Characteristic length of the solidified melt poolin SLM 1. In this paper, a practical method was proposed for the evaluation ofcharacteristic length of melt pool.
According to the type of scan, two methodsof evaluation were proposed based on observed shape of solidified melt pool.For the observation of contour profiles of the molten pool in correspondence tothe type of scans, parts were manufactured with the help of SLM with varioushatch spaces, by keeping all other parameters constant. 2. The results showed that the shapeof the solidified melt pool changes with the hatch spacing and can be horizontal, oval or flat..Furthermore, there is change in hardness with hatch spacing.
3. The reason can be explained with the understanding of hydrodynamics inthe molten pool. For the situation with an overlap region with the increase of hatchspacing the energy density is reduced but the radial acceleration strength ofthe molten pool due to the decrease of conduction effect with reduction of areaof contact which results in the expansion of molten pool. The decrease of thelaser control or the expansion of the scanning speed would diminish the keyholeimpact, and the base contour of the molten pool would be changed to ahorizontally oval shape. On the flip side, for the situation with no overlap, amolten pool is near to isolated condition by surrounding powder that has alower thermal conductivity. The condition results in increasing the workingtemperature in the focal point of the beam and actuate solid Marangoniconvection. The solid Marangoni convection on the pool surface causes strong meltflow and makes more powders fall into the molten pool, bringing about theexpansion of the width of the molten pool. The reason for the change in hardness of material with hatch spacing canbe explained on the basis of rates of cooling, as hardness decreases linearlyand the hardness variance increases with the hatch spacing as the rate ofcooling decreases and the hardness irregularity within the solidified melt poolincreases.
Effect of process parameterssettings and thickness on surface roughness of EBM 1. In this paper, a model is developed on the base of response surfacemethodology(RSM) to examine surface roughness with variable thickness andvariable parameter settings. 2. The results indicate that parts manufactured with EBM has recognizable surfaceroughness. The surface roughness Ra varies between 1-20 mm for various samplesrelying on thickness and process parameters. The Ra values are found to beincreasing with increase in thickness of sample and beam current and are foundto be decreasing with increasing offset focus and scanning speed. 3. The reason for rough surface of the parts produced by EBM can beaccounted to various factors.
The reason for rough surface is that sinteredpowder is sticked on the part’s surface and the other reason for the roughsurface can be the size of the molten pool and energy density generated byelectron beam at the curved points and high marangoni’s convection which makesthe molten pool unstable The impact of high surface roughness value for samples that aregenerated by high beam current, offsetfocus values and low scanning speeds can be described on the base of energydensity of the molten pool. The low scanning speeds, offset focus and high beamcurrent brings about molten pool of moderately higher energy densities. Thishigh energy molten pool upgrades the phenomenon of sintering by giving moreenergy to sinter powder from the environment. On slow scanning speeds, it takeslong time at the defining moment likewise contributing in sintering. For highoffset focus the beam is focused sharply and consequently energy density of thepool diminishes. For the instances of distinction in surface roughness due tosample thickness, the reason for this is that the measure of total heat of thebuilt, with the increase in the thickness of the sample there is rise in theheat energy of sample which is utilized as a source for the sintering.
Experimental design approach to optimize SLM 1. In this paper author used the method of partial factorial to change andto find the perfect plan of process parameters using three different powdersfor 17-4 PH steel. This paper describes the effect of various factors such asmaterial and process parameters which are surface roughness and estimation ofsingle lines and single layers.
2. The effect of properties of material and process parameters on singleline and single layer are proved in this paper. The impact of every processparameter on single layer and single line stability and quality are examined,and an objective function which analyses stability of single lines is proposedin this paper. Results indicate that 17-4PH powder is the most appropriate powder formanufacturing of regular and stable single tracks. 3.
The reason for this powder is that 17-4 PH powder has the mostimperative specific area that fundamentally depends on powder shape and sizedistribution of particles. The greatersurface area of fine particles results inhigher rates of melting . Subsequently,it can be concluded that the usage of fine powders is good for the SLM machine.Heat transfer and fluid flow during EBM 1.
In this paper Electron beamwelding of two different alloys (Ti–6Al–4V and 21Cr–6Ni–9Mn) has been studied theoretically and practically. In thetheoretical research fusion zone geometry, velocity, temperature vs time werestudied. The theoretically studied fusion zone geometries and temperature vstime graphs were compared with the experimental results for the laser beamwelding. 2.
The theoretical and experimental results indicate that size of fusionzone in Ti–6Al–4V alloy was bigger than 21Cr-6Ni-9Mn stainless steel forelectron beam as well as laser welding. Low thermal conductivity in solid stateand high boiling points of Ti-6Al-4V results in high temperatures in Ti-6Al-4Vduring welding in comparison to 21Cr-6Ni-9Mn. The temperatures of keyhole wallfor EBW were lower at low pressure than LBW at same heat at atmosphericpressure. 3.
In the keyhole vapour pressure increases with the increase in depth andthe pressures are very high near the bottom. As the radius of keyhole decreaseswith increase in depth, the vapour pressure increases at a much higher rate. Inthe estimation of keyhole radius decreases from its maximum value to minimumvalue.
In all actuality, the keyhole base is assumed to be negligible andradius is assumed to have some finite values. This is the reason that vapourpressures that are calculated near the keyhole base are higher than itsoriginal value. Peak Temperatures obtained at thetop of the surface in case of Ti–6Al–4V were much higher than 21Cr–6Ni–9Mn. The reason for this is thehigh boiling point and low thermal conductivity in solid state. The reason for lower keyhole temperatures in EBW is due to low atmosphericpressure results in more deeper penetrations in comparison to LBW.Heat transfer and fluid flow during keyhole modelaser welding 1.
In this paper, pre-existing modelto calculate fluid flow and heat transfer is developed for the understanding oflaser welding of keyhole mode for particular condition in welding Ti-6Al-4V,vanadium, 304L stainless steel and Tantalum. The thing that is required and notpresently accessible is a phenomenological model for the keyhole mode weldingwhich is utilized for welding an extensive number of alloys and metals withextraordinary physical properties under different welding conditions. In thispaper, a phenomenological model is developed. 2. The participation of convectionwith respect to conduction in the heat exchange was higher for 304L stainlesssteel and least for tantalum. The relative significance of these two componentsin the heat exchange relied upon the thermal diffusivity and temperaturecoefficient of surface pressure of alloys and metals. On comparison with 304Lstainless steel, heat exchange by conduction is found to be more efficient fortantalum because it has lower temperature coefficient an higher thermaldiffusivity. The shape and weld penetration of metals and alloys are affected bythermophysical properties.
Temperature coefficient of surface effects the shapeof weld pool. High melting point and high thermal diffusivity of tantalumresults in little weld pools contrasted to other materials. 3. The main principle of heat exchange for all the materials is Convectiveheat transfer which was higher for 304L stainless steel and least for tantalum.Influence of process parameters onsurface quality 1, . In this paper the effect of process parameters onflatness, surface quality, surface roughness, and overlapping are assessed. Therecognizing feature is the melting of single layers with a nonstop laser.
Inview of these outcomes joined with visual perception of the solid tracks, theimpact of process parameters on the surface roughness is examined. Themeasurement of surface roughness is done by SV-2000 profilometer. 2. The outcomes demonstrate that the factors influencingsurface roughness are laser power, scanning speed and scan spacing. To evaluatequality the peak height, and depth of lowest point of profile are veryimportant parameters.
With the increase of layer thickness there is increase inpeak height. It is found that how a little change in values of laserpower can change the surface roughness of part. The emitted energy givesindication of extremely significant variety in the layer quality. On the flipside, the peaks that are framed between the contiguous tracks are influenced bylayer thickness of the underlying powder. .
Consequently, for high thicknesses,there is lost congruity and homogeneity in the melted layer. 3. In low layer thickness, a good packing ofmolecules takes place which results in a smaller contact area which relates tovery less accumulation of heat and bigger densification which is the reason forno balling effect and successful layering.Thisphenomenon may be explained because with a low layerthickness, a good particle packing is more likely to occur.Consequently, a smaller contact area takes place and inconsequence,a less heat accumulated a fuller densification and atlast, a successful layer without ballingeffect Influence of the particle sizedistribution on surface quality and mechanical properties 1. In this paper the mechanical properties, part density and surfacequality of three different materials are compared.
2With the use of modified powders, low surface roughness materials can beobtained. The process of blasting can help further in improving surfaceroughness of materials but does not effects the rank of material. Mechanicalproperties can be further improved with the use of modified powders in additivemanufacturing by SLM. 3. The reason for the low surface roughness and high density with the useof finer particles is that fine particles are melted easily in comparison withcoarse particles which results in higher mechanical strengths Also, finerparticles provide smoother melting pool and generate better surfaces. Influences of processing parameters on surface roughness 1. The impact of processing parameters on surface roughness in Hastelloy Xalloy. As the processing parameters like laser control, laser speed, layer thickness and angle of asurface were systematically fluctuated to comprehend their impacts on surfaceharshness.
The average roughness, Ra, was measured for both up-skin surfacesand down-skin surfaces . The development system for the roughness on these twokinds of surfaces has been considered. Simulation was likewise utilized to understand thermalprofiles and their resultant impact onsurface harshness. The simulated result has been observed to be predictablewith the deliberate outcome 2. Formation of melt pool and results of surface roughness for inclinedsurfaces were explored by comparison of different bulk solid material andpowders in terms of conduction and heat transfer . At high scanning speedsformation of large balling was observed because of Rayleigh instability, poorwettability and the loss of contact between the melt and the substrate. Littleballing was seen at low scanning speeds and high scanning power because of long fluid lifetimes, expanded meltvolumes and decreased melt viscosities.
Large overlapping because of littlehatch distance advances the particle attachment on surface which results in theincrease of surface roughness. On Optimization of Surface Roughness 1. The re-melting process for the improvementof surface roughness of Additively Manufactured parts utilizing a measurableapproach. Laser remelting (LR) as post- processing technique was performed witha specific end goal to explore surface roughness through parameter optimisation.The use of optimized process parameterswas depended on statistics data analysis inside the Design of Experimentsystem, from which a model was then developed. 2. The results obtained in this paper demonstrated that LR has high potential for the improvement of surfaceroughness related to the parts manufactured with the SLM process.
Themicrostructure dendrites, for example, balling, agglomeration, waviness, andthe microstructures of shrinkage pits can be wiped out up to a great extent,when the ideal parameters are utilized. The surface roughness values can beimproved up to 80% with the use of remelting process in comparison to SLM process.Also, outer and inner porosities were totally disposed of, leaving the meltedzone with a completely thick microstructure. 3. LR results in the improvement of surface roughness and the reason forthis improvement is that the remelting process results in the change ofmicrostructure of material of thin surface layer with a specific depth whichresults in a material with surface free from any defects and very highsmoothness. Prediction of porosity in metal 1. A predictive model was developed on the basis of Gaussian process tolearn and predict the porosity.
Further, a Bayesian inference system was usedfor the estimation of porosity and statistical model parameters at anyparticular point is predicted using the Kriging method. Porosity is a defectthat has been found commonly in SLM manufactured metal parts which results inthe compromise of performance and mechanical properties. The parameters that has a greatly affect the porosity of SLMmanufactured parts are laser power, Scan speed, layer thickness, hatch distance and size oflaser beam. 2. Further it is found that there is decrease in porosity with increase inlaser power and there is increase in porosity with increase in speed of scan.
.Energy deposition into the power bed is increased with high laser power whichresults in better powder melt and densification and subsequently the quality ofsurface improved Surface Morphology in SLM 1. Processing parameters for example laser power,hatch spacing, etc.
on the surface morphology were analysed. 2. The reduction of the hatch spacing changes the thermo-physical condition of synthesis, the laser beam is interacted with the powder, the substrate and thesynthesized track. A melt pool has more reflectivity than free powder. The energy thatwas absorbed is reheats the previous track or the substrate, the heat ispromoted through the substrate causing sintering of the powder. It is foundthat increasing the scan speed and layer thickness pores becomes more orientedthus increasing surface roughness and similarly for smaller layer thickness themetal results in smoother surface was obtained Surface roughness analysis 1.
Morphology and surface roughness of Steel 316L alloys was manufacturedby SLM process.. The surface investigation has demonstrated an increase inthickness of particles situated on the progression edges, as the angle ofsurface slope increases. At the point when thickness of layer is practicallyidentical to diameter of particle, the particles stuck along step edges canfill the holes between adjacent layers, in this way influencing the actualsurface roughness. 2.
It is demonstrated that results of surface roughness anticipated by thismodel are very similar to thesurface roughness found experimentally. This paper describes the key variablesaffecting surface morphology, and a hypothetical model for the prediction ofsurface roughness that gives valuable data for the enhancement of surfacequality of SLM manufactured parts, hence limiting the need of surface finish. The study demonstrates the significance ofconsidering particle presence in the plan of hypothetical models, for a preciseexpectation of surface roughness in the SLM process of steel.