PVD Coating – Cutting Tools

- Mar 21, 2018-

1. Tool life

For tool life, it usually depends on different workpieces and tool materials, as well as different cutting processes. The continuous development of the best tool substrate, coating and cutting edge preparation technology is important to limit tool wear and resist cutting temperature. These factors, together with chip breaker groove and corner radius used on indexable inserts, determine the applicability of each tool for different workpieces and cutting processes. The best combination of all these elements can lengthen the tool life and make the machining more economical and more reliable.

2. Change the substrate

By changing the grain size of tungsten carbide in the range of 1-5 μm, the substrate properties of cemented carbide tools can be changed. The particle size of the substrate material plays an important role in the cutting performance and tool life. The smaller the particle size, the better the abrasive resistance of the tool.

In addition, the cobalt content of carbide cutting tool material is increased by 6% to 12%, which can be achieved better toughness. And the requirements of a specific cutting process can be met by adjusting the cobalt content.

The performance of tool substrate can also be enhanced by forming cobalt rich layer near the outer surface, or by selectively adding other alloy elements (such as titanium, tantalum, vanadium, niobium, etc.) in the cemented carbide materials. The cobalt rich layer can significantly improve the cutting edge strength, thus improving the performance of rough machining and intermittent cutting tools.

In addition, when selecting the tool substrate matching with workpiece material and processing method, there are five other substrate properties, including fracture toughness, transverse fracture strength, compressive strength, hardness and thermal shock resistance, need to be considered. For example, for machining occasions with higher cutting temperatures (such as dry cutting), high hardness tool materials should usually be preferred. In the case of machining where hot cracking of the tool can be observed (most common in milling), it is recommended to use tool materials with good thermal shock resistance.

3. Coating selection

The PVD coating helps to improve the cutting tool performance. Current coating technology includes:

TiN coating: This is a general type of PVD and CVD coating, which can improve the hardness and oxidation temperature of the tool.

TiCN coating: By adding carbon element to TiN improved the hardness and surface roughness of the coating.

TiAlN and AlTiN coating: The composite application of the alumina (Al2O3) layer with these coatings can improve the tool life of the high temperature cutting. The alumina coating is especially suitable for dry cutting and near dry cutting. The content of aluminum in AlTiN coating is higher, compared with TiAlN coating with higher titanium content, it has higher surface hardness.

CrN coating: This coating has good adhesive resistance.

DLC coating: Diamond coating can significantly improve the cutting performance of machined non-ferrous family materials, and is very suitable for machining graphite, metal substrate composite, high silicon aluminum alloy and other high abrasive materials.

In recent years, the market share of PVD-coated tools has been expanded and its prices are comparable to CVD coated tools. CVD coating thickness is usually 5-15μm, while the thickness of PVD coating is about 2-6μm. When coated to the tool substrate, the CVD coating does not produce beneficial stress to the substrate, and the PVD coating helps to form beneficial compressive stress on the substrate. The thicker CVD coating usually significantly reduces the strength of the cutting edge of the tool. Therefore, the CVD coating cannot be used for cutting tools that require very sharp cutting edges.

IKS has actively cooperated with domestic and foreign companies and scientific research institutes, and has made gratifying achievements in some more commonly used coating applications. The coating process can be used to coating the film with high hardness, thermal stability and chemical stability. And various physical vapor deposition coatings, such as TiN, TiCN, AlTiN, AlTiSiN,CrN, DLC, etc.