Upload
vunga
View
218
Download
0
Embed Size (px)
Citation preview
International Journal of Performability Engineering, Vol. 12, No. 2, March 2016, pp. 155-172.
© Totem Publisher, Inc., 4625 Stargazer Dr., Plano, Texas 75024, U.S.A
*Corresponding author’s email:[email protected] 155
Orbital TIG Welding Process Parameter Optimization using Design of Experiment for Satellite Application
M. KARTHIKEYAN1*, VALLAYIL N. A. NAIKAN2, R. NARAYAN1 and D.
P. SUDHAKAR1
1Liquid Propulsion System Centre (LPSC), Indian Space Research Organisation (ISRO),
Bangalore –560008, India. 2Reliability Engineering Centre (REC), Indian Institute of Technology (IIT), Kharagpur–
721302, India
(Received on October 26, 2015, revised on January 29, 2016)
Abstract: This paper highlights the optimization of Orbital Tungsten Inert Gas (OTIG)
welding process parameters by Design of Experiment (DOE) using Taguchi method
forwelding of stainless steel of 6mm diameter and 0.7 mm thickness for satellite
propulsion feed system. This proposed methodology identifies the optimum parameters
for welding and brings out the significance of the individual parameter, combination of
any of the two parameters (interaction effect) using Taguchi method by linear model
analysis of Signal to Noise (SN) ratio and means verses input parameters. Detailed
experiments were carried out and optimum parameters are arrived. Further these are tested
by different methods to evaluate the strength required for intended application. This
ensures sound and reliable weld joint. The optimum levels of these parameters thus
developed are being followed and no call for any rework is reported thereafter. By varying
the input parameters (current, RPM, gap between electrode and the job), the weld
penetration level or weld quality has been studied in several 6mm diameter tube
specimens andthe significance were studied and discussed in the test results.The Factorial
Factor design is followed for minimum of 27 (three parameters and three levels=3×3=27)
samples for this experiment. By further fine tuning the experiment, the optimized values
achieved are current 18.35 Amps, electrode rotation 10 rpm and gap between electrode
and job 0.8 mm. The weld specimen quality was verified in accordance with the user’s
quality standards and found satisfactory. This approach is easy to develop and easy to use
that assures the best combination of parameters required for Orbital TIG welding which
yield strong and defect free weld joint for Satellite application.
Keywords: OTIG, Power supply, failure effects, propulsion, satellite integration, optimal
current etc.
1. Introduction
The propulsion system provides the reaction control capability for attitude control and
orbit positioning in Polar & Geosynchronous orbits. The propulsion configuration consists
of many components and includes 6mm & 10mm outer diameter plumb lines (Propellant
feed lines) end connection with thickness of 0.7mm requiring Orbital TIG welding during
final integration of Satellites. The factors affecting the weld joints are precise control of
weld current, voltage input, gap between work pieces (plumb lines with propulsion
components), gap between electrode and work pieces, selection of electrode geometry,
bandwidth, electrode travel speed (RPM), flow rate of shielding gas used etc.
M. Karthikeyan, Vallayil N. A. Naikan, R. Narayan and D. P. Sudhakar
156
Figure 1: Feed Lines (Propulsion Schematic)
The variation of any of these parameters will certainly affect quality of weld in the
propulsion system resulting in weld defects such as undercut, lack of penetration, non-
uniformity, cracks, excessive weld bead width, excessive weld-puddle overlap etc. Hence
it becomes necessary to optimize the parameters based on experts’ opinion. Here control
Orbital TIG Welding Process Parameter Optimization using Design of Experiment for
Satellite Application
157
of weld current, RPM and gap between electrode and tube are taken as parameters for
study purpose. The initial setting of tubes to be welded is carried out by an experienced
operator to ensure the quality and rest of the welding operation is carried out by machine.
The Orbital TIG Welding power supply used for this welding provides consistent and
repeatable weld results. This welding study was done to evaluate the impact of individual
parameter and combination of parameters on the quality and reliability of weldments for
Spacecraft Propulsion system. This analysis involves selection of different matrices as
shown in the Table4 to determine the quality of each weld joint. Further to this analysis,
optimized values/ measures were suggested to avoid defects leading to critical failure of
weld joints. Therefore the analysis has been performed based on parameters given in the
table during integration phase of propulsion system to achieve defect free welding and
ensure high reliability.
The propulsion system is configured as Gas module (gas bottle, pyro valves, filter,
pressure regulators, check valve, latch valve, fill and drain valves etc.), Liquid module
(propellant tanks, pyro valves, filters, fill and drain valves) and Thruster module as shown
in the schematic (Figure 1). There are about 350 numbers of Orbital TIG weld joints to
interconnect propulsion components using 6mm and 10 mm plumb lines.
As the feed lines carry the propellants to the propulsive device, any leak in the welds
shall lead to catastrophic mission failure and the losses in terms of effort and money will
be substantial. Even a minor leakage will lead to disaster. In view of this, it is essential
that all the joints in the propellant feed lines need to be totally leak proof and this
demands the effective implementation of orbital TIG welding. In order to ensure this,
various reliability analysis tools such as FMECA, CED, FTA and PA are applied for this
process to guarantee improvements and effectiveness. This paper discusses the optimum
set of parameters for OTIG Welding, significance of each vital parameter and the
interaction behaviour using Taguchi Methodology by linear model analysis of Signal to
Noise (SN) ratio and Mean versus input parameters
2. Literature survey
Orbital TIG welding for feed lines of a propulsion system is a specialized application and
hence not many literatures are available in public domain. However, the related welding
investigations carried out by others are given here.
Sarafin [1]stressed the importance of high quality, integral weldments for space
applications and outlined the merits of orbital welding towards this. Devereaux and
Franscois [2] covered the details of MMH/NTO bipropellant propulsion system involving
propellant feed system that helps for transfer orbit manoeuvres and station keeping
operations. Synder [3] highlighted a complex ‘bang-bang’ xenon feed system and
suggested that a more simplified feed system is desirable in future. Selding [4] highlighted
the importance of leak proof propellant storage and feed systems and outlined the failure
of a communication satellite launched by Ariane 5 rocket due to leak in feed system. A
small leak of propellant can lead to a failure of a big mission with huge cost and enormous
efforts. Cristiano [5] highlighted the water hammer effect in the propellant feed line. He
also cautioned about the adiabatic compression detonation due to vapour or propellant. He
suggested the limit for pressure surge. Lin [6] cautioned about water hammer effect in
propellant feed system due to rapid propellant/gas entry during pressurization and
propellant feeding. Leca [7] analysed the water hammer effect in satellites due to sudden
M. Karthikeyan, Vallayil N. A. Naikan, R. Narayan and D. P. Sudhakar
158
pyro valve opening by experimental and software computations. Claude [8] has enlisted
spacecraft failures and the reasons there of since 1957. Chang[9] clearly enumerated the
huge losses (in millions of dollars) due to launch failures and analyzing the failure
between 1957 and 1999 indicated that out of 4378 launches, 390 failed and major causes
pointed to propulsion system failure due to fuel leakage among other reasons, this point to
the importance of defect free strong welding. Peasura [11] studied the shielding gas effect
on properties of HAZ and fusion zone on GTAW of Al – alloy AA5083 evaluating
hardness. Ding [12] outlined the importance of failure analysis to improve reliability. The
author used Fish bone analysis to bring out the relationship between failure modes and
causes. Samardžić [12] emphasized pipe welding for steam boiler using metal arc
welding, and the application of TIG welding and automatic orbital welding process.
Deshmukh and Sorte [14] have shown that the welding input parameters play a very
significant role in determining the quality of a weld joint with minimum distortion.Kumar
[15] studied TIG parameters and pitting corrosion of Al – alloys using ANOVA,
regression analysis and mathematical models. He found that Peak current (Ip) and
frequency have direct and base current (Ib) and pulse on time have inverse relation to
pitting. Kumara and Sundarrajan [15] have presented the results of extensive research on
improving the mechanical properties of AA 5456 aluminium alloy welds by pulsed TIG
deploying Taguchi method, regression models and analysis of variance. They also studied
the effect of planishing on properties. Palani [17] studying TIG parameters of Al-65032
using Taguchi and mathematical models found that welding speed impacts weld strength
and percentage elongation more than other parameters. Padmanabhan [18] studied
optimization of pulse TIG parameters on tensile strength of AZ31B Mg alloy and found
that the parameters peak current 210A, base current 80A, pulse frequency 6 Hz gave the
maximum tensile strength of 188 Mpa. Mahadevi and Manikandan [19] worked on TIG
welding parameters of AZ61 magnesium alloy by using response surface methodology
and analysis of variance and studied the effect of current, speed, voltage, electrode stick
out on tensile strength and percentage elongation. Sudhakar [20]analyzed the brazing
parameters for joining stainless steels by Ni braze alloy for rocket chamber application by
employing L9 Taguchi orthogonal array and AVOM and ANOVA. The influence of
parameters on strength and the interaction effects were studied. Joshi [20] studied the
MIG and TIG weldings. The authors have used the Design of Experiment method for
conducting the experiments and data analysis. Welding current, gas flow and wire feed
rate were the input parameters and the tensile strength of the weld was the output
parameter. Full factorial experimental design was used for this. Arya [22] utilized grey
relational analysis and Taguchi method to optimize the process parameters of MIG
welding such as weld current, arc voltage, welding speed, gas flow and wire diameter with
respect to bead geometry. Lothongkum [23]studied pulsed TIG parameters on Delta –
ferrite, shape factor and bead quality in orbital welding of AISI 316L. Trivedi [24]
reported that the shape and dimension of the weld bead affects strength, metallurgical
aspects and weld cracking effects. Karadeniz [25] studied the influence of weld
parameters on weld penetration in ERD emir 6842 steel of 2.5 mm thickness by robotic
GMAW and found that increasing weld current increased the penetration. Kumar and
Jindal [25] investigated the optimization of weld parameters such as current, voltage and
gas flow for GMAW using L9 Taguchi experimental design. Kumar etal. [26] studying
pulse TIG parameters using L27 Taguchi array found weld speed and input current
influenced weld strength more than other parameters such as voltage, stand-off distance,
pulse on –off times and gas flow. Gracia [28] researched on these welding programs for
Orbital TIG Welding Process Parameter Optimization using Design of Experiment for
Satellite Application
159
orbital TIG welding i.e., pulsed current & increasing speed, constant current, pulsed
current & decreasing speed and suggested that constant current provided better results
based on mathematical tests. Ratnayake and Vik [29] suggested a methodology to
recognize the most frequently appearing imperfect and defective welds by grouping based
on welding procedure specifications (WPSs) that contribute to the highest level of quality
deterioration. It is also emphasized that the kind of training that should additionally be
provided to the welders.
From the above literature reviews, it has been observed that there is need for
improving quality and reliability of the thin propellant feed tube welding for satellite
applications. These literatures provide that the penetration level of stainless steel is either
more or less depending on certain parameters during normal welding process of orbital
Pulsed-TIG welding process. Hence it is essential to increase the weld strength or
efficiency by optimizing the process parameters like current, RPM, gap between tube and
electrode to improve weld quality. The DOE approach appears to be appropriate to
address the quality issues on OTIG welding and to develop a robust process capable of
providing the required strength and quality of the propellant feed system for satellite
applications. As large numbers of reworks are reported in real practice, it is also felt the
need for optimizing weld parameters on stainless steel 304L tube by Taguchi analysis to
yield strong and reliable joints for satellite application.
3. Plan of investigation
In this work, the OTIG welding process is analyzed by experimental methods. Good
quality welding is influenced by several parameters (variables and constants) such as
current, RPM, standoff distance, gap between tubes where they butt each other, thickness
of the tube, purge/shield gas, electrode geometry, and voltage input etc. These are
enumerated in the Table 1. The cleanliness of tubes is another factor to be considered
prior to welding. This study is focused on only those parameters that have direct and
significant impact on the soundness of weld joints. The following steps are involved in
carrying out this experiment.
Table 1: Variables and Constants (Parameters)
Parameters (their units) Range Type V/C*
Current (Amps) 17.8 to 18.9 V
RPM (Nos) 9 to 10.5 V
Gap: Electrode & Tubes (mm) 0.7 to 0.9 V
Gap between Tubes (mm) 0.05 to 0.5 V
Thickness of Tubes (mm) 0.7 C
Purge Gas flow (Psi) 3 to 4 V
Electrode Geometry (mm) Sharp/Wider V
Voltage input (Volt) 240 C
* V-Variable, C-Constant
3.1 Identification of parameters
The ranges in which the parameters are being used for performing the welding
experiments are given in Table 2. Only three parameters that have direct significant
M. Karthikeyan, Vallayil N. A. Naikan, R. Narayan and D. P. Sudhakar
160
impact in the soundness of weld joints such as current, RPM and stand-off distance (gap
between electrode and tubes) are chosen for this experiment. These parameters are chosen
based on the previous experience in the welding process and the supporting literature as
discussed in the earlier section.
Table 2: Identification of Process Parameters
Factors Low (L) Medium(M) High(H)
Current(C) (Amps) 17.8 (C1) 18.35(C2) 18.9(C3)
RPM(R) (Nos.) 9.5(R1) 10(R2) 10.5(R3)
Gap(G) (mm) 0.7(G1) 0.8(G2) 0.9(G3)
3.2 Selection of Parameter ranges
In this paper, Swagelok welding machine is used for experimentation. The bead on trials
is made in 6mm Stainless Steel tube of wall thickness 0.7mm. The welding parameters
were selected on the basis of various trial runs by checking their effect on depth of
penetration. Though several parameters influencing welding are listed in Table 1, after
analyzing the direct significance, only three parameters at three levels were considered for
this experiment. The trials were taken for low, medium and high levels of the selected
three process parameters as shown in Table 2. Further, the Design of Experiment (DOE) is
carried out as shown in Table 4.
3.3 Material Properties
Propulsion system employs both stainless steel tubes and titanium tubes and we consider
here stainless steel 304L tubes. The parent metal, its Chemical Composition and
Mechanical properties are furnished in Table 3.
Table 3: Properties of SS 304 L
Chemical composition
percent by weight Mechanical properties
C 0.03 Tensile strength Ultimate 590 MPa
Cr 18-20 Yield Strength 250 MPa
Ni 8-12 Comp. Strength 250 MPa
Mn 2 Density 7890 kg/m3
P 0.045 Poisson ratio 0.29
S 0.03 Melting Point 1399 - 1454 °C
Si 0.75 Percent Elongation 35-50%
Al 0.1 Hardness 80(Rc)
Fe Balance Young Modulus 200 GPa
3.4 Testing Methods
After performing welding, normally the following tests can be done to validate the
weldment to ensure whether it meets the satellite requirements.
Liquid penetrant test
Pressure Decay by pressure transducer
Pressure Decay by pressure gauge
Orbital TIG Welding Process Parameter Optimization using Design of Experiment for
Satellite Application
161
Hydraulic Test
X-Ray Radiography
Grey method
Tear down method and UT test
Though above tests are possible in specimen level, liquid penetrant test and
hydraulic test are not recommended to do in the spacecraft level as those are involved
with specific liquids to perform the test which are not advisable after the final stage of
integration of tubes in the spacecraft. Tear down method and UT test are not possible
after integration. However remaining tests are recommended in system level.
3.5 Design of Experiments (DOE)
Taguchi methods are statistical methods developed to improve the quality of
manufactured goods and more recently applied to other domains such as engineering,
biotechnology, marketing etc. Professional statisticians appreciated the improvements
brought out by Taguchi’s development of designs for studying variation leading to
innovations in the design of experiments. The different reasons that cause variation in
design parameters and in the manufacturing process are termed as noises. The optimum
and most efficient way to solve these problems of variation is to make the design &
process insensitive to the effect of noises which are the causes of variation. This
underlying principle of robust design is the back bone of Taguchi analysis. It is a
scientifically disciplined mechanism for evaluating and implementing improvements in a
process with parametric optimization for the objective function, minimizing the effects of
undesirable noises. The purpose is to determine the optimum level for each process
parameter and to establish their relative significance.
Analysis of variance (ANOVA) is similar to regression in that it is used to investigate
and model the relationship between a response variable and one or more independent
variables. In this study general linear model is used to determine the influence of welding
speed, current and gas flow rate on ultimate tensile strength and % Elongation. After
conducting the experiments, the data taken are analyzed to determine the effects of
various parameters. The analysis of variance (ANOVA) and Taguchi analysis are used to
interpret the data. The statistical software MINITAB 14 is used for design of experiment.
4. Experimentation
OTIG welding experiments were initially carried out on specimens and then on tubes of
diameter 6mm and thickness 0.7mm as per the L27 matrix given in Table 4. This array has
three columns for process parameters and twenty seven rows of the combination of
parameters used for conducting the experiments and study three levels of parameters. The
welded specimens were tensile tested after radiography and bend tested subsequently.
4.1 Edge Preparation of Tubes
Extreme care has been taken for the edge preparation as a part of contamination control.
The required plump lines to be welded are cut from the source using chip-less cutter.
Further tube end connections are squared to 90o to match for butt welding as shown in
Fig. 2, de-burring by standard tool, cleaning by Isopropyl alcohol, drying by Nitrogen gas
and ensuring cleanliness through magnifying glass are standard procedure followed during
M. Karthikeyan, Vallayil N. A. Naikan, R. Narayan and D. P. Sudhakar
162
edge preparation. The specimen are prepared in the same method and tested as per
standard.
Figure 2: Edge Preparation Prior to Weld
4.2 Experimental trials
Orbital TIG welding has been carried out using Swagelok welding machine for stainless
steel specimens.
Figure 3: Experimental Set Up for OTIG Welding
Figure 3shows the welding experiment set up. After getting satisfied with the results
of specimen, trials were made on 6mm tube used for propellant feed lines as per
experimental design as shown on Fig.5. As explained in section 3.2, the three important
welding parameters were experimented at three levels i.e. low, medium, and high of each.
Totally 27 experiments were conducted as per L27 array of experiments. The current
sequence and the current levels are given in Fig. 4.
Orbital TIG Welding Process Parameter Optimization using Design of Experiment for
Satellite Application
163
Figure 4: Current Sequence
4.3 Testing
The ultimate tensile strength of the trial pieces welded was tested in the calibrated
universal tensile testing machine. The tensile tests were carried out according to the
ASTM standards. Due to pulling effect of machine, tube undergoes deformation. Twenty
seven specimens were tested and values obtained are given in Table.4. The specimen after
the test is shown in Fig. 6 and the welded tubes as seen in X-ray film is given in Fig.
7.The Input matrix of Taguchi design is given in Table 4 as shown below.
Figure 5: L-27 Matrix Welded Tubes Figure 6: Specimen after the Test
M. Karthikeyan, Vallayil N. A. Naikan, R. Narayan and D. P. Sudhakar
164
Figure 7: Welded Tubes in X-Ray Film
Table 4: Experimental Layout Using L27 Array and Responses
Sl.No Current(A) RPM Gap(mm) Max.
Load(N)
UTS
(N/mm2)
1 C1 17.8 R1 9.5 G1 0.7 5010 407.10
2 C1 17.8 R1 9.5 G2 0.8 6910 447.39
3 C1 17.8 R1 9.5 G3 0.9 6930 470.47
4 C1 17.8 R2 10 G1 0.7 7010 485.98
5 C1 17.8 R2 10 G2 0.8 7020 501.01
6 C1 17.8 R2 10 G3 0.9 7030 535.54
7 C1 17.8 R3 10.5 G1 0.7 7070 541.16
8 C1 17.8 R3 10.5 G2 0.8 7090 547.72
9 C1 17.8 R3 10.5 G3 0.9 7120 551.45
10 C2 18.35 R1 9.5 G1 0.7 7140 566.84
11 C2 18.35 R1 9.5 G2 0.8 7240 562.70
12 C2 18.35 R1 9.5 G3 0.9 7370 578.33
13 C2 18.35 R2 10 G1 0.7 7390 585.55
14 C2 18.35 R2 10 G2 0.8 7420 591.60
15 C2 18.35 R2 10 G3 0.9 7380 582.78
16 C2 18.35 R3 10.5 G1 0.7 7320 563.31
17 C2 18.35 R3 10.5 G2 0.8 7170 557.92
18 C2 18.35 R3 10.5 G3 0.9 7140 556.03
19 C3 18.9 R1 9.5 G1 0.7 7130 547.96
20 C3 18.9 R1 9.5 G2 0.8 7120 546.41
21 C3 18.9 R1 9.5 G3 0.9 7110 539.40
22 C3 18.9 R2 10 G1 0.7 7090 512.03
23 C3 18.9 R2 10 G2 0.8 7060 499.16
24 C3 18.9 R2 10 G3 0.9 7040 472.71
25 C3 18.9 R3 10.5 G1 0.7 7010 460.77
26 C3 18.9 R3 10.5 G2 0.8 6920 436.17
27 C3 18.9 R3 10.5 G3 0.9 4320 337.25
Orbital TIG Welding Process Parameter Optimization using Design of Experiment for
Satellite Application
165
5. Analysis of data and recording the responses (signal to noise ratio)
The S/N ratio is the ratio of size of signal factor effect to the size of error factor effect.
The S/N ratio consolidates several repeated output responses into a single value which
reflects the amount of variation present. The S/N ratio measures the sensitivity of quality
characteristic to external noise factor which is not under control. The highest S/N ratio
implies the least sensitivity of output response to noise factors. On the basis of
characteristic, three S/N ratios are available namely lower the better, higher the better and
nominal the better. In this paper higher-the-better is used for maximizing tensile strength
of the weld.
Table 5: Results of Signal to Noise Ratio Analysis
CURRENT RPM GAP UTS N/mm2 SNR
17.8 9.5 0.7 407.1 52.194
17.8 9.5 0.8 447.39 53.0137
17.8 9.5 0.9 470.47 53.4506
17.8 10 0.7 485.98 53.7324
17.8 10 0.8 501.01 53.9969
17.8 10 0.9 535.54 54.5758
17.8 10.5 0.7 541.16 54.6665
17.8 10.5 0.8 547.72 54.7712
17.8 10.5 0.9 551.45 54.8301
18.35 9.5 0.7 566.84 55.0692
18.35 9.5 0.8 562.7 55.0055
18.35 9.5 0.9 578.33 55.2435
18.35 10 0.7 585.55 55.3513
18.35 10 0.8 591.6 55.4406
18.35 10 0.9 582.78 55.3101
18.35 10.5 0.7 563.31 55.0149
18.35 10.5 0.8 557.92 54.9314
18.35 10.5 0.9 556.03 54.902
18.9 9.5 0.7 547.96 54.775
18.9 9.5 0.8 546.41 54.7504
18.9 9.5 0.9 539.4 54.6382
18.9 10 0.7 512.03 54.1859
18.9 10 0.8 499.16 53.9648
18.9 10 0.9 472.71 53.4919
18.9 10.5 0.7 460.77 53.2697
18.9 10.5 0.8 436.17 52.7931
18.9 10.5 0.9 337.25 50.559
The higher-the-better performance characteristic is expressed
S/NHB= -10 log {(1/y12+1/y22…1/yn2)/n} (1)
Where n is the number of repetition of output response in the same trial and y is the
response. Table.5 shows the result of Signal to Noise Ratio (SNR).
The above table shows the result obtained from the orthogonal array and signal-to-
noise ratio. Here there is a need to increase the tensile strength of the tube, hence higher-
the-better is selected and the main effects for the Signal to noise ratio is plotted.
M. Karthikeyan, Vallayil N. A. Naikan, R. Narayan and D. P. Sudhakar
166
6. Data Analysis using Taguchi techniques
Results of the ANOVA are presented in this section
Figure 8: Linear Model Analysis: SN Ratio
Versus Current, RPM and Gap
Figure 9: Linear Model Analysis: Men Versus
Current, RPM and Gap
Orbital TIG Welding Process Parameter Optimization using Design of Experiment for
Satellite Application
167
7. Experimental Results and Discussion
This section presents the results of the experiments such as effects of each parameter and
their combinations and analysis of residual plots.
7.1 Effect of Parameter Analysis
Analysis of Variance (ANOVA) is used to investigate and model the relationship between
a response variable and one or more independent variables. In this study, Taguchi notation
tells the number of runs, factors, and levels for each factor in the design. In this example,
the notation L27 (3x3) means a Taguchi orthogonal array with 3 factors with 3 levels
each. The experiment includes a signal factor which is ultimate tensile strength.
A dynamic response experiment, in which the goal is to optimize the relationship
between the input and the output of the system, includes a signal factor. Taguchi linear
model is used to study the influence of welding current, RPM, gap between tube as input
and electrode on ultimate tensile strength as output. In this experiment, the influence of
individual parameter and combination of parameters are also studied. The following are
the effects or results of parameters. The MINITAB software is used for this analysis. The
analysis shows Current is the most influencing parameter having rank 1, then the RPM
stands second followed by the Gap between tube and electrode in the third place.
For the S/N ratios, Current (p=0.000) and RPM (p=0.023) are significant at the 0.05
α-level.The remaining factor gap is not significant to the response.
If combination is considered for the S/N ratios, current* RPM (p=0.000), and current
*gap (p=0.017) are significant at the 0.05 α-level. The remaining RPM*gap is not
significant to the response.
R-Sq = 96.9% R-Sq (adj) = 89.8% shows that the process desired signal is more
Factors Current, RPM and gap between tube and electrode could explain the
variability of response of UTS with 89.8%
By this analysis, the effect or significance and rank of individual parameters were
obtained from the Linear Model Analysis of SN ratios. In addition, the individual
parameters contribution is also obtained from the Linear Model Analysis of Mean. i.e the
influence or the contribution by current, RPM and gap between tube and electrode are
88.1, 23.8 and 7.3 respectively.
In the experiment, pin hole or burn through is observed due to high current. Due to
that, the tensile strength obtained is the lowest among all values. This also apparently
appeared in the analysis as Unusual Observations for SN ratios as 27th element. R denotes
an observation with a large standardized residual. In Response Table for Signal to Noise
Ratios, higher is better was chosen as higher the ultimate strength, it is always better.
7.2 Main and Interaction Effects
The main and the interaction effects on SN ratio are shown in the figures 10 and 11
respectively. Figure 10 clearly shows that the mean of SN ratio increases with increase of
current till 18.35Amps and decreases with increase of current further. The mean of SN
ratio also increases with increase of RPM till 10 and decreases with increase of RPM
further. However, this effect is not appreciable when compared to that with respect to the
M. Karthikeyan, Vallayil N. A. Naikan, R. Narayan and D. P. Sudhakar
168
variation in the current. The mean of SN ratio does not significantly change with increase
or decrease of the gap. Similar observations are seen for mean also in the main effect plot
(Fig 11).
The mean of SN ratio increases with the combination of increase of current and RPM
till 18.35Amps and RPM of 10 and decreases with increase of current and RPM further
(Fig. 12). The figure also shows that the mean of SN ratio increases with the combination
of current and RPM. It can also be seen in the figure that the mean of SN ratio does not
appreciably increase with the combination of RPM and gap for low and medium level and
further decreases for higher gap. Similar observations can also be seen for mean in the
main effect plot (Fig. 13).
Figure 10: Main Effect Plot for SN ratio Figure 11: Main Effect Plot for Means
7.3 Residual plots
In residual plots, two outliers are found and remaining data fall within the confidence
limits of 95%. This is also understood from frequency curve. Residual verses the fitted
value shows that data are scattered. Fig. 14 shows the Residual plot for SN ratio and Fig.
15 shows the residual plot for means. Unusual observation is noticed in 27th data as it has
reduced the UTS value (Fig. 14). Similar observations are seen in residual plots for mean
also.
Figure 12: Interaction Plot for SN ratio Figure 13: Interaction Plot for Means
Me
an
of
SN
ra
tio
s
18.9018.3517.80
55.0
54.5
54.0
53.5
10.510.09.5
0.90.80.7
55.0
54.5
54.0
53.5
CURRENT RPM
GAP
Main Effects Plot (data means) for SN ratios
Signal-to-noise: Larger is better
Me
an
of
Me
an
s
18.9018.3517.80
560
540
520
500
480
10.510.09.5
0.90.80.7
560
540
520
500
480
CURRENT RPM
GAP
Main Effects Plot (data means) for Means
CURRENT
55
54
53
10.510.09.5
RPM
55
54
53
18.9018.3517.80
55
54
53
GA P
0.90.80.7
CURRENT
18.90
17.80
18.35
RPM
10.5
9.5
10.0
GAP
0.9
0.7
0.8
Interaction Plot (data means) for SN ratios
Signal-to-noise: Larger is better
CURRENT
600
500
400
10.510.09.5
RPM
600
500
400
18.9018.3517.80
600
500
400
GA P
0.90.80.7
CURRENT
18.90
17.80
18.35
RPM
10.5
9.5
10.0
GAP
0.9
0.7
0.8
Interaction Plot (data means) for Means
Orbital TIG Welding Process Parameter Optimization using Design of Experiment for
Satellite Application
169
Figure 14: Interaction Plot for Means Figure 15: Residual Plot for SN ratio
8. Conclusions
This paper has presented the optimization of process parameters of OTIG welding of 6mm
propellant feed tubes made of 304L Stainless Steel material for satellite system using
statistical optimization techniques. Design of experiments as per Taguchi’s L27 array was
used for the study. Taguchi linear model analysis of Signal to Noise (SN) ratio and means
versus input parameters were carried out. Analysis of variance, interaction effects and
residual plots were also made. Based on experimental results and confirmation tests, the
following conclusions can be drawn.
The optimum values obtained from the selected factors for welding of 6mm
SS304L tube are Current 18.5 A, RPM 10 and Gap between tube and electrode
0.8mm.
The most important parameter affecting the responses have been identified as
Current and this is followed by the RPM. Therefore, keeping good control over
the weld current is the key action which decides the weld strength and its quality.
Validation of weld strength is determined by tensile test. Also it was found that
there is good improvement in tensile strength values after optimizing the
parameters. Hence a good quality weld is obtained from optimized current, RPM
and gap chosen in the experiment.
By this study, the optimized process parameters would definitely improve the
reliability of propellant feed system for satellite propulsion which is highly
essential for the successful space missions.
References
[1]. Serafin, M. Orbital Welding for Space Program Applications: Producing Welds that
Withstand the Rigors of Deep Space.TPJ - The Tube & Pipe Journal., July-August 2000.
[2]. Devereaux, A. and François Cheuret. Development Testing Of a New Bipropellant
Propulsion System for the GMP-T Spacecraft.46th AIAA/ASME/SAE/ASEE Joint
Propulsion Conference & Exhibit, Nashville, Tennessee, July 25-28, 2010.
[3]. Synder, J. S., T. M. Randolph, R. R. Hofer and D. M. Goebel. Simplified Ion Thruster
Xenon Feed System for NASA Science Missions. IEPC-2009-064, Presented at the 31st
International Electric Propulsion Conference, University of Michigan, Ann Arbor,
Michigan, USA, September 20 – 24, 2009.
[4]. Selding, P. B. Brand New Satellite (Eutelsat W3B) Declared Dead After Launch. Space
Residual
Pe
rce
nt
20100-10-20
99
90
50
10
1
Fitted Value
Re
sid
ua
l
600500400
20
10
0
-10
-20
Residual
Fre
qu
en
cy
151050-5-10-15-20
8
6
4
2
0
Observation Order
Re
sid
ua
l
2624222018161412108642
20
10
0
-10
-20
Normal Probability Plot of the Residuals Residuals Versus the Fitted Values
Histogram of the Residuals Residuals Versus the Order of the Data
Residual Plots for Means
Residual
Pe
rce
nt
0.500.250.00-0.25-0.50
99
90
50
10
1
Fitted Value
Re
sid
ua
l
5554535251
0.50
0.25
0.00
-0.25
-0.50
Residual
Fre
qu
en
cy
0.40.20.0-0.2-0.4
8
6
4
2
0
Observation Order
Re
sid
ua
l
2624222018161412108642
0.50
0.25
0.00
-0.25
-0.50
Normal Probability Plot of the Residuals Residuals Versus the Fitted Values
Histogram of the Residuals Residuals Versus the Order of the Data
Residual Plots for SN ratios
M. Karthikeyan, Vallayil N. A. Naikan, R. Narayan and D. P. Sudhakar
170
News Staff Writer, October 29, 2010; 11:08am ET., 2010.
[5]. Cristiano, B., T. Tobias and M. Chiara. Experimental and Numerical Analysis of Water
HammerDuring the Filling Process of Pipelines. International Conference, Space
Propulsion, Cologne, Germany, May 19-22, 2014.
[6]. Lin,T. Y. and D. Baker. Analysis and Testing of Propellant Feed System Priming
Process. Journal of Propulsion and Power, May-June 1995; 11(3): 505-512.
[7]. Leca, C. MON and MMH pressure surges for a simplified propellant feed system. Third
International Conference on Spacecraft Propulsion, Cannes, France, October 10-13,
2000; 125-130.
[8]. Claude, L. Space Craft (Known) Failures. Space Craft Encyclopedia.
http://claudelafleur.qc.ca/Spacecrafts-index.html.
[9]. Chang, I. S. Space Launch Vehicle Reliability. Crosslink, The Aerospace Corporation
Magazine of Advance in Aerospace Technology, Winter 2001; 23-32.
[10]. http://www.aero.org/publications/ crosslink/ winter2001/03.html, 2001.
[11]. Peasura, P. and A. Watanapa. Influence of Shielding Gas on Aluminum Alloy 5083 in
Gas Tungsten Arc Welding. International Workshop on Information and Electronics
Engineering (IWIEE), 2012; 29: 2465 – 2469.
[12]. Ding, S. H., N. A. Muhammad, N. H. Zulkurnaini, A. N. Khaider and S. Kamaruddin.
Application of Integrated FMEA and Fish Bone Analysis – A Case Study in
Semiconductor Industry. Proceedings of the International Conference on Industrial
Engineering and Operations Management Istanbul, Turkey, July 3–6, 2012; 1233
1238.
[13]. Samardžić, Ivan, B. Despotović, and S. Klarić. Automatic Pipe Butt Welding Processes
in Steam Boilers Production.
https://bib.irb.hr/datoteka/301629.SamardzicDespotovic_Klaric.pdf., 2005.
[14]. Deshmukh, P. and M. B. Sorte. Optimization of Welding Parameters Using Taguchi
Method for Submerged Arc Welding On Spiral Pipes. International Journal of Recent
Technology and Engineering (IJRTE), November 2013; 2(5): 2277-3878.
[15]. Kumar, T. S., V. Balasubramanian and M. Y. Sanavullah. Influences of Pulsed Current
Tungsten Inert Gas Welding Parameters on the Tensile Properties of AA 6061
Aluminium Alloy. Materials and Design, 2007; 28(7): 2080 – 2092.
[16]. Kumar, A. and S. Sundarrajan. Optimization of Pulsed TIG Welding Process
Parameters on Mechanical Properties of AA 5456 Aluminum Alloy Weldments.
Materials and Design, April 2009; 30 (4): 1288–1297.
[17]. Palani, P. K., and M. Saju. Modelling And Optimization of Process Parameters For Tig
Welding Of Aluminium-65032 Using Response Surface Methodology. International
Journal of Engineering Research and Applications, March-April 2013; 3 (2): 230 – 236.
[18]. Padmanaban, G. and V. Balasubramanian. Optimization of Pulsed Current Gas
Tungsten Arc Welding Process Parameters to Attain Maximum Tensile Strength in
AZ31B Magnesium Alloy. Transactions of Nonferrous Metals Society of China, March
2011; 21 (3): 467 – 476.
[19]. Mahadevi, D. and M. Manikandan. Modelling and Parametric Optimization using
Factorial Design Approach of Tig Welding of AZ61 Magnesium Alloy. SSRG
International Journal of Mechanical Engineering (SSRG-IJME), Feb 2014; 1(1): 18-22.
[20]. Sudhakar, D. P., M. Rajmohan, Abhay K Jha, V. V. Babu and A. E. Muthunayagam.
Optimisation of Vacuum Brazing Conditions for Joining Stainless Steel 321 Sheets by
Nickel Based Braze Foil for Regenerative Rocket Nozzle Applications by Taguchi
Method. Journal of Aerospace Sciences and Technologies, August 2011; 63 (3): 230-
236.
[21]. Joshi, Jay, Manthan Thakkar, and Sahil Vora. Parametric Optimization of Metal Inert
Gas Welding and Tungsten Inert Gas Welding By Using Analysis of Variance and Grey
Relational Analysis. International Journal of Science and Research (IJSR), June 2014; 3
Orbital TIG Welding Process Parameter Optimization using Design of Experiment for
Satellite Application
171
(6): 1099-1103.
[22]. Arya, Dinesh Mohan, Vedansh Chaturvedi and Jyoti Vimal. Application of Signal to
Noise Ratio Methodology for Optimization of MIG Welding Process Parameters.
International Journal of Engineering Research and Applications, Jul-August 2013; 3(4):
1904–1910.
[23]. Lothongkum, G., E. Viyanit and P. Bhandhubanyong. Study on the Effects of Pulsed
TIG Welding Parameters on Delta-Ferrite Content, Shape Factor and Bead Quality in
Orbital Welding of AISI 316L Stainless Steel Plate. Journal of Materials Processing
Technology, 19 March 2001; 110(2): 233-238.
[24]. Trivedi, Parthiv T. and Ashwin P. Bhabhor. A Review on Techniques for Optimizing
Process Parameters for TIG Welding Aluminium, International Journal for Scientific
Research And Development., 2013; 1(9): 1752-1755.
[25]. Karadeniz, Erdal, Ugur Ozsarac, and Yildiz Ceyhan. The Effect of Process Parameters
on Penetration in Gas Metal Arc Welding Processes. Materials and Design, 2007; 28(2):
649-656.
[26]. Kumar, Deepak and Sandeep Jindal. Optimization of Process Parameters of Gas Metal
ARC Welding by Taguchi’s Experimental Design Method. International Journal of
Surface Engineering & Materials Technology, January-June 2014; 4(1): 24-27.
[27]. Kumar, R. Dinesh, S. Elangovan, and N. Siva Shanmugam. Parametric Optimization of
Pulsed – TIG Welding Process in Butt Joining Of 304l Austenitic Stainless Steel Sheets.
International Journal of Research in Engineering and Technology, June 2014; 3(11):
213-219.
[28]. Garcia, Jose A. Orlowski de, Nilton Souza Dias, Gérson Luiz de Lima, Wilson D.
Bocallão Pereira, and Nívio Fernandes Nogueira. Advances of Orbital Gas Tungsten Arc
Welding for Brazilian Space Applications. Journal of Aerospace Technology and
Management, May-August 2010; 2(2): 203-210.
[29]. Ratnayake, R. M. Chandima and K. T. Vik. Quality Surveillance Methodology for Pipe
Welding: An Industrial Case Study”, International Journal of Performability
engineering, November 2012; 8(6): 635-643.
Acknowledgment
Authors wish to thank Shri S. Ravi, Shri V. N. Misale, Shri C. Paulmany and team, and
Dr. Heeralal Gargama for their useful contributions in this work. Authors wish to express
their gratitude to Shri G. Narayanan, Deputy Director, SRQA, ShriS . Somanath, Director
LPSC and ASC Committee for their constant encouragements and kind permission to
submit this paper in any technical journal.
M. Karthikeyan is a Deputy Division Head for Satellite control components in System
Reliability and Spacecraft Propulsion and Sensors Group, LPSC (Liquid Propulsion
System Centre), ISRO (Indian Space Research Organisation), Bangalore. He took his
Master degree in Quality Management (MS) from Birla Institute of Technology and
Science, Pilani. He has wide experience in handling Chemical propellants like Cryogenic,
Bi and Mono propellants for Rockets and Satellites. He has been responsible for filling
propellants to Rocket stage and Spacecraft at launch Pad like Sriharikota, India and
KOUROU, French Guyana. He is responsible for quality surveillance which involves
OTIG welding for satellite integration. He is recipient of Team excellence award for
GSAT-12 (2011). He worked as Project Manager for several Indian satellite missions in
propulsion aspects. [email protected]
M. Karthikeyan, Vallayil N. A. Naikan, R. Narayan and D. P. Sudhakar
172
Vallayil N.A.Naikan is a Professor and Head in Reliability Engineering Centre at Indian
Institute of Technology (IIT), Kharagpur, India. He took his Masters and Doctorate degree
in Industrial Engineering and Management with specialization in Quality and Reliability
Engineering from IIT, Kharagpur, India. He has worked with Union Carbide (India),
Indian Institute of Management, Ahmedabad, and Indian Space Research Organization,
Ahmedabad, India. He has visited the Chinese University of Hong Kong for doing
research and has worked and visiting professor in the University of Maryland USA. He
has published his research works in many international journals, and presented papers in
many conferences. He is also actively involved in industrial consultancy and sponsored
projects. His research interests include condition monitoring, mechanical system
reliability, probabilistic risk and system assessment, quality planning and management,
reliability of engineering systems, and simulation. [email protected].
R. Narayan is Group Director in System Reliability and Spacecraft Propulsion and
Sensors Group, LPSC, ISRO, Bangalore. He joined in ISRO and served in
Thiruvananthapuram and presently in Bangalore. He took his Master degree in Quality
Management from Birla Institute of Technology and Science, Pilani. He has got
experience in filling propellant to Rocket stages and Space crafts at launch Pad like
Sriharikota, India and KOUROU French Guyana. He has been chief of Quality Assurance
for several Indian satellites in propulsion aspects. He has been responsible for effecting
essential improvements in propulsion components. He is the chief consultant for
resolving any satellite problem during launch. He has published many international
journals, and presented papers in conferences. [email protected]
D. P. Sudhakar is a Deputy General Manager in LPSC, ISRO responsible for delivering
all Liquid stages for PSLV and GSLV of Indian launch vehicles. He has completed his
Master degree in Anna University Chennai and his Doctorate degree in Kerala University
India. He has published in many international journals, and presented papers in
conferences. He is a manufacturing specialist and trained in Russia in Cryogenic Rocket
technology. He worked as Quality Control chief for Liquid propulsion rocket systems. He
is a recipient of best alumina award in school and team excellence award in ISRO.