Miroslav Piska

Drilling efficiency and temperature elevation of three types of Kirschner-wire point

An innovative Kirschner (K-) wire point was developed and compared in fresh pig femora in terms of drilling efficiency and temperature elevation with the trochar and diamond points currently used in clinical practice. The tips of thermal couples were machined to the defined geometry and the temperature measured during drilling. Using the same drill speed (rev/min) and feed rate, the new K-wire point produced the lowest thrust force and torque as measured by a Kistler dynamometer. Drill point temperatures were highest with the trochar geometry (129 +/- 6 degrees C), followed by the diamond (98 +/- 7 degrees C). The lowest temperatures were recorded with the Medin K-wire (66 +/- 2 degrees C). On repeated drilling it could be used for up to 30 holes before reaching the less satisfactory drill performance of the diamond tip. The new K-wire provides a better alternative as it requires less effort for insertion, generates less heat and may be re-used.

Material Analysis of Titanium Alloy Produced by Direct Metal Laser Sintering

This paper focuses on the testing of samples made by Direct Metal Laser Sintering (DMLS). This additive method is based on the continuous melting of fine layers of metal powder by laser beam. The paper focuses on the DMLS process description, analysis of the titanium alloys and experimental procedures. The experimental section is a structural comparison of the materials produced by hot forming and powder metallurgy (DMLS) using scanning electron microscopy (SEM) analysis. Results from the DMLS technology and conventional powder metallurgy are compared to show the advantages of the former technology.

On the Cutting Performance of Nano-(Tix,Al1-x)N PVD Coatings

It is well known that hard coatings can extend the lifetime of production tools in many industrial applications significantly [1]. Higher cutting speeds, dry cutting or a better quality of machined surface can present the typical benefits of the protective surfaces so hard coatings receive a great interest from industrial and research organizations. Among the most important parameters of the coatings belong properties such as resistance to oxidation, thermal and abrasion, and good adhesion and tribological properties. The hard coatings based on (Tix,Al1-x)N prevails with unique properties belong to the most used coatings today. These coatings are deposited by PVD technology using either arc technologies or magnetron sputtering systems. New nanocomposite coatings (Ti,Al)N and (Ti0.4,Al0.6)N were tested in dry and wet cooling conditions and this paper deals with material analyses of the coating, testing of the cutting performance for a grooving technology in hardened low-alloyed steel.

On the Structural Integrity of the Nano-PVD Coatings Applied on Cutting Tools

Many modern trends in metal cutting, high speed/feed machining, dry cutting, hard cutting and ecological impacts set more demanding characteristics for cutting tool materials. The exposed parts of the cutting edges must be protected against the severe mechanical and chemical loading conditions resulting in wear of tools and quality of products. The paper deals with three modifications of the hard (Ti1-xAlx)N/a nano-crystallites embedded in an x-ray nearly amorphous Si3N4 matrix, analyses of the WC carbide-coating interface, its integrity and cohesion to the substrate. Advanced cutting tests and wear morphology in the operation of longitudinal turning of carbon steel C45 were done. Some technological and economical impacts for an application of the coatings are also highlighted that confirms their a very good cutting performance, characterized by the very good of chip formation, mean standard deviation of the machined surface from Ra = 1.00–1.50 μm to Ra = 6.30–12.50 μm (start and end of testing), convenient cutting force composition, tool life 52–56 min (compared to the expected 15–20 min) for cutting speed 130 m/min, depth of cut 1.5 mm and feed per revolution 0.18 mm. Two mechanism of wear have been watched — sub-layers delaminating and abrasion.

Hard Nano-Crystalline Coatings for Cutting Tools

Modern trends in metal cutting, high speed/feed machining, dry cutting and hard cutting set more demanding characteristics for cutting tool materials. The exposed parts of the cutting edges must be protected against the severe loading conditions and wear. The most significant coatings methods for cutting tools are PVD and CVD/MTCVD today. The choice of the right substrate or the right protective coating in the specific machining operation can have serious impact on machining productivity and economy. In many cases the deposition of the cutting tool with a hard coating increases considerably its cutting performance and tool life. The coating protects the tool against abrasion, adhesion, diffusion, formation of comb cracks and other wear phenomena.

A Study of Progressive Milling Technology on Surface Topography and Fatigue Properties of the High Strength Aluminum Alloy 7475-T7351

The paper investigates the effect of key cutting parameters of shoulder milling on the surface structure and fatigue properties of high strength aluminum alloy 7475-T7351. The very advanced milling whole carbide cutter and progressive milling process conditions have been analyzed in the respect of force loading, specific cutting energies, the volumetric surface parameters and fatigue life of thin-walled components used for the dynamically loaded primary aerospace structures. The evaluation of the surface structure of the machined samples prior the fatigue testing and morphologies of the fracture surfaces afterwards was done using the modern optical high-resolution 3D surface microscope ALICONA-IF G4 and Tescan Mira 3GM scanning electron microscope. Cyclic fatigue testing for three loading levels was performed using the axial BISS testing machine with an advanced control of the testing. The results confirmed a statistically significant influence of cutting conditions on the surface structure, however, the material inclusions dispersed in the adherent machined surfaces seems to be the most decisive factor affecting the material integrity that triggers the fatigue crack initiations and propagations. Some unique studies like tensile tests in situ in scanning electron microscopy have been also made.

On the Advanced Milling Technology of Thin-Walled Parts for Aerospace Industry

This paper is focused on advanced analysis of a progressive milling technology of high strength alumina alloy 7475-T7351 that is used in modern aerospace industry today. The analyses comprises a study of the material, its mechanical properties, use of alternative monolithic-carbide tool designs, micro-geometries of the milling cutters, coatings and a study of cutting parameters on dynamics of cutting , its productivity, quality of the surfaces and other specific cutting phenomena. This work includes an experimental verification of the proposed technology using 5-axis CNC machining centre, evaluation of 2D/3D surface structures using optical high-resolution 3D surface device. Dynamometer Kistler 9575B/SW DynoWare were used for measuring of instantaneous force loading in long time series. The results are relevant for milling of thin-walled parts and the up and down milling strategies without any other surface treatment of the parts. Some fatigue studies are in progress.

Analysis of Selective Laser Melting Process Parameters Effect on Mechanical and Material Properties for Stainless Steel 316L

This paper deals with a testings of the Selective Laser Melting (SLM) process parameters on mechanical properties, material behavior, surface quality and on machinability of austenitic steel 316L. The SLM process conditions were changed to assess their effect on mechanical properties of the sintered material measured in tensile testing. The laser power, the scanning velocity of laser beam, the layer thickness and the laser focus plane were set to find the most appropriate set of process parameters to obtain the mechanical properties of parts.

A NEW DESIGN OF ROUGHING MILLING CUTTER AND ITS MACHINING PERFORMANCE

2016 | OCTOBER | SCIENCE JOURNAL | 1035

On the Cutting Performance of Coated HSS Taps When Machining of Austenitic Steel

Abstract The paper deals with a quality of the PVD coated HSS taps when cutting the stainless austenitic chromiumnickel non-stabilized steel DIN 1.4301 (X5CrNi 18-10). The main attention is focused on the analysis of loading (cutting moment, specific energy) of the HSS taps by means of pieso-electrical dynamometer Kistler 9272 and the relation between the quality of duplex and triplex PVD coatings and their effects on the quality of machined thread surfaces and tool life of the taps. The results showed a safe and stabilized cutting with acceptable quality of threads for HSSE with the TiN+TiCN+DLC coating.