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Titanium alloys find extensive applications in aviation, maritime, and chemical engineering applications. Nonetheless, these alloys encounter significant challenges during the conventional forging process, which include high deformation resistance, limited processing temperature ranges, and inhomogeneous microstructure. Isothermal forging, as a near-net-shape forming technique, can alleviate the microstructural inhomogeneity caused by deformation dead zones in conventional forging, thus enabling the direct production of complex shapes. This process enhances the overall performance and utilization of materials while reducing manufacturing costs. This paper comprehensively reviews how isothermal near-net-shape forging process parameters influence the intricate microstructure and essential properties of titanium alloys. The unique properties of isothermal forging applied to high-performance titanium alloys are also discussed in depth, and the intricate interplay between process parameters and the microstructure and properties of recoloration is clarified. That is to say, temperature is a vital element influencing the phases and microstructure of titanium alloys during the forming process. Grain size, microstructural homogeneity, and phase transformation are influenced by the strain rate, thereby affecting the plasticity, fracture toughness, and strength of titanium alloys. The extent of deformation significantly governs the grain size, the thickness of secondary α phase, dynamic recrystallization, and primary α phase. Cooling rate affects the grain size and precipitates, contributing to grain refinement. The frequency of isothermal forging affects the grain refinement and microstructural uniformity of titanium alloys. Finally, this paper summarizes the scientific questions that remain unresolved in this field and outlines future research directions to promote the further development of isothermal near-net-shape forging processes and facilitate the broader industrial applications of high-performance titanium alloys and other difficult-to-form alloys.

This paper presents a new selection methodology that for the first time supports the identification of Near Net Shape (NNS) processes. The methodology, known as “Product, Geometry, Manufacturing and Materials Matching” (ProGeMa3), is composed of four steps, which aim to minimize raw material usage and machining by adopting a NNS approach. A key component of the methodology is the Process Selection Matrix (ProSMa) that associates a component’s shape and production volume with its material requirements to reduce the number of candidate NNS processes. A final selection is then made from this shortlist by using fuzzy logic and considering other constraints and functional requirements. The ProGeMa3 selection process is illustrated by its application to an industrial component that resulted in changes to the processes used for its commercial manufacture. The ProGeMa3 and ProSMa presented in this paper aspires to be current and comprehensive for solid metallic components produced by casting, forging and additive technologies. However, ProSMa is also accessible as an open source resource available for other researcher to extend and adapt.

The die undergoing severe loads induces inevitable wear in the pressure forming process, and the wear of die arouses obsessions about the die’s service lifetime. In order to predict the wear and lifetime for a pair of rollers in net-shape blade rolling process, this paper quantified the distributions and evolutions of the local wear over roller cavities based on the local contact load responses and predicted the lifetime which related to wear by a mathematical model. Firstly, the net-shape blade rolling process and the local contact load responses were summarized. Then, an improved wear model was provided based on the Archard formula, and the impact factors of the model were standardized by a regression analysis experiment. The transient wear distributions and evolutions over the roller cavities were enumerated, and the wear distribution for one rolling cycle was calculated based on wear accumulation effect. Finally, a lifetime prediction model was proposed to predict the service lifetime of the rollers according to the wear accumulation effect, and an experimental verification was carried out to validate the model. The results show that the wear model and lifetime prediction model can be used for investigating the wear and lifetime of the roller cavities for the net-shape blade rolling process.

The coupler knuckle of railway wagon is a complex forging component with big section change. In this paper, a near-net-shape forming process for coupler knuckle based on closed-die forging without flash was proposed and the preforming operation was designed and optimized. Firstly, the shape and the dimension of the preforging were preliminarily designed based on the geometric features of forged knuckle and the flow characteristics of metal in the forging process, and then a multi-objective optimization approach based on the filling capacity, deformation homogeneity, and damage degree of forgings was established, and the response surface method combined with the finite element simulation was used to obtain the optimum geometric parameters of preforging. In order to verify the effectiveness of the near-net-shape forming process and the optimized results on preform design, forming experiments and measurements were carried out; the analyzed results show that based on the designed preforging, near-net-shape forming process is capable of producing coupler knuckle of high quality and without forming defect.

The crankshaft is a critical component in large marine ships, often regarded as the “heart” of the vessel due to its role in transmitting power and motion. This article addresses the technological challenges in the forging of marine crank throws, a key segment of the crankshaft. The study employed finite element simulations to evaluate three Near-Net-Shape (NNS) forming methods: One-Step Extrusion (OSE), Upsetting/Backward Extrusion (U/BE), and Grooving–upsetting/Backward Extrusion (G–U/BE). The results show that the G–U/BE method requires the lowest load. The grooving–upsetting step in the G–U/BE process forms a rigid journal end web shape that influences the subsequent backward extrusion, with the relative groove depth (the ratio of groove depth to width) playing a crucial role in the final forging quality. Optimal crank throw formation occurs when the ratio is 1.5; deeper grooves increase the load required, diminishing the effectiveness of the grooving–upsetting step. Scaled-down experiments validate G–U/BE as a practical and feasible method for producing large marine crank throw forgings, ensuring both the desired shape and microstructural properties.

The aim of this research is to develop a geometry-based adaptive toolpath laser powder deposition method for the manufacturing and repair of advanced turbine engine compressor or blisk airfoils. To realize that, the design of experiments (DoE) method was used to study the deposition geometric responses of a single-pass multilayer Inconel 718 laser powder deposition process. In the first step, the processing feasibility domain was quickly explored with a set of screening DoE. The dominating factors, which have significant effects on the deposition bead width and maximum stable layer height, were identified among the various deposition parameters. Based on this result, a more accurate quadratic regression transfer function was developed to predict the deposition bead width as a function of the dominating processing parameters identified in the first step. With the transfer function, deposition toolpath for net shape airfoil fabrication or repair was designed with predetermined bead width, stable layer height, and bead overlap ratios. Adaptive deposition bead widths were obtained by varying the laser power according to the transfer function, so that a constant bead width overlap ratio was maintained. Finally, compressor and blisk airfoils repaired by the geometry-based adaptive toolpath deposition method are demonstrated.

A reliable constitutive model is a prerequisite to simulate a new complex forming technique, which is represented by the near-net shape forging process of aluminum wheels in this study. The aim of the present work was to identify the physical-based constitutive model parameters of Al-Zn-Mg alloy via the inverse analysis method based on experimental data and numerical analysis: the stress–strain curves at different temperatures and strain rates were obtained based on hot compression tests. On the basis of the shape of the compressed specimens and experimental force–displacement data, the friction coefficients and the optimized physical-based constitutive model were determined by using two-times inverse analysis techniques. Results showed that the global average error between the predicted and experimental force–displacement curves was only 3.8%. Then, thermo-mechanical finite element models were built in the Deform-3D software to simulate the two-stage forging processes of the near-net shape forging of aluminum alloy wheels, and the results showed that the predicted load–stroke curves were in good agreement with the experimental ones in all forging stages, which verified the prediction accuracy of the optimized physical-based constitutive model. In addition, the identification of the physical-based constitutive model parameters by the inverse analysis method provides a theoretical basis for formulating and optimizing the near-net shape forging process parameters of aluminum alloy wheels.

This paper reports friction-stir forming (FSF) of gear-racks of JIS A5083 aluminum alloy with semi-closed dies. FSF is a modified friction-stir process suggested by Nishihara in 2002. The process generates frictional heat and internal forces, enabling massive deformation of the material. It has been successfully utilized for mechanical joining and microforming, but seems to offer an opportunity for net-shape forming of bulk products as well. We put a material in a semi-closed gear-rack die and conducted friction stirring on its top surface. The material deformed and filled the cavity of the die due to high pressure and heat caused by friction stirring. This study investigates the forming conditions and the corresponding results, including the material fill ratio in the tooth. We also investigated the difference between this method and open-type FSF that had been conducted with an open-die structure.

In this paper, the use of the finite element method in conjunction with abductive network is presented to predict the maximum forging force and the volume of billet during near net-shape helical bevel gear forging. The maximum forging load and volume of billet are influenced by the process parameters such as modules, number of teeth, and die temperature. A finite element method is used to investigate the forging of helical bevel gear. In order to verify the prediction of FEM simulation for forging load, the experimental data are compared with the results of current simulation. A finite element analysis is also utilized to investigate the process parameters on forging load and volume of billet. Additionally, the abductive network was applied to synthesize the data sets obtained from the numerical simulation. The prediction models are then established for the maximum forging load and volume of billet of near net-shape helical bevel gear forging under a suitable range of process parameters. After the predictions of the maximum forging force and the volume of billet, the optimum of the power of forging machine and the dimensions of billet are determined.

This paper reports observation of material flow in friction-stir forming of aluminum alloy gear racks. Friction-stir forming was newly developed by Nishihara and is dedicated for material forming. In the process, a material plate is placed on the die and friction stirring is conducted on its back surface. The material deforms due to high pressure and heat caused by the friction-stir process and deforms precisely to the shape of the die. The process has mainly been studied for microforming and mechanical jointing; however it was successfully utilized for net-shape forming of A5083 aluminum alloy gear racks. The authors observed the appearance of products, change of mark-off lines on its surface, and deformation of its longitudinal cross section by photo-processing. In addition, we evaluated the distribution of hardness in transverse cross sections of a product tooth. As a result, it was observed that the material did not flow in the transverse direction of the cavity of the gear-rack die, though more material filled at the retreating side than at the advancing side. The material filled the tooth-cavity mostly before passage of the tool probe over the tooth.