Extrusion Details...docx

1. What is extrusion? 2. Types 3. Advantages 4. Disadvantages 5. Applications What is extrusion? Extrusion is a type of forming process (which is a type of manufacturing process) in which a metal is confined in a closed cavity and then allowed to flow through only one opening side so that the metal takes the shape of opening. This process is exactly same as squeezing toothpaste out of the tube. In this process we can see that the toothpaste becomes cylindrical (since the opening of tube is circular) when it comes out of tube.

Video attached below will help in understanding the extrusion process in a better way. Types of extrusion processes Cold extrusion: Material which is to be extruded is below recrystallisation temperature(0.3 times of melting Temp.) Hot extrusion: Material which is to be extruded is above recrystallisation temperature(0.3 times of melting Temp) Note: Forward and direct extrusion are the two different names of the same process Backward and indirect extrusion are the two different names of the same process

Types of Extrusion Process With the help of above hierarchy diagram, we can easily understand types of various extrusion processes. In below images red colour shows hot metal billet.

Forward Extrusion In forward or direct extrusion the direction of movement of ram and the extruded metal is same.

Backward Extrusion In backward or indirect extrusion the direction of movement of ram and the extruded metal is opposite. Image source of forward and backward extrusion diagrams. Hydrostatic Extrusion: This process uses fluid to apply pressure on billet. In this process, the friction is eliminated because the billet is neither contact with cylinder wall or plunger. There is a fluid between the billet and plunger. The plunger applies force on fluid which further applied on billet. Normally vegetable oils,SAE 30,Glycerine,Ethyle Glycol are used as fluid.This process accomplished by leakage problem and uncontrolled speed of extrusion.

Why Backward Extrusion is needed? For reducing frictional force between container wall/die and ram backward is exist.

Backward Impact Extrusion Impact extrusion is a cold process for forming metals that marries forging with extrusion. In a nutshell, backward impact extrusion is a method of forming hollow metal parts by striking a metal billet (or disk), which is confined within a cylindrical or square die, so hard that the metal is forced upward into the space between the “hammer” (or punch) and the die. The gap between the punch and the inside of the die determines the wall thickness of the final component.

Advantages of extrusion 1. Low cost per part 2. Flexibility of operation 3. In hot extrusion, post execution alterations are easy because product is still in heated condition 4. Continuous operation

5. High production volumes 6. Many types of raw materials can be used 7. Good mixing (Compounding) 8. Surface finish obtained is good 9. Good mechanical properties obtained in cold extrusion Disadvantages of extrusion 1. Variations in size of product 2. Product limitations because of only one type of cross section can be obtained at a time 3. High initial cost setup Applications of extrusion process 1. Electrical wires, bars and tubes are some of the items produced by hot extrusion 2. Collapsible tubes, gear blanks, aluminum cans, cylinders are some of the items produced by cold extrusion After reading this article I hope now you understand extrusion in a better way, if you still have some doubts, you can always connect with me through the comments section.

According to the working temperature Hot Extrusion: If the extrusion process takes place above recrystallization temperature which is about 50-60% of its melting temperature, the process is known as hot extrusion. Advantages:

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Low force required compare to cold working. Easy to work in hot form. The product is free from stain hardening. Many types of raw materials can be used Continuous operation No residual streses.. Disadvantages:

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Low surface finish due to scale formation on extruded part.

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Increase die wear. High maintenance required and cost. Low tool life

Application of Hot Extrusion:     

Long pieces of uniform cross section Strip of Aluminium and Brass. Structural shape of rod.bars,tubes All forms of Al and St. Popet bar,turbine

Cold Extrusion: If the extrusion process takes place below crystallization temperature or room temperature, the process is known as cold extrusion. Aluminum cans, cylinder, collapsible tubes etc. are example of this process.

Advantages:     

Low cost per part High mechanical properties. High surface finish No oxidation at metal surface. Decrease wear to die

Disadvantages:     

High force required. Product is accomplished with strain hardening. Production rate low. Ductile materials only Residual stress increase

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Application: 

Extrusion is widely used in production of tubes and hollow pipes.

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Aluminum extrusion is used in structure work in many industries. This process is used to produce frames, doors, window etc. in automotive industries. Extrusion is widely used to produce plastic objects. Automobile piston,Cans,Sheel,Fire Extiguished cans.