Metal Forming & Shaping: Lecture Introduction
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The document introduces metal forming processes. It defines metal forming as shaping metallic materials through plastic deformation, where the shape changes permanently in contrast to elastic deformation. It describes bulk deformation processes as involving large plastic deformation without changing volume. These include hot working like forging above the recrystallization temperature for easier forming, and cold working like rolling at room temperature for better accuracy. Sheet forming processes change the shape but not the cross-section, operating on thin metal sheets using stamping presses.
Metal Forming & Shaping: Lecture Introduction
- 1. 17-01-2013 Page 1 of 14 Introduction to Metal Forming Processes Definition of Metal Forming “Metal forming refers to shaping of metallic materials by means of plastic deformation”. The term plastic deformation describes permanent shape change, in contrast to elastic deformation. An elastic deformation disappears when the load is removed. Many industrial materials are shaped into useful products by plastic deformation.
- 2. 17-01-2013 Page 2 of 14 Bulk Deformation and Sheet-Forming Processes A- Bulk Deformation Processes These processes involve large amount of plastic deformation. The cross-section of workpiece changes without volume change. The ratio cross-section area/volume is small. For most operations, hot or warm working conditions are preferred although some operations are carried out at room temperature. Bulk Deformation Processes includes a wide variety of techniques, which make use of suitable force, pressure or stresses, like compression, tension and shear or their combination to cause a permanent deformation of the raw material to impart required shape. These processes are also known as mechanical working processes and are mainly classified into two major categories i.e., hot working processes Warm working and cold working processes. In these processes, no material is removed; however it is deformed and displaced using suitable stresses like compression, tension, and shear or combined stresses to cause plastic deformation of the materials to produce required shapes.
- 3. 17-01-2013 Page 3 of 14 Such processes lead to production of directly usable articles which include kitchen utensils, rods, wires, rails, cold drink bottle caps, collapsible tubes etc. Some of the important metals forming processes are: Hot working Processes (1) Forging, (2) Rolling, (3) Hot spinning, (4) Extrusion, (5) Hot drawing Cold working processes (1) Cold forging, (2) Cold rolling, (3) Cold heading, (4) Cold drawing, (5) Wire drawing,(6) Stretch forming,
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- 5. 17-01-2013 Page 5 of 14 Cold working is metal forming performed at room temperature. Advantages: better accuracy, better surface finish, high strength and hardness of the part, no heating is required. Disadvantages: higher forces and power, limitations to the amount of forming, additional annealing for some material is required, and some material are not capable of cold working. Warm working is metal forming at temperatures above the room temperature but below the recrystallization one. Advantages: lower forces and power, more complex part shapes, no annealing is required. Disadvantages: some investment in furnaces is needed. Hot working involves deformation of preheated material at temperatures above the re-crystallization temperature. Advantages: big amount of forming is possible, lower forces and power is required, forming of materials with low ductility, no work hardening and therefore, no additional annealing is required.
- 6. 17-01-2013 Page 6 of 14 Disadvantages: lower accuracy and surface finish, higher production cost, and shorter tool life. Importance of Rolling Example:
- 7. 17-01-2013 Page 7 of 14 Forging Example:
- 8. 17-01-2013 Page 8 of 14 B- Sheet-Forming Processes In sheet metal working operations, the cross-section of workpiece does not change—the material is only subjected to shape changes. The ratio cross-section area/volume is very high. Sheet metal working operations are performed on thin (less than 6 mm) sheets, strips or coils of metal by means of a set of tools called punch and die on machine tools called stamping presses. They are always performed as cold working operations. Sheet metal working processes such as piercing, punching, lancing, notching, coining, squeezing, deep drawing, bending etc.
- 9. 17-01-2013 Page 9 of 14 Characteristics of Metal Forming Following are some general characteristics of metal forming processes: The work piece is completely or partially subjected to plastic deformation during the forming operation; that is, it is plasticized. The plastic deformation is most commonly large. Little or no material is removed during the forming process. The microstructure of the as-cast workpiece is broken down by the plastic deformation. Therefore, the final component, or product, made by metal forming usually will have better mechanical properties than a similar product manufactured by casting or machining. During cold deformation, mechanical properties, such as the yield strength and tensile strength, will increase because of the accumulation of plastic strain in the material.
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- 13. 17-01-2013 Page 13 of 14 Animation Tensile Test (Stress-Strain Diagram)
- 14. 17-01-2013 Page 14 of 14 Final Neckin g Fracture