Machining of aluminum

In comparison with other construction materials aluminum and its alloys are relatively easily machined.

Machinability of aluminum

Machining usually includes all cutting processes: turning, milling, stroganie, boring, sawing, etc.. d. Because of different aluminum alloys are quite a few, they may have different characteristics machinability.

The term includes all the workability properties, which are relevant to the machining process:

wear of the cutting tool;
required cutting force;
chip shape;
surface quality after machining.

Machinability is not as material property, which could be defined by one characteristic parameter. It is a complex technological term. The workability depends on the physical and chemical properties of the aluminum or aluminum alloy, and from the production process, which was used in the manufacture of aluminum semi-finished products or articles.

Machining parameters

Kinematic interaction of the tool and workpiece is a decisive criterion for the machining process. Strictly speaking, the term "machinability" should be defined separately for each individual machining process (turning, drilling, etc.. d.). Typically, due to a well-defined interaction between tool and workpiece, the term "processability" refers to the process of turning.

each technology, which is used for machining, depends on several independent parameters:

cutting parameters and tool geometry;
equipment used;
a cutting tool material.

See. Cutting tools for aluminum

Aluminum shavings

The shape of chips is an important criterion for machining aluminum. Usually try to get a short cylindrical retinue chips, helically wound spiral chips or just chips.

Various types of aluminum chips pretty much. With a large variety of aluminum alloys, they can produce almost all known forms of chips. The following pattern is usually observed: the harder and stronger the aluminum alloy, the shorter its chips. The following general rules follow from it:

Pure aluminum is soft and deformable aluminum produce very long chips, forcing to take specific corrective measures, for example, Special tools for chip breaking.
High strength aluminum alloys (for example, AlMg5, AlMgSi1,0) do not present any problems with the shape of the chips;
Hypoeutectic casting aluminum alloys (AlSi8Cu3, AlSi10Mg etc.. give short circular and spiral shaped chips, which is easily removed.
Eutectic cast aluminum alloys (AlSi12) tend to form long chips;
Casting hypereutectic aluminum alloys always form short, fragmented chips, which it is often difficult to remove.

Aluminum alloys with improved machinability contain low melting soft metals, that promote the formation of short chips. Usually - it alloys with the addition of lead or bismuth.

One of the technological parameters, that affect the shape of the chips, a cutter tooth geometry. So, under reduced front angle formed shorter chips in those alloys, which is usually characterized by long chips. This is due to the compression of the chips (figure 1).

Figure 1 - Compression chip with high and low tooth rake angle

Surface quality when machining

In general, the surface quality, which is formed during machining of aluminum and aluminum alloy, depends on three independent parameters:

Kinematic roughness: theoretical roughness depth (bottom to top), which is calculated based on the relative movement of the cutting tool and workpiece.
Roughness of a machined surface: the characteristic behavior of the material during its mechanical separation, associated with the features of its microstructure;
External influences: such parameters, as the stability of the system, the condition of the cutting edges, etc.. P.; these parameters are especially important when machining aluminum at high cutting speeds.

In general, the effect of material on the degree of roughness of the workpiece surface after the machining, i.e. the quality of the machined surface, It depends on the same factors, and that the form of chips.

With respect to wrought aluminum alloys, this pattern looks like this:

the higher the strength and hardness of the aluminum alloy, which is machined, the more smooth surface, you can get it.

As for the casting of aluminum alloys, then machined to their surface certain influence their microstructure. solid particles, are embedded in a soft matrix, can be pulled out to form a rough surface. Nonetheless, generally, surface quality of the machined surface of the cast alloys can also be considered as good, and often very good.

Cutting speed

Cutting speed is an important parameter of machining, which influences the surface quality. Typically, the roughness value is inversely proportional to the cutting speed. At low speeds, the cutting surface roughness increases very rapidly because of the increased adhesion on the cutting edge. In mechanical machining aluminum low cutting speeds, usually, avoided. Sticking to the cutting edge - a phenomenon, which is typical for aluminum. It consists in the repeated adhesion of aluminum particles to the cutting edge of the tool, followed by their tearing off the edge (Figure 2).

Figure 2 - Adhesion of aluminum on a cutting edge at a low cutting speed

Aluminum machinability: classification

Groups machinability aluminum

From the point of view of machinability, aluminum alloys are divided into the following groups (in order of increasing difficulty of machining):

Group 1: Low strength wrought aluminum alloys;
Group 2.1: Deformable aluminum alloys of increased strength;
Group 2.2: Aluminum alloys for machining;
Group 3.1: Aluminum-silicon alloys with silicon content up to 10 %;
Group 3.2: Eutectic aluminum-silicon alloys;
Group 3.3: Hypereutectic aluminum-silicon alloys.

Group 1: Low-strength wrought aluminum alloys

1) Thermally non-hardenable alloys in annealed state or partially cold-worked state:

Examples of alloys:

AlMn,
AlMg1,
AlMgMn.

2) Heat-hardening alloys in unaged state:

Examples of alloys:

AlMgSi0,5,
AlMgSi1.

Characteristic properties for machining:

soft,
Plastic,
low strength,
no solids,
tendency to stick to the cutting edge.

Group 2.1: High strength wrought alloys

1) Heat-hardened thermally unhardened alloys:

Examples of alloys:

AlMn
AlMg1, AlMg2, AlMg3, AlMg4, AlMg5
AlMgMn
AlMg4,5Mn

2) Heat treated alloys in aged and / or cold-worked condition:

Examples of alloys:

AlCuMg1
AlZnMg1
AlZnMgCu0,5
AlZnMgCu1,5

Characteristic properties for machining:

strength from 300 to 600 N / mm2 with good elongation,
no solids - low tool wear,
decrease in strength with increasing tendency to stick to the cutting edge.

Group 2.2: Aluminum alloys for machining

Thermally treated wrought alloys with additives for chipbreaking

Examples of alloys:

AlMgSiPb
AlCuBiPb
AlCuMgPb

Characteristic properties for machining:

short chips due to the presence of Pb and Bi additives;
strength from 280 to 380 H / mm²;
low tendency to stick on the cutting edge.

Group 3.1: Al-Si cast alloys with silicon content up to 10 %

1) AlSiCu alloys

Examples of alloys:

AlSi5Cu1
AlSi6Cu4
AlSi8Cu3

2) AlSiMg alloys

Examples of alloys:

AlSi7Mg
AlSi9Mg
AlSi10Mg

Characteristic properties for machining:

strength from 250 to 360 N / mm²;
increased wear of the cutting tool due to hard components of the microstructure and inclusions;
good chip brittleness and smooth surface;
the tendency to stick to the cutting edge with the content aremniya more 5 %.

Group 3.2: Low hardness Al-Si cast alloys

Al-Si alloys with a silicon content of about 12 %

Alloy example:

AlSi12

Characteristic properties for machining:

low hardness of the aluminum matrix;
solid metal microstructure components and inclusions;
high propensity to stick on the cutting edge.

Group 3.3: High hardness Al-Si cast alloys

Al-Si alloys with silicon contents exceeding 12 %

Examples of alloys:

AlSi18CuMgNi
AlSi21CuNiMg
AlSi25CuMgNi
AlSi17Cu4FeMg

Characteristic properties for machining:

medium strength;
high hardness;
very low plasticity;
high wear of the cutting tool due to very hard intermetallic particles and primary silicon;
high propensity to stick on the cutting edge.

Source: TALAT 3100

See. Cutting tools for aluminum