What is definition of extrusion?
extrusion is a process in which a heated billet or slug of a metal is forced by high pressure through an orifice that is shaped to provide the desired form to the finish the part or product. So lets see extrusion and its types.
Extrusion and its types.
An everyday and analogy is the squeezing of toothpaste from a collapsible tube. Because of the large forces required in extrusion, most metal are extruded hot under conditions where the deformation resistance of metal is low.
Which metals can be extruded using extrusion process?
However, cold extrusion is possible for many metals and is rapidly taking and important commercial position. Most commercial metal and their alloys,such as Steel, aluminium, copper, nickel, and magnesium are directly extruded at high temperatures. structural shapes, rods, tubes, molding trim, brass cartridge, flooring strips, lead covered cables, aircraft parts, and many hardware items such as window sach, door trim,etc. These are typical products of extrusion.
The reaction of extrusion billet with container and die results in high compressive stresses which are effective in reducing the cracking of the material during primary breakdown from the the ingot. This is an important reason for greater use of extrusion in the working of metals difficult to form,e.g stainless steel, molybdenum and nickel base alloys
What temperatures, common sizes and pressure used in extrusion process?
Most hot extrusion is done on horizontal hydraulic presses especially constructed for this purpose. Common sizes are rated from 250 to 5500 tonnes. Temperature of billets are 350°C to 425°C for magnesium, 425°C to 475°C for aluminium 650°C to 1300°C for copper alloys,and 1200°C to 1300°C for steel. Pressure normally vary from 4998 to 7038 kgf per sq cm.
How to do Lubrication of Extrusion Chamber, Die and Ram?
Lubrication of the the extrusion chamber,die, and ram is necessary and is ordinarily achieved by mopping with oil supported graphite. Vegetable oils are better than petroleum oils for this purpose.The extrusion of steel at high temperatures is most successfully done by using glass which,at the temperatures involved,act as lubricant. There are different ways to extrude metals. So till now we learned what is Extrusion? Now we will learn types of extrusion process.
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Types of extrusion process.
- 1)Direct or Forward extrusion.
- 2) Indirect or backward extrusion.
- 3)Tube extrusion.
- 4) Impact Extrusion.
1)Direct or Forward extrusion:-
Direct extrusion or forward extrusion shown in image. In this a press operated ram and cylinder or container into which the work-piece is placed for confinement. A dummy block used between hot metal & the ram . by using ram pressure, the metal first Plastically fills the cylinder shape & its then forced out through the die opening until small amount remains in the container. Its then sawed off next to the die and the butt end removed. Know more about direct extrusion process.
2) Indirect or backward extrusion:-
It is similar to direct extrusion except that the extruded part is forced through the hollow Ram as shown in figure. It consists no friction between the metal billet container walls. as the billet does not moves the container. Compared with direct extrusion, less total force is required but the equipment used is more complicated mechanically in order to accommodate the passage of the extruded shapes through the center of hollow Ram.Know more about indirect extrusion process.
3) Tube extrusion:-
It is a form of direct extrusion but use a mandrel to shape the inside of the tube. After the heated billet is placed inside the container, the die containing the mandrel is pushed through the billet. The RAM then advances and extrudes the metal through the die and around the mandrel as shown in figure. know more about tube extrusion process.
4) Impact extrusion:-
Extrusion are also made by striking slug of metal and forming then by high impact. This is essentially a cold working operations. Below is diagram of impact extrusion – Image credits – The library of Manufacturing – Impact Extrusion.
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