EFFECT OF THE PROCESS PARAMETERS ON GEOMETRICAL CHARACTERISTICS OF THE PARTS IN DIRECT METAL DEPOSITION: A REVIEW

International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print),
ISSN 0976 – 6359(Online), Volume 5, Issue 4, April (2014), pp. 116-122 © IAEME
116
EFFECT OF THE PROCESS PARAMETERS ON GEOMETRICAL
CHARACTERISTICS OF THE PARTS IN DIRECT METAL DEPOSITION:
A REVIEW
1
Subodh Kumar, 2
Ajit Kumar Singh Choudhary, 3
Rakesh
1
Department of Production Engineering, B. I. T. Sindri, Dhanbad, Jharkhand(India)
2
Department of Mechanical Engineering, Manav Rachna International University, Faridabad (India)
3
Department of Production Engineering, B. I. T. Sindri, Dhanbad, Jharkhand(India)
ABSTRACT
Direct Metal Deposition (DMD) is a blending of five common technologies: laser, CAD,
CAM, Sensor and Powder Metallurgy. It builds metallic parts layer by layer directly from the CAD
data. The process has been widely used in manufacturing, part repairing/coating and metallic rapid
prototyping. However, success of this technology depends mainly upon the geometrical quality of
the components produced, which in fact strongly dependent upon various parameters such as laser
power, beam diameter, scanning speed, powder mass flow rate, etc. This paper presents a review on
the DMD process, its parameters and influence of the parameters on geometrical characteristics of
the components.
Keywords: Direct Metal Deposition, CAD, CAM, Sensor, Powder Metallurgy, Process Parameters,
Product Characteristics.
1. INTRODUCTION
Direct Metal Deposition (DMD), is one of the material additive rapid manufacturing
techniques which in fact is the blending of five common technologies – Laser, CAD, CAM, Sensors
and Powder metallurgy [1, 2]. This technique has shown tremendous potential for different fields of
application such as rapid manufacturing [3], parts repairing etc.[4, 5]. The process is known by
several names, most of which are trademarks of various machine manufacturers or research
establishments, these include laser metal deposition (LMD), direct laser deposition (DLD), laser
engineered net shaping (LENS), laser cladding, laser deposition welding and powder fusion welding.
In DMD, laser beam is used to form a melt pool on a metallic substrate, into which powder is fed.
The powders get melted by the heat of laser and form a deposit on the substrate by fusion bonding.
INTERNATIONAL JOURNAL OF MECHANICAL ENGINEERING
AND TECHNOLOGY (IJMET)
ISSN 0976 – 6340 (Print)
ISSN 0976 – 6359 (Online)
Volume 5, Issue 4, April (2014), pp. 116-122
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Once a layer is deposited, the powder delivery nozzle and focusing lens assembly is incremented up,
and another layer is deposited. The process is repeated until the part is complete. When the process is
correctly controlled a wide range of metal like Titanium, Nickel, Cobalt, Steel alloys etc. can be
deposited. The as-deposited microstructure is similar to that of an as-welded structure, so post-
deposition heat treatment may be required. [6]
One of the important features for of the DMD process is the fabrication of parts with accurate
geometries. The dimensional accuracy of the parts produced by DMD technique depends on the
uniformity and repeatability of deposition height. This can only be achieved if the laser retracted
distance is equal to the height of the layer deposited. This fact necessitates knowing in advance the
layer thickness deposited so that laser processing head can be retracted by equal distance.
This paper, therefore, focuses on a review of the process and various research efforts made to
find out the effects of the DMD parameters and the relationship between process parameters and
product/process characteristics. Fig1. shows a schematic of the process.
Fig.1: Schematic Diagram of the DMD process
2. LBDMD PROCESS PARAMETERS AND PRODUCT CHARACTERISTICS
2.1 Process Parameters
In DMD, a large number of operating parameters govern the process. Understanding the
relationship between these parameters and their effects on the process are crucial to the geometrical
and physical quality of the parts. In general, these parameters are classified into four groups as
shown Table 1.
Table 1: Main Process Parameters [7]
Laser Motion Device Powder Feeder Materials
- Average power
- Spot size
- Wavelength
- Pulsed/CW
- Beam profile
- Laser pulse shaping
- Relative velocity
- Relative acceleration
- System accuracy
- Powder feed rate
- Inert gas flow arte
- Nozzle specification
- Powder stream
Profile
-Substrate geometry
- Composition
- Powder size
- Surface tension
- Metallurgical,
thermo-physical
and optical
properties

118
2.2 Parts Quality
The properties of the deposited layers using the DMD process can be classified in the
following four groups: geometrical, mechanical, metallurgical and qualitative properties. Table 2
shows the parameters which contribute to these four groups. Some of these may be inter-related; for
instance, the wear resistance can be affected by hardness, the microstructure, the number of cracks
and their depth and direction, and the bonding between base materials and substrate.
Table 2: Clad properties [7]
Geometrical Mechanical Metallurgical Qualitative
- Clad dimension
- Dilution
- Roughness
- Hardness
Distribution
- Residual stress
- Wear resistance
- Tensile strength
- Microstructure
- Dilution
- Grain size
- Homogeneity
- Corrosion
resistance
- Porosity
- Cracking
3. PROCESS PARAMETERS AND GEOMETRICAL PROPERTIES
In order to comprehend in detail the process nature and furthermore, control the process
outcome, a number of numerical and analytical models have been developed for simulation of the
process. One of the first attempts to model the process was performed by Picaso et al. [9], who
developed a simplified model for predicting the process speed and the powder feed rate for the
specified laser power, beam diameter and clad height. Their work concentrated on the multi-pass
laser cladding and used analytic three dimensional modelling, having assumed however that powder
was pre deposited on the substrate.
Kiecher et al. [10] attempted to relate build parameters to deposition using an energy density
approach. They integrated the supplied energy over the area of the layer to be built and were able to
show that deposition varied linearly with energy density. Their approach only studied two build
parameters – laser power and velocity- and did not consider material input, which must also
influence deposition.
Toyserkani et al.[11,12] investigated the laser cladding process by using transient three
dimensional finite element modelling. The effect of the powder feed rate as well as the travel speed
were investigated in [11] where as the laser pulse shaping effect was investigated in [12]. These
investigations have showed that the clad height increases by decreasing the process speed, or by
increasing the powder feed rate and the laser pulse energy or the laser pulse frequency.
Kummailil et al.[13] studied the effect of laser power, scan velocity, hatch spacing and
powder mass flow rate on deposition using two level fractional designed experiment to develop
simple relationships between build parameters and deposition. Their approach did not consider
material properties. Result of their designed experiment suggests that increasing mass flow rate or
laser power increases deposition, while increasing hatch spacing or scan velocity decreases
deposition. According to them mass flow rate and scan velocity seem to have the highest effect on
deposition. Also, deposition appears to be related to the product of energy per unit area and mass
flow rate through a power relationship as:

119
a
xu
PAm
Z 



∆
∝
(1)
where P is the power; A, the absorptivity; m, the mass flow rate rate; ∆x, the hatch spacing and u, the
scan velocity.
Apart from these four build parameters studied in [13], Kumar et al; [8] considered other
builds parameters and material properties also for developing their generalized theoretical model to
calculate the layer thickness. They used dimensional analysis as their modelling tool. For physical
modelling they have considered DMD as a function of both material delivery and energy delivery.
Accordingly, they developed material delivery model and energy delivery model separately
considering their associated factors and finally combined them as:
4
1
4
4
1
2
)(



 −








∆
=
u
PPm
TC
h
CZ c
mp
f
DMD
ρ
ε
Where ZDMD is the layer thickness, ρ the powder density, m powder flow rate, u laser scan velocity,
ε absorptivity, hf heat of fusion, Cp specific heat capacity, ∆Tm temperature difference, P laser power,
Pc critical power and C dimensionless constant. The validity of this generalized model has been
verified from experimental data of H13 and Ti material and it was found in good agreement with
experimental finding by other researcher. The error of prediction using this model is 12.899%.
Both the model developed in [13] and [8], deposition appears to be through a power
relationship within the range of parameters tested. In model by [13], it seems that increasing velocity
by one unit should be approximately equivalent to decreasing the mass flow rate by one unit,
however, it is not so in model developed by [8]. It is probably due to the other build parameters and
material properties considered in same model.
Considering surface tension as a dominant phenomenon, Lalas et al.[14] developed an
analytical model to estimate the clad width, depth and height. They first calculated the liquid clad
volume per unit length by the powder feed rate assuming the substrate is still solid. They then
considered substrate and powder both liquefied and estimated the clad geometry. Their model
estimates the clad width with a deviation of 1.5% for high powder feed rate and 13% with low
powder feed rate when compared with the experimental results.
Zhu et al.[15] fabricated thin wall parts of stainless steel 316L with different laser and
powder defocusing distances. The found that adopting the powder focussed below the substrate and
laser focussed above the substrate process can improve the surface quality.
Smuggerskey et al.[16] conducted a set of statistically designed experiments with LENS
apparatus consisting of 1.8 kW continuous wave Nd:YAG laser to sort through the various process
parameters and identify significant process variable for improving surface finish. With their test
material as stainless steel 316L their experimental result suggests that the optimal surface finish is
primarily a function of laser power and powder volume. The best surface finish (8 micrometers)
should be achieved at an intermediate power of 325 watts, an intermediate flow rate, and will be
independent of travel speed.
However, Ludovico et al; [17], performed roughness test on Nickel alloy, using six axis
machine equipped with a welding head and with a CO2 laser with a maximum power of 3kW. Result
for roughness showed that it increases with powder flow rate and laser power but it decreases with
scanning speed. It means that good surface sample can be obtained setting the powder flow rate and
laser power to the minimum value and the scanning speed to the maximum value.
(2)

120
The size of the molten pool is also influenced by the heat stored in the substrate or in the
previously deposited material. If the heat loss occurs very quickly, the width of the molten pool
decreases, on contrary, if the heat loss occurs very slowly, the width of the molten pool increases.
Setting the laser power and the processing speed, the width of the molten pool can be determined.
This is important because size of the molten pool affects the properties of the final product[18].
Vasinonta et al.[19] has provided a more fundamental understanding of the dependence of
melt pool size on process parameters by presenting melt pool length prediction for thin walled
structures in the form of “process map” based on non-dimensional process variables. They
demonstrated that melt pool length is a strong function of laser power and velocity, and a weak
function of preheat temperature.
Fig. 2: Parameters interaction and their effect on geometrical characteristics of part
4. CONCLUSION
Various parameters involved in Direct Metal Deposition process has been categorized
on the basis of laser, motion drive of the system, powder feeder and materials properties. Also,
the property of the deposited layer has been classified into different groups such as
geometrical, mechanical, metallurgical and qualitative properties. Interaction of these
parameters such as dilution, laser power distribution, powder flow rate etc has been discussed and
finally the research conducted by various authors and their methodology in terms of geometrical
characteristics of the parts produced through Direct Metal Deposition has been reviewed and presented
in the table.3.
Direct Metal Deposition
Energy Delivery System & associated
factors:
Laser power
Critical power to initiate
melting
Absorptivity
Focal point position
Spot size
Temperature difference
Specific heat capacity
Heat of fusion
Material Delivery System & associated
factors:
Powder shape, size
Nozzle geometry
Nozzle stand-off-distance
Shielding gas flow rate
Feeder type
Powder composition
Powder density
Thermal property of powder
Laser Power
Density
Powder
flow rate
Melt pool temperature
Dilution
Laser scan velocity
Clad heightClad width
Cladding rate Overlap factor
Surface finish
Geometrical characteristics
Miscellaneous factors:
Powder catchment efficiency
Substrate temperature
Interaction time
Microstructure
Layer bonding

121
Table 3: Summary of the reviewed papers
S.
No.
Author Title of the Paper Year Parameters
considered
Characteristics
of the parts
studied
Methodology
1. Picaso et.al A simple but realistic model for
laser cladding
1994 Process speed
and the powder
feed rate
Clad height Analytic three –
dimensional
modelling
2. Kiecher et al. The laser forming of metallic
components using particulate
materials
1997 Laser power and
scanning speed
Deposition Energy density
approach.
3. Smugeresky et. al Laser Engineered Net
Shaping(LENSTM
) Process:
Optimization of Surface finish and
Microstructural Properties
powder volume
Surface finish Design of
Experiment
*4. Lewis et.al Practical considerations and
capabilities for laser assisted direct
metal deposition
2000 laser power and
the processing
speed
Melt pool size
5. Vasinonta et.al A process map for consistent build
conditions in the solid freeform
fabrication of Thin – Walled
Structure
velocity
Melt –Pool
length
Process Map
6. Toyserkani et. al Three- dimensional finite element
modelling of laser cladding by
powder injection: effect of powder
feed rate and travel speed on the
process
2003 Powder feed
rate and travel
speed
Clad height Transient three
dimensional
finite element
modelling
7. Toyserkani et. al Three- dimensional finite element
modelling of laser cladding by
powder injection: effect of laser
pulse shaping on the process
2004 Laser pulse
shaping
Clad height Transient three
dimensional
finite element
modelling
8. Kummailil et.al Effect of select LENSTM
processing
parameters on the deposition of Ti-
6Al-4V
2005 Laser power,
scan velocity,
hatch spacing
and powder
mass flow rate
Clad height Two level
fractional
designed
experiment
9. Lalas et. Al An analytical model of the laser
clad geometry
2007 Powder feed
rate
Clad geometry Analytical
modelling
11. Zhu et. Al The influence of laser and powder
defocusing characteristics on the
surface quality in laser direct metal
deposition
2012 laser and
powder
defocusing
characteristics
Track height &
Surface quality
Theoretical
calculation,
adjusting
relative locations
of focus points
10. KumarS et. Al Determination of layer thickness in
direct metal deposition using
dimensional analysis
2013 Both build
parameters and
material
properties
Layer thickness Dimensional
analysis
12. Ludovico et.al Experimental analysis of the direct
laser metal deposition process
2013 powder flow
rate and laser
power
Roughness Design of
Experiment
5. REFERENCES
[1] Krar S (2007) Direct metal deposition: manufacturing at the speed of light. p 3
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[3] Xiuli H, Lijun S, Gang Y et al (2011) Solute transport and composition profile during direct
metal deposition with coaxial powder injection. Appl Surf Sci 258:898-907.
[4] Santos EC, Shiomi M, Osakada K, Laoui T (2006) Rapid manufacturing of metal components
by laser forming. Int J Mech Tool Manuf 46:1459-1468.

122
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[14] Lalas C, Tsirbas K, Salonitis K, Chryssolouris G (2007) An analytical model of the laser clad
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laser metal deposition process. www.intechopen.com.
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EFFECT OF THE PROCESS PARAMETERS ON GEOMETRICAL CHARACTERISTICS OF THE PARTS IN DIRECT METAL DEPOSITION: A REVIEW

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EFFECT OF THE PROCESS PARAMETERS ON GEOMETRICAL CHARACTERISTICS OF THE PARTS IN DIRECT METAL DEPOSITION: A REVIEW