chapter 03- metal forming and sheet metal working

8/8/2019 Chapter 03- Metal Forming and Sheet Metal Working

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A Glance of Metal Forming:

A simple metallic geometry is transformed into desiredshape and size through plastic deformation

Requires high force to move and deform the materialto desired shape with little or no waste

Tools or dies impart pressure on the material in order

to form into desired shapesDivided in terms of hot metal working process andcold working processE.g. forging, roll forming, extrusion, drawing and sheetmetal forming(bending)


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Expensive equipment because of the large forceinvolved

Large capital expenditure because of heavy presses anddies

Suited for large number of parts only

Production rate is fast

Advantage for near net-shape forming


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N o or very small loss of material, little or no scrap

Increase in ductility (hot forming of cast ingots)

Increase in strength and hardness

High production rate, generate final shape in short time

Better mechanical and metallurgical properties

(strength, toughness, grain size)


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H ot working is performed above the recrystallization

temperature of the material and cold working isbelow the recrystallization temperature of the material.Recrytallization temperature the approximateminimum temperature at which completerecrystallization of a cold worked metal occurs within aspecified time.

Approximate temperature range :HW about 0.5 to 0.75 of the melting temperatureWW 0.3 to 0.6 melt temp of the materialCW less than 0.3 of the melting temperature of the material

Definition :


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N o strain hardening taking place

no limit on the amount of metal workingeven brittle materials can be hot worked

Higher amount of ductility

Requires much less force to achievenecessary deformation

G iving rise to mechanical properties

A favorable grain size

N ot effecting the yield strength, hardness orductility


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Some of the material cannot be hot workedbecause of their brittleness at hightemperature

Surface finish rather poor due to scaling athigh temperature

Dimensional accuracy is difficult to achievebecause of thermal expansion

Troublesome in handling and maintaining hotmetal

oor tolerance due to shrinkage


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Increase the strength and hardness due to strain hardening

G ood surface finish due to no oxide formed

Dimensional accuracy can be achieved

Far easier to handle since no heating is required

Improved strength, fatigue, and wear properties


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P roperties H ot Rolled C old Rolled

Ultimate tensile strength, MPa 427 558

Yield strength, MPa 220.5 345

Brinell Hardness N umber 94 174


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Limited by the capability of the presses and hammers used

Maximum amount of deformation is limited due to strainhardened

Some brittle material can not be hard worked

Higher forces are required and therefore heavy requirementis needed

Less ductility available


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Term applied to metal forming process of shaping and reducing metalthickness by pressing it between rolls

Defined as the process of reducing the thickness or cross section of a long workpiece by compressive forces applied through a set of rotating rolls

Flat rolling thinner and longer products from slab

Shape rolling hot rolling of structural shapes from billets andblooms


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Start with a raw material in some form, typically longdimension, either hot or cold

Hot rolled products such as sheets, plates, bars andstrips serve as input materials

Reduces thickness, change cross-section bycompressive forces

Converts metal ingots to simple stock member, i.e.blooms, slabs and billets using cylindrical rolls

Rawmaterial

Passingthrough

Rolls

Desiredshape


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SlabA semi finishedsteel productintermediatebetween ingotand plateRoughly 50-150mm thick,600-1500mmwide

BilletA semis finished,hot rolled orcontimuous castmetal productRectangularcross sectionmore than155mm x155mm

BloomA solid semifinished, hotrolled orcontinuous castmetal product of uniform sectionRectangular withrounded cornersand crosssection up to155mm

RodA solid roundwroughtproduct, long inrelation to itscross sectionCommonlydrawn into wireproducts or usedto make boltsand nails


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Source: Prof. Madya Mohd Yusuff Mohd,

Manufacturing Processes Course Manual 1A, 2009

chapter 03- metal forming and sheet metal working

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