Cutting Tool Materials in Machining Operations

Machining is a very important area in that we produce different kinds of parts from different materials. In machining operations, we use cutting tools that must be harder and stronger than the workpiece material. So, here we explain the cutting tool materials and types of them in general.

What are the Cutting Tool Materials?

In general, we use different kinds of materials in the cutting tool technology. But firstly, we need to know the general characteristics that we are expecting from cutting tool materials.

Toughness

This is one of the most important properties that we are expecting from cutting tool materials. Toughness is the energy-absorbing ability of materials without any deformation. So, the tıughness of the cutting tool materials must be very high. Because, if any deformations take place, the machining operation will not be successful.

Hot Hardness

In machining operations, the most important parameter is the high temperatures. Because temperature rises in machining operations is a very problematic issue.

And the cutting tool material must withstand high temperatures and its hardness must not change with the increasing temperatures.

Think about a cutting tool that loses its hardness at elevated temperatures. And an ordinary turning operation will fail because of the tool.

Wear Resistance in Cutting Tool Materials

This is also a very important parameter that we need to consider in the cutting tool materials. Every cutting tool wears eventually. Because wearing is about the nature of the material. But the wearing must not be rapid for cutting tools.

So, the level of wear resistance is very important for cutting tool materials. Because they reduce the expense of the cutting tools.

If we consider these parameters, we can state these materials in general;

• High-speed steels,
• Cast cobalt alloys,
• Cemented carbides,
• Cermets and coated carbides,
• Ceramic materials,
• Synthetic diamonds,
• Cubic boron nitride(CBN),

If we take a look at the cutting tool market, 905 of the cutting tools are high-speed steel and cemented carbides, cermets, and coated carbides.

So, they are common in machining operations. We can take a closer look at all of these materials.

High-Speed Steel(HSS)

The predecessors of high-speed steels were the high carbon plain carbon steels as cutting materials. Because they possess relatively high toughness and hardness values. But with the increasing temperatures, these steels lose their hardness properties. But with the advancing technologies, the emergence of high-speed steel takes place.

So, the developments of HSS solved the problem of the high-temperature hardness of the low alloy and high carbon steels. They become very common cutting tool materials. And also, there are different types of HSS.

High-speed steels are one of the most common cutting tool materials among the others in the market. Because, the production and the mechanical capabilities of high-speed steels are superior for lots of kinds of applications such as milling broaching, drilling, and other operations.

If we compare it with other kinds of materials, the toughness of the general high-speed steel is better. Also, the ability to machine complex shapes is very good. Because of this property, machinists generally use HSS tools.

Tungsten HSS

They are also very different and important high-speed steels that have very high compositions of Tungsten material inside them. The composition of Tungsten is around 18%. Also, there are other alloying elements such as 4% Chrome and 1% Vanadium.

Tungsten HSS have very high hardness and toughness values which they use in the toughest machining operations in high-speed applications.

Molybdenum HSS

Also, there are applications where the primary constituent is Molybdenum. The percentage of Molybdenum is high as the Tungsten HSS. Also, the addition of Cobalt improves the hot hardness values of the HSS.

Cast Cobalt Alloys as Cutting Tool Material

In typical cast cobalt alloys, the composition is around 40% to 50% chromium and 25% to 30% of Tungsten, and other portions of other alloying elements.

The most important advantage of cast cobalt alloys as cutting tool materials is that they have very high hardness values even from high-speed steels. Also, the wear resistance capabilities of cast cobalt alloys are higher than at high speeds. But their toughness is their downside.

Cast cobalt alloy tools are better for rough machining of materials.

Cemented Carbides as Cutting Tool Material

Cemented carbides are also a very common material in machining operations and cutting tools. They are produced from the tungsten carbide which is sşntered with Cobalt.

Among the properties of cemented carbide cutting tool materials;

• They possess very high compressive strength. But the tensile strength them are not high.
• They are generally hard materials and because of these hardness values, they are very good for machining operations.
• Also, the hot hardness of these cutting tool materials is very high. This is also another important property that makes them suitable materials for machining operations.
• Wear resistance capacities are also very good.
• The high thermal conductivity of these materials gives them very good dissipation of the heat rise in machining operations.
• But the toughness of cemented carbide tool materials is lover than the HSS.

In general, there are two classes of cemented carbide cutting tool materials: non-steel cutting grades which are for machining aluminum, brass, and copper materials.

The second class is the steel cutting grades that we use in the machining of steel materials.

Cermets

Cermets are also very common materials in cutting tool technology. They are composite materials which compose of ceramics and metals. The most common cermet materials for cutting tool applications; are TiCN, TiN, and TiC. So, use of the Titanium is very common in cutting tool material applications.

Coated Carbides

They are the cemented carbide tools that are coated with thin layers of wear-resistant coating to increase the wear resistance of these materials. In general, these coating materials are titanium carbide, aluminum oxide, and titanium nitride.

The applications of these coating materials are generally made with physical vapor deposition techniques. The general coating thickness is 2.5 to 13 micrometers or 0.0001 to 0.0005 inches.

They are appropriate in the milling and turning applications.

Ceramics as Cutting Tool Material

The application of ceramic materials as cutting tool materials was very common in history. Because ceramic materials are very hard materials for these kinds of applications. The most common ceramic material in these applications is aluminum oxide.

The production of aluminum oxide materials is obtained with sintering operations. With the proper sintering operations without binders, we can obtain cutting tool inserts.

Also, the addition of other oxides in small amounts are common application.

Diamonds and Cubic Boron Nitrides

You know from the general engineering and chemistry classes diamonds are one of the hardest materials in nature. Also, they are very tough and suitable for machining operations. But natural diamonds are very precious to use in these kinds of applications.

But the manufacturing techniques to produce diamonds. One of these synthetic diamonds is sintered polycrystalline diamonds. We apply sintering operations to produce the polycrystalline synthetic diamonds to create the general structures.

The hardness values of these diamonds can be high as 3-4 times of the cemented carbide tools.

The most cutting-edge technologies are the cBN cutting tools. They are nearly the same as the sintered polycrystalline diamonds but there are protective coatings on these inserts. These protective coatings are generally WC-Co coatings to increase wear resistance. In general, we use these cubic boron nitride cutting tools in steel and nickel alloy applications.

Effects of Different Alloying Elements in Cutting Tools

As you see above, the applications of different alloying elements in cutting tools are very common. They use these materials because of their different effects. Here we summarize these effects in general.

Chromium

Chromium is a very important alloying element in steel applications. In general, they use this alloying element in 3.75 to 4.5% of the total weight. The most important effect of Chromium is the increase in hardenability. Also, the abrasion resistance of the cutting tool materials is increasing.

So, they generally use Chromium in the cutting tool materials.

Carbon in Cutting Tool Materials

Carbon is also a very important and common material in cutting tool applications. The general weight percentage of Carbon elements is 0.75 to 1.5%.

They are the principal hardening element of steel which is compounded with iron. So, steels with high carbon content will be harder in structure. Also, they use Carbon to form tough carbides such as cemented carbide cutting tools. The addition of Carbon increases the wear resistance.

Cobalt

As we stated above, hot hardness is a very important property in machining operations. Because the cutting tool material must stay hard in temperature rises.

Cobalt is the most important element to add to the materials to obtain hot hardness. They generally add up to 125 Cobalt to the materials.

Vanadium

Vanadium is also a very important element to increase the wear resistance of the materials. Also, we can obtain finer grain structures with the Vanadium addition to obtain better toughness values.

The general percentage of Vanadium in cutting tool materials is 1 to 5% weight percentages.

Tungsten

In HSS Tungsten is a very important element that we use. In T-Type and M-Type materials, we use Tungsten material. The most important effect of Tungsten that is increases the hot hardness. Also, it improves the abrasion resistance with the hard carbide formation in the microstructure of High-Speed Steels.

In general, they use the Tungsten as 12-20% in wweiht ing T-ype HSS, and 1.5-6% in M-Types HSS.

Molybdenum

Also, Molybdenum is a very important material in High-Speed Steels. This is another material that increases the hot hardness of these materials. Also, it increases the abrasion resistance. So, the effect of the Molybdenum is the same as the Tungsten.

We generally do not use Molybdenum as an alloying material in T-type HSSs. But we use them in M-type HSSs around 5-10% in weight.

Conclusion on Cutting Tool Materials

As you see above, there are various kinds of materials that we use in the production of cutting tools. They must be very hard and very tough to machine the hardest materials such as steel. So, different kinds of materials with different production methods are used in this technology.

In the cutting tool materials, cemented carbides and high-speed steels are the most common ones. Also, there are very important materials that we use as alloying elements in these materials. These materials are improving the hot hardness values in general.

They are the general points that we need to state about this topic. Finally do not forget to leave your comments and questions below about this topic.

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FAQs About Cutting Tool Materials