INTRODUCTION AND CONCEPTS OF ROLLING, FORGING
INTRODUCTION AND CONCEPTS OF ROLLING, FORGING AND EXTRUSIONIn mechanical working process the raw material is the metal in some form which is subjected toexternal force.The raw material is obtained by pouring molten metal into a metallic mould and aftersolidification the solid metal is taken out. This will have a given cross section such as square orrectangle or circular etc,. and of a given length. This is referred to as Ingot.Typical Ingot MouldIngot is the starting raw metal for all metal working process.Molten metal from the furnace is taken and poured into metal moulds and allowed to cool orsolidify. The cooled solid metal mass is then taken out of the mould. This solid metal is referredto as Ingot.This Ingot is later on converted to other forms by mechanical working.Let us see the conversion throughRolling and ForgingRolling: It is a process wherein the ingot is passed between the gaps of two rotating rolls to getdeformation. It is similar to sugar cane juice making . Here there will be two rotatingcylindrical rolls between which sugar cane is passed and crushed to get the juice. The sugar caneis getting crushed.Forging: Here the metal is pressed between two hard surfaces to get a reduced section.
It is similar to pressing a model clay ball between two fingers or palms. The clayto smaller thickness.gets crusheda) Rolling Route*Molten metal poured into metal moulds and cooled Ingot ( 250x250mm)*Ingot rolled Blooms( 200x200mm)*Bloom rolled Billets( 150x150mm)*Billet rolled Bars/Rods( 40x40mm)*Bar drawn into Wires( 5mm dia.)*Billet rolled Slabs(t b)*Billet rolled Structural shapes I,U,L,V etc.*Slabs Plates(t b and t 4mm)*Plate Sheets(t 4mm) Foils(microns)b)Forging Route*Ingot Open die Blooms Billets Bars*Ingot Closed die Shaped objects like crank shaft, spanner, connecting rod etc.,As said earlier one has to apply external force or load or stress to bring about the deformation inthe metal.We shall learn what types of stresses are present in each of the mechanical working process.*Rolling --- Direct Compressive StressHere Plastic deformation takes place in metal when passed through a set of two rotatingcylindrical rolls.As the hot metal is passed through the gaps of two rotating rolls the metal is dragged inside andthe compression of the metal takes place and the cross section is reduced. During the processthere is a contact point at the start and an exit point at the other end. During these points themetal is in complete contact with the rolls and the metal experiences direct compressive stress asshown in the figure.*Forging ----- Direct Compressive StressHere a simple open type forging is taken for discussion. There will be two flat hard surfacescalled as dies. The gap between the dies can be adjusted and the metal is placed between the twodies and load is applied. When the dies press against the metal it gets squeezed and the crosssection is reduced. The metal will experience direct compressive stress. Fig.shows this.
*Extrusion and Wire Drawing Indirect CompressionHere a conical die is used for deforming the metal. The die is a converging one.In Extrusion the metal is pushed from one end towards the conical opening and the cross sectionis reduced.In Wire drawing the metal is pulled from the front end of the conical end and the cross section isreduced.In both cases the metal is subjected to indirect compressive stress.Fig. shows this.Extrusion*Bending of Sheet ----Bending StressTwo dies with matching contours are used. The metal in the form of sheet is placed on thebottom die and the top die is brought in contact with the metal and force is applied and the metaltakes the contour of the dies. The metal is subjected to differential stresses on either side of thesheet resulting in bending stresses in the metal. Fig. shows this.
*Stretching of Sheet ---Tensile StressHere sheet metal is held between grippers and the sheet is made to press against a contouredmandrel. The process is repeated to get a permanent change in the shape. Normally this is used todeform large surfaces. The sheet is being stretched and hence experiences tensile stresses. Fig.shows this.*Shearing of Sheet ----Shear StressThis is used to cut the sheet into two pieces. Here two sharp edges called as shears areused(similar to scissors). The sheet metal is kept between the two shears and force is applied.The metal pieces get separated. Fig. shows this.
Source : vtu-e-notesmpiii-2.pdf
*Forging ----- Direct Compressive Stress Here a simple open type forging is taken for discussion. There will be two flat hard surfaces called as dies. The gap between the dies can be adjusted and the metal is placed between the two dies and load is applied. When the dies press against the
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diameter bar hot-rolling procedure has been refined after studying the influences of processing parameters such as micro-structure of continuous rolling billet, rolling start temperature, continuous rolling deformation ratio, rolling line rate, and control cooling parameters on microstructure and properties of IN718 bars.
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rolling at 10,20,30,40 and 50% deformations in thickness using a two-high rolling mill at ambient temperature. This work examines the effect of rolling on mechanical properties like ductility, Ultimate Tensile Strength (UTS) and Hardness (BHN) behave with the increase in the percentage of rolling from 0 to 50 percent.
