INVESTIGATING THE INPACT OF TEMPERATURE VARIATIONS AND ADHESIVE PHENOMENA ON THE RESISTANCE OF A HARD-ALLOY TOOL UNDER INTERRUPTED CUTTING
Keywords:
intermittent cutting, fracture, durability, temperature, adhesion, transient processes.Abstract
The wear of the cutting surfaces of a tool during metal processing by cutting is a complex set of several simultaneously active destruction mechanisms, the degree of influence of which depends on the conditions of contact interaction between the work stock and the tool. The practice of operating cutting tools shows that a significant part of them is subjected to brittle fracture in the form of pitting and chipping.
The intensity of brittle fracture increases with intermittent cutting processes, the peculiarity of which is the presence of alternations of working and idle strokes, i.e. transient processes that occur during the plunge cutting and exit of the tool from the cutting zone, causing cyclic effects of force and thermal character on the brittle material of the tool, lead to its intensive wear and fatigue fracture, while the presence of impact during plunge cutting can lead to premature failure of the tool due to brittle destruction.
In the process of cutting steels, conditions arise between the tool and the work stock that favor the adhesive seizure, which requires the rubbing surfaces to approach at distances of the order of the crystal lattice parameter of the polycrystal, which leads to the seizure of chips with the surface of the cutting wedge at the exit from the cutting zone and its separation from the particles of the tool material during subsequent cutting.
Opinions concerning the causes of brittle fracture of the tool are not unambiguous: some consider the cause of the thermal fatigue to be the nature of the loading of the tool into the material, others - the impact nature of the force when the tool plunges into the work stock.
There is also an opinion that when cutting viscous, prone to adhesion with the tool material, especially heat-resistant and stainless alloys, adhesion (stagnation) phenomena, manifested in the seizure of chips with the surface of the cutting wedge at the exit from the cutting zone and its separation during the subsequent plunge, can have a great influence on the tool life. The ability of materials for adhesive seizure increases sharply at temperatures close to the recrystallization temperature.
