Workpiece Hardness Research Articles

Study on Polishing Characteristics of Pyramidal Structured Polishing Pad

We conducted a polishing test to clarify the change in polishing characteristics resulting from the wear of a pyramidal-structured polishing tool, and discuss the polishing mechanism unique to the pyramidal-structured polishing pad. When the pyramidal-structured polishing pad is used for polishing, there exists an initial polishing stage in which the removal rate is high but the finished surface is rough; followed by a steady-state polishing stage in which the wear rate is low, removal rate is stable, and a high-quality finish is obtained. The true polishing pressure is constant in the steady-state polishing stage regardless of the nominal polishing pressure, although it differs with workpiece hardness. Polishing was carried out using the pyramidal-structured polishing pad containing 6 μm alumina abrasive grains for 90 min without any scorching or clogging. This resulted in finished surfaces of 0.4 μmRzand 0.07 μmRzfor oxygen-free copper and S45C, respectively.

Influence of Different Grades of CBN Inserts on Cutting Force and Surface Roughness of AISI H13 Die Tool Steel during Hard Turning Operation.

Now-a-days, the application of hard tuning with CBN tool has been massively increased because the hard turning is a good alternative to grinding process. However, there are some issues that need to be addressed related to the CBN grades and their particular applications in the area of hard turning process. This experimental study investigated the effects of three different grades of CBN insert on the cutting forces and surface roughness. The process of hard turning was made using the AISI H13 die tool steel at containing different hardness (45 HRC, 50 HRC and 55 HRC) levels. The work material were selected on the basis of its application in the die making industries in a range of hardness of 45–55 HRC. Optimization by the central composite design approach has been used for design and analysis. The present study reported that the cutting forces and surface roughness are influenced by the alloying elements and percentage of CBN in the cutting tool material. The work material hardness, feed rate and cutting speed are found to be statistically significant on the responses. Furthermore, a comparative performance between the three different grades of CBN inserts has been shown on the cutting forces and surface roughness at different workpiece hardness. To obtain the optimum parameters from multiple responses, desirability approach has been used. The novelty/robustness of the present study is represented by its great contribution to solve practical industrial application when is developed a new process using different CBN grades for hard turning and die makers of workpiece having the hardness between 45 and 55 HRC.

Machinability investigation with Wiper Ceramic Insert and Optimization during the Hard Turning of AISI 4340 Steel

Abstract Production cost is the highest motivating factor to initiate the introduction of new manufacturing technologies and application of optimization techniques in the production industries. In this paper an attempt is made to establish the influence of workpiece hardness on Surface roughness (Ra), cutting force (Fy) and tool wear (Vb) during the performance evaluation of wiper ceramic cutting insert. Experiments are planned according to Box-Behnken Design approach during the hard turning of Hardened AISI 4340 steel on a CNC lathe. RSM based Desirability approach used for multi-objective optimization of the machining parameter and optimum cutting conditions are proposed based on this approach. Experimental result confirms that the workpiece hardness have significant statistical influences on the surface roughness, cutting force and tool wear.

Wear performance and mechanisms of PCBN tool in dry hard turning of AISI D2 hardened steel

In this paper, the wear performance and mechanisms of PCBN tool in dry hard turning of AISI D2 hardened steel at various hardness levels (40–60 ± 1 HRC) were investigated at a fixed 250-m/min cutting speed, 0.10-mm/r feed, and 0.15-mm depth of cut. The results showed that the workpiece hardness has a great influence on the flank wear. The principle wear mechanisms in the flank wear of the PCBN tools are the abrasive wear in the cases of 40–55 ± 1 HRC, and abrasive and delamination wear in a case of 60 ± 1 HRC due to an abrupt increase of friction at tool-workpiece interfaces, while the crater is the principle wear in the rake face of PCBN tools.

Nanoplastic removal function and the mechanical nature of colloidal silica slurry polishing

AbstractThe nanomechanical deformations on a broad range of optical material surfaces (single crystals of Al2O3 [sapphire], SiC, Y3Al5O12 [YAG], CaF2, and LiB3O5 [LBO]; a SiO2–Al2O3–P2O5–Li2O glass‐ceramics [Zerodur]; and glasses of SiO2:TiO2 [ULE], SiO2 [fused silica], and P2O5–Al2O3–K2O–BaO [Phosphate]) near the elastic‐plastic load boundary have been measured by nanoindentation and nanoscratching to mimic the nanoplastic removal caused by a single slurry particle during polishing. Nanoindenation in air was performed to determine the workpiece hardness at various loads using a commercial nanoindenter with a Berkovich tip. Similarly, an atomic force microscope (AFM) with a stiff diamond coated tip (150 nm radius) was used to produce nanoplastic scratches in air and aqueous environments over a range of applied loads (~20‐170 μN). The resulting nanoplastic deformation of the nanoscratches were used to calculate the removal function (i.e., depth per pass) which ranged from 0.18 to 3.6 nm per pass for these materials. A linear correlation between the nanoplastic removal function and the polishing rate (using a fixed polishing process with colloidal silica slurry on a polyurethane pad) of these materials was observed implying that: (a) the polishing mechanism using colloidal silica slurry can be dominated by mechanical rather than chemical interactions; and (b) the nanoplastic removal function, as opposed to interface particle interactions, is the controlling factor for the polishing material removal rate. Furthermore, this correlation is consistent with the Ensemble Hertzian Multi‐Gap (EHMG) microscopic material removal rate model described previously. The nanoplastic removal depth was also found to correlate to the measured nanoindentation hardness (H1) of the optical material, scaling as H1−3.5. Two‐dimensional (2D) finite element analysis simulations of nanoindentation showed a similar nonlinear dependence of plastic deformation with the workpiece material hardness. The findings of this study are used to determine an effective Preston coefficient for the material removal rate expression and enhance the predictive nature of the nanoplastic polishing rate for various materials utilizing their material properties.

Simultaneous machining and surface alloying of AISI 1040 steel by electrical discharge machining with boron oxide powders

In PM/EDM, it is known that when used electrically conductive powders, highly homogeneous alloyed layers can be formed where the gap extends slightly more than using non-conductive powders and regulates spark discharge and machining voltage more uniform. Boron element is non-conductive but when alloyed with steel, materials with high abrasion and corrosion resistance are obtained. In this study, the effects of boron oxide powders addition into dielectric fluid on microstructure and hardness of steel workpiece in electrical discharge machining (EDM) were investigated. For this purpose, by using a prismatic steel workpiece and a copper electrode in kerosene mixed with boron oxide (B2O3) powders, the morphology of the machined specimens at different powder concentrations and pulse duration settings were observed and investigated. In addition, the micro hardness of the layers occurred as a result of EDM was measured and discussed. The highest surface hardness value of 941 HV is measured over machined specimen with B2O3 powder addition, whereas the lowest surface hardness value of 413 HV is measured.

Experimental investigation and analysis of the influence of tool edge geometry and work piece hardness on surface residual stresses, surface roughness and work-hardening in hard turning of AISI D2 steel

Surface integrity of the machined component significantly affects its in-service performance in terms of fatigue life and resistance to corrosion. Residual stresses, work hardening, microstructure alterations and surface roughness are the major issues that constitute the surface integrity of a machined surface which are a resultant of the plastic deformation. The current study attempts to investigate the effect of the different tool edge geometries and the process parameters in CBN hard turning of AISI D2 steel on the tri-axial surface residual stresses, surface roughness and work hardening in the machining affected region. XRD in conjunction with nano indentation has been utilized for measurement of the surface integrity parameters. The behavior of the residual stresses is correlated to the input parameters. Sensitivity of the tri-axial stresses to the input parameters is obtained by Monte Carlo Simulation and optimum ranges of the input parameters and the probabilities of inducing compressive stresses have been determined. The sensitivity analysis indicates that the axial residual stress has maximum sensitivity to depth of cut while the radial and circumferential residual stresses and surface roughness are most sensitive to feed rate. The certainty analysis indicates that machining with light honed tool edge geometry in the low to moderate range of process parameters induces a compressive state of residual stresses and better surface quality.

Simulation and experimental investigation of drilling of Ti-6Al-4V alloy

Titanium alloys are considered as poor machinability material due to high chemical reactivity with the cutting tool and low thermal conductivity properties. Thus, high cutting temperature and pressure at cutting-edge result high tool wear and tool damage. The drilling parameters are the one alternative to reduce high temperature which increases tool life. In this investigation, to avoid the cost of the material and time in the machining of Ti-6Al-4V, a 3D FEM has been proposed to study the drilling operation. The simulation model has been carried out with DEFORM software by varying cutting speed and feed rates to study thrust, torque, effective stress, effective strain and drill bit temperature. According to this investigation, the drill bit temperature was increased with the increase of all range feed rates, whereas an increase of cutting speed reduced the hardness of workpiece due to thermal softening, thus low temperature on drill bit was observed. The better surface finish was observed at high cutting speed and low feed rate. To validate the simulation model, a series of experiments have been performed in the same cutting condition. Torque, thrust, and circularity have been evaluated and compared with the simulated results. A close agreement with fewer errors between them was observed which reveals that the simulation model is correct.

Modeling of Machining Force in Hard Turning Process

In this work, we develop a modeling based on an Artificial Neural Network (ANN) and Multiple Linear Regression (MLR) to predict the machining force components generated during hard turning of a bearing steel with CBN cutting tool. The inputs of the ANN model were the cutting parameters (cutting speed, feed and depth-of-cut) and the workpiece hardness. The network training is performed by using experimental data. The optimal network architecture is determined after several simulations by Matlab Neural Network Toolbox. Back-propagation by Bayesian Regularization in combination with Levenberg–Marquardt algorithm is employed for training. The ANN approach is suitable to estimate the machining force components such as feed-force, radial-force and tangential-force; for this purpose, the results are compared to those obtained by experiment, and the maximum average MAPE value of 4.58 % was obtained for the machining force prediction. Also, the ANN results were compared to those obtained by MLR model. It was shown that the ANN model produced more successful results. DOI: http://dx.doi.org/10.5755/j01.mech.24.3.19146

Experimental investigations on wiper inserts’ edge preparation, workpiece hardness and operating parameters in hard turning of AISI D2 steel

Review of the available literature indicates that hard part turning requires tailored cutting edge for specific tool workpiece combination. Incidentally, much work could not be found that evaluates the role of wiper insert’s cutting edge while hard turning. The objective of presented work is to evaluate the effect of wiper inserts’ micro geometry for critical hardness regime of the material. The work employs two distinct edge geometries namely chamfer (0.15 mm × 25°) and chamfer plus hone (0.15 mm × 25°–25 μm) for wiper inserts in finish hard turning of AISI D2 steel without cutting fluid. Taguchi L18 array is used for tool wear/life, material removed and surface roughness and comparison has been done with a conventional insert (chamfered plus honed edge geometry). Three levels of feed rate and depth of cut have been used while machining workpieces of two different hardness (55HRC and 60HRC). Contrary to the influence of edge preparation typically reported for conventional inserts, here, it is found that its role is somewhat suppressed in the presence of wiper macro-geometry for both the output parameters namely tool wear/life and surface roughness. More specifically, workpiece hardness is found to play most significant role (with PCR of 70.11%) for tool life whereas for surface roughness, insert type (wiper inserts are seen to clearly outperform conventional tools) and feed rate are found to be more dominant. Interestingly, maximum wear scar has been observed at the minor cutting edge with “Notching” being the prevalent wear mode. Oxidation and seizure pull-out seem to be principal wear mechanisms. Microhardness is seen to be increased beneath the machined surface for both new and worn tools up to a depth of 200 μm. At highest feed (0.281 mm/rev) and depth of cut (0.20 mm) combination, material pull-out was revealed as the major microstructural damage.

Analytical model of work hardening and simulation of the distribution of hardening in micro-milled nickel-based superalloy

During the process of micro-milling nickel-based superalloy, the cutting surface is strengthened along with the high strain and strain rate, which leads to work hardening and affects the quality of parts and the tool’s life. At present, there are few analytical models that can predict the micro-hardness of the micro-milled surface. Therefore, the authors focus on the research of the micro-milling work hardening of nickel-based superalloy. Firstly, based on the stress-strain relationship and strain-hardening characteristics of Inconel718, the relationship between hardness and strain of Inconel718 is obtained. Then, based on the established micro-milling force model, the stress of a point in the process of micro-milling is derived. Finally, the surface hardness value of the machined surface is predicted by combining the relationship between the stress-strain and the hardness of the workpiece. In addition, a 3D simulation model of micro-milling nickel-based superalloy groove is established by Deform-3D software to research the distribution of micro-hardness of the machined surface. The research offers reference for improving the surface integrity and fatigue performance of micro-milling nickel-based superalloy and explores a feasible way for revealing the mechanism of micro-milling hardening.

Investigating the Tribological Characteristics of Burnished Polyoxymethylene—ANFIS and FE Modeling

ABSTRACTPolymers are utilized in numerous tribological applications because of their excellent characteristics; for example, accommodating shock loading and shaft misalignment. A high surface finish is required to ensure consistently good performance and extended service life of manufactured polymeric components. Burnishing is the best choice as a finishing process for this study due to its ability to increase hardness, fatigue strength, and wear resistance and also introduce compressive residual stress on the burnished workpiece. Due to the complexity and uncertainty of the machining processes, soft computing techniques are preferred for anticipating the performance of the machining processes. In this study, ANFIS as an adaptive neuro-fuzzy inference system was applied to anticipate the workpiece hardness and surface roughness after the roller burnishing process. Five burnishing variables, including burnishing depth, feed rate, speed, roller width, and lubrication mode, were analyzed. A Gauss membership function was used for the training process in this study. The predicted surface roughness and hardness data were compared with experimental results and indicated that the Gauss membership function in ANFIS has satisfying accuracy as high as 97% for surface roughness and 96% for hardness. Furthermore, the generated compressive residual stress on the burnished surface was studied by a 2D finite element model (FEM). The simulated results of residual stress were validated with the experimental results obtained from X-ray diffraction (XRD) tests.

Determining the Effect of Material Hardness During the Hard Turning of AISI4340 Steel

In the present manufacturing industries hardened steels are most widely used in the applications like tool design and mould design. It enhances the application range of hard turning of hardened steels in manufacturing industries. This study discusses the impact of workpiece hardness, feed and depth of cut on Arithmetic mean roughness (Ra), root mean square roughness (Rq), mean depth of roughness (Rz) and total roughness (Rt) during the hard turning. Experiments have been planned according to the Box–Behnken design and conducted on hardened AISI4340 steel at 45, 50 and 55 HRC with wiper ceramic cutting inserts. Cutting speed is kept constant during this study. The analysis of variance was used to determine the effects of the machining parameters. 3-D response surface plots drawn based on RSM were utilized to set up the input–output relationships. The results indicated that the feed rate has the most significant parameter for Ra, Rq and Rz and hardness has the most critical parameter for the Rt. Further, hardness shows its influence over all the surface roughness characteristics.

Influence of Workpiece Hardness on Tool Wear in Profile Micro-milling of Hardened Tool Steel

Influence of Workpiece Hardness on Tool Wear in Profile Micro-milling of Hardened Tool Steel

Mechanism of the crack propagation in the chip root in dry hard orthogonal turning of the hardened steel

Analytic model of the crack-tip field in the cutting tool tip located in the chip root in dry hard orthogonal turning (DHOT) of the hardened steel was established in this paper according to the metal cutting principle and fracture mechanics theory. The relationship between the crack inclination angle ψ to the direction of the tensile stress σ and the crack propagation angle θ0 in I-II mixed model also was proposed. The control equation, displacement function, and boundary condition of crack dynamic propagation in the chip root were derived. The mathematical model for the relationship between the shear angle ϕ and the crack propagation angle θ0 also was presented. Furthermore, formation mechanisms of the serrated chip in DHOT of the hardened steel Cr12MoV (40–60 ± 1HRC) by utilizing the Polycrystalline Cubic Boron Nitride (PCBN) inserts were experimentally investigated. The results showed that the cutting speed and quenching hardness of workpiece have great influence on the crack propagation angle θ0. The shear angles ϕ calculated by the mathematical model are basically in agreement with the experimental results. The thermal softening chip squeezed from the cutting tool rake face begins to shear and slip at high speed along the direction of the crack propagation angle θ0 in the chip root and then the serrated chip forms.

Experimental and numerical investigation of thermal loads in Inocnel 718 machining

ABSTRACTInducing high thermal loads in machining of difficult-to-cut materials changes the mechanical properties of a machined surface/subsurface. In particular, a thermally affected layer leads to tensile residual stresses and microstructure changes. Nickel-based alloys are hard materials and frequently used in different industries. Since the generation of thermal loads in machining Inconel 718 is evident, in this paper an experimental and numerical investigation were performed to evaluate thermal loads and the depth of the affected layer in the machining of Inconel 718 superalloy. First, the effect of cutting parameters was studied on the average machined surface temperature by experimental tests. Then, the results of experiments were used to validate a 3D numerical model. Using the calibration strategy, the heat transfer coefficient at the chip–tool interface was found to be dependent on the cutting conditions. Next, the effect of the initial workpiece hardness and tool geometry, including tool nose radius and edge radius, was evaluated on thermal loads and the depth of the recrystallized layer. The critical strain criterion was used to estimate the depth of the recrystallized layer and then, the numerical results were compared with experimentally measured depth of the affected layer at different machining parameters.

Investigations into hard turning process using wiper tool inserts

Now a day, major objectives of industries are to increase productivity and quality of product at low cost with minimum energy consumption which in turn lead to economic and eco-friendly manufacturing. Hard turning with the tool having wiper geometry possess these advantages over conventional turning process followed by grinding process. Hard turning is a primary metal cutting process which is extensively used for reduction of the diameter of workpiece to specified dimension and generation of smooth surface finish on the workpiece material having hardness greater than 45 HRC without supplementing it with grinding. Wiper geometry technology which is used for hard turning operation is made by carefully developed series of radii which make up the cutting edge. In conventional insert, nose of the edge has only one radius while in wiper geometry, wiper cutting edge has large main radius complemented by a number of smaller radii. Materials used for hard machining are hardened alloy steel, tool steels, case hardened steels, Inconel, nitride irons, hastelloys, Hadfield steel, hard chrome coated steels and heat treated powder metallurgical parts etc. While the cutting tool material used for hard turning are coated carbide tool, tungsten carbide, ceramics, CBN, PCBN etc. Few researchers have identified that efficient turning of material having high hardness is achieved through proper selection of process parameter to minimise surface roughness and cutting forces and for this optimization of process parameter is required available conventional and non-conventional optimization processes. Process parameter for hard turning are cutting speed, feed rate, depth of cut, cutting angle, hardness of workpiece, diameter of workpiece, nose radius of tool etc. while output parameter are surface roughness, material removal rate, energy consumption etc. While other researchers have used numerical techniques like Finite Element method to perform various analysis like thermal, vibration, buckling, stress and modal analysis related to hard turning. It is felt that a comprehensive review is required to identify the challenges exist in hard turning using wiper geometry tool and measures needed to overcome them. This paper presents a study of such research contributions, mechanics of material removal, finite element analyses, associated challenges and possible remedies related to hard turning with wiper geometry tool so as to propose a guideline for fresh researchers and practising production engineers.

Effect of Cryogenic Machining for Titanium Alloy Based on Indirect, Internal and External Spray System

Due to the excellent properties of Ti-6Al-4V titanium alloy such as lightweight, high wear and corrosion resistance and able to maintain high strength at high elevated temperature, this material has been used mostly in aerospace and biomedical industries. However, titanium alloy being considered as a hard-to-cut material with poor machinability due to its low thermal conductivity which leads to the excessive tool wear during machining and requires high machining cost. To overcome these problems, cryogenic machining has been taken place as a promising method for machinability improvement in terms of tool wear reduction, lower energy consumption and low machining cost. Even though this method has been implemented for titanium alloy machining, it is difficult to handle the excessive extremely low-temperature coolant (up to -150 ℃) that exposed directly to the workpiece. As a result, the workpiece hardness will be increased, hence will increase the required cutting force for the machining process. In concern with the problem, this paper presents a novel cryogenic cooling mechanism (indirect cryogenic cooling) that will be used as one of the cooling and lubrication strategy. The performance of the indirect cryogenic cooling will be compared with flood cooling, Minimum Quantity Lubrication (MQL) and conventional cryogenic cooling method by using the external and internal spray system. Liquid nitrogen (LN2) being selected as the cooling medium in this work since its temperature can reach lower -196 ℃, odorless and more environmentally friendly. A specially designed tooling kit that able to supply the liquid nitrogen to the cutting tool internally is used in this method. The developed indirect cryogenic supply method able to improve the machinability of Ti-6Al-4V. The cutting force is reduced by 54% and the tool life is improved by 90% compared to the conventional flood coolant strategy.

Experimental Study of Electrical Discharge Machining of Inconel X-750 Using Tungsten-Copper Electrode

Nickel-based alloys have wide applications in many industries due to their outstanding properties like high temperature, corrosion resistant and creep rupture. Inconel X-750, a Nickel based super alloy, precipitation hardenable material used especially in aircraft structures, rocket engine thrust chambers, gas turbines, nuclear reactors and pressure vessels due to its excellent properties. However, it is very difficult to machine using traditional methods due to their low thermal conductivity, strong strain hardening, and high strength at elevated temperatures. Therefore, electrical discharge machining (EDM), which is a thermal process irrespective of work piece hardness, is used to machine Nickel-based alloys by electrical erosion. In this process cu-w electrode was used as an electrode because of its excellent thermal properties and high thermal conductivity of copper component and low thermal expansion, high melting point of tungsten gives the better surface integrity on machining .The objective of this investigation is to optimize the EDM process parameters on Inconel X-750 alloy over the performance parameters like material removal rate (MRR), surface roughness (SR) and recast layer thickness (RLT) and to study the influence of operating parameters of tungsten-copper electrode on the machining characteristics .The experiments were performed based on one factor at a time approach. In this report, the considered input parameters like pulse peak current, pulse on time, pulse off time and type of electrode. It has been noticed that most of the authors focused on reducing the surface roughness and increasing the material removal rate using different materials like copper, graphite, brass. However, very few authors have been experimental investigated on Inconel X-750 with W-Cu electrode

Relationship between Cutting Force and the Workpiece Hardness of the File

Relationship between Cutting Force and the Workpiece Hardness of the File