The Extrusion Process: A Complete Guide to Types, Steps & Applications

Extrusion is a highly versatile manufacturing process used to create products with uniform shape and density by forcing raw materials through a die under controlled conditions. This process plays a crucial role in various industries, including plastics, rubber, metal forming, food production, pharmaceuticals, and 3D printing. By applying high compression to a billet and pushing it through a die with a specific cross-sectional profile, extrusion enables the efficient production of complex shapes with excellent surface finish and minimal material waste.

What Is Extrusion Manufacturing? How the Extrusion Process Works

Well, extrusion is a process that has been used for centuries. This manufacturing process has been used to make all kinds of products, from aluminum cans to plastic pipes. Extrusion is a manufacturing technique that creates objects with a fixed cross-sectional profile.

In the extrusion process, metal is compressed and forced to flow through a die with a specific shape, resulting in a product with a reduced but constant cross-section. This can be done either hot or cold, though hot extrusion is often used to lower the required forces, eliminate the effects of cold working, and reduce directional properties. Essentially, the extrusion process is similar to squeezing toothpaste out of a tube. Types of extrusion include non-lubricated hot extrusion, lubricated direct hot extrusion, and hydrostatic extrusion.

Extrusion Terminology You Should Know

A few terms come up throughout this guide:

• Billet: the cylindrical block of metal loaded into the extrusion press before forming.
• Ram: the hydraulic piston that pushes the billet through the die.
• Die: the shaped tool that determines the final cross-sectional profile of the extrusion.
• Mandrel: an internal tool used to form hollow profiles, such as tubing.
• Extrusion ratio: the ratio of the billet’s cross-sectional area to the die opening’s area, a key factor in how much force the press needs.
• Quench: the controlled cooling step after extrusion that locks in the material’s mechanical properties.

The 5 Steps of the Extrusion Process

1. Billet and die preparation: the billet is cut to length and, for hot extrusion, heated to the target temperature; the die is preheated and lubricated as needed.
2. Loading: the billet is loaded into the container of the extrusion press.
3. Extrusion: the ram forces the billet through the die, producing a continuous profile with the die’s cross-section.
4. Quenching: the extruded profile is cooled, by air or water, to set its mechanical properties.
5. Finishing: the profile is stretched to straighten it, cut to length, and, for age-hardenable alloys, heat-treated before shipping.

Types of Extrusion: Direct, Indirect, Impact & Hydrostatic Explained

First things first, let’s talk about the different types of extrusions. There are four main types of extrusion: direct extrusion, indirect extrusion, impact extrusion, and hydrostatic extrusion. Even though each process might vary slightly, the extrusion process involves a billet being pushed through the die opening using a pressing stem (ram) and dummy block.

What is an example of extrusion?

An example of products that have been extruded is aluminum cans. In this process, a cylindrical billet of aluminum is heated to a specific temperature. It is then forced through a die to create a can with a uniform cross-sectional profile. This method is also used to manufacture a variety of other products, such as pasta, pipes, window panes, gears, snack foods, railings, shower stalls, and windshield wipers, all of which are formed by extruding material through a die to achieve a specific shape.

Direct vs. Indirect vs. Hydrostatic vs. Friction Extrusion: Comparing the Methods

Here’s how the four main extrusion methods compare:

Method	How It Works	Friction / Force	Best For
Direct	Ram pushes the billet through a stationary die at the opposite end of the container.	Highest friction — billet surface slides against the container wall.	High-volume simple to moderately complex profiles (the most common method).
Indirect	The die moves with the ram while the billet stays stationary relative to the container.	25–30% lower friction than direct extrusion.	Longer production runs and profiles where lower force is an advantage.
Hydrostatic	Billet is surrounded by pressurized fluid (often castor oil) that transmits force evenly through the die.	Very low friction, enabling higher speeds and reduction ratios.	Brittle materials and high-precision, low-temperature extrusion.
Friction / Impact	Rotational or impact energy generates localized heat to deform the material through the die.	Variable — heat comes from deformation, not a heated billet.	Powder consolidation (friction) and short, high-precision parts like cans (impact).

What is direct extrusion used for?

Direct extrusion is a type of extrusion process that involves pushing a heated metal billet through a die. Direct extrusion is used for a wide range of applications. This process can manufacture simple shapes like rods and tubes to more complex profiles like those used in the construction, automotive, and aerospace industries. Some of the key advantages of direct extrusion include:

1. High production rates: Direct extrusion can produce parts at a high rate of speed, making it a cost-effective way to manufacture large quantities of parts.
2. Tight tolerances: Direct extrusion can produce parts with tight tolerances and precise dimensions, making it an ideal process for creating complex shapes and profiles.
3. Minimal waste: Direct extrusion produces very little waste, as the metal is simply pushed through the die and shaped into the desired profile.

Some specific examples of parts and products that can be manufactured using direct extrusion include:

• Aluminum extrusions for window frames, door frames, and other building components
• Automotive parts like chassis components, heat exchangers, and engine components
• Aerospace components like structural components and landing gear components

What is shape extrusion?

Shape extrusion is a type of extrusion process that involves pushing a heated metal billet through a shaped die to create a specific shape or profile. Unlike direct extrusion, which typically produces simple shapes, shape extrusion is used to produce more complex shapes with varying cross-sectional geometries. A billet is then pushed through a shaped die, which gives the metal its final form.

Some of the key advantages of shape extrusion include:

1. Precision and complexity: Shape extrusion can produce parts with high precision and complex shapes, allowing manufacturers to create customized parts for specific applications.
2. Reduced waste: Shape extrusion produces very little waste, as the metal is shaped directly into the desired form.
3. Cost-effective: Shape extrusion can be a cost-effective way to produce complex shapes and profiles, as it can be used with a wide range of metals and can produce parts at high rates of speed.

What types of shapes are extruded?

Some of the most common shapes that metals and metal alloys can be extruded into using shape extrusion include:

• Hollow and solid profiles: Shape extrusion can be used to produce both hollow and solid profiles, such as round or oval tube shapes and hollow square tube shapes.
• Channels and tubes: Shape extrusion is often used to produce tubes and channels with complex cross-sectional geometries, such as Zee or Z-shaped channels.
• T-sections and I-beams: Shape extrusion can also be used to produce Tee or T shapes, H or I beam shapes, L shapes, and other structural shapes that are commonly used in construction and engineering applications.

Extrusion Process Variables: Temperature, Motor Load & Melt Pressure

The three most important process variables that affect the extrusion process, include melt temperature (T), motor load (I), and melt pressure (P). However each of these can be affected by other factors, for example, the extrusion pressure can be affected by the die angle, reduction in cross-section of the material, extrusion speed, and lubrication. As a result, all these variables must be carefully controlled to ensure that the final product meets the required specifications. When the extruder is not functioning correctly one, two, or all three of the process variables could be the problem.

How does temperature affect extrusion?

While extruding materials temperature plays a crucial role. The material must be heated to a specific temperature to soften it enough to flow through the die. If the temperature is too low, the material will not flow properly, and if it is too high, it could cause defects in the final product. It is also important to remember that the deformation energy is converted into heat, thereby increasing the temperature of the extrudate and in turn affecting the microstructure and mechanical properties of the material.

How does metal flow in the extrusion process?

Metal flows through the die in a process called deformation which is a result of the force being applied to the metal to push it through a die. As the metal is pushed through the die, it is compressed and elongated, causing it to take on the shape of the die. The metal endures compressive and shear stress to achieve the die shape. If there is too much friction during the extrusion process, the metal will not flow properly resulting in a dead zone where you have stagnant metal that is not flowing. Below are the types of metal flow that can be experienced while extruding with square dies.

1. Flow pattern obtained at low friction or in indirect extrusion.
2. The flow pattern obtained with high friction at the billet–chamber interfaces.
3. The pattern obtained at high friction or with cooling of the outer regions of the hot billet in the chamber; this type of pattern, observed in metals whose strength increases rapidly with decreasing temperature, leads to a defect known as pipe (or extrusion) defect.

Hot Extrusion Temperature Ranges by Metal (Aluminum, Steel, Copper & More)

Aluminum is the most common hot extruded metal, the typical extrusion temperatures range from 700° to 890° Fahrenheit, or 375° to 475° Celsius. See the chart below for extrusion temperature ranges for various materials.

Types of Extrusion Dies: Flat-Face, Pocket & Feeder Dies

There are several types of dies used for extrusion, including flat-face dies, pocket dies, and feeder dies. The type of die used depends on the shape of the final product.

1. Flat-face dies: die for nonferrous metals
2. Pocket dies: die for ferrous metals
3. Feeder dies: die for a shaped extrusion typically made of hot-work die steel and used with molten glass as a lubricant

How Aluminum Tube Extrusion Works: Direct vs. Indirect Methods

There are two ways to manufacture a seamless aluminum tube direct and indirect, both require a powerful ram to push the aluminum alloy material through a die with a specific tube cross-sectional profile.

1. Direct Extrusion: uses an internal mandrel that moves independently of the ram
2. Indirect Extrusion: has the mandrel integral with the ram and uses a spider die to produce seamless tubing.

Extruded Heat Sinks: Aluminum Alloy 6063 vs. 6061

An extruded heat sink is a type of heat sink that is made using the extrusion process. It is used to dissipate heat (thermal management) from electronic components on printed circuit boards. Heat sink and architectural profiles typically use 6063-T5 for its excellent extrudability and surface finish, while structural components that need higher strength, such as brackets and load-bearing frames, favor 6061-T6 instead. The trade-off extrusion die designers weigh is formability and surface finish (6063) versus mechanical strength (6061).

Cold Extrusion Examples: Rivets, Bolts, Fasteners & More

Cold extrusion is a process that involves deforming metal at room temperature. This process is often used to manufacture parts that require high strength and durability. The process can be used with a variety of metals, including aluminum, lead, tin, brass, and steel. Cold extrusion is commonly used to manufacture a wide range of, high-strength parts. Some examples of cold extruded parts are rivets, bolts, screws, fasteners, collapsible tubes, fire extinguisher cases, shock absorber cylinders, spark plugs, and gear blanks.

What Is Impact Extrusion?

Impact extrusion is a type of extrusion manufacturing process that involves deforming a metal slug using a high-velocity impact to force the material into a die or mold with a punch. This process is commonly used to manufacture parts that require high precision and strength. Some examples of this process are aluminum cans, tubes, and containers.

3 Common Extrusion Defects: Surface Cracking, Chevron Cracking & Buckling

The three principal extrusion defects are surface cracking, Chevron cracking (central burst), and buckling. These defects can be caused by a variety of factors, including improper die design, temperature control, and material properties. Internal defects such as central bursts are dangerous because unless the products are inspected, such internal defects may remain undetected and later cause failure of the service part. The tendency toward chevron cracking increases if the two plastic zones do not meet. To reduce the likelihood of internal cracking the plastic deformation zone must be made larger by either decreasing the die angle or by increasing the reduction in cross-section. Other defects include:

• Aesthetic flaws (e.g., pits, black specs, pinholes, drag marks, die lines, sink marks)
• Size variance (which can be intermittent or contiguous)
• Dimensional variations.

Extrusion Design Best Practices

Good design practices for extrusion and drawing parts include considerations like:

• Selecting the appropriate material for the application
• Designing to eliminate sharp corners
• Keeping section thickness uniform
• Avoiding undercuts

Extrusion vs. Forging vs. Rolling: Choosing the Right Metal Forming Process

Extrusion is one of several core metal forming processes covered in our metalworking guide, alongside forging and rolling. All three reduce a billet or workpiece into a more useful shape through compressive force, but they solve different problems:

• Extrusion produces a continuous, constant cross-section (rods, tubes, channels, structural profiles) by forcing material through a die. It’s the go-to process when you need a long part with a consistent profile.
• Forging uses compressive force (hammer or press) to shape a discrete part, refining the grain structure for high-strength components like crankshafts and gears. It doesn’t produce continuous profiles the way extrusion does.
• Rolling passes material between rotating rollers to reduce thickness and produce flat stock, sheet, plate, and structural shapes at very high volumes. It’s typically the first step that turns cast ingots into workable stock, which may then be extruded, forged, or formed into sheet metal parts.

In practice, these processes are complementary rather than competing: a rolled aluminum billet might be extruded into a structural profile, sections of which are later machined (see our guide to machining operations) to final tolerance. Choosing between them comes down to part geometry, required strength, production volume, and cost.

Frequently Asked Questions About the Extrusion Process

What is the extrusion process in simple terms?

Extrusion is a manufacturing process that pushes a material, usually a heated metal billet, through a shaped die to produce a long part with a constant cross-section, similar to squeezing toothpaste out of a tube.

What metals can be extruded?

Aluminum is by far the most commonly extruded metal, but copper, brass, steel, magnesium, zinc, and titanium are also extruded, each with its own hot-extrusion temperature range and die requirements.

What is the difference between hot and cold extrusion?

Hot extrusion heats the billet above its recrystallization temperature to lower the force required and produce complex shapes, while cold extrusion deforms the material at room temperature, producing higher-strength parts with a better surface finish but requiring significantly more force.

Is extrusion cheaper than machining?

For long parts with a constant cross-section and high production volumes, extrusion is generally far more cost-effective than machining because it produces near-net shapes with minimal material waste. Machining is typically reserved for final-tolerance features that extrusion can’t produce directly.

What is the difference between extrusion and forging?

Extrusion forces material through a die to create a continuous profile with a constant cross-section, while forging uses compressive impact or pressure to shape a discrete part and refine its internal grain structure. See our forging guide for more detail.

Conclusion

There you have it, folks! A beginner’s guide to extrusion manufacturing. We hope this article has given you a better understanding of what extrusion is, how it works, and some of the key factors that can impact the process and the final product. In addition to extrusion, most parts also may be made by casting, forging, or machining. Deciding what metalworking process is best for your specific application depends on the material’s part dimensions, wall thickness, and the properties desired. Economic considerations also are important in the final metalworking process selection. I hope you found this article informative and helpful. Thanks for reading!