High-strength Parts Research Articles

Effect of Runner Distance on Microstructure and Properties of Semi-Solid Squeeze Casting CuSn10P1 Alloy

It is easy to form reverse segregation and shrinkage porosity defects during the solidification of CuSn10P1 alloy, which leads to the poor properties and limits its application in high strength and toughness parts. In this paper, semi-solid CuSn10P1 alloy slurry was prepared by enclosed cooling slope channel (for short ECSC). The effect of runner distance on microstructure and properties by liquid squeeze casting and semi-solid squeeze casting was studied. The results showed that the microstructure of semi-solid squeeze casting is finer than that of liquid squeeze casting, and the shrinkage defects are improved. The solid fraction with 65 mm runner is lower than that without runner in liquid squeeze casting and semi-solid squeeze casting due to the retention effect of solid phase in semi-solid slurry flow, but the properties with 65 mm runner is better than that without runner. The ultimate tensile strength, yield strength and elongation of semi-solid squeeze casting CuSn10P1 alloy with 65 mm runner distance reached 466.5 MPa, 273.6 MPa and 13.4%, which were improved by 26%, 19% and 97%, respectively, as compared to that of liquid squeeze casting.

Survey on compression property of sandwich 3D printed PLA components

Additive Manufacturing (AM) is a trending technology to manufacture functional parts from 3D design to real-time products. Lightweight structure with expected mechanical property is a difficult task in conventional manufacturing. In aircraft, interior design parts should have high-strength parts with a low weight ratio. The high strength to low weight ratio can be developed using different materials, but the influenced factor is cost. Making a sandwich component is one of the best methods to fabricate the parts with high strength to low weight ratio. Sandwich structure is one type of design that can be fabricated using additive manufacturing with different materials. Sandwich structures comprise three components: a lightweight core and two face sheets at the top and bottom. Many materials can be used in this technique to produce sandwich parts, but this article focused on existing PLA and its composites. PLA is widely renowned for its characteristics and environmental awareness. This review is focused on the compression property investigation of the 3D printed Sandwich Structure and methods to improve the mechanical property of 3D printed parts.

成形-相変態連成CAEによるホットスタンプ部材の形状予測

The hot stamping method is established for manufacturing high-strength automotive parts with good shape fixability. Recently, the hot stamping method has been applied to higher performance parts with tailored properties. CAE is indispensable in designing such parts. For designing hot-stamped parts, the forming simulation must be coupled with thermal analysis considering the temperature effect on formability. The final shape need not necessarily be predicted because of its good fixability. However, in high-performance parts with tailored properties, it is important to predict how the final shape is affected by phase transformation. To predict the final shape of hot-stamped parts, a CAE method that takes into account phase transformation effects has been developed. The accuracy of the calculation of the final shape by the CAE method was investigated. Hot-stamping experiments were carried out to obtain parts of different shapes by cooling control, and the CAE analysis of the final shape for each experimental condition was conducted. It was clarified that the final shape was varied by changing the cooling process, and that the results of CAE including phase transformation were in good agreement with the tendency of shape change in cross section.

Selective Laser Melting of High Relative Density and High Strength Parts Made of Minor Surface Oxidation Treated Pure Copper Powder

Pure Copper (Cu) is very difficult to prepare using selective laser melting (SLM) technology. This work successfully prepared the pure Cu with high relative density and high strength by the SLM technology using a surface oxidation treatment. The gas-atomized pure Cu powder was used as the feedstock in this work. Before the SLM process, the pure Cu powder was initially handled using the surface oxidation treatment to coat the powder with an extremely thin layer of Cu2O. The SLMed highly dense specimens contain α-Cu and nano-Cu2O phases. A relationship between the processing parameters (laser power (LP), scanning speed (SS), and hatch space (HS)) and density of Cu alloy in SLM was also investigated. The microstructure of SLMed Cu consists of fine grains with grain sizes ranging from 0.5 to ~30 μm. Tensile testing and detailed microstructural characterization were performed on specimens in the as-SLMed and pure copper state specimens. The mechanical property experiments showed that the specimens prepared by SLM technology containing nano-oxide phases had higher yield strength and tensile strength than that of other SLM-built pure copper. However, the elongation was remarkably decreased compared to other SLM-built pure copper, due to the fine grains and the nano-oxides.

Exploiting the rapid solidification potential of laser powder bed fusion in high strength and crack-free Al-Cu-Mg-Mn-Zr alloys

This work describes a systematic alloy design strategy resulting in the development of a high strength aluminum alloy adopted for L-PBF. First, based on the composition of a reference Al-Cu-Mg alloy, three Al-Cu-Mg-Mn-Zr-based alloys were investigated using computational thermodynamic tools. Subsequently, the L-PBF processing behavior, microstructure, and concomitant mechanical properties of the L-PBF-fabricated alloys were investigated. Alloys with different compositions showed substantial differences in microstructure: the alloy without Zr addition showed a coarse columnar microstructure and suffered from solidification cracking, alloys with low to mediate Zr additions (1–1.98 wt%) showed a mixed columnar and equiaxed microstructure, while alloys with high Zr addition (3.72 wt%) showed a fully equiaxed microstructure, accompanied by a grain size reduction down to 0.7 ± 0.3 µm. All alloys containing ≥ 1.98 wt% Zr were crack-free. The L-PBF-processed Al-4.40Cu-1.51Mg-1.15Mn-3.72Zr (wt%) alloy showed an extended Zr solid solubility in the Al matrix of ~ 1.3 ± 0.1 wt%. Coherent primary Al3Zr particles with a cubic L12 structure were formed in all the Zr-containing alloys. The mechanical properties of as-built alloys increased consistently with increasing Zr contents from 0 to 3.72 wt%. The designed Al-4.40Cu-1.51Mg-1.15Mn-3.72Zr (wt%) alloy combined a yield strength of 561 ± 24 MPa, an ultimate tensile strength of 580 ± 16 MPa, and an elongation at break of 6.0 ± 1.3%. The exceptionally high strength of this alloy is attributed to a combination of grain refinement, Orowan, solid solution, and dislocation strengthening. The current work shows the intrinsic potential of rapid solidification occurring during L-PBF for the fabrication of geometrically-complex, high-strength lightweight parts made of ultra-fine-grained hyper-peritectic aluminum alloys containing transition element additions.

A Study on the Effect of Process and Material Variables on the Hot Stamping Formability of Automotive Body Parts

Hot stamping is a method capable of manufacturing high-strength automotive body parts by inducing a martensitic phase transformation through forming and die quenching after heating a metal sheet into a high temperature austenite phase. However, it is not easy to solve various formability problems occurring in the hot stamping process due to the complexity of the process and material behavior during high temperature forming. In this study, fracture-related forming limits and martensite phase ratio were selected as criteria for evaluating hot stamping formability. First, a hot stamping test was performed on a T-type part that simplified the B-pillar, an automotive body part, and the fracture behavior according to the temperature and thickness of the sheet blank was investigated. Additionally, forming analysis was performed on the hot stamping process of mass-produced B-pillar parts by varying the temperature of the sheet blank, the thickness of the sheet blank, the die-blank friction coefficient, and the strain-rate sensitivity of material among various process and material variables. Based on the analysis results, the effect of each process and material variable on the hot stamping formability of B-pillar parts was quantitatively analyzed. By utilizing the results of this study, it will be possible to solve the formability problem that occurs in the mass-production hot stamping process for automotive body parts and improve the quality of parts in the future.

In-Situ Reduction of Mo-Based Composite Particles during Laser Powder Bed Fusion

Raw powders are processed in water during the freeze-dry pulsated orifice ejection method (FD-POEM), leading to the inclusion of oxygen impurities. This study proposes a strategy for removing the oxygen content and enhancing the mechanical performance of laser powder bed fusion (L-PBF) builds from powders using carbon nanotubes (CNTs) and H2 reduction. Spherical 1.5 wt.% CNT/Mo composite powders with uniform dispersion were fabricated via FD-POEM. The quantity of MoO2 decreased significantly, and a hexagonally structured Mo2C phase was simultaneously formed in the L-PBF build. The Mo2C with network structure was distributed along the boundaries of equiaxed Mo grains, leading to an increased Vickers hardness of the matrix. This study demonstrates the feasibility of fabricating oxygen-free and high-strength refractory parts during L-PBF for ultrahigh-temperature applications.

A review on the topology optimization of the fiber-reinforced composite structures

According to the requirements of the aerospace industry for high strength, high stiffness, and lightweight structural parts, topology optimization has been proved to be an effective product design method. As one of the most conceptual and prospective structural optimization design methods, topology optimization intends to seek the optimal layout of materials in an allowed design region under a given load and boundary conditions. Thus, the object of study in the article is the method of topological optimization of aircraft structures. The goal of this article is to analyze the existing approaches, algorithms, as well as application of the method of topological optimization in the aerospace field in applied problems. The tasks are to describe the existing various approaches methods, features, and research directions of topological optimization as well as to study the possibility of application in the manufacturing process of composite structures. The following results were obtained. The optimization methods are briefly explained and compared, and the advantages and limitations of each approach are discussed. The various ways of simultaneous optimization of fiber orientation and structural topology were described and analyzed. The features of different methods of continuous fiber orientation optimization method were reviewed. The discrete fiber orientation optimization methods were represented. The possibility of multi-scale concurrent topological optimization was described. The combination of topology optimization and additive manufacturing was considered. Finally, the topology optimization of FRC structures which have been resolved in literature are reviewed and the potential research fields requiring more investigation are pointed out. Conclusions. In the article, a comprehensive review of the topology optimization design of FRC structures was presented. The promising way is to combine topology optimization with additive manufacturing techniques. However, these proposed methods may not suitable for other more complex problems, such as bucking stability and natural frequency. Hence, the topology optimization design of complex FRC components under complicated conditions is the main challenge in the future. This can be a new trend in the topology design of FRC structures.

Effects of surface area and topography on 3D printed tricalcium phosphate scaffolds for bone grafting applications.

Additive manufacturing (AM), or 3D printing, of bioceramic scaffolds promises personalized treatment options for patients with site-specific designability for repair and reconstruction of bone defects. Although the theory for creating these complex geometries has already been made possible through AM's advancement, such shapes' manufacturability is difficult due to printing with ceramics' inherent complexities. Ceramics have the added challenge of being highly brittle, poor handleability of green (pre-sintered) parts, making complex shape high strength parts challenging to manufacture. This has led to a significant literature gap regarding the feasibility of creating bioceramic scaffolds with unique architectures that can be used in site-specific, individualized patient treatment. This work aims to successfully create complex topographical surfaces of cylindrical bone-like scaffolds to understand the correlation of increasing the scaffold surface area on mechanical properties and in vitro osteoblast cell proliferation. An increase in osteoblast cell proliferation and facilitation in cellular attachment can ultimately lead to improved bone healing. This work explores the printing parameters within an Innovent+® ExOne binder jet 3D printer to produce scaffold designs from synthesized tricalcium phosphate powder. Mechanical testing reveals the designed structures enhance scaffold compressive strength by 30% compared to control dense cylindrical scaffolds. Osteoblast cell proliferation is also increased due to changes in surface topography with a nearly 2-fold increase. Our work incorporates macro-level topographical changes to increase surface area, which is another avenue that could be combined with other scaffold features such as porosity. Results show bulk surface topography modifications via 3D printing can increase surface area to support enhanced biological response without compromising mechanical properties. This discovery may enable a future generation of porous scaffolds with external structures for further progress towards proper defect-specific synthetic bone grafts.

Development of metal matrix composites using recycled secondary raw materials from aluminium wastes

Metal matrix composites have proven to be a class of materials with high potential to replace a large number of materials used in the automotive, aerospace, electronics, defence and manufacturing industries, where the requirement for light and high-strength parts is increasing. The possibility of combining different materials (metal–ceramic–nonmetal) provides the opportunity to change the properties of metal matrix composites, which are mainly determined by the properties of the component materials. Therefore, there is the question of finding recycling technologies, replacing new materials with recycled materials in order to minimise the amount of waste, which does not involve too much expenditure with their implementation and at the same time does not raise particular problems when applying them in industrial practice. The purpose of this study is to highlight the most efficient methods of recycling aluminium alloys in order to be applied in the practice of composites. This research concerns the liquid mixing (Vortex method) processing of composite materials with metal matrix of aluminium alloys, reinforced with ceramic particles. This technology uses common and cheap raw materials, matrix alloys in the moulded state, from recycling. This process has general economic and technological advantages, consisting of a small number of operations, with low durations and low energy consumption. Also, liquid mixing can be obtained by composite materials with a homogeneous distribution of ceramic reinforcement particles in the metal matrix. This study was carried out using laboratory installations designed and carried out within the Department of Engineering and Management of the Faculty of Engineering Hunedoara, University Politehnica Timisoara, within a doctoral program.

Generative design of conformal cubic periodic cellular structures using a surrogate model-based optimisation scheme

Cellular structures (CSs) exhibit unique combinations of physical properties, including low weight, high structural strength, and substantial energy absorption, which could be useful in a variety of applications. Further, with the advent of additive manufacturing (AM), CSs are now easier to fabricate. While CSs and AM open up transformative opportunities, their potential for everyday use in industrial practice still lies largely idle. One of the major reasons is the lack of computational tools that allow us to automatically explore, verify, and optimise CSs and skin elements to create an optimised component that meets the exact specification. In this paper, we outline a periodic CS-based generative design pipeline that offers automated modelling, analysis, and inverse design solving of CS through the use of an integrated optimisation and finite-element analysis (FEA) framework. Specifically, a surrogate model-based optimisation scheme is proposed to design light-weight and high-strength functional parts by taking advantage of spatially varying conformal cubic periodic cellular structures.

Binder jetting additive manufacturing of 316L stainless-steel green parts with high strength and low binder content: Binder preparation and process optimization

• A self-developed binder with A-stage phenolic resin as a key agent was prepared. • High strength 316 L green part with low binder saturation was fabricated by BJAM. • The uneven distribution of binder hinders the strength of green parts. Recently, binder jetting additive manufacturing (BJAM) was used to manufacture complex metal parts in an economical and large-scale way. However, the usage of resin to bond metal powder renders as-printed green parts with low strength, which is potential to cause the structural damages of final parts during post treatments. To overcome the intractable problem, a self-developed binder mainly consisting of A-stage phenolic resin was explored for BJAM to achieve relatively high-strength as-printed green parts. The binder can be cured as a C-stage phenolic resin with 190 ℃ and then provide a high strength for the green parts. The effect of layer thickness and binder saturation on the strength, dimensional accuracy, and surface roughness of the BJAM-printed 316 L stainless-steel green samples using the developed binder was investigated systematically. With the optimized parameters (a layer thickness of 100 μm and a binder saturation of 30.2 %), green samples can possess the ultimate bending strength (UBS) of 10.08 MPa and the ultimate compressive strength (UCS) of 25.56 MPa, which are beneficial for the structural stability of the printed samples during subsequent treatments. A reduction in strength and an increase in roughness are observed with increasing the layer thickness for the as-printed green samples. An increment in binder saturation results in the improvement in strength and surface roughness of the green samples. The relationships between the binder and the mechanical performance of the green samples were discussed from the viewpoint of the uneven distribution of binder in depth. This work explored a promising binder with a low saturation for BJAM to fabricate 316 L green parts with desirable mechanical strength and acceptable surface roughness.

Hierarchical combinatorial design and optimization of non-periodic metamaterial structures

Abstract As advanced manufacturing techniques like additive manufacturing have enabled the fabrication of complex geometries, it is worthwhile to explore potential techniques that can be used to design metamaterial structures to achieve desired behaviors or physical properties. Designing the fine-scale geometry of a metamaterial structure to perform a specific behavior defines an inverse problem that is often intractable. To make this inverse problem tractable, most researchers represent metamaterial structures relying on a single-type periodic unit cell that is repeated in regular grids. Such a representation simplifies modeling and simulation tasks but at the cost of conceivably limiting the spectrum of physical properties that can be achieved by using more than one type of unit cells. This paper defines a non-periodic representation via implicit functions that generate two types of unit cells in pairs, which cope with the geometric frustration of interface connection in non-periodic metamaterial design. To solve the inverse problem of non-periodic metamaterial design, we propose a genetic algorithm-based combinatorial optimization scheme to design light-weight and high-strength functional parts by optimizing relevant parameters in the generating functions of non-periodic unit cells.

Estimating of the Size of the Maximum Non-Metallic Inclusions in Martensitic Steels and their Influence on Fatigue Properties

Fatigue cracks can start from non-metallic inclusions in the subsurface zone at low stress amplitude level and high number of cycles. This phenomenon was observed mainly at high strength steels and parts with hardened surface zone. Fatigue strength of steel can be then estimated on the basis of hardness and maximum size of defect/inclusions measurements. Many inclusions rating methods exist, some of which have been adopted as the standards. However, “standard” methods for characterization of inclusion content are not convenient for assessment of their influence on fatigue strength of materials. This contribution deals with assessment of maximum sizes of inclusions in three types of martensitic steels used for production of rotating blades of steam turbines (Böhler T552, Böhler T671, and MLX 17) using extreme value statistics methods. Murakami´s concept of √AREAmax parameter and procedure according to ASTM E2283-08 were applied. Results were compared one another and also with the result of standard methods, too. Founded parameters were used for calculation of expected limit of the fatigue strength and compared with results of fatigue test of these steels.

Microstructure and Properties of Glass Fiber-Reinforced Polyamide/Nylon Microcellular Foamed Composites.

The automobile and aerospace industries require lightweight and high-strength structural parts. Nylon-based microcellular foamed composites have the characteristics of high strength and the advantages of being lightweight as well as having a low production cost and high product dimensional accuracy. In this work, the glass fiber-reinforced nylon foams were prepared through microcellular injection molding with supercritical fluid as the blowing agent. The tensile strength and weight loss ratio of microcellular foaming composites with various injection rates, temperatures, and volumes were investigated through orthogonal experiments. Moreover, the correlations between dielectric constant and injection volume were also studied. The results showed that the “slow–fast” injection rate, increased temperature, and injection volume were beneficial to improving the tensile strength and strength/weight ratios. Meanwhile, the dielectric constant can be decreased by building the microcellular structure in nylon, which is associated with the weight loss ratio extent closely.

A Study on Strengthening Mechanical Properties of a Punch Mold for Cutting by Using an HWS Powder Material and a DED Semi-AM Method of Metal 3D Printing

The post-processing (punching or trimming) of high-strength parts reinforced by hot stamping requires punch molds with improved mechanical properties in hardness, resistance to wear, and toughness. In this study, a semi-additive manufacturing (semi-AM) method of heterogeneous materials was proposed to strengthen these properties using high wear resistance steel (HWS) powder and directed energy deposition (DED) technology. To verify these mechanical properties as a material for the punch mold for cutting, specimens were prepared and tested by a semi-AM method of heterogeneous material. The test results of the HWS additive material by the semi-AM method proposed in this study are as follows: the hardness was 60.59–62.0 HRc, which was like the Bulk D2 specimen. The wear resistance was about 4.2 times compared to that of the D2 specimen; the toughness was about 4.0 times that of the bulk D2 specimen; the compressive strength was about 1.45 times that of the bulk D2 specimen; the true density showed 100% with no porosity. Moreover, the absorption energy was 59.0 J in a multi-semi-AM specimen of heterogeneous materials having an intermediate buffer layer (P21 powder material). The semi-AM method of heterogeneous materials presented in this study could be applied as a method to strengthen the punch mold for cutting. In addition, the multi-semi-AM method of heterogeneous materials will be able to control the mechanical properties of the additive material.

A new class of lightweight, stainless steels with ultra-high strength and large ductility

Steel is the global backbone material of industrialized societies, with more than 1.8 billion tons produced per year. However, steel-containing structures decay due to corrosion, destroying annually 3.4% (2.5 trillion US$) of the global gross domestic product. Besides this huge loss in value, a solution to the corrosion problem at minimum environmental impact would also leverage enhanced product longevity, providing an immense contribution to sustainability. Here, we report a leap forward toward this aim through the development of a new family of low-density stainless steels with ultra-high strength (> 1 GPa) and high ductility (> 35%). The alloys are based on the Fe–(20–30)Mn–(11.5–12.0)Al–1.5C–5Cr (wt%) system and are strengthened by dispersions of nano-sized Fe3AlC-type κ-carbide. The alloying with Cr enhances the ductility without sacrificing strength, by suppressing the precipitation of κ-carbide and thus stabilizing the austenite matrix. The formation of a protective Al-rich oxide film on the surface lends the alloys outstanding resistance to pitting corrosion similar to ferritic stainless steels. The new alloy class has thus the potential to replace commercial stainless steels as it has much higher strength at similar formability, 17% lower mass density and lower environmental impact, qualifying it for demanding lightweight, corrosion resistant, high-strength structural parts.

Warm stamping of ultra-high strength steel sheets at comparatively low temperatures using rapid resistance heating

A warm stamping process of 1 and 1.2 GPa ultra-high strength steel sheets at comparatively low temperatures using rapid resistance heating was investigated to produce high strength parts. The effects of the heating temperature and rate on mechanical and surface properties of warm-stamped parts were examined. For a rapid heat rate of 100 °C/s around a heating temperature of 300 °C, the hardness of the formed parts increased from that of the as-received sheets, and the hardness for the 1.2 GPa sheet approached that of conventional hot-stamped parts from 22MnB5 steel sheets. The increase in hardness appeared only for rapid heating, and not for slow heating using a furnace. The increase in hardness is due to the transformation of retained austenite into martensite at comparatively low temperatures using rapid resistance heating and cooling. For the comparative low heating temperature, the non-coated sheet hardly oxidised, and the galvannealed sheet having high corrosion resistance did not exhibit the exfoliation of the coating layer, whereas the springback did not improve.

Laser powder bed fusion of AA7075 alloy: Influence of process parameters on porosity and hot cracking

Laser powder bed fusion (LPBF) is an attractive technology of manufacturing high-strength aluminium alloy parts for the aircraft and automobile industries, limited by poor processability of these alloys. This work was aimed at finding the process window for the LPBF manufacturing of defect-free components of AA7075 alloy. Optimization of the parameters was performed at each stage of the multi-stage research, i.e. for single tracks, thin walls and volumetric specimens. At each stage, the relation between LPBF parameters and defect formation with a focus on hot cracking was investigated and discussed. Due to the optimization of process parameters, the density of volumetric specimens above 99 % was reached and vaporization losses of the alloying elements were significantly reduced, but solidification cracks could not be eliminated. It was found that solidification cracks were formed by the liquid film rupture mode, mainly along columnar grain boundaries. The EDS microanalysis showed intergranular microsegregation, not only of the main alloying elements (Zn, Mg, Cu) but also of minor elements such as Si. Silicon may play a significant role in increasing susceptibility to cracking by increasing the stability of the liquid film. Reduction in the silicon impurity content in the AA7075 powder gives a chance to reduce susceptibility to cracking with no change of the alloy specification.

Mechanical characterization of biocompatible PEEK by FDM

The flexibility and rapidity in manufacturing of high-strength but lightweight polymeric parts has become more widespread in aerospace development and human implants. As a typical semicrystalline thermoplastic, polyether-ether-ketone (PEEK) has desirable mechanical properties and environmental resistance over extended temperatures. In this paper, the Fused Deposition Modelling (FDM™) was employed to fabricate the PEEK samples for performing tensile tests to investigate the relationship between various thermal processing conditions (the raster angle, nozzle temperature and ambient temperature) in FDM process, post heat treatment temperature after FDM and the mechanical properties of pure PEEK material. The fracture mechanisms was revealed. A phenomenological model was established to represent the change of the maximum tensile strength (MTS) with the processing conditions for FDM samples. Beyond that, the mechanical performance of the manufactured cranial implant was investigated by uniaxial static compression tests. The finds of this work provide guidelines for FDM of PEEK to the clinical implementation and application of cranial implants.