Aluminum cutting

Cutting non-ferrous metals is problematic. This is due to their physical and chemical properties. These metals tend to soften, deform and "flow" under the tool during cutting, especially if the temperature increases significantly during cutting.

The visible consequence are significant burrs and overall deformation of the workpiece at the edges in the direction of the tool action during cutting (fig. 1).

Therefore, tools with special properties have been developed for cutting these materials, which largely eliminate undesirable phenomena when cutting them.

To understand why cutting non-ferrous metals presents different problems than cutting steel, let's first explain how non-ferrous metals differ from ferrous metals.

We will clarify this by comparing the physical and chemical properties of typical representatives of both groups of metals: aluminum and iron.

Fig. 1. Burrs after cutting aluminum

Both of these materials are metals, but they differ significantly:

• density: iron is heavier, has a specific weight of 7.87g/cm³, compared to aluminum, which has a specific weight of 2.7g/cm³
• strength: iron is stronger and harder than aluminum
• thermal conductivity: iron has significantly lower thermal conductivity compared to aluminum
• melting point: iron has a higher melting point, approximately 1538°C (aluminum: 660°C)

These differences arise from differences in their atomic structure and metallic bonds.

Atomic structure: Iron has a more complex crystal structure, typically a body-centered cubic arrangement. This arrangement of atoms makes iron stronger and more resistant to deformation. In contrast, aluminum has a face-centered cubic crystal structure, which allows for easier deformation because these structures have more planes along which atoms can slide more easily.

Atomic bonds: The bonds in iron are stronger due to it having a higher number of delocalized electrons in the atomic structure, which contribute to stronger metallic bonds. These bonds require more energy to break, resulting in the greater hardness and strength of iron.

Atomic weight and atomic size: larger aluminum atoms are placed further apart in the crystal lattice, which reduces the strength of interactions between them.

There are other differences (magnetism, corrosion, etc.), but these do not affect the behavior of the material during machining.

In practice, however, pure aluminum or iron is rarely used. Additional additives (alloys) are always added to these raw materials, which change the properties of the material depending on the purpose for which the future final product will be used - these targeted changes in properties can further increase the difference between the two metals.

What tools and methods are used to cut aluminum?

In industrial conditions, especially where there are higher requirements for accuracy and cleanliness of the cut and different thicknesses of the processed materials, circular, band and mitre saws for metal with appropriate arrangement, cutting geometry and tooth spacing are used. Excellent results can be achieved with a mitre saw in particular, but it is necessary to ensure that the individual teeth have an even engagement, which is why the machine feed of the saw relative to the workpiece is ideal. Cooling the workpiece and the tool is not necessary, but it will help to create an even cleaner cut, especially with thicker profiles. Various coolants can be used for cooling, e.g. for saw blades, turpentine is mainly used when cutting non-ferrous metals.

Fig. 2. Cutting surface of an aluminum profile after laser cutting

For the most demanding applications, where a perfect cut of even thicker workpieces is required without the need for subsequent surface treatment by grinding or polishing, technically advanced methods such as laser cutting (fig. 2), high-pressure water jet cutting or plasma cutting are suitable. Caution is required with the latter two methods, as they can create heat-affected zones in the workpiece.

All of these methods require you to have relatively expensive and complex tools and technologies.

However, non-ferrous metals can also be cut using simpler, less expensive mechanical methods. This is mainly cutting with tools that are quite widespread, whether it is a hacksaw, reciprocating saw or circular saw.

If you have a reciprocating saw, you can successfully use it to cut aluminum profiles. When using a suitable saw blade, the result is quite satisfactory, but it is necessary to take into account that if a clean cutting surface is required, additional surface treatment by grinding or polishing is unavoidable. Any bimetallic saw blade is suitable for cutting metals or metal profiles, but the speed of the cut and its quality - cleanliness - depend on the distance between the teeth and the cutting geometry. Most of the time, these are milled teeth arranged alternately on the right and left with the cutting geometry MS (milled & side set), or with smaller spacings, they are wavy milled teeth with the cutting geometry MWS (milled & wavy set).

For illustration purposes, we cut a 40x40mm structural aluminum profile with internal crossbars with our HERMAN RX-41F SteelCut and HERMAN RX-61F SteelCut saw blades. The first one is designed for cutting thick-walled metals with a thickness of 4-12mm, has a tooth pitch of 8-10 TPI (distance between teeth 2.5-3.2mm) and an MS cutting geometry.

The second is designed for cutting thin-walled metals with a thickness of 1-4mm, has a tooth pitch of 18 TPI (distance between teeth 1.4mm) and wavy milled teeth with MWS cutting geometry. You can see what the cutting surface of an aluminum profile looks like after cutting with these tools in fig. 3.

It can be seen that the burrs after cutting are slightly smaller with the finer saw blade. The cutting logically took a little longer (RX-41F SteelCut – 12 seconds, RX-61F SteelCut – 15 seconds).

Fig. 3. Cutting surface of an aluminum profile when cutting with a reciprocating saw. RX-41F SteelCut saw blade (A) and RX-61F SteelCut saw blade (B)

Fig. 4. Cutting surface of an aluminum profile when cutting with a jigsaw. JX-51F saw blade (A) and JX-71F saw blade (B)

If a reciprocating saw is not available, but you have a jigsaw, you can also use it to cut non-ferrous metals with approximately the same results. For comparison, we chose two saw blades with different characteristics: HERMAN JX-51F SteelCut for cutting metal materials with a wall thickness of 2.5-6.0mm, with a tooth pitch of 12 TPI (tooth spacing of 2.1mm) and a MWS cutting geometry, and HERMAN JX-71F SteelCut for cutting thin sheets of 0.4-1.5mm, with a tooth pitch of 32 TPI (tooth spacing of 0.75mm) and a MWS cutting geometry. In this case, the saw blade had very fine teeth with a very small pitch and the cutting speed was significantly slower - caused by clogging of the teeth with aluminum filings and thus significantly reduced material removal. There is no significant difference in the appearance of the cut surface (fig. 4).

Whether you use a reciprocating saw or a jigsaw, the result is determined by the principle of operation of these tools: the vibrations of the tool are transmitted to the workpiece and leave marks on it in the form of grooves. The cutting speed is low when cutting with these tools, and practically every movement of the saw blade is visible on the cut. If you took the trouble to count the grooves on the workpiece, you would find that each stroke of the saw during the cutting process left its own mark on the cutting surface. On top of all this, when cutting metal with these tools, it is quite difficult to maintain an accurate cutting line by hand.

To achieve a much cleaner cut, you need to use a circular saw. When used with the HERMAN CX-30 AlCuCut saw blade, the cut surface looks much better (fig. 5).

This 160mm diameter blade is specially designed for cutting non-ferrous metals with hand-held circular saws. Up to 48 alternating flat and trapezoidal teeth made of cemented carbide with a 6% cobalt content and a positive rake angle ensure a very acceptable cut. The slight protrusion of the teeth over the edge of the blade body helps to reduce friction even when the tool is deflected to the side during cutting, and the significantly higher cutting speed also has a great influence on the cut quality. The blade has a thin body and a smooth surface, and compared to a hacksaw or straight saw, the tool moves faster relative to the workpiece and the direction of movement of the tool is always in one, the same direction. In addition to the very hard and precise teeth, the fact that it is much easier to maintain a straight cut line also contributes to the clean cut profile.

Fig. 5. Cutting surface of an aluminum profile when cutting with a circular saw using the CX-30 AlCuCut saw blade

Conclusion

All of the methods described for cutting non-ferrous metals have their pros and cons, advantages and disadvantages. What they have in common, however, is that they require tools that are not a common part of every workshop. You will never achieve as straight and clean cuts with a reciprocating or jigsaw as with a circular saw - but the advantage is the ability to cut curves if you need to. A circular saw with the right blade will achieve a nice and clean cut, but forget about curves.

In the following article we will talk about how you can handle cutting these materials even if you don't own the above-mentioned saws. All you need is a universal helper at hand - an angle grinder.

Keywords: cutting non-ferrous metals, cutting aluminum, burrs, cutting geometry, deformation of non-ferrous metals, cutting tools, reciprocating saw, jigsaw, circular saw

Sources:
HERMAN internal technical and training materials
The science of metals / Jozef Čech

Ing. Anton Tokár