In situ monitoring methods for selective laser melting additive manufacturing process based on images-A review

Selective laser melting(SLM)has been widely used in the fields of aviation,aerospace and die manufacturing due to its ability to produce metal components with arbitrarily complex shapes.However,the instability of SLM process often leads to quality fluctuation of the formed component,which hinders the further development and application of SLM.In situ quality control during SLM process is an effective solution to the quality fluctuation of formed components.However,the basic premise of feedback control during SLM process is the rapid and accurate diagnosis of the quality.Therefore,an in situ monitoring method of SLM process,which provides quality diagnosis information for feedback control,became one of the research hotspots in this field in recent years.In this paper,the research progress of in situ monitoring during SLM process based on images is reviewed.Firstly,the significance of in situ monitoring during SLM process is analyzed.Then,the image information source of SLM process,the image acquisition systems for different detection objects(the molten pool region,the scanned layer and the powder spread layer)and the methods of the image information analysis,detection and recognition are reviewed and analyzed.Through review and analysis,it is found that the existing image analysis and detection methods during SLM process are mainly based on traditional image processing methods combined with traditional machine learning models.Finally,the main development direction of in situ monitoring during SLM process is proposed by combining with the frontier technology of image-based computer vision.

An in situ monitoring campaign of a hard rock pillar at great depth within a Canadian mine

A recent research campaign at a Canadian nickel-copper mine involved instrumenting a hard rock sill drift pillar with an array of multi-point rod extensometers,distributed optical fibre strain sensors,and borehole pressure cells(BHPCs).The instrumentation spanned across a 15.24 m lengthwise segment of the relatively massive granitic pillar situated at a depth of 2.44 km within the mine.Between May 2016 and March 2017,the pillar’s displacement and pressure response were measured and correlated with mining activities on the same level as the pillar,including:(1)mine-by of the pillar,(2)footwall drift development,and(3)ore body stoping operations.Regarding displacements of the pillar,the extensometers provided high temporal resolution(logged hourly)and the optical fibre strain sensors provide high spatial resolution(measured every 0.65 mm along the length of each sensor).The combination of sensing techniques allowed centimetre-scale rock mass bulking near the pillar sidewalls to be distinguished from microstrain-scale fracturing towards the core of the pillar.Additionally,the influence and extent of a mine-scale schistose shear zone transecting the pillar was identified.By converting measured rock mass displacement to velocity,a process was demonstrated which allowed mining activities inducing displacements to be categorised by time-duration and cumulative displacement.In over half of the analysed mining activities,displacements were determined to prolong for over an hour,predominately resulting in submillimetre cumulative displacements,but in some cases multi-centimetre cumulative displacements were observed.This time-dependent behaviour was more pronounced within the vicinity of the plumb shear zone.Displacement measurements were also used to assess selected support member load and elongation mobilisation per mining activity.It was found that a combined static load and elongation capacity of reinforcing members was essential to maintaining excavation stability,while permitting gradual shedding of stress through controlled pillar sidewall displacements.

Distributed optical fiber acoustic sensor for in situ monitoring of marine natural gas hydrates production for the first time in the Shenhu Area,China

The distributed acoustic sensor(DAS)uses a single optical cable as the sensing unit,which can capture the acoustic and vibration signals along the optical cable in real-time.So it is suitable for monitoring downhole production activities in the process of oil and gas development.The authors applied the DAS system in a gas production well in the South China Sea for in situ monitoring of the whole wellbore for the first time and obtained the distributed acoustic signals along the whole wellbore.These signals can clearly distinguish the vertical section,curve section,and horizontal production section.The collected acoustic signal with the frequency of approximately 50 Hz caused by the electric submersible pump exhibit a signal-to-noise ratio higher than 27 dB.By analyzing the acoustic signals in the production section,it can be located the layers with high gas production rates.Once an accurate physical model is built in the future,the gas production profile will be obtained.In addition,the DAS system can track the trajectory of downhole tools in the wellbore to guide the operation.Through the velocity analysis of the typical signals,the type of fluids in the wellbore can be distinguished.The successful application of the system provides a promising whole wellbore acoustic monitoring tool for the production of marine gas hydrate,with a good application prospect.

In situ monitoring of Suzuki-Miyaura cross-coupling reaction by using surface-enhanced Raman spectroscopy on a bifunctional Au-Pd nanocoronal film

Surface-enhanced Raman spectroscopy(SERS), a powerful surface vibrational spectroscopic technique, is ideally suited for in situ monitoring the chemical transformations occurred at surfaces and/or interfaces.For in situ SERS monitoring, a platform integrated both plasmonic and catalytic activity is a prerequisite. Here, we fabricate a bifunctional Au-Pd nanocoronal film for in situ SERS monitoring Suzuki-Miyaura cross-coupling reaction. This excellent bifunctional substrate leads to the coupling of high catalytic activity with a strong SERS effect at the center of two adjacent Au cores and shows fine reproducibility and stability of SERS signals. During investigating the Suzuki reaction with in situ SERS, we found two distinct catalytic kinetic processes resulted from two disparate catalytic sites on a Au-Pd nanocoronal. Comparing with conventional analytical techniques, this work provides a novel approach for studying Suzuki reactions at surfaces and/or interfaces with in situ SERS.

Generation and Suppression of Pendant Droplet Oscillation in Electron Beam Directed Energy Deposition

Electron beam–directed energy deposition(EB–DED)has emerged as a promising wire-based metal additive manufacturing technique.However,the effects of EBs on pendant droplets at wire tips have not yet been determined.The aim of this study is to enhance the understanding of this action by analyzing the mechanism of droplet oscillation.The pendant droplet oscillation phenomenon hinders the stable transfer of droplets to the molten pool and limits the feasibility of manufacturing complex lattice structures by EB–DED.Hence,another aim of this study is to create an oscillation suppression method.An escalating asymmetric amplitude is the main characteristic of droplet oscillation.The primary oscillationinducing force is the recoil force generated from the EB-acted local surface of the droplet.The physical mechanism of this force is the rapid increase and uneven distribution of the local surface temperature caused by the partial action of the EB.The prerequisites for droplet oscillation include vacuum conditions,high power densities,and bypass wire feeding processes.The proposed EB–dynamic surrounding melting(DSM)method can be applied to conveniently and effectively suppress oscillations,enable the accurate transfer of droplets to the molten pool,and achieve stable processes for preparing the strut elements of lattice structures.Lowering the temperature and improving the uniformity of its distribution are the mechanisms of oscillation suppression in EB–DSM.In this study,the physical basis for interpreting the mechanism by which EBs act on droplets and the technical basis for using EB–DED to prepare complex lattice structure parts are provided.

Groundwater recharge via precipitation in the Badain Jaran Desert,China

Precipitation infiltration serves as a significant source of groundwater in the Badain Jaran Desert.To investigate variations in precipitation infiltration within the desert,this study collected data on moisture content and temperature from the vadose zone through in-situ field monitoring.Utilizing these data,a numerical model is employed to explore the mechanism of groundwater recharge via precipitation.The results are as follows:(1)Moisture content and temperature in the shallow vadose zone exhibit significant seasonal variations,with moisture content diminishing with increasing depth;(2)Groundwater recharge via precipitation infiltration initially increases and then decreases with groundwater level depth(GWD).Peak groundwater recharge via precipitation occurs at a GWD of 0.75 m,decreasing to merely 0.012 cm at GWDs exceeding 2 m;(3)Groundwater is no longer susceptible to phreatic water evaporation when the GWD reaches approximately 3.7 m.Therefore,GWD plays a crucial role in governing groundwater recharge via precipitation in the Badain Jaran Desert.

Mineral fibres and environmental monitoring:A comparison of different analytical strategies in New Caledonia

Covered by ultrabasic units for more than a third of its surface,the New Caledonia(South West Pacific)is one of the largest world producers of Ni-ore from lateritic deposits.Almost all outcrops of geological units and open mines contain serpentine and amphibole,also as asbestos varieties.In this geological context,in which weathering processes had a great contribution in the production and dispersion of mineral fibres into the environment,the development of a routinely analytical strategy,able to discriminate an asbestiform fibre from a non-harmful particle,is a pivotal requisite.However,the acquisition of all these parameters is necessary for determining the risk associated to fibres exposition.A multidisciplinary routinely approach,based on the use of complementary simply-to-use but reliable analytical methods is the only possible strategy.In addition,the instrumental apparatus must be easily transportable on the field,directly on the mining site.The employment of specialized tools such as Polarized Light Microscopy associated to Dispersion Staining method(PLM/DS)and portable Raman spectroscopy for identification of environmental asbestos,are proved extremely effective in the improvement of the performance and rapidity of data acquisition and interpretation.Both PLM/DS and handheld Raman devices confirmed to be discriminant in the detection and characterization of asbestos fibres for both serpentine and amphibole.Furthermore,these techniques proved extremely effective even in the presence of strongly fibrous and altered samples.