Cost-effective way of hard turning with newly developed HSN2-coated tool

EN-31 (AISI 52100, hardness 55 HRC) is one of the difficult-to-cut steel alloys and it is commonly used in shafts and bearings. Nowadays, it is becoming a challenge to the cutting tool material for economical machining of extremely tough and hard steels. In general, CBN and PCBN tools are used for machining hardened steel. However, machining cost using these tools becomes higher due to high tool cost. For this purpose, carbide tool using selective coatings is the best substitute having comparable tool life, while its cost is approximately one-tenth of CBN tool. In this work, the newly developed second-generation TiAlxN super nitride (i.e., HSN²) is selected for PVD coating on carbide tool insert and further characterized using thermogravimetric analysis and differential scanning calorimetry for oxidation and thermal stability at high temperature. Later, HSN²-coated carbide inserts are successfully tested for their sustainability to expected tool life for turning of AISI 52100 steel. In the present study, forces, surface finish, and tool wear are used as a measure to appraise the performance of hard turning process. Experimentally, it is found that speed, feed rate, and depth of cut have considerable impact on forces, insert wear, and surface roughness of the machined surface.     

Comparative investigation towards machinability improvement in hard turning using coated and uncoated carbide inserts: part I experimental investigation

The investigation of low cost uncoated and coated carbide insert in the hard turning of hardened AISI D2 steel (≥55 HRC) will definitely open up a new arena as an economical alternative suitable to industrial machining sectors. Thus, this paper reports the comparative machinability assessment for the hard turning of AISI D2 steel ((55 ±1) HRC) by coated and uncoated carbide insert in a dry environment. Micro hardness and abrasion tests were carried out to assess resistance capability against wear. The above test results confirmed the greater wear resistance ability of Al₂O₃ coated carbide insert over uncoated carbide. Based on the extensive investigation of comparative machinability, the coated carbide insert (TiN-TiCN-Al₂O₃) outperformed the uncoated carbide insert with regard to surface roughness, flank wear, chip-tool interface temperature, and chip morphology. Abrasion and diffusion were observed as the principal tool wear mechanisms in the investigated range. The uncoated carbide failed completely due to the severe chipping and quick dulling of the cutting edge, which led to its unsuitability for machining hardened steel. The full text can be downloaded at https://link.springer.com/article/10.1007/s40436-018-0215-z     

Comparative Wear Behavior of Ceramic and Carbide Tools During High Speed Machining of Steel

Two types of oxide-based ceramic cutting tools have been developed for high speed machining of hardened steel. These tools were made of alumina (A1₂O₃) and zirconia toughened alumina (ZTA). Commercially available tungsten carbide (WC)-based tools were also used during machining for comparison. In general, ceramic tools exhibited superior performance as compared to the WC tools, especially at higher machining speeds, both in terms of tool life and surface finish of the work-piece. The worn-out tools were observed under a stereo-microscope for studying the role of different wear mechanisms on the tool life. While severe crater wear was observed in the WC tools, only a small amount of edge chipping and nose wear occurred in the ceramic tools during high speed machining. The correlation between the mechanical properties of the tool material, the tool lives and their wear behavior was also studied.     

Drehen und Fräsen pulvermetallurgischer Hartlegierungen für warmgehende Werkzeuge

Turning and Milling of Powder Metallurgical Hard Alloys for Tools in Hot Working Applications Hard metals are high wear resistant materials. The microstructure of these composites consists of hard phases which are embedded in a metal matrix. The high hardness and the high content of the hard phases lead to a difficult machining of these materials. The present study investigates the turning and milling of D3 cold work steel (X210 Cr 12) and the powder metallurgical Fe‐based alloys ASP60 and ASP23 + WC/W₂C. The cutting tool materials were polycrystalline cubic boron nitrides (CBN) and ceramic inserts. The machining process could be judged by means of tool wear and machining quality (surface roughness and changes in the surface near zone). The investigations illustrate that the machinability of the different hard metals depends on the cutting speed and the cutting tool material.     

An Investigation on Turning Hardened Steel Using Different Tool Inserts

Turning of hard materials usually presents poor machinability. However, for high productivity, it is desirable to employ turning of hard materials rather than grinding. In this work, turning of hardened 16MnCrS5 steel with hardness of 43 HRC was explored to judge machining performance with plain and wide-groove-type chip-breaking TiC-coated carbide inserts under dry and wet environmental conditions, different cutting velocity, and feed. Tool wear tests were also done in dry and wet conditions. Satisfactory tool performance was observed under wet condition using TiC-coated plain and wide-groove carbide inserts even at 268 m/min cutting velocity, when dry machining could not be done effectively.     

Comparative assessment of coated and uncoated ceramic tools on cutting force components and tool wear in hard turning of AISI H11 steel using Taguchi plan and RMS

This study investigated the cutting performance of coated CC6050 and uncoated CC650 mixed ceramics in hard turning of hardened steel. The cutting performance was mainly evaluated by cutting force components and tool wear. The planning of experiments was based on Taguchi’s L₃₆ orthogonal array. The response surface methodology and analysis of variance were used to check the validity of multiple linear regression models and to determine the significant parameter affecting the cutting force components. Tool wear progressions and, hence, tool life, different tool wear forms and wear mechanisms observed for tools coated with TiN and uncoated mixed ceramics are presented along with the images captured by digital and electron microscope. Experimental observations indicate higher tool life with uncoated ceramic tools, which shows encouraging potential of these tools to hard turning of AISI H11 (50 HRC). Finally, tool performance indices are based on units which characterise machined cutting force components and wear when hard turning.     

The influence of cutting force on surface machining quality

Appropriately controlled cutting forces can contribute not only to the safety and efficiency of machining but also to the quality of machined surfaces. It is even more important when hardened material is cut. The correlation between the cutting force and the surface quality in ball-end milling operations has been investigated by machining P20 steel (HRC 30) work-pieces using solid carbide ball-end cutters. Plane surfaces with different depth of cut were machined using two different cutting strategies. The first strategy cut the test-piece using a cutting force model, whereas the other machined with a feed rate optimization product, which uses the removal rate as an analogue of cutting force to control the feed rate. The test results show that constant surface quality is possible when the cutting forces are controlled through feed rate adjustment. Conversely, a desired surface quality can also be maintained by controlling the cutting force in a predetermined manner.     

Numerical simulation of finish hard turning for AISI H13 die steel

A coupled thermo-mechanical model of plane-strain orthogonal turning of hardened steel was presented. In general, the flow stress models used in computer simulation of machining processes are a function of effective strain, effective strain rate and temperature developed during the cutting process. However, these models do not adequately describe the material behavior in hard machining, where the workpiece material is machined in its hardened condition. This hardness modifies the strength and work hardening characteristics of the material being cut. So, the flow stress of the work-material was taken with literature [H. Yan, J. Hua, R. Shivpuri, Development of flow stress model for hard machining of AISI H13 work tool steel. The Fourth International Conference on Physical and Numerical Simulation of Materials Processing, Shanghui in China, 2004, p. 5] in order to take into account the effect of the large strain, strain-rate, temperature and initial workpiece hardness. Then a series of numerical simulations had been done to investigate the effect of machining parameters on the machinability of hardened steel AISI H13 in finish turning process. The results obtained are helpful for optimizing process parameters and improving the design of cutting inserts in finish turning of hardened steel AISI H13.     

The CAM as the centre of gravity of the five-axis high speed milling of complex parts

The use of multi-axis high-speed milling has increased in different industrial sectors such as automotive, aeronautical, and the manufacturing of complex moulds. This trend can be observed at the latest technical fairs and the catalogues of the main machine tool manufacturers. Furthermore, for machining impossible shapes, multi-axis machining introduces two main advantages. First it gives the option of performing all operations in only one set-up of the raw block, which can be a prismatic block or a near-to-net shape form. Second it offers the capability of setting the cutting speed, depth of cut and feed to optimize tool life and part quality.

However, multi-axis milling is a very complex process that requires special care in the CNC program preparation in the CAM stage, which is critical for a successful process. Thus, the use of a virtual machining simulation utility is highly recommended. Collisions, over-cuts, interferences and dangerous machine movements can be predicted and avoided. On the other hand, continuous variation of the tool can be used to optimize cutting parameters such as cutting forces. Final result is the minimization of tool deflection due to the cutting forces and, in this way, the precision and roughness of finished parts are improved.

In this paper a reliable method for multi-axis HSM is presented. This methodology is based on two aspects. First a cutting force estimation in order to get minimum cutting force tool-paths. Second a complete virtual simulation to ensure a collision-free tool-path. A final objective is to generate reliable CNC programs. In this manner, the CAM becomes the centre of gravity of the machining planning procedure.

The methodology has been applied to the machining of two plastic moulds in hardened steel (32 HRC), a 7075-T6 aluminium honeycomb part for aeronautical purposes and a 65 HRC AISI 1.2379 part. Times, tolerances and surface roughness have been measured to check the success of the purposed methodology.     

Effect of a nanoparticle-filled lubricant in turning of AISI 316L stainless steel (SS)

Release of heat and generation of friction associated with machining operation ever posture a problem which not only reduce the tool life but also impair the quality of the product. Nano cutting fluids play a significant role in machining operations and impact tool life and quality of work. In the present work, tool flank wear is analyzed during turning AISI 316L Stainless steel (SS) under a nano cutting environment. Experiments are conducted by turning of AISI 316L SS under wet machining with and without multiwalled carbon nanotube (MWCNT) inclusions in the conventional lubricant. The second order quadratic models were developed to predict tool wear using response surface methodology (RSM) based D-optimal design. Machining parameters such as speed, feed rate, and depth of cut are chosen as numerical factors and the type of lubricant is considered as the categorical factor. The results show that the influence of the feed rate is more significant while machining the AISI 316L SS with a whisker reinforced ceramic insert. The addition of MWCNTs in SAE20W40 enhances the tool performance with their enhanced penetration. After turning experiment, a scanning electron microscope (SEM) with energy dispersive X-ray (EDS) was used to investigate the tool wear.     

Prediction of cutting force based on machining parameters on AL7075-T6 aluminum alloy by response surface methodology in end milling

Cutting forces modeling is the basic to understand the cutting process, which should be kept in minimum to reduce tool deflection, vibration, tool wear and optimize the process parameters in order to obtain a high quality product within minimum machining time. In this paper a statistical model has been developed to predict cutting force in terms of geometrical parameters such as rake angle, nose radius of cutting tool and machining parameters such as cutting speed, cutting feed and axial depth of cut. Response surface methodology experimental design was employed for conducting experiments. The work piece material is Aluminum (Al 7075-T6) and the tool used is high speed steel end mill cutter with different tool geometry. The cutting forces are measured using three axis milling tool dynamometer. The second order mathematical model in terms of machining parameters is developed for predicting cutting forces. The adequacy of the model is checked by employing ANOVA. The direct effect of the process parameter with cutting forces are analyzed, which helps to select process parameter in order to keep cutting forces minimum, which ensures the stability of end milling process. The study observed that feed rate has the highest statistical and physical influence on cutting force.     

Experimental investigations on cryogenic cooling by liquid nitrogen in the end milling of hardened steel

Milling of hardened steel generates excessive heat during the chip formation process, which increases the temperature of cutting tool and accelerates tool wear. Application of conventional cutting fluid in milling process may not effectively control the heat generation also it has inherent health and environmental problems. To minimize health hazard and environmental problems caused by using conventional cutting fluid, a cryogenic cooling set up is developed to cool tool–chip interface using liquid nitrogen (LN₂). This paper presents results on the effect of LN₂ as a coolant on machinability of hardened AISI H13 tool steel for varying cutting speed in the range of 75–125 m/min during end milling with PVD TiAlN coated carbide inserts at a constant feed rate. The results show that machining with LN₂ lowers cutting temperature, tool flank wear, surface roughness and cutting forces as compared with dry and wet machining. With LN₂ cooling, it has been found that the cutting temperature was reduced by 57–60% and 37–42%; the tool flank wear was reduced by 29–34% and 10–12%; the surface roughness was decreased by 33–40% and 25–29% compared to dry and wet machining. The cutting forces also decreased moderately compared to dry and wet machining. This can be attributed to the fact that LN₂ machining provides better cooling and lubrication through substantial reduction in the cutting zone temperature.     

Dynamic phenomena in finish turning of hardened steels with cBN-based tools

The paper presents some findings of the investigation of finish turning of KhVG hardened steel (60–62 HRC) using a cutting tool with an insert made of a cubic boron nitride based composite (cBN-Si₃N₄ system). The influence of machining process variables on the cutting force components, vibrations, and machined surface roughness is clarified. The authors propose some practical recommendations of how to choose machining modes and conditions.     

High-feed turning of AISI D2 tool steel using multi-radii tool inserts: Tool life,material removed,and workpiece surface integrity evaluation

Multi-radii tool inserts offer novel configuration that comprises of multiple radii at tool nose. A review of the available literature indicates that there exists a need for experimental investigation on certain key machining characteristics of such tools. This paper reports on tool wear/life, material removed, and workpiece surface roughness when multi-radii mixed alumina TiN coated tool inserts are employed for turning D2 steel. Inserts of three different nose radii (0.40, 0.80, 1.20?mm) at six levels of feed rates (ranging from 0.157 to 0.562?mm/rev) are used. Results show that flank wear is the dominant wear mode with catastrophic tool failure occurring at highest nose radius (1.20?mm) and feed rate (0.562?mm/rev) combination. Also, there is ～59% reduction in tool life accompanied by ～62% increase in quantity of material removed as the feed rate increases from 0.157 to 0.562?mm/rev at maximum nose radius (1.20?mm). Feed rate is found to be statistically significant factor for all three responses considered herein at 95% confidence level. Surface integrity assessment at maximum feed rate reveals presence of a strain hardened layer extending to the depth of 150?µm below the machined surface without any observance of white layer for all the tool conditions and nose radius.     

Prediction of Tool Wear in the Turning Process Using the Spectral Center of Gravity

The recent increase in machining productivity is closely related to longer tool life and good surface quality. In the present study, an experimental technique is proposed to evaluate the performance of a cemented carbide inset during the machining of AISI D3 steel. The aim of this technique is to find a relationship between the vibratory state of the cutting tool and the corresponding wear during machining in order to detect the beginning of the transition period to excessive wear. A spectral indicator named spectral center of gravity, SCG, is proposed to highlight the three phases of tool wear using the spectra of the accelerations measured. Very promising results are obtained which can be used to underpin an industrial monitoring system capable of detecting the onset of transition to excessive wear and alerting the user of the end of the tool’s life. The purpose of this study is to review the vibration analysis techniques and to explore their contributions, advantages and drawbacks in monitoring of tool wear.     

Vibration-Assisted Precision Machining of Steel with PCD Tools

This article presents experimental results of precision machining of steel alloys with polycrystalline diamond tools. Ultrasonic vibration-assisted cutting was tried out for expanding the application of diamond tools for high-precision and high-quality machining of ferrous materials. The experimental results show that compared with conventional turning, the cutting performance, in terms of cutting force, surface finish, and tool life, was improved by applying ultrasonic vibration to the cutting tool. The cutting forces and tool wear measured in vibration cutting are much lower than those in conventional cutting. The tool wear mechanism was discussed on the basis of the observation of wear zone.     

Experimental study on the meso-scale milling of tungsten carbide WC-17.5Co with PCD end mills

Tungsten carbide is a material that is very difficult to cut, mainly owing to its extreme wear resistance. Its high value of yield strength, accompanied by extreme brittleness, renders its machinability extremely poor, with most tools failing. Even when cutting with tool materials of the highest quality, its mode of cutting is mainly brittle and marred by material cracking. The ductile mode of cutting is possible only at micro levels of depth of cut and feed rate. This study aims to investigate the possibility of milling the carbide material at a meso-scale using polycrystalline diamond (PCD) end mills. A series of end milling experiments were performed to study the effects of cutting speed, feed per tooth, and axial depth of cut on performance measures such as cutting forces, surface roughness, and tool wear. To characterize the wear of PCD tools, a new approach to measuring the level of damage sustained by the faces of the cutter's teeth is presented. Analyses of the experimental data show that the effects of all the cutting parameters on the three performance measures are significant. The major damage mode of the PCD end mills is found to be the intermittent micro-chipping. The progress of tool damage saw a long, stable, and steady period sandwiched between two short, abrupt, and intermittent periods. Cutting forces and surface roughness are found to rise with increments in the three cutting parameters, although the latter shows signs of reduction during the initial increase in cutting speed only. The results of this study find that an acceptable surface quality (average roughness R_a<0.2 μm) and tool life (cutting length L>600 mm) can be obtained under the conditions of the given cutting parameters. It indicates that milling with PCD tools at a meso-scale is a suitable machining method for tungsten carbides.The full text can be downloaded at https://link.springer.com/article/10.1007/s40436-020-00298-y     

WEAR OF ALUMINUM OXIDE TOOLS IN STEEL CUTTING

Ceramic cutting materials like aluminum oxide and silicon nitride are used for machining of metallic materials. Especially during steel cutting with A1₂ O₃ -tools cracks and notch wear occur at the tools. For this reason extended investigations were carried out to understand the mechanisms of cracking and notch wear formation. In doing so cutting tests, stability calculations and chemical experiments were executed. During cutting tests the influence of cutting parameters and cutting geometry on notch wear was investigated. Stability calculations with the Finite Element Method elucidated critical load conditions and weak points of the tool material. Chemical experiments and x-ray-analysis show that chemical reactions are going on during the cutting process and can influence decisively wear progress.     

Tool life and surface integrity when milling inconel 718 with coated cemented carbide tools

Abstract

This paper presents a study of tool life and surface integrity while machining superalloy Inconel 718 using coated cemented carbide tools. In the machining of heat resistant superalloys used in aeronautical applications and classified as difficult‐to‐machine, tool life is an important parameter in evaluating the performance of the cutting tools. Surface quality of the workpiece is one of the important criteria in determining tool life. Our tests have been done under various combinations of speed, feed rate, and depth of cut to verify the change in surface roughness due to increasing tool wear. The behavior of the uncoated, TiN, and TiCN layers using various cutting conditions was analyzed. At the end, a choice of coating and optimization of the cutting conditions has been proposed.     

The study of wear of cutting tools of cBN-based composite material and the influence of tool wear on cutting forces in turning hardened steels

The paper presents some findings of the investigation of finish turning of KhVG hardened steel using a cutting tool with an insert made of a cubic boron nitride based composite (cBN-Si₃N₄ system). The behavior of tool wear throughout the machining time as well as the influence of the tool wear on cutting force components and resulting cutting force have been clarified.