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Metal Extrusion and Drawing Metal Extrusion and Drawing Processes and EquipmentProcesses and Equipment

Text Reference: “Manufacturing Engineering and Text Reference: “Manufacturing Engineering and Technology”, Kalpakjian & Schmid, 6/e, 2010Technology”, Kalpakjian & Schmid, 6/e, 2010

Chapter 15Chapter 15

ExtrusionExtrusionA cylindrical billet is forced through a die A cylindrical billet is forced through a die (‘push’)(‘push’)

DrawingDrawingThe cross section of solid rod wire orThe cross section of solid rod wire orThe cross section of solid rod, wire, or The cross section of solid rod, wire, or tubing is reduced or changed in shape by tubing is reduced or changed in shape by pulling it through a die (‘pull’)pulling it through a die (‘pull’)

FIGURE 15.1 FIGURE 15.1 Schematic illustration of the directSchematic illustration of the direct--extrusion process.extrusion process. ExtrusionExtrusionLarge deformations can take place without Large deformations can take place without fracture because material is under triaxial fracture because material is under triaxial compressioncompressionProduce products with constant cross Produce products with constant cross section; cut to lengthsection; cut to lengthsection; cut to lengthsection; cut to lengthA batch process; one length per billetA batch process; one length per billetLow tool costs; Economic for large & short Low tool costs; Economic for large & short production runsproduction runsPerform cold or at elevated temperatures; Perform cold or at elevated temperatures; depends on ductility of materialdepends on ductility of materialMaterials: Al, Cu, Steel, Mg, Pb, otherMaterials: Al, Cu, Steel, Mg, Pb, other

Extruded ProductsExtruded ProductsRailings for sliding doorsRailings for sliding doorsWindow framesWindow framesTubing (various, constant, cross sections)Tubing (various, constant, cross sections)Aluminum ladder framesAluminum ladder framesStructural & architectural shapesStructural & architectural shapesStructural & architectural shapesStructural & architectural shapesBrackets; Gears; Coat hangarsBrackets; Gears; Coat hangarsCold Extrusion (combine with forging)Cold Extrusion (combine with forging)

FastenersFastenersComponents for automobiles, bicycles, Components for automobiles, bicycles, motorcycles, heavy machinery, transportation motorcycles, heavy machinery, transportation equipmentequipment

FIGURE 15.2 FIGURE 15.2 Extrusions and examples of products made by Extrusions and examples of products made by sectioning off extrusions. sectioning off extrusions. Source: Source: Courtesy of Plymouth Extruded Courtesy of Plymouth Extruded

Shapes.Shapes.

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Extrusion ProcessExtrusion Process

Direct (or Forward) ExtrusionDirect (or Forward) ExtrusionBillet in chamber is pushed through die by hydraulic Billet in chamber is pushed through die by hydraulic ramram

Indirect (or Reverse, Inverted, Backward) Indirect (or Reverse, Inverted, Backward) ExtrusionExtrusion

The die moves toward the billetThe die moves toward the billetHydrostatic ExtrusionHydrostatic Extrusion

Billet in chamber is surrounded by fluidBillet in chamber is surrounded by fluidLateral (or Side) ExtrusionLateral (or Side) ExtrusionImpact ExtrusionImpact Extrusion

Punch descends rapidly on blank which is extruded Punch descends rapidly on blank which is extruded backwardsbackwards

FIGURE 15.3 FIGURE 15.3 Types of extrusion: Types of extrusion: (a) indirect; (b) hydrostatic; (c) lateral.(a) indirect; (b) hydrostatic; (c) lateral.

FIGURE 15.4 FIGURE 15.4 Process variables in direct extrusion. The die angle, Process variables in direct extrusion. The die angle, reduction in cross section, extrusion speed, billet temperature, and reduction in cross section, extrusion speed, billet temperature, and

lubrication all affect the extrusion pressure.lubrication all affect the extrusion pressure.

Extrusion ForceExtrusion ForceForce, F, depends on:Force, F, depends on:

Strength of billet materialStrength of billet materialExtrusion Ratio, R, AExtrusion Ratio, R, Aoo/A/Aff

Friction between billet and chamber & die surfacesFriction between billet and chamber & die surfacesProcess variables: temperature, velocityProcess variables: temperature, velocity

F = AF = A00k ln(Ak ln(A00/A/Aff)) Eq. 15.1Eq. 15.1

The Extrusion constant, k, is determined The Extrusion constant, k, is determined experimentally, see Figure 15.5experimentally, see Figure 15.5

FIGURE 15.5 FIGURE 15.5 Extrusion constant Extrusion constant kk for various metals at different for various metals at different temperatures.temperatures. Source: Source: After P. Loewenstein.After P. Loewenstein. Metal Flow in ExtrusionMetal Flow in Extrusion

Influences quality & mechanical properties Influences quality & mechanical properties of extruded productof extruded productMaterial flows longitudinallyMaterial flows longitudinallyMaterial flows longitudinallyMaterial flows longitudinallyElongated grain structureElongated grain structure

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FIGURE 15.6 FIGURE 15.6 Types of metal flow in extruding with square dies. Types of metal flow in extruding with square dies. (a) Flow pattern obtained at low friction or in indirect extrusion. (a) Flow pattern obtained at low friction or in indirect extrusion.

(b) Pattern obtained with high friction at the billet(b) Pattern obtained with high friction at the billet––chamber interfaces. chamber interfaces. (c) Pattern obtained at high friction or with cooling of the outer regions (c) Pattern obtained at high friction or with cooling of the outer regions

of the billet in the chamber. This type of pattern, observed in metals of the billet in the chamber. This type of pattern, observed in metals whose strength increases rapidly with decreasing temperature, leads to whose strength increases rapidly with decreasing temperature, leads to

a defect known as pipe (or extrusion) defect.a defect known as pipe (or extrusion) defect.

Hot ExtrusionHot ExtrusionUse higher temperatures to improve ductility & Use higher temperatures to improve ductility & metal flowmetal flowCan cause excessive die wear, result of abrasion Can cause excessive die wear, result of abrasion from surface oxidesfrom surface oxidesCan have nonuniform deformation caused by Can have nonuniform deformation caused by cooling surfaces of billet and diecooling surfaces of billet and diecooling surfaces of billet and diecooling surfaces of billet and die

Improve by preheating dieImprove by preheating dieSurface oxides on product may be undesirable Surface oxides on product may be undesirable when good surface finish is importantwhen good surface finish is importantCan prevent extrusion of surface oxides by Can prevent extrusion of surface oxides by making the diameter of the dummy block a little making the diameter of the dummy block a little smaller than the container; this keeps a thin smaller than the container; this keeps a thin shell shell (“skull”)(“skull”) of oxides in the containerof oxides in the container

Figure 15.1Figure 15.1TABLE 15.1 TABLE 15.1 Typical Extrusion Temperature Ranges for Various Typical Extrusion Temperature Ranges for Various

Metals and AlloysMetals and Alloys

FIGURE 15.7 FIGURE 15.7 Typical extrusionTypical extrusion––die configurations: die configurations: (a) die for nonferrous metals; (a) die for nonferrous metals;

(b) die for ferrous metals; (b) die for ferrous metals; (c) die for a T(c) die for a T--shaped extrusion made of hotshaped extrusion made of hot--work die steel work die steel

and used with molten glass as a lubricant.and used with molten glass as a lubricant.Source: Source: (c) Courtesy of LTV Steel Company.(c) Courtesy of LTV Steel Company.

Die DesignDie DesignSquare dies (shear dies)Square dies (shear dies)

Are used for nonferrous metals (Aluminum)Are used for nonferrous metals (Aluminum)Develop deadDevelop dead--metal zones, causing a ‘die metal zones, causing a ‘die angle’ of metal flowangle’ of metal flowHave burnishing at the interface between the Have burnishing at the interface between the deaddead--metal zone and die angle; result is a metal zone and die angle; result is a bright surface finishbright surface finish

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FIGURE 15.8 FIGURE 15.8 Extrusion of a seamless tube Extrusion of a seamless tube (a) using an internal mandrel that moves independently of (a) using an internal mandrel that moves independently of

the ram. (An alternative arrangement has the mandrel the ram. (An alternative arrangement has the mandrel integral with the ram.) integral with the ram.)

(b) using a spider die (see Fig. 15.9) to produce seamless (b) using a spider die (see Fig. 15.9) to produce seamless tubing.tubing.

FIGURE 15.9 FIGURE 15.9 (a) An extruded 6063(a) An extruded 6063--T6 aluminumT6 aluminum--ladder lock ladder lock for aluminum extension ladders. This part is 8 mm (5/16 in.) thick for aluminum extension ladders. This part is 8 mm (5/16 in.) thick

and is sawed from the extrusion (see Fig. 15.2). and is sawed from the extrusion (see Fig. 15.2). (b) through (d) Components of various dies for extruding intricate (b) through (d) Components of various dies for extruding intricate

hollow shapes.hollow shapes.Source: (b) through (d) after K. Laue and H. Stenger.Source: (b) through (d) after K. Laue and H. Stenger.

FIGURE 15.10 FIGURE 15.10 Poor and good examples of cross sections to be extruded. Poor and good examples of cross sections to be extruded. Note the importance of eliminating sharp corners and of Note the importance of eliminating sharp corners and of

keeping section thicknesses uniformkeeping section thicknesses uniform..Source: Source: J.G. Bralla (ed.), J.G. Bralla (ed.), Handbook of Product Design for ManufacturingHandbook of Product Design for Manufacturing. McGraw. McGraw--Hill Publishing Company, 1986. Used Hill Publishing Company, 1986. Used

with permission.with permission.

Die MaterialsDie Materials

For hot extrusion:For hot extrusion:Hot worked die steelsHot worked die steelsFor simple shapes without severe stressFor simple shapes without severe stressFor simple shapes without severe stress For simple shapes without severe stress gradients, may apply coatings (e.g. partially gradients, may apply coatings (e.g. partially stabilized zirconia) to extend die lifestabilized zirconia) to extend die life

LubricationLubricationUseful in hot extrusion:Useful in hot extrusion:

Material flow during extrusionMaterial flow during extrusionSurface finish & integritySurface finish & integrityProduct qualityProduct qualityExtrusion forcesExtrusion forces

Glass is excellent lubricant for:Glass is excellent lubricant for:Glass is excellent lubricant for: Glass is excellent lubricant for: Steels Steels Stainless steelsStainless steelsHighHigh--temperature metals & alloystemperature metals & alloys

Glass applied as powder to billet surface, orGlass applied as powder to billet surface, orInsert glass pad at die entrance; when heated, Insert glass pad at die entrance; when heated, melted glass lubricates die surfacemelted glass lubricates die surface

FIGURE 15.11 FIGURE 15.11 (a) Aluminum extrusion used as a heat sink for a printed circuit board, (a) Aluminum extrusion used as a heat sink for a printed circuit board,

(b) Extrusion die and extruded heat sinks.(b) Extrusion die and extruded heat sinks.Source: Source: Courtesy of Aluminum Extruders Council.Courtesy of Aluminum Extruders Council.

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Cold ExtrusionCold Extrusion

Uses slugs cut from cold finished or hot rolled Uses slugs cut from cold finished or hot rolled bars, wire, or platesbars, wire, or platesSmaller slugs (Smaller slugs (≤ 40 mm or 1.5”) are sheared; ≤ 40 mm or 1.5”) are sheared; ends squared if necessaryends squared if necessaryLarger slugs are machined to specific lengthsLarger slugs are machined to specific lengthsStresses on tool dies are very highStresses on tool dies are very highLubrication is critical, especially with steelsLubrication is critical, especially with steels

Apply phosphateApply phosphate--conversion coating on workpiece, conversion coating on workpiece, followed by soap or wax (Sec. 34.10) followed by soap or wax (Sec. 34.10)

FIGURE 15.12 FIGURE 15.12 Two examples of cold extrusion. Thin arrows indicate the Two examples of cold extrusion. Thin arrows indicate the

direction of metal flow during extrusion.direction of metal flow during extrusion.

Cold ExtrusionCold Extrusion

Force = F = 1.7AForce = F = 1.7AooYYavgavgέέ Eq. 15.2Eq. 15.2

AA is cross sectional area of blankis cross sectional area of blankAAoo is cross sectional area of blankis cross sectional area of blankYYavgavg is average flow stress of metalis average flow stress of metalέέ is true strain that piece undergoesis true strain that piece undergoes

= ln(A= ln(Aoo/A/Aff))

Advantages Cold vs. Hot ExtrusionAdvantages Cold vs. Hot Extrusion

Improved mechanical properties due to Improved mechanical properties due to work hardeningwork hardeningGood control of dimensional tolerancesGood control of dimensional tolerancesGood control of dimensional tolerancesGood control of dimensional tolerancesImproved surface finishImproved surface finishCompetitive production rates & costsCompetitive production rates & costs

FIGURE 15.13 FIGURE 15.13 Production steps for a coldProduction steps for a cold--extruded spark plug. extruded spark plug. Source: Source: Courtesy of National Machinery Company.Courtesy of National Machinery Company. FIGURE 15.14 FIGURE 15.14

A cross section of A cross section of the metal part in the metal part in Fig. 15.13, Fig. 15.13, showing the grainshowing the grain--flow pattern.flow pattern.

Source: Source: Courtesy of National Courtesy of National Machinery Company.Machinery Company.

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FIGURE 15.15 FIGURE 15.15 Schematic illustration of the Schematic illustration of the impactimpact--extrusion processextrusion process. . The extruded parts are stripped by the use of a stripper The extruded parts are stripped by the use of a stripper

plate, because they tend to stick to the punch.plate, because they tend to stick to the punch.

FIGURE 15.16 FIGURE 15.16 (a) Impact extrusion of a collapsible tube by the Hooker process. (a) Impact extrusion of a collapsible tube by the Hooker process. (b) and (c) Two examples of products made by impact extrusion. (b) and (c) Two examples of products made by impact extrusion. These parts also may be made by casting, forging, or machining. These parts also may be made by casting, forging, or machining.

The choice of process depends on the materials involved, part dimensions and The choice of process depends on the materials involved, part dimensions and wall thickness, and the properties desired. wall thickness, and the properties desired.

Economic considerations also are important in final process selection.Economic considerations also are important in final process selection.

Hydrostatic ExtrusionHydrostatic ExtrusionThe pressure required in the chamber is supplied The pressure required in the chamber is supplied via a piston through an incompressible fluid via a piston through an incompressible fluid medium surrounding the billetmedium surrounding the billetThe fluid in contact with die surfaces reduces The fluid in contact with die surfaces reduces frictionfrictionA cold process A cold process

The viscosity of the fluids used (vegetable oils such The viscosity of the fluids used (vegetable oils such as castor oil) does not change with heatas castor oil) does not change with heat

Can use to extrude brittle materialsCan use to extrude brittle materialsDuctility is increasedDuctility is increased

Limited applicationsLimited applicationsComplex tooling; specialized equipment; uneconomic Complex tooling; specialized equipment; uneconomic

Extrusion DefectsExtrusion DefectsSurface crackingSurface cracking

High extrusion temperature, friction, speed High extrusion temperature, friction, speed cause high surface temperaturescause high surface temperaturesCracks are intergranular (along grain Cracks are intergranular (along grain boundaries)boundaries)boundaries)boundaries)Caused by Caused by hot shortinghot shorting: local cooling of : local cooling of constituents or impurities at grain boundariesconstituents or impurities at grain boundariesMay also occur at lower temperaturesMay also occur at lower temperatures

Caused by sticking of extrusion along die landCaused by sticking of extrusion along die landSticking raises pressureSticking raises pressureCyclic action produces circumferential cracks, Cyclic action produces circumferential cracks, “bamboo effect”“bamboo effect”

Extrusion Extrusion DefectsDefects

continuedcontinued

PipePipe (aka (aka pipe defect, tailpipe, fishtailingpipe defect, tailpipe, fishtailing))MetalMetal--flow pattern in (c) tends to draw surface flow pattern in (c) tends to draw surface oxides and impurities toward the centre of the billetoxides and impurities toward the centre of the billetCan be minimized Can be minimized

By modifying flow pattern to be more uniformBy modifying flow pattern to be more uniformControl frictionControl frictionMinimize temperature gradientsMinimize temperature gradients

Improve billet surface by machining or etching to remove Improve billet surface by machining or etching to remove scale & surface impurities prior to extrusionscale & surface impurities prior to extrusion

Extrusion Defects Extrusion Defects (continued)(continued)

Internal CrackingInternal CrackingAka Aka centre cracking, centrecentre cracking, centre--burst, arrowhead burst, arrowhead fracture, chevron crackingfracture, chevron crackingThese cracks in the centre of the extrusion are These cracks in the centre of the extrusion are attributed to a state of hydrostatic tensile stressattributed to a state of hydrostatic tensile stressattributed to a state of hydrostatic tensile stress attributed to a state of hydrostatic tensile stress at the centreline in the deformation zoneat the centreline in the deformation zoneIncreases with increasing die angleIncreases with increasing die angleIncreases with increasing amount of impuritiesIncreases with increasing amount of impuritiesDecreases with increasing extrusion ratio & Decreases with increasing extrusion ratio & friction friction

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FIGURE 15.17 FIGURE 15.17 (a) Chevron cracking (central burst) in extruded round steel (a) Chevron cracking (central burst) in extruded round steel bars. Unless the products are inspected, such internal defects may remain bars. Unless the products are inspected, such internal defects may remain

undetected and later cause failure of the part in service. This defect can also undetected and later cause failure of the part in service. This defect can also develop in the drawing of rod, of wire, and of tubes. develop in the drawing of rod, of wire, and of tubes.

(b) Schematic illustration of rigid and plastic zones in extrusion. The tendency (b) Schematic illustration of rigid and plastic zones in extrusion. The tendency toward chevron cracking increases if the two plastic zones do not meet. Note toward chevron cracking increases if the two plastic zones do not meet. Note that the plastic zone can be made larger either by decreasing the die angle, that the plastic zone can be made larger either by decreasing the die angle,

by increasing the reduction in cross section, or both. by increasing the reduction in cross section, or both. Source: Source: After B. Avitzur.After B. Avitzur.

Extrusion EquipmentExtrusion Equipment

Horizontal Hydraulic PressHorizontal Hydraulic PressCan control stroke & speedCan control stroke & speedCan apply constant force over long strokeCan apply constant force over long stroke

Vertical Hydraulic PressVertical Hydraulic PressVertical Hydraulic PressVertical Hydraulic PressUsed for cold extrusionUsed for cold extrusionLower capacity, smaller footprintLower capacity, smaller footprint

FIGURE 15.18 FIGURE 15.18 General view of a 9General view of a 9--MN (1000MN (1000--ton) hydraulicton) hydraulic--extrusion press. extrusion press. SourceSource: Courtesy of Jones & Laughlin Steel : Courtesy of Jones & Laughlin Steel

Corporation.Corporation.

DrawingDrawingDrawn rods used for:Drawn rods used for:

Shafts, spindles, small pistonsShafts, spindles, small pistonsRaw material forRaw material for

Rivets, Bolts, Screws, NailsRivets, Bolts, Screws, Nails

R d d h d tiR d d h d tiRound and shaped cross sectionsRound and shaped cross sections‘Rod’ is larger diameter than ‘wire’‘Rod’ is larger diameter than ‘wire’‘Wire’ is reduced at least once from ‘rod’‘Wire’ is reduced at least once from ‘rod’The cross section of a long rod or wire is The cross section of a long rod or wire is reduced by pulling (or ‘drawing’) through reduced by pulling (or ‘drawing’) through a a “draw die”“draw die”

FIGURE 15.19 FIGURE 15.19 Process variables in wire drawing. The Process variables in wire drawing. The die angle, the reduction in crosssectional area per pass, the die angle, the reduction in crosssectional area per pass, the speed of drawing, the temperature, and the lubrication all speed of drawing, the temperature, and the lubrication all

affect the drawing force, affect the drawing force, F.F.

Drawing ForceDrawing Force

FrictionlessFrictionless

F = YF = YavgavgAAffln(Aln(Aoo/A/Aff)) Eq. 15.3Eq. 15.3

Friction & Redundant WorkFriction & Redundant Work

F = YF = YavgavgAAff[(1+[(1+μμ//αα)ln(A)ln(Aoo/A/Aff)+2)+2αα/3]/3] Eq. 15.4Eq. 15.4

αα is die angle, in radiansis die angle, in radians

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Drawing ForceDrawing Force

Drawing force increases as reduction Drawing force increases as reduction increasesincreasesMaximum ideal (no friction) theoretical Maximum ideal (no friction) theoretical reduction in cross sectional area per passreduction in cross sectional area per passreduction in cross sectional area per pass reduction in cross sectional area per pass is 63%is 63%There is an There is an optimum die angleoptimum die angle for for minimum force for a certain reduction in minimum force for a certain reduction in diameterdiameter

FIGURE 15.20 FIGURE 15.20 Examples of tubeExamples of tube--drawing operations, with and drawing operations, with and without an internal mandrel. Note that a variety of diameters and wall without an internal mandrel. Note that a variety of diameters and wall thicknesses can be produced from the same initial tube stock (which thicknesses can be produced from the same initial tube stock (which

has been made by other processes).has been made by other processes).

Drawing PracticeDrawing PracticeUsually, the smaller the initial cross section, the Usually, the smaller the initial cross section, the smaller the reduction per passsmaller the reduction per pass

Fine wires: 15 Fine wires: 15 –– 25% reduction25% reductionLarger wires: 20 Larger wires: 20 –– 45% reduction45% reduction

Usually a ‘cold’ process (room temperature)Usually a ‘cold’ process (room temperature)y p ( p )y p ( p )Sizing Pass Sizing Pass

A small reduction on rods to improve finish & A small reduction on rods to improve finish & dimensional accuracydimensional accuracyResults in nonResults in non--uniform deformation across sectionuniform deformation across section

Drawing Drawing Practice Practice

continuedcontinued

PointingPointing –– A ‘push’ operation to create a feathered A ‘push’ operation to create a feathered tip at start to be threaded through diestip at start to be threaded through diesDrawing speeds:Drawing speeds:Drawing speeds: Drawing speeds:

Depend on material & % reductionDepend on material & % reductionHigh speeds may raise temperatures, affecting propertiesHigh speeds may raise temperatures, affecting properties

TemperTemper::A designation for hardness (1/4 hard, ½ hard) due to A designation for hardness (1/4 hard, ½ hard) due to work hardeningwork hardeningMay need to anneal (soften) metal between passes to May need to anneal (soften) metal between passes to maintain ductilitymaintain ductility

Drawing Practice Drawing Practice continuedcontinued

Bundle DrawingBundle DrawingDraw many (100s) wires togetherDraw many (100s) wires togetherTo increase productivity, esp. fine wiresTo increase productivity, esp. fine wiresKeep wires separated by suitable metallic Keep wires separated by suitable metallic material, lower chemical resistance; later material, lower chemical resistance; later leachedleachedProduces polygonal xProduces polygonal x--sectionsection

Can alternatively produce fine wires of different Can alternatively produce fine wires of different size & shapesize & shape

FIGURE 15.21 FIGURE 15.21 Terminology pertaining to a typical die used for Terminology pertaining to a typical die used for drawing a round rod or wire.drawing a round rod or wire.

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Die DesignDie DesignDie angles usually 6Die angles usually 6oo to 15to 15oo

Two angles: entering & approachTwo angles: entering & approachLand Land

Sets final diameter of drawn wireSets final diameter of drawn wireMaintains diameter with wearMaintains diameter with wearMaintains diameter with wearMaintains diameter with wear

Profile DrawingProfile Drawing (non(non--round)round)Requires a set of dies, Requires a set of dies, Involves stages of deformationInvolves stages of deformationMay be one die or several in a retaining ringMay be one die or several in a retaining ringUse computerUse computer--aidedaided--design techniquesdesign techniques

FIGURE 15.22 FIGURE 15.22 TungstenTungsten--carbide die insert in a steel casing. carbide die insert in a steel casing. Diamond dies used in drawing thin wire are encased in a similar Diamond dies used in drawing thin wire are encased in a similar

manner.manner.

LubricationLubrication

To improve die lifeTo improve die lifeTo improve product surface finishTo improve product surface finishTo reduce drawing forcesTo reduce drawing forcesTo reduce temperatureTo reduce temperatureTo reduce temperatureTo reduce temperatureEspecially critical at mandrel/tube Especially critical at mandrel/tube interface for tube drawinginterface for tube drawingCommonly use phosphate coatingsCommonly use phosphate coatings

Methods of LubricationMethods of LubricationWet drawingWet drawing

Dies & rod are immersed in lubricantDies & rod are immersed in lubricantDry drawingDry drawing

Surface of rod is coated with lubricant in a stuffing box Surface of rod is coated with lubricant in a stuffing box prior to drawing through dieprior to drawing through dieprior to drawing through dieprior to drawing through die

Metal coatingMetal coatingCoat rod/wire with soft metal (Cu, Sn) that acts as solid Coat rod/wire with soft metal (Cu, Sn) that acts as solid lubricantlubricant

Ultrasonic VibrationUltrasonic VibrationVibrate dies & mandrels; Vibrations reduce forces, Vibrate dies & mandrels; Vibrations reduce forces, improve surface finish & die life; allow greater improve surface finish & die life; allow greater reductionsreductions

Drawing DefectsDrawing Defects

Centre Centre crackingcracking

Seams Seams Longitudinal scratches or foldsLongitudinal scratches or foldsMay open up in later forming operationsMay open up in later forming operationsCause serious qualityCause serious quality--control problemscontrol problems

Surface defects (scratches, die marks)Surface defects (scratches, die marks)Improper selection of process parametersImproper selection of process parametersPoor lubricationPoor lubricationPoor die condition (e.g. scratches)Poor die condition (e.g. scratches)

Residual StressResidual StressCaused by nonCaused by non--uniform deformation during cold uniform deformation during cold drawingdrawingLight reductionsLight reductions

LongitudinalLongitudinal--surface residual stresses are compressive; surface residual stresses are compressive; bulk is in tensionbulk is in tensionImprove fatigue lifeImprove fatigue lifeImprove fatigue lifeImprove fatigue life

Heavier reductionsHeavier reductionsSurface stresses in tension; bulk in compressionSurface stresses in tension; bulk in compression

Can be significant cause of stressCan be significant cause of stress--corrosion corrosion cracking over timecracking over timeMay cause part to May cause part to warpwarp if a layer is removed (as if a layer is removed (as part of a forming operation such as slitting, part of a forming operation such as slitting, machining, grinding)machining, grinding)

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FIGURE 15.23 FIGURE 15.23 Cold drawing of an extruded channel on a draw bench to Cold drawing of an extruded channel on a draw bench to reduce its cross section. Individual lengths of straight rods reduce its cross section. Individual lengths of straight rods

or of cross sections are drawn by this method.or of cross sections are drawn by this method.

FIGURE 15.24 FIGURE 15.24 An illustration of multistage wire drawing An illustration of multistage wire drawing typically used to produce copper wire for electrical wiring. typically used to produce copper wire for electrical wiring.

Source: Source: After H. Auerswald.After H. Auerswald.

SummarySummaryExtrusion:Extrusion: Push billet through die to reduce xPush billet through die to reduce x--sect; sect; Hot for lower force, better ductilityHot for lower force, better ductilityExtrusion FactorsExtrusion Factors: Die design; extrusion ratio; : Die design; extrusion ratio; billet temperature; lubrication; speed. Cold billet temperature; lubrication; speed. Cold improves some mechanical propertiesimproves some mechanical propertiesDrawing (rod, wire, tube):Drawing (rod, wire, tube): pulling through die(s); pulling through die(s); usually round; mandrels for tubesusually round; mandrels for tubesDrawing Factors:Drawing Factors: Die design, % reduction/pass, Die design, % reduction/pass, die materials, lubricantsdie materials, lubricantsExternal/internal defects minimized by die angle, External/internal defects minimized by die angle, % reduction, material quality % reduction, material quality