetallurgyProduction of simple or complex shapes by compacting and sintering metal powdersCompetitive with casting, forging, and machining processesRequiresModerate to high die and equipment costsLow labor costsLow labor skill

    ISAT 430 Dr. Ken Lewis

    Module 7

    Forming and Shaping Processes8Processing of plastics and composite materialsProduction of a variety of continuous or discrete productsExtrusion, spinning, molding, castingCan be competitive with metal partsRequiresModerate to high die and equipment costsHigh operator skill in composite fabrication

    ISAT 430 Dr. Ken Lewis

    Module 7

    Forming and Shaping Processes9Forming and shaping of ceramicsProduction of discrete ceramic products by a variety of waysShaping, drying , firing processesRequiresModerate to high die and equipment costsLow to moderate labor costsModerate to high labor skill

    ISAT 430 Dr. Ken Lewis

    Module 7

    RollingRolling is a process to reduce the thickness of a long workpiece by compressive forces applied through a set of rolls.

    First developed in the late 1500s

    ISAT 430 Dr. Ken Lewis

    Module 7

    Sequence of eventsA steel ingot is cast into a rectangular moldPlaced in a furnace while just solidified and held for many hours (36) until the temperature is uniform.This process is called soaking Furnaces are called soaking pits.Implies that properties will be uniform throughout the ingot and process that way.The rolling temperature for steel is about 1200CFrom here the ingot goes to the rolling mill.

    ISAT 430 Dr. Ken Lewis

    Module 7

    RollingStarting material depends upon what you are producing.BloomSquare cross section 6 x 6 in or largerSlabRolled from an ingot or a bloomRectangular cross section 10 x 1.5 in or moreBilletRolled from a bloomSquare cross section 1.5 x 1.5 in or larger.

    ISAT 430 Dr. Ken Lewis

    Module 7

    ISAT 430 Dr. Ken Lewis

    Module 7

    ISAT 430 Dr. Ken Lewis

  • Metal behavior in formingAn aside

    ISAT 430 Dr. Ken Lewis

    Module 7

    Stress -- strainElasticity below the elastic limitStrain hardening above it.In the plastic region, the metals behavior is expressed as:Where K = strength coefficient psi (MPa)n is the strain hardening exponent.

    ISAT 430 Dr. Ken Lewis

    Module 7

    Flow StressAs the metal deforms its strength increases (strain hardening)Thus the stress required to deform must be increasedFlow stressInstantaneous value of the stress needed to keep the metal flowingYf = flow stress MPa

    ISAT 430 Dr. Ken Lewis

    Module 7

    Average Flow StressThe average flow stress is the average stress needed over entire strain region.Just integrate the flow stress over the strain region of interest:

    ISAT 430 Dr. Ken Lewis

    Module 7

    Effect of Strain RateIn theory, a metal in hot working should be perfectly plastic with n = 0.The rate of metal deformation is directly related to the speed of deformation v.v is the velocity of the roll or ramh is the instantaneous height of the piece being deformed.

    ISAT 430 Dr. Ken Lewis

    Module 7

    Effect of Strain RateNote that if v is constant, the strain rate will increase with decreasing h.

    ISAT 430 Dr. Ken Lewis

    Module 7

    Effect of strain rateSimilar

    C is strength constantm is the slope, called the strain rate sensitivity exponent.

    The effect of temperature is pronounced.

    ISAT 430 Dr. Ken Lewis

    Module 7

    Effect of temperature on stress

    ISAT 430 Dr. Ken Lewis

    Module 7

    TemperatureCold working (~room temperature)AdvantagesaccuracySurface finishStrain hardening increases strengthGrain flow can provide directional propertiesNo heating required

    ISAT 430 Dr. Ken Lewis

    Module 7

    TemperatureCold working (~room temperature)DisadvantagesHigher forces and power neededPart must be dirt and scale free (stress risers)Ductility and strain hardening limit the amount forming that can be done without part fracture or cracking.

    ISAT 430 Dr. Ken Lewis

    Module 7

    TemperatureWarm Working (0.3Tm 0.5Tm)Working above room temperature but below recrystallization temperatures.AdvantagesLow forces and powerMore intricate work geometries possibleNeed for annealing may by reduced

    Tm = melting T.

    ISAT 430 Dr. Ken Lewis

    Module 7

    TemperatureHot working (0.5Tm 0.75Tm)The recrystallization temperature is about one half the melting point. So hot working is above these temperatureDisadvantagesDeformation process causes localized heating which can cause localized melting (bad Ju Ju)Scale formation increases as the temperature increases.Lower dimensional accuracyPoorer surface finishShorter tool life.Tm = melting T.

    ISAT 430 Dr. Ken Lewis

    Module 7

    TemperatureHot working (0.5Tm 0.75Tm)AdvantagesCan produce SIGNIFICANT PLASTIC DEFORMATION of the metal.Lower forces and powerBrittle metals can be hot worked.Strength properties are usually isotropicNo work hardeningTm = melting T.

    ISAT 430 Dr. Ken Lewis

  • Back to Flat Rolling

    ISAT 430 Dr. Ken Lewis

    Module 7

    Flat RollingA strip of thickness h0 enters the roll gap and leaves at a thickness of hf.The initial velocity V0 increases to Vf at the exit.Note that because the surface speed of the roll is constant, there must be relative sliding between the roll and the strip

    ISAT 430 Dr. Ken Lewis

    Module 7

    Flat RollingAt one point (no slip point), Vstrip = Vmill.To the left, the roll moves faster than the stripTo the right the roll moves slower than the stripFriction is necessaryToo much ruins the surface and costs powerToo little and nothing happens.

    ISAT 430 Dr. Ken Lewis

    Module 7

    Flat RollingThe draft is (h0 hf)The maximum draft is a function of the coefficient of friction and the big roll radius RHigher friction and bigger roll, the greater draft.CompareLarge tires and rough treads on tractors and off road vehicles.

    ISAT 430 Dr. Ken Lewis

    Module 7

    Flat RollingThe roll force F is shown as perpendicular to the strip (rather than perpendicular to the point of contact)Because R >>> hThe roll force may be estimated as:

    ISAT 430 Dr. Ken Lewis

    Module 7

    Flat RollingL = roll strip contact lengthw = strip widthYavg = average true stress on the strip in the roll gap

    ISAT 430 Dr. Ken Lewis

    Module 7

    Flat RollingEquation assumes no frictionThe higher , the further off the formula (low side).The power per roll can be estimated by assuming F acts in the middle of the arc of contactThe torque/roll is F x a so in S. I. Units (Newton, meters, seconds) the power per roll is:

    F is in NewtonsL is in metersN is rpm

    ISAT 430 Dr. Ken Lewis

    Module 7

    Flat RollingEquation assumes no frictionThe higher , the further off the formula (low side).The power per roll can be estimated by assuming F acts in the middle of the arc of contactThe torque/roll is F x a so in English Units (Pounds, feet, seconds) the power per roll is:

    F is in Pounds forceL is in feetN is rpm

    ISAT 430 Dr. Ken Lewis

    Module 7

    Example: An annealed copper strip, 9 in (228 mm) wide, and 1 inch (25 mm) thick is rolled to a thickness of 0.8 in (20 mm) in one pass. The roll radius is 12 in (300 mm), and the rolls rotate at 100 rpm. What is the roll force and power required?From Table 3.4 pg 51 Groover, K =