Properties Of Final Component Research Articles

Effects of varying mixing ratios of components A and B on optical liquid silicone rubber

AbstractThe processing of optical liquid silicone rubber (LSR) formulations is associated with significant quality issues and high rejection rates. Often, the quality issues can be attributed to deviations in LSR dosing. To address these issues, specific mixing ratios of components A and B that deviate from the standard 1:1 ratio were intentionally created. These mixtures were characterized via differential scanning calorimetry, rheometer, and Fourier‐transform infrared spectroscopy. The mixtures were then processed via injection molding and mechanical properties such as shrinkage, density, hardness, and tensile properties were determined and analyzed. The results show that deviating mixing ratios for optical LSR have a significant influence on processing in terms of shifts in cross‐linking temperature and exothermic energy released, viscosity, and cavity pressure, as well as on the final component properties in terms of varying shrinkage, density, hardness, tensile strength, and elongation at break. This study shows that even small deviations have a major influence and should therefore be avoided. The requirements for the accuracy of the dosing system with regard to the mixing ratio must therefore be very high. In practice, such deviations in the mixing ratios are most likely to be detected in geometry via shrinkage, hardness, or tensile properties.Highlights More component A leads to faster but less dense cross‐linking Component B can be characterized by Fourier‐transform infrared spectroscopy via Si–H bending band at 905 cm−1. More component B leads to higher shrinkage, density, hardness, and strength. Deviations in the mixing ratio must be avoided as they lead to drastic changes. A general shift of the mixing ratio in favor of component B is less dramatic.

Layer thickness influence on impact properties of FDM printed PLA material

Polylactic Acid (PLA) is a widely used material in Fused Deposition Modeling (FDM) technology. Additive Manufacturing (AM) parameters are known to have an influence on the mechanical properties of final components. In FDM, the layer thickness is an influencing parameter providing overall better mechanical properties with lower layer thickness values. In that case, the air gaps created between layers and raster lines have a lower share in total volume. However, layer over-compression might be an issue when choosing the lowest layer thickness options. This research paper investigates the impact properties of PLA material with variations in layer thickness namely, 0.1, 0.2, and 0.3 mm are considered here. Charpy tests were used for the impact property assessment, and all specimens were prepared with 100% infill percentage and honeycomb infill structure. Worth mentioning is that specimens have AMed notches. The impact tests were carried out on 7 specimens per batch (a total of 21 specimens). Therefore, obtained impact results from an instrumented pendulum were observed between groups to have an insight into the beneficial influence of lower layer thickness on impact properties and lower result scatter that finer layer resolution should produce.

Effect of Heat Treatments on Microstructure and Mechanical Properties of Nitinol Prototype Stents Produced by Laser Powder Bed Fusion

Laser Powder Bed Fusion (L-PBF) is turning out to be very promising for biomedical components production and stents are among the devices that would be suitable for tailor-made production. One of the most common stent types are the self-expandable, manufactured with Nitinol (NiTi). The use of NiTi alloy with L-PBF needs to be well controlled, as Ni evaporation during the process leads to significant variations in the final component properties. In the present work, prototype NiTi stents were produced via L-PBF and heat treated to examine the possibility of employing this technology for their application, also considering the Ni evaporation resulting from the layer-by-layer deposition. Samples were characterized through differential scanning calorimetry (DSC), microstructural observations, and compression tests in plate-to-plate configuration according to the standard. In parallel, a commercially available stent manufactured with traditional technology was tested for comparison.

On the three‐dimensional numerical analysis of residual stresses on two scales in hot bulk forming parts

AbstractCurrent research focuses on the induction of residual stresses in a component during its manufacturing process, which shows a significant impact on the final component's properties. During the manufacturing of a hot bulk forming component, the temperature evolution allows to influence the resulting residual stress state efficiently and purposefully. Following the characterization of residual stresses on different scales, single‐scale finite element simulations are carried out on macro‐ and microscale. In contrast to previous findings for two‐dimensional boundary value problems, the effects of the third dimension are demonstrated. Furthermore, it is shown that the residual stress distribution is effectively influenced by choosing different cooling routes in targeted manner. Eventually, the importance of microscopic residual stress investigations is discussed.

Elasto-Plastic Mechanical Modeling of Fused Deposition 3D Printing Materials

Fused deposition modeling (FDM) is one of the most common 3D printing technologies and is becoming a well-established production method. Short fiber-reinforced polymers represent a new class of printing materials that enhance the mechanical properties of final components, thus informing an interesting subject of analysis for this study. FDM-printed parts are characterized by a strong anisotropy, so their behavior should be analyzed accordingly. The authors proposed a modeling strategy based on a transversely isotropic behavior hypothesis, representing material behaviors associated with an elasticity matrix in relation to the elastic field and a combination of Hill's yield criterion and Voce's isotropic hardening law for the plastic field. Material properties of materials were experimentally identified through tensile tests on dog bone specimens printed with different orientations in space. The numerical model was then calibrated using the finite element software LS-DYNA and the optimization software LS-OPT. An agreement between numerical and experimental results showed the robustness of the modeling strategy proposed to describe the stress behaviors of printed materials until a maximum load is reached, while strain behaviors have yet to be correctly defined due to the difficulties associated with evaluating an equivalent deformation.

Investigation of the Influence by Size Effects on the Material Characterization of the Uniaxial Compression Stress State

For the evaluation of final component properties under consideration of production-induced material characteristics, it is necessary to determine the mechanical parameters of parts and structures. Thus, there is a need of new test methods for the material characterization and quality control of produced goods. The miniaturization of the test specimens offers the potential for the local testing of the material properties at almost any position on the component. However, due to the reduction in size of the test specimens, size effects can occur which may affect the material behavior. For this reason, this contribution analyses the influence of size effects on the derived material parameters in dependence of the specimen size and material by using upsetting tests according to DIN 50106:2016 standard. The materials Cu-OFE (copper), X5CrNi18-10 (stainless steel) and AA7075-T6 (aluminum) are investigated to ensure a broad transferability of the findings. The specimens are cut from a bar stock by using a high precision 3D micro electrical discharge milling machining. Due to the small size, every specimen is measured with an optical 3D coordinate measuring system to determine the exact size. Through these investigations, the reproducibility and scatter in the determination of material properties for scaled cylindrical upsetting specimens are evaluated. Furthermore, limits of geometric dimensions at constant aspect ratios are derived. The results of this investigation enable an estimation of the geometrical influence of the specimen size in regard to the mechanical properties.

Numerical modelling of equiaxed dendritic growth with sedimentation in the melt of binary alloys by using an anisotropic lattice Boltzmann-phase field model

An anisotropic lattice Boltzmann-phase field (LB-PF) model is developed to simulate the equiaxed dendritic growth with sedimentation in the melt of binary alloys under the effect of gravity. In present model, the anisotropic lattice Boltzmann scheme is applied to solve the phase field equation describing the evolution of dendritic morphologies, while the finite volume scheme is employed to solve the advection–diffusion equation of solute with anti-trapping current. The multiple-relaxation-time lattice Boltzmann scheme is employed to compute the complex melt flow. Validity of the present model is demonstrated by the quantitative agreement between the references and simulations of circular particle sedimentation, while the shape preservation performance is verified by the simulations of non-deformation dendrite movement. Then, the effects of solid–liquid density ratio, initial supersaturation and preferred crystallographic orientation on the growth and sedimentation behaviour of a single equiaxed dendrite in the supersaturated melt of binary alloys are numerically investigated. Moreover, the growth and sedimentation process of dendrites with multiple nuclei is successfully simulated. The results demonstrate that the present model has great application potential in the simulations of dendritic growth with sedimentation of binary alloys, which has important instructional significance for regulating the microscopic dendritic morphologies during solidification, and further improving the macroscopic mechanical properties of final components.

Induction coil as sensor for contactless, continuous in-process determination of steel microstructure by means of Magnetic Induction Spectroscopy (MIS)

In hot forming and machining process chains heat treatment of steels is controlled by temperature and time. The process parameters significantly influence the material microstructure, which is important for the final component properties. The dependence between the predominant microstructure and the magnetic properties can be determined by means of Magnetic Induction Spectroscopy (MIS). In this paper, we propose to use the induction coil as an in-process sensor element to implement MIS in induction heating processes with subsequent cooling of steel sheets. This novel approach enables contactless, continuous in-process measurement of complex inductance and allows a non-destructive determination of steel microstructure. The novel measurement method can differentiate discrete microstructural states and determine phase transformation points during continuous heating and cooling, by analysing the inductance curve. The realized combination of sensor and actuator features enables both process monitoring and closed-loop control of production processes with integrated heat treatment.

Microstructure and mechanical properties of forging-additive hybrid manufactured Ti–6Al–4V alloys

The forging-additive hybrid manufacturing technology has combined the advantages of traditional manufacturing in efficiency and cost with those of additive manufacturing in flexibility and rapid prototyping, thus can provide an effective solution for the efficient forming of large and complex components. In this kind of manufacturing technology, the heat affected zone (HAZ, also called as bonding zone) between the wrought substrate zone (WSZ) and the laser deposition zone (LDZ) is the key to the properties of final components. In this study, the powder-feeding laser additive manufacturing technology was employed to deposit bulk samples on a wrought Ti–6Al–4V substrate containing bimodal microstructures. The microstructures and mechanical properties of hybrid manufactured Ti–6Al–4V alloys were studied with emphasis on the HAZ. The results show that, due to the different history of thermal, a graded microstructure was formed from the bottom to the top of HAZ. The bimodal microstructure at the bottom-HAZ gradually transformed to a mixed structure contained equiaxed α, lamellar α, and a large number of secondary α in the middle-HAZ, while the top-HAZ exhibits Widmanstätten structures consisting lamellar α and the so-called ghost structures due to the insufficient diffusion of alloying elements. The measurement of mechanical properties shows that, the sample with bonding zones presents higher tensile strength and yield strength, but lower elongation than those without bonding zones (WSZ or LDZ). The fracture positions of all samples with bonding zones are in WSZ and far away from HAZ, indicating a better strength of bonding zone than that of the wrought substrate and the laser deposition part due to the formation of secondary α and fine lamellar α in HAZ.

Dynamic and Post-Dynamic Recrystallization of Haynes 282 below the Secondary Carbide Solvus

Thermomechanical processes, such as forging, are important steps during manufacturing of superalloy components. The microstructural development during processing, which controls the final component properties, is complex and depends on e.g., applied strain, strain rate and temperature. In this study, we investigate the effect of process parameters on the dynamic and post-dynamic recrystallization during hot compression of Ni-base superalloy Haynes 282. Specifically, we address the effect of deformation below the grain boundary carbide solvus temperature. During deformation, discontinuous and continuous dynamic recrystallization was observed at the grain boundaries, and particle-stimulated nucleation occurred at primary carbides. Strain rate was determined to be the governing factor controlling the recrystallization fraction for strain rates up to 0.5 s−1 above which adiabatic heating became the dominating factor. Careful examination of the temperature development during deformation showed that the response of the closed-loop temperature control system to adiabatic heating can have important effects on the interpretation of the observed behavior. During a 90 s post-deformation hold, grain growth and an increasing fraction of twin boundaries significantly changed the deformation-induced microstructure and texture. The microstructure developed during post-dynamic recrystallization was mainly controlled by the temperature and only weakly coupled to the prior deformation step.

A numerical study of the effect of phase evolution on residual stresses during cooling

AbstractThe consideration of residual stresses in forming processes is a promising opportunity to influence the final component's properties in a positive manner. Instead of their minimization, a targeted application of residual stresses can extend life time or durability and enhance manufacturability of metallic components. For this reason, detailed experimental and numerical analyses are an object of current research. Here, the cooling process is simulated in order to analyze the influence of the microscopic phase evolution on the macroscopic stress distribution in a cylinder with eccentric hole made of steel 100Cr6.

New Developments and Future Trends in Low-Temperature Hot Stamping Technologies: A Review

Improvement of the hot stamping process is important for reducing processing costs and improving the productivity and tensile properties of final components. One major approach to this has been to conduct all or part of the process at lower temperatures. The present paper reviews the state of the art of hot stamping techniques and their applications, considering the following aspects: (1) conventional hot stamping and its advanced developments; (2) warm stamping approaches in which complete austenitisation is not attained during heating; (3) hot stamping with a lower forming temperature, i.e., low-temperature hot stamping (LTHS); (4) advanced medium-Mn steels with lower austenitisation temperatures and their applicability in LTHS. Prospects for the further development of LTHS technology and the work required to achieve this are discussed.

High deposition wire arc additive manufacturing of mild steel: Strategies and heat input effect on microstructure and mechanical properties

Abstract Wire Arc Additive Manufacturing (WAAM) is a layer-by-layer production concept that is proposed as a promising alternative to traditional subtractive techniques due to its potential to manufacture large metallic components of medium geometrical complexity. In recent years, this technology has created interest due to the advantages it proposes, such as a low cost and high deposition rates in comparison with other Additive Manufacturing (AM) techniques. In this study, the Gas Metal Arc Welding (GMAW)-based WAAM system was developed to deposit mild steel material. To that end, a comprehensive methodology to understand the main process variables and their influence in the final component properties is shown. The aim of the present study was to compare the influence of oscillatory and overlapping deposition strategies in terms of productivity, growth per layer, obtained microstructure and mechanical properties using the control volume concept to compare volume-dependent parameters. Although some characteristics of these strategies have been documented in literature, the heat input influence has not yet been comprehensively demonstrated and understood. For example, heat input, analyzed deeply in the present study, is a critical factor for the stability of the WAAM process, influencing the mechanical properties and microstructural evolution of as-fabricated parts. The results indicate that the oscillated strategy increases productivity.

Characterization of Hot Deformation Behavior and Dislocation Structure Evolution of an Advanced Nickel-Based Superalloy

The hot deformation behavior of an advanced nickel-based Haynes282 superalloy was systematically investigated employing isothermal compression tests in the sub-solvus and super-solvus temperature with various strain rates. The influence of deformation temperature and strain rate on the microstructure was studied by transmission electron microscope. The results reveal that the interaction between work hardening and dynamic softening did not reach equilibrium under lower deformation temperature and higher strain rate. The active energy of alloy is around 537.12 kJ/mol and its hot deformation constitutive relationship equation was expressed. According to the processing map and microstructure observations, two unsafe flow instability domains should be avoided. The optimum hot processing condition for homogeneous and fine dynamic recrystallization grains are obtained. TEM micrograph observations indicated that deformation temperature and strain rate affected recrystallization by affecting the evolution of dislocation substructures within the alloy. The nucleation and growth of DRX grains can be promoted by the relatively high deformation temperature and low strain rate. The main mechanism of dynamic recrystallization nucleation preferred to discontinuous dynamic recrystallization and the typical feature of discontinuous dynamic recrystallization showed grain boundary migration nucleation. The findings improve the understanding of hot deformation behavior and dislocation substructures evolution of the superalloy, which benefits the accurate control of microstructures of nickel-based superalloys, and tailors the properties of final components used in the land-based gas turbine.

An Innovative Approach on Directed Energy Deposition Optimization: A Study of the Process Environment’s Influence on the Quality of Ti-6Al-4V Samples

Blown powder additive manufacturing technologies are not restricted to the use of a process chamber. This feature allows to build larger components with respect to conventional powder bed processes. This peculiarity is mostly promising for manufacturing large components or repairing/rebuilding parts of large systems. The main downside of using an open environment, even if a protective shielding gas system is adopted, is the lack of control of process atmosphere. This is particularly critical for titanium alloys which are very sensitive to oxygen/nitrogen pick-up; they have a detrimental effect on ductility, by causing embrittlement and possibly leading to the formation of cracks. It is then important to address how environmental factors, such as process atmosphere and platform temperature, impact not only on the processability but also on the final component properties, both from a compositional and mechanical point of view. The correlations between these environmental factors and microstructure, interstitials content, grain size, and hardness were investigated. Moreover, the Hall–Petch equation was then adopted to additive manufacturing microstructures, characterized by a columnar grain morphology, and used to further investigate the relationship intercurring between grains and hardness and how different microstructures might influence this correlation.

Phase transformation and grain growth behaviors of superalloy IN718 during heat treatment

The morphology of phase and grain of superalloy IN718 are important for the properties of final components as well as the forming process with repeated heating. Phase transformation and grain growth behaviors of IN718 at 920℃-1080℃ were studied by XRD and SEM. A model of volume fraction and size evolution of phases δ, γ′ and γ″ was established and used to predict the effect of phase transformation on the concentration of solute elements in the matrix. Based on the phase transformation model, a grain growth model of IN718 was established with consideration of solute drag and phase pinning effects. It was found that the drag effect of Mo and Nb is greater than that of the phase δ due to the 1.7 % phase δ content in the as-received alloy. The effect of phase δ content on grain growth was then studied by increasing the volume fraction of phase δ without change of grains. It was found that the needle-like phase δ has greater hindrance than short rod-like phase δ on grain growth and needs a correction coefficient for it in the grain growth model. The research provides a good understanding and develops a reliable method to design heat treatment process.

DDRX and CDRX of an as-cast nickel-based superalloy during hot compression at γ′ sub-/super-solvus temperatures

Taking the importance of γ′ phase into consideration, an as-cast nickel-based superalloy was investigated by uniaxial compression experiments performed at sub-solvus and super-solvus temperatures. Several different strains were utilized to trace the processes of deformation and microstructural evolution. Electron backscatter diffraction was employed to characterize the microstructures. The results reveal that the volume fraction of DRX grains increased with strain at both sub-solvus and super-solvus temperatures, and also the fraction of high angle grain boundaries. Meanwhile, both the correlated and uncorrelated misorientations gradually approached the random distribution curves during continuous strains. Specially, the fast migration of grain boundaries caused by the unpinning from γ′ particles promoted twin nucleation and generated a number of twins at sub-solvus temperatures. Sub-solvus deformations were found to be more efficient to weaken the initial textures of as-cast superalloys. Finally, it was confirmed that discontinuous dynamic recrystallization (DDRX) dominated the DRX process during the hot deformation carried out at both sub-solvus and super-solvus temperatures. Continuous dynamic recrystallization (CDRX) was the second mechanism, and played a very important role during plastic deformation at sub-solvus temperatures, which is different from the DRX mechanisms reported in the fine-grain structures of wrought billets. The findings improve the understanding of DDRX and CDRX, which does benefit to the accurate control of microstructures of nickel-based superalloys, and also tailoring the properties of final components used in aero-engine.

Thermal contact conductance estimation and experimental validation in hot stamping process

The variation in temperature of the blank would make major contribution to the mechanical properties of final component in hot stamping of ultra high strength steel (UHSS). It is important to use accurate thermal contact conductance (TCC) to carry out finite element simulation of hot stamping for reliable caculation results. In this paper, a flat compression test was performanced on a servo press. A fast response temperature measurement and data acquisition system was designed to obtain the temperature history of blank and die under different pressures. The thermal contact conductance between blank and die was got using an optimization algorithm. The error between the temperature curves using calculated thermal contact conductance and the curves of measurement temperature was analyzed. Result shows that reliable simulation results of temperature can be got through accurate thermal contact conductance.

Using Raman spectroscopy to monitor surface finish and roughness of components manufactured by selective laser sintering

AbstractSelective laser sintering (SLS) is an additive manufacturing process used to realise fully functional component manufacture. Numerous parameters are used in the process to control variables such as laser power, scan speed, laser spot size and overlap of scan vectors. All of these parameters can dramatically alter the sintering process and therefore final component properties. This paper presents how Raman spectroscopy intensity effects, caused by the surface roughness of the components produced, can be used to monitor the degree of sintering between particles in the SLS process. Copyright © 2010 John Wiley & Sons, Ltd.

Simulation of Integrated Heat‐treatment of Precision Forged Components

Precision forging with integrated heat-treatment (cooling from the forging temperature by means of spray cooling) is an innovative process for manufacturing high performance components such as surface hardened and tempered gear wheels. Using a process chain which is shortened in comparison with conventional process sequences, production times can be lowered and processing energy can be saved. With respect to the work piece, a numerical computation of the process steps from precision forging, quenching and tempering from the residual heat can be performed to support the process design. Here, the aims are to predict suitable process parameters and mechanical properties of final components. In the following, the modelling approach exemplified using of a gear wheel of hardening and tempering steel 42CrMo4 is to be introduced which is employed for the collaborative research centre 489 “Process chain for manufacturing precision forged high performance components” at the Leibniz Universitat Hannover. Microstructure developments, as e.g. recrystallisation, grain growth and microstructural transformations, as well as mechanical properties due to tempering by the residual heat are considered for this process using the commercial finite element software ANSYS®. For this purpose user specified sub routines were developed to enhance the capabilities of ANSYS® by the application of the Ansys Parametric Design Language (APDL) and User Programmable Features (UPF), respectively. Results of the computation can be verified by micrographs and hardness measurements.