TWO CUTTING TURNING OF BODIES OF REVOLUTION

The technology of two-cut rough and rough turning of rotation bodies in relation to lathes is considered. Dynamics of part working surfaces formation by longitudinal oscillations of cutters with phase delay of finishing cutter from rough one is shown. Dynamics of finishing cutter in function of damping coefficient is considered. The mathematical model of two-cut turning process is given.

Investigation of the Wear Performance of TiB2 Coated Cutting Tools during the Machining of Ti6Al4V Alloy

The machining of Ti6Al4V alloy, especially at low cutting speeds, is associated with strong Built-Up Edge (BUE) formation. The PVD coatings applied on cutting tools to machine such materials must have the necessary combination of properties to address such an underlying wear mechanism. The present work investigates and shows that TiB2 PVD coating can be designed to have certain mechanical properties and tribological characteristics that improve machining in cases where BUE formation is observed. Three TiB2 coatings were studied: one low hardness coating and two high hardness coatings with varied coating thicknesses. Wear performances for the various TiB2 coated carbide tools were evaluated while rough turning Ti6Al4V. Tool wear characteristics were evaluated using tool life studies and the 3D wear volume measurements of the worn surface. Chip morphology analyses were done to assess the in-situ tribological performance of the coatings. The micro-mechanical properties of the coatings were also studied in detail to co-relate with the coatings’ performances. The results obtained show that during the rough turning of Ti6Al4V alloy with intensive BUE formation, the harder TiB2 coatings performed worse, with coating delamination on the rake surface under operation, whereas the softer version of the coating exhibited significantly better tool life without significant coating failure.

Investigation of the Wear Behavior of PVD Coated Carbide Tools during Ti6Al4V Machining with Intensive Built Up Edge Formation

Tool wear phenomena during the machining of titanium alloys are very complex. Severe adhesive interaction at the tool chip interface, especially at low cutting speeds, leads to intensive Built Up Edge (BUE) formation. Additionally, a high cutting temperature causes rapid wear in the carbide inserts due to the low thermal conductivity of titanium alloys. The current research studies the effect of AlTiN and CrN PVD coatings deposited on cutting tools during the rough turning of a Ti6Al4V alloy with severe BUE formation. Tool wear characteristics were evaluated in detail using a Scanning Electron Microscope (SEM) and volumetric wear measurements. Chip morphology analysis was conducted to assess the in situ tribological performance of the coatings. A high temperature–heavy load tribometer that mimics machining conditions was used to analyze the frictional behavior of the coatings. The micromechanical properties of the coatings were also investigated to gain a better understanding of the coating performance. It was demonstrated that the CrN coating possess unique micromechanical properties and tribological adaptive characteristics that minimize BUE formation and significantly improve tool performance during the machining of the Ti6Al4V alloy.

Study of the optical parameters of a silica-polymeric optical fiber with a reflective coating made of a thermoplastic fluoropolymer

Silica optical fibers (OF) having a core diameter of 400 – 800 μm made of biocompatible materials are widely used in laser medicine. The results of studying the optical parameters of novel silica-polymeric optical fiber with a reflective thermoplastic copolymer coating (tetrafluoroethylene – ethylene) and the influence of coating conditions on these optical parameters are presented. Coatings from polymer melt were applied to the silica fiber surface by orifice drawing. The numerical aperture of the drawn OF was measured by distribution of the laser radiation emerging from OF in the far field. The optical losses were determined by the distribution of the radiation scattered by the reflective coating along the OF length. The scattering parameters of the laser radiation transmitted through OF were estimated by the intensity and indicatrix of scattering. We studied OF samples up to 50 m in length with a silica core of about 400 μm in diameter and reflective coating with a thickness of 70 – 90 μm, the reflective coating also performed a protective function. The quality of applied coating and optical parameters of the OF samples depended on the speed of fiber drawing (coating speed) Vd. A smooth coating was obtained at Vd ≤ 2 m/min. When Vd > 2 m/min the coating became rough, turning into the so-called «shark skin» at Vd = 6 m/min. Observed scattering of radiation passing through the studied OF samples was attributed to the polymer structure which contained both crystalline and amorphous phases with different values of the refractive index. The smallest scattering was observed in a smooth-coated OF. The total optical loss at a wavelength λ = 532 nm amounted to 300 – 720 dB/km (a nominal numerical aperture was 0.44). Short (1.5 – 3 m) OF samples were shown to provide a transmission of 80 – 93% of the input power.

TECHNOLOGICAL PROCESS OF PROCESSING COMPOSITES USING THE DEVELOPED DESIGN OF THE CUTTER FOR ROUGH TURNING

The article considers the technological process of mechanical processing of composite materials. The characteristic of composite materials and their physical and mechanical properties is given. The rationale for the need to improve the design of the cutting tool is given. The design of the cutting head has been developed for the cutting process. It consists of a rough and finishing incisors. To determine the optimal geometry of these incisors, 20 incisors of each type were manufactured with a modified geometry. Experiments with changing the values of the back and front corners were carried out. Recommended minimum front angle values for soft and hard materials. The radius of rounding of the roughing tool is recommended. The technological process of processing composite materials is given. The design of the roughing tool is described in detail, which largely eliminates the disadvantages of processing, increases productivity, improves quality, and increases durability.

Selection of the quantity of the allowance at rough treatment of large – size parts from titanium alloy of BT6 (Russian State Standard GOST 19807-91)

The article presents the results of experimental studies of the effect of cutting depth on cutting force and the procedure of assignment of allowance value at rough turning and melting of stamped blanks for large- size parts of rocket equipment from titanium alloy VT6. As a result of the studies carried out, empirical dependence of cutting force on cutting depth was obtained, and method of allocation of allowance value was created, which is very important in processing of large-size stamped blanks.

SIMULATION TESTS OF ADAPTIVE CONTROL STRATEGIES FOR CNC MACHINE TOOLS

The issue addressed in the article concerns the current needs and possibilities of computer-aided design of adaptive control strategies in machining processes. A simulative method of selecting the adaptive feed control strategy while rough turning materials difficult to machine, effective and inexpensive in its implementation, based on controlling the load placed on the machine's drives, has been presented. The results of a number of virtual tests of the proposed feed control strategy have been included, while paying particular attention to the stability of the machining process during moments of sudden change in the machining allowance. The obtained results meet the accepted quality indicators of the control algorithm. At the same time, the experiences collected by the author while conducting the tests confirmed the complexity of the issue and the resulting necessity to implement a comprehensive simulation testing program.