Near-net Forming Research Articles

Research Status and Development Trend of Wire Arc Additive Manufacturing Technology for Aluminum Alloys

It is difficult for traditional aluminum alloy manufacturing technology to meet the requirements of large-scale and high-precision complex shape structural parts. Wire Arc additive manufacturing technology (WAAM) is an innovative production method that presents the unique advantages of high material utilization, a large degree of design freedom, fast prototyping speed, and low cast. As a result, WAAM is suitable for near-net forming of large-scale complex industrial production and has a wide range of applications in aerospace, automobile manufacturing, and marine engineering fields. In order to serve as a reference for the further development of WAAM technology, this paper provides an overview of the current developments in WAAM both from the digital control system and processing parameters in summary of the recent research progress. This work firstly summarized the principle of simulation layering and path planning and discussed the influence of relative technological parameters, such as current, wire feeding speed, welding speed, shielding gas, and so on. It can be seen that both the welding current and wire feeding speed are directly proportional to the heat input while the travel speed is inversely proportional to the heat input. This process regulation is an important means to improve the quality of deposited parts. This paper then summarized various methods including heat input, alloy composition, and heat treatment. The results showed that in the process of WAAM, it is necessary to control the appropriate heat input to achieve minimum heat accumulation and improve the performance of the deposited parts. To obtain higher mechanical properties (tensile strength has been increased by 28%–45%), aluminum matrix composites by WAAM have proved to be an effective method. The corresponding proper heat treatment can also increase the tensile strength of WAAM Al alloy by 104.3%. In addition, mechanical properties are always assessed to evaluate the quality of deposited parts. The mechanical properties including the tensile strength, yield strength, and hardness of the deposited parts under different processing conditions have been summarized to provide a reference for the quality evaluation of the deposition. Examples of industrial products fabricated by WAAM are also introduced. Finally, the application status of WAAM aluminum alloy is summarized and the corresponding future research direction is prospected.

Numerical Simulation and Process Parameter Optimization of Warm Forging Near-Net Forming for Spiral Bevel Gear

Numerical Simulation and Process Parameter Optimization of Warm Forging Near-Net Forming for Spiral Bevel Gear

Study on the effects of the processing parameters on the single tracks and the block support structures fabricated by selective laser melting

In order to prevent the deformation of the part, enhance heat conduction, and establish a stable foundation, additional support structures are typically incorporated beneath the parts during the selective laser melting (SLM) process. These structures are subsequently eliminated once the SLM process is completed, thereby facilitating the attainment of near-net forming. Therefore, their SLM processing parameters should be different from those of the solid parts to obtain the desirable functions and removability. However, there is so far very little research focusing on the optimization of the SLM processing parameters of the support structures compared with the solid objects. In this work, the widely used block support was illustrated as an instance, and an optimization strategy of its SLM processing parameters was provided. The effects of laser power, scanning speed, and layer thickness on the morphology and qualities of single track, support sample, and support tensile sample were systematically investigated. The results showed that the SLM processing parameters have a significant impact on the properties of the block support by regulating the qualities of the single tracks. At last, a group of optimal SLM processing parameters (80 W of laser power, 400 mm/s of scanning speed, 60 μm of layer thickness) was determined for the Ti-6Al-4V titanium alloy, and the corresponding ultimate tensile strength of the support structure reached 416 MPa.

Forming characteristics analysis of variable-process alternated overlapping strategy based on contour description for laser melting deposition

To predict the geometric characteristics and improve the forming quality and macro-micro defects of multi-track overlapping cladding layer effectively, the experimental research of laser melting deposition single-track Co-based alloy on 42CrMo substrate was carried out. The influence trends of laser process parameters on the single-track cladding height and cladding width were analyzed, and the regression prediction models were established. A variable-process alternated overlapping strategy was proposed using the geometric functions to fit the single-track profile. The surface forming quality and macro-micro defect of different overlapping cladding layers were compared and evaluated. The results showed that the cladding height and cladding width regression models established by an improved optimization algorithm had an excellent prediction effect. The variable-process alternated overlapping cladding layer prepared by the parabolic function had a flat surface, and the fluctuation distance was 81.56 μm, which was significantly improved compared with other overlapping strategies. The surface flatness of the continuous overlapping cladding layer was the worst and the spheroidization defect was the most unsatisfied. The internal defects of the constant-process alternated overlapping cladding layer were the most terrible, with more non-fusion and cracks caused by oxides. The variable-process alternated overlapping strategy proposed in this study can effectively prepare a multi-track cladding layer with a smooth surface and dense interior, which provides essential theoretical guidance for the near-net forming of component surface deposition and repair.

The study of near-net shape lithium aluminosilicate glass-ceramics by direct ink writing

3D printing, a competitive manufacturing technology, has opened up new possibilities for fabricating complex structure ceramic components, but near-net forming is still difficult. This work presented a kind of near-net forming lithium aluminosilicate (LAS) glass-ceramics using direct ink writing (DIW) method by controlling thermal shrinkage. To achieve this goal, a high solid-loading ink was prepared using low thermal expansion LAS glass-ceramic powder containing β-spodumene as raw material. And we comprehensively evaluated the effects of the rheological properties of the slurry and sintering process on the thermal and mechanical performances. Attributed to the restricted sintering activity and thermal deformation of LAS glass-ceramic particles, the 3D-printed samples sintered at 1300 ◦C for 2 h showed an average linear shrinkage of 0.84% with a flexural strength of 45.59 ± 2.82 MPa and a compressive strength of 65.58 ± 3.99 MPa, respectively. The results suggested that LAS glass-ceramics were excellent candidate materials for near-net forming 3D printing.

Predicting solidification cracking in directed energy deposition of Hastelloy X alloys based on thermal-mechanical model

Directed energy deposition (DED) has received extensive attention in recent years owing to its advantages of near-net forming and high design freedom. However, the thermal stress induced by rapid heating and cooling during fabrication of DEDed Hastelloy X (HX) alloys usually results in solidification cracking. To suppress or even eliminate solidification cracking by optimizing processing parameters, it is necessary to establish a correlation between stress in the last stage of solidification and solidification cracking sensitivity (SCS) of DEDed HX alloys. In this study, we first confirmed the critical role of stress in solidification cracking by comparing the simulation results calculated by a thermal-mechanical model with an experimental crack distribution and then proposed a stress-related index for describing the SCS. By calculating the index in different deposited regions and with different processing parameters, we successfully predicted the crack-prone regions at the part scale and the relationship between processing parameters and SCS. The results show that there are almost no cracks in the edge region of the DEDed HX alloy sample, while cracks are mainly generated in the region within a quarter of the width from the edge of the DEDed HX alloy sample. Moreover, solidification cracking can be effectively suppressed under a high heat input. All these simulated results are in good agreement with the experimental results. These findings are of significance to understand the solidification cracking mechanism in DED, which can be used to guide the fabrication of DED crack-free HX alloys.

Effect of hydrostatic pressure on multilevel structure and bending progressive damage of 3D braided composites under simulated deep-sea environment

Compared to metal materials and laminated composites, three-dimensional (3D) braided composites are showing innovatively great potential in deep-sea pressure shell applications owing to their light-weight, excellent out-of-plane mechanical properties and near-net forming capacity. In this paper, three-dimensional six-directional (3D6D) braided composites with different epoxy resins are designed and fabricated. The samples are put in a deep-sea pressure simulator at 10 MPa pressure for 80 h and experimentally test via the three-point bending method. A multi-level evaluating approach, namely nano-scale, micro-scale, meso-scale and macro-scale, is proposed. The effect of the hydrostatic pressure on multilevel structure and progressive failure behaviours are analyzed. Results indicate that, although the moisture absorption does not lead to the generation of new chemical bonds on the nanoscale in the carbon/epoxy composites, the moisture absorption has significant effects on the bending mechanical properties and damage initiation of 3D6D braided composites. Moreover, after deep-sea hydrostatic pressure, the strength of 3D6D braided composites decrease by 15.64–30.93 %, and the damage volumes increase by 0.039–0.405 %. Furthermore, the final failure mechanism of 3D6D braided composites after deep-sea hydrostatic pressure are largely governed by the fiber-matrix debonding and matrix cracking.

Near-net forming of porous Co-Al by isothermal treatment: Phase formation sequence and diffusion kinetics

Near-net forming of porous Co-Al by isothermal treatment: Phase formation sequence and diffusion kinetics

Hot Forging Die Design Optimization Using FEM Analysis for Near-Net Forming of 18CrNiMo7-6 Steel Pinion Shaft

The objective of the presented work was to develop a new forging process for a pinion shaft as a component of a wind turbine. A study of near-net-shape forming using Deform 3D software was performed to reduce operational cost, time, and material scrap; enhance specific properties; increase productivity. Near-net forged products have good dimensional accuracy and continuous metal flow lines, which are characteristic of improved mechanical properties. To avoid the traditional trial-and-error experimental method, the process and tool design were accomplished with a careful and detailed numerical simulation approach. In the present work, the Finite Element Method was used to develop a process model for the existing hot forging process of the 18CrNiMo7-6 steel pinion shaft used in a wind turbine. The developed numerical process model was validated via experiment including a comparison of the metal flow lines from the FEM model with the metallography results of the forged part. Two new die designs were proposed, and the simulation results were compared to the actual process to achieve improved geometry. The results for the new geometries showed improvements in terms of the die cavity filling for the new proposed dies and better results in grain flow orientation. Compared to the initial non-optimized die, the new designs improved the mechanical properties and savings associated with the lower volume of required raw material and fewer finishing operations. Considering the applied stresses and wear in the new near-net shape, the die geometry shall be updated to accommodate more severe solicitations. Naturally, all the improvements carried out are dependent on other factors such as the conditions of the equipment, operator skills, lubrication, and other variables. A surface heat treatment is also suggested for stress relief as a reliability improvement.

A Novel Manufacturing Process for Nanosilica Carbide Reinforced Al2024 Matrix Composites

Fabrication of SiC nanoparticle enhanced Al2024 composite material with near-net form SiC nano particles is discussed in this research using the flake powder metallurgy (PM) technique. Analysis of particle size and quantity of Silicon Carbide (SiC) nanoparticles in flake Al2024 matrix granules along with their effect on particle distribution, structure, relative compactness, and hardness were conducted. The granules Al2024 substrate particles were combined to 3 various size of some as Al2024 powders using a ball milling process. With intergranular wide enough to incorporate reinforcements, the Al2024 matrix powders were discovered to have flake-like microstructures with distributed SiC nanoparticles spread throughout. Hot pressed density raised as a result of the slight frictional forces among the thin flake elements. The rigidity of Aluminium Alloy 2021/Silicon carbide nanocomposites was employed to expand the size of matrix particles.

Mechanical properties of wire arc additive manufactured carbon steel cylindrical component made by cold metal transferred arc welding process

Abstract Wire arc additive manufacturing (WAAM) offers high-quality technology for producing large complex geometry structures in close proximity to near-net form, using cost-effective manufacturing resources, such as welding and wiring materials. In this study, the cold-metal-transfer-based WAAM system was utilized to manufacture the steel cylindrical component. The mechanical properties and microstructure analysis of the component were analyzed at two regions (bottom and top region) along the building direction. The results showed that the microstructure of the part differed from the bottom to the top region, resulting in a hardness difference between 169 and 181 (Hv0.5), and impact toughness varied from 72 to 80 J. There were also anisotropic features in the tensile properties: the yield strength and the ultimate tensile strength ranging from 401 to 457 MPa and between 492 and 543 MPa, respectively.

Processing of Aluminium-Silicon Alloy with Metal Carbide as Reinforcement through Powder-Based Additive Manufacturing: A Critical Study.

Powder-based additive manufacturing (PAM) is a potential fabrication approach in advancing state-of-the-art research to produce intricate components with high precision and accuracy in near-net form. In PAM, the raw materials are used in powder form, deposited on the surface layer by layer, and fused to produce the final product. PAM composite fabrication for biomedical implants, aircraft structure panels, and automotive brake rotary components is gaining popularity. In PAM composite fabrication, the aluminium cast alloy is widely preferred as a metal matrix for its unique properties, and different reinforcements are employed in the form of oxides, carbides, and nitrides. However, for enhancing the mechanical properties, the carbide form is predominantly considered. This comprehensive study focuses on contemporary research and reveals the effect of metal carbide's (MCs) addition to the aluminium matrix processed through various PAM processes, challenges involved, and potential scopes to advance the research.

Systematic Review on Investment Casting

Abstract: The Investment casting (IC) method is now used to make all precision components in the medical, hydropower, defence, car, and other sectors. IC has a wide range of applications and is well-known for its ability to make complex near-net form items with great dimensional precision and surface polish. Various scholars are making ongoing efforts to investigate the topic of investment casting. This publication offers a comprehensive survey of the studies in this vast topic. It emphasises improvements in the earliest stages of the investment casting process. It focuses on pattern creation improvements, mould composition, casting materials, and typical flaws, as well as preventative actions. Keywords: Investment casting, Pattern modelling, Mould, TiAl alloys, defects

The effect of hydrogen treatment on microstructures evolution and mechanical properties of titanium alloy fabricated by selective laser melting

The selective laser melting additive manufacturing can realize near-net forming and produce complex high-precision parts. However, β-columnar crystals will be formed in building direction, which leads to the decrease of material reliability, causing stress concentration and accelerating material fracture. Here, we perform hydrogenation treatment, solution treatment, aging treatment, and finally dehydrogenation treatment on Ti-6Al-4V titanium alloy fabricated by selective laser melting. The results show that the β grains of hydrogenated samples are refined after subsequent heat treatment. After the solution treatment, α' and α'' martensite coexist in the microstructure and decomposed during the subsequent aging and dehydrogenation treatment, resulting in the refinement of the structure within the grains, but still retaining the grain morphology of the previous alloy. When compressed at room temperature，the compressive strain and ultimate compressive strength of hydrogenated samples after heat treatment increase with the increase of hydrogen concentration, and the yield strength decreases. After dehydrogenation, the yield strength and ultimate compressive strength are increase.

Optimization of laser energy density and scanning strategy on the forming quality of 24CrNiMo low alloy steel manufactured by SLM

Selective laser melting (SLM) is among the best technologies to realize near-net forming of metal parts. The process involves the matching of various process parameters to achieve the full density of the products. This study was dedicated to understanding the influence of laser energy density and various scanning strategies on the formability of the SLM-fabricated 24CrNiMo specimens, which were characterized in terms of densification, surface quality and microstructure. Firstly, the experiments focused on the adjustment of laser energy density, which was aimed at determining an optimal parameter for the 24CrNiMo steel with the minimum porosity and optimum microstructure. The experimental results illustrated that the relative density of the specimen was promoted to 99.14% and its surface roughness decreased to 19.002 μm by applying the energy density of 56.00 J/mm3. In addition, the microstructure was mainly composed of lower bainite with high strength, and the irregularly oriented grains ensured the homogeneity of the specimen. Subsequently, the residual stress distribution and warping deformation of the specimens prepared by various scanning strategies were thoroughly analyzed to clarify the most suitable strategy for 24CrNiMo steel. It was observed that the specimen prepared by orthogonal scanning strategy exhibited no obvious defects, relatively stable residual stress distribution and optimal surface quality, which could be regarded as a reference for preparing high-quality 24CrNiMo steel via SLM.

Constitutive Model of 30CrMoA Steel with Strain Correction

It is necessary to establish a constitutive model of 30CrMoA steel to optimize the forming shape and mechanical properties of high-speed train axles. The experimental stress–strain curve of 30CrMoA steel was obtained by an isothermal compression test on a Gleeble-3500 thermal simulation test machine under temperature of 1273~1423 K and strain rate of 0.01~10 s−1. Considering the effect of strain on the material constant, an empirical constitutive model was proposed with strain correction for 30CrMoA steel. In addition, the material constant in the constitutive model is determined by linear regression analysis of the experimental stress–strain curve. Comparing the theoretical value and experimental value of flow stress, the correlation R is 0.9828 and the average relative error (ARRE) is 4.652%. The constitutive model of 30CrMoA steel with strain correction can reasonably predict the flow stress under various conditions. The results provide an effective numerical tool for further study on accurate near-net forming of high-speed train axles.

Microstructures refinement and mechanical properties enhancement of aluminum and magnesium alloys by combining distributary-confluence channel process for semisolid slurry preparation with high pressure die-casting

Abstract A simple and efficient semisolid slurry preparation technique, called distributary-confluence channel (DCC), was developed to prepare high-quality semisolid slurries of aluminum and magnesium alloys. The DCC process was coupled with the use of a high pressure die-casting (HPDC) machine to successfully achieve near-net forming and implement production applications with rheological high pressure die-casting (Rheo-HPDC) for various Al and Mg alloy castings. The changes in the flow state and in the physical field of the melt during the slurry preparation via the DCC technique were investigated by numerical simulations. The nucleation mechanism and the growth law of the primary grain during the DCC process were discussed. The microstructures, porosities, and mechanical properties of the aluminum and magnesium alloys prepared via DCC Rheo-HPDC were studied. The results show that semisolid slurries containing a large amount of primary grains with an average size 0.8, and uniformly dispersed in the liquid matrix can be prepared via DCC. The simulation results indicate that the melt exhibits opposite velocity vectors on the upper part and on the lower part of the DCC. Moreover, it encounters and collides at the confluence to generate convection, which is beneficial to obtain uniform melt temperature, composition fields, nuclei exfoliation, and spherical growth. The random particle tracking simulation results show that the DCC process improves the composition field of the slurry. The DCC process facilitates the melt nucleation by using multi-channel chilling and increasing the nucleation area. The self-stirring generated during the flow of the melt produces a large amount of free nuclei inside the melt. There exist two main mechanisms behind the formation of the spherical primary grains. The one is the mechanism of explosive nucleation and spheroidal growth, the other is the dendrite arm necking, fusing, grain ripening, and rounding. Furthermore, by comparing identical alloy castings produced via traditional HPDC and other Rheo-HPDC processes, the DCC Rheo-HPDC castings present finer and rounder grains, a lower porosity, and more performant mechanical properties.

Implementation of hybrid additive manufacturing based on extrusion of feedstock and milling

Abstract In the current industry, fabrication of metallic and ceramic artifacts by means of feedstock extrusion additive manufacturing is receiving attention because of the capacity of this technology to deal with low costs and materials that possess a low Additive Manufacturability Index when treated with high power beam technologies. However, the extrusion additive manufacturing lacks in achievable accuracy and productivity therefore techniques that can improve the overall performances are required to increase the impact that this technology can have on industry. This paper demonstrates how extrusion additive technology of metals and ceramics can be enhanced by integrating green-state milling into the manufacturing cycle. In the hybrid cycle, the additive and subtractive processes act alternatively on the green-state part to shape its near-net form. This work shows how this innovative method, that integrates cutting and micro-cutting operations on the feedstock, allows compensating the lack of accuracy and micro reachability that characterize the extrusion-based additive manufacturing method. In the manuscript, the promising aspects of the hybrid concept are presented and discussed. Some examples of manufactured parts are illustrated showing how complex geometries, with good surface quality can be addressed with higher production flexibility. The developed hybrid machine prototype adopted for that scope is described along with the AISI316L parts that are obtained by depositing, green-state milling, debinding and sintering the feedstock. Another contribution is provided regarding the feedstock machinability that is studied under different cutting conditions. The feasibility of the hybrid implementation is confirmed and future steps to improve the process are discussed.

Near-Net Forming Complex Shaped Zr-Based Bulk Metallic Glasses by High Pressure Die Casting

Forming complex geometries using the casting process is a big challenge for bulk metallic glasses (BMGs), because of a lack of time of the window for shaping under the required high cooling rate. In this work, we open an approach named the “entire process vacuum high pressure die casting” (EPV-HPDC), which delivers the ability to fill die with molten metal in milliseconds, and create solidification under high pressure. Based on this process, various Zr-based BMGs were prepared by using industrial grade raw material. The results indicate that the EPV-HPDC process is feasible to produce a glassy structure for most Zr-based BMGs, with a size of 3 mm × 10 mm and with a high strength. In addition, it has been found that EPV-HPDC process allows complex industrial BMG parts, some of which are hard to be formed by any other metal processes, to be net shaped precisely. The BMG components prepared by the EVP-HPDC process possess the advantages of dimensional accuracy, efficiency, and cost compared with the ones formed by other methods. The EVP-HPDC process paves the way for the large-scale application of BMGs.

Effect of pre-cold rolling on the evolution of microstructure, microtexture, and mechanical properties of the mushy state rolled in-situ Al-4.5Cu-5TiB2 composite

The mushy state rolling has been found as a promising technique for near-net forming of the cast Al-4.5 wt% Cu-5 wt% TiB2 in-situ composite to obtain microstructural refinement and moderate mechanical properties. Cold rolling with 30% reduction in thickness was carried out before mushy state rolling, for achieving a relatively more homogeneous distribution of CuAl2-TiB2 particles as well as an appropriate microstructure to enhance the mechanical properties. A comparative investigation on the microstructural and microtextural evolution, along with mechanical properties of both the mushy state rolled composite (MRC) and pre-cold rolled mushy-state rolled composite (PCMRC) was performed, and the microstructure-property correlation was established. The PCMRC exhibited the lowest homogenized lengthscale parameter (LH 29 μm) indicating the maximum uniformity of particle distribution, computed with the help of multi-scalar analysis of area fractions (MSAAF) technique. Electron back-scattered diffraction (EBSD) and transmission electron microscopy (TEM) studies revealed the presence of fine sub-grains within centrally located deformed Al grains due to dynamic recovery, as well as the particle stimulated nucleation of equiaxed fine Al grains by dynamic recrystallization or rapid solidification of liquid near edges for both the investigated composites. The PCMRC displayed a superior combination of hardness (96.82 ± 4.5 HV5kgf), 40% higher ultimate tensile strength (301.4 ± 1.8 MPa), and 68% more uniform elongation (30.8% ± 0.5%), compared to the MRC. The improvement in mechanical properties is attributed to the uniform particle distribution and presence of both higher density of low angle boundaries and recrystallized grains adjacent to the particles, obtained from prior cold rolling.