Vol 39, No 1 (2019)

The damping decrements of pressure fluctuations in the combustion chambers of liquid-propellant rocket engines may be estimated on the basis of hard excitation of acoustic vibrations of a specific mode. A device for hard excitation of high-frequency pressure fluctuations has been developed. This device prevents damage to the components of the combustion chamber by flying metal fragments. Recommendations are made regarding the calculation of the acoustic characteristics for complex channels.

The dependence of the pressure angle on the angle of cam rotation is considered. Analytical methods are outlined for determining the minimum size of cam mechanisms with sliding and rocking shafts.

Laser welding is shown to be preferable to traditional soldering in the assembly of nonferrous and mineral components. Welding conditions that prevent cracking of minerals are presented.

Methods of producing intermetallic compounds of p and d metals are reviewed.

The relation between the cutting properties of superhard tool inserts and their eigenfrequency is studied. The relation between the life of inserts and their acoustic properties is confirmed experimentally in the turning of high-temperature nickel alloys and quenched steels. A method is developed for determining the eigenfrequency of cutting inserts, along with the corresponding equipment.

The turning of quenched steel by a cutting ceramic is optimized on the basis of simplex planning.

A critically important high-tech industrial enterprise forms part of a territorially distributed cooperative production system. Precise optimization of management decisions regarding fault prevention in its stock of machine tools is very important. Up-to-date tools for management decisions must be used for that purpose. Those tools must support the basic management functions and include software for high-level mathematical models of machine-tool operation (models of the state of the equipment and a model of its use in the course of production) and a model of the economic potential of the enterprises.

Attention focuses on means of improving the efficiency and capabilities of multipurpose machine tools by expanding the range of available tools and the methods of surface machining. As an example, new approaches are applied to the manufacture of complex parts by means of a multipurpose machine tool. The machining efficiency is improved.

A composite mill with single-use cutting inserts is considered. This mill is intended for dry cutting. Instead of traditional cooling of the cutting zone by means of lubricant fluids, this mill relies on autonomous tool cooling by phase transitions of the first kind (evaporation and melting). Operational tests show that the temperature in the cutting zone and hence the tooth wear decrease when using this mill.

It is established that intercrystallite corrosion of cutting-ceramic inserts arises when the chromium content in the peripheral zone of the grains is depleted by the deposition of chromium carbides at the grain boundaries, in the presence of stress due to the fast cooling of the inserts from high temperatures. This is especially apparent when 12Kh18N10Т, 40Kh13, 14Kh17N2, and other steels that are hard to machine are worked by a tool equipped with inserts of VOK-60M modified cutting ceramic. Research shows that the intercrystallite corrosion of cutting-ceramic inserts may be attributed to the stress arising in the surface layers of the grains as a result of carbide or nitride deposition. Heating cutting-ceramic inserts at 650–800°С lowers this stress and restores their resistance to intercrystallite corrosion. Research also shows that chromomanganese cutting-ceramic inserts are less susceptible to intercrystallite corrosion than are chromium–manganese–nickel inserts, while chromium–manganese–nickel cutting-ceramic inserts are less susceptible than are chromonickel inserts. The benefits of chromium–manganese–nickel cutting-ceramic inserts are especially pronounced with relatively brief machining of 12Kh18N10Т, 40Kh13, 14Kh17N2, and other such steels, in rigorous conditions, with a temperature of 600–650°С in the workpiece–tool contact zone. A new theory of the intercrystallite corrosion of VOK-60M modified cutting ceramic is based on the role of the kinetic factor at the relatively low tempering temperatures associated with the deposition of metastable carbide, although this does not lead to maximum change in free energy of the system but only to a relative change. In the cutting ceramic, this carbide may be chromium carbide (Cr, Тi)₂₃C₆, which is greatly enriched with titanium. With increase in tempering temperature, the deposited carbide tends toward the stable composition Cr₂₃С₆. Prolonged holding at the tempering temperature also tends to favor thermodynamic equilibrium. In other word, the chromium carbide is gradually enriched to reach the stable composition Cr₂₃С₆. This process is more rapid at higher temperatures. Obviously, the variation in composition of the carbide deposited at the grain boundaries in VOK-60M cutting ceramic with change in temperature and holding time will affect the kinetics of electrochemical solution of the system consisting of the carbide in contact with a solid solution. Research shows that vacuum sintering and annealing markedly improve the thermal stability. For the cutting ceramic, this is explained not only by the removal of fusible impurities but also by the larger quantity of aluminum and other alloying elements that remain in the strengthening phase, rather than being bound in oxides. Sintering in vacuum ensures greater plasticity of cutting ceramic based on nickel and cobalt in cutting 12Kh18N10Т and 14Kh17N2 steel at high speeds, with high temperatures in the machining zone. In addition, on sintering in vacuum furnaces, the content of small nonmetallic inclusions in the basic structure is 5–7 times less than in regular cutting ceramic. That significantly improves the deformability of the ceramic inserts.

The assembly of ball screws is considered theoretically and experimentally in the case where the screw and nut are combined with an optimal combination of systematic and random errors in the screw pitch (optimal pitch error ratio).