Characteristic the keyhole impact, and the base contour of

Characteristic length of the solidified melt pool
in SLM

 

1.

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In this paper, a practical method was proposed for the evaluation of
characteristic length of melt pool. According to the type of scan, two methods
of evaluation were proposed based on observed shape of solidified melt pool.
For the observation of contour profiles of the molten pool in correspondence to
the type of scans, parts were manufactured with the help of SLM with various
hatch spaces, by keeping all other parameters constant.

 

2.

 

The results  showed that the shape
of 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 in
the molten pool.

 

 

For the situation with an overlap region with the increase of hatch
spacing the energy density is reduced but the radial acceleration strength of
the molten pool due to the decrease of conduction effect with reduction of area
of contact which results in the expansion of molten pool. The decrease of the
laser control or the expansion of the scanning speed would diminish the keyhole
impact, and the base contour of the molten pool would be changed to a
horizontally oval shape. On the flip side, for the situation with no overlap, a
molten pool is near to isolated condition by surrounding powder that has a
lower thermal conductivity. The condition results in increasing the working
temperature in the focal point of the beam and actuate solid Marangoni
convection. The solid Marangoni convection on the pool surface causes strong melt
flow and makes more powders fall into the molten pool, bringing about the
expansion of the width of the molten pool.

 

The reason for the change in hardness of material with hatch spacing can
be explained on the basis of rates of cooling, as hardness decreases linearly
and the hardness variance increases with the hatch spacing as the rate of
cooling decreases and the hardness irregularity within the solidified melt pool
increases.

 

Effect of process parameters
settings and thickness on surface roughness of EBM

 

1.

 

In this paper, a model is developed on the base of response surface
methodology(RSM) to examine surface roughness with variable thickness and
variable parameter settings.

 

2.  The results indicate that parts manufactured with EBM has recognizable surface
roughness. The surface roughness Ra varies between 1-20 mm for various samples
relying on thickness and process parameters. The Ra values are found to be
increasing with increase in thickness of sample and beam current and are found
to be decreasing with increasing offset focus and scanning speed.

 

 

3.

 

The reason for rough surface of the parts produced by EBM can be
accounted to various factors. The reason for rough surface is that sintered
powder is sticked on the part’s surface and the other reason for the rough
surface can be the size of the molten pool and energy density generated by
electron beam at the curved points and high marangoni’s convection which makes
the molten pool unstable

 

 

 

 

The impact of high surface roughness value for samples that are
generated by high  beam current, offset
focus values and low scanning speeds can be described on the base of energy
density of the molten pool. The low scanning speeds, offset focus and high beam
current brings about molten pool of moderately higher energy densities. This
high energy molten pool upgrades the phenomenon of sintering by giving more
energy to sinter powder from the environment. On slow scanning speeds, it takes
long time at the defining moment likewise contributing in sintering. For high
offset focus the beam is focused sharply and consequently energy density of the
pool diminishes. For the instances of distinction in surface roughness due to
sample thickness, the reason for this is that the measure of total heat of the
built, with the increase in the thickness of the sample there is rise in the
heat 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 and
to find the perfect plan of process parameters using three different powders
for 17-4 PH steel. This paper describes the effect of various factors such as
material and process parameters which are surface roughness and estimation of
single lines and single layers.

 

2.

 

The effect of properties of material and process parameters on single
line and single layer are proved in this paper. The impact of every process
parameter on single layer and single line stability and quality are examined,
and an objective function which analyses stability of single lines is proposed
in this paper. Results indicate that 17-4PH powder  is the most appropriate powder for
manufacturing of regular and stable single tracks.

 

 

 

3.

 

The reason for this powder is that 17-4 PH powder has the most
imperative specific area that fundamentally depends on powder shape and size
distribution of particles. The greatersurface area of fine particles results in
higher  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 beam
welding of two different alloys (Ti–6Al–4V and

 

21Cr–6Ni–9Mn) has been studied theoretically and practically. In the
theoretical research fusion zone geometry, velocity, temperature vs time were
studied. The theoretically studied fusion zone geometries and temperature vs
time graphs were compared with the experimental results for the laser beam
welding.

 

 

2.

 

The theoretical and experimental results indicate that size of fusion
zone in Ti–6Al–4V alloy was bigger than 21Cr-6Ni-9Mn stainless steel for
electron beam as well as laser welding. Low thermal conductivity in solid state
and high boiling points of Ti-6Al-4V results in high temperatures in Ti-6Al-4V
during welding in comparison to 21Cr-6Ni-9Mn. The temperatures of keyhole wall
for EBW were lower at low pressure than LBW at same heat at atmospheric
pressure.

 

3.

 

In the keyhole vapour pressure increases with the increase in depth and
the pressures are very high near the bottom. As the radius of keyhole decreases
with increase in depth, the vapour pressure increases at a much higher rate. In
the estimation of keyhole radius decreases from its maximum value to minimum
value. In all actuality, the keyhole base is assumed to be negligible and
radius is assumed to have some finite values. This is the reason that vapour
pressures that are calculated near the keyhole base are higher than its
original value.

 

Peak Temperatures obtained at the
top of the surface in case of

 

Ti–6Al–4V were much higher than 21Cr–6Ni–9Mn. The reason for this is the
high boiling point and low thermal conductivity in solid state.

 

The reason for lower keyhole temperatures in EBW is due to low atmospheric
pressure results in more deeper penetrations in comparison to LBW.

Heat transfer and fluid flow during keyhole mode
laser welding

 

 

 

1.    
In this paper, pre-existing model
to calculate fluid flow and heat transfer is developed for the understanding of
laser welding of keyhole mode for particular condition in welding Ti-6Al-4V,
vanadium, 304L stainless steel and Tantalum. The thing that is required and not
presently accessible is a phenomenological model for the keyhole mode welding
which is utilized for welding an extensive number of alloys and metals with
extraordinary physical properties under different welding conditions. In this
paper, a phenomenological model is developed.

 

 

 

 

2.

 

 The participation of convection
with respect to conduction in the heat exchange was higher for 304L stainless
steel and least for tantalum. The relative significance of these two components
in the heat exchange relied upon the thermal diffusivity and temperature
coefficient of surface pressure of alloys and metals. On comparison with 304L
stainless steel, heat exchange by conduction is found to be more efficient for
tantalum because it has lower temperature coefficient an higher thermal
diffusivity.

 

The shape and weld penetration of metals and alloys are affected by
thermophysical properties. Temperature coefficient of surface effects the shape
of weld pool. High melting point and high thermal diffusivity of tantalum
results in little weld pools contrasted to other materials.

 

3.

 

The main principle of heat exchange for all the materials is Convective
heat transfer which was higher for 304L stainless steel and least for tantalum.

Influence of process parameters on
surface quality

 

1, .

 

In this paper the effect of process parameters on
flatness, surface quality, surface roughness, and overlapping are assessed. The
recognizing feature is the melting of single layers with a nonstop laser. In
view of these outcomes joined with visual perception of the solid tracks, the
impact of process parameters on the surface roughness is examined. The
measurement of surface roughness is done by SV-2000 profilometer.

 

2.

 

 

The outcomes demonstrate that the factors influencing
surface roughness are laser power, scanning speed and scan spacing. To evaluate
quality the peak height, and depth of lowest point of profile are very
important parameters. With the increase of layer thickness there is increase in
peak height.

 

It is found that how a little change in values of laser
power can change the surface roughness of part. The emitted energy gives
indication of extremely significant variety in the layer quality. On the flip
side, the peaks that are framed between the contiguous tracks are influenced by
layer 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 of
molecules takes place which results in a smaller contact area which relates to
very less accumulation of heat and bigger densification which is the reason for
no balling effect and successful layering.

This

phenomenon may be explained because with a low layer

thickness, a good particle packing is more likely to occur.

Consequently, a smaller contact area takes place and in
consequence,

a less heat accumulated a fuller densification and at

last, a successful layer without balling
effect

 

 

 

 

 

 

 

 

 

Influence of the particle size
distribution on surface quality and mechanical properties

 

 

 

1.

 

In this paper the mechanical properties, part density and surface
quality of three different materials are compared.

 

2

With the use of modified powders, low surface roughness materials can be
obtained. The process of blasting can help further in improving surface
roughness of materials but does not effects the rank of material. Mechanical
properties can be further improved with the use of modified powders in additive
manufacturing by SLM.

 

 

 

 

 

3.

 

The reason for the low surface roughness and high density with the use
of finer particles is that fine particles are melted easily in comparison with
coarse particles which results in higher mechanical strengths Also, finer
particles 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 X
alloy. As the processing parameters like laser control,  laser speed, layer thickness and angle of a
surface were systematically fluctuated to comprehend their impacts on surface
harshness. The average roughness, Ra, was measured for both up-skin surfaces
and down-skin surfaces . The development system for the roughness on these two
kinds of surfaces has been considered. Simulation  was likewise utilized to understand thermal
profiles  and their resultant impact on
surface harshness. The simulated result has been observed to be predictable
with the deliberate outcome

 

 

 

2.

 

Formation of melt pool and results of surface roughness for inclined
surfaces were explored by comparison of different bulk solid material and
powders in terms of conduction and heat transfer . At high scanning speeds
formation of large balling was observed because of Rayleigh instability, poor
wettability and the loss of contact between the melt and the substrate. Little
balling was seen at low scanning speeds and high scanning power  because of long fluid lifetimes, expanded melt
volumes and decreased melt viscosities. Large overlapping because of little
hatch distance advances the particle attachment on surface which results in the
increase of surface roughness.

 

 

 

 

 

 

 

 

On Optimization of Surface Roughness

 

1.

 

 The re-melting process for the improvement
of surface roughness of Additively Manufactured parts utilizing a measurable
approach. Laser remelting (LR) as post- processing technique was performed with
a specific end goal to explore surface roughness through parameter optimisation.
The use of optimized process  parameters
was depended on statistics data analysis inside the Design of Experiment
system, from which a model was then developed.

 

 

 

 

2.

 

The results obtained in this paper demonstrated that LR has high  potential for the improvement of surface
roughness related to the parts manufactured with the SLM process. The
microstructure dendrites, for example, balling, agglomeration, waviness, and
the microstructures of shrinkage pits can be wiped out up to a great extent,
when the ideal parameters are utilized. The surface roughness values can be
improved 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 melted
zone with a completely thick microstructure.

 

3.

 

LR results in the improvement of surface roughness and the reason for
this improvement is that the remelting process results in the change of
microstructure of material of thin surface layer with a specific depth which
results in a material with surface free from any defects and very high
smoothness.

 

 

 

 

 

 

 

 

Prediction of porosity in metal

 

 

 

 

1. A predictive model was developed on the basis of Gaussian process to
learn and predict the porosity. Further, a Bayesian inference system was used
for the estimation of porosity and statistical model parameters at any
particular point is predicted using the Kriging method. Porosity is a defect
that has been found commonly in SLM manufactured metal parts which results in
the compromise of performance and mechanical properties.

 

The parameters that has a greatly affect the porosity of SLM
manufactured parts are laser power, Scan speed,  layer thickness, hatch distance and size of
laser beam.

 

2.

 

Further it is found that there is decrease in porosity with increase in
laser 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 which
results in better powder melt and densification and subsequently the quality of
surface 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 the
synthesized track. A melt pool has more  reflectivity than free powder. The energy that
was absorbed is reheats the previous track or the substrate, the heat is
promoted through the substrate causing sintering of the powder. It is found
that increasing the scan speed and layer thickness pores becomes more oriented
thus increasing surface roughness and similarly for smaller layer thickness the
metal results in smoother surface was obtained

 

 

 

 

 

 

 

 

 

 

Surface roughness analysis

 

 

 

 

1.

Morphology and surface roughness of Steel 316L alloys was manufactured
by SLM process.. The surface investigation has demonstrated an increase in
thickness of particles situated on the progression edges, as the angle of
surface slope increases. At the point when thickness of layer is practically
identical to diameter of particle, the particles stuck along step edges can
fill the holes between adjacent layers, in this way influencing the actual
surface roughness.

 

 

2.

 

It is demonstrated that results of surface roughness anticipated by this
model are very similar to    the
surface roughness found experimentally. This paper describes the key variables
affecting surface morphology, and a hypothetical model for the prediction of
surface roughness that gives valuable data for the enhancement of surface
quality of SLM manufactured parts, hence limiting the need of surface finish. The
 study demonstrates the significance of
considering particle presence in the plan of hypothetical models, for a precise
expectation of surface roughness in the SLM process of steel.