Lecture 7 Metal Forming Fundamentals.pdf

5 Pages
169 Views
Unlock Document

Department
Mechanical Engineering
Course
308806
Professor
Alokesh Pramanik
Semester
Spring

Description
Lecture 7: Metal Forming Fundamentals Saturday, 2 November 2013 9:07 PM • Introduction: Definition of metal forming; stresses in forming processes • Variables: Independent and dependent • ProcessModelling • General parametersin Metal Forming: Material characteristics, friction, lubrication • Temperatureclassification of forming Metal Forming • Utilizes a remarkableproperty of metals (and alloys), their ability to flow plastically in the solid state without deteriorationof properties • Plastic deformation:permanent deformation,non-recoverableafter unloading, involves permanent atomic displacements • In metal forming, the tool, usually called a die, applies stresses that exceed the yield strength of the metal. The metal takes a shape determined by the geometryof the die • Advantages: ○ Good mechanical properties of product ○ Favourable grain flow ○ Little waste ○ Cast structure improved,cast defects eliminated ○ No handling of molten • Disadvantages ○ High forces required to deform materials ○ Machinery and tooling often expensive ○ Most economicalfor large quantities Stresses in Metal Forming • Stresses used in metal forming to plastically deform the metal are usually compressive;typical examples are rolling, forging and extrusion • Howeversome forming processes apply other stresses: ○ Stretching: Tensile stresses ○ Bending: Tensile and compressing ○ Shearing: Shear stresses Rolling: Biaxial compression Forging: Triaxial compression Extrusion: Triaxial compression Wire & Tube Drawing: Biaxial compressionand Tension Straight bending: Biaxial tension Deep Drawing: Biaxial tension & compressionand simple and Biaxial compression uniaxial tension Material properties in forming • The mechanical properties of materials desirable in metal forming processes are: • The mechanical properties of materials desirable in metal forming processes are: ○ High ductility: allow for large plastic deformation ○ Low yield strength: Allow for lower deformationforces ○ Values of strain hardening exponent n appropriate: high n is better in shearing, low n better in cold rolling • Materials with these desirable properties are called malleable materials or are said to have good formabilityor workability Independent Variables • Selected or controlled by engineer • Choice of material ○ Initial properties and characteristics ○ Choice dictated by: ease of fabrication, desirable properties (eg. Corrosion resistance), suitability for application • Starting geometryof workpiece ○ Dictated by previous processing ○ Selected from available shapes ○ Economicconsiderations • Tool or die geometry ○ Area of major significance: induces and controls metal flow, affects process success or failure ○ Examples:Diameter/profileof rolling mill roll, die angle extrusion, bend radius and bend angle and die cavity details • Lubrication ○ Up to 50% of power can be used to overcomefriction ○ Other functions: coolants, thermal barriers, corrosion inhibiters, parting compounds ○ Lubricant specifications: Lubrication type, applied amount, methodof application • Starting temperature ○ Temperatureselection and control ○ Temperaturesof workpiece and tooling ○ Affected material properties ○ As temperatureincreases: material strength decreases, ductility increases, rate of strain hardening decreases • Speed of operation ○ Affects productivity ○ Range of speeds available ○ Direct influence also on required force for deformation,lubricant effectiveness,time for heat transfer, speed of deformation(strain rate) • Amount of deformation ○ Depends on material:ductility at forming temperature ○ Controlled by tool design: eg. Impression-die forging ○ Adjusted by operator:eg. Flat rolling • Independent variables affect dependent variables Dependant Variables • Consequences of independent variables • Limited control by engineer • Force or power requirements ○ Depends on material, tool geometry,lubricant, speed of operation, starting temperature ○ Needed to select: appropriate equipment, tool or die materials ○ Estimationnecessary to optimize process • Material properties of product ○ Important to customers:function and lift of product ○ Final properties depend on combined effects of deformationand temperature variation ○ where A io the original cross sectional area and Adis the area after deformation • Final Temperature • Final Temperature ○ Temperaturecontrol important: average temperatureand localised temperature ○ Effect of temperaturechange on: deformationprocess and product properties • Surface finish and dimensional precision ○ Depend on details of forming processes ○ Influence product function, assembly, quality, reliability • Nature of material flow ○ Depends on process and tool geometry ○ Affects product properties ○ Customersatisfaction requires not only the production of a desired geometricshape, but also that the shape possesses the right set of companion properties, without any surface or internal de
More Less

Related notes for 308806

Log In


OR

Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Sign up

Join to view


OR

By registering, I agree to the Terms and Privacy Policies
Already have an account?
Just a few more details

So we can recommend you notes for your school.

Reset Password

Please enter below the email address you registered with and we will send you a link to reset your password.

Add your courses

Get notes from the top students in your class.


Submit