Drawing and Extrusion

Metal Drawing

1. Department of Mechanical Engineering Unit: 02 By A Nirala

2. Wire Drawing Process Akhileshwar Nirala, GCET, Greater Noida Wire drawing is a metalworking process used to reduce the cross-section of a wire by pulling the wire through a single, or series of drawing die(s). The deformation is accomplished by a combination of tensile and compressive stresses. The die geometry determines the final dimensions, the cross sectional area of the drawn product, and the reduction in area.

3. Deformation in Wire Drawing Akhileshwar Nirala , GCET, Greater Noida The deformation is accomplished by a combination of tensile and compressive stresses. The tensile force is created by the pulling at the exit end and compressive force is arises from the reaction of the metal with the die in deformation zone.

4. Forces acting in wire drawing Akhileshwar Nirala, GCET, Greater Noida Drawing force, F, represents the total force that must be applied at the die exit to overcome friction at the die-work interface and resistance of the deforming material.

5. Process Parameters Akhileshwar Nirala, GCET, Greater Noida The major processing variables in drawing are Reduction in cross-sectional area Die angle Friction between the die-work-piece interface drawing speed. Temperature

6. Analysis of wire drawing Akhileshwar Nirala, GCET, Greater Noida Assumptions:- A uniform state of stress is assumed to exist at all points in a plane normal to the die axis A cylindrical state of stress is assumed to exist within the contact zone. The principle stresses are σ x and –p Coulomb`s law of friction is assumed to exists within the contact zone The coefficient of friction µ is assumed to be constant for the die and wire, Material, and also for the given surface conditions.

7. Calculation of Drawing stress acting on an element in Akhileshwar Nirala, GCET, Greater Noida [1] Strip Drawing [2] Wire Drawing [3] Tube Drawing

8. [1] Strip Drawing Akhileshwar Nirala, GCET, Greater Noida Strip drawing is a process of drawing in which, metal of large thickness gets reduced in thickness and increase in length through a converging die.

9. [2] wire drawing Akhileshwar Nirala, GCET, Greater Noida

10. continue……. Akhileshwar Nirala, GCET, Greater Noida +

11. continue……. Akhileshwar Nirala, GCET, Greater Noida σ x

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14. Extrusion Process Akhileshwar Nirala, GCET, Greater Noida It is a Compression forming process in which the work metal is forced to flow through a die opening to produce a desired cross-sectional shape. It is used to produce long cylindrical bars of uniform cross-sections and hollow tubes. Most metals are hot extruded due to large amount of forces required in extrusion. Types of Extrusion: Direct Extrusion (forward extrusion) Indirect Extrusion (backward extrusion) Hydrostatic Extrusion Impact Extrusion

15. Akhileshwar Nirala, GCET, Greater Noida Direct Extrusion: Direct extrusion, also called forward extrusion, is a process in which is the billet moves along the same direction as the ram and punch do. Because of sliding of billet against the container wall, friction between the container and billet is high. As a result, greater forces are required. Direct extrusion can be used for extruding solid circular or non-circular sections, hollow sections such as tubes or cups by providing mandrel with ram.

16. Akhileshwar Nirala, GCET, Greater Noida Indirect Extrusion: Indirect extrusion (backward extrusion) is a process in which punch moves opposite to that of the billet. Here there is no relative motion between container and billet. Hence, there is less friction and hence reduced forces are required for indirect extrusion.

17. Akhileshwar Nirala, GCET, Greater Noida Hydrostatic Extrusion: In hydrostatic extrusion the container is filled with a fluid. Extrusion pressure is transmitted through the fluid to the billet. Friction is eliminated in this process because of there is no contact between billet and container wall. Greater reductions are possible by this method. Pressure involved in the process may be as high as 1700 MPa . Pressure is limited by the strength of the container, punch and die materials. Vegetable oils such as castor oil are used.

18. Akhileshwar Nirala, GCET, Greater Noida Impact Extrusion: Impact extrusion is a discrete manufacturing process, in which a metal part is extruded through the impact of a die with the work stock. The part is formed at a high speed and over a relatively short stroke. In standard metal extrusions, the force to extrude the work is commonly delivered by way of a hydraulic press. 

19. Extrusion Calculation Akhileshwar Nirala, GCET, Greater Noida [1] Wire Extrusion [2] Strip Extrusion

20. Analysis of wire extrusion Akhileshwar Nirala, GCET, Greater Noida Assumptions:- A uniform state of stress is assumed to exist at all points in a plane normal to the die axis A cylindrical state of stress is assumed to exist within the contact zone. The principle stresses are σ x and –p Coulomb`s law of friction is assumed to exists within the contact zone The coefficient of friction M is assumed to be constant for the die and wire, Material, and also for the given surface conditions. [1] Wire Extrusion

21. Continue… Akhileshwar Nirala, GCET, Greater Noida

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23. Continue … Akhileshwar Nirala, GCET, Greater Noida σ x

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27. [2] Strip Extrusion Akhileshwar Nirala, GCET, Greater Noida Strip extrusion is a process in which, metal of large thickness gets reduced in thickness and increase in length through a converging die.

28. Analysis of strip extrusion Akhileshwar Nirala, GCET, Greater Noida

29. Continue….. Akhileshwar Nirala, GCET, Greater Noida The stresses acting on volume element of unit width are shown in figure.

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34. Friction And Lubrication In Metal Forming Akhileshwar Nirala, GCET, Greater Noida Metal forming processes are characteristic of high pressures between two contacting surfaces. In hot forming operations, these high pressures are accompanied by extreme temperatures. Friction and die wear are a serious consideration in metal forming manufacturing. A certain amount of friction will be necessary for some metal forming processes, but excessive friction is always undesirable. Friction increases the amount of force required to perform an operation, causes wear on tooling, and can affect metal flow, creating defects in the work. Where friction is involved, lubricants can usually help. For some metal forming processes and materials no lubrication is used, but for many lubrication is applied to contacting surfaces to reduce friction forces. Lubricants used in industry are different depending upon the type of metal forming process, the temperature at which the operation occurs, and the type of material formed. Lubricants should be effective and not produce any toxic fumes. Lubricants used in manufacturing industry for metal forming processes include, vegetable and mineral oils, soaps, graphite dispensed in grease, water based solutions, solid polymers, wax, and molten glass.