What is aluminium machining?
As a subtractive manufacturing process, machining involves taking material out of a workpiece to produce the desired part. It is exceptionally adaptable, supporting a variety of metal and non-metal substrates. Aluminium is one of the metals that is machined the most frequently.
Aluminium is the best material for machining and other manufacturing processes because of its smaller weight, lower material hardness, and improved formability.
“Machining” is a catch-all for various subtractive manufacturing techniques, including milling, turning, and drilling. Additionally, several machining technologies and methods include vertical and horizontal milling, Swiss screw machining, electrical discharge machining, and CNC machining (EDM). The processing of aluminium in each of these machining techniques is described below.
Computer software and machinery compatible with CNCs are used in the computer numerical control (CNC) machining process to direct the movement and motion of machine tools from across the surface of the workpiece. It enables the manufacturing of aluminium CNC products and parts that are exact.
Swiss screw machining is the best method for creating small, incredibly accurate cylindrical parts made of aluminium, such as those used in electronics or medicine.
Milling is a machining technique that uses rotating cutting tools to remove extra material from the workpiece in both the vertical and horizontal planes. Vertical units are best for small quantities of simple aluminium parts, while horizontal units are better suited for large amounts of complex aluminium parts. Milling equipment can have either a vertical or horizontal structure.
Electronic discharge machining, also known as EDM, removes material from the workpiece by using the electrical discharge produced between two electrodes. However, it can be used on any electrically conductive material, even aluminium, even though it is typically used to process more complicated and challenging-to-machine materials.
Getting the highest material removal rates possible while successfully machining aluminium is a critical problem.
If there is too much heat, the aluminium may melt and fuse to the instrument. Since the aluminium binds to the tool, even if it slices like butter, it will only last for a while if the user winds up using friction stir welding rather than machining.
In addition to minimising friction, chatter may be destructive while pushing the machine. When attempting to machine-clean pockets, this is particularly challenging.
What are the tools required for aluminium machining?
One should never cut aluminium with a general-purpose cutter. Although technically sound, aluminium differs significantly from steel.
Carbide is a popularly used cutting tool material. Carbide will outperform high-speed steel in value for both tool costs during the tool’s service life and in surface finish, even in non-performance applications.
Even yet, there are a few valuable facts regarding carbide that anyone should be aware of to choose the right tool for the job. There should be a general awareness of what is needed from a tool. Because aluminium is soft to cut, cutting tools are not subjected to high impact pressures.
Maintaining a razor-sharp edge is essential. Due to this, hardness would be preferred over toughness in terms of material properties. The carbide particle size and binder ratio are the key factors influencing this characteristic.
Greater grain size results in a harder material, whereas smaller grain results in a tougher, more impact-resistant substance. For optimum edge retention in aluminium, a small grain size is needed. This is to preserve the sharpness of the edge.
The binder ratio is an additional component. The binder used in carbide-cutting tools is cobalt. This could contain anywhere between 2% and 20% cobalt. More cobalt equals a tough tool; less cobalt equals a harder tool since cobalt is softer than the carbide grains. Therefore, we’re all searching for a carbide cutter with a big grain size and little cobalt.
- Feeds and Speeds
Many people use 1000 SFM when determining their RPM. One will only be moving if they do this.
This is often the advice given to most cutters. The spindle should run at speeds between 1000 and 1500 SFM. But it is achieved three times as fast by using harmonic testing. Later, more on that.
Where a lot of guys falter is with the feed rate. It is a waste of time if one feeds a 1/2″ endmill at 0.003″ per tooth. It should be pushed for production by at least 1% of the cutter diameter.
This indicates that a 1/2″ endmill requires at least 0.005″ of feed. One might even double that with a reliable setup and quick tool.
There is just one exception to this rule when using little tools, such as those that are 1/8′′ or less. There may be a need to slow down for thinner chips because chip clearance may become a problem.
- Tool design
Different characteristics of a tool’s shape affect how effectively it can machine aluminum. Among them is the number of flutes. Cutting tools for CNC machining aluminium should have two to three flutes to avoid problems with chip evacuation at high speeds. Smaller chip troughs are the result of more flutes. Large chips made of aluminium alloys will become lodged as a result. Use two flutes when the procedure requires essential chip clearance and minimal cutting forces. Use three flutes to achieve the ideal balance between chip clearance and tool strength.
- Helix angle
The angle formed by a tool’s centre line and a straight line tangent to its cutting edge is known as the helix angle. It is a crucial component of cutting instruments. A higher helix angle speeds up chip removal from a workpiece but increases heat and friction during cutting. During high-speed CNC machining of aluminium, this could lead to chips welding to the tool surface. On the other side, a lower helix angle generates less heat but might not correctly remove chips. A 35° or 40° helix angle works well for roughing applications when milling aluminium, whereas a 45° helix angle works well for finishing.
- Clearance angle
Another crucial element for a tool’s successful operation is the clearance angle. An extremely steep angle would make the tool rattle and dig into the work. On the other hand, a too-small angle would result in friction between the tool and the task. The optimal clearance angles for CNC milling aluminium are between 6° and 10°.
- Tool material
In CNC machining, aluminium carbide is the chosen material for cutting tools. Since aluminium is soft to cut, a cutting tool’s ability to maintain a razor-sharp edge is more crucial than its hardness. This capability exists in carbide tools and relies on the carbide’s binder ratio and grain size.
While a smaller grain size ensures a more robust, more impact-resistant material, which is a needed feature, a greater grain size produces harder material. Cobalt is necessary to provide a high-quality structure and the material’s strength in smaller grains.
On the other hand, at high temperatures, cobalt and aluminium react, forming an aluminium-rich edge on the tool’s surface. To limit this reaction and preserve the necessary strength, the trick is to use a carbide tool with the proper quantity of cobalt (2–10%). Carbide tools can generally tolerate the high speeds used in CNC aluminium cutting well than steel tools. Tool coating is an important factor in increasing the efficiency of tool cutting by adding material to the tool. For tools used in the CNC machining of aluminium, suitable coatings include diamond-like coatings, titanium di-boride, and zirconium nitride (ZrN).
What are the operations of aluminium machining?
Here is a list of typical uses for aluminium, along with some pointers:
To utilise a shell mill, one should use polished inserts and a very aggressive rake angle. A fantastic finish can be easily achieved, and the RPM can also be pushed.
The majority of users need to do this correctly. Two things will go wrong if the user steps over the cutter’s diameter by half and half:
More can be cut using the cutter. Move almost too full width. 95% of the cutter flat. This is necessary because the cutter will already be hidden in the corners.
This means one will need to reduce the feed speed to prevent the tool from blowing up in the corners. Due to the cutter and material deflection, if one goes 100%, one could have paper wafers between the tool paths.
When roughing at a fair rate, 50% of stepovers are terrible for harmonics. The tool slaps in with every tooth and makes the worst possible impact as it enters the workpiece. The amount of chatter will be significantly reduced even by increasing the tool to 65% stepover.
Another advice is to choose a cutter diameter, just a hair smaller than the radius of the pockets inside.
When cutting 1/4′′ rad pockets with a 1/2′′ endmill, there is the risk of gouging the corners with chatter as the tool changes direction. Tools can unload, cutting pressure at high speeds because they can’t shift focus quickly. These are the sounds one hears chirping.
For tidy corners, those rads can be resized to 0.265″. As a result, there is less contact between the tool and the part shape. At higher speeds, the machine can manage that rounded turn. Just picture a car racing down a track. The car slows down if the corner is sharp. A greater radius eliminates the need for the machine to slow down. This will primarily stop the chirping in the corners that make the parts look unattractive.
For really deep slots, it has been found that either trochoid milling, which lessens chatter and deflection in the cutter, or a stub flute endmill both work well.
Stub flutes are preferred because they are more robust and don’t waste any motion as they zip back and forth.
One application where it’s frequently beneficial to utilize a specialist tool is deep slotting. No special considerations are required for shallow slotting (4xD and under).
There should always be sharp drills. Carbide drills are only sometimes the solution; if one doesn’t have the production volume or spindle RPM to support them, there is no purpose in running an expensive carbide drill.
The user will be generally OK if they use a 135-degree split-point drill. They put a lot of extra heat into the cut if the drill tip has a web.
Although general-purpose taps theoretically function, taps designed specifically for aluminium are far more dependable. Their much sharper rake angle results in cleaner cuts and less heat.
One wastes time if one never turns the machine past 200 RPM. Of course, some machines are simply sluggish and worn out, and the blowback makes cutting any faster impossible. Though using this equipment won’t make them competitive, the takeaway is that tapping aluminium is simple.
How to obtain surface finishing on aluminium?
High or large RPM, which is not that secret. Turn it up. A finishing tool with a highly aggressive rake angle, high helix, and razor-sharp edge will also help achieve a highly glossy surface finish.
However, it is essential to note that no one should waste time making the portion more beautiful than it needs to be. There are instances where one will want to amaze the consumer and make them happy, but remember that being gleaming is not the same as having a high Ra.
One should perform the surface finish calculations to estimate the maximum feed rate for the finish cuts. Usually, after doing the calculations, it is generally safe to back off by around 10%. One will be incorrect 50% of the time while walking that line.
Advantages of Aluminum Machining?
In addition to having excellent machinability, aluminium exhibits qualities that make it appropriate for use in machining operations, including:
- High strength-to-weight ratio
Aluminum has both the strength and lightness needed for machined parts used in high-performance operations, such as those used in the aerospace and automotive industries.
- Corrosion resistance
Aluminum comes in several grades, each with a different level of corrosion resistance. One of the most popular grade in machining operations is 6061 which offers high corrosion resistance.
- Electrical conductivity
Aluminum has a higher electrical conductivity than other widely machined metals like carbon steel, which is 7 million siemens / meter, and stainless steel, which is 1.5 million siemens / meter, measuring about 37.7 million siemens / meter at ambient temperature. Machined aluminium components are suitable for usage as electrical as well as electronic components because of this characteristic.
Potential for surface finishing and anodizing: Aluminum is easily adaptable to various surface treatment and finishing procedures, including painting, tinting, and anodizing. This feature enables producers to enhance the machined aluminium item’s aesthetic and practical qualities.
Aluminium is highly recyclable, allowing businesses to repurpose construction materials from finished goods discarded after their valuable lives and scrap material created during machining operations.
Aluminum is less expensive without significantly losing performance compared to other machining materials (such as brass, titanium, and PEEK). Additionally, because of its ease of machining and smaller weight, it has cheaper production and shipping expenses.
As previously mentioned, the machining process accepts a range of materials, including metal, plastic, paper, and wood. In addition to aluminium, other metals such as steel, stainless steel, and thermoplastics are routinely used in machining operations. Aluminum is superior to various materials in many ways, including Aluminium exhibits a substantially lower material weight and superior machinability than steel and stainless steel.
Types of aluminium machined parts:
Aluminium is used in machining processes by industry professionals to create various parts and goods. These parts are used in multiple industries, such as automotive and aerospace, communications, electronic and electrical goods, lighting, and medical.
Dowel pins, EMI housings, panels used in the front, lighting fixtures, medical equipment, and spline shafts are a few notable examples of typical products.
Types of aluminium used for machining:
The following five aluminium grades are most often utilised for CNC machining.
Copper makes up 4–5% of the alloying elements in this aluminium alloy. It is a short-chip alloy with the same excellent mechanical qualities as AW 2030 and is strong, light, and highly useful. It is also appropriate for high-speed machining, heat treating, and threading. Because of all these qualities, EN AW 2007 is frequently used to create machine parts, bolts, rivets, nuts, screws, and threaded bars. However, due to this grade of aluminium’s limited weldability and low corrosion resistance, it is advised to perform protective anodizing after part machining.
The AW 5083 is well known for its outstanding performance in challenging situations. Magnesium is present, along with trace amounts of chromium and manganese. This grade has extreme corrosion resistance in both chemical and marine conditions. AW 5080 is the most durable non-heat treatable alloy, and its strength is retained even after welding. Although applications requiring temperatures above 65 °C shouldn’t use this alloy, low-temperature applications are where it shines.
AW 5080 is employed in many applications, such as cryogenic equipment, maritime and chemical applications, pressure equipment, welded constructions, and the bodies of various vehicles, because of its different desirable qualities.
The most significant percentage of aluminium in a wrought aluminium-magnesium alloy, AW 5754, can be rolled, forged, and extruded. It can also be cold-worked to increase strength, but at the expense of ductility because it cannot be heat-treated. This alloy also has high strength and excellent corrosion resistance. Given these characteristics, it makes sense why AW 5754 is among the most widely used CNC aluminium grades. Flooring, fishing equipment, car bodywork, food processing, rivets, and welded constructions are examples of typical applications.
This wrought aluminium alloy contains silicon and magnesium. It can be heat treated, is moderately strong, weldable, and formable. It is also heat treatable. Additionally, it has a high corrosion resistance, which anodizing can further enhance. Construction, the food processing industry, various medical equipment, and the automobile engineering field frequently employ this type of aluminium.
The main alloying component in this grade of aluminium is zinc. Despite having medium machinability, subpar cold forming capabilities, and an inability to be used for welding and soldering, EN AW 7075 offers strength that is on par with other steel alloys, a high strength-to-density ratio, and excellent resistance to atmospheric and marine conditions. This alloy is used in various products, including frames for hanging gliders and bicycles, rock climbing gear, weapons, and mould-making tools.
With traces of copper, this alloy primarily consists of silicon and magnesium alloying elements. This high-strength alloy has a tensile strength of 180 MPa and is ideal for heavily loaded structures, including scaffolds, rail coaches, machine parts, and aerospace components.
This alloy, typically produced by rolling along with extrusion, has medium strength, excellent weldability, and excellent thermal conductivity. It resists corrosion and cracking under high tension. Tensile strength varies between 140 and 330 MPa. It is widely used in containers and offshore construction.
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