Diamond is characterized by its great affinity

The aerospace industry uses a wide range of materials due to its characteristics, such as strength, density and stiffness.

Examples of such materials are nickel based superalloys and composites. But they are difficult to cut, and special methods of machining are required. As a result, diamonds are used wherever conventional tools can not be used to achieve the ultimate goal of the production process.

Use of diamonds to increase tool life and improve cutting conditions

The success of the use of diamond tools in the aerospace industry is mainly due to the properties that this material possesses and which lead to an increase in the service life of the tool and improvement of the cutting regimes in comparison with conventional materials.

Diamond has the highest value of hardness of minerals on the Mohs scale (Mohs). This scale allows you to classify the resistance of the material to the appearance of scratches and has a range from 1 (the softest) to 10 (the hardest).

The diamond has a hardness of 10 on the Mohs scale, which corresponds to a hardness four times higher than that of corundum (Al2O3), which is 9 on the Mohs scale.

Diamond tools can be created using different materials depending on the application and the requirements for the product. Diamonds can be divided into natural or synthetic. Materials from synthetic diamonds can be divided into different classes: grains and powders, PCD (polycrystalline diamonds) and diamonds obtained by CVD (chemical vapor deposition).

Grains from synthetic diamonds

Fine grains of diamonds and synthetic diamond powders (abrasives) are used as abrasive materials by binding them to the surface of the tool. This can be achieved in various ways, depending on the required technological characteristics, for example, the tool rotation speed.

Diamond particles can be deposited on the surface of the tool either by electrolytic deposition using a nickel solution or by sintering using a tungsten matrix. Another method, known as high-temperature brazing, is that diamond particles are soldered onto the metal surface of the tool.

Each of these bonding methods has the corresponding advantages and disadvantages associated with the time required to produce the tools and the ability of the binder to retain the diamond particles depending on the final performance.

Instruments using PCD (polycrystalline diamond)

In tools using PCD (or polycrystalline diamond inserts), diamond segments are connected, usually by high-temperature soldering, to a carbide substrate. PCD elements are produced by sintering micron powders of synthetic diamonds to adhere particles to a process characterized by high temperature and pressure.

This material is produced using cemented carbide firing, which provides the desired source of metal, usually cobalt, for the sintering process. During the manufacturing process, the metal from the carbide carbide substrate penetrates between the grains of the diamond, ensuring their adhesion.

The content of metals in tools with PCD provides the material with electrical conductivity, allowing the use of such a machining process as cutting on EDM (EDM) for cutting diamond elements.

Instruments using synthetic CVD diamonds

Another type of synthetic diamond is produced using a technique known as chemical vapor deposition (CVD). Diamonds obtained with CVD are deposited as thin layers on the surface of the tool during the process, with careful monitoring of the growth conditions.

One of the main advantages when using this type of synthetic diamond is the possibility of obtaining additional geometric dimensions and cutting edges, using a material characterized by highly predictable properties.

The use of diamonds in aerospace manufacturing processes

At present, diamonds are used in a number of manufacturing processes in aerospace engineering, mainly because of their high wear resistance and the ability to machine materials that are difficult to cut. As already mentioned, diamonds can be produced in various ways, obtaining a number of products with characteristics specially specified for the end use of tools. They can be used in processes that use tools with geometric parameters of the cutting edge (turning, milling and drilling) and not geometric parameters (grinding and finishing).

The use of diamonds in machining is limited to colored materials. Diamond is characterized by its great affinity with iron and nickel, especially at high temperatures. Particular attention must be paid at the maximum process temperature to avoid the transformation of diamond into graphite due to the unstable nature of this material.

In particular, at low pressures, the diamond surface was graphitized at a temperature below 1700 ° C; The conversion temperature can be reduced to 400 ° C if iron components are present.

As a result, carbide tools are currently used in the machining of titanium alloys, nickel alloys and stainless steel using tools with geometric parameters of the cutting edge. Conversely, in the case of abrasive processes, materials such as CBN (cubic boron nitride), aluminum oxide and SiC (silicon carbide) are used for machining steel, nickel alloys, ceramics and titanium alloys.

Another alternative to diamond in the machining of materials from ferrous metals is PCBN (polycrystalline cubic boron nitride), a composite material produced by sintering CBN powder of micron fractions with various types of ceramics.

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