Tool wear when turning hardened AISI 4340 with coated PCBN tools using finishing cutting conditions

Tool wear is one of the most important aspects in metal cutting, especially when machining hardened steels. The present work shows the results of tool wear, cutting force and surface finish obtained from the turning operation on hardened AISI 4340 using PCBN coated and uncoated edges. Three different coatings were tested using finishing conditions: TiAlN, TiAlN-nanocoating and AlCrN. The lowest tool wear happened with TiAlN-nanocoating followed by TiAlN, AlCrN and uncoated PCBN. Forces followed the same pattern, increasing in the same order, after flank wear appears. At the beginning of cutting, there was no significant difference amongst the coated tools, only the uncoated one showing higher cutting force. Ra values were between 0.7 and 1.2 μm with no large differences amongst the tools. Finite element method (FEM) simulations indicated that temperature at the chip–tool interface was around 800 °C in absence of flank wear, independently of coating. In that range only the TiAlN coating oxidize since AlCrN needs higher than 1000 °C. Therefore, due to a combination of high hardness in the cutting temperature range and the presence of an oxidizing layer, TiAlN-nanocoating performed better in terms of tool wear and surface roughness.     

An analysis of the machinability of ASTM grades 2 and 3 austempered ductile iron

The main goal of this work is to perform an analysis of the machinability of two ASTM grades of ADI, namely 2 and 3. The samples used in this work were cast and austempered according to ASTM standards for the production of grade 2 (G2) and grade 3 (G3) ADI. Characterization was accomplished through tensile and hardness tests, metallography and X-ray diffraction. Machinability was evaluated by analyzing tool life, cutting forces, surface finish and chip characteristics in turning operations. A quick-stop test was also performed in order to verify some mechanical processes during the chip formation and to analyze the shear plane angle. Tool life when machining G2 was 33% lower than G3 (18 min against 26 min), although the latter is a harder material. Abrasion and adhesion were the wear mechanisms observed through SEM images, whereas in other cast irons mainly abrasion is observed. Cutting forces measurements showed that the value of K_c1,1 decreased 19%, from 1448 to 1175 N/mm², for G2 as the depth of cut increased from 2 to 5 mm at a cutting speed of 80 m/min and 18%, from 1501 to 1236 N/mm², for G3. Surface roughness measurements proved that a smoother surface is obtained for both alloys at f = 0.10 mm/rev when using an insert with nose radius 1.6 mm instead of smaller radii. Both alloys presented similar surface quality. All chips observed were segmented.     

Wear behaviour of cryogenically treated tungsten carbide inserts under dry and wet turning conditions

Cryogenic treatment has been acknowledged as a means of extending the life of tungsten carbide inserts but no study has been reported in open literature regarding the effect of coolant on the performance of cryogenically treated tungsten carbide inserts in turning. In order to understand the effect of coolant, a comparative investigation of the wear behaviour of cryogenically treated tungsten carbide inserts in dry and wet orthogonal turning has been carried out in this study. The commercially available uncoated square-shaped tungsten carbide inserts with chip breakers were procured and cryogenically treated at ?196 °C and the cutting tests were executed in accordance to the International Standard Organisation, ISO 3685-1993 for continuous and interrupted machining mode. The criterion selected for determining the tool life was based on the maximum flank wear (0.6 mm) and the selection of cutting conditions was made to ensure the significant wear at a suitable time interval. The results showed that cryogenically treated tungsten carbide inserts performed significantly better in wet turning conditions under both continuous and interrupted machining modes especially at higher cutting speeds. A considerable increase in tool life was also recorded in interrupted machining mode as compared with continuous machining mode.     

Cutting performance and wear mechanisms of Sialon ceramic cutting tools at high speed dry turning of gray cast iron

In the present work, the phase composition and microstructure of two Sialon cutting inserts (named sample A and sample B) were characterized by XRD and SEM. The cutting performance and wear mechanism of the cutting inserts were investigated at high-speed dry turning of gray cast iron. The results showed that the main phases of them were α- and β-Sialon, and the sample A contained more α-Sialon than that of sample B. The grains of the Sialon cutting inserts are mainly elongated shape, and the aspect ratios are about 5.32 and 5.09, respectively. The tool life of sample B was longer than that of sample A at low speed. However, with the speeds increased, the tool life of sample A was getting closer to that of sample B and then exceeded that of sample B. The wear mechanisms of the two cutting inserts were abrasive and adhesive wear, however, as the cutting speeds increased, the dominant wear mechanisms were different.     

Determination of the chip geometry, cutting force and roughness in free form surfaces finishing milling, with ball end tools

CAD/CAM systems offer various possibilities for finishing milling of parts such as dies and moulds, turbine blades and other high quality components, but most of them do not take into account the surface topomorphy expected, which is significantly affected, among others, by the milling kinematics and the contact conditions between the tool and the workpiece. In order to predict the workpiece roughness in multiaxis finishing milling with ball end tools, the computer supported milling simulation algorithm ‘ ’ was developed. By means of this algorithm, considering the individual movements of the cutting tool and of the workpiece due to the milling kinematics, the undeformed chip geometry, the cutting force components, the tool deflections and the final surface topomorphy expected are determined. Numerous investigations concerning the parameters mentioned above, with various workpiece materials have been carried out in order to determine the correlation of the experimental results with the corresponding calculated ones with the aid of the algorithm. Moreover the algorithm validity was extensively evaluated in milling of free form surfaces of large hydroturbine blades. The convergence between the experimental and the related calculated surface topomorphies by means of the computer program was found out to be satisfactory. Thus, the prediction of appropriate cutting conditions and milling kinematics to fulfill surface topomorphy requirements was enabled.     

Morphological and kinetic study of copper corrosion when covered with digenite sulphide layer,in sulphur,under covellite formation conditions

The sulphurization of copper covered with a digenite protective layer, under covelliteformation conditions occurs in two stages: metal valence value change in the sulphide and then metal transformation. The first stage involves an external growth and covellite precipitation in the copper vacancies supersaturated in digenite, the second an external growth similar to that of metals alone.     

Wear characteristics of TiC, Ti(C,N), TiN and Al2O3 coatings in the turning of conventional and Ca-treated steels

The wear characteristics of single layers of TiC, Ti(C,N), TiN and Al₂O₃ were investigated during turning of conventional and Ca-treated quenched and tempered Al-killed steels. The experimental coatings were deposited using chemical vapour deposition (CVD) or moderate temperature CVD (MTCVD) on cemented carbide substrates of a single composition and the coatings were of similar thicknesses (7 ± 1 μm). The wear mechanisms and layer formation were studied using scanning electron microscopy, optical microscopy and X-ray diffraction. Inclusion modification appeared to be an effective means of enhancing machinability and all experimental coatings exhibited about 20% better performance as a result of Ca-treatment. In particular, the crater wear of the experimental coatings — excluding Al₂O₃ — was clearly reduced. Comparative cutting tests revealed important differences between the coating materials. Wear mechanisms of the experimental coatings are discussed in detail.     

Wear behavior of Al2O3/Ti(C,N)/SiC new ceramic tool material when machining tool steel and cast iron

Design, fabrication and application of ceramic cutting tools are one of the important research topics in the field of metal cutting and advanced ceramic materials. In the present study, wear resistance of an advanced Al₂O₃/Ti(C,N)/SiC multiphase composite ceramic tool material have been studied when dry machining hardened tool steel and cast iron under different cutting conditions. Microstructures of the worn materials were observed with scanning electronic microscope to help analyze wear mechanisms. It is shown that when machining hardened tool steel at low speed wear mode of the kind of ceramic tool material is mainly flank wear with slight crater wear. The adhesion between tool and work piece is relatively weak. With the increase of cutting speed, cutting temperature increases consequently. As a result, the adhesion is intensified both in the crater area and flank face. The ceramic tool material has good wear resistance when machining grey cast iron with uniform flank wear. Wear mechanism is mainly abrasive wear at low cutting speed, while adhesion is intensified in the wear area at high cutting speed. Wear modes are dominantly rake face wear and flank wear in this case.