First we answered these questions in the articles on the individual coatings (TiN, TiAlN, AlTiN, TiCN and RUnaTEC): What is the inherent nature of the coating? When do I use which coating? Which coating is suitable for which materials?
Here we put together an overview of the properties of the coatings. Of course, you can also read the individual articles to get more information.
Basics on coating
A coating is a very thin (micrometer-thin), firmly adhering layer of a chemical compound that is applied to a workpiece. The coating has the following positive influences on the precision tool:
- Increased service life / wear resistance
Friction and wear occur on the tool surface between two moving parts (workpiece and drill). This friction puts a strain on the drill and is reduced by the coating. This extends the life of the tool.
- Enabling higher cutting speeds
The cutting speed can be increased due to the protection of the coating.
- Corrosion prevention
The coating protects the tool from being destroyed by reactions to the environment, e.g. rust.
- Optical upgrading
The coating thickness is given in micrometers (μm) and does not exceed 0.7 μm as thicker layers are susceptible to cracking.
Depending on the material to be machined and the precision tool, coating reguirments must be considered. Two factors play an important role here:
- the application, i.e. into which material is to be drilled
Is it e.g. mild steel, stainless steel or aluminium? The harder the material, the higher the nano hardness of the coating.
- the type of cutting (e.g. drill, mill, thread)
For example, threading uses a lower speed than drilling with a twist drill, so the requirements for the maximum application temperature are different.
Increased tool life
The service life is defined as the time until the permissible wear is reached. In other words: The service life is the time until you are no longer satisfied with the drilling result, or the performance of the tool suffers.
Besides the coating, the service life depends on:
- cutting speed
- tool steel
- chip cross section (size of the cut surface)
- machine use (guided, manually operated)
A major advantage of a coating is the extension of the service life of the precision tool.
Even the most commonly used standard coating TiN increases the service life by a factor of three to four. So if you are cutting a lot and do not want to buy new drills every week, you should use a coated drill.
You can also extend the service life by cooling.
Cutting speed and max. application temperature
The cutting speed is given in meters per minute (m/min). During cutting, the cutting edges of the tool wear out due to friction, break-outs and diffusion at high temperatures. This changes the cutting edge geometry and reduces the quality and accuracy of the tool. By setting the exact cutting speed, you can achieve optimum results and minimize tool wear.
As already mentioned above, a lower cutting speed is required for threading than for drilling.
The maximum application temperature depends on the cutting speed. The higher the cutting speed, the higher the maximum application temperature of the coating.
What are the individual coatings in our product range and in which applications are they used? The table below gives you a good overview depending on the type of cutting and tool steel.
For very hard materials (e.g. stainless steel) that are to be cut with twist drills, TiAlN on tungsten carbide drill can be the coating of your choice.
As you can see in the table, you can only find the TiN coating on HSS tool steel. Tools made of harder steels are also used for cutting harder materials. The TiN coating cannot withstand the resulting high temperature.
TiAlN bridges the gap between the tool steels HSS and tungsten carbide for drilling, as it can also be used for high cutting speeds.
Cooling has a positive effect on the tool, regardless of the coating. Therefore, we always recommend cooling the tool, even if it is not absolutely necessary.
Coolants ensure the
- reduction of friction
- removal of chips
- removal of heat
- increase of service life
- improvement of material surface
- cleaning of workpiece
- avoidance of corrosion
Cooling is not absolutely necessary for some coatings.
The nano hardness is expressed in gigapascal (GPa) and indicates the pressure exerted by a force of one Newton on an area of one square meter. (The formula is: 1 kg·m−1·s−2 = 1 N·m−2)
With nano hardness, harder materials can be cut and higher cutting speeds can be achieved. This has a positive effect on the required working time.
During drilling, the moving tool meets a stationary material. This results in friction and corresponding heat. The aim is to transmit the resulting forces with low friction losses.
The coefficient of friction is expressed in μ.
With cooling, for example, the coefficient of friction from steel on steel can be reduced from 0.2 to 0.07 μ.
Summary and conclusion
Coatings always have a positive influence on the tool. Depending on the field of application, a different coating is advantageous.
The following table shows you a comparison of the different technical parameters and fields of application of the five coatings.
|Coating||Nano hardness up to [GPa]||Coat thickness [μm]||Coefficient of friction||Max. application temperatur [ºC]||Application|
|TiN||24||1-7||0,55||600||less hard materials (Steel (N/mm²) <900)|
|TiCN||32||1-4||0,2||400||hard materials (Steel (N/mm²) <1.300, stainless steel)|
|TiAlN||35||1-4||0,5||700||hard materials (Steel (N/mm²) <1.100, stainless steel)|
|AlTiN||38||1-4||0,7||900||very hard materials (Steel (N/mm²) <1.300, stainless steel)|
|RUnaTEC||45||1-4||0,45||1.200||very hard materials (Steel (N/mm²) <1.300, stainless steel)|
In this PDF (0.5 MB). you have a overview of coatings used for which application.