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IE370Lecture16

IE370Lecture16 - BULK DEFORMATION PROCESSES IN METALWORKING...

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1 BULK DEFORMATION PROCESSES IN METALWORKING Rolling Other Deformation Processes Related to Rolling Forging Other Deformation Processes Related to Forging Extrusion Wire and Bar Drawing Bulk Deformation Metal forming operations which cause significant shape change by deformation in metal parts whose initial form is bulk rather than sheet Starting forms: cylindrical bars and billets, rectangular billets and slabs, and similar shapes These processes work by stressing metal sufficiently to cause plastic flow into desired shape Performed as cold, warm, and hot working operations Importance of Bulk Deformation In hot working, significant shape change can be accomplished In cold working, strength can be increased during shape change Little or no waste - some operations are near net shape or net shape processes - The parts require little or no subsequent machining Four Basic Bulk Deformation Processes 1. Rolling – slab or plate is squeezed between opposing rolls 2. Forging – work is squeezed and shaped between between opposing dies 3. Extrusion – work is squeezed through a die opening, thereby taking the shape of the opening 4. Wire and bar drawing – diameter of wire or bar is reduced by pulling it through a die opening
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2 Rolling Deformation process in which work thickness is reduced by compressive forces exerted by two opposing rolls Figure 19.1 - The rolling process (specifically, flat rolling) The Rolls The rotating rolls perform two main functions: Pull the work into the gap between them by friction between workpart and rolls Simultaneously squeeze the work to reduce cross section Types of Rolling By geometry of work: - Flat rolling - used to reduce thickness of a rectangular cross-section - Shape rolling - a square cross-section is formed into a shape such as an I-beam By temperature of work: - Hot Rolling – most common due to the large amount of deformation required - Cold rolling – produces finished sheet and plate stock Figure 19.2 - Some of the steel products made in a rolling mill
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3 Figure 19.3 - Side view of flat rolling, indicating before and after thicknesses, work velocities, angle of contact with rolls, and other features Flat Rolling – Terminology Draft = amount of thickness reduction f o t t d - = where d = draft; t o = starting thickness; and t f = final thickness Flat Rolling – Terminology Reduction = draft expressed as a fraction of starting stock thickness: o t d r = where r = reduction Shape Rolling Work is deformed into a contoured cross-section rather than flat (rectangular) Accomplished by passing work through rolls that have the reverse of desired shape Products include: - Construction shapes such as I-beams, L-beams, and U-channels - Rails for railroad tracks - Round and square bars and rods
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4 Flowchart of Rolling Operations Figure 16-1 Flow chart for the production of various finished and semifinished steel shapes. Note the abundance of rolling operations. (Courtesy of American Iron and Steel Institute, Washington, D.C.)
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