Innovative Approaches in Metal Forming and Joining Technologies

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Institute of Science and Innovation in Mechanical and Industrial Engineering (INEGI), 4200-465 Porto, Portugal
Interests: manufacturing; metal forming; joining by plastic deformation
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Special Issue Information

Dear Colleagues,

Metal forming and joining technologies are at the forefront of modern manufacturing, enabling the production of high-performance components for industries such as automotive, aerospace, and energy. With the increasing demand for lightweight, durable, and sustainable structures, innovative approaches are essential to overcoming the challenges associated with processing advanced metals and manufacturing multi-material components.

This Special Issue aims to showcase cutting-edge research on metal forming and joining processes, addressing key challenges such as material formability and joinability, process efficiency, defect mitigation, and performance optimization. We welcome original contributions on experimental and numerical advancements, novel forming and joining techniques, hybrid processes, and the integration of digital and AI-driven approaches. By bringing together insights from academia and industry, this Special Issue seeks to advance our understanding and the application of next-generation manufacturing technologies.

We encourage the submission of innovative approaches in the following research areas:

  • Material characterization;
  • Constitutive modeling;
  • Metal forming;
  • Joining;
  • Hybrid joining;
  • Joint analysis and performance evaluation;
  • Process optimization;
  • Numerical modeling;
  • Tool design;
  • Artificial intelligence for forming and joining;
  • Sustainability and recyclability in forming and joining.

Dr. Mohammad Mehdi Kasaei
Guest Editor

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Keywords

  • material characterization
  • metal forming
  • joining
  • hybrid joining
  • joint design
  • optimization
  • machine learning
  • sustainability

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Published Papers (10 papers)

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Research

16 pages, 6279 KB  
Article
Joinability and Performance of Double-Flush Riveted and Resistance-Welded Lap Joints in High-Strength Steel Sheets
by Rui F. V. Sampaio, João P. M. Pragana, Ivo M. F. Bragança, Carlos M. A. Silva and Paulo A. F. Martins
J. Manuf. Mater. Process. 2026, 10(3), 91; https://doi.org/10.3390/jmmp10030091 - 4 Mar 2026
Viewed by 522
Abstract
The applicability of two different joining processes for producing lap joints from high-strength steel sheets is investigated, reflecting their increasing use in advanced lightweight structures with demanding performance requirements. The work is primarily focused on the joining-by-forming process known as double-flush riveting, evaluated [...] Read more.
The applicability of two different joining processes for producing lap joints from high-strength steel sheets is investigated, reflecting their increasing use in advanced lightweight structures with demanding performance requirements. The work is primarily focused on the joining-by-forming process known as double-flush riveting, evaluated in two variants: one utilizing forged holes and the other employing machined holes. The performance of these two variants is compared with conventional fusion-based resistance spot welding using lap joints fabricated from 2 mm high-strength low-alloy S500MC steel sheets under varying geometric and process conditions, with support from finite element modelling. Results indicate that both double-flush riveting variants produce similar joint cross-sectional geometries, but the machined hole variant simplifies sheet preparation and eliminates the need for a progressive tooling system. Tensile lap-shear and peel test results reveal that double-flush riveted joints with forged holes exhibit superior strength, attributed to strain hardening in the forged regions. Furthermore, for nuggets and rivets of equivalent size, both double-flush riveting variants surpass resistance spot welding in terms of the mechanical strength of the final joints. These results suggest that double-flush riveting represents a promising alternative for assembling high-strength steel sheets in lightweight structural applications. Full article
(This article belongs to the Special Issue Innovative Approaches in Metal Forming and Joining Technologies)
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16 pages, 4957 KB  
Article
A Comparative Analysis of the Weld Pools Created with DC Single-, DC Double-, and PC Double-Electrode Configurations in Autogenous GTAW
by Shahid Parvez
J. Manuf. Mater. Process. 2026, 10(1), 32; https://doi.org/10.3390/jmmp10010032 - 13 Jan 2026
Viewed by 863
Abstract
Three different Gas Tungsten Arc Welding methods—DC single electrode, DC double electrode, and PC double electrode—were analyzed using SS304 steel as the base material. Numerical models were developed to simulate the arc plasmas and calculate heat flux, current density, and wall shear stress [...] Read more.
Three different Gas Tungsten Arc Welding methods—DC single electrode, DC double electrode, and PC double electrode—were analyzed using SS304 steel as the base material. Numerical models were developed to simulate the arc plasmas and calculate heat flux, current density, and wall shear stress on the surface of the workpiece. These data were used as input to simulate the weld pools across all three configurations. Experimental validation showed a good agreement with the numerical results. In the double-electrode setup, electromagnetic interaction caused the arcs to deflect, resulting in an 8% reduction in the maximum heat flux and a 4% decrease in the maximum current density. Marangoni stress had a notable effect on the weld pool shape, creating a -shaped pool with the stationary single-electrode setup, whereas the double-electrode setup produced a -shaped pool after 2 s. In the moving weld pool configurations, the sizes of the pools were maximum at the trailing electrodes. The pool was 1.7 mm deep and 5.6 mm wide in DC double- and 1.4 mm deep and 5.4 mm wide in PC double-electrode configurations. The pool depth and width were only 1.0 mm and 4.2 mm when a DC single-electrode setup was used. Comparing the three methods, the DC double-electrode setup produced the largest pool size. The findings of this research offer guidance for enhancing different arc settings and electrode arrangements to attain the intended welding quality and performance. Full article
(This article belongs to the Special Issue Innovative Approaches in Metal Forming and Joining Technologies)
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16 pages, 5764 KB  
Article
Effect of Bonding Pressure and Joint Thickness on the Microstructure and Mechanical Reliability of Sintered Nano-Silver Joints
by Phuoc-Thanh Tran, Quang-Bang Tao, Lahouari Benabou and Ngoc-Anh Nguyen-Thi
J. Manuf. Mater. Process. 2026, 10(1), 22; https://doi.org/10.3390/jmmp10010022 - 8 Jan 2026
Cited by 1 | Viewed by 1683
Abstract
Sintered nano-silver is widely investigated as a die-attach material for next-generation power electronic modules due to its high thermal conductivity, favorable electrical performance, and stability at elevated temperatures. However, how bonding pressure and joint thickness jointly affect densification, interfacial diffusion, and mechanical reliability [...] Read more.
Sintered nano-silver is widely investigated as a die-attach material for next-generation power electronic modules due to its high thermal conductivity, favorable electrical performance, and stability at elevated temperatures. However, how bonding pressure and joint thickness jointly affect densification, interfacial diffusion, and mechanical reliability has not been systematically clarified, especially under the low-pressure conditions required for large-area SiC and GaN devices. In this work, nano-silver lap-shear joints with three bond-line thicknesses (50, 70, and 100 μm) were fabricated under two applied pressures (1.0 and 1.5 MPa) using a controlled sintering fixture. Shear testing and cross-sectional SEM were employed to evaluate the relationships between microstructural evolution and joint integrity. When the bonding pressure was increased from 1.0 to 1.5 MPa, more effective particle rearrangement and reduced pore connectivity were observed, together with improved metallurgical bonding at the Ag–Au interface, leading to a strength increase from 15.3 to 28.2 MPa. Although thicker joints exhibited slightly higher bulk relative density due to greater heat retention and accelerated local sintering, this densification advantage did not lead to improved mechanical performance. Instead, the lower strength of thicker joints is attributed to a narrower Ag–Au interdiffusion region, which limited the formation of continuous load-bearing paths at the interface. Fractographic analyses confirmed that failure occurred predominantly by interfacial delamination rather than cohesive fracture, indicating that the reliability of the joints under low-pressure sintering is governed by the quality of interfacial bonding rather than by overall densification. The experimental results show that, under low-pressure sintering conditions (1.0–1.5 MPa), variations in bonding pressure and bond-line thickness lead to distinct effects on joint performance, with the extent of Ag–Au interfacial interaction playing a key role in determining the mechanical robustness of the joints. Full article
(This article belongs to the Special Issue Innovative Approaches in Metal Forming and Joining Technologies)
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22 pages, 3276 KB  
Article
Deep Neural Network-Based Inverse Identification of the Mechanical Behavior of Anisotropic Tubes
by Zied Ktari, Pedro Prates and Ali Khalfallah
J. Manuf. Mater. Process. 2025, 9(12), 410; https://doi.org/10.3390/jmmp9120410 - 14 Dec 2025
Viewed by 839
Abstract
Tube hydroforming is a versatile forming process widely used in lightweight structural applications, where accurate characterization of the hoop mechanical behavior is crucial for reliable design and simulation. The ring hoop tensile test (RHTT) provides valuable experimental data for evaluating the elastoplastic response [...] Read more.
Tube hydroforming is a versatile forming process widely used in lightweight structural applications, where accurate characterization of the hoop mechanical behavior is crucial for reliable design and simulation. The ring hoop tensile test (RHTT) provides valuable experimental data for evaluating the elastoplastic response of anisotropic tubes in the hoop direction, but frictional effects often distort the measured force–displacement response. This study proposes a deep learning-based inverse identification framework to accurately recover the true hoop stress–strain behavior from RHTT data. Convolutional and recurrent neural network architectures, including CNN, long short term memory (LSTM), gated recurrent unit (GRU), bidirectional GRU (BiGRU), bidirectional LSTM (BiLSTM) and ConvLSTM, were trained using numerically generated datasets from finite element simulations. Data augmentation and hyperparameter tuning were applied to generalization. The hybrid ConvLSTM model achieved superior performance, with a minimum mean absolute error (MAE) of 0.08 and a coefficient of determination (R2) value of approximately 0.97, providing a close match to the Hill48 yield criterion. The proposed approach demonstrates the potential of deep neural networks as an efficient and accurate alternative to traditional inverse methods for characterizing anisotropic tubular materials. Full article
(This article belongs to the Special Issue Innovative Approaches in Metal Forming and Joining Technologies)
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26 pages, 9708 KB  
Article
Heat Treatment and Fracture Behavior of Aluminum/Steel FSW Joints: A Comprehensive Analysis of a Curved Interface
by Tiago Oliveira Gonçalves Teixeira, Reza Beygi, Masih Bolhasani Hesari, Ricardo João Camilo Carbas, Eduardo Andre Sousa Marques, Mohammad Mehdi Kasaei and Lucas Filipe Martins da Silva
J. Manuf. Mater. Process. 2025, 9(11), 381; https://doi.org/10.3390/jmmp9110381 - 20 Nov 2025
Viewed by 1289
Abstract
Joining dissimilar metals, such as aluminum and steel, presents an attractive option for creating lightweight yet durable structures. However, challenges arise from the formation of brittle intermetallic compounds (IMCs) at the interface of dissimilar joints, which significantly impact joint strength under load and [...] Read more.
Joining dissimilar metals, such as aluminum and steel, presents an attractive option for creating lightweight yet durable structures. However, challenges arise from the formation of brittle intermetallic compounds (IMCs) at the interface of dissimilar joints, which significantly impact joint strength under load and often lead to brittle failure. This research elaborates on how an S-shaped Al/Steel interface made by a modified friction stir welding (FSW) process mitigates the detrimental effect of IMC thickening on joint strength. This study aims to explore the effects of various post-weld heat treatments on steel and aluminum joints produced through FSW (100–400 °C for 30–90 min). Al/steel FSW joints were characterized by SEM/EDS for interface microstructure and composition, microhardness mapping, tensile testing, and fractography. Any post-weld heat treatment above the temperature of 100 °C caused a drop in joint strength from 2400 N to 1800 N due to the elimination of protrusions in the IMC layer. Further post-weld heat treatment had a negligible effect on the joint strength due to an S-shaped interface. A finite element simulation using a cohesive model for the joint interface is used to study the fracture mechanism of the joint. Both experimental observations and simulation results suggest that the portion of the S-shaped interface perpendicular to the loading direction acts as an initiation site of fracture and fails in a brittle manner. The top and bottom of the interface, which are inclined to the loading direction, fail in a ductile manner with noticeable plastic deformation in the steel adjacent to the interface. The proposed method for FSW of aluminum to steel significantly improves joint durability at elevated temperatures, particularly up to 400 °C. Full article
(This article belongs to the Special Issue Innovative Approaches in Metal Forming and Joining Technologies)
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22 pages, 9513 KB  
Article
Hindering Effect of Solid-Solutioning on Intermetallic Growth in Aluminum–Matrix Composite Reinforced with Mechanically Alloyed Ni-Cu Particles
by Masih Bolhasani Hesari, Reza Beygi, Ali Bayrami, Mohammad Mehdi Kasaei, Majid Zarezade Mehrizi, Eduardo A. S. Marques and Lucas F. M. da Silva
J. Manuf. Mater. Process. 2025, 9(11), 364; https://doi.org/10.3390/jmmp9110364 - 4 Nov 2025
Viewed by 1226
Abstract
In the present study, aluminum matrix composites (AMCs) were fabricated by friction stir processing (FSP) using Ni-Cu particles. Ni-Cu particles were added to the Al matrix in two ways. First, without any treatment and in the form of a mixture of as-received powders. [...] Read more.
In the present study, aluminum matrix composites (AMCs) were fabricated by friction stir processing (FSP) using Ni-Cu particles. Ni-Cu particles were added to the Al matrix in two ways. First, without any treatment and in the form of a mixture of as-received powders. Second, treated through mechanical alloying to form Monel solid-solution particles. The particles were added to a groove to be processed by the FSP tool to produce a local AMC. To investigate the kinetics of intermetallic compounds (IMCs) growth in reinforcement particles, the produced AMCs were annealed at 500 °C for 2 h. To characterize the reinforcing particles, several analyses were performed on the samples. Field-emission scanning electron microscopy (FE-SEM) was used to study the size, morphology, and IMC thickness. TEM was performed to characterize the IMCs through high-resolution chemical analyses. Tensile testing was used to understand the mechanical properties and fracture behavior of AMCs. Tensile testing revealed a noticeable improvement in strength for the as-mixed sample, with a UTS of 90.3 MPa, approximately 22% higher than that of the base aluminum. In contrast, the mechanical alloying sample with annealing heat treatment exhibited a severe drop in ductility, with elongation decreasing from 17.98% in the as-mixed sample to 1.52%. The results showed that heat treatment thickened the IMC layer around the reinforcing particles formed during the FSP process with as-mixed particles. In the AMC reinforced with mechanically alloyed Ni-Cu powders, IMC formation during FSP was significantly suppressed compared to that of as-mixed particles, despite the finer size resulting from milling. Additionally, the heat treatment resulted in only a slight increase in IMC thickness. The IMC layer thickness after heat treatment in both the mechanically alloyed sample and the as-mixed sample was approximately 2 µm and 20–40 µm, respectively. The reason behind this difference and its effect on the fracture behavior of the composite were elaborated in this study, giving insights into metal-matrix production with controlled reaction. Full article
(This article belongs to the Special Issue Innovative Approaches in Metal Forming and Joining Technologies)
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11 pages, 10135 KB  
Article
Optimization of Direct Bonding Process for Lotus-Type Porous Copper to Alumina Substrates
by Sang-Gyu Choi, Sangwook Kim, Jinkwan Lee, Keun-Soo Kim and Soongkeun Hyun
J. Manuf. Mater. Process. 2025, 9(11), 352; https://doi.org/10.3390/jmmp9110352 - 27 Oct 2025
Cited by 1 | Viewed by 1014
Abstract
The effects of processing conditions and holding time on the direct bonding (DBC) of lotus-type porous copper to alumina substrates were systematically investigated. The evolution of copper morphology and the resulting shear strength were evaluated under varying pressures (0.3–0.6 Torr) and bonding durations [...] Read more.
The effects of processing conditions and holding time on the direct bonding (DBC) of lotus-type porous copper to alumina substrates were systematically investigated. The evolution of copper morphology and the resulting shear strength were evaluated under varying pressures (0.3–0.6 Torr) and bonding durations (5–160 min) at a fixed bonding temperature. It was found that pressure within the tested range exerted a negligible influence on joint quality, as direct bonding occurred consistently. In contrast, holding time was found to be a critical factor: a duration of 10 min yielded optimal bonding with high shear strength while preserving the porous structure, whereas shorter times led to incomplete bonding, and longer times caused structural collapse due to liquid-phase flow. The oxidation behavior, governed by parabolic growth kinetics, was identified as the primary mechanism controlling morphological evolution. These findings provide practical guidance for optimizing DBC bonding of porous copper in power semiconductor applications, balancing joint strength and structural integrity. Full article
(This article belongs to the Special Issue Innovative Approaches in Metal Forming and Joining Technologies)
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17 pages, 9040 KB  
Article
Adaptive Torque Control for Process Optimization in Friction Stir Welding of Aluminum 6061-T6 Using a Horizontal 5-Axis CNC Machine
by Austin Clark and Ihab Ragai
J. Manuf. Mater. Process. 2025, 9(7), 232; https://doi.org/10.3390/jmmp9070232 - 7 Jul 2025
Cited by 2 | Viewed by 2299
Abstract
The research presented herein investigates the impact of axial force and feed rate in the Friction Stir Welding (FSW) of aluminum alloy 6061-T6 in a GROB G552 horizontal 5-axis CNC machine with adaptive torque control enabled. The purpose of this study is to [...] Read more.
The research presented herein investigates the impact of axial force and feed rate in the Friction Stir Welding (FSW) of aluminum alloy 6061-T6 in a GROB G552 horizontal 5-axis CNC machine with adaptive torque control enabled. The purpose of this study is to further advance the performance and characteristics of FSW aluminum alloys in 5-axis CNCs, particularly in conjunction with adaptive torque control. The Taguchi and ANOVA methods were utilized to define parameter tables and analyze the resulting data. Optical microscopy and tensile tests were performed on the welded samples to evaluate weld quality. The results from this study provide clear evidence that axial force has a significant effect on tensile strength in FSW AA6061-T6. The maximum UTS found in this study, welded with an axial force of 9.4 kN, retained 69% tensile strength of the base material. Conversely, a decrease in strength and an increase in void formation was found at higher feed rates with this force. Ideal welds, with minimal defects across all feed rates, were performed with an axial force of 8.3 kN. A feed rate of 300 mm/min at this force resulted in a 67% base metal strength. These findings contribute to improving joint strength and application efficiency in FSW AA6061-T6 performed in a horizontal 5-axis CNC machine where adaptive torque control is enabled. Full article
(This article belongs to the Special Issue Innovative Approaches in Metal Forming and Joining Technologies)
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25 pages, 6526 KB  
Article
Engineering Perfection in GTAW Welding: Taguchi-Optimized Root Height Reduction for SS316L Pipe Joints
by Mohammad Sohel, Vishal S. Sharma and Aravinthan Arumugam
J. Manuf. Mater. Process. 2025, 9(6), 188; https://doi.org/10.3390/jmmp9060188 - 6 Jun 2025
Viewed by 3709
Abstract
This study presents a systematic optimization of GTAW welding parameters to achieve a pipe-to-pipe butt weld with a root height consistently below 2 mm when joining stainless-steel 316L material, employing the Taguchi design of experiments. To the authors’ knowledge, no similar studies have [...] Read more.
This study presents a systematic optimization of GTAW welding parameters to achieve a pipe-to-pipe butt weld with a root height consistently below 2 mm when joining stainless-steel 316L material, employing the Taguchi design of experiments. To the authors’ knowledge, no similar studies have been conducted to explore the optimization of welding parameters specifically aimed at minimizing weld root height under 2 mm in stainless-steel EO pipeline welding applications. This gap in the existing literature highlights the innovative aspect of the current study, which seeks to address these challenges and improve welding precision and joint reliability. Root height, also referred to as weld root reinforcement, is defined as the excess weld metal protruding beyond the inner surface root side of a butt-welded joint. The input parameters considered are the welding current, voltage, speed, and root gap configurations of 1, 1.5, and 2 mm. Welding was performed according to the Taguchi L-09 experimental design. Nine weld samples were evaluated using liquid penetrant testing to detect surface-breaking defects, such as porosity, laps, and cracks; X-ray radiography to identify internal defects; and profile radiography to assess erosion, corrosion, and root height. Among the nine welded plate samples, the optimal root height (less than 2 mm) was selected and further validated through the welding of a one-pipe sample. An additional macro examination was conducted to confirm the root height and assess the overall root weld integrity and quality. Full article
(This article belongs to the Special Issue Innovative Approaches in Metal Forming and Joining Technologies)
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12 pages, 7004 KB  
Article
Bonding Characteristics in Air of a Decomposable Composite Sheet Containing Sn-3.0Ag-0.5Cu Particles for Formation of a Robust Metallic Solder Joint in Die Attachment
by Hye-Min Lee and Jong-Hyun Lee
J. Manuf. Mater. Process. 2025, 9(5), 161; https://doi.org/10.3390/jmmp9050161 - 15 May 2025
Viewed by 1164
Abstract
To address solder paste drawbacks, such as die contamination and flux residue, a polymer-based sheet containing Sn-3.0 (wt%) Ag-0.5Cu solder particles as fillers was fabricated, and its bonding characteristics were analyzed. The reductant in the manufactured sheet evaporated while removing the oxide layers [...] Read more.
To address solder paste drawbacks, such as die contamination and flux residue, a polymer-based sheet containing Sn-3.0 (wt%) Ag-0.5Cu solder particles as fillers was fabricated, and its bonding characteristics were analyzed. The reductant in the manufactured sheet evaporated while removing the oxide layers on the solder and copper finish surfaces during heating. Subsequently, the resin component (polymethyl methacrylate) began to decompose thermally and gradually dissipated. Ultimately, the resulting joint formed a solder interconnection with a small amount of residual resin. This joint is expected to exhibit superior thermal conductivity compared with composite joints with a polymer matrix structure. Die-attach tests were conducted in air using the fabricated sheet between Cu finishes. Results showed that joints formed at 300 °C for 30 s and 350 °C for 10 s provided excellent shear strength values of 48.0 and 44.3 MPa, respectively, along with appropriately developed intermetallic compound (IMC) layers at the bonding interface. In contrast, bonding at 350 °C for 60 s resulted in excessive growth of IMC layers at the interface. When comparing size effects of solder particles, type 6 particles exhibited superior shear strength along with a relatively thinner total IMC layer thickness compared to when type 7 particles were used. Full article
(This article belongs to the Special Issue Innovative Approaches in Metal Forming and Joining Technologies)
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