Nowadays, we want to produce products as quickly as possible and thus make the most of our machines, which brings us greater profit. How do we achieve such productivity?
We can improve or perfect the tool path, but when this is no longer enough, we want to increase the speed and movement of the tool. There may be a problem here. The tools are usually made of carbide, but they only have loads to a certain extent and what is more can ultimately result in tool breakage. As a result of the continuous development of production processes, protective PVD coatings have been developed, which have been established in the industry for many years. It all started with the gold TiN coating, which is still used in some places, but in most applications it has been replaced by special coatings designed only for certain materials.
We wanted to see for ourselves what impact the correct choice of coating has on the life of the cutting tool itself, so we tested cutters and drills refined with different coatings in the processing of carbon steel OCR (1.2379) and hardened steel 42CrMo4. This article presents the testing section - drilling with a drill Ø8 in 42CrMo4 steel. We compared an uncoated drill bit with a Ti4Al-coated drill bit and a 4HARD-coated drill bit, with all drills having a similar initial sheath of 12 μm in diameter and exposed to the same processing conditions.
Ti4Al as well as 4HARD are the latest generation of PVD coatings, which have a very fine grain structure and a very smooth surface and do not round the cutting edge.
The 4HARD coating is designed for the processing of very hard hardened materials, at the same time it is highly resistant to high temperatures and extremely suitable for processing without cooling.
Ti4Al coating is used to process all types of steels up to a hardness of around 55 HRC, which makes this coating the first choice for tested hardened steel 42CrMo4 with a hardness of 53 HRC.
Cutting parameters:
- vc = 160 m/min
- f = 0,2 mm/obr
- L = 4xD
- emulsion cooling through cooling channels
The upper wear limit was VB = 0.12 mm, which represents the wear on the cutting surface. Of course, the VB criterion for tool sharpening or changing can be higher if we do not need to achieve very smooth workpiece surfaces.
Coated drills reached the required criterion with different number of holes, while the uncoated drill had to finish processing prematurely, and the wear of the cutting edge itself significantly exceeded the set limit.
Test results:
- Uncoated drill: 18 holes
- Drill with 4HARD coating: 456 holes
- Drill with Ti4Al coating: 960 holes
The results and the picture show that an uncoated tool is not suitable for processing at high regimes, but at the same time we see that the correct choice of PVD coating is also important, as 4HARD coating is primarily used for processing very hard materials, but for certain not-so-hard materials it achieves 50% or even less efficiency compared to the best currently possible coatings.
That’s why we, a team of engineers and technologists, are here to advise you and select the best coating for your application!
Gazela d.o.o.
Žan Dobrovnik