Transcription of E4 Warm and cold forging - EKO Endüstri
1 1 warm AND cold FORGINGPRECISION FORGINGCOLD HEADINGCOLD EXTRUSION2 Precision forgingMain characteristics: Closed die forging Temperature is below the hot range, itis warm forging (T~0,5*TmoK) Close tolerances, acceptable surfacefinish near net shaping process Good material yield Good mechanical properties3 Economic considerations Precision forging is more costly thanconventional forging , ..but! Savings in material and machiningcosts are significant Forming complex shapes is possible Precision forging represents a highervalue product than a conventionalforging (higher added value)4 Temperature of forgingLow alloy steels:950 .. 1150 oCHot forging540 .. 815 oCWarm forging < 250 oCCold forgingControlled cooling may be necessary afterforging to avoid distorsion and to control themicrostructure of the workoiece5 Tooling (1) Dimensions Allowances (thermal contraction, machining) Draft angles, no sharp corners goodmaterial flow Workability High deformation levels needs goodformability Try to avoid cracking!
2 6 Tooling (2) Precision: Tolerance bands of tool: of theworkpiece High-precision machining (EDM) Rigid alignment Preform considerations (volume, weighting, appropriate shape) Conditions: good lubrication, removecontaminants, good control of billet and tooltemperature7 forging equipment Billet separation: shearing or sawing Heating: Furnace oxide formation Induction heating Resistance heating Presses: Hammers Crank presses Hydraulic presses8 Comparison of forgings9 cold forging Processes: Upsetting cold forging of components Effect of cold working on material properties the ductility of the material drops, strengths and hardness increases (because of higher dislocation density - strain hardening) the microstructure changes, crystals (grains) become elongated in the direction of major deformation10 cold heading To upset the metal in a portionof wire or rod blank The cross-sectional area ofthe initial material is increasedas the height of the workpieceis decreased variants: Free (head formed between flatpunch and die) Closed (head formed in punchand die)11 Limits of deformationMaterial dependent: dD kD3,2 dLMaterial independent:12 Calculation of forceWhere.
3 Kfflow stressAcross-sectional areaR radius of headhheight of head coefficient of friction)Rh321(AfkF +=13 Two-stroke upsetting If L/d > 2,3 then twooperations areneeded: Preforming Finish heading Preforming head: conic-cylindrical Finish: closedheading punch14 Example: screwhead heading reduction shearingshearing15 Example: screws and bolts16 Example: heading Closed-die cold heading Die can be opened for feeding and removing theworkpiece17 Head shearing18 cold extrusion of parts Principle: a punch applies pressure tothe preform or billet, causing the workmetal to flow in the required direction Process variants: Direct indirect or forward backward Extrusion of rod, can and hollow part Single or combined operations19 Forward extrusion of rodbilletpunchdieworkpiece20 Backward extrusion of canbilletpunchworkpiecediecounter punch21 Combined : forward andbackward extrusion of canpunchdiecounter punchworkpiecebillet22 Combined: forward extrusion ofrod, backward extrusion of candieworkpiecepunchcounter punchbillet23 cold extrusions Forward extrusion of rod Back extrusion of can Forward extrusion of can24 Extrusion pressure and force Extrusion pressure:where:kfmmean flow stress logarithmic strain.
4 Ln(Ao/A1) coefficient of extrusion (0, ,7) fmkp=25 Extrusion pressure and force Punch load (force)F = p A Work (energy)W = c F h(c=0, ,8) where: A cross sectionalarea h punch travelLoadPunchtravel hFmaxW26 Materials and lubrication Good formability: mild steel, copper, aluminium Medium formability:low alloy steels, Zn Preparation for cold forging : Surface treatment Lubrication Forging27 Equipment Machines: Crank presses Knuckle-joint presses Hydraulic presses Special purpose cold forging and headingmachines Requirements: Sufficient flywheel energy and loadcapacity Rigid frame28 Pressescrank press knuckle-joint press29 Automated pressCoining andsizingColdheadingPreformingof headFeeding, shearing30 cold forging Machines31 cold forged parts32 Example: multiple-step forging123 Forward extrusionof rod, backextrusion of canand rodForwardextrusionof hollowpart radialextrusion33 Example: multiple-step forgingRadialextrusionPiercingBackextrus ionof canBillet34 Example: production of nut35 Comparison of material yield andenergy forging4185 warm forging4185 cold forgingEnergy, 106J/kgMaterialyield, %Process
