This paper investigates the influence of laser-beam intensity distribution (LBID) on the performance of the annular laser-beam directed energy deposition (DED) process with axial powder delivery. ...Three different LBIDs: Gaussian-like (G-LBID), top-hat-like (TH-LBID) and ring (R-LBID) at two LBID diameters were used. The process performance was characterised qualitatively in terms of the melt-pool shape and the process stability and quantitatively by powder-catchment efficiency, selected geometrical and metallurgical properties of the clad. The observed influence of LBID on process performance, as determined by the relationship between LBID and powder stream density distribution (PSDD), decreased with increasing mean surface-energy density and was more significant at larger LBID diameter. The highest powder-catchment efficiencies (90% and 87%) were achieved with the G-LBID and TH-LBID, whose high-intensity centre is aligned with the peak of the Gaussian-like PSDD. A lower powder-catchment efficiency of 77% was achieved with the R-LBID, whose high-intensity region is located at the edge of the melt pool with minimum powder density. However, this also results in the highest and most uniform dilution, the highest metallurgical bond ratio and the lowest lack of fusion porosity at the clad-substrate interface. In addition, the process was stable at the lower values of mean surface-energy density with R-LBID, while balling instability was observed with G-LBID and TH-LBID. It can be concluded that the use of R-LBID at lower values of mean surface-energy density improves the performance of the DED process with axial powder feed in terms of process stability and metallurgical properties of the clad.
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•Influence of laser-beam intensity distribution in metal-powder DED was investigated.•Gaussian-like, top hat, and ring laser-beam intensity distributions were considered.•Effect of intensity distribution was more pronounced at a low surface-energy density.•Gaussian-like distribution provided the highest powder-catchment efficiency.•Ring-intensity distribution improved process stability and clad properties.
This study investigates the long-term performance of the mesophilic (35 °C) anaerobic mono-digestion of process waters (PW) from the hydrothermal carbonisation (HTC) of spent coffee grounds. At an ...organic loading rate (OLR) of 0.4 gCOD L−1 d−1, initial instability was seen, but after 40 days and supplementary alkalinity, the digestion stabilised with the chemical oxygen demand (COD) in the untreated PW degraded with 37.8–64.6% efficiency and the yield of methane at 0.16 L gCOD−1. An increase in OLR to 0.8 gCOD L−1 d−1 caused a collapse in biogas production, and resulted in severe instability in the reactor, characterised by falling pH and an increasing volatile fatty acid concentration. Comparatively, the digestion of a treated PW (concentrated in nanofiltration and reverse osmosis after removal of the fouling fraction), at OLR between 0.4 and 0.8 gCOD L−1 d−1, was stable over the entire 117 days of treated PW addition, yielded methane at 0.21 L gCOD−1 and the COD was degraded with an average efficiency of 93.5% - the highest efficiency the authors have seen for HTC PW. Further anaerobic digestion of untreated PW at an average OLR of 0.95 gCOD L−1 d−1 was stable for 38 days, with an average COD degradation of 69.6%, and methane production between 0.15 and 0.19 L gCOD−1. The digestion of treated PW produced significantly higher COD degradation and methane yield than untreated PW, which is likely to be related to the removal of refractory and inhibitory organic material in the post-HTC treatment by adsorption of hydrophobic material.
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•Process waters from the HTC of spent coffee grounds anaerobically digested.•Novel pre-treatment of process water for P-recovery enhanced digestion performance.•Adsorption of hydrophobic organics removes recalcitrant compounds before AD.•COD degradation efficiencies of 69.6% (untreated PW) and 93.5% (treated PW).•Specific CH4 yields of 0.16 L gCOD−1 (untreated PW) and 0.21 L gCOD−1 (treated PW).
Chatter vibration in micro-milling is critical for the breakage of the cutting tools. Therefore, the dynamic stability is important and chatter vibration should be avoided. This paper presents a ...comparative study between two models for prediction of chatter. The difference between the two models is in the source of cutting forces. The first chatter model uses a mathematical cutting force model while the second chatter model uses direct measured cutting forces. Both chatter models are solved in the time domain and the same criteria for chatter is applied. The results showed that the chatter model using direct measured cutting forces was in better agreement with fast Fourier transform analyses.
Magnesium (Mg)-based wires are in the focus of interest for numerous applications like micro-forming technologies or medical engineering. Manufacturing thin Mg-based wires is widely realized by ...applying a conventional multiple pass cold wire drawing process. This requires a complex manufacturing schedule of multiple passes with intermediate heat treatments to overcome work hardening, because of the cold forming process. Especially Mg and its alloys are known for their rather low formability at room temperature associated with the hexagonal close-packed lattice structure. The dieless drawing process uses local heating to initialize a localized plastic zone under an external tensile load to achieve higher reductions in diameter in a single wire drawing pass. It can therefore present a solution for a more efficient warm manufacturing process of Mg-based wires. In this study, the stability of the steady state material flow during a dieless wire drawing process and its reproducibility was investigated. For this purpose, a variation of process parameters was selected and wire manufacturing was carried out using magnesium alloy AZ31. A single and double dieless drawing process was applied. Additionally, a conventional cold wire drawing process including a die with the same forming schedule was executed as a benchmark experiment. The results of this study show, that the dieless drawing process is not only a stable process after reaching the steady state, but it is also a reproducible and accurately adjustable process. Moreover, the dieless drawing process maintains the property profile of the starting material to a large extend.
Aiming at a higher deposition rate, robotic gas tungsten arc additive manufacturing (GTA AM) always uses the front feed mode in which the wire is fed in front of the arc along the torch travel ...direction. However, fabricating corner structures in this mode is still a challenging issue in robotic GTA AM, since the serious hump height at corner points during torch rotation will hinder the process stability and automation of corner structures. The novelty of this study is to solve this issue by developing an in-situ monitoring and control strategy. An arc voltage sensor is designed to monitor the arc voltage that can characterize the deposition height. The arc voltage decreases first and then keeps stable at the corner points during torch rotation. It increases rapidly as the torch runs away from the corner points. An empirical mode decomposition (EMD) algorithm filters noises in sampled arc voltages. The peak arc voltage is selected to characterize the arc length since it presents fewer fluctuations than the base arc voltage. A Fuzzy-PID controller is developed for the peak arc voltage control by regulating the wire feed speed (WFS). Open-loop and closed-loop control tests of corner structures confirm that the deposition process with the fixed WFS is forced to terminate due to the serious hump height, and that with the controlled WFS can lower the hump height markedly at the corner points. This study demonstrates that the developed arc voltage sensing and control system can remove metal humps at the corner points and enhance the process automation of corner structures in robotic GTA AM.
•Metal humps at corner points are measured by sensing peak arc voltage.•Arc voltage decreases first and then keeps stable at corner points during torch rotation.•Metal humps are eliminated by regulating WFS via a closed-loop control system.
Shortcut nitrification-denitrification (SCND) is widely concerned because of its low energy consumption and high nitrogen removal efficiency. However, the current difficulty lies in the stable ...maintenance of SCND performance, which leads to the challenge of large-scale application of this new denitrification technology. In this study, the nitrogen removal pathway from complete nitrification-denitrification (CND) to SCND was rapidly realized under high free ammonia (FA), high pH and low dissolved oxygen (DO) conditions. The variations of specific oxygen uptake rate (SOUR) of activated sludge in both processes were investigated by an online SOUR monitoring device. Different curves of SOUR from CND to SCND process were observed, and the ammonia peak obtained based on SOUR monitoring could be used to control aeration time accurately in SCND process. Accordingly, the SOUR ratio of ammonia oxidizing bacteria (AOB) to nitrite oxidizing bacteria (NOB) (SOURAOB/SOURNOB) was increased from 1.40 to 2.93. 16S rRNA Miseq high throughput sequencing revealed the dynamics of AOB and NOB, and the ratio of relative abundance (AOB/NOB) was increased from 1.03 to 3.12. Besides, SOURAOB/SOURNOB displayed significant correlations to ammonia removal rate (P < 0.05), ammonia oxidation rate / nitrite oxidation rate (P < 0.05), nitrite accumulation rate (P < 0.05) and the relative abundance of AOB/NOB (P < 0.05). Thus, a strategy for evaluation the SCND process stability based on online SOUR monitoring is proposed, which provides a theoretical basis for optimizing the SCND performance.
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Invar alloy has been widely used in composite molds due to its low coefficient of thermal expansion (CTE). The cold metal transfer (CMT) based wire arc directed energy deposition (Wire-arc DED) makes ...the rapid fabrication of large-scale composite molds a reality. The present study proposes a novel deposition strategy that combines voltage and current online monitoring and interlayer temperature control. The results show that the optimization of the process parameters obtained by online monitoring of the electrical signals and extending the interlayer dwell time (IDT) contributes to improved mechanical properties and elimination of tensile anisotropy. The elongation (EL) at fracture of vertical and horizontal specimens is increased by 29.9 % (EL: 30 %) and 28.1 % (EL: 34.6 %), respectively. This is attributed to the improvement of heterogeneous microstructure and the significant refinement of the long-chain-like micron-scale (Nb, Ti) C. Based on the analysis of grain size, (Nb, Ti) C distribution and defect distribution, the main mechanisms for the synergistic strengthening-ductility effect are discussed in detail. Controlling the interlayer temperature enhances the residual compressive stress within the component, resulting in excellent low CTE (0.33 × 10−6/°C, 25–100 °C). This provides a convenient way for the improvement of mechanical properties and thermal expansion of Wire-arc DED Invar alloy.
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•A novel deposition strategy that combines process online monitoring and interlayer temperature control was proposed.•Tensile properties were enhanced by tailoring the heterogeneous microstructure and refining the micro-scale (Nb, Ti) C phase.•Increasing the compressive residual stress is conducive to reducing the thermal expansion of Wire-Arc DED Invar alloy.
•Pilot treated raw wastewater at variable flow rate and ambient temperature for 500 days.•HRAS pilot plant was stabilized at extremely low SRT (< 0.5 d) and HRT (< 1 h).•HRAS harvested 60% of the COD ...in front the 35–40% of primary clarifiers.•Biomass monitoring was a successful strategy to control HRAS process stability.•Pilot plant HRAS performance was validated with a SUMO simulations.
In high-rate activated sludge (HRAS) processes, reducing the solid retention time (SRT) minimizes COD oxidation and allows to obtain the maximum energy recovery. The aim of this research was to operate a pilot plant with an automatic control strategy to assure the HRAS process stability and high COD fractions removal at very low SRT. This study combines simulation and experimental tools (pilot plant 35 m3·d − 1) operating at SRT (0.2 d), HRT (0.6 h) and DO (0.5 mg·L − 1) treating high-strength raw wastewater, at 18–26°C, at variable flow. The research includes the effects of temperature, influent concentration and MLSS reactor concentration over the sCOD, cCOD and pCOD removal.
The study points out that the best parameter to control the HRAS at a low SRT is not strictly the SRT but rather the reactor MLSS concentration: operating at 2,000±200mg·L − 1 assured a stable process despite the large influents variation. Low SVI values of 50–70ml·g − 1 indicated the good settling properties of the biomass. With only a 6.9% COD oxidation, a high organic matter removal (57±9% for COD and 56±10% for BOD5), was reached. The high removal efficiencies for pCOD (74%) compared to the (29%) for sCOD and (12%) for cCOD also confirmed the importance of settling efficiency and stability in the HRAS. The direct correlation between COD influent and COD removal makes advisable to use the HRAS as a replacement of the primary clarifier. The HRAS acted efficiently as a filter for COD and pCOD peak loads and, in a lesser extent, for BOD5, while sCOD peaks were not buffered. The adopted model presented a good fit for COD fractions except for pCOD when the temperature exceeds 23 °C.
•Synergistic effects were found in CS:CM ratios of 3:1 and 1:1.•In W-AD and HSS-AD, highest methane yields were obtained at CS:CM ratio of 3:1.•Highest volumetric productivity of 14.2L/L was found in ...SS-AD at CS:CM of 1:1.•VFA/TA value of 0.4 was a more important criterion than NH3-N or FA concentration.
Corn stover (CS) and chicken manure (CM) are ubiquitous agricultural wastes at low cost and have the potential to achieve a nutrient-balance when mixed together to produce biomethane via anaerobic digestion (AD). The main objective of this work was to investigate methane production at different CS to CM ratios and to evaluate the process stability under wet (W-AD), hemi-solid state (HSS-AD) and solid state (SS-AD) conditions. Results showed that synergistic effects were found when mixing two substrates at CS:CM ratios of 3:1 and 1:1 (on volatile solid basis). The highest methane yield of 218.8mL/g VSadded was achieved in W-AD at CS:CM ratio of 3:1. In SS-AD, the highest volumetric methane productivity of 14.2Lmethane/Lreactor volume was found at CS:CM of 1:1. The results of this work provide useful information to improve the efficiency and stability of co-digestion of CS and CM under different AD conditions.
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