Aluminium is one of the most versatile metals – making it an ideal candidate for numerous manufacturing methods, the top two being aluminium extrusion and casting.
Newbies in the manufacturing space might find themselves asking what is the difference between the aluminium extrusion process and aluminium casting. The former process involves passing aluminium billets through a die to achieve a desired cross section. Meanwhile, aluminium casting involves pouring molten aluminium into a cast to achieve a desired shape after it solidifies.
It will help to note that aluminium casting and extrusion have their benefits and downsides. Nevertheless, aluminium extrusion and aluminium casting allow you to save time, and this is why these two methods are more popular than machining aluminium parts or components.
Process of aluminium extrusion
Aluminium extrusion facilitates the creation of aluminium materials that have predetermined shapes, and the process involves the forcing of aluminium alloy material into dies that have predetermined cross-sectional shapes. Also, remember that a ram pushes the aluminium alloy material through the die before it exits the die aperture.
You can get acquainted with aluminium extrusion without breaking a sweat since the technique is easy to comprehend. The force used during aluminium extrusion is comparable to the force you use when pushing toothpaste out of its tube. Moreover, the toothpaste assumes the shape of the tube’s aperture. So, you can liken the function of a toothpaste tube’s aperture to the function of an extrusion die.
It will help to get acquainted with the two main processes of aluminium extrusion before manufacturing aluminium-based parts and components. Direct aluminium extrusion involves keeping the dye head in a stationary position while removing ram forces aluminium alloy material through the die. In contrast, indirect aluminium extrusion involves holding the billet stationery as the die assembly moves against it to create the much-needed pressure for forcing the aluminium alloy material through the die.
Below are the steps you need to follow during aluminium extrusion:
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Preparing the die
Machine around shaped die if you don’t have a ready one available. Remember to preheat the die to about 450 to 500 degrees Celsius before you begin the extrusion process, especially if you want to achieve even metal flow while maximising your die’s life cycle. You can now load the preheated die into your extrusion press.
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Preheat the Aluminium Billet for the extrusion process
Next is cutting the billet AKA a dense cylindrical aluminium alloy block from elongated blocks of the material. Remember to preheat the oven to about 400 to 500 degrees Celsius. Do not skip this step if you want your billet to be malleable and now for the aluminium extrusion operation.
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Transfer the Billet to your Extrusion Press
Mechanically transfer your preheated billet to the press machine. Do not place the billet on the press machine before adding a little lubricant. Also, remember to apply the release agent to mitigate the unnecessary binding of the ram and the billet.
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Fill the Extrusion Press Container using Billet Material
Your malleable aluminium billet ought to be on the extrusion press during this stage. Now watch the hydraulic ram apply approximately 15000 tons of pressure to push the malleable billet into the extrusion press container. Here, you will notice the expansion of the aluminium materials as it fills its container’s walls.
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Press Extruded Alloy Material Against the Die
The aluminium alloy material gets pressed again to your designated extrusion die as the material fills the wall of the extrusion press container. Meanwhile, the hydraulic ram will be continually applying pressure to the aluminium material during the extrusion process. Consequently, the aluminium alloy material is left with only one opening for exit– die openings– explain why the early materials take the shape of the dies they emerge from.
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Cool/Quench the Extrusions
Be on the lookout for a puller that holds the emerging aluminium extrusion in place during the aluminium extrusion process. The puller also protects the emerging aluminium extrusion as it exits the press.
You will also witness a process known as quenching, which involves the cooling of the metal alloy using a fan or water bath. Yes, quenching happens as the metal alloy moves across the table.
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Shear the Extrusions to Table Length
As soon as the extrusion reaches the full table length, share it using a hot saw. Temperature is essential at each step of the extrusion process. Despite quenching the extrusion after leaving the press, it is not fully cool yet.
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Cool Extrusions using Tensile Cutting Machine
Wait for the extrusion to reach a full table length then use a hot saw to shear it. Remember that maintaining optimum temperature levels aluminium extrusion process will help you enjoy a successful aluminium extrusion. To avoid burns, do not touch the aluminium extrusion until it cools down.
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Place Extrusions on the Stretcher to Stretch Them into Alignment
Some aluminium extrusions might develop twists that you need to fix or correct. Fortunately, the stretcher is all you need to make this correction. During the aluminium extrusion process, the stretcher works by holding and pulling the ends of the affected aluminium extrusions until they are straight.
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Move Extrusions to the Finish Saw and Cut Them to Length
Now it’s time to transfer your extrusion to a saw table after confirming that they are straight and hardened. It is here that you should cut the extrusion into desired designated lengths mostly between 8 to 21 feet. Now you can proceed to extrusion ageing to enhance the quality and lifespan of your aluminium extrusions.
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Perform Secondary Operations
The extrusion process is not complete until you treat the extrusion profiles with heat to enhance their properties. You may want to correct the dimensions of your aluminium extrusions, and this calls for the fabrication of the extrusions after heat treatment. Finally, consider adding a surface finish to your extrusions to enhance their appearance and corrosion resistance capabilities.
Pros & cons of aluminium extrusion process
Here are top benefits and must mention downsides of aluminium extrusion
Pros
High product quality. You can improve aluminium’s structural and mechanical properties using extrusion moulding. Also, remember that quenching aluminium extrusions results in the improved mechanical properties in extruded products when compared to products manufactured using aluminium casting.
More production flexibility. The creation of products of different specifications, shapes, varieties, and sizes is hassle free thanks to aluminium extrusion. Moreover, you can enjoy a great deal of flexibility when you opt for aluminium extrusion since you can create all your products using one machine.
Cons
Varying product tissue properties. Unfortunately, aluminium extrusion results in varying products’ tissue properties. Consequently, expect uneven surfaces, centres, and, feel across extruded products– and this results from uneven metal flow during the extrusion process.
Aluminium Casting
Aluminium casting is the other popular method of machining aluminium products. There are three main aluminium casting techniques; sand casting, die casting, permanent mould casting. Read on to explore the difference between the three aluminium casting techniques.
Sand casting: In this aluminium casting technique, a sand mixture is used to create a mold containing a cavity into which molten aluminium alloy will be powered to create a designated part or component. Remember that you will have to wait for the molten aluminium to cool and solidify before breaking it away from the sand cast.
Permanent mould casting: Unlike in sand casting where the sand cast is broken to reveal the cast aluminium product, permanent mould casting relies on a reusable metal mould. Permanent mould casting technique involves the filling of mould cavity with molten aluminium. Remember that the mould is separated after the molten aluminium cools down to reveal a designated product.
Die casting: Permanent mould casting and die casting are similar. The two aluminium casting techniques use molten aluminium on permanent metallic moulds. The only difference between the two techniques is that permanent mould casting relies on gravity to fill the mould’s cavity with molten aluminium whereas die casting relies on pressure to fill the metal mould cavity with molten aluminium.
Pros & cons of aluminium casting process
Below are the benefits and downsides of using aluminium casting
Pros
- Aluminium casting is suitable for designing products with complex shapes
- Aluminium casting is ideal for producing a large number of small parts
- Streamlines mass production of components and part due to fast production cycles
- Aluminium casting achieves smooth surface finishes, which can be texted to meet personalised tastes and preferences
Cons
- Aluminium casting results in limitations on product or component thickness
- Aluminium casting has a high initial startup cost. Consequently, not ideal for low volume component production
Comparison summary
Both aluminium casting and aluminium extrusion have excellent advantages and a few disadvantages that make them better suited for certain applications. To help you decide which process is best for you, take a look at the side-by-side comparison below:
Die/ Aluminum Casting
- Aluminium casting is ideal for creating complex shapes
- Aluminium casting can make high quality and large finished products
- Aluminium casting moulds are costly and time-consuming to make
- Boasts a rough surface finish that makes other imperfections visible
- Not as strong as their counterparts made from aluminium extrusion
Extrusion
- Aluminium extrusion dies are affordable than aluminium casting moulds. Therefore, you can add new extrusion dies profiles without breaking a sweat.
- Boasts smooth surface finishes
- Ideal for creating a variety of shapes that have a consistent cross section.
- Creates structurally strong and products
- The size of the finished products is dependent on the size of their aluminium billet.
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