Manufacturing Process Parameters Research Articles

Densification behavior of monolithic SiC fabricated by pressureless liquid phase sintering method

As a preliminary investigation of process development for SiC fiber-reinforced SiC matrix composites (SiCf/SiC composites) via a pressureless liquid phase sintering (PLPS) method, the manufacturing process parameters of monolithic SiC fabricated with/without very low pressure during the sintering under high temperature (1850 and 1900 °C) were optimized. Two kinds of sintering additive system (only Al2O3 and Al2O3–Y2O3 mixtures) can be achieved full densification corresponding to 99% of the theoretical density without high pressure during the sintering. Monolithic SiCs of both sintering additive systems applied with prepressure of 20 or 40 MPa possessed the flexural strength and porosity comparable to those of conventional liquid-phase sintered SiC with high pressure during the sintering. The low pressure (0.63 MPa) during sintering reduced the densification in particular for the materials sintered with just Al2O3. The additions of BN particles led to a gradual decrease in mechanical strength with an increase in porosity.

Additive manufacturing of polyaniline electrodes for electrochemical applications

Polyaniline (PANI), particularly in its emeraldine salt form (PANI-ES), possesses several desirable properties such as high tuneable conductivity, pseudocapacitance and chemical stability, which make PANI a promising material for a wide range of electrochemical applications. However, its use is severely limited by its poor processability due to its non-thermoformable nature. In this work, a novel additive manufacturing method to process PANI is introduced, which enables the fabrication of electrodes with complex geometries exhibiting conductivities of up to 20000 mS/cm. This novel additive manufacturing process is based on the thermal doping of PANI in its low-conductive emeraldine base form (PANI-EB) with dodecyl benzene sulfonic acid (DBSA). For this purpose, a commercially available 3D printer was modified with a custom-made syringe extrusion system to enable the extrusion of a viscous PANI-EB/DBSA paste. The influence of the additive manufacturing process parameters on the conductivity of printed electrodes was evaluated, and the resulting printed materials were characterised by Fourier-transform infrared spectroscopy – attenuated total reflection, X-ray powder diffraction, thermo-gravimetric analysis and scanning electron microscopy. The feasibility of the 3D printed PANI-ES/DBSA electrodes was studied by conducting a proof-of-concept electrochemical study of 3D printed interdigitated symmetric electrochemical capacitors, demonstrating how the printed structures could be easily integrated in prototypes of electrochemical devices. Although the fabricated devices did not exhibit superior capacitance, they presented a memristive behaviour with a potential for other applications such as artificial neural networks. Moreover, the results of this proof-of-concept study illustrate the significant importance of the conductivity of the printed electrodes, hence the importance of the additive manufacturing process parameters on the electrochemical performance.

Effects of the Pre-Consolidated Materials Manufacturing Method on the Mechanical Properties of Pultruded Thermoplastic Composites

The choice of a manufacturing process, raw materials, and process parameters affects the quality of produced pre-consolidated tapes used in thermoplastic pultrusion. In this study, we used two types of pre-consolidated GF/PP tapes—commercially available (ApATeCh-Tape Company, Moscow, Russia) and inhouse-made tapes produced from commingled yarns (Jushi Holdings Inc., Boca Raton, FL, USA)—to produce pultruded thermoplastic Ø 6 mm bars and 75 mm × 3.5 mm flat laminates. Flat laminates produced from inhouse-made pre-consolidated tapes demonstrated higher flexural, tensile, and apparent interlaminar shear strength compared to laminates produced from commercial pre-consolidated tapes by as much as 106%, 6.4%, and 27.6%, respectively. Differences in pre-consolidated tape manufacturing methods determine the differences in glass fiber impregnation and, thus, differences in the mechanical properties of corresponding pultruded composites. The use of commingled yarns (consisting of matrix and glass fibers properly intermingled over the whole length of prepreg material) makes it possible to achieve a more uniform impregnation of inhouse-made pre-consolidated tapes and to prevent formation of un-impregnated regions and matrix cracks within the center portion of the fiber bundles, which were observed in the case of commercial pre-consolidated tapes. The proposed method of producing pre-consolidated tapes made it possible to obtain pultruded composite laminates with larger cross sections than their counterparts described in the literature, featuring better mechanical properties compared to those produced from commercial pre-consolidated tapes.

Chance-constrained robust co-design optimization for fuel cell hybrid electric trucks

The co-design optimization that simultaneously couples embodiment design and control design is widely applied in fuel cell hybrid electric vehicles. However, due to imperfect manufacture process, modeling simplification and uncertain parameters during vehicle operation, the optimal results obtained from a deterministic co-design optimization might not be robust to variations of parameters and optimization variables. This paper introduces a chance-constrained robust co-design optimization framework, where the chance constraint firstly translates into a deterministic constraint. The robust objective is computed as a function of the second-order approximated mean and inequality constraints are computed by shifting 3 times of their standard deviations inside of deterministic bounds. The vehicle movement in long-haul trucking application is considered as an uncertain parameter and the propagation of uncertainties to state variables are also illustrated with considerations of uncertainties in design decision variables. A deterministic and stochastic co-design problem are formulated and decomposed into two steps, i.e. electric machine sizing and sizing of fuel cell and battery as well as the energy management. A case study of a fuel cell hybrid electric long-haul truck indicates the importance of the robust approach in the joint component sizing and energy management. The uncertainties of the truck movement results in uncertainties of the battery energy and power, leading to a bigger battery capacity. The energy capacity is around 2.34 times higher than that without considering uncertainties.

Risk Analysis Method by the Extreme Data of Dependent Exogenous Variables

Many practical tasks of data multivariate statistical analysis from the standpoint of a risk-oriented process approach (in accordance with ISO 9001: 2015, 31000: 2018) requires the definition of the risk values for the dependent exogenous variables of some processes. This paper proposes the method, which consist of original stages sequence for calculating value-at-risk (VaR) or conditional-value-at-risk (CVaR) of dependent exogenous variables, presented of the extreme data frame of critical manufacture process parameters or other parameters, for example, extreme data of environmental monitoring and etc. Risk analysis method by the extreme data of dependent exogenous variables, presented of the data matrix, uses the result of solving the formalized problem of defines the tails parameters of the joint distributions of exogenous variables as components of a bivariate random variable. It can be argued that the tails parameters of the joint distributions of dependent exogenous variables make the validated corrections of the VaR and CVaR estimates for such variables. This method expands the practical application of extreme value theory for the value at risk analysis of any dependent variables as process parameters.

Filament Transport Control for Enhancing Mechanical Properties of Parts Realised by Fused Filament Fabrication.

The fused filament fabrication (FFF) process is widely used for producing prototypes and functional parts for diverse applications. While FFF is particularly attractive due to its cost-effectiveness, on the other hand, the fabricated parts have limitations in terms of large manufacturing time and reduced mechanical properties. The latter is strongly influenced by the fabrication process parameters, which affect the interlayer bonding and the adhesion between consecutive layers. Several works presented in the literature analysed the correlation between mechanical properties and process parameters. It was demonstrated that an increase in the fabrication feed rate causes slippage between filament and the feeding system, which leads to a decrease in the extruded material flow, and thus in part density. This work aims to investigate how the limitation of the slippage phenomenon affects the mechanical properties of parts fabricated using the FFF process. A prototype machine, equipped with a closed-loop control system on filament transport, was used to fabricate samples for tensile tests and dynamical mechanical analysis. Samples fabricated enabling the filament transport control showed an increase both in ultimate tensile strength and elongation at break for those fabricated with disabled control, whilst a decrease in stiffness was observed. In addition, the results showed that the use of a filament transport control system on a FFF machine increases the possibility of fabricating high value-added parts.

Pure tantalum manufactured by laser powder bed fusion: Influence of scanning speed on the evolution of microstructure and mechanical properties

To improve the performance of pure tantalum manufactured by selective laser melting (SLM) and meet its application requirements in medicine and industry, this paper studied the influence of SLM process parameters on the as-built surface morphology and mechanical performance, and successfully obtained a sample with a relative density of over 99%, ultimate tensile strength of 706Mpa and fracture elongation over 32%. It's found that the scanning speed has a significant influence on the microstructure. Moreover, the fractured morphology shows that it is easy to cause cracks at the lower energy density. However, at a higher energy density, it is easy to induce defects such as keyhole induced pores. The appropriate process parameters of additive manufacturing matching the pure tantalum with higher relative density and better mechanical properties have precious value for its application in medicine and industry.

Evaluation of HCF strength of Alloy 625 with non-optimum additive manufacturing process parameters

An extensive experimental program was undertaken to generate the process-structure-HCF property data for additive-manufactured Alloy 625. Round tensile and flat dog-bone HCF specimens were fabricated using a laser powder bed fusion process. Several builds were fabricated with different processing parameters. The fatigue strengths were determined using a step-test method and fracture surfaces were characterized to identify the critical microstructure feature associated with the formation of the fatigue crack. A fracture mechanics-based methodology using fatigue crack growth data measured on a wrought alloy is shown to provide conservative estimates of the HCF lives for the additive-manufactured alloy.

Influence of machining parameters on fretting fatigue life of Inconel 718

This work focuses on the analysis of the influence of different machining factors on the fretting fatigue behaviour of Inconel 718. Fretting fatigue tests using a flat-to-flat with rounded edges contact were carried out using specimens with different manufacturing process parameters. The results pointed out the high impact that machining parameters possess in the Inconel 718 fatigue lifetime. Tool wear has shown to be the most significant parameter. Residual stresses measured along the direction of fatigue load have proved to be a relevant indicator of the fretting fatigue behaviour. Lastly, surface roughness has been shown to possess a weaker influence.

Fabrication and Formability of Continuous Carbon Fiber Reinforced Resin Matrix Composites Using Additive Manufacturing

In the current process for additive manufacturing of continuous carbon fiber reinforced resin matrix composites, the fiber and resin matrix are fed into the molten chamber, and then impregnated and compounded in the original position, and finally extruded and deposited on the substrate. It is difficult to control the ratio of fiber and resin, and to achieve good interface fusion, which results in an unsatisfactory enhancement effect. Therefore, an additive manufacturing process based on continuous carbon fiber reinforced polylactic acid composite prepreg filament was explored in this study. The effects of various process parameters on the formability of composites were studied through systematic process experiments. The results showed that the process parameters of additive manufacturing have a systematic influence on the forming quality, accuracy and efficiency, and on the mechanical properties of CFRP. Through the experimental optimization of various process parameters, a continuous and stable forming process was achieved when the nozzle aperture was 0.8 mm, the nozzle printing temperature was 240 °C, the substrate temperature was 60 °C, the wire feeding speed was 5 mm/s, the nozzle moving speed was 5 mm/s, the path bonding rate was 40%, and the printing layer thickness was 0.7 mm. Based on the optimized process parameters, direct additive manufacturing of a lightweight and high-strength composite cellular load-bearing structure could be realized. Its volume fraction of carbon fiber was approximately 7.7%, and the tensile strength was up to 224.3 MPa.

Pico-washing: simultaneous liquid addition and removal for continuous-flow washing of microdroplets

Droplet microfluidics is based on a toolbox of several established unit operations, including droplet generation, incubation, mixing, pico-injection, and sorting. In the last two decades, the development of droplet microfluidic systems, which incorporate these multiple unit operations into a workflow, has demonstrated unique capabilities in fields ranging from single-cell transcriptomic analyses to materials optimization. One unit operation that is sorely underdeveloped in droplet microfluidics is washing, exchange of the fluid in a droplet with a different fluid. Here, we demonstrate what we name the “pico-washer,” a unit operation capable of simultaneously adding fluid to and removing fluid from droplets in flow while requiring only a small footprint on a microfluidic chip. We describe the fabrication strategy, device architecture, and process parameters required for stable operation of this technology, which is capable of operating with kHz droplet throughput. Furthermore, we provide an image processing workflow to characterize the washing process with microsecond and micrometer resolution. Finally, we demonstrate the potential for integrated droplet workflows by arranging two of these unit operations in series with a droplet generator, describe a design rule for stable operation of the pico-washer when integrated into a system, and validate this design rule experimentally. We anticipate that this technology will contribute to continued development of the droplet microfluidics toolbox and the realization of novel droplet-based, multistep biological and chemical assays.

Optimization of MWCNTs/Al nanocomposite fabrication process parameters for mass density and hardness

Engineering materials and their development are essential for a civilized society, and they have always played a key role in the industrialization of a country. The performance of materials can be increased by selecting appropriate fabrication process parameters. In this paper, the effect of fabrication processing parameters on multi-responses of lightweight material, namely, functionalized multiwalled carbon nanotubes-aluminum nanocomposite have been investigated through Taguchi-based grey relational analysis. Ethanol wt. %, milling time, compaction pressure, and sintering temperature were considered controlled parameters. Phase, surface morphology, and chemical compositions of the nanocomposite have been analyzed by X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray techniques. The scanning electron microscope images revealed that the optimal parameter combination is essential for decreasing void and crack formation during the powder metallurgy process and increasing the material performance index. Grey relational analysis was performed to evaluate optimal sample fabrication processing parameters by using grey relational grade as performance index measurement. The most influential parameter was investigated using main effect plots, interaction plots, contour plots, and analysis of variance. The results show that the optimal combination of sample fabrication parameters is A1B2C3D3. The results also show that the compaction pressure has a stronger correlation to the responses with a 46.92% contribution followed by sintering temperature. The % error between the predicted and experimental grey relational grades at the optimum-level combination is 1.83%. The Monte Carlo simulation data distribution plots show that the ranges of experimental mass density and hardness values are consistent with estimated simulated model values. Further, a regression equation has also been developed to establish the predictive model for the grey relational grade. The model analysis shows that the predictive model is adequate for evaluating grey relational grades. Therefore, this study confirms that the proposed approach can be a useful tool for improving materials’ performance.

Evaluation of the effects of the print parameters in additive manufacturing process for dimensional control of printed parts using a traceable coordinate measuring machine

Until now, selective laser melting (SLM) process has become more extensive as one of the useful additive manufacturing (AM) techniques. During the course of AM process, there are a number of print parameters (e.g., laser power, hatch spacing, scanning speed, powder layer thickness, scanning strategy, beam offset, X-axis scaling , Y-axis scaling and Z-axis scaling and etc) affecting the dimensional accuracy of final part printed. Among these parameters, four print parameters (beam offset, X-axis scaling, Y-axis scaling and Z-axis scaling) have direct effects. The aim of this study is to investigate the influence of the four SLM print parameters on dimensional accuracy of parts fabricated from Inconel 718 alloy. Specific artefacts were designed for AM process and related measurements were conducted using a high accurate coordinate measuring machine (CMM) traceable to the International System of Units (SI) of metre. The CMM measured results were analyzed to demonstrate how the four print parameters result in dimension variation due to adjustment of the print parameters. It was found both external and internal diameters of the artefact are changing in an opposite direction with the beam offset setting. The measured results show: (1) there is a good linearity of the dimensions (6 mm to 30 mm) to a beam offset within ± 0.1 mm. The 0.1 mm change of beam offset could systematically introduce 0.2 mm change in external and internal dimensions; (2) both linear dimension and form error (e.g., cylindricity) are sensitive to the X-axis scaling , Y-axis scaling and Z-axis scaling. The dimensional accuracy of AM printed parts could be optimized by the adjustments of these setting parameters in AM machine.

The manufacturing process optimization and the mechanical properties of FeCoCrNi high entropy alloys fabricated by selective laser melting

The quality of metal parts fabricated by selective laser melting (SLM) is strongly depended on the manufacturing process parameters. The establishment of relationship between manufacturing parameters and the formability is the effective way to obtain forming parts with high density, defect-free and excellent mechanical properties by SLM. In this study, the effect of SLM process parameters on the relative density (RD) and mechanical properties of FeCoCrNi high entropy alloys (HEAs) were systematically investigated, involving single tracks, single layers and block samples. By optimizing the laser power, scanning speed and hatching space, the highest RD of 99.85% was obtained under the moderate energy density of 95.24 J/mm3, with no defect as prosity, cracks, un-melted powders and spheroidization under other SLM parameters. The tiny changes in RD significantly affected the mechanical properties of FeCoCrNi HEAs. The highest RD sample corresponded to the optimal comprehensive mechanical properties of 585 MPa in yield strength, 714 MPa in ultimate strength and 45.30% in elongation. The elevation of mechanical properties attributed to the high RD, defect-free, grain refinement and the unique cellular substructure.

Vibration suppression using tuneable flexures acting as vibration absorbers

Vibration suppression is an area of engineering that is vital for the development of manufacturing of low stiffness structures. A diversity of passive, active and semi-active vibration control techniques exist in the literature, many of them focused on the tool or the workpiece, while little attention has been paid into the dissipation capabilities of the fixtures. In this paper, the vibration attenuation capabilities of tuneable flexures are presented, proving the ability of beam-shaped supports to mitigate the vibration induced by the manufacturing process (e.g. machining loads) to the workpiece. The proposed modelling approach puts a solid theoretical basis on how to construct flexures tuned in such a way to allow their natural frequency to match the frequency of excitation, thus absorbing the energy from the workpiece and keeping it at low vibration levels. By means of a multiple-degree-of-freedom (MDOF) model and considering the system as three different bodies with springs and dampers, the dynamic behaviour of the system is examined theoretically starting from the geometry and material of the flexures on which the fixturing system is based. This is further validated with finite element analysis (FEA) as well as experimental results showing a low discrepancy between the models on the prediction of the resonant frequencies of up to a 0.6%. The importance of understanding the critical clamping load for the locking of the contact surfaces is also presented, as it is indispensable for the proper functioning of the flexures-based fixturing system. Finally, the vibration suppression capability of the flexures at the targeted frequency is experimentally validated and proved to substantially reduce (ca. 90%) the vibration response of the workpiece when compared with the non-suppressed frequencies. The proposed model represents an avenue to address the inverse problem for the design of a fixture with vibration absorption capabilities, depending on the manufacturing process parameters, the workpiece and the chatter that needs to be suppressed.

High performance epoxy/ MWCNTs nanocomposite sensors for multi-purpose sensing in structural health monitoring

Structural health monitoring (SHM) is necessary for modern technical development. It can be achieved by detecting different quantities such as pressure and strain using highly sensitive and stable sensors. In this work, epoxy/multiwalled carbon nanotubes (MWCNTs) is used as sensing material to detect both strain and pressure. To ensure better performance, dispersion fabrication process was firstly optimized via electrical and microscopic measurements. Then, the piezoresistive performance such as the sensitivity, linearity, stability and drift were investigated under pressure and strain for films prepared with different carbon nanotubes (CNTs) concentration and thickness to define the optimal conditions for each sensing target. The piezoresistive measurement shows good sensitivity to strain at very low CNTs concentration 0.3 wt. % with a gauge factor (GF = 11.094); which is around 6 times higher than conventional strain sensor, proving the efficiency of the optimized fabrication process parameters that ensure a homogenous distribution. Furthermore, the sensing layer shows also the ability to sustain high pressure load. The sensitivity is found to be highly dependent on the film thickness with higher sensitivity for thicker films in case of pressure sensing in addition to the good sensitivity at very low-pressure range. All these results prove the efficiency of Epoxy/MWCNTs as multi-purpose sensor material.

High performance epoxy/ MWCNTs nanocomposite sensors for multi-purpose sensing in structural health monitoring

Structural health monitoring (SHM) is necessary for modern technical development. It can be achieved by detecting different quantities such as pressure and strain using highly sensitive and stable sensors. In this work, epoxy/multiwalled carbon nanotubes (MWCNTs) is used as sensing material to detect both strain and pressure. To ensure better performance, dispersion fabrication process was firstly optimized via electrical and microscopic measurements. Then, the piezoresistive performance such as the sensitivity, linearity, stability and drift were investigated under pressure and strain for films prepared with different carbon nanotubes (CNTs) concentration and thickness to define the optimal conditions for each sensing target. The piezoresistive measurement shows good sensitivity to strain at very low CNTs concentration 0.3 wt. % with a gauge factor (GF = 11.094); which is around 6 times higher than conventional strain sensor, proving the efficiency of the optimized fabrication process parameters that ensure a homogenous distribution. Furthermore, the sensing layer shows also the ability to sustain high pressure load. The sensitivity is found to be highly dependent on the film thickness with higher sensitivity for thicker films in case of pressure sensing in addition to the good sensitivity at very low-pressure range. All these results prove the efficiency of Epoxy/MWCNTs as multi-purpose sensor material.

Thermal and Mechanical Properties of Amorphous Silicon Carbide Thin Films Using the Femtosecond Pump-Probe Technique

Nanoscale amorphous silicon carbide (a-SiC) thin films are widely used in engineering applications. It is important to obtain accurate information about their material properties because they often differ from those of the bulk state depending on the fabrication technique and process parameters. In this study, the thermal and mechanical properties of a-SiC thin films were evaluated using the femtosecond pump-probe technique, which provides high spatial and temporal resolutions sufficient to measure films that have a thickness of less than 300 nm. a-SiC films were grown using a plasma-enhanced chemical vapor deposition system, and the surface characteristics were analyzed using ellipsometry, atomic force microscopy, and X-ray reflectometry. The results show that the out-of-the-plane thermal conductivity of the films is lower than that of bulk crystalline SiC by two orders of magnitude, but the lower limit is dictated by the minimum thermal conductivity. In addition, a decrease in the mass density resulted in a reduced Young’s modulus by 13.6–78.4% compared to the literature values, implying low Si-C bond density in the microstructures. The scale effect on both thermal conductivity and Young’s modulus was not significant.

Bridging the Gap between Physical and Circuit Analysis for Variability-Aware Microwave Design: Modeling Approaches

Process-induced variability is a growing concern in the design of analog circuits, and in particular for monolithic microwave integrated circuits (MMICs) targeting the 5G and 6G communication systems. The RF and microwave (MW) technologies developed for the deployment of these communication systems exploit devices whose dimension is now well below 100 nm, featuring an increasing variability due to the fabrication process tolerances and the inherent statistical behavior of matter at the nanoscale. In this scenario, variability analysis must be incorporated into circuit design and optimization, with ad hoc models retaining a direct link to the fabrication process and addressing typical MMIC nonlinear applications like power amplification and frequency mixing. This paper presents a flexible procedure to extract black-box models from accurate physics-based simulations, namely TCAD analysis of the active devices and EM simulations for the passive structures, incorporating the dependence on the most relevant fabrication process parameters. We discuss several approaches to extract these models and compare them to highlight their features, both in terms of accuracy and of ease of extraction. We detail how these models can be implemented into EDA tools typically used for RF and MMIC design, allowing for fast and accurate statistical and yield analysis. We demonstrate the proposed approaches extracting the black-box models for the building blocks of a power amplifier in a GaAs technology for X-band applications.

Research on Optimization of Process Parameters of Traditional Chinese Medicine Based on Data Mining Technology.

Data mining technology and methods are used to effectively optimize manufacturing process parameters due to the complexity and uniqueness of the process parameters. The data-mining-based optimization method for traditional Chinese medicine (TCM) process parameters is presented, along with a list of process parameters that have shown to be effective in actual production. The influencing factors of process parameters are analyzed and modeled using an attribute weight analysis and classification analysis algorithm. The optimization scheme of process parameters that meet the requirements is selected, and an example is given for verification, by selecting data records that fall within a certain error range and incorporating the rules of association knowledge discovery. The support vector classification algorithm has a higher accuracy, despite the algorithm's results being understandable. The support vector regression algorithm developed a reliable process optimization model.