Complex-shaped Components Research Articles

SERIES PARTS MANUFACTURING BY INFRARED SUPERPLASTIC FORMING WITH NUMERICAL TECHNIQUES FOR THERMAL REGULATION

Materials used for Superplastic forming (SPF) are mainly titanium alloys which are good candidates to produce lightweight complex-shaped components for high performance aerospace applications. SPF process has limitations because it involves a high-temperature furnace with poor heat efficiency and expensive tooling with low management flexibility. Enhancing this manufacturing process is a major challenge for the aerospace industry which is facing to important production ramp-up and cost reductions. Direct heating combined with tool heat management result in significant savings of SPF process: production time savings by drastically reduce the heating time, reduction of maintenance costs and energy savings by significant heat efficiency improvement. Aurock developed direct heating by Infrared emitters and succeed in forming series 1.5x1m² Ti6Al-4V blanks. A key point with this new technology is to ensure a homogeneous blank temperature all along the forming. This point is achieved thanks to lamp power modulations and numerical techniques to secure the blank thermal regulation with a full radiative flux control at different forming stages. Results obtained are stable and repeatable regarding to dimensional criteria, post-forming thicknesses distribution and microstructure. Numerical predictions are in very good agreement with the experimental results, enabling robust machine setup for series Infrared SPF parts production.

Process planning strategy for wire-arc additive manufacturing: Thermal behavior considerations

Wire arc additive manufacturing (WAAM) has become a promising metal 3D printing technology for fabricating large-scale and complex-shaped components. One major problem that limits the application of WAAM is the difficulty in controlling the dimensional accuracy under constantly changing interlayer temperatures. During the deposition process, as the wall height increases, the heat accumulates on the upper layers, which leads to the variation of the layer dimensions. Normal practices such as introducing idle time and actively cooling the workpiece to mitigate such problems lack efficiency and practicality, respectively. A novel process planning strategy is proposed in this paper and aims to achieve a continuous deposition process while ensuring dimensional accuracy. With the aid of a finite element model, the typical thermal transfer cycle of the workpiece was analyzed and then divided into different stages. When depositing material, the interlayer temperature of the subsequent layers can be predicted using the developed algorithm. Hence, the process parameters (e.g., wire feed speed and travel speed) can be varied according to the predicted interlayer temperature using the developed adaptive process model, and this will ensure the uniform layer dimensions. The effectiveness of the proposed technique is verified by a large-scale shell-shaped component with a total of 753 layers. The result shows that such technique succeeds in a continuous fabrication of the component with high accuracy and efficiency.

An Investigation of the Deep Drawing Behavior of Automotive Aluminum Alloys at Very Low Temperatures

Sheet metal aluminum alloys in the 5000 and 6000 series show increased formability if deformed at sub-zero temperatures which is beneficial for processing industries using sheet metals where evermore highly complex-shaped components are produced. In order to evaluate a cryogenic forming process, the temperature-dependent forming limits of the selected materials need to be known. For this determination, a device has been developed which allows deep drawing operations with circular specimens at cryogenic temperatures. The limiting drawing ratio (LDR) of the commercial aluminum alloys EN AW-5182 and EN AW-6016 are investigated in a temperature range from 298 K to 77 K. It is shown that the deep drawing behavior of both materials is generally enhanced at very low temperatures, although the LDR of the EN AW-6016 alloy increases only at temperatures T ≤ 77 K. Furthermore, using mathematical formulations and numerical (finite element) simulations the influence of friction on the punch forces could be predicted. The calculated results and experimental data are compared, and then subsequently discussed.

Effect of novel impact hydroforming technology on the formability of Al alloys

Currently, Aluminium (Al) alloys are increasingly used in the aerospace and automobile industries because of their outstanding properties such as lightweight and corrosion resistance properties. On the other hand, the applications of these materials are limited due to their poor formability especially at room temperature. Although hydroforming technology is one of the technique used to improve the formability of Al alloys, it still cannot fulfil the requirements of designers and manufacturers to form thin-walled complex shaped components. It has been found that high-speed forming is able to improve the formability of lightweight metals at room temperature. Thus, this investigation aims at investigating the effect of the novel technology called impact hydroforming (high-strain-rate forming) on the formability of Al alloys. Impact hydroforming (IHF) technology is proposed by combining the advantages of high-speed forming and hydroforming, and it was used to address the issues of quasi-static hydroforming. A high strain rate uniaxial tensile test was accomplished using Hopkinson tensile bar to investigate the effect of high strain rate on the formability of Al alloys. Thereafter, an IHF bulge experiment setup was developed by making use of a light gas gun which can accelerate the projectile up to 300m/s. The results show that the ductility and the formability of the Al alloy increased under high strain rate conditions, which means that the high-speed forming which is the basics of IHF technology is an appropriate method to improve the formability of Al alloys and form complex shape components.

Fatigue Crack Growth in Maraging Steel Obtained by Selective Laser Melting

Selective Laser Melting (SLM) is an additive manufacturing technology, ideal for the production of complex-shaped components. Design against fatigue is fundamental in the presence of cyclic loads, particularly for these materials which typically have significant porosity, high surface roughness and residual stresses. The main objective here is to study fatigue crack growth (FCG) in the 18Ni300 steel obtained by SLM. Typical da/dN-ΔK curves were obtained in C(T) specimens, indicating that cyclic plastic deformation may be the controlling mechanism. A complementary analysis, based on plastic CTOD range, showed a relatively low level of crack tip plastic deformation, and consequently a reduced level of plasticity induced crack closure. The curve da/dN versus plastic CTOD range is clearly above the curves for other materials.

Experimental investigation of a new low-temperature hot stamping process for boron steels

This paper demonstrates the promise of a new low-temperature hot stamping process with pre-cooling for 22MnB5 boron steels. It is the first time for the new process being successfully implemented for producing an automotive demonstrator component assisted with thorough experimental studies. The studies mainly include hot forming experiments carried out on an industrial prototyping line, post-form examinations, and in-die quenching tests. Automotive B-Pillar components with two designed drawing depths (50 and 64 mm) were hot stamped at a wide range of temperatures and forming speeds, through both the conventional hot stamping processes and the new processes with pre-cooling applied. For the as-formed B-Pillars, 3D shape scanning was conducted to investigate the thickness distribution of the components; uniaxial tensile testing, hardness testing, and scanning electron microscopes (SEM) observation were conducted to assess the final mechanical properties and microstructures. To understand the benefit of the low-temperature hot stamping in reducing cycle time, a separate set of in-die quenching experiments were designed and carried out, with combinations of three different process parameters: workpiece start quenching temperature, initial tool temperature, and die-workpiece contact pressure. The results of this work confirmed that low-temperature hot stamping could be performed successfully in producing complex-shaped components, such as automotive B-Pillars, with much reduced cycle time.

Oxidation behavior and control method in laser solid forming of Rene 104 superalloy

To meet the increasing demand for complex-shaped components in aeronautical and naval industries, laser solid forming (LSF) technology has been used in the fabrication and field repair of superalloy components. In this study, fabricating Rene 104 superalloy parts by LSF was experimentally investigated. However, a severe oxidation problem was found in the LSF Rene 104 superalloy part even if the manufacturing area was protected by shielding gas, and the oxides would badly affect the mechanical performance of the LSF part. An optical microscope, a field emission scanning electron microscope, an energy dispersive x-ray spectrometer, and an x-ray diffractometer were used to analyze the oxidation phenomenon. The experimental result demonstrated that Al2O3 and Ti2O3 were the main components of oxides in the LSF sample and the oxidation problem deteriorated when the laser power increased. The reasons for the formation of oxides were analyzed according to the results from the temperature field simulation and oxygen concentration testing experiments. To solve the oxidation problem, a new method to control oxidation was proposed and a new protection device was designed in this study. The effect of the new method was verified by experiments, and the result showed that the oxygen concentration in the manufacturing area was effectively controlled using the new protection device and the oxidation of Rene 104 superalloy was prevented. It is believed that the new protection device can replace the glove box in the fabrication and field repair of large superalloy parts.

Effect of Optimized Heat Treatments on the Tensile Behavior and Residual Stresses of Selective Laser Melted AlSi10Mg Samples

The use of additive manufacturing (AM) technique is recently increased due to its ability in producing complex-shaped components. AlSi10Mg alloy is largely employed for AM and, in particular, for selective laser melting (SLM). Hence, the interest on this alloy is growing, together with the studies to control its mechanical performances, which can be increased by microstructure modification. With this focus, low temperature heat treatments to enhance AlSi10Mg mechanical behavior have been proposed in the recent literature. The present work focuses on two post-additive thermal treatments, with temperatures specifically selected for SLMed AlSi10Mg alloy. The study investigates their effect on mechanical performances, with a particular attention to residual stresses. Experimental measurements of residual stresses obtained by an X-ray diffractometer (XRD) are presented, considering samples produced with their main dimension along the in-plane scanning directions (XY configuration) and the Z direction. Different conditions are accounted: 1) as-built; 2) after heat treatment at 244°C for 180 minutes; 3) after heat treatment at 290°C for 45 minutes. Tensile properties are correlated with the measurements of the residual stresses, allowing for a critical discussion and for a deeper insight on the correlation of the mechanical performance with the process parameters and the following thermal treatments.

Antireflection coating with consistent near-neutral color on complex-shaped substrates prepared by ALD

Color distortions of common antireflective (AR) multilayer coatings are detrimental to their appearance. These are due to the shift of the reflectance maxima toward shorter wavelengths at oblique incidence angles. Layer thickness variations of coatings on inclined surfaces of complex-shaped components additionally contribute to strong color variations. To improve the residual color consistency, a near-neutral color AR coating has been developed and deposited by atomic layer deposition (ALD) on complex-shaped substrates. This results in a uniform color appearance across the optical surface.

Basis of the Lattice Boltzmann Method for Additive Manufacturing

Additive manufacturing (or 3D printing) is constantly growing as an innovative process for the production of complex-shape components. Among the seven recognized 3D printing technologies, powder bed fusion (PBF) covers a very important role for the production of structurally functional components starting from different metal powder. However, being PBF a production process involving very high thermal gradients, non-negligible deformations and residual stresses may affect the 3D printed component. One of the characterizing aspects of PBF is the evolution of the melt pool and the heat exchange with the surrounding solid powder. In literature many attempts to simulate melt pool evolution have been carried out, however the only approaches leading to interesting results rely on the lattice Boltzmann method. In this work, starting from the Boltzmann’s equation, we derive the lattice Boltzmann equation and we introduce the needed assumptions in order to recover the lattice Boltzmann method. Finally, we apply the lattice Boltzmann method to study some interesting problems related to powder bed fusion process, including droplets wetting, thermal convection and solid–liquid phase change.

Quasi-Isotropic and Pseudo-Ductile Highly Aligned Discontinuous Fibre Composites Manufactured with the HiPerDiF (High Performance Discontinuous Fibre) Technology.

Conventional composite materials reinforced with continuous fibres display high specific strength but have a number of drawbacks including: the elastic-brittle behaviour, difficulties in producing defect-free components of complex shape with high-volume automated manufacturing processes, and inherent lack of recyclability. Highly aligned, discontinuous fibre-reinforced composites (ADFRCs) are truly beneficial for mass production applications, with the potential to offer better formability and comparable mechanical properties with continuous fibre-reinforced composites. In previous publications, the High Performance Discontinuous Fibre (HiPerDiF) technology has been shown to offer the possibility to intimately hybridise different types of fibres, to achieve pseudo-ductile tensile behaviour, and remanufacture reclaimed fibres into high-performance recycled composites. However, to date, the work has been conducted with unidirectional (UD) laminates, which is of limited interest in engineering applications with mechanical stresses acting across many directions; this paper reports, for the first time, the mechanical behaviour of quasi-isotropic (QI) ADFRCs. When compared with randomly-oriented discontinuous fibre composites (RODFRCs), QI ADFRCs offer enhanced stiffness (+26%) and strength (+77%) with higher consistency, i.e., a reduction of the coefficient of variance from the 25% of RODFRCs to the 6% of ADFRCs. Furthermore, hybrid QI ADFRCs retain the pseudo-ductility tensile behaviour previously observed in unidirectional (UD) lay-up.

Induction Skull Melting of Ti-6Al-4V: Process Control and Efficiency Optimization

Titanium investment casting is one of the leading and most efficient near-net-shape manufacturing processes, since complex shape components are possible to obtain with a very low amount of material waste. But melting these reactive alloys implies the usage of specific melting technologies such as the Induction Skull Melting (ISM) method. In this work the ISM was extensively studied with the aim of deepening the characteristics of this specific melting method and improving the too low energy efficiency and overall process performance. A 16 segment copper crucible and 3 turns coil was employed for the melting of 1 kg of Ti-6Al-4V alloy. Through the calorimetric balance, real-time evolution of the process parameters and power losses arising from the crucible and coil sub-assemblies was displayed. Results revealed the impact of coil working conditions in the overall ISM thermal efficiency and titanium melt properties, revealing the use of these conditions as an effective optimization strategy. This unstudied melting control method allowed more heat into charge and 13% efficiency enhancement; leading to a shorter melting process, less energy consumption and increased melt superheat, which reached 49 °C. The experimental data published in this paper represent a valuable empiric reference for the development and validation of current and future induction heating models.

Quality Parameters of 3D Print Products by the DMLS Method

Additive technologies are a dynamically evolving category of manufacturing methods for a wide range of industries, particularly engineering and related fields. Compared to traditional technologies based on chip machining, molding and casting, they offer new production options, particularly for complex shape components. At the same time, however, there are differences and limits that must be taken into account when designing functional machine parts. The important quality parameters of the products are in particular the dimensions and the quality of the surface. These factors are of fundamental importance for the subsequent assembly and function of a component in a plant assembly. They determine, together with the structural material properties, the usability of the component and the economic efficiency of the production in order to achieve the finished product with the minimum need for postprocessing the finished part. The submited text presents the results of the quality parameter research carried out on 3D print products made by the DMLS method, where the focus is put on the assessment of linear dimensions and the surface quality of samples from three selected materials and a combination of two print modifications. The measurement results are compared to generally valid standards and tabulated values to verify and eventually modify table values for use when designing a design solution with the use of 3D print products.

Process modelling of discontinuous long fibre carbon/polyether ether ketone composites: Defect prediction

A numerical model was developed to predict the defect formation during processing of compression moulded discontinuous long fibre carbon/polyether ether ketone composites. The model inputs are the material's temperature-dependant properties (through-thickness modulus and thermal shrinkage), the temperature distribution of the part during cooling and the applied moulding pressure. The material properties of carbon/polyether ether ketone prepreg were measured during cooling from melt using thermal analyses. The model was employed to identify regions on manufactured panels where pressure could be lost during cooling, which are prone to defect formation. Validation was performed by comparing the predicted defect areas against those found on flat panels moulded at pressures ranging from 10 to 110 bar. The model was then employed in a case study to show the importance of the cooling strategy in order to prevent defects on complex-shape components.

Alternative Process Routes to Manufacture Porous Ceramics-Opportunities and Challenges.

Porous ceramics can be realized by different methods and are used for various applications such as cross-flow membranes or wall-flow filters, porous burners, solar receivers, structural design elements, or catalytic supports. Within this paper, three different alternative process routes are presented, which can be used to manufacture porous ceramic components with different properties or even graded porosity. The first process route is based on additive manufacturing (AM) of macro porous ceramic components. The second route is based on AM of a polymeric template, which is used to realize porous ceramic components via replica technique. The third process route is based on an AM technology, which allows the manufacturing of multimaterial or multiproperty ceramic components, like components with dense and porous volumes in one complex-shaped component.

Impact of Intensification Pressure and Grain Refiner on the Hot Tearing Susceptibility of a Semi-Solid Cast Al-Zn-Mg-Cu Alloy

The commercial application of wrought aluminum alloys to semi-solid casting would be extremely beneficial, as wrought alloys often exhibit better strength-ductility combinations than cast aluminum alloys. Semi-solid casting typically reduces the hot tearing tendency, as it requires a globular microstructure and produces grain refinement, but hot tearing often still occurs during the semi-solid die casting of complex-shaped components produced from wrought alloys. This study examined the impact of intensification pressure and grain refinement on the hot tearing tendency of an Al-Zn-Mg-Cu alloy. Semi-solid slurries were produced using the SEED (Swirled Equilibrium Enthalpy Device) process. A specially designed constrained rod mold was used to evaluate hot tearing. Results showed the tendency for hot tearing decreased with increasing of intensification pressure. Grain refinement (with 0.06Ti) was also found to be beneficial to the elimination of hot tearing.

Influence of tool path strategies on the residual stress development in single point incremental forming

Abstract The prevailing residual stress state in a formed metal component highly affects its mechanical properties. The single point incremental forming (SPIF) process allows a flexible adjustment of the process parameters during the forming process to influence the residual stress state. A selective induction of compressive residual stresses in the component can improve product properties, such as the fatigue strength. The effect of the dominant forming mechanisms on the residual stress state of the manufactured component is analyzed. Linear grooves are formed into aluminum alloy 5083 sheets and their resulting residual stress state is measured by means of X-ray diffraction (XRD). The grooves are manufactured in a multiple-stage process to ensure the transferability of the results to the incremental forming process of complex-shaped components. Different unidirectional and bidirectional tool path strategies were used to analyze the residual stress development. To set the dominant forming mechanism, the process parameter step-down increment Δz was adjusted, the other process parameters were kept constant. The dominant forming mechanisms were evaluated numerically. The results suggest that the influence of the tool path strategy on the resulting residual stress amplitude is unincisive. Distinctive residual stresses can be observed in bending-dominated regions. In case of shear domination, the resulting residual stress state is less pronounced.

Forging Process Design and Simulation Optimization of a Complex-Shaped Aluminium Alloy Component

In order to meet the requirements of lightweight and replace steel with the aluminum for a component on the high speed rail, the forging process of a complex-shaped aluminum alloy component was researched and the parameters were optimized with the DEFORM-3D finite element simulation technology. The qualified products were finally obtained instead of the original steel castings by reducing weight of 65%. It is noted that the parts with complicated shape and non-symmetry, metal flow uneven during forging process that lead to incomplete forming, higher forging pressure problems. In this paper, such problems were analyzed couple with numerical simulation method based on a certain forming pressure. Moreover, the model and slot was reasonably designed. In addition, the size of blank was constantly optimized to change the metal flows direction and cavity filling mode. Finally, the forgings with good surface quality and mechanical properties were obtained by production test, and can be used as reference for this kind of forging components.

Research on the Application of MWCNTs/PLA Composite Material in the Manufacturing of Conductive Composite Products in 3D Printing.

As an advanced manufacturing technology that has been developed in recent years, three-dimensional (3D) printing of macromolecular materials can create complex-shaped components that cannot be realized by traditional processing. However, only a few types of macromolecular materials are suitable for 3D printing: the structure must have a single function, and manufacturing macromolecular functional devices is difficult. In this study, using poly lactic acid (PLA) as a matrix, conductive composites were prepared by adding various contents of multi-walled carbon nanotubes (MWCNTs). The printability and properties of MWCNT/PLA composites with different MWCNT proportions were studied by using the fused deposition modeling (FDM) processing technology of 3D printing. The experimental results showed that high conductivity can be realized in 3D-printed products with a composite material containing 5% MWCNTs; its conductivity was 0.4 ± 0.2 S/cm, its tensile strength was 78.4 ± 12.4 MPa, and its elongation at break was 94.4% ± 14.3%. It had a good melt flow rate and thermal properties, and it enabled smooth printing, thus meeting all the requirements for the 3D printing of consumables.

Feasibility study on direct flame impingement heating applied for the solution heat treatment, forming and cold die quenching technique

The solution heat treatment, forming and cold die quenching (HFQ) process has been developed and adopted for forming high strength complex-shaped components of light alloys in the automotive industry. In order to exploit and increase the competitiveness of this technology, production cycle time and manufacturing costs need to be reduced to enable high productivity and energy efficiency. This can be realised by reducing the cycle time for heating a metallic sheet to its solution heat treatment temperature during the HFQ process, and by decreasing post ageing time. Rapid heating methods are capable of providing a solution to be integrated into this novel forming technique of HFQ. This paper presents feasibility study on the adoption of the direct flame impingement (DFI) heating method that has a high potential for non-ferrous blanks to achieve higher heating rate in HFQ processes, compared to convection heating in a conventional furnace. The adaptability of DFI heating for HFQ process has been validated, in terms of capability of high heating rate, quality of surface layer examination and lap-shear strength measurement of bonded samples.