ANALYSIS OF CHIP FORMATION DURING HARD TURNING THROUGH ACOUSTIC EMISSION

The paper deals with analysis of chip formation and related aspects of the chip formation during turning hardened steel 100Cr6. The paper draws a comparison of some aspects of the chip formation between turning annealed and hardened roll bearing steel. The results of the analysis show that there is the formation of a segmented chip in the case of hard turning. Frequency of segmentation is very high. A conventional piezoelectric dynamometer limits the frequency response to about 3.5 kHz. On the other hand, the frequency of process fluctuation may by obtained by using accelerometers or acoustic emission. This paper reports about the dynamic character of cutting process when hard turning and correlation among the calculated segmentation frequencies and the experimental analysis

Influence of cutting speed on intensity of the plastic deformation during hard cutting

The paper deals with an analysis of deformation processes and the aspects related to a chip formation such as the chip thickness, the chip ratio, the shear angle and the chip segmentation during turning the hardened steel 100Cr6. This paper investigates the influence of the cutting speed through a metallographic analysis, a calculation of significant aspects of deformation processes and the resulting experimental study. This experimental study is based on an application of acoustic emission. The results of this study indicate that the cutting speed significantly affects the parameters such as the chip ratio, deformation angle or the speeds in the cutting zone. On the other hand, the experimental study allows an analysis of the specific characters of deformation processes and their real intensity.Web of Science47675574

Properties and comparison of PVD coatings

Razvoj i primjena novih materijala u strojarskoj praksi dovode do mnoštva pitanja u odnosu na njihovu tehnološku primjenu. Ovaj je rad usmjeren na istraživanje problema povezanih s cementiranim karbidom premazanim primjenom PVD (Physical Vapour Deposition) metode. U teorijskom dijelu rada upoznaje se PVD tehnologija nanošenja sloja i detaljnije opisuje metoda isparavanja luka. Opisuju se također materijali i vrste slojeva, njihova svojstva, moguće primjene i na kraju objašnjavaju načela eksperimentalnih metoda primijenjenih u ispitivanju slojeva. U eksperimentalnom dijelu rada opisuju se postupci mjerenja i ispitivanja te daju rezultati ispitivanja. Adhezija i trajnost slojeva uspoređeni su na izrezanim umetcima s različitim PVD – premazi s nanostrukturom i nanoslojem. Ispitivanja su provedena glodanjem ugljičnog čelika 1.1191 (C45) budući da se taj čelik uvelike rabi u mnogim industrijskim primjenama, a također i kao referentni material. Na kraju se ocjenjuju rezultati ispitivanja na temelju dobivenih podataka.Development and application of new materials in mechanical engineering practice create a lot of questions concerning their technological application. This paper focuses on research problems related to the PVD coated cemented carbide. The theoretical part of the paper informs about principle of PVD coating technology and describes the arc evaporation method used for coating in greater detail. It also deals with coating materials and types, their properties, possible applications and finally principles of the experimental methods used for coatings testing are explained. In the experimental part of the paper, the measuring and testing procedures are described and the test results are listed. Adhesion and layer durability were compared by cutting inserts with different PVD – nanostructure and nanolayer coatings. The tests were carried out by milling of carbon engineering steel 1.1191 (C45), because this steel is widely used in many industrial applications and it is used as reference material too. In conclusion the testing results are evaluated on the basis of obtained information

Svojstva i usporedba PVD slojeva premaza

Development and application of new materials in mechanical engineering practice create a lot of questions concerning their technological application. This paper focuses on research problems related to the PVD coated cemented carbide. The theoretical part of the paper informs about principle of PVD coating technology and describes the arc evaporation method used for coating in greater detail. It also deals with coating materials and types, their properties, possible applications and finally principles of the experimental methods used for coatings testing are explained. In the experimental part of the paper, the measuring and testing procedures are described and the test results are listed. Adhesion and layer durability were compared by cutting inserts with different PVD – nanostructure and nanolayer coatings. The tests were carried out by milling of carbon engineering steel 1.1191 (C45), because this steel is widely used in many industrial applications and it is used as reference material too. In conclusion the testing results are evaluated on the basis of obtained information.Razvoj i primjena novih materijala u strojarskoj praksi dovode do mnoštva pitanja u odnosu na njihovu tehnološku primjenu. Ovaj je rad usmjeren na istraživanje problema povezanih s cementiranim karbidom premazanim primjenom PVD (Physical Vapour Deposition) metode. U teorijskom dijelu rada upoznaje se PVD tehnologija nanošenja sloja i detaljnije opisuje metoda isparavanja luka. Opisuju se također materijali i vrste slojeva, njihova svojstva, moguće primjene i na kraju objašnjavaju načela eksperimentalnih metoda primijenjenih u ispitivanju slojeva. U eksperimentalnom dijelu rada opisuju se postupci mjerenja i ispitivanja te daju rezultati ispitivanja. Adhezija i trajnost slojeva uspoređeni su na izrezanim umetcima s različitim PVD – premazi s nanostrukturom i nanoslojem. Ispitivanja su provedena glodanjem ugljičnog čelika 1.1191 (C45) budući da se taj čelik uvelike rabi u mnogim industrijskim primjenama, a također i kao referentni material. Na kraju se ocjenjuju rezultati ispitivanja na temelju dobivenih podataka.Web of Science23257456

Barkhausen Noise Emission in Hard Milled Surfaces of Steel C55

This paper deals with the application of the Barkhausen noise technique in the nondestructive monitoring of hard milled surfaces. The paper discusses strong magnetic anisotropy linked with microstructural transformations of a machined surface with regard to variable flank wear of cutting inserts. Effective values of Barkhausen noise, peak positions derived from the raw Barkhausen noise signals, the shape of hysteresis loops as well as the Barkhausen noise envelopes are compared with metallographic observations and theoretical background regarding the magnetic domains configuration in the near surface region. A possible concept by which hard milled surfaces could be monitored in real industrial conditions in a non-destructive manner is driven by the specific surface state of the microstructure as well as by the magnetic point of view

Anisotropic magnetic properties of milled bearing steel surface

For many reasons, the steel surfaces are machined to obtain required physical properties. Suitable methods are required for the management and control of the manufacturing processes, which are simultaneously sufficiently robust and sensitive. The non-destructive testing methods, sensitive to the magnetic properties of the surface, are very suitable for this purpose. The Barkhausen noise (BN) measurement, which reveals the discontinuous movement of the magnetic domains in the thin surface layer during magnetisation reversal process is very robust, while magneto-optical Kerr effect (MOKE) method, using polarized light for orientation measurements of magnetic domains at the surface, is very sensitive and provides detailed information about hysteresis curves (HC) of the materials. In this contribution our results obtained on the milled 100Cr6 bearing steel are presented. These properties were obtained by MOKE laboratory measurements and bring very interesting facts about the magnetisation reversal process, which depends on the orientation of the magnetic field with respect to the cutting direction. Our results clarify the strong anisotropy of BN, which is observed during the industrial application of this method.Web of Science12741423142

Heat distribution when nickel alloy grinding

Stvaranje i razdioba topline tijekom obrade odvajanjem čestica jedna je od fenomenoloških karakteristika tih postupaka, koja znatno utječe na funkcionalnost obrađenih površina. Rad se bavi proučavanjem distribucije topline tijekom brušenja nikaljnih legura i njenim utjecajem na kvalitetu brušenih površina uslijed pojave napetosti (zaostalih naprezanja). Analiza razdiobe topline temelji se na mjerenju kontaktnih temperatura između brusnog kotača i obradka te tangencijalne komponente sile rezanja. Razdioba topline tijekom brušenja nikaljnih legura različita je od one tijekom brušenja uobičajenih željeznih legura, primjerice čelika za kotrljajuće ležajeve, prvenstveno zbog njihove niže toplinske provodnosti. Također, uporaba bor-nitridnih (CBN) i dijamantnih bruseva značajno smanjuje toplinska opterećenja obradaka, prvenstveno uz uporabu rashladnih fluida. Ta činjenica znatno utječe na pojavu napetosti nakon brušenja. Rezultati analize pokazuju da postoji povezanost između razdiobe toplinske energije i napetosti.Heat distribution in machining is one of the phenomenological characteristics of this process because it significantly influences functional properties of machined surfaces. This paper deals with heat distribution during grinding of Ni alloy and its relationship to the quality of ground parts in terms of residual stresses. The analysis of the heat distribution is based on measurement of the temperature in the contact of the grinding wheel and the workpiece, and the tangential component of cutting force. The heat distribution when Ni alloy grinding differs from the heat distribution when grinding a conventional Fe alloy such as roll bearing steel mainly because of the low heat conductivity of Ni alloys. Also, the application of CBN and diamond grinding wheels significantly reduce the thermal exposition of the ground parts, primarily when applying cutting fluid. This fact significantly influences the residual stresses after grinding. The results of the analysis show that there is correlation between energy partitioning and residual stresses

Deformations after heat treatment and their influence on cutting process

Ovaj se članak bavi utjecajem toplinske obrade na deformacije dijelova i strojnom obradom koja slijedi. Režim toplinske obrade znatno utječe na takva gledišta materijala kao što je struktura, tvrdoća i inducirano naprezanje. Različit proces toplinske obrade rezultira različitim deformacijama dijelova i promjenama s obzirom na njihove dimenzije. Sva su ova gledišta povezana s uzastopnim operacijama rezanja, kao što je brušenje ili grubo tokarenje, njihovom stabilnosti, preciznosti proizvedenih dijelova, itd. Deformacija dijelova također je povezana sa strukturom materijala prije toplinske obrade, postavljanjem u peći, režimom toplinske obrade i raspodjelom naprezanja oko dijelova. Rezultati ovog eksperimentalnog istraživanja prikazani u ovom članku pokazuju povezanost između različitih režima toplinske obrade i obrade dijelova koja slijedi.This paper deals with the influence of heat treatment on the deformation of parts and the following machining process. The regime of heat treatment significantly affects such aspects of material as structure, hardness and induced stress. Different process of heat treatment results in different deformation of parts and changes considering their dimensions. All these aspects are connected with the consecutive cutting operations such as grinding or hard turning, their stability, precision of produced parts, etc. Deformation of parts is also connected with the structure of material before heat treatment, placement in the furnace, regime of heat treatment and stress distribution around the parts. The results of the experimental study presented in this paper illustrate the connection between different heat treatment regimes and the following processing of parts

Influence of domain walls thickness, density and alignment on Barkhausen noise emission in low alloyed steels

This study deals with the characterization of low alloyed steels of diferent yield strengths (varying in the range of 235–1100 MPa) via Barkhausen noise emission. The study investigates the potential of this technique to distinguish among the low alloyed steels and all signifcant aspects contributing to Barkhausen noise, such as the residual stress state, microstructure expressed in terms of dislocation density, grain size, prevailing phase, as well as associated aspects of the domain wall substructure (domain wall thickness, energy, their spacing and density in the matrix). Barkhausen noise in the rolling as well as transversal direction grows along with the yield strength (up to 500 MPa) and the corresponding grain refnement of ferrite. As soon as the martensite transformation occurs in a high strength matrix, this evolution saturates, and remarkable magnetic anisotropy is developed when Barkhausen noise in the transversal direction grows at the expense of the rolling direction. The contribution of residual stresses as well as the domain wall thickness is only minor, and the evolution of Barkhausen noise is driven by the density of the domain walls and their realignment.Web of Science131art. no. 568