AN EXPERIMENTAL INVESTIGATION ON WEAR ASPECTS OF TAPPING OPERATION ON HARDENED STEELS

Tapping is one of the most intensively used operations for internal threads with diameters below about 15 mm. When a tap fails, the workpiece has a significant added value. The present work investigates some aspects of wear and performance when solid carbide coated taps M10 × 1.5 cut hardened AISI H13 and AISI D2. The results indicated that it was possible to make threads on hardened AISI D2, although the number of holes was essentially low and tool breakage was often. Threads on hardened AISI H13 was possible with reasonably low tool wear. Cutting surface presented some indication of small flaws due to the adhered material on the taps.     

Comparison of wear properties of tool steels AISI D2 and O1 with the same hardness

Two commercial cold work tool steels, AISI D2 and O1, were heat treated in order to obtain the same hardness 700 HV (60 HRc) and were subsequently tested in three different modes of wear, namely in adhesion, three-body and two-body abrasion, by using pin-on-disk, dry sand/rubber wheel apparatus and pin abrasion on SiC, respectively. Even though AISI O1 and D2 steel are heat treated to the same hardness, they perform differently under the three modes of wear examined. The results show that the steel microstructures play the most important role in determining the wear properties. For relatively low sliding speeds AISI O1 steel performs up to 12 times better than AISI D2 steel in adhesive wear. For higher sliding speeds, however, this order is reversed due to oxidation taking place on the surface of the AISI D2 steel. The wear rate of both tool steels in three-body and two-body abrasion wear is proportional to the applied load. In three-body abrasive wear, AISI D2 exhibits a normalised wear rate about two times lower than the AISI O1 tool steel, and this is due to the presence of the plate-like hard carbides in its microstructure. Both tool steels perform 3–8 times better in three-body abrasive wear conditions than in two-body abrasive wear.     

Tribological Performance of Boronized,Nitrided, and Normalized AISI 4140 Steel against Hydrogenated Diamond-Like Carbon-Coated AISI D2 Steel

In the current work, AISI 4140 steel was pack-boronized at 950°C for 3 h and gas-nitrided at 550°C for 72 h. All specimens used in this work were prepared from the same steel bar. A 3-µm-thick diamond-like carbon (DLC) coating (a-C:H) was deposited on the AISI D2 high-carbon, high-chromium, cold-worked tool steel by a plasma-assisted chemical vapor deposition technique. Normalized, boronized, and nitrided steel pins were tested against DLC-coated AISI D2 steel at various normal loads (15, 30, 60, and 80 N) for 1,000 and 3,000 m sliding distance in ambient air. Specific wear rate of all pins decreased with increasing load, and a similar trend was observed for the coefficient of friction (COF). Microscopic and energy-dispersive spectroscopic (EDS) analysis confirmed the role of the transfer layer for a low COF with increasing load. At all loads, the specific wear rate of boronized pins was lower than that of the nitrided and normalized pin specimens. Boronized pins showed a specific wear rate in the range of 0.27 × 10^?8 to 0.44 × 10^?8 mm³/Nm and the COF was about 0.1.     

Influence of the countermaterial on the dry sliding friction and wear behaviour of low temperature carburized AISI316L steel

Low temperature carburising (LTC) allows a significant hardness increase, with a consequent increase in wear resistance, without deteriorating corrosion behaviour. However, wear resistance strongly depends on contact conditions, therefore this work focuses on the dry sliding behaviour of LTC-treated AISI316L austenitic stainless steel against several countermaterials (AISI316L, LTC-treated AISI316L, hard chromium or plasma-sprayed Al₂O₃–TiO₂). LTC produced a hardened surface layer (C-supersaturated expanded austenite), which improved corrosion resistance in NaCl 3.5% and increased wear resistance, to an extent which depends on both normal load and countermaterial. The best results were obtained when at least one of the contacting bodies was LTC-treated, because this condition led to mild tribo-oxidative wear. However, LTC did not improve the behaviour in terms of friction.     

Sliding wear behaviour of ZrN and (Zr, 12 wt% Hf)N coatings

In the present study, the sliding wear resistances of ZrN and (Zr, 12 wt% Hf)N coatings deposited on a hardened AISI D2 tool steel by arc-physical vapor deposition (PVD) technique were examined by a ball-on-disc wear tester. Alloying of ZrN coating with 12 wt% Hf did not change the hardness significantly, but achieved an improvement on adhesion strength and dry sliding wear resistance against steel (AISI 52100-55HRC) and Al₂O₃ balls.     

The cutting tool stresses in finish turning of hardened steel with mixed ceramic tool

Precision hard machining is an interesting topic in manufacturing die and mold, automobile parts, and scientific research. While the hard machining has benefit advantages such as short cutting cycle time, process flexibility, and low surface roughness, there are several disadvantages such as high tooling cost, need of rigid machine tool, high cutting stresses, and residual stresses. Especially, tool stresses should be understood and dealt with to achieve successful performance of finish hard turning with ceramic cutting tool. So, the influence of cutting parameters on cutting stresses during dry finish turning of hardened (52 HRC) AISI H13 hot work steel with ceramic tool is investigated in this paper. For this aim, a series finish turning tests were performed, and the cutting forces were measured in tests. After literature procedure about finite element model (FEM), FEM is established to predict cutting stresses in finish turning of hardened AISI H13 steel with Ceramic 650 grade insert. As shown, effect of the cutting parameters on cutting tool stresses in finish turning of AISI H13 steel is obtained. The suggested results are helpful for optimizing the cutting parameters and decreasing the tool failure in finish turning applications of hardened steel.     

Design of micro square endmills for hard milling applications

In experiments of machining hardened tool steels (such as AISI H11, H13, and D2, up to 56 HRC) by commercial ? 0.5?mm square endmills, it is observed that the tested micro endmills showed severe wear at an early stage of the process due to chipping off around cutting edge corners, resulting in unsatisfactory tool life and product appearance (burr formation). Detailed examination of current tool geometry shows that it is mainly inherited from that of macro endmills, making the cutting edge corners the weakest part on the tool. As the micromilling process is characterized by small values of machining parameters, the cutting edge corners of the micro endmill are the most loaded part of the cutting edges. New design rules are studied for improving the stiffness and strength of micro endmills used in micro hard milling applications. Analytical modelling and finite element method analysis are used to aid the design of tool geometry. By using a larger neck angle, optimizing tool core geometry, and choosing a negative rake angle, tool stiffness and cutting edge strength are improved. The new endmill designs, both two-flute and four-flute, are tested in experiments on hardened tool steels and showed considerable lower tool wear and increased tool life. Furthermore, the geometrical accuracy and appearance of the workpiece (burr formation) has been improved drastically.     

Tool wear and chip analysis after the hard turning of AISI D6 steel assisted by LN2

Abstract

Sustainability is a concept which is widely considered nowadays, including in factories where machining operations are present. The search for methods able to improve the performance of industrial processes without damaging the environment or the worker’s health has been the main goal of several investigations. In this context, cryogenic machining is a technique that has been studied as an alternative to the use of mineral oil-based cutting fluids, mainly in the machining of titanium and nickel alloys. Investigations on the cryogenic machining of hard tool steels are still scarce in the literature. This article presents results from a series of turning trials under dry and cryogenic conditions using a hardened AISI D6 tool steel bar (57 HRC) as the workpiece. For the cryogenic machining tests, liquid nitrogen was delivered to the flank face, rake face and on both faces of PCBN inserts. The main cutting parameters (cutting speed, feed rate, and depth of cut) were kept constant during the trials. Tool wear and chip morphology were the output variables studied. The results show that the liquid nitrogen was able to reduce the cutting tool wear, providing a tool lifetime around 50% longer compared with the dry process. Moreover, the frequency of chip segmentation was diminished under cryogenic conditions in comparison with the dry process.     

Electrical discharge machining of the AISI D6 tool steel: Prediction and modeling of the material removal rate and tool wear ratio

In this investigation, response surface method was used to predict and optimize the material removal rate and tool wear ratio during electrical discharge machining of AISI D6 tool steel. Pulse on time, pulse current, and voltage were considered as input process parameters. Furthermore, the analysis of variance was employed for checking the developed model results. The results revealed that higher values of pulse on time resulted in higher values of material removal rate and lower amounts of tool wear ratio. In addition, increasing the pulse current caused to higher amounts of both material removal rate and tool wear ratio. Moreover, the higher the input voltage, the lower the both material removal rate and tool wear ratio. The optimal condition to obtain a maximum of material removal rate and a minimum of tool wear rate was 40 μs, 14 A and 150 V, respectively for the pulse on time, pulse current and input voltage.     

Study of face milling of hardened AISI D3 steel with a special design of carbide tools

This paper studies the impact of a special carbide tool design on the process viability of the face milling of hardened AISI D3 steel (with a hardness of 60 HRC), in terms of surface quality and tool life. Due to the advances in the manufacturing of PVD AlCrN tungsten carbide coated tools, it is possible to use them in the manufacturing of mould and die components. Experimental results show that surface roughness (R_a) values from 0.1 to 0.3 μm can be obtained in the workpiece with an acceptable level of tool life. These outcomes suggest that these tools are suitable for the finishing of hardened steel parts and can compete with other finishing processes. The tool performance is explained after a tool wear characterization, in which two wear zones were distinguished: the region along the cutting edge where the cutting angle (κ) is maximum (κ_max) for a given depth of cut, and the zone where the cutting angle is minimum (κ?=?0) that generates the desired surface. An additional machining test run was made to plot the topography of the surface and to measure dimensional variations. Finally, for the parameters optimal selection, frequency histograms of R_a distribution were obtained establishing the relationship between key milling process parameters (V_c and f_z), surface roughness and tool wear morphology.     

Refinement of tempered martensite structure and its effect on wear mechanism in SAE 8620

All mechanical components that undergo sliding or rolling contact are subjected to some degree of wear. Carburising treatment is important in improving wear characteristics of AISI 8620 gear steel. An experimental investigation was conducted on carburised AISI 8620 steel. Gas carburising of the specimens was carried out in sealed quenched furnace at 1198 K for 6 h followed by hardening at 1133 K, oil quenching at 393 K and followed by tempering at 453 K. Carburised cryotreated samples were cooled in a controlled manner soaked at 88 K for 16 h in a cryoprocessor subsequently followed by soft tempering at 373 K. Specimens were characterised by microhardness test, wear test and retained austenite content by XRD. 3D wear surface response and 2D contour map showed that wear rate decreased by 32% in the case of carburised cryotreated specimens as compared to only carburised specimens. It was concluded that there was an improvement in hardness and wear resistance of carburised cryotreated steel as compared to only carburised steel. Refinement and densification in martensitic structure resulted in shift in wear transition from severe wear regime to mild wear regime.     

Wear behaviour of AISI D3 and AISI M3:2 tool steels in a mass production shearing operation

The wear of two tool steels (AISI D3 and AISI M3:2) was compared in a normal production shearing operation by scanning electron microscopy at fixed production intervals.After the wear-in period, in which plastic deformation was observed, abrasive wear occurred by the action of small carbides. Wear was more uniform with AISI M3:2 tool steel than with AISI D3 tool steel and the AISI M3:2 tool produced a better finish of the sheared sheet lips.     

Experimental investigation and economic analysis of surfactant (Span-20) in powder mixed electrical discharge machining (PMEDM) of AISI D2 hardened steel

Abstract

Powder mixed EDM (PMEDM) is recognized as an advanced and innovative technique with enhanced performance and limited drawbacks in comparison to conventional EDM method. This study investigates the effect of powder particle size, various powder concentrations (C_p), and surfactant concentrations (C_s) on the performance of EDM. Since the machining characteristics are highly dependent on the dielectric performances, significant attention has been directed to introduce Cr powder and Span-20 surfactant into the dielectric fluid to achieve higher productivity and enhanced surface integrity. The EDM machining was carried out on AISI D2 hardened steel through ´Plug & Plaý dielectric circulating system attached to the main machine in order to evaluate the machining performances (i.e. MRR, EWR, and R_a). Interestingly, machining performance was improved with combination of Cr powder mixed and span-20 surfactant. By comparing the performance of span-20 surfactant and micro-nano chromium, the result within selected parameters shows that the span-20 surfactant and nano-chromium is the better choice for the EDM of AISI D2 hardened steel. In the machinability studies, the EDM machining of AISI D2 hardened steel by using span-20 surfactant and nano-chromium has exhibited the excellent machining performances, which led to 45.08% MRR enhancement and 68.89% R_a enhancement comparing to micro-chromium powder and span-20 surfactant led to 35.28% MRR and 28.96% R_a. Furthermore, cost analysis revealed that the nano-Cr powder size was approximately 4 times more economical than micro-Cr powder in machining of AISI D2 hardened steel, although the price for 1?kg is quite expensive.     

Erosion of metals using angular silicon carbide particles

ABSTRACT

In this work, erosion tests conducted to evaluate the resistance of two materials, Metal Babbitt Grade 7 and AISI T1 against SiC particles. The erosion rates of these two metals compared with those obtained using AISI D2 steel in a previous work with similar testing conditions. Metal Babbitt and AISI T1 steel selected due to their high ductility and strength, respectively. A test rig similar to that shown in ASTM G76-95 standard used to perform the tests. Silicon carbide particles had a particle size between 350–450 µm. Tests carried out using different impact angles, 30°, 45°, 60° and 90° with a particle velocity of 24 ± 2 m/s and the abrasive flow rate was 0.7 ± 0.5 g/min. SEM photographs used to identify the wear mechanisms on the Babbitt and T1 steel and also obtained cross-section images of the wear scars on metal Babbitt to measure their depth.     

H13淬硬模具钢精车过程的数值模拟

采用热力学耦合有限元方法研究了淬硬钢精车过程中切屑形成规律。运用H13 淬硬模具钢流动应力模型进行数值模拟,考查了H13淬硬模具钢精车过程中工艺参数对工件性能和刀具的影响。结果表明:切削速度愈高,进给量愈小,刀具刀尖半径愈大,则工件加工层上的静水拉应力愈小,表面质量愈好; 淬硬钢精车时径向力起主要作用,大于切削力;切削速度愈大,切削力和径向力则愈小,愈有助于改善工件加工层上的表面质量;切削速度、进给量和刀具刀尖圆角半径愈大,工件和刀具温度愈高,愈易导致刀具前刀面扩散磨损和刀具后刀面磨损。研究结论有助于优化H13淬硬模具钢精车过程中工艺参数选择和改进刀具镶片设计。     

The effects of cutting parameters on tool life and wear mechanisms of CBN tool in high-speed face milling of hardened steel

High-speed face milling of AISI H13 hardened steel is conducted in order to investigate the effects of cutting parameters on tool life and wear mechanisms of the cubic boron nitride (CBN) tools. Cutting speeds ranging from 400 to 1,600 m/min are selected. For each cutting speed, the metal removal rate and axial depth of cut are fixed, and different combinations of radial depth of cut and feed per tooth are adopted. The tool life, tool wear progression, and tool wear mechanisms are analyzed for different combinations of cutting parameters. It is found that for most of the selected cutting speeds, the tool life increases with radial depth cut and then decreases. For each cutting speed, the CBN tool life can be enhanced by means of adopting suitable combination of cutting parameters. When the cutting speed increases, the normal wear stage becomes shorter and the tool wear rate grows larger. Because of the variations of cutting force and tool temperature, the tool wear mechanisms change with different combinations of cutting parameters even at the same cutting speed. At relatively low cutting speed, in order to acquire high tool life of the CBN tool, the tool material should possess sufficient capability of resisting adhesion from the workpiece. When relatively high cutting speed is adopted, retention of mechanical properties to high cutting temperature and resistance to mechanical impact are crucial for the enhancement of the CBN tool life.     

Tool life and wear mechanism of coated and uncoated Al2O3/TiCN mixed ceramic tools in turning hardened alloy steel

The focus of this paper is the continuous turning of hardened AISI 52100 (～63HRc) using coated and uncoated ceramic Al₂O₃–TiCN mixed inserts, which are cheaper than cubic boron nitride (CBN) or polycrystalline cubic boron nitride (PCBN). The machinability of hardened steel was evaluated by measurements of tool wear, tool life, and surface finish of the workpiece. Wear mechanisms and patterns of ceramic inserts in hard turning of hardened AISI 52100 are discussed. According to the results obtained, fracture and chipping type damages occur more frequently in uncoated tools, whereas crater wear is the more common type of damage in TiN coated tools. Most important result obtained from the study is that TiN coating and crater wear affect chip flow direction. In uncoated ceramic tool, the crater formation results in decrease of chip up-curl radius. Besides, uncoated cutting tool results in an increase in the temperature at the tool chip interface. This causes a thermal bi-metallic effect between the upper and lower sides of the chip that forces the chip to curl a smaller radius. Chips accumulate in front of the tool and stick to the workpiece depending on the length of the cutting time. This causes the surface quality to deteriorate. TiN coating not only ensures that the cutting tool is tougher, but also ensures that the surface quality is maintained during cutting processes.     

WEAR STUDIES AND CUTTING TESTS OF Ti–Al–N–C NANOCOMPOSITE COATINGS IN MILLING OPERATIONS – TECHNICAL COMMUNICATION

New carbon-based nanostructured composite coatings of the material system Ti–Al–N–C were deposited on cemented carbide milling tools, and their feasibility for selected dry high-speed machining operations was assessed. For this purpose, wear studies with instrumented cutting machines in dry cutting tests were carried out in milling operations on Uddeholm hardened steels (AISI H13, and, AISI A2, respectively). The tools were coated in an industrial sputtering machine of the Hauzer HTC 625 type. The new nanocomposite coatings showed a good performance in the dry cutting operations and were benchmarked versus industrial state-of-the-art coatings.     

Studies on wears of ultrafine-grained ceramic tool and common ceramic tool during hard turning using Archard wear model

Hardened steels are difficult to be machined due to their high tensile strength and work-hardening rate, low thermal conductivity, and abrasive behavior. In this paper, finite element modeling (FEM) approaches with lagrangian increment method for 3D metal turning of hardened steel H13 by common ceramic tool and ultrafine-grained tool respectively have been investigated by simulation of DEFORM-3D software and turning test. Conditions of initial and boundary and turning process parameters have been chosen. Material properties of H13 and ceramic have been described in details. Johnson–Cook model of H13 model has been applied to the hard turning modeling. Archard wear model has been built, and the correlation coefficients were decided by reciprocating friction experiments. The simulation results showed that predicted primary turning force and maximum temperature in common ceramic are bigger than which was caused by ultrafine-grained ceramic tool for the ultrafine-grained ceramic tools have better thermal stability and bigger hardness. The wear depths of common ceramic tool are about many times than that of ultrafine-grained ceramic tool according to the simulation and experimental results. And their wear patterns are very different. The FEM simulation results have entirely explicated experimental results. The obtained results would provide the fundamental and practical guidelines of tool material choice for hard turning.     

不同涂层刀具切削淬硬H13钢加工性能研究

为了研究不同涂层刀具切削淬硬H13钢的切削性能,进行了多层Ti化合物涂层、TiAlN涂层以及MTTiCN厚Al_2O_3TiN涂层材料刀具车削加工淬硬H13钢试验,分析了不同的涂层材料刀具与切削力、切削温度、涂层刀具磨损以及刀具寿命的关系。研究得出:多层Ti化合物涂层刀具受到三个方向的力都大于其它两种涂层的刀具,而且切削温度最高;用TiAlN涂层刀具切削时温度最低;切削过程中三种刀具后刀面磨损程度不同,发现多层Ti化合物涂层刀具磨损最为严重,寿命最短;MT-TiCN厚Al_2O_3Ti N涂层材料刀具比多层Ti化合物涂层刀具寿命长30%;TiAlN涂层刀具的切削寿命最长比多层Ti化合物涂层刀具寿命长45%。