PSI - Issue 59

Viktor Kovalov et al. / Procedia Structural Integrity 59 (2024) 779–785

784

6

V. Kovalov et al. / Structural Integrity Procedia 00 (2019) 000 – 000

Table 1 presents the results of statistical analysis of the system operation time structure when machining parts on heavy lathes of different sizes (the characteristic of the machine size is the largest diameter above the bed of the workpiece D max ).

Table 1. Structure of heavy lathes operation time structure Cause of system condition

Machine dimensions D max , mm

1250

2500

4000

Percentage of system uptime

Part replacement and inspection

0,15 0,03 0,13 0,08 0,61

0,10 0,03 0,07 0,06 0,74

0,16 0,03 0,04 0,19 0,68

Machine control Other downtime

Downtime related to cutting tool maintenance

Cutting

The downtime associated with cutting tool maintenance accounts for 8-9% of the total system operation time and 25-27% of the time in which the system is out of operation. The downtime associated with cutting tool maintenance includes the time of tool replacement, sharpening, repair, adjustment outside the machine tool, the time of machine operator's (adjuster's) visits to the tool room, etc. Statistical studies show that the distribution of the total downtime of the system related to the cutting tool maintenance (the time of system operability recovery) does not contradict the exponential law G(t)=1-e -  t , and the time of occurrence of cutting tool failures F(t)=1-e -  t . To increase the stability of cutting properties of the tool, carbide inserts of prefabricated picks were subjected to treatment with pulsed magnetic field. The results of comparative operational tests for machining 41Cr4 steel are given in Table 2.

Table 2. Results of operational tests of T15K6 prefabricated picks when machining 41Cr4 steel Tool Cutting modes Average durability period, min Coefficient of variation

γˉ -% endurance period, Тγ , min

Parameters of the Weibull Gnedenko law

t, mm

S, mm/rev

V, m/min

a

b

3

0.86

78

42

0.82

12.6

44

1.3

Т15К6 (P10)

3

0.86

78

48

0.47

24.5

55

2.25

Т15К6 (P10)+ PMFT Т15К6 (P10)+ VT + +PMFT

3

0.86

78

52

0.36

27

59

3

The position of the diffraction maximum of the cobalt phase lines before and after treatment with a pulsed magnetic field was recorded. A shift of the maximum towards higher angles was registered. This can be related both to changes in the composition of the solid solution of tungsten and carbon in cobalt and to changes in the stress state of the crystal lattice. Since the fracture of the carbide occurs through the (Ti, W)C phase, and the cobalt phase can inhibit the development of a fracture crack, the stability of the structure of the cobalt phase affects the strength characteristics and stability of the cutting properties of the tool. The increase in the strength of carbide tools treated with pulsed magnetic field, confirmed by laboratory tests of turning cutters by the destructive feed method (Table 3 ), is explained by the reduction of tensile stresses in the cobalt phase, which prevents the propagation of destructive cracks in the cobalt phase of the carbide, i.e. leads to an increase in its strength Table 3. Comparative tests of prefabricated turning cutters (40X steel, t=8 mm, feed range 0.8-2.05 mm/rev, cutting speed 20 m/min) Tool Durability period T, min Coefficient of variation V т Breaking feed rate Sp, min average T р gamma percentage Тγ Т5К10 (P30) 38 12 0,38 1.63 Т5К10 (P30)+ PMFT 42 14 0,25 2.05