HOT WORKING PROCESSES

HOT WORKING PROCESSESPRESENTED TO: DR. TAHIRPRESENTED BY:E13-300 ASAD AHMED E13-303- RANA HAMZA E13-304 SHAAF AMJADE13-305 RAZI ULLAHDEPARTMENT OF METALLURGICAL AND MATERIALS ENGINEERINGUNIVERSITY OF THE PUNJAB

HOT WORKINGHot working refers to processes where metals are plastically deformed above their recrystallization temperature.Being above the recrystallization temperature allows the material to recrystallize during deformation. This is important because recrystallization keeps the materials from strain hardening.This keeps the yield strength and hardness low and ductility high.Deformation energy requirements are less than for cold work. The lower limit of the hot working temperature is determined by its recrystallization temperature. The upper limit for hot working is determined by excessive oxidation, grain growth, undesirable phase transformation.

HOT WORKING PROCESSESFOLLOWING ARE SOME OF THE FAMOUS HOT WORKING PROCESSESRollingForgingExtrusionDrawingROLLINGIt is ametal formingprocess in whichmetalstock is passed through one or more pairs ofrollsto reduce the thickness. commonly, hot working tooling is heated to 500850F (325450C).Rolling is classified according to the temperature of the metal rolled. If the temperature of the metal is above the recrystallizationtemperature, then the process is known ashot rolling.The principle of this process is that most metal rolling operations are similar in that the work material is plastically deformed by compressive forces between two constantly spinning rolls. These forces act to reduce the thickness of the metal and affect its grain structure. The reduction in thickness can be measured by the difference in thickness before and after the reduction, this value is called the draft.

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ADVANTAGESFollowing are the advantages of metal rolling:

1. Required tools are inexpensive and can be manufactured fast.2. Short manufacturing time and prompt delivery.3. Excellent strength/weight ratio.4. Relatively little waste.

FORGINGMetal forgingis a metal forming process that involves applying compressive forces to a work piece to deform it, and create a desired geometric change to the material.Metal forging, specifically, can strengthen the material by sealing cracks and closing empty spaces within the metal. The hot forging process will highly reduce or eliminate inclusions in the forged part by breaking up impurities and redistributing their material throughout the metal work.Forging is often classified according to the temperature at which it is performed: cold forging (a type ofcold working), warm forging, or hot forging (a type of hot working).

FORGINGAll of the following forging processes can be performed at various temperatures, however they are generally classified by whether the metal temperature is above or below the recrystallization temperature. If the temperature is above the material's recrystallization temperature it is calledhot forging.If the temperature is below the material's recrystallization temperature but above 30% of the recrystallization temperature (on an absolute scale) it is called aswarm forging; if below 30% of the recrystallization temperature (usually room temperature) then it is calledcold forging.

WORKINGAoAdforcedieblankforceoften atelev. TEXTRUSIONA bar of metal is forced through a die orifice by a compressive force that is applied to a ramThe extruded piece that emerges has the desired shape and a reduced cross-sectional area.Extrusion products include rods and tubing, but shapes of irregular cross-sections may be produced form the more readily extrudable metals, like Al.Extrusion is increasingly utilized in the working of metals difficult to form, like stainless steels, Ni-based alloys, and other high-temperature materials

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DRAWINGDrawing is the pulling of a metal piece through a die having a tapered bore by means of a tensile force that is applied on the exit sideRod, wire and tubing products are commonly fabricated in this way.Wiredrawing usually starts with a coil of hot-rolled rodDraw speeds vary from about 30 to 300 ft/minIn general, the term wire refers to small diameter products under 5 mm that may be drawn rapidly on multiple-die machines.

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REFERENCES

1. Hot Working Guide: A Compendium of Processing Maps edited by Y. V. R. K. Prasad, S. Sasidhara. 2. Handbook of Workability and Process Designedited by George E. Dieter, Howard A. Kuhn, S. Lee Semiatin.3. Hot Deformation and Processing of Aluminum Alloys by Hugh J. McQueen, Stefano Spigarelli, Michael E. Kassner, Enrico Evangelista.4. Materials Processing and Manufacturing ScienceBy Rajiv Asthana, Ashok Kumar, Narendra B. Dahotre. Page no. 35.5. slideshare.net6. www.wikipedia.com