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Forging Calculations

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Forging operations Edging is used to shape Edging is the ends of the bars and to gather metal. The metal flow is confined in the horizontal direction but it is free to flow laterally to fill the die. www.jsc-pfm.com Drawing is used to reduce the cross-sectional area of Drawing is the workpiece with concurrent increase in length. Piercing and punching are punching are used to produce holes in metals. Suranaree University of Technology Tapan Tap any y Ud Udomp ompho holl Jan-Mar 2007 Forging operations Fullering is used to reduce the cross-sec Fullering is cross-sectional tional area of a portion of the stock. The metal flow is outward out ward and away from the centre of the fuller. f uller. i.e., forging of connecting rod for an internalcombustion engine. • Fulle Fullerr move move fast and and moves moves metal metal perpendicular to the face Fullers come in different shapes www.anvilfire.com Fullers Suranaree University of Technology Tapan Tap any y Ud Udomp ompho holl Jan-Mar 2007 Forging operations Swaging is used to produce a bar with a smaller Swaging is diameter (using concave dies). • Swag Swaging ing is a special special type type of forging forging in which metal is formed by a succession of rapid hammer blows Swaging at the ends, ready for next forming process. Suranaree University of Technology • Swag Swaging ing provides provides a reduced reduced round round cross section suitable for tapping, threading, upsetting or other subsequent forming and machining operations. Tapan Tap any y Ud Udomp ompho holl Jan-Mar 2007 Classification of forging processes By equipment  1) Fo Forg rgin ing g hamme hammerr or dr drop op ham hamme merr 2) Press fo forging By process 1) Open - die forging 2) Closed - die forging Suranaree University of Technology Tapan Tap any y Ud Udomp ompho holl Jan-Mar 2007 Forming machines There are four basic types of forging machines Suranaree University of Technology Tapan Tap any y Ud Udomp ompho holl Jan-Mar 2007 Hammer and press forging processes Forging hammers There are two basic types of forging hammers used; • Board hammer  • Power hammer  Forging presses There are two basic types of forging  presses available; available; • Mechanical presses • Hydraulic presses Suranaree University of Technology Tapan Tap any y Ud Udomp ompho holl Jan-Mar 2007 Board hammer –forging hammer  • The upper upper die and and ram are are raised raised by friction rolls gripping the board. • After relea releasing sing the board board,, the ram falls falls under gravity to produce the blow energy . • The hammer hammer can can strike strike between between 60-150 blows per minute depending on size and capacity. • The board board hammer hammer is is an energy energy-restricted machine. The blow energy supplied equal the potential the potential energy due energy due to the weight and the height of the fall. Potential energy = mgh Board hammer  Suranaree University of Technology …Eq 1 • This energy energy will will be delivere delivered d to the metal metal workpi wor kpiece ece to produce produce plastic  plastic deformation.. deformation Tapan Tap any y Ud Udomp ompho holl Jan-Mar 2007 Forging hammer or drop hammer  • Provide rapid rapid impact blows blows to the surface of the metal. • Die Dies s are are in two two halve halves s - Lower : fixed to anvil  Belt - Uppe Upperr : moves moves up and and down with with the TUP. TUP. • Energy (from a gravity gravity drop) drop) is adsorbed adsorbed onto the the metal, in which the maximum impact is on the metal surface. TUP Metal  Anvil • Dies are expensiv expensive e being accurately accurately machined machined from special alloys (susceptible to thermal shock). • Drop forging is forging is good for mass production of complex shapes. Drop hammer Suranaree University of Technology Tapan Tap any y Ud Udomp ompho holl Jan-Mar 2007 Example: Forging hammer or drop hammer The energy supplied by the blow is equal to the potential energy due to the weight of the ram and the height of the fall. Potential energy = mgh …Eq 1 Forging machine Suranaree University of Technology Tapan Tap any y Ud Udomp ompho holl Jan-Mar 2006 Power hammer  • Power hammer provides hammer provides greater capacity, in which the ram is accelerated  on the downstro downstroke ke by steam steam or air pressure pressure in addition to gravity. • Stea Steam m or air pressur pressure e is also used used to raise raise the ram on the upstroke. • The total energy supplied energy supplied to the blow in a power drop hammer is given by  W  = 1 2 mv 2 +  pAH  = (mg  +  pA) H  Where Power hammer  Suranaree University of Technology …Eq 2  m = mass v  = velocity of ram at start of deformation g  = acceleration of gravity  p = air or steam pressure acting on ram cylinder on downstroke  A = area of ram cylinder  H = height of the ram drop Tapan Tap any y Ud Udomp ompho holl Jan-Mar 2007 Hydraulic press forging  High pressure fluid • Usi sin ng a hydraulic press or a mechanical  press to forge the metal, therefore, gives continuous forming at a slower rate. Ram • Prov Provide ide deeper deeper pene penetratio tration. n. • Bette Betterr properties properties (more (more homogeneo homogeneous). us). Die Metal • Eq Equi uipm pmen entt is expensive expensive.. Die Hydraulic press Suranaree University of Technology Tapan Tap any y Ud Udomp ompho holl Jan-Mar 2007 Example: Hydraulic Press forging • Hydraulic presses are loadrestricted machines in which hydraulic pressure moves a piston in a cylinder. • The full full press press load is available available at any point during the full stroke of the ram. Therefore, hydraulic presses are ideally suited for extrusion-type forging operation. operation. • Due to slow slow spe speed, ed, contact time is longer at longer at the die-metal interface, which causes problems such as heat lost from workpiece and die deterioration. • Also provide provide closeclose-toler tolerance ance forging. forging. • Hyd Hydraulic raulic pres presses ses are more expensive than mechanical presses and hammers. Suranaree University of Technology Tapan Tap any y Ud Udomp ompho holl Jan-Mar 2007 Mechanical press forging  • Cran Crank k press transla translates tes rotary rotary motion into into reciprocating linear motion of the press slide. • The ram stroke stroke is short shorter er than in a hammer hammer or hydraulic press. • Pres Presses ses are are rated on the the basis of the the force developed at the end of the stroke. • The blow press is more like squeeze than like the impact of the hammer, therefore, dies can be less massive and die life is longer than with a hammer. • The total energy supplied energy supplied during the stroke of a press is given by Mechanical press 1 W  =  I [ω o2 − ω  f  2 ] 2 …Eq 3 Where  I  is moment of inertia of the flywheel ω is angular velocity, ω  after deformation, rad.s-1 ωo   -original, ω  ωf   - after Suranaree University of Technology Tapan Tap any y Ud Udomp ompho holl Jan-Mar 2007 Typical values of velocity for different forging equipment  Forging machine Velocity range, ms-1 Gravity drop hammer 3.6-4.8 Power drop hammer 3.0-9.0 HERF machine 6.0-24.0 Mechanical press 0.06-1.5 Hydraulic press 0.06-0.30 Remark:: HERF – High Energy Remark Energy Rate Rate Forging Forging Suranaree University of Technology Tapan Tap any y Ud Udomp ompho holl Jan-Mar 2007 Closed and open die forging processes Open-die forging Closed-die forging Impression-die forging Suranaree University of Technology Tapan Tap any y Ud Udomp ompho holl Jan-Mar 2007 Open-die forging  • Open-die forging is forging is carried out between flat dies or dies of very simple shape. • The proce process ss is is used used for for mostly large objects or when the number of parts produced is small. • Open Open-die -die forging forging is often often used to preform to  preform the workpiece for closed-die forging. Suranaree University of Technology Tapan Tap any y Ud Udomp ompho holl Jan-Mar 2007 Closed-die forging (or impression-die forging) • The workpiec workpiece e is deformed deformed between between two die halves which carry the impressions of the desired final shape. • The workpie workpiece ce is deformed deformed under under high high pressure in a closed cavity. • Nor Normal mally ly used used for for smaller components. components. • The process process provid provide e precision precision forging forging with close dimensional tolerance. tolerance. • Cl Clos osed ed die dies s are are expensive expensive.. Suranaree University of Technology Tapan Tap any y Ud Udomp ompho holl Jan-Mar 2007 Closed-die forging operation billet Preshaped Rough-forge Die cavity completely filled    d   a   o    l   g   n    i   g   r   o    F Flash begins to form Dies contact workpiece Trimming die Final product   e    t   e    l   p   m   o   c   g   n    i   g   r   o    F Forging stroke Typical curve of forging load vs. stroke for closed-die forging. Suranaree University of Technology Finishing die Flash is the excess metal, which squirts out of the cavity as a thick ribbon of metal. Tapan Tap any y Ud Udomp ompho holl Jan-Mar 2007 Functions of flash The flash serves two purposes: • Ac Acts ts as a ‘safety value’ value’ for excess metal. • Bu Buil ilds ds up high pressure to ensure that the metal fills all recesses of the die cavity. Remark: It is necessary to achieve complete filling of the forging cavity without generating excessive pressures against the die that may cause it to fracture. Suranaree University of Technology Tapan Tap any y Ud Udomp ompho holl Jan-Mar 2007 Example: Die set and forging steps for the manufacturing of an automobile engine connecting rod  • Preforming of Preforming  of a round piece in an open die arrangement. • Roug Ro ugh h sh shap ape e is fo form rmed ed us usin ing g a bl bloc ock k di die. e. • The Th e fin finis ishi hing ng di die e is is use used d to to bri bring ng th the e par partt to to final tolerances and surface finish. • Remo Re mov val of fla flas sh (exce cess ss me meta tal) l).. Steering knuckle Rail  Flange http://www.hirschvogel.de/en/produkti  onsverfahren/warmumformung.php See simulation Suranaree University of Technology Tapan Tap any y Ud Udomp ompho holl Jan-Mar 2007 www.nitrex.com Die materials Required properties • Therm Thermal al shock shock resis resistanc tance e • Therm Thermal al fatigu fatigue e resista resistance nce • High temp temperatu erature re stren strength gth Forging die Die materials: alloyed steels (with Cr, Mo, W, V ), ), to tool ol st stee eels ls cast steels or cast iron (Heat treatments such are nitriding or chromium plating are required to improve die life) , • Hig High h wear wear resista resistance nce • Hg Hgh h to toug ughn hnes ess s and and du duct ctili ility ty • Hig High h hard hardenab enabili ility ty . • High dimensiona dimensionall stability stability during hardeni hardening ng • Hig High h mach machina inabil bility ity Note: 1) Carbon steels with 0.7-0.85% C are appropriate for small tools and flat impressions. 2) Me Medi dium um-a -all lloy oyed ed too tooll ste steel els s for hammer dies. 3) Hi High ghly ly al allo loye yed d ste steel els s for high temperature resistant dies used in  presses and horizontal horizontal forging machines. Suranaree University of Technology Tapan Tap any y Ud Udomp ompho holl Jan-Mar 2007 Die materials Common steels used for forging dies Forging materials Forging dies Die inserts Steels Copper and copper alloys DIN AISI DIN AISI Light alloys DIN AISI C70 W2 - C85 W2 - 60MnSi4 - X30WCrV53 H21 X30WCrV53 - 40CrMnMo7 - X38CrMoV51 H11 X38CrMoV51 H11 X32CrMoV33 H10 55NiCrMoV6 6F2 55NiCrMoV6 56NiCrMoV7 6F3 56NiCrMoV7 6F2 57NiCrMoV77 - 35NiCrMo16 - X38CrMoV51 57NiCrMoV77 - 57NiCrMoV77 6F3 H11 X30WCrV93 H21 X38CrMoV51 H11 X32CrMoV33 H10 X32CrMoV33 H10 X32CrMoV33 H10 X30WCrV53 - X30WCrV52 - X30WCrV53 - X37CrMoW51 H12 Suranaree University of Technology Tapan Tap any y Ud Udomp ompho holl Jan-Mar 2007 Die materials Die life can be increased by 1) Impro Improving ving die materia materials ls such such as using using compo composite site die or or 2) Usin Using g surfa surface ce coat coating ing or selfself-lubri lubricating cating coatin coatings gs Ultra hard surface coatings Future forging Current forging Ultra hard surface coating on die surface is used to I    n   m   n  o   a  t   v  a   e  r   t  i    i    a  l    v  e   s   d    i    e   • Imp Improv rove e die die life life..  c e   f a   r   u   s  e   n   v   i   t   t  o   i o   v a  c a  o   i   f   i   n  n  d   I  o   m • Re Reduc duce e energy energy inpu input. t. • Re Redu duce ce die die-r -rela elate ted d up upti time me and downtime. http://www.eere.energy.gov/industry/supporting_industries  /pdfs/innovative_die_materials.pdf   /pdfs/innovative_di e_materials.pdf  Suranaree University of Technology • Redu Reduce ce particu particulate late emis emission sion from lubricants. Tapan Tap any y Ud Udomp ompho holl Jan-Mar 2007 Die failures Different types of die failure Wear (abrasion) Thermal fatigue Mechanical fatigue Permanent deformation • Diffe Different rent parts parts of of dies are liable liable to perm permanent anent deform deformation ation and wea wearr resulting from mechanical and thermal fatigue. fatigue. • Important factors: shape of the forging, die materials, how the workpiece is heated, coating of die surface, surface, the operating operating temperature (should not exceed the annealing temperature). Suranaree University of Technology Tapan Tap any y Ud Udomp ompho holl Jan-Mar 2007 Calculation of forging loads The total energy required energy required for deformation process; U total  = U ideal + U friction + U redundant  Note: redundant work work = work work that does not contribute contribute to shape change of the workpiece η is Efficiency of Efficiency  of a given deformation process η η  = U ideal  U total  Note: η  η  = 0.3-0.6 for extrusion = 0.75-0.95 for rolling  = 0.10-0.20 for closed die forging  The calculation for forging load can can be divided into three cases according to friction friction:: • In the absence of friction • Low friction condition (lower bound analysis or sliding condition) • High friction condition (sticky friction condition) Suranaree University of Technology Tapan Tap any y Ud Udomp ompho holl Jan-Mar 2007 1) In the absence of friction By assuming that there is no friction at die-workpiece interface, the forging load is therefore the compressive force (P ) acting on a round metal bar. Then  P  = σ o A Where P  ….Eq. 4 is the compressive force is the yield stress of the metal is the cross sectional area of the metal. σ  σo    A  And the compressive stress ( p  p ) produced by this force force P  P can can be obtained from Do  p = D ho h  Do2 h =  D 2 h Where h ho Do 4 Ph  D π  2 → 4 Ph 2 o o  D π  h = 4σ o Ah 2 o o  D π  ….Eq. 5  h Note: from volume constant is the instantaneous height of the metal bar during forging is the original height of the metal bar  is the original diameter of the t he metal bar. Suranaree University of Technology Tapan Tap any y Ud Udomp ompho holl Jan-Mar 2007 Do D ho h We have engineering strain in compression, e= ∆h ho = h − ho ….Eq. 6  ho  And true strain in compression, h ε  = ∫ ho dh h = ln h ho = − ln ho h ….Eq. 7  The relationship between e and ε  ε is ε  = Suranaree University of Technology ln(e + 1) Tapan Tap any y Ud Udomp ompho holl ….Eq. 8  Jan-Mar 2007 2) Low friction condition (Lower bound analysis) By considering considering the equilibrium of forces forces acting acting on the workpiece at any instant of deformation. • For example, example, if we consider consider the effect effect of friction friction on an upset forging operation in plane in plane strain condition (rigid-plastic behaviour, see Fig ). ). • To cal calcu culat late e the the total forming load , we have to determine the local stresses needed to deform each element of a workpiece of height h and width 2a 2a.. • In plane strain condition condition,, as the workpiece is reduced in height, it expands laterally and all deformation is confined in the x-y  the x-y plane. plane. This lateral expansion causes frictional forces to act in opposition to the movement. • Assu Assuming ming that there there is no no redundant work  and the material exhibits rigid-plastic behaviour , and all stress on the body are compressive. Suranaree University of Technology Tapan Tap any y Ud Udomp ompho holl Jan-Mar 2007 • Cons Consider ider the force force acting acting on a vertica verticall element of unit length and width dx . The element is at some distance x  distance  x from from the central ‘no-slip ‘no-slip’’ po poin int, t, in in this this case to the right. • The vertical force acting on the element is  stress × area = σ  y dx ….Eq. 9 • If the coefficien coefficientt of friction for for the die-workp die-workpiece iece interface is µ  µ,  the magnitude of the friction force will be µσ y dx. The frictional force acts at both ends of the element so the t he total horizontal force µσ y dx. from the right is 2 µσ  • Acti Acting ng on the the left will will be the the force force σ  σ x    h and from the right the force ( σ  σ x    +d σ  σ x    )h. The horizontal compressive stress σ  σ x    varies from a maximum at the centre of the workpiece to zero at the edge and changes by d σ  σ x    across the element width dx . Suranaree University of Technology Tapan Tap any y Ud Udomp ompho holl Jan-Mar 2007 Balancing the horizontal horizontal forces acting on the element: h(σ  x + d σ  x ) + 2µσ  y dx = hσ x ….Eq. 10  Rearranging, we have 2µσ  y dx = − hd σ  x ….Eq. 11 and therefore d σ  x =− σ  y Suranaree University of Technology Tapan Tap any y Ud Udomp ompho holl 2 µ  h dx ….Eq. 12  Jan-Mar 2007  As the frictional force force µσ y  is usually much smaller than both σ  σ x    and σ  σy    , which are principal stresses. Thus we can use them in the yield criterion when the slab will yield σ  y Where σ ‘ o − σ  x = 2 3 σ o = σ o' ….Eq. 13 is the yield stress in plane strain. Differentiation of the yield condition gives d σ  σy    = d σ  σ x    , and substituting for d σ  12 gives σ x    in Eq. 12 gives d σ  y =− σ  y 2µ  h dx ….Eq. 14 Integrating both sides of this differential equation gives ln σ  y = − 2 µ  x h + C o ….Eq. 15  or  σ  y   2 µ  x  = C exp −  h     ….Eq. 16  where C o is a constant of integration. Suranaree University of Technology Tapan Tap any y Ud Udomp ompho holl Jan-Mar 2007 We can evaluate C  C by by looking at the boundary conditions. At the edge of the σ   σ  workpiece where x = a, σ  σ x    = 0 and from the yield criterion σ  σy    -  σ  σ x    = σ  σ ‘ o, so σ  σy    = σ  σ‘   o and therefore:   2 µ a  ' C exp −  = σ o ….Eq. 17    h   ' σ o  2µ a  exp  h     σ  σy    ' σ o Friction hill so C  = ' σ o  2µ a  exp  h      2µ  (a − x )  h  exp  σ  ‘ o  σ‘  ….Eq. 18  a -a σ o  X  Using this in Eq.16 , we find σ  y  2µ   = σ o' exp  (a − x )  h  Suranaree University of Technology ….Eq. 19 x = -a Tapan Tap any y Ud Udomp ompho holl x=0 x=a Jan-Mar 2007  _   P  = 2  p aw The total forging load, P , is given by Where  p w  ….Eq. 20  is the average forming pressure across the workpiece is the width of the workpiece (in the plane of the paper). This equals σ  Eq.19:: σy    and can be estimated by integrating Eq.19 −  p = a ∫ σ  y o a a dx = ∫ o ' σ o a  2 µ  (a −  x )dx  h  exp  ….Eq. 21 The integration in Eq. 18 can 18 can be simplified if we make the following approximation to Eq. 16 . The general series expansion for exp x is x is exp x = 1 +  x + Since µ  µ is  x 2 2! + x3 3! + ... ….Eq. 22  usually small (<1) we can approximate exp x as (1+x) for small x . Suranaree University of Technology Tapan Tap any y Ud Udomp ompho holl Jan-Mar 2007 Thus we can approximate Eq.19 as  2µ (a −  x )  = σ o' 1 +  h  σ  y ….Eq. 23 and Eq.21 becomes  _   p = a ∫  2µ (a −  x )  1+ dx a  h ' σ o 0 ….Eq. 24 Integrating this gives: a  2 µ ax µ  x 2   p =  x + −   a  h h 0  _  ' σ o ….Eq. 25  So that the average axial tooling pressure, p, is  _      '  p = σ o 1 + µ a   h   ….Eq. 26  We can see that as the ratio a/h increases, the forming pressure p and hence the forming load rises rapidly. Suranaree University of Technology Tapan Tap any y Ud Udomp ompho holl Jan-Mar 2007 Example: The flash has high deformation resistance than in the die (due to much higher a/h ratio), therefore the material completely fills the cavity rather than being extruded sideward  sideward out out of the die. Suranaree University of Technology Tapan Tap any y Ud Udomp ompho holl Jan-Mar 2007 3) High friction condition (sticky friction) In the situation where the friction force is high, the stress acting on the metal is σ  y  a −  x   = σ o'  − 1   h   ….Eq. 27  and the mean forging pressure is  _    a   + 1  2h    p = σ o'  ….Eq. 28  Under these conditions, the forming load is dependent on the flow stress of the material and the geometry of the workpiece. For example: example: if the a/h ratio is high, say a/h = 8, then p = 5 σ  σ’   o. The local stress on the tooling can therefore be very high indeed in deed and 5 σ  σ’    o  is probably high enough to deform the tooling in most cold forming operation. Solutions: • re redu duci cing ng µ  µ to ensure that sticking friction conditions do not apply. • chan changing ging the the workpiece workpiece geometry geometry.. • re redu duci cing ng σ  σ’   o by increasing the temperature. Suranaree University of Technology Tapan Tap any y Ud Udomp ompho holl Jan-Mar 2007 In the case of sticky friction, friction, if we replace the force µσ y  with k (the average shear stress of the material) in Eq.14 d σ  y =− σ  y h ….Eq. 14 dx  _  then we have d σ  y = − 2 k  h Integrating Since then 2µ  dx = − σ  y= σ  σy    = σ  σ’   o at x = a, 2σ o dx −σ o' 3 h  x h = −σ o' dx h + C  C  = σ o' + σ o' ….Eq. 29 a ….Eq. 30  ….Eq. 31 h Replacing C  C in in Eq. 30 we 30 we then have σ  y = −σ o' Suranaree University of Technology  x h + σ o' + σ o'  a −  x   = σ o'  + 1 h   h   a Tapan Tap any y Ud Udomp ompho holl Or Eq. 27  Jan-Mar 2007 Example: Dieter, page 574-575   A block of lead 25x25x150 25x25x150 mm3 is pressed between flat dies to a size 6.25x100x150 mm3. If the uniaxial flow stress σ  σo   = 6.9 MPa and µ  µ = 0.25, determine the pressure distribution over the 100 mm dimension (at x  (at x = = 0, 25 and 50 mm and the total forging load in the sticky st icky friction condition. Since 150 mm dimension does not change, change, the deformation is plane plane strain. From Eq.19 Eq.19.. 2  2µ   where σ o' = 2 σ o a−x  σ  y = σ o exp 3   h 3 ( )   At the centreline of the slab slab ( x =  x = 0 ) σ max = 2(6.9) 3  2(0.25) (50 − 0) = 435MPa  6.25  exp  Likewise, Likewi se, at 25 25 and 50 mm, the str stress ess dis distri tribut bution ion wi willll be be 58.9 58.9 and 8.0 MPa respectively. Suranaree University of Technology Tapan Tap any y Ud Udomp ompho holl Jan-Mar 2007 The mean forging load (in the sticky friction condition) from Eq.28  Eq.28 is is  _   p =  _   p = 2 3   a   + 1  2h   σ o  2(6.9)   50   + 1 = 39.8 MPa  3  12.5   We calculate the forging load on the assumption that the stress distribution is based on 100 percent sticky friction. Then The forging load is P Suranaree University of Technology = stress x area = (39.8x106)(100x10-3)(150x10-3) = 597 kN = 61 tonnes. Tapan Tap any y Ud Udomp ompho holl Jan-Mar 2007 Effect of forging on microstructure grain structure resulting from (a) forging, (b) machining and (c) casting. • The formation formation of a grain grain structure structure in forged forged parts is elongated in the direction of the deformation. • The metal metal flow durin during g forging forging provides provides fibrous microstructure (revealed by etching). This structure gives better mechanical properties in the plane of maximum strain but (perhaps) lower lo wer across the thickness. • The workp workpiece iece often often under undergo go recrystallisation recrystallisation,, therefore, provide finer grains compared to the cast dendritic structure resulting in improved mechanical properties. Suranaree University of Technology Tapan Tap any y Ud Udomp ompho holl Jan-Mar 2007 Forming textures Redistribution of metal structures occurring during forming process involves two principle components; 1) redistribution of inclusions and 2) crystallographic orientation of the grains 1) The redistr redistributi ibution on of of inclusi inclusions ons Redistribution during forming of (a) soft inclusions (b) hard inclusions Suranaree University of Technology Tapan Tap any y Ud Udomp ompho holl Jan-Mar 2007 Forming textures 2) Crystallographic orientation of the grains Castings Forgings Cast iron structure Fibre struct structure ure in forged stee steels ls Mainly epitaxial, dend de ndri ritic tic or equi eq uiax axed ed gr grai ains ns Suranaree University of Technology Redistribution of grains in the working directions Tapan Tap any y Ud Udomp ompho holl Jan-Mar 2007 Residual stresses in forging • The residual stress produced in forgings as a results of inhomogeneous deformation are generally small because the deformation is normally carried out well into the hot-working region. • How Howeve ever, r, apprecia appreciable ble residual stresses and warping can warping can occur on the quenching of steel forgings in heat treatment. • Larg Large e forgings forgings are subjected subjected to the formation formation of small cracks, or flakes at the centre of the cross section. This is associated with with the high hydrogen content usually present in steel ingots of large size, coupled with the presence of residual stresses. • Larg Large e forgings forgings therefo therefore re have have to be slowly cooled from cooled from the working temperature. Examples: burying burying the forging forging in ashes ashes for a period of time or using a controlled cooling furnace. • Finit Finite e element element analysis analysis is used to pred predict ict residual residual stress stresses es in forgi forgings. ngs. Suranaree University of Technology Tapan Tap any y Ud Udomp ompho holl Jan-Mar 2007 Typical forging defects • Inc Incomp omplet lete e die filling filling.. files.bnpmedia.com Fluorescence penetrant  reveals Forging laps • Die mis misalig alignme nment. nt. • Fo Forg rgin ing g laps laps.. • Incom Incomplete plete forgin forging g penetrat penetrationion- should forge on the press. • Mic Micros rostru tructu ctural ral differ differenc ences es res result ulting ing in pronounced property variation. • Hot shortne shortness, ss, due due to high sulphur sulphur concentration in steel and nickel. www.komatsusanki.co.jp See simulation Suranaree University of Technology Tapan Tap any y Ud Udomp ompho holl Jan-Mar 2007 Typical forging defects www.mece.ualberta.ca • Pitte Pitted d surface, surface, due to oxide oxide scales occurri occurring ng at high temperature stick on the dies. • Buc Buckling kling,, in upsetting upsetting forging. forging. Subjec Subjectt to high compressive stress. • Surf Surface ace crackin cracking, g, due to tempera temperature ture differential between surface and centre, or excessive working of the surface at too low temperature. • Micr Microcra ocracking cking,, due to residual residual stress. stress. http://upload.wikimedia.org  Buckling  Suranaree University of Technology Tapan Tap any y Ud Udomp ompho holl Jan-Mar 2007 Typical forging defects Cracking at the flash Cold shut or fold Internal cracking • Flash line crack , after trimming-occurs more often in thin workpieces. Therefore should increase the thickness of the t he flash. • Cold shut or fold , fold , due to flash or fin from prior forging steps is forced into the workpiece. • Internal cracking, due to secondary tensile stress. Suranaree University of Technology Tapan Tap any y Ud Udomp ompho holl Jan-Mar 2007 Summary • Mainly hot forging  –  – Blacksmith, now now using water power, power, steam, electricity, hydraulic machines. • Heavy forging  - Hyd Hydraulic raulic press = slow slow,, high high forc force e squee squeeze. ze. - Pieces up to 200 200 tonnes with with forces up to 25,000 25,000 tonnes. - Simple tools squeeze squeeze metal into shape shape (open-die forging). - Sufficient deformation deformation must must be given to break up the ‘as cast ’ structure. - Reheating is often needed to maintain sufficient sufficient temperature for hot working. - Forg Forging ing is costly costly but eliminates eliminates some some as-cast as-cast defects defects - Co Cont ntin inuo uous us ‘grain flow ’ in the direc direction tion of metal flow is revealed by etching. - Impu Impurities rities (inclusio (inclusions ns and segregation) segregation) have become become elongated and (unlike casting) gives superior properties in the direction of elongation. Suranaree University of Technology Tapan Tap any y Ud Udomp ompho holl Jan-Mar 2007 References • Di Diet eter er,, G.E., G.E., Mechanical metallurgy , 1988, SI metric edition, McGraw-Hill, ISBN 0-07-100406-8. • Edw Edwards, ards, L. and and Endean, Endean, M., Manufacturin Manufacturing g with materials, materials, 1990, Butterworth Heinemann, ISBN 0-7506-2754-9. • Be Bedd ddoe oes, s, J. J. and and Bibb Bibbly ly M. M.J. J.,, Principles of metal manufacturing  process,, 1999, Arnold, ISBN 0-470-35241-8.  process • La Lang nge, e, K., K., Handbook of metal forming , 1919, McGraw-Hill Book company, ISBN 0-07-036285-8. • Lectu Lecture re note, Sheffie Sheffield ld University University,, 2003. • Metal forming forming proces processes, ses, Prof Prof Manus. Manus. Suranaree University of Technology Tapan Tap any y Ud Udomp ompho holl Jan-Mar 2007