Experimental investigations on the wear behaviour of micro-EDM-fabricated textured tools during dry turning of Ti6Al4V

Purpose This paper aims to focus on analysing the wear characteristics of tungsten carbide tools on which various micro patterns are fabricated to study its effect on the machinability of Ti-6Al-4V at dry turning conditions. Design/methodology/approach Micro-patterns such as dimples, linear grooves and a novel combination of dimples and linear grooves were fabricated on rake faces of uncoated tools by micro-EDM process. Impact of these patterns on tool wear and chip morphology characteristics under dry machining conditions were analysed, and their performances were compared with the non-textured tool (NTT). Findings Encouraging results in terms of minimal tool wear and favourable chip morphology characteristics were observed in case of all the textured tools, which demonstrated better tribological characteristics in contrast to NTT. The average flank wear was reduced by 43.5, 32 and 24.7% in dimple textured tool (DTT), linear textured tool (LTT) and hybrid textured tool (HTT), respectively, as compared to NTT. The average chip curl diameters measured for NTT, DTT, LTT, and HTT were observed to be 6.60, 3.51, 4.0 and 4.31 mm, respectively. Originality/value The contribution of this work lies in fabricating innovative patterns using cost-effective micro-EDM process and analysing how the patterns, depending upon their dimensional area and wear debris accumulation characteristics, influence the machinability of Ti-6Al-4V in the absence of any lubrication mediums.

Study on Chip Formation in Grinding of Nickel-Based Polycrystalline Superalloy GH4169

Based on the variation of the actual cutting depth during the grinding process, a 3D finite element (FE) simulation model for grinding nickel-based superalloy GH4169 with single abrasive was initially constructed. Then the morphological evolution of the grinding chips during the grinding process was studied. In addition, the effect of the single abrasive cutting depth and the grinding speed on chip morphology and segmentation frequency was investigated. Finally, experimental results with the same test parameters verify the finite element simulation results. The results showed that in the experimental grinding speed range, the sawtooth lamellar chip with the free surface being serrated and the contact surface being smooth due to the extrusion of the abrasive is easy to produce when grinding nickel-based superalloy GH4169. As the grinding speed increases, the chip morphology changes from a unitary lamellar chip to a continuous serrated chip, developing into a continuous ribbon chip. The chip segmentation frequency is mainly determined by grinding depth and grinding speed. To be specific, the smaller the grinding depth and the greater the grinding speed, the greater the chip formation frequency.

EXPERIMENTAL MILLING STUDIES ON HARDENED STEELS - A REVIEW

Hardened steels have numerous applications in the construction of molds and dies due, in particular, to their outstanding thermo-mechanical characteristics, such as wear resistance and high stiffness, but especially dimensional stability at high temperatures. Machined surfaces are conditioned to have important tribological characteristics. Thus, a high quality of machined surfaces is achieved by milling processes with high cutting speeds. These types of processes even manage to replace grinding or electro-erosion machining processes with a solid electrode. The paper presents a review of experimental studies in recent years from industry and scientific research. Issues are outlined which justify the utility of machining hard metals by machining processes, with a focus on machining by milling processes. Starting from input parameters, such as technological parameters, blank material, cutting tool material and machining environment, their influence is analysed on output parameters, such as chip morphology, cutting tool wear and surface integrity.

Performance Assessment and Chip Morphology Evaluation of Austenitic Stainless Steel under Sustainable Machining Conditions

Sustainable manufacturing has received great attention in the last few decades for obtaining high quality products with minimal costs and minimal negative impacts on environment. Sustainable machining is one of the main sustainable manufacturing branches, which is concerned with improving environmental conditions, reducing power consumption, and minimizing machining costs. In the current study, the performance of three sustainable machining techniques, namely dry, compressed air cooling, and minimum quantity lubrication, is compared with conventional flood machining during the turning of austenitic stainless steel (Nitronic 60). This alloy is widely used in aerospace engine components, medical applications, gas power industries, and nuclear power systems due to its superior mechanical and thermal properties. Machining was performed using SiAlON ceramic tool with four different cutting speeds, feeds and a constant depth of cut. Consequently, various chip characteristics such as chip morphology, chip thickness, saw tooth distance and chip segmentation frequency were analyzed with both optical and scanning electron microscopes. Performance assessment was performed under the investigated cutting conditions. Our results show that the tool life under MQL machining are 138%, 72%, and 11% greater than dry, compressed air, and flooded conditions, respectively. The use of SiAlON ceramic tool results is more economically viable under the MQL environment as the overall machining cost per component is lower ($0.27) as compared to dry ($0.36), compressed air ($0.31), and flooded ($0.29) machining conditions. The minimum quantity lubrication technique outperformed the other investigated techniques in terms of eco-friendly aspects, economic feasibility, and technical viability to improve sustainability.

A modified Zerilli–Armstrong constitutive model for simulating severe plastic deformation of a steel alloy

A modified Zerilli–Armstrong model has been proposed and validated in previous works for simulating distinct deformation mechanisms of continuous-shear and shear-localization during severe plastic deformation of a face centered cubic alloy. In this paper, the validity of the modified Zerilli–Armstrong model has been further tested by using it for modeling the severe plastic deformation of another face centered cubic material, a steel alloy. In particular, the modified Zerilli–Armstrong model is used as a constitutive relation for simulating behavior of AISI 1045 steel alloy while undergoing severe plastic deformation through orthogonal and plane-strain machining. Accordingly, the performance of the constitutive relation in predicting flow stress distribution along the primary shear zone is validated by comparing with forecasts made using the distributed primary zone deformation, the original Zerilli-Armstrong and Johnson-Cook models. Furthermore, finite element simulations of orthogonal cutting of this steel alloy were carried out, and good agreement was observed between the predicted chip morphology and attendant cutting forces with experimental values reported in literature for a range of cutting conditions. The force predictions also fared better compared to those predicted by using the Zerilli-Armstrong and Johnson-Cook models. These validations provide further corroboration of using the modified Zerilli–Armstrong model as a constitutive relation for simulating the behavior of face-centered cubic materials under conditions of high plastic strains and also high strain-rates.

Study on the Formation Mechanism of Surface Adhered Damage in Ball-End Milling Ti6Al4V

Ball-end cutters are widely used for machining the parts of Ti-6Al-4V, which have the problem of poor machined surface quality due to the low cutting speed near the tool tip. In this paper, through the experiments of inclined surface machining in different feed directions, it is found that the surface adhered damages will form on the machined surface under certain tool postures. It is determined that the formation of surface adhered damage is related to the material adhesion near the cutting edge and the cutting-into/out position within the tool per-rotation cycle. In order to analyze the cutting-into/out process more clearly under different tool postures, the projection models of the cutting edge and the cutter workpiece engagement on the contact plane are established; thus, the complex geometry problem of space is transformed into that of plane. Combined with the case of cutting-into/out, chip morphology, and surface morphology, the formation mechanism of surface adhered damage is analyzed. The analysis results show that the adhered damage can increase the height parameters Sku, Sz, Sp, and Sv of surface topographies. Sz, Sp, and Sv of the normal machined surface without damage (Sku ≈ 3) are about 4–6, 2–3, and 2–3 μm, while Sz, Sp, and Sv with adhered damage (Sku > 3) can reach about 8–20, 4–14, and 3–6 μm in down-milling and 10–25, 7–18, and 3–7 μm in up-milling. The feed direction should be selected along the upper left (Q2: β∈[0°, 90°]) or lower left (Q3: β∈[90°, 180°]) to avoid surface adhered damage in the down-milling process. For up-milling, the feed direction should be selected along the upper right (Q1: β∈(−90°, 0°]) or upper left (Q2: β∈[0°, 90°)).

Machinability analysis of dry and liquid nitrogen–based cryogenic cutting of Inconel 718: experimental and FE analysis

Inconel 718 is famous for its applications in the aerospace industry due to its inherent properties of corrosion resistance, wear resistance, high creep strength, and high hot hardness. Despite the favorable properties, it has poor machinability due to low thermal conductivity and high hot hardness. To limit the influence of high cutting temperature in the cutting zone, application of cutting flood is recommended during the cutting operation. Cryogenic cooling is the recommended method when machining Inconel 718. However, there is very limited literature available when it comes to the numerical finite element modeling of the process. This current study is focused on the machinability analysis of Inconel 718 using numerical approach with experimental validations. Dry and cryogenic cooling methods were compared in terms of associated parameters such as chip compression ratio, shear angle, contact length, cutting forces, and energy consumption for the primary and secondary deformation zones. In addition, parameters related to chip morphology were also investigated under both lubrication methods. Chip formation in cryogenic machining was well captured by the finite element assisted model and found in good agreement with the experimental chip morphology. Both experimental and numerical observations revealed comparatively less chip compression ratio in the cryogenic cooling with larger value of shear plane angle. This results in the smaller tool–chip contact length and better comparative lubrication.