Tool-Workpiece Interaction in the Cutting Process and Its Use

The paper analyzes the influence of natural tool wear on parameters of chip shaping and machining forces and proposes the adjustment of tool geometry based on natural shape of crater wear to extend time of machining. The contact of the cutting tool and the workpiece at actual cutting speed is a complex physical process, the result of which is a specific shape and characteristics of the machined surface and the modification of tool cutting characteristics. Due to the fact that there is no existing cutting material which would resist wear in the conditions of working high stress and temperature, it is necessary to take into account that tool cutting conditions change with cutting time. This is caused by the change in tool geometry after its functional areas become worn out. One of the practical effects of those changes is gradual modification of machined surface geometry, its fortification, formation of residual stress, character of chip formation and shaping, the development of friction temperature and deformation in the zone of the contact of the tool and workpiece. This means that the cut part changes its characteristics. It is up to date to eliminate or at least mitigate this negative influence of tool wear based on the results of cutting.

Wear Mechanism of Nomex/PTFE Fiber Reinforced Composites

This paper is aimed at the problems of abnormal tribological damage and fluctuation of tribological performance in the self-lubricating composite serving in heavy load spherical plain bearing in aerospace field. The Nomex/PTFE fiber reinforced composite was used to carry out a reciprocating block on ring tribological test, investigating the tribological performance of the material and its wear evolution. Results show that the influence of oscillating frequency on material wear is obviously higher than that of load under high load condition (more than 90 MPa or 180 kN). Under a certain load and frequency condition, friction temperature is a key factor to affect wear behavior of the material. Friction heat plays a dominant role in the process of worn out failure of the material. Too high friction temperature greatly weakens the friction and wear performance, resulting in material failure in a short time. Thermal fatigue is the main tribological damage mode of the material under the high load and high frequency condition, with local worn out occurred. This finding was also verified by SEM analysis of the worn surface and wear debris.

Thermal Correlation Assessment of the Resource of Interfaces with Solid Lubricating Coatings Based On Mos2 Applied by Magnetron and Other Methods, for Vacuum Conditions

The analysis of tribotechnical parameters of interfaces with solid lubricating coatings based on MoS2, applied by different methods, was carried out according to the results of tests in vacuum. The surface friction temperature is calculated on the basis of the performed assessment of the load-speed characteristics of these interfaces. Based on the results of tribovacuum tests, the thermocorrelation dependence of the resource of a friction pair with solid lubricating coatings MoS2, applied by vacuum (magnetron and high-frequency) and suspension methods, on the surface friction temperature of the interface was determined. On the basis of this dependence, a method for calculating the resource of the studied tribointerfaces is proposed.

Friction coefficient of solid lubricating coating as a function of contact pressure: experimental results and microscale modeling

The paper presents experimental analysis of relation between friction coefficient and contact pressure of $$\hbox {MoS}_2$$ MoS 2 film deposited on $$\hbox {Ti}_6\hbox {Al}_4\hbox {V}$$ Ti 6 Al 4 V substrate in contact with sapphire ball during reciprocating sliding motion. It is shown that the value of friction coefficient decreases with increasing contact pressure. A microscale modeling approach is next developed to mimic the experimental observations. Representative volume element is defined based on the actual topography of outer surface of $$\hbox {MoS}_2$$ MoS 2 film. Assuming thermo-elastic material properties, the calculations on the asperity level are performed in two steps. Firstly, the mechanical contact between two surfaces is calculated. As a result, the relation between the global load and micro-stress distribution is obtained. Secondly, for a given stress load, thermal analysis is performed providing temperature fluctuation within simplified conical asperity. By assuming relation between friction coefficient and temperature on the microscale, it is possible to obtain macroscopic friction coefficient as a function of contact pressure. In the end, model results are compared with experimental data. The novel aspects of presented approach lie in the selection of three main factors on a micro-level defining macroscopic friction. They are actual surface topography, microscopic temperature and microscopic friction-temperature relation.

The Development of Efficient Contaminated Polymer Materials Shredding in Recycling Processes

Recently, a dynamic increase in the number of polymer elements ending their life cycle has been observed. There are three main ways of dealing with polymer waste: reuse in an unchanged form, recycling (both material and energy), and disposal (mainly in the form of landfilling or incineration). The legislation of European countries promotes in particular two forms of waste management: reuse and recycling. Recycling processes are used to recover materials and energy especially from contaminated waste, which are structurally changed by other materials, friction, temperature, machine, process, etc. The recycling of polymers, especially of multi-plastic structural elements, requires the use of special technological installations and a series of preparatory operations, including crushing and separating. Due to the universality and necessity of materials processing in recycling engineering, in particular size reduction, the aim of this study is to organize and systematize knowledge about shredding in the recycling process of end-of-life polymeric materials. This could help properly design these processes in the context of sustainable development and circular economy. Firstly, an overview of the possibilities of end-of-life plastics management was made, and the meaning of shredding in the end-of-life pathways was described. Then, the development of comminution in recycling processes was presented, with special emphasis given to quasi-cutting as the dominant mode of comminution of polymeric materials. The phenomenon of quasi-cutting, as well as factors related to the material, the operation of the shredding machine, and the technological process affecting it were described. Research conducted on quasi-cutting as a phenomenon when cutting single material samples and quasi-cutting as a machine process was characterized. Then, issues regarding recycling potentials in the context of shredding were systematized. Considerations included the areas of material, technical, energy, human, and control potentials. Presented bases and models can be used to support the innovation of creative activities, i.e., environmentally friendly actions, that produce specific positive environmental results in the mechanical processing of recycled and reused materials. The literature survey indicates the need to explore the environmental aspect of the shredding process in recycling and connect the shredding process variables with environmental consequences. This will help to design and control the processes to get the lowest possible environmental burdens.

Composite polypropylene polymer materials that work in contact with raw cotton

Physicomechanical and tribotechnical properties of structural composite materials based on thermoplastic polymer and organomineral ingredients operating under friction and wear conditions during contact with pulp (raw cotton) have been investigated. The regularities of changes in the physical, mechanical and tribotechnical properties of structural composite materials during contact interaction with raw cotton were determined, the dependence of their properties on the type and content of graphite, mineral and fibrous fillers in structural composite materials was studied. It has been established that the nature and structure of fillers has a certain effect on the physical and mechanical properties of composite materials based on polypropylene. At the same time, fiber-filled compositions have the highest mechanical strength. It was also found that when mineral fillers are introduced into composite polymer materials, their coefficient of friction with raw cotton increases significantly, while the wear rate decreases, except for fillers with a plate structure (kaolin, talc), when used, a decrease in the coefficient of friction is observed. The introduction of carbon-graphite fillers into the composition of composite materials leads to a significant decrease in the coefficient of friction, temperature and static electricity charge in the friction zone with raw cotton. The introduction of fillers with a fibrous structure leads to a significant decrease in the rate of wear of the composites. It provides high strength and resistance of the material under thermomechanical action. Effective compositions of structural composite materials for work under conditions of contact interaction with fibrous mass have been developed, and their physical, mechanical and tribotechnical properties have been investigated.

Effect of ambient temperature on the formation mechanism of PTFE liner transfer film of spherical plain bearings

The relationship between the formation of the transfer film and the tribological properties of the self-lubricating spherical plain bearing was studied at the ambient temperature of 25–145 °C. The results show that the wear, friction coefficient and friction temperature increase of the spherical plain bearings all decreased first and then increased with the increase of the ambient temperature. The general trend is that the bearing has the most excellent anti-friction and wear resistance at 55–85 °C. An increase in ambient temperature will accelerate the formation speed of PTFE transfer film and shorten the running-in period of the bearing, but the ambient temperature above 85 °C will shorten the duration of the PTFE transfer film, thus accelerating the bearing into the degradation period. The transfer film coverage of the liner after wear was characterized, and it was found that the transfer film coverage was the largest when the ambient temperature was 85 °C. The wear form of the bearing is mainly abrasive wear and adhesive wear, and the aramid fiber is more prone to adhesive wear. The anti-friction effect of the bearing is determined by the PTFE transfer film. Elevated ambient temperature can promote the formation of PTFE transfer film and enhance the antifriction effect, but if the ambient temperature is too high, the wear resistance of the PTFE transfer film will be reduced, thus reducing the friction reduction effect.