Extrusion Process

Of course, in order to produce products and their components, it is necessary not only to create a mold but also to fix it. Therefore, the simple example of a toothpaste tube does not exactly correlate with the extrusion processes used in industry.

Most materials are extruded in the extruder chamber under conditions where the material becomes plastic and can therefore be pushed into the die opening. In most cases, an elevated temperature is used in the extruder chamber. As a result, the material becomes sufficiently pliable to be forced through the molding hole, whereafter it cools as it exits the chamber and thus retains its shape. Such processes are called hot or warm extrusion.

An interesting exception, in which it is the increased temperature after extrusion helps to maintain the shape of the product, is baking. Dough extruders are widely used in this industry, and dough is a very plastic material. In this case, the shape is retained during the baking process due to chemical transformations of the confectionery components. While the shape of most structural materials is maintained by cooling, where the general principle of increasing the hardness of materials with decreasing temperature works.

There are also methods of cold extrusion. In this case, sufficient plasticity of the materials is achieved by mechanical force, i.e., by creating increased pressure in the extruder chamber. The process takes place without significant heating the material. This process can be used to create high-quality metal parts that can be used in a variety of industries. The metal, usually in the form of a cylinder, is inserted into the extruder chamber and then mechanical force is applied to it. This causes the metal to be pushed out through the opening of the die, forming a product of the desired shape. The process is carried out using presses or special mechanical devices that provide the necessary mechanical force.

Cold extrusion is well suited for metals that have high ductility, such as aluminum, copper, brass, and stainless steel, although the specific alloy composition can significantly affect the applicability of the metal to this process. The main advantages of cold extrusion are the high precision and quality of the products obtained and the cost-effectiveness of the process.

The pressure to be used for metal extrusion depends not only on the properties of the metal itself, but also on the diameter and thickness of the material, as well as on the profile of the product to be manufactured. Typical pressures for cold extrusion range from 200 to 1500 bar. However, for larger output blocks or thinner profiles, significantly higher pressures may be required. In addition to pressure, other parameters such as extrusion speed, material temperature, product length, and die design must also be considered for successful cold extrusion. All of these parameters have an impact on the quality and accuracy of the resulting product.

In addition to metals, cold extrusion is also used for other materials such as plastics, ceramics, even glass and some types of food, such as sausages, candies, and more.

Extrusion is a compressive deformation process in which a block of metal is squeezed through an orifice or die opening in order to get a reduction in diameter and increase in length of the metal block. The resultant product has the desired cross-section. Extrusion involves forming of axisymmetric (symmetrical about an axis) parts. Dies of circular on non-circular cross-section are used for extrusion. Extrusion normally involves high forming forces. Large hydrostatic stress in extrusion helps in the process by improving the ductility of the material.

Metals like aluminium, which are easily workable, can be extruded at room temperature. Other difficult to work metals are normally hot extruded or warm extruded. Both circular and non-circular parts can be obtained by extrusion. Channels, angles, rods, window frames, door frames, tubes, and aluminium fins are some of the extruded parts. Difficult to form materials such as steels, nickel alloys are extruded because of its inherent advantage, such as, no surface cracking because of reaction between the billet and the extrusion container. Extrusion results in better grain structure, better accuracy, and surface finish of the components. Less wastage of material in extrusion is another attractive feature of extrusion.

The applications of extrusions are constantly increasing because of the ability of the process to produce net bulk shapes in long lengths, frequently with complex cross sections. Depending on the alloy, extrusions serve the transportation, construction, mechanical, and electrical industries. Extrusions are used for durable goods, industrial equipment, heating and air conditioning applications, petroleum production, and the production of nuclear power. Practically all metals can be extruded, but extrudability varies with the deformation properties of the metal. Soft metals are easy to extrude. Hard (or high-strength) metals need higher billet temperatures and extruding pressures as well as higher-rated presses and dies.