The intention behind sharing this article is to discuss choosing coatings of tools to improve their life in CNC machining. Mainly, four questions will get answered: what is tool surface coating technology, what are the benefits of tool coating, what are the different characteristics of the tool coating, and what are the widely used tool coatings. So, let us move on to their answers without any delay.
What is Tool Surface Coating Technology?
Tool coating technology is related to the surface modification of a tool that can improve its strength and work while performing machining. After the emergence of high-speed cutting tools, there has been seen a surge in the mainstreaming of tool coating technology. Meanwhile, tool coating is considered one of the most critical parts of the high-speed tool manufacturing industry.
Typically, the cutting tool’s surface is coated with the thin film, usually done using physical and chemical methods. The coating makes the cutting tool able to perform at its best while machining. Here are some of the characteristics of tool surface coating technology:
- The coating on the tool considerably increases its hardness without compromising its strength. Presently, the achievable hardness has reached the number of 100GPa.
- With persistently evolving coating technology, high-temperature oxidation resistance and chemical stability of coating on the tool has become even better and offer the best possible performance.
- Lubrication films possess exceptional solid-phase lubrication to improve the quality of processing.
- The coating on the tool does not disturb the accuracy while machining is being done.
What are the Benefits of Tool Coating?
Here are the most noteworthy benefits of tool coating:
- The service life of the tool gets better.
- Cutting efficiency becomes improved.
- Tool coating offers a better surface quality.
- It reduces costs and the need for cooling fluid while machining.
However, every tool coating can inflict excellent benefits and damages depending upon their use and selection. Accordingly, the nature of the work must be kept in mind while choosing the tool coating.
What are the Widely Used Tool Coatings?
Followings are some of the widely used coatings:
- Diamond Coating
When it comes to non-ferrous metal materials, CVD (chemical vapor deposition) diamond coating is an ideal choice. Besides, it is a perfect coating for metal matrix composite (MMC), high silicon aluminum alloy, processing graphite, and other abrasive materials. Remember, pure diamond-coated tools are not used to cut steel, as a considerable amount of heat is generated, and chemical reactions might damage the machining operation.
- Titanium Nitride Coating (TiN)
Titanium Nitride is a PVD (physical vapor deposition) coating used to improve the tool’s hardness and oxidation temperature. It is suitable for carbide and high-speed cutting tools.
- Chromium Nitride Coating (CrN)
Chromium nitride coating remains a top consideration to get built-up edges generated easily. It is almost invisible and offers services against carbide tools, high-speed steel tools, and forming tools.
- Nitrogen Titanium Carbide Coating (TiCN)
To meliorate the lubricity and hardness of the tool, TiCN is added with the carbon component. This coating provides the best performance against high-speed cutting tools.
- Aluminum Nitride Coating or Aluminum Nitride Titanium (AITiN/ TiAIN)
This coating is useful for carbide tools and the tools used for semi-dry cutting. Their performance depends upon the ratio of titanium added.
What are the Different Characteristics of the Tool Coating?
Let us discuss different characteristics of tool coating:
- Oxidation Temperature
Oxidation temperature is alluded to as the temperature at which the coating of the tool begins separating. The greater the oxidation value, the better will be the coating. Given that, TiAIN offers the highest oxidation temperature as the alumina layer gets developed between the tool and the chip. That is how the heat transfers to the work-piece or chip.
Hardness also plays a vital role in the long-life of the tool. If compared, TiCN coating has higher hardness than TiN coatings, and that is why TiCN is widely used for hardness purposes. Due to the increased carbon content in TiCN, the hardness becomes higher up to 33%, and the range remains between 3000-4000 (HV).
With surface hardness up to 9000 (HV), the CVD coating is a much better option than the PVD coated tool, increasing the life up to 10-20 times.
- Abrasion Resistance
The ability of a coating to resist wear is called Abrasion resistance. Since some tools are not inherently hard enough to sustain the machining operation, they are coated with suitable material.
- Lubricity of Surface
A high coefficient of friction usually heats tool and work-piece that adversely affect the efficiency of the process. Nevertheless, a smooth or textured regular coated surface reduces the heat during the process because frictional losses are now avoidable. Meanwhile, coated tools can also help have better-cutting speed due to the absence of friction.
- Adhesion Resistance
The coating largely avoids interaction between the tool’s real surface and the work-piece, improving the surface finishing and preventing the work-piece from getting deposited on the tool. This anti-sticking property can avoid the need for cooling fluid and external lubricity without compromising machining quality.
Many factors need to get looked after to have cost-effective and efficient coating applications, including cutting depth, speed, heat, wear, friction, and others. Also, the right choice of tool coating and its properties can significantly improve the machining process’s overall efficiency and performance.
Finally, the best way to choose the right tool coating to improve the machining process tool is test cutting.