Cermet Tooling Explained

Cermet tooling, as the name implies, is a cross between ceramic and metal tools.

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Made of ceramic particles bonded together with a nickel binder, these tools are capable of running at higher speed than carbide tools, and are much more wear-resistant. The surface of these inserts is very smooth, allowing the chip to flow easily and prevent built-up edges.

Ceramic tooling traditionally has been used for high-temperature cutting, especially in hard materials. However, these tools are very brittle and can handle only light interrupted cutting. When combined with metal, the properties of the carbide tool allow cermets to deform slightly because it is not a true ceramic insert.

'The nickel binder can handle the heat that is generated in the cutting process better than the cobalt binder of carbide inserts. Heat is the enemy in any cutting application,' explained Iscar Canada Senior Product Manager Steve Geisel.

Cermets were invented for high-quality surface finishes, cutting with high spindle speeds (800 to 1,200 SFM), and cutting for a long period of time without interruption.

'While carbide tooling now can run at 1,000 SFM because of new coatings and substrates, they still cannot compete with cermet tooling in terms of surface finish,' said Geisel. 'Less friction is created when using a cermet insert compared to a carbide insert, and this means less vibration.'

The more friction that is created, the more difficult it is to maintain a high-quality surface finish. According to Geisel, the only way to get close to the surface finishes created by cermet tooling is with a carbide insert with a wiper setup.

Coating Technology

Iscar's cermets are physical vapor deposition- (PVD-) coated and multilayered, usually with titanium nitride (TiN), titanium carbonitride (TiCN), and titanium carbide (TiC). Cermet tooling also is usually sharp, which is why it is PVD-coated instead of chemical vapor deposition- (CVD-) coated.

'Coatings help extend tool life,' said Geisel. 'Coated cermets will definitely last longer, and that helps control the costs of consumables.'

Tool life also is easier to predict with cermet tooling when compared to carbide, because the tool is engaged in the cut all of the time.

Cermet tooling is suitable for cutting carbon and alloy steels to tight tolerances, but can also be used to cut stainless steels and even high-temp alloys. It should not, however, be used to cut cast iron and aluminum.

Coolant Usage

A flood coolant setup is recommended for cutting with cermet tooling.

'The coolant lubricates the cut while cooling the chip,' said Geisel. 'Because of the high cutting speeds achieved in the finish pass, more heat is generated. Coolant cools the area and creates an environment for proper chip control.'

Chip control is very important at this stage because the last thing you want to do at the finish stage is scratch the surface of the workpiece. There may already be many, many hours of machining in the part.

'People have definitely not forgotten about cermets even with all of the advancement in carbide tooling,' said Geisel. 'Even though carbides have been making significant advances over the past few years, cermets are changing, too, with new chipformers and geometries available.'

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1. What is carbide?

Cemented carbide is a powdery metallurgical material: a composite of tungsten carbide (WC) particles and a binder rich in metallic cobalt (Co). Cemented carbides for metal cutting applications consist of more than 80% of hard-phase WC. Other important components are additional cubic carbonitrides, especially in gradient-sintered grades. The cemented carbide body is formed, either through powder pressing or injection molding techniques, into a body, which is then sintered to full density. Carbides exhibit excellent properties such as high hardness, wear resistance, good strength and toughness, heat resistance, and corrosion resistance. Particularly noteworthy are their high hardness and wear resistance, which remain largely unchanged even at temperatures as high as 500°C and maintain significant hardness at °C.

Carbides are widely used as cutting tool materials, including turning tools, milling cutters, planers, drill bits, boring tools, etc. They are employed for machining a variety of materials, including cast iron, non-ferrous metals, plastics, synthetic fibers, graphite, glass, stone, and common steel. Additionally, carbides can be utilized for cutting challenging materials like heat-resistant steel, stainless steel, high manganese steel, and tool steel.

2. What is cermet?

Cermet is a composite material composed of ceramic and metal. It is defined by the ASTM (American Society for Testing and Materials) committee as a heterogeneous composite material consisting of metal or alloy and one or more ceramic phases, where the latter typically constitutes 15% to 85% by volume. Importantly, at the preparation temperature, there is minimal solubility between the metal and ceramic phases. In a narrow sense, cermet refer to a category of materials within composite materials where both metal and ceramic phases have interfaces in three-dimensional space.

Composition of cermet

Cermet are created by adding metal powder to the clay used in ceramic production, allowing the ceramic to withstand high temperatures without becoming easily breakable. Metal matrix cermet, also known as dispersion-strengthened materials, are produced by adding oxide fine powders to a metal matrix. Examples include sintered alumina (aluminum-alumina), sintered beryllium (beryllium-beryllium oxide), TD nickel (nickel-thorium oxide), and others. These are composite materials composed of one or more ceramic phases and metal or alloy phases.

In a broader sense, cermet also encompass refractory compound alloys, carbides, and metal-bonded diamond tool materials. The ceramic phase in cermet consists of oxides or refractory compounds with high melting points and high hardness, while the metal phase primarily consists of transition elements (iron, cobalt, nickel, chromium, tungsten, molybdenum, etc.) and their alloys.

3. Differences between Cermet and Carbide

Cutting performance

Cermet inserts offer higher precision and smoother cutting surfaces than WC carbide inserts. With cermet inserts, high precision machining is usually achieved in a single cut. Tungsten carbide inserts perform better in softer materials and often cut faster.

Cutting life

Cermet inserts have better wear resistance and therefore longer life, while WC tungsten carbide inserts are generally better suited for mass production machining of workpieces.

Machining performance

Cermet inserts are relatively brittle and are prone to breakage under impact. In contrast, WC (tungsten carbide) carbide inserts are simple to manufacture and easy to use and maintain.

4. Conclusion

Compared to cemented carbide, cermet has improved wear resistance and reduced smearing tendencies. On the other hand, it also has lower compressive strength and inferior thermal shock resistance. In conclusion, WC (tungsten carbide) carbide inserts and cermet inserts each have their own advantages and disadvantages. Choosing the appropriate inserts depends on the workpiece and processing characteristics, considering factors such as cost-effectiveness, machining lifespan, and overall effectiveness.

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