Production Technology - Metal Forming Operations PDF

Production Technology Lect. : Metal Forming Operations Associat. Prof. Mohamed A. Bhlol  Topics Metal Forming Definition Types of deformation processes Classification of Metal Forming Processes Bulk Forming Processes (rolling, Forging, Extrusion, Wire Drawing)...

Production Technology Lect. : Metal Forming Operations Associat. Prof. Mohamed A. Bhlol  Topics Metal Forming Definition Types of deformation processes Classification of Metal Forming Processes Bulk Forming Processes (rolling, Forging, Extrusion, Wire Drawing) Sheet Metal processes (Bending, Deep Drawing, Shearing)  Metal Forming Definition ❑ Metal forming is a process in which the desired size and shape are obtained through the deformation of metals plastically under the action of externally applied forces.  Metal Forming Definition Stresses in Metal Forming ❑ Stresses to plastically deform the metal are usually compressive. Examples: rolling, forging, extrusion ❑ However, some forming processes stretch the metal (tensile stresses). ❑ Others bend the metal (tensile and compressive) ❑ Others apply shear stresses (shearing)  Metal Forming Definition Starting materials in metal forming Manufacturing companies producing metals supply them in form of ingots which are obtained by casting liquid metal. Sometimes continuous casting methods are also used to cast the liquid metal into slabs, blooms or billets. These shapes are further processed by forming operations, to produce materials in standard form such as plates, sheets, rods, tubes and structural sections.  Metal Forming Definition Slabs Blooms Billets - Rectangular cross sections - produced from the Ingot - produced from Blooms - Used as starting by forging or strand cast - Round or square cross material for flat - used in manufacture of : Section prodcuts such as: steel structural profiles, rails - used for: plates Or hot rolled and columns. bars, rods, pipes, coils. tubes, wire Metal Forming Definition  Types of deformation processes ❑Three temperature ranges in metal forming: Cold working Warm working Hot working Deformation processes Hot Warm Cold Deformation Deformation Deformation  Types of deformation processes Cold working (deformation) ❑ Performed at room temperature or slightly above. ❑ Occurs at temperature below the recrystallization temperature. ❑ Minimum or no machining usually required. Advantages of Cold Forming Better accuracy, closer tolerances Better surface finish Strain hardening increases strength and hardness No heating of work required  Types of deformation processes Cold working (deformation) Disadvantages of Cold Forming ❑ Higher forces and power required in the deformation operation ❑ Ductility and strain hardening limit the amount of forming that can be done ❑ In some cases, metal must be annealed to allow further deformation ❑ In other cases, metal is simply not ductile enough to be cold worked  Types of deformation processes Warm working (deformation) ▪ Performed at temperatures above room temperature but below recrystallization temperature ▪ Dividing line between cold working and warm working often expressed in terms of melting point: (0.3-0.5)Tm Where: Tm = melting point (absolute temperature) for metal)  Types of deformation processes Hot working (deformation) Deformation at temperatures above the recrystallization temperature Recrystallization temperature = about one-half of melting point on absolute scale In practice, hot working usually performed somewhat above 0.6Tm Metal continues to soften as temperature increases above 0.6Tm, enhancing advantage of hot working above this level  Types of deformation processes Advantages of Hot Working ▪ Workpart shape can be significantly altered. ▪ Lower forces and power required. ▪ Metals that usually fracture in cold working can be hot formed. ▪ No strain hardening occurs during forming. ▪ Large amount of deformation/pass Disadvantages of Hot Working Lower dimensional accuracy in case of bulk forming Higher total energy required (due to the thermal energy to heat the workpiece) Work surface oxidation (scale), poorer surface finish Shorter tool life Classification of Metal Forming Processes  Bulk Deformation Processes ❑ Characterized by significant deformations and massive shape changes ❑ "Bulk" refers to work parts with relatively low surface area-to-volume ratios ❑ Starting work shapes include cylindrical billets and rectangular bars ❑ Mostly done in hot working conditions.  Bulk Deformation Processes Rolling process In this process, the workpiece in the form of slab or plate is compressed between two rotating rolls in the thickness direction, so that the thickness is reduced. The rotating rolls draw the slab into the gap and compresses it. The final product is in the form of sheet.  Bulk Deformation Processes Types of Rolling Based on Based on No. and Based on work workpiece arrangement of temperature geometry rolls – Flat rolling - used to – Hot Rolling – most Two high roll mill reduce thickness of a common due to the Three high roll mill rectangular cross section large amount of Four high roll mill deformation required Cluster roll mill – Shape rolling - square Planetary roll mill. cross section is formed - Cold rolling – Tandem roll mill into a shape. produces finished sheet and plate stock  Bulk Deformation Processes Typical arrangement of rollers for rolling mills Two-High Rolling Mill Three-High Rolling Mill Four-High Rolling Mill  Bulk Deformation Processes Typical arrangement of rollers for rolling mills Cluster rolling mill Planetary rolling mill Tandem Rolling Mill  Bulk Deformation Processes ❑ Some Rolling processes 1) Thread Rolling ❑ Deformation process used to form threads on cylindrical parts by rolling them between two dies  Bulk Deformation Processes Some Rolling processes 2) Ring Rolling ❑ Deformation process in which a thick-walled ring of smaller diameter is rolled into a thin-walled ring of larger diameter.  Bulk Deformation Processes Some Rolling processes 3) Shaped or section Rolling ❑ special type of cold rolling in which flat slap is progressively bent into complex shapes by passing it through a series of driven rolls.  Bulk Deformation Processes Forging process ❑ The workpiece is compressed between two dies containing shaped contours. ❑ The die shapes are imparted into the final part.  Bulk Deformation Processes Classification Of Forging Processes ❑ Forging processes can be classified by the degree to which the flow of the material is constrained during the process. (a) open-die forging (b) impression-die forging (c) flashless forging  Bulk Deformation Processes Classification Of Forging Processes (a) Open-die forging ▪ It is the process in which the work is compressed between two flat dies, that do not constrain the work during the process. Thus, allowing metal to flow laterally without constraint.  Bulk Deformation Processes (b) Impression-die forging (closed die forging) ▪ is a hot bulk forming process. It is a pressure forming process where shaped dies are moved towards one another so that the material is forced in a certain direction, taking on the shape of the cavity in the die. ▪ Workpiece is formed under high pressure in a closed cavity. ▪ Some material is not constrained by the cavities and flows outward from the die, this material is called flash.  Bulk Deformation Processes (b) Impression-die forging (closed die forging)  Bulk Deformation Processes (c) Flashless forging In flashless forging the entire work piece is contained within the die in such a way that no material can flow out of the die cavity during the compression of the part, hence no flash is produced. Often classified as a precision forging process  Bulk Deformation Processes (c) Flashless forging  Bulk Deformation Processes Extrusion process ❑ In this process, the workpiece is compressed or pushed into the die opening to take the shape of the die hole as its cross section.  Bulk Deformation Processes Wire drawing process ❑ similar to extrusion, except that the workpiece is pulled through the die opening to take the cross-section.  Sheet metalworking processes ❑ Forming and related operations performed on metal sheets, strips, and coils ❑ High surface area-to-volume ratio of starting metal, which distinguishes these from bulk deformation ❑ Often called pressworking because presses perform these operations ❑ Parts are called stampings Usual tooling: punch and die  Sheet metalworking processes Bending process ❑ In this, the sheet material is strained by punch to give a bend shape (angle shape) usually in a straight axis.  Sheet metalworking processes Deep or cup drawing process ❑ In this operation, forming of a flat metal sheet into a hollow or concave shape like a cup, is performed by stretching the metal in some regions. ❑ A blank-holder is used to clamp the blank on the die, while the punch pushes into the sheet metal. ❑ The sheet is drawn into the die hole taking the shape of the cavity.  Sheet metalworking processes Shearing process ❑ This is nothing but cutting of sheets by shearing action. Thank you