Metallurgy

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  • Topic: Metalworking, Metal forming, Sheet metal
  • Pages : 5 (1471 words )
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  • Published : April 21, 2013
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INDUSTRIAL SHAPING OF METALS
Explain hot working processes.
“It is process in which the metal is subjected to forces above recrystallisation temperature to give it a desired shape” OR “Hot working refers to processes where metals are plastically deformed above their recrystallization temperature” It includes:

a. Rolling.
b. Forging.
c. Drop forging.
d. Heading.
e. Hot pressing.
f. Extrusion
ADVANTAGES OF HOT WORKING PROCESSES
Advantages of hot working process
         (i)Due to refinements of grains, mechanical properties such as toughness, ductility, elongation and reduction in area are improved. (ii) Great latitude in shape and size of farm is possible to reduction of elastic limit. (iii) The power required to finish the part from ingot is less. (iv) Directional property resulting from a fiber structure is obtained. (v) The strength and hardness decreases at elevated temperature DISADVANTAGES OF HOT WORKING PROCESSES

Disadvantages of hot working process
(i) The life of the tools used is less.
(ii) Tooling and handling costs are high.
(iii) Close tolerances cannot be maintained, oxide films are surface characteristics.

a: Rolling.
HOT ROLLING
Rolling is a fabricating process in which the metal, plastic, paper, glass, etc. is passed through a pair (or pairs) of rolls. In metalworking, rolling is a metal forming process in which metal stock is passed through a pair of rolls If the temperature of the metal is above its recrystallization temperature, then the process is termed as hot rolling

b. Forging.
Forging is a manufacturing process involving the shaping of metal using localized compressive force. There are many different kinds of forging processes available, however they can be grouped into three main classes:[1] * Drawn out: length increases, cross-section decreases

* Upset: length decreases, cross-section increases
* Squeezed in closed compression dies: produces multidirectional f es. C: Drop forging
Drop forging is a forging process where a hammer is raised and then "dropped" onto the workpiece to deform it according to the shape of the die. There are two types of drop forging:
* open-die drop forging
* closed-die drop forging.
Drop forging is a metalworking process that gradually shapes a heated piece of metal, called an ingot. It involves forming the ingot with repeated blows from a hammer or die that is raised and then dropped onto the part, flattening it or forcing it into a mold. Depending on the complexity of the part design, the process sometimes requires using several dies in progression. The drop forging process usually produces a close approximation of the finished piece, but additional machining typically is required to bring it within tolerance. Drop forging is widely used throughout the automotive industry in producing various engine parts, gears and axles.

Extrusion process : The process of extrusion consists of compression a metal inside a chamber to force it out through a small opening called die. Extrusion is a metal forming process in which a work piece of a certain length and cross section is forced to flow through a die of a smaller cross sectional area, thus forming the work to the new cross section. The extrusion process can be classified as :

(i) Direct or Indirect extrusion 
direct or forward extrusion the work billet is contained in a chamber. The ram exerts force on one side of the work piece, while the die through which the material is extruded is located on the opposite side of the chamber. The length of extruded product flows in the same direction that the force is applied. (ii) Forward or backward extrusion

indirect extrusion, the work piece is located in a chamber that is completely closed off at one side. The forming die are located on the ram, which exerts force from the open end of the chamber. As the manufacturing process proceeds the extruded product flows in the...
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