FORMING PROCESSOPEN DIE FORGING ANDCLOSED DIE FORGINGN PRAKASANME METALLURGY
FORGING PROCESSESFORGING PROCESSESThe two broad categories of Forgingprocesses are,1) Open Die Forging2) Closed Die Forging(or Impression die forging)
1) Open Die Forging1) Open Die ForgingOpen die forging is carries out between two flatdies or simple shapes.This process is used mostly for large objectsand smaller quantities.It is also used to preform the work piece forclosed die forging.
1) Open Die Forging1) Open Die ForgingAdvantagesSimple, inexpensive dies; widerange of sizes; good strengthLimitationsSimple shapes only; difficult tohold close tolerances;machining necessary; lowproduction rate; poor utilizationof material; high skill required
2) Closed Die Forging2) Closed Die ForgingThe work piece is deformed between twodie halves which carry the impressionsof the desired final shape.It uses carefully machined matching dieblocks to produce forgings to closedimensional tolerances.Normally used for smaller components
2) Closed Die Forging2) Closed Die ForgingThe basic steps in Closed die forging:1) The Billet is usually Fullered (reduce thecross sectional area) and Edged (shapethe ends and gather metal) to use themetal for subsequent forging.
2) Closed Die Forging2) Closed Die Forging2) The pre-shaped billet is placed in the cavity ofthe blocking die and rough – forged to the finalshape. The greatest change in the shape of themetal occurs in this step.3) The part is transferred to the finishing die toforge to get final shape and dimensions.4) Removal of Flash with a trimming die.Forging dies must be tapered to facilitate removal ofthe finished part. This draft allowance is approximately 5Ofor steel forgings.
2) Closed Die Forging2) Closed Die Forging• FlashWhen the dies come together for the finishingstep, the excess metal squirts out of the cavityas a thin ribbon of metal called Flash.In order to prevent the formation of a very wideflash, a flash gutter is provided.
2) Closed Die Forging2) Closed Die ForgingPurposes of Flash• Flash regulates the escape of metal and thusthin flash increases the flow resistance of thesystem so that the pressure builds up to highvalues to ensure that metal fills all recesses ofthe die cavity.• Flash acts as a ‘safety valve’ for excess metalin the closed die cavity.
2) Closed Die Forging2) Closed Die ForgingForging pressure increases with decreasingflash thickness and increasing flash width.
2) Closed Die Forging2) Closed Die ForgingEffective forging operation requires anunderstanding of,• Flow stress of the material• Frictional conditions• Metal flow in order to develop the optimumgeometry for the dies. Metal flow consists of two basic types,• Extrusion – Flow parallel to the direction of the die motion• Upsetting – Flow perpendicular to the direction of the diemotion
2) Closed Die Forging2) Closed Die Forging• Closed die design:The design of a part for production by closed dieforging involves the prediction of,• Work piece volume and weight• Number of preforming steps and theirconfiguration• Flash dimensions in preforming and finishingdies• The load and energy requirement for eachforging operation
2) Closed Die Forging2) Closed Die ForgingAdvantagesGood utilization of material; betterproperties than open die forging;good dimensional accuracy; highproduction rate; goodreproducibilityLimitationsHigh die cost for small quantities;machining often necessary
2) Closed Die Forging2) Closed Die Forging• Example : Die set and forging steps for themanufacturing of Automobile engine connectingrod:
References:References:Mechanical Metallurgy by Dieter, G.E.Lecture Notes, Suranaree university oftechnology