PSI - Issue 32

V.B. Dementyev et al. / Procedia Structural Integrity 32 (2021) 291–294 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

293 3

These coatings are based on metallic and nonmetallic compounds like carbides, nitrides, borides and oxides of high strength materials films with thickness less than 0.02 mm. Coating materials have high hardness and wear resistance. Application of thin hard coatings on the work surfaces of cutting tools made of hard alloys and tool steels provides 20-50% decrease in friction force during machining of structural steel. It also allows 15-20% decrease in chip shrinkage ratio, results in temperature reducing during cutting and considerably increases tool resistance (by 3-5 times). Nowadays, there are many variants of such coatings. They differ in application technologies, chemical composition (carbides, nitrides and carbonitrides of titanium, molybdenum, zirconium, hafnium, vanadium, niobium, chrome, aluminum oxide, cubic boron nitrides). The number of coating layers and their thickness also vary (single layer, two layer and multilayer structure with thickness in the range of 3 to 15 microns). Research on efficiency of high-strength coating during drilling was conducted using the vertical drilling machine CORMAK. Parameters of cutting modes: cutting force – 30 …5 0 m/min., feed – 0.15 …0.21 rpm. Sharpening geometry: bewel lead angle 130°, back rake angle 5°, relief angle 10°. The quality of the coatings was determined visually. The coatings were applied as follows: As the tool wears, there is a moment, when further cutting should be stopped and the tool should be replaced or resharped. The moment of tool blunting is determined by the criterion of wear. Linear wear of flank is accepted as the criterion of wear, because flank surface of the tool wears regardless of the material machined and cutting mode. Besides, the measuring of worn area width is not complicated. Studies of wear of flank surface of the tool had been going for 1,5 months. During this period the wear of tools without coating and the tools with TiN coating had been measured in different moments of operation. The wear of drill bits has been measured along the flank surface on zones of transition from cutting edges to calibrated rims. The results are demonstrated in Table 1. - drill bits have been covered from the side of the flank without rotation; - plates have been covered from the side of the face without rotation. Base tools and tools with coatings have been tested at the same time.

Table 1. Results of testing of bits

Types of parameters

Base tool

Tool with coating

Number of machined workpieces, pcs

40

60

160

40

60

160

Number of cutting tools, pcs

4

4

12

1

2

3

Average wear of cutting edge in mm

0.33 14.3

0.62 21.8

0.64 109

0.15

0.4

0.8

8

12

80

Average wear resistance, microns per part

Conclusions As it was obtained in the most of the tests of axial tools, the number of parts, machined by the tool before its resharpening, has increased by three or more times. Therefore, the application of coatings on cutting tools can be recommended as the main method of increasing the efficiency of their use. Coatings on drill bits and boring bits gives a considerable effect only before the first resharpening operation, it is necessary to apply coating again after resharpening process. Having implanted the coating from the side of flank surface of the tool, it is necessary to implant the coating from the side of cutting rim. That is why it is necessary to have a cutting tool with rotation in horizontal direction. When the coating is applied as mentioned above, we can reach the strengthening of the corners, from which the wear starts to develop. The use of this method also allows reduction of coefficient of chip friction during its moving along the tool grooves. Thus, the results of the research on influence of wear-resistant coatings on tool operation efficiency allow us to make a conclusion that the use of titanium nitride coatings helps to increase the operation efficiency by 30% or more. The roughness of the surface, machined by the cutting tool with titanium nitride coating, also drops.