What is Metal Extrusion? Types & Characteristics
Metal extrusion is a manufacturing process where a solid metal billet (a tubular or rectangular block) is forced through a die to create a desired shape. This creates objects with a fixed cross-sectional profile. It refers to the shape of a metal piece when viewed as if it were cut straight across its length.
It’s very similar to squeezing toothpaste out of a tube or pushing playdough through a stencil – but on a much larger scale. The metal extrusion process is commonplace in pipe and steel rod manufacturing. The most common materials extruded are aluminium and plastic.
The metal extrusion process is not considered a form of sheet metal fabrication, as it involves a solid metal billet and not a flat sheet of metal. Here at Salamander Fabrications, we offer a range of sheet metal fabrication services that we’re more than happy to elaborate on further. Or continue reading for more information on the extrusion process, the different types, its applications, advantages, and disadvantages.
Basic metal extrusion process
Generally speaking, here is a rundown of how the metal extrusion process works:
- The billet is produced and prepared.
- The billet is heated in hot extrusion or remains at room temperature (more on that later) and placed into an extrusion press. It’s pushed by a piston into a cylinder, where a die is fitted at the other end.
- Compressive force is applied by the piston (also known as a plunger) as it pushes the billet towards the die.
- This force makes the metal flow through the die as it is converted into the desired shape.
- The extruded part is removed from the press. It may also be heat treated for improved mechanical properties.
Types of metals used in the metal extrusion process
Each metal presents different challenges and advantages in the metal extrusion process. Manufacturers must always think about these when choosing the correct metal for a given application. Below are just a few examples of the types of metals used in metal extrusion.
Aluminium and aluminium alloys
These are the most commonly extruded metals due to their lightweight nature, corrosion resistance, and excellent machinability. Common applications include window frames, automotive components, and aerospace structures.
Copper and copper alloys
Copper and copper alloys are known for high electrical and thermal conductivity, making them ideal for electrical applications. They are often used in electrical conductors, plumbing pipes, and heat exchangers. The drawback is that copper is expensive and has lower mechanical strength when compared to other extruded metals.
Steel and stainless steel
Used when strength and durability are the primary concerns. They also provide excellent corrosion resistance, making them suitable for the marine, medical, and food processing industries. Steel often needs higher extrusion pressures and often hot extrusion due to its toughness.
Titanium and titanium alloys
Titanium is famous for its strength-to-weight ratio and corrosion resistance. For this reason, it is often used in the aerospace, medical, and automotive industries. It is very expensive when compared to aluminium and steel and more challenging to extrude.
Magnesium alloys
This is one of the lightest structural metals; it’s even lighter than using aluminium, but still offers good strength qualities. It is sometimes used in automotive, aerospace, and electronics to reduce weight. However, it is more prone to corrosion than aluminium.
Nickel alloys
Nickel alloys are resistant to high temperatures and harsh environments. They are commonly used in chemical processing, aerospace, and marine applications.
Types of metal extrusion (direction of flow)
Direct extrusion: The metal is forced to flow in the same direction of the piston feed. The piston pushes the metal through a cylinder towards and out the other end of the die.
Indirect extrusion: The die is fitted to a hollow piston that pushes the metal into a closed container. The metal flows in the opposite direction during extrusion, out through the hollowed-out piston.
Hydrostatic extrusion: This metal extrusion process uses fluid to apply pressure on the billet. The billet is not in contact with the cylinder wall or the piston, which causes less friction. Vegetable oils are often used as the fluid.
Types of metal extrusion (temperature)
Hot extrusion: This is where the metal extrusion process takes place above the recrystallisation temperature (around 50 to 60% of its melting temperature). This requires low force when compared to cold extrusion and is easier to work with. However, it causes increased wear on the die, and higher maintenance is required.
Cold extrusion: This is where the metal extrusion process takes place below crystallisation temperature or at room temperature. It offers high mechanical properties and a smooth surface finish with no chance of oxidation. However, high force is required.
Advanced metal extrusion techniques
Hydrostatic extrusion: Instead of a mechanical piston, pressurised fluid is used to force the billet through the die. This reduces friction, allowing for higher extrusion ratios. It can be used for brittle materials like tungsten.
Impact extrusion: A piston forces the material into a die with a single, powerful impact rather than a ‘slow push’. This high speed process produces thin-walled, seamless components.
Friction extrusion: This is a relatively new process that combines extrusion with heat, which is generated by friction. This is meant to reduce energy consumption.
Co-extrusion: This involves extruding two or more different metals together, as the name suggests. It allows manufacturers to combine the strength of one metal with the corrosion resistance of another.
Micro extrusion: This specialised form of extrusion is used to create very small, precise parts – again, as the name suggests! It enables the production of components in medical devices, microelectronics, and aerospace, amongst many others.
Benefits of metal extrusion
- Easily create complex cross sections
- Can be applied to brittle and ductile materials
- High mechanical properties can achieved
Drawbacks of metal extrusion
- High initial setup cost
- A high compressive force is required, which requires a lot of energy
- Not environmentally friendly
Common applications of metal extrusion
- Automotive Industry: Used for making parts like engine components, chassis sections, and crash management systems.
- Construction: Aluminium extrusions are widely used for window frames, doors, and structural components.
- Aerospace: Lightweight and strong extrusions are used for fuselage frames, seat tracks, and structural supports.
- Electrical Industry: Copper and aluminium extrusions are used for busbars, heat sinks, and cable trays.
- Consumer Goods: Used in ladders, furniture, and sporting goods like bicycle frames.
As mentioned in this blog numerous times, aluminium is perhaps one of the most commonly extruded metals. For more information on this particular metal, you can read our other blog, ‘11 Advantages of Aluminium’.
Quality control in the metal extrusion process
Manufacturers must use several quality control and testing methods to ensure that extruded metal products meet high standards. Even with precise manufacturing processes, defects can still occur.
These can include:
- surface cracks and scratches caused by excessive friction or overheating
- air pockets
- incomplete or inconsistent material flow
- warping or distortion due to uneven cooling or residual stresses
- dimensional variations due to the die being worn
Inspection and testing methods
Dimensional checks: Callipers, micrometres, and laser scanners are used to measure extruded components to ensure they match specifications.
Ultrasonic testing: High-frequency sound waves detect internal flaws or inconsistencies.
X-ray inspection: Helps identify internal voids (like air pockets) that might weaken the structure.
Hardness and strength testing: Measures how much force a material can withstand before breaking.
Corrosion and fatigue testing: Simulates real world conditions to ensure extruded metals can withstand environmental exposure, stress, and loading.
Surface finish inspection: Profilometers or a simple visual inspection will ensure that no defects affect the material’s performance. Smooth surfaces are critical for aesthetic and functional purposes.
Future trends and innovations in metal extrusion
As technology advances, the metal extrusion industry is evolving to become more efficient, sustainable, and precise. Several innovations and emerging trends are shaping the future of metal extrusion, improving material properties, production efficiency, and environmental impact.
Advanced materials and alloy development
High performance alloys will improve strength, corrosion resistance, thermal stability, and weight reduction. This includes the development of new heat-resistant aluminium alloys for applications in electric vehicles and aerospace components. Lighter and stronger metal alloys (such as Titanium and Magnesium) are being refined for structural applications where weight reduction is critical.
Automation and machine learning
This seems to be the hot topic for almost every industry in the world these days! The rise of AI and smart manufacturing is transforming the metal extrusion process through automation and real-time monitoring. Predictive algorithms can optimise extrusion parameters, reduce defects, and improve material efficiency. Robotic handling and automated quality control also help to ensure the highest quality finished products.
Sustainable and green technology
More and more industries are pushing for eco-friendly solutions to manufacturing and general operations. Metal extrusion, too, is moving towards sustainable materials and energy-efficient processes. More manufacturers may start using recycled materials to lower carbon footprints while maintaining material strength.
Hydraulic electric hybrid presses also help to reduce energy consumption compared to traditional hydraulic presses.
Other metal forming techniques
Welding
Welding services provide professional metal joining solutions for industries like construction, automotive, and manufacturing. We use several different types of welding techniques here at Salamander Fabrications, such as MIG (metal inert gas), robotic MIG welding, TIG (tungsten inert gas), and spot welding.
Cutting and shaping
Metals can be cut into shape using techniques such as shearing, laser cutting, and plasma cutting. We have 24/7 running capability on both of our laser cutting machines and the ability to hold up to 200 different metal materials.
Sheet metal folding
CNC press brakes or folding machines are used to bend sheets of metal into a desired shape. Sheet metal folding allows for accurate bends and angles, which is essential for manufacturing parts with tight tolerances.
Forming and fabrication
Sheet metal fabrication may involve bending, rolling, or stamping metals into various forms. This produces sheets, strips, or bars as opposed to complex cross-sections, as with metal extrusion. Before you begin this stage, you may use 2D and 3D CAD design services to wireframe and design your vision first.
Coating and finishing
Powder coating services improve the aesthetic appearance and corrosion resistance of the finished product. It is often important for outdoor-use metals.
Casting
This technique is used to create complex shapes from molten metals like cast iron. The molten metal is poured into a mould and allowed to solidify into a desired shape. Common applications include the automotive industry, aerospace components, construction and infrastructure, and artistic and decorative items. This produces more material waste in comparison to metal extrusion due to excess molten metal and the required finishing.
Heat treatment
Heat treatment can include annealing, quenching, and tempering. These processes are used to alter the physical and mechanical properties of metals by heating and cooling them in a specific way. This improves hardness, strength, ductility, and wear resistance. This process can often be employed after the metal extrusion process takes place.
Here for all of your sheet metal fabrication service needs
We have a wealth of information available on our main news page on a range of different topics related to sheet metal fabrication.
The team here at Salamander Fabrications is more than happy to share their expertise and talk to you some more about some of the services we have to offer. If you would like some more information or advice, please feel free to contact us. Give us a call on 01484 843599 or send an email to sales@salamanderfabs.com.
