COMPARISON OF PARAMETERS OF SURFACE INTEGRITY OF MACHINED DUPLEX AND AUSTENITE STAINLESS STEELS IN RELATION TO TOOL GEOMETRY

The goal of this contribution was to describe parameters of surface integrity of two machined materials; austenite and duplex stainless steel. Residual stresses and presence of straininduced martensite were studied as a function of the side rake angle. Residual stresses of surface and sub-surface layers were determined using X-ray diffraction techniques and hole-drilling method. By using X-ray diffraction, it is possible to determine residual stresses in each phase separately, in comparison with hole-drilling method. The presence of strain-induced martensite was investigated using Barkhausen noise and optical microscope

Microstructure, mechanical and wear behaviour of deep cryogenically treated EN 52 Silchrome valve steel

This study has compared the performance of cryogenically processed EN 52 Silchrome valve steel with untreated material. After completing the standard heat treatment process, EN 52 steel material specimens are subjected to a deep cryogenic process with varying soaking temperatures. The parameters of the deep cryogenic procedure were changed to find the best wear qualities. The key features of valve steel, such as microstructure, mechanical, and wear behaviour are evaluated by conducting a test study. The evolution of wear mechanisms after enhancing qualities of EN 52 steel is studied using scanning electron microscopy. The mechanical and wear behaviour improved due to factors such as fine carbide precipitation, conversion of residual austenite, and carbide refining formed after cryogenic treatment. With a maximum reduction in wear rate of up to 45%, the deep cryogenic treatment of EN 52 steel with a soaking temperature of -140 degrees C was the ideal parameter. All three cryo-treated samples had better properties than the untreated EN 52 valve steel.Web of Science1516art. no. 548

Experimental investigation of suitable cutting conditions of dry drilling into high-strength structural steel

Dry machining is one of the main ways to reduce the environmental burden of the machining process and reduce the negative effect of the cutting fluid and aerosols on operators. In addition, dry machining can reduce overall machining costs and, in the case of large workpieces, reduce the extra work associated with removing residual cutting fluid from the workpiece and adjacent area. For high-strength structural steel products, it is typical to drill holes with larger diameters of around 20 mm. Therefore, this work is devoted to the investigation of the dry drilling process carried out on a workpiece made of S960QL steel with a helical drill with a diameter of 21 mm. The aim was to find suitable cutting conditions for dry drilling with regard to process stability and workpiece quality. An experiment performed with a coolant served as a comparison base. A dry drilling experiment was performed with cutting speeds from 30 to 70 m center dot min(-1) and feeds from 0.1 to 0.3 mm center dot rev(-1), and with the results of this experiment, the same experiment with flood cooling was performed. During the drilling process, spindle torque values were recorded using the indirect spindle current recording method. The macroscopic chip morphology was studied to understand the cutting process. The chip thickness ratio was measured, as well as the maximum diameter of spiral chips. On the final workpiece, the qualitative and dimensional parameters of the holes were evaluated, such as the diameter, cylindricity and surface roughness, depending on the change in the cutting conditions and cutting environment. Evaluation of the obtained data led to the following conclusions. When drilling the S960QL material, there is only a very small increase in the drilling torque during dry drilling compared to drilling with cutting fluid. The increase in friction demonstrated by the chip thickness coefficient is significant. The influence of the environment on the dimensional accuracy showed a tendency for a slight increase in the holes' diameters during dry machining. In comparison, the cylindricity of the dry-drilled holes shows a lower deviation than the holes drilled with cutting fluid. The surface roughness of the holes after dry drilling is affected by the increased friction of the outgoing chips, despite the resulting parameters being very good due to the drilling technology standards. This work provides a comprehensive view of the dry drilling process under defined conditions, and the results represent suitable cutting conditions to achieve a stable cutting process and a suitable quality of drilled holes.Web of Science1416art. no. 438

Surface Integrity after Turning a Duplex Stainless Steel with Respect to Tool Geometry

This study deals with surface integrity expressed in terms of stress state as well as microstructure alterations after turning a duplex stainless steel. Residual stresses and the presence of strain-induced martensite are studied as functions of the rake angle. Residual stresses of surface and sub-surface layers were determined by the use of the X-ray diffraction and hole-drilling techniques. X-ray diffraction enables us to distinguish between residual stresses in each phase separately, which is not possible when the hole-drilling method is applied. Furthermore, alterations in the near surface region are also analysed by the use of the magnetic Barkhausen noise and metallographic observation

Novel drill geometries for dry drilling of stainless steel

One completely new geometry and two modified chip breaker geometries were designed to increase the stability and reliability of the stainless steel dry drilling process. Experiments were performed and the results of individual tools were compared with a conventional solid carbide twist drill Gühring Ratio with a diameter of 5 mm. A matrix of three feed rates (0,03–0,07 mm/rev) and three cutting speeds (20–30 m/min) was designed for the cutting conditions. Precipitation-hardenable stainless steel 17-4 PH was chosen as a workpiece. During the experiment, the values of thrust force, spindle torque, temperature of the tool, surface roughness, chips morphology and chips division were recorded and compared with the reference tool. The results showed that compared to the reference tool A, the tool C - a multipoint drill with grooves through the cutting edge achieve approximately 4 % lower values of thrust force and 10–15 % lower values of spindle torque. Tool D with a step drill geometry achieve approximately 17 % lower values of thrust force and 10–15 % lower values of spindle torque and there is no chip clogging in the flute with C and D geometries. This effect is confirmed by the fact the spindle torque basically does not increase with the increasing depth of drilling. Tool B – new designed geometry achieve approximately 15 % lower values of thrust force and similar spindle torque values as the reference drill A. Tool temperature is a very important factor when dry drilling. Compared to the reference drill A, it was possible to achieve the tool temperature reduction of 20 % with the new geometry B, as well as with the multipoint drill C reduction by 26 % and with the step drill D reduction approximately by 30 %. All the modified drills also achieved a reduction in the surface roughness of the drilled holes. By 17 %, 35 % and 48 % lower surface roughness Ra was achieved with drills B, C and D. Chip morphology was significantly different for the tested drills. Conventional twist drills A and B generated helical short chips. While C and D twist drills with divided cutting edges generated ribbon snarled chips. Thanks to the reduction of cutting forces and temperature, it is possible to stably operate the drilling process with a higher cutting speed and feed rate, which leads to an increase in the efficiency and reliability of the machining process.Web of Science9252050

The effect of cutting tool geometry on surface integrity: A case study of CBN tools and the inner surface of bearing rings

In this paper, a practical issue of the application of cubic boron nitride (CBN) cutting tools for the machining of steel 100Cr6 thin-walled bearing rings is addressed. Three geometries of the commercially available CBN cutting inserts were tested at different machining parameters. The effect of geometry was assessed in terms of surface integrity, considering 2D profile parameters, 3D topography of the surface, and residual stresses in the surface layer. The results were sometimes contradictory, since the same cutting inserts provided the largest and the lowest values of the topography parameters, dependent on different cutting conditions. In general, CBN cutting inserts with XCEL geometry ensured the smallest profile parameters Ra and Rz, and the spatial parameters of Smr1 exhibited the largest values among all tested tools, suggesting reduced wear resistance. Residual stresses analysis did not reveal any inacceptable or potentially dangerous surface layer state after machining.Web of Science136art. no. 354

Research of the Surface Structure of Composite Materials Regarding Their Medical Use

ústav technologie obrábění, projektování a metrologi

Design and manufacturing testing artefakt for ecucation measuring on coordinate measuring machines

V tomto článku je popsán návrh a výroba testovacího artefaktu, který slouží pro výuku měření na souřadnicovém měřicím stroji. Jedná se o součást, která obsahuje tvarové plochy a jejich různé kombinace. V tomto případě jde o duralový kvádr, na kterém byly frézováním, soustružením a vrtáním vyrobeny tvarové plochy jako např. díra, kuželová díra, otvory na roztečné kružnici, pole děr, rádiusy, drážky, šikmé plochy, obecná plocha atd. Kompletní výroba probíhala ve strojních laboratořích Fakulty strojní ČVUT Praha, jejichž možnosti byly limitující. K dispozici byly klasické mechanické stroje (soustruh, frézka, vrtačka) i CNC stroje (3-osá frézka a soustruh).measurements on coordinate measuring machine. It is a component that has shaped the area and their various combinations. In this case, the block of duralumin, in which the milling, turning and drilling produced shaped surface such as a hole, conical hole, holes in the pitch circle, pole holes, radii, grooves, a slippery slope, general area etc. Complete production took place in the laboratories of the Faculty of Mechanical Engineering, CTU, Prague, whose options were limiting. There were classic mechanical machines (lathe, milling machine, drilling machine) and CNC machines (3-axis milling machine and lathe). Made a test artefact was used to build the manual measurement, which includes practical explanations of certain concepts, advantages and disadvantages of different methods of measurement, etc. The handbook is focused mainly on the measurement where the use of CAD model of the measured parts and is complemented by practical tasks

Acceptance and reverification tests for coordinate measuring machines

Článek pojednává o přejímacích zkouškách ve smyslu ČSN EN ISO 10 360-2:2010, které specifikuje výrobce souřadnicových měřicích strojů (CMM), používaných pro měření lineárních rozměrů, pro ověření jejich způsobilosti. Pojednává rovněž o periodických zkouškách, které umožňují uživateli v opakovaných časových odstupech ověřit způsobilost CMM. Zkoušky popsané zde jsou použitelné na kartézské CMM s kontaktními snímacími hlavami jakéhokoliv operačního typu v režimu snímání diskrétních bodů