principle of Extrusion Type of extrusion Hot Extrusion, Cold Extrusion, Direct Extrusion, Indirect Extrusion, Impact Extrusion advantages benefits difference

principle of Extrusion Type of extrusion  Hot Extrusion, Cold Extrusion, Direct Extrusion, Indirect Extrusion, Impact Extrusion advantages benefits difference

 Table of content (toc)

Extrusion, Hot Extrusion, Cold Extrusion, Direct Extrusion, Indirect Extrusion, Impact Extrusion

Principle of extrusion :             

The process of forcing metal to flow through a die opening to form a desired cross sectional shape. extrusion principle             

This process can be combined with squeezing toothpaste out of a toothpaste tube. During extrusion, the metal is subject to plastic deformation and it undergoes reduction and elongation. It is most widely used in the manufacture of solid and hollow sections from ferrous, non-ferrous metals and their alloys. The section of the product depends on the size of the die. Vegetable oil and oil containing graphite are widely used as lubricants. Extrusion is generally considered to be closed die forging. The difference is, the main part of the metal is the product and the flash is cut off and there are almost no slugs left. But the ash is the only product in the extrusion and there is a slug left in the die. extruded product

There are different types of extrusions

1. Hot Extrusion 

2. Cold Extrusion 

3. Direct Extrusion 

4. Indirect Extrusion 

5. Extrusion effect.  

 

hot extrusion:                 

It is the process of closing a hot billet or slug of metal in a closed cavity and then passing it through only one die opening so that the metal takes the shape of the opening. 

hot extrusion  :           

Pressure is applied either hydraulically or mechanically. The extrusion process is similar to squeezing toothpaste out of a toothpaste tube. The extrusion setup consists of a cylinder container into which a hot billet or slug of metal is loaded. At one end of the container, the die plate with the required opening is fixed. From the other end, a plunger or ram compresses the metal billet against the container walls and die plate, thus forcing it to flow through the die opening, achieving the shape of the opening. The extruded metal is then transported by the metal handling system as it comes out of the die. Tubes, rods, hoses, casings, brass cartridges, molding-trims, structural shapes, aircraft parts, gear profiles, cable sheathing, etc. are some of the typical products of extrusion. sectional view of hot extrusion   

 

Advantages and Disadvantages of Hot Extrusion Advantages of hot extrusion: 

1. Big reduction can be achieved. 
2.  Very complex shapes can be created. 
3. The forces involved are compressive. 
4.  Relatively brittle materials can be extruded. 
5.  Excellent dimensional tolerance can be maintained. 
6. Very high surface finishing. 

 

Disadvantages of Hot Extrusion: 

1. It produces a condition of homogeneous distortion. 
2. Extrusion of steel requires high pressure and temperature.
   
3. The heat generated during extrusion can cause cracks in the surface.  

 

Cold Extrusion:               

Similar to hot extrusion, except that the metal has the plasticity required to deform it without heating. Metals that are cold drawn will have a high degree of ductility. This is done to improve the physical properties of the metal. Generally used to produce discrete parts, often in finished form. Metals such as aluminum alloys, copper, brass and bronze are extruded. Aluminum is the most ideal metal for extrusion [hot and cold].  

 

Direct or forward extrusion:  

              The ram pushes the billet through a die of the desired size into a stationary container or cylinder. direct extrusion or forward extrusion             There is relative motion between the billet and the container. The deformed metal [product] flows in the same direction for the ram motion [forward] through the opening of the die. The workpiece [hot billet] is placed in the container and sealed. A dummy block is placed between the ram and the hot metal. The press-operated ram first pushes hot metal to fill the cylinder, and it is then forced through the die opening. At the end of the extrusion process, a small piece of metal called a butt end scrap remains in it and cannot be pulled out. It is then sawed next to the die and the butt end is removed. As the ram moves in the direction of the die, the metal exits through the annular clearance and forms a tube.  

 

Indirect or backward extrusion:                   

Similar to direct extrusion, except the product is extruded through hollow rams. The die is located in front of the hollow stem and is pushed against the billet by a forward motion of the closed container at the rear. 

Indirect Extrusion or Backward Extrusion : 

 No relative movement between billet and container. There is no friction between the metal billet and the walls of the container as the billet does not move the container. The deformed metal [product] flows through the die opening in the direction opposite to the ram motion [backward]. Requires less total force than direct extrusion. The force is independent of the billet length. But the tools used are more complex mechanically. To reduce the friction force, a hydraulic press is used, so that it can also act 

 

Impact extrusion:

                 It is a different manufacturing process in which a part is extruded by the impact of a die with a work piece.

             The product is formed at high speed and with relatively short strokes. Impact extrusion is most often done cold, sometimes with certain metals and thick-walled structures by heating the work before impact forming. This process is best suited for soft metals, with aluminum being a great material to forge by impacting. During the manufacturing operation of impact extrusion, a workpiece is placed in a mold and struck with great force, causing the metal to rapidly return to its position in an instant.