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.

A Finite Element Study of Large Strain Extrusion Machining Using Modified Zerilli–Armstrong Constitutive Relation

The objective of this work is to study the performance of modified Zerilli–Armstrong constitutive relation proposed in our previous study for the finite element modeling of a severe plastic deformation technique called large strain extrusion machining. The modified Zerilli–Armstrong constitutive relation is implemented in a finite element model of large strain extrusion machining of Inconel 718 to analyze the influence of process parameters, i.e., the chip compression ratio and tool–chip friction, on deformation, effective strain distribution, and hydrostatic pressure distribution along the extruded chip. The predicted strain values for different chip compression ratios were validated by comparison with those obtained through an analytical model. The finite element predictions also served as a guideline in designing the large strain extrusion-machining setup on which experiments were conducted to generate Inconel 718 foils with superior mechanical properties. The predicted limits of chip compression ratio were in close agreement with experimentally realizable values. Furthermore, the predicted strain distribution through the thickness of the chip was validated with the results of hardness measurement tests. Microstructural characterization of the Inconel 718 foils was carried out by using both optical and transmission-electron microscopic studies in order to reveal the presence of fine-grain structures. The validations showed the effectiveness of the modified Zerilli–Armstrong constitutive relation in modeling large strain extrusion machining—a variant of the conventional machining process.

Machinability Assessment in High Speed Turning of High Strength Temperature Resistant Superalloys

The paper discusses the effect of cutting parameters and cutting tool material on chip compression ratio, cutting forces and surface roughness in turning of high strength temperature resistant superalloys (HSTR). The experiments were performed in dry cutting environment on precision CNC lathe with fixed depth of cut of 0.5[Formula: see text]mm. Analytical model is developed to determine chip segmentation frequency, shear angle and shear strain and it is correlated with the machining parameters. The machinability of the selected superalloys is assessed in terms of cutting force, chip compression ratio and surface roughness. It is found from the experimental analysis cutting force magnitude is less at higher cutting speed for all the superalloys. Chip compression ratio is found maximum in case of Inconel 718 due to precipitation hardening of alloy and followed by Inconel 600 and Inconel 800. The chip segmentation frequency is high at lower cutting speed for Inconel 600 due significant strain hardening. Serrated chips are produced during machining of three selected superalloys and it is found that serrated tooth spacing decreases with cutting speed. Shear plane angle increases on cutting speed increases which effect tool workpiece contact length during machining resulted thin, short and snarled chips was produced. From analytical modeling it shows that shear strain decreases with cutting speed which indicate that at higher cutting speed material deformed elastically than plastically. The effect of cutting tool material is observed on the surface roughness. The better surface finish is obtained with coated carbide inserts as compared to ceramic inserts for all the selected superalloys. However, Inconel 800 shows higher surface roughness due to combination of (Ni–Cr–Fe) alloying element which is responsible for carburization of surface layer during machining.

On the analysis of chip shaping after finishing turning of Ti6Al4V titanium alloy under dry, wet and MQL conditions

The shape and type of chip give general information about the cutting process. This paper presents the results of testing the shape and type of chips of Ti6Al4V titanium alloy after it finishes turning. The process was carried out under dry, wet and MQL (Minimum Quantity Lubrication) conditions at variable cutting speeds and feed rates and a constant depth of cutting. For planning the tests, the PSI (Parameter Space Investigation) method was used, which allows the experiment to be carried out while minimizing the number of experience points. It was found that the cutting speed and feed affect the type and shape of the chip, and clear differences were observed between dry and wet cooling conditions, and MQL conditions. During turning, the intensity of the cutting speed and feed influence on the chip compression ratio was changed. It was similar for dry and wet cooling conditions but smaller for MQL conditions. The purpose of this research is to analyze the chip shaping when Ti6Al4V titanium alloy finishes turning under dry, wet and MQL cooling conditions.

Effect of Cutting Speed on Chipping and Wear of the SiAlON Ceramic Tool in Dry Finish Turning of the Precipitation Hardenable IN100 Aerospace Superalloy

Inconel 100 (IN100) aerospace superalloy is used in manufacturing aero-engine components that operate at intermediate temperatures. It is considered to be a hard-to-cut material. Chipping of the tool edge is one of the major failure mechanisms of ceramic tools in finish cutting of superalloys, which causes a sudden breakage of the cutting edge during machining. Cutting temperature significantly depends on cutting speed. Varying the cutting speed will affect the frictional action during the machining operations. However, proper selection of the cutting variables, especially the cutting speed, can prevent chipping occurrence. In this work, the influence of controlling the cutting speed on the chipping formation in dry finish turning of IN100 aerospace superalloy using SiAlON ceramic tool has been investigated. Scanning electron microscope (SEM)/energy dispersing spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), and three-dimensional wear measurements were used to make the investigations of the worn tool edges. It was found that variations of the cutting speeds in a certain range resulted in the generation of different lubricious and protective tribo-films. The presence of these tribo-films at the cutting region proved essential to prevent chipping of the cutting tool edge and to improve its wear resistance during finish turning of age-hardened IN 100 using SiAlON ceramic tools. Chip compression ratio and calculated values of the coefficient of friction at the tool–chip interface confirmed these results.

Chip formation and similarity in the plano-grinding of explosive surrogates

The processing of polymer-bonded explosives is not widely reported in the literature, especially the machining of explosive surrogates in the combined planing and grinding operation known as plano-grinding. The process of machining long pieces of an inert substitute using a wax binder to hold sugar particles together and then subjecting the surrogate material to a linear cutting motion to generate chip fragments is described. The aim and purpose of this work is to analyze the machining of explosive surrogates in terms of chip formation models (oscillating and stress ratio models) and similarity models (chip compression ratio, Poletica, and Peclet numbers). The analysis of machining is compared to standard engineering materials so that the explosives engineer can benchmark machining performance of explosive surrogates to standard materials. The article concludes with statements on how to improve the understanding of machining of explosive surrogates with specifically engineered abrasive cutting tools.

Experimental Assessment of Laser Textured Cutting Tools in Dry Cutting of Aluminum Alloys

To improve the friction conditions and reduce adhesion at the tool's rake face in dry cutting of aluminum alloys, three types of laser surface textures were generated on the rake face of cemented carbide tools. Orthogonal dry cutting tests on 6061 aluminum alloy tubes were carried out with the textured and conventional tools (CT). The effect of the texture geometry on the cutting performance was assessed in terms of cutting forces, friction coefficient, chip compression ratio, shear angle, tool adhesions, chip morphology, and machined surface quality. The results show that the textured tools can improve the cutting performance at low cutting speeds, and that the tool with rectangular type of textures is the most effective.

Analysis of Large-Strain Extrusion Machining with Different Chip Compression Ratios

Large-Strain Extrusion Machining (LSEM) is a novel-introduced process for deforming materials to very high plastic strains to produce ultra-fine nanostructured materials. Before the technique can be exploited, it is important to understand the deformation behavior of the workpiece and its relationship to the machining parameters and friction conditions. This paper reports finite-element method (FEM) analysis of the LSEM process to understand the evolution of temperature field, effective strain, and strain rate under different chip compression ratios. The cutting and thrust forces are also analyzed with respect to time. The results show that LSEM can produce very high strains by changing in the value of chip compression ratio, thereby enabling the production of nanostructured materials. The shape of the chip produced by LSEM can also be geometrically well constrained.