In this paper, extraordinarily-high-speed (EHS) turning of Alloy 718 is investigated using a mixed alumina ceramic (Al2O3/TiC) tool. Although ceramic tools have been applied to high-speed turning of nickel-based alloys, previous studies have been limited to cutting speeds of 500 m/min or less. On the other hand, previous studies have suggested that cutting temperature saturation may occur in an extraordinarily-high-cutting-speed range. Therefore, cutting force, cutting temperature, and tool wear measurements are conducted over a wide cutting speed range from 100 to 1700 m/min to investigate the cutting temperature behavior and the corresponding tool wear characteristics in each speed range. As a result, the occurrence of cutting temperature saturation is confirmed for Alloy 718 in the EHS cutting regime. Furthermore, it is also found that the tool wear progression saturates in the temperature saturation region. Comprehensive analyses of cutting temperature, tool wear, cutting-edge profiles, and SEM/EDS observations clarify the speed-dependent tool wear mechanism. These findings suggest that the EHS turning can significantly improve cutting efficiency without sacrificing tool life.
The cutting temperature is an important aspect of the cutting process, and various methods have been devised to measure it. However, most previous studies have focused on the rake-face temperature since the highest temperature is generally observed near the cutting edge on the rake face. On the other hand, tool life and surface quality are strongly related to flank wear; therefore, the flank-face temperature is also of considerable practical importance. This study proposes a method that combines an electrically insulating layer with the tool–workpiece thermocouple method. By placing the insulating layer on the rake face or flank face, the flank-face or rake-face temperature can be measured directly and independently. The proposed method is first validated in the cutting of brass by comparing the rake-face, flank-face, and dual-face temperatures. The method is then applied to the cutting of medium carbon steel to investigate the evolution of the flank-face temperature during flank-wear progression. The results support the feasibility of directly and independently measuring the apparent average temperatures of the flank and rake faces and demonstrate that the measured flank-face temperature increases with flank wear.
The surface integrity of γ-TiAl alloys is critical for the performance and reliability of aerospace components due to their limited ductility and inherent brittleness. Although wire electrical discharge machining (W-EDM), milling and heat treatments are commonly employed during the manufacture of γ-TiAl parts, their combined influence on surface integrity remains insufficiently understood. This study investigates the effects of finishing operations and post-machining heat treatments on a Ti-48Al-2Cr-2Nb alloy produced by vacuum arc remelting (VAR). Specimens were sectioned by W-EDM and subsequently finished by dry milling. Surface integrity was evaluated through metallographic observations, microhardness measurements, and residual stress analysis, while annealing treatments between 700 and 1100 °C for 2 h were applied to assess the recovery of machining-induced alterations. W-EDM generated a cracked surface layer, revealing a significant limitation of this process for γ-TiAl components. Milling removed the damaged layer and produced a defect-free surface, however, it induced a plastically deformed subsurface region about 50 μm thick, accompanied by increased hardness and residual stresses. Annealing at 700 °C provided only partial recovery, whereas treatments at 900 °C and above promoted complete recrystallization of the affected layer, restoring hardness to values close to those of the bulk material. The results demonstrate that milling followed by annealing at 900 °C for 2 h effectively restores surface integrity without altering the bulk microstructure.
This study evaluates label-free clustering of active acoustic responses acquired under prescribed compressive-load conditions from fully debound and sintered 17-4 PH stainless-steel specimens fabricated by Metal Fused Filament Fabrication. One physical specimen was tested for each of three geometries: dog bone, I-beam, and obround plate. Surface Response to Excitation measurements were acquired using surface-mounted and post-fabrication cavity-mounted piezoelectric transducers. Six force conditions were applied sequentially from 0 to 500 N in 100 N increments, with 50 acoustic measurements collected while each load remained applied. These conditions represented prescribed force levels rather than manufacturing defects or verified damage states. Engineered three-channel spectrograms were evaluated using convolutional-autoencoder latent features followed by principal component analysis (PCA) and a protocol-matched direct-PCA baseline. Clustering was performed separately for 14 geometry–sensor–location combinations using automatically selected cluster counts and a specified count of six. Withheld load labels were introduced only after clustering to calculate the adjusted Rand index, normalized mutual information, and post hoc mapped clustering accuracy. Direct PCA achieved configuration-averaged mapped accuracies of 89.74% with automatic cluster-count selection and 98.52% with six specified clusters, compared with 85.23% and 91.42%, respectively, for the tested autoencoder pipeline. Direct PCA therefore provided stronger aggregate agreement with the prescribed force labels under the evaluated settings, while automatic recovery of six clusters remained configuration-dependent. These findings demonstrate within-specimen separation of the recorded responses. However, repeated acquisitions from one specimen per geometry do not establish specimen-to-specimen reproducibility, and sequential loading cannot fully exclude acquisition-order or loading-history effects. Cross-geometry generalization and practical deployment performance remain unverified.
Low-pressure carburizing (LPC) models can support recipe screening, but numerical agreement must be separated from experimental validation and calibration. A one-dimensional model using concentration-dependent Ågren diffusivity, a prescribed boost carbon flux, zero-flux diffusion windows, a carbide reservoir and a non-isothermal tail is compared with four industrial trials on 16MnCr5 at 940–950 °C. Numerical verification includes an analytical solution, grid refinement and an independent COMSOL implementation. With no parameter fitted to this campaign, depths at 0.36 wt.% C are 894 and 866 µm for two free-surface trials, compared with hardness-based CHD550 values of 1036 and 907 µm measured at HV0.3: point deviations of −13.7% and −4.6%. A joint flux fit gives residuals of −4.9% and +5.2%; two-point leave-one-out transfer gives +10.6% and −9.6%. These are conditional deviations, not uncertainty-inclusive accuracy bounds. An empirical hardness bridge changes the uncalibrated depths by about 11%, and the available hardness traverses do not support statistical confidence intervals. The primary experimental limitation is the absence of measured carbon profiles: comparison is restricted to depth criteria, and predicted surface concentrations remain unverified. Flux and diffusivity sensitivities are nearly collinear for the two schedules. A single bore observation is 36% shallower than a free-surface observation from another trial, with unresolved load, quench and laboratory effects. Nominal gas-supply calculations suggest scope for flow-reduction experiments but disagree with cylinder weighing and do not establish transfer efficiency. The practical application is preliminary recipe screening and selection of informative follow-up measurements within the studied conditions; broader accuracy, concentration-profile validation and geometry corrections require further experiments.
