In this article we are going to learn about Cold Extrusion, its definition, Applications and examples, Advantages and Disadvantages.
Cold extrusion is a process done at room temperature or at slightly elevated temperatures with the assistance of Extruders and Extrusion Machines. These machines and equipment have been specially designed on the basis of cutting-edge Extrusion Technology.
Definitions of Cold Extrusion
Cold extrusion is also known as the process of shaping a cold metal by striking it with a slug. This striking is accomplished with a punch (in a closed cavity), which forces the metal upward around the punch. Cold Forging, Cold Pressing, Extrusion Pressing, and Impact Extrusion are all names for this process.
Cold extrusion is also defined as a compressive forming process (push-through) in which the starting material is billet / slug and the process is carried out at room temperature. Several hundred degrees of deformation heating of the deforming material occurs during the cold extrusion process. Deformation heating is the process of converting deformation work to heat. In general, a punch is used to apply pressure to the enclosed billet in the stationary die. This pressure can be applied partially or completely depending on the situation.
Types of Cold Extrusion Process
Cold extrusion can be divided into three major processes based on punch and die design, as well as the resulting material flow:
- Forward extrusion
- Backward extrusion
- Lateral extrusion
1. In forward extrusion, the material flows in the same direction as the punch dis-placement. In forward extrusion, the diameter of a rod or tube is reduced by forcing it through an orifice in a die (Fig. 1a).
2. In backward extrusion, the material flows in the opposite direction of the punch displacement. The billet is enclosed in a die and is forced to flow backward through the annular region between the punch and the
die (Fig. 1b).
Backward extrusion is differ-entiated from impact extrusion where typically a nonferrous material is extruded backward by a rapidly moving punch and a shallow die with minimal material contact. Forward and back-ward extrusion can also be simultaneously achieved through die design (Fig. 1c).
3. In lateral extrusion, the material flows perpendicular to the direction of punch displacement. The material is enclosed by the die and the punch and is forced
through radially placed orifices (Fig. 1d). Hooker extrusion is a variation of the forward extrusion process where a tubular billet is forced through a forward extrusion die with a punch that acts as a pusher and a mandrel to reduce the outer diameter and elongate the tubular portion (Fig. 1e).
Cold extrusion, being a forging operation, has the typical advantages of material savings, work hardening (strengthening), and grain flow or directional strengthening. Compared to other forging operations cold extrusion is particularly attractive for the following reasons: dimensional precision, superior surface finish, net-shaped features, lower energy consumption, higher production rates, and cleaner work environment.
Drawbacks of cold extrusion are higher loads, lubrication cost, limited deformation, and limited shape complexity.
Difference Between Hot Extrusion and Cold Extrusion
Hot extrusion is a hot working process, which means it is done above the material’s recrystallization temperature to keep the material from work hardening and to make it easier to push the material through the die.
Cold extrusion is done at room temperature or near room temperature. The advantages of this over hot extrusion are the lack of oxidation, higher strength due to cold working, closer tolerances, better surface finish, and fast extrusion speeds if the material is subject to hot shortness.
Applications and Example of Cold Extrusion
Materials that are commonly cold extruded include: lead, tin, aluminum, copper, zirconium, titanium, molybdenum, beryllium, vanadium, niobium, and steel.
Examples of products produced by this process are: collapsible tubes, fire extinguisher cases, shock absorber cylinders and gear blanks.
Applications of Cold Extrusion
1. The cold extrusion process is widely used to manufacture products from Copper, Lead, Tin, Aluminum Alloys, Titanium, Molybdenum, Vanadium, Steel, Zirconium, and Niobium.
2. Some of the products that are developed using this process include various parts such as Collapsible Tubes, Gear Blanks, Aluminum Cans, Cylinders, Fire Extinguisher Cases, Shock Absorber Cylinders, and Automotive Pistons.
3. Cold Extrusion is also used in the Automobile Sector, in various applications such as:
> Injection technology
>Safety systems (restraint systems)
Advantages and Disadvantages of Cold Extrusion
Cold extrusion is extremely advantageous because it is used to withstand all of the stresses created by the extrusion process. Cold extrusion has several advantages over hot extrusion, some of which are listed below:
- No oxidation process Higher strength due to cold working
- Good mechanical properties that are provided the temperatures created, are below the re-crystallization temperature
- Closer tolerances
- Good surface finish
- Fast extrusion speeds, in case the material is subjected to hot shortness
- Dimensional precision
- Net-shaped features
- Lower energy consumption
- Higher production rates
- Cleaner work environment.
However apart from the advantages mentioned above, there are some disadvantages associated with cold extrusion. These are the costs of lubrication, higher loads, a limited shape complexity, and a limited deformation.
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