chapter18;19;20

# chapter18;19;20 - 18.1 What are the differences between...

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18.1 What are the differences between bulk deformation processes and sheet metal processes? Sheet metal process has High surface area-to-volume ratio of starting metal, which distinguishes these from bulk deformation 18.2 Extrusion is a fundamental shaping process. Describe it. Answer . Extrusion is a compression process in which the work material is forced to flow through a die orifice, thereby forcing its cross section to assume the profile of the orifice. 18.3 Why is the term pressworking often used for sheet metal processes? Answer . Because most sheet metal operations are performed on presses. 18.4 What is the difference between deep drawing and bar drawing? Wire and bar drawing – diameter of wire or bar is reduced by pulling it through a die opening Deep drawing—sheet metal forming to make cup-shaped, box-shaped, or other complex-curved, hollow-shaped parts 18.5 Indicate the mathematical equation for the flow curve. Y f =Kε^n 18.6 How does increasing temperature affect the parameters in the flow curve equation? Decrease the parameters 18.7 Indicate some of the advantages of cold working relative to warm and hot working. Answer . Advantages of cold working are (1) better accuracy, (2) better surface finish, (3) increased strength due to work hardening, (4) possible directional properties due to grain flow, and (5) no heating of work required. 18.8 What is isothermal forming? Answer . A forming operation performed in such a way as to eliminate surface cooling and thermal gradients in the workpart. This is accomplished by preheating the forming tools. 18.9 Describe the effect of strain rate in metal forming? As strain rate is increased, resistance to deformation increases. 18.10 Why is friction generally undesirable in metal forming operations? a. metal follow in the work is retarded, causing residual stresses and sometimes defects in the product b. forces and power to perform the operation are increased c. tool wear can lead to loss of dimensional accuracy, resulting in defective parts and requiring replacement of the tooling.

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18.11 What is sticking friction in metalworking? Answer . Sticking friction is when the work surface adheres to the surface of the tool rather than slides against it; it occurs when the friction stress is greater than the shear flow stress of the metal. 19.1 What are the reasons why the bulk deformation processes are important commercially and technologically? When performied as hot working operations, they can achieve significant change in the shape of the workpart When performed as cold working operations, they can be used not only to shape the product, but also to increase its strength through strain hardening These processes produce little or no waste as a by-product of the operation. Some bulk deformation operations are near net shape or net shape processes;
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## This note was uploaded on 08/09/2011 for the course MAE 183 taught by Professor Cjkim during the Winter '10 term at UCLA.

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chapter18;19;20 - 18.1 What are the differences between...

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