International Journal of Material Forming最新文献

The study investigates the effects of process parameters for Electrical Discharge Machining (EDM) on the machining performance of hard materials, such as ceramic matrix composites (CMC). For difficult-to-machine materials (Silicon Nitride-Titanium Nitride), EDM provides benefits including low machining force and affordable equipment. To improve control parameters, like discharge current, pulse-on (Pon) and pulse-off times, and dielectric pressure, experiments were carried out utilizing a complete factorial method and Taguchi L₂₅ Orthogonal Array. Significant results were examined, including geometric tolerances, surface roughness, electrode wear rate (EWR), and material removal rate (MRR). The most important components were found to be current and pulse-on time after correlations between input parameters and output features were established using Response Surface Methodology (RSM). Optimal Pareto solutions were found using Genetic Algorithm-based Particle Swarm Optimization (GAPSO), which was validated by confirmation studies. The findings showed notable gains in machining efficiency, such as shorter machining times, higher rates of MRR (0.0118 g/min), decreased rates of EWR (0.001 g/min), and better geometric tolerances to roughness (3.108 μm). The outcome of a global optimization that factored in all seven replies is also shown According to these results, EDM may be used for intricate ceramic parts with ideal process parameters, advancing contemporary manufacturing sectors.

Industrial sheet metal components often have complex geometries with both concave and convex features. For small batch sizes, such components can be manufactured by incremental sheet forming, using the pressure of an active medium underneath the workpiece to create the convex feature. However, the additional load superimposed by the pressure causes instability and renders the process more prone to failure, in particular to cracking of the workpiece. The reliability of the manufacturing process could be improved if the occurrence of failure were predictable and thus preventable. To achieve this goal, the trend of the forming forces and the change of the workpiece geometry prior to cracking are experimentally analyzed. Subsequently, the dataset obtained from the experiments is used to fit a model based on long short-term memory and on a sliding window approach. This model reliably predicts the probability of failure with an accuracy and recall of 0.97 and 0.89 respectively, demonstrating its potential for online monitoring of the manufacturing process.

Optimisation and machine learning techniques are increasingly used with net-shape composites forming methods like resin transfer moulding (RTM) for process monitoring, control, and defect detection. However, the standard finite element-control volume modelling approach used in these simulations is discontinuous with respect to model parameters and time. We demonstrate that the use of a neural network surrogate, designed with smooth activation layers, can approximate these models, while eliminating any nonsmooth or discontinuous behaviour. To illustrate the benefits of this method, we use Bayesian inference to predict permeability and race tracking strengths from pressure measurements, where the neural network prevents discontinuities from propagating to the posterior, forming smooth posterior distributions that incorporate the model approximation error.

Workability is the term that is commonly used to refer to the ease with which metal can be shaped during bulk forming processes. Experimental tests of compression testing are performed on cylindrical, ring, tapered and flanged samples in different geometries. For each of the different strain paths, axial and circumferential strains are calculated and the workability diagram is extracted. One of the most important theoretical methods to obtain these diagrams is the method of continuous damage mechanics. Thermodynamically consistent, non-associative and fully anisotropic elastoplastic constitutive equations strongly coupled with ductile anisotropic damage developed in previous work are used to study compression tests validation which includes Hill's yield criterion and combined nonlinear isotropic and kinematic hardening. The implemented formulation has been defined in the framework of thermodynamics of irreversible processes and a symmetric second-order tensor is adopted to describe the anisotropic damage state variable.The damage model is implemented with VUMAT coding and ABAQUS/Explicit software, and is used to simulate experiments to determine the workability diagram of C22000 alloy in bulk forming processes. But of course, damage level is being unknown in this diagram. Thus, with this method, extraction of diagram is drawn more comprehensively. The intended failure point is not the only point. Different levels of damage and damage evolution can be used to express different regions of the workability diagram.

As cast whisker-reinforced Al matrix composites are prone to cracking in subsequent forming processes due to numerous micro defects and poor formability, which limits their application. This work investigates the healing effects of current-assisted rolling and upsetting on cracks and micropore defects in a 6061Al composite reinforced with a total of 20 vol% (SiCw and Al₁₈B₄O₃₃w), as well as the impact on the mechanical properties. The thermal compression behavior of the 20 vol% (SiCw + Al₁₈B₄O₃₃w)/6061Al composite was also analyzed systematically to investigate their thermal deformation characteristics. The results show that the combination of current with upsetting and rolling can improve interfacial adhesion between the matrix and the reinforcement phase, reduce internal micropores and microcracks, and increases the density of the composite to 1.009 and 1.053 times that of the die-cast state, respectively. The fracture mode partially transitions to ductile fracture, while the composite’s ultimate tensile strength increases by up to 101.63%. The formation of a high-temperature, high-pressure coupled field leads to crack closure is the main reason for defect healing in current-assisted forming processes. This work provides insights into solving the problem of poor formability of as cast whisker-reinforced Al matrix composites.

Advanced high-strength steels, particularly dual-phase (DP) steels like DP1000, are widely used in the automotive industry due to their exceptional strength and ductility. However, DP steels are sensitive to edge cracking caused by damage and edge surface roughness from conventional cutting processes such as punching. Laser-polishing has emerged as a technique to enhance edge quality by melting and reshaping the material, potentially improving formability. This study aims to investigate the enhanced formability of DP1000 steel achieved through laser-polishing using a multi-scale simulation approach. Hole expansion tests were conducted on DP1000 steel samples with varying edge profiles: punched and laser-polished edges with different geometries. Surface roughness profiles were characterized using white-light confocal microscopy. The modified coupled Bai-Wierzbicki damage model is used in the numerical calculations. Considering the effect of surface roughness, a surface factor is applied in the proposed damage and fracture locus to characterize the material behavior more accurately. Multi-scale FE simulations combined macroscopic modeling of the hole expansion test and microscopic modeling that incorporated actual surface roughness profiles. The numerically predicted force–displacement curves and hole expansion ratios for punched and laser-polished specimens align well with the experimental results. The inclusion of the surface factor in the MBW model effectively captured the influence of surface roughness and microstructural transformations on the material's formability.

Biomedical titanium alloys provide a unique mix of favorable biomechanical and biocorrosion characteristics and are lightweight, non-toxic, and highly biocompatible. These qualities make them highly desirable for the fabrication of medical implants. Hot working methods are crucial in producing titanium components as they break down the lamellar microstructure into a finer structure. This phase is essential in shaping the final microstructure and determining the qualities of the components. This review delved into the hot deformability, phase and microstructural evolution, and related constitutive equations used in biomedical titanium flow stress modelling. It describes the counteractive effect of the dynamic recrystallisation (DRX) and dynamic recovery (DRV) deformation mechanisms on the working hardening behaviour of the biomedical titanium alloys after hot deformation processing. It also discusses the effect of forming necklace structures and lamellar kinking structures. Notably, in biomedical titanium alloys, the hot deformation behaviour and dynamic softening effect are significantly influenced by the alloy composition and microstructural characteristics like dislocation movement and grain boundary diffusion. The use of processing maps to identify the instability regime—which includes cracks, flaws and flow instabilities that may arise as the biomedical titanium alloys are undergoing hot processing and to ascertain the best processing conditions is covered in the article. Finally, the article's conclusion includes suggestions for possible future research directions.

Forming small to medium composite parts with complex geometries presents significant challenges to engineers, primarily due to material-induced, in-process defects such as fibre bridging and wrinkling, leading to poor mould conformity. These issues are characteristic of continuous fibre preforms and the inextensibility of the fibres. HiPerDiF (High Performance Discontinuous Fibre) technology is a novel manufacturing technique to produce high-performance, aligned discontinuous fibre pre-preg materials. This study investigates the forming characteristics of prepreg manufactured using the HiPerDiF method, highlighting its viability for complex part manufacture where mould conformity is critical. Additionally, a previously developed finite element (FE) model, able to predict the behaviour discontinuous fibre preforms during double diaphragm forming (DDF), was used to obtain insights into the experimentally observed material deformation. The results demonstrated the advantage of the enhanced formability of the HiPerDiF preform, owing to its stretchability in the double-diaphragm vacuum forming process. The FE simulations were shown to be a powerful tool to gain understanding of preforms deformation and thickness variation which are otherwise difficult to measure experimentally.

Graphical abstract

In this paper, a new method of the cogging process of a forging (type: shaft) consisting in the application of the multi-stage process composed of a preparatory shaping on three different kinds of convex anvils, and also in a primary forging on the flat anvils and the asymmetrical V-shaped ones, is presented. The new, implemented method of forging was subjected to tests in the aspect of the formation of conditions favourable for the location of the maximum values of effective strain in the particular zones of the forging being deformed whereas simultaneously marked by the absence of tensile stresses. That renders it possible to develop a scientific foundation for the development of the rational technology of the cogging process. The effective geometrical parameters of new convex anvils were determined, and the efficiency of different applied technological parameter was analysed, in the aspect of the intensity of the re-forging of the particular zones of an ingot. The investigations were complemented by prognosing the formation of ductile fractures in the course of forging with the application of the Normalized Cockcroft and Latham criterion. The analysis of the spatial strain state and stress was conducted with the application of the finite element method and of the DEFORM-3D software. The comparison between theoretical outcomes, and the outcomes of experiments, within the scope of the investigation indicates a good level of their commensurateness.