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Investigation of Thermal Efficiency and Depth of Penetration during GTAW Process
Available online at www.sciencedirect.com
ScienceDirect Materials Today: Proceedings 18 (2019) 2962–2969
www.materialstoday.com/proceedings
ICMPC-2019
Investigation of Thermal Efficiency and Depth of Penetration during GTAW Process Bharat Singha*, Piyush Singhala, Kuldeep Kumar Saxenaa a
Department of Mechanical Enggineering, Institute of Engineering & Technology, GLA University, Mathura, U.P., 281406, India.
Abstract A numerical and experimental investigation of gas tungsten arc welding (GTAW) of AISI 304L was carried out to obtain the thermal field, depth of penetration with varying input process parameters. A three-dimensional finite element model is developed to simulate the GTAW welding process considering double ellipsoidal heat source with Gaussian heat flux distribution. A novel iso-volume approach is used to estimate the melting efficiency of the process and calculated maximum melting efficiency of the process is found 44 %. Calculated results in terms of thermal histories and depth of penetration have compared with measured results and are in good agreement. © 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the 9th International Conference of Materials Processing and Characterization, ICMPC-2019
Keywords: AISI 304L; Thermal efficiency; GTAW.
1. Introduction Fusion welding is a commonly used joining method, which deals with material heating, subsequent phase transformation. The controlling of welding process variables plays a vital role to obtain the desired weld quality and joint strength. There has been a changing trend in increasing use of AISI 304L Austenitic Stainless Steel weldment since past decades due to wide applications. Austenitic stainless steel grade AISI 304L is a most commonly used stainless steels due to its excellent temperature, pitting and corrosive resistance property in an aggressive environment [1]. AISI 304L, in addition to iron, contains chromium and nickel as
* Corresponding author. Tel.: +91-8273113063; E-mail address: [email protected]
2214-7853© 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the 9th International Conference of Materials Processing and Characterization, ICMPC-2019
B. Singh et al./ Materials Today: Proceedings 18 (2019) 2962–2969
2963
principal alloying elements which lead to enhanced resistant to corrosion. There is the variousestablished application of these steels as in nuclear reactor coolant piping, food processing industries, chemical and petrochemical industries, dairy industries etc. [2]. Arc welding has been considered as a viable process in austenitic stainless steel for leak-proof fabrication. Arc welding deals with the mechanical, electrical and chemical phenomenon, which involves melting or thermal evolution, fluid dynamics of the molten weld pool, metal –flux/filler reaction, electromagnetic effects, the width of heat affected zone (HAZ), physics of phase transformation, depth of penetration, and welding process parameters [3]. Due to these complexities in welding, weld joint has a tendency of inhomogeneities in the weld, cold laps, hot cracks, microfissure, and porosity etc. In fusion welding process, welding input parameters play a vital role to obtain the high strength joint [4-8]. Kant et al. [6] has investigated the effect of GTAW and SMAW process parameters on tensile strength, hardness, and structure and found sound weld joint of AISI 304L and AISI 316 dissimilar metal by using ER-309L in terms of fine austenitic structure and less HAZ. A sound weld joint quality mainly depends upon heat input to the base metal, filler metal to be used, type of welding process, type of shielding used to joint, and cooling rate [9, 10]. Singh et.al [11] has made an overview of different inversions of the GTAW process and compared the depth of penetration with conventional GTAW process. Activated flux, flux bounded and pulse current GTAW processes provides the deeper penetration as compared to conventional GTAW process. Arc welding process characterized by high energy consumption and low thermal efficiency [12]. Where the large investment in existing equipment is not required, the parameter optimization of energy reduction continues to be the area of research for the researcher. Thermal efficiency plays a vital role in energy transfer efficiency and sound weld joint. The determination of fusion or melting efficiency in the welded joint is still controversial. Many equations are available in the literature to calculate the melting efficiency in welding and give distinct results [5, 12-15]. The thermal efficiency of process and depth of penetration can be calculated based on thermal histories of the plate. Sufficient fusion of faying surface is depended on the depth of penetration and base material properties. Accurate modeling of welding phenomenon can reduce the cost of trials and experiments. In order to understand the usefulness of AISI 304L austenitic stainless steel, GTAW process is used on rectangular plates by varying welding parameters. The evolution of the thermal cycle of the welded plate is predicted by using FEA (Finite Element Analysis). It sought to analysis influence of welding process parameters as welding current (I), arc voltage (V), and welding speed (S) on calculated and measured values of temperature field and depth of penetration (DOP). Additionally, iso-volume approach is used to calculate the thermal efficiency.
2. Numerical Model The welding is considered as 3D heat conduction and transient problem. Thermo physical properties are assumed dependent on temperature which makes the problem nonlinear transient. The transient temperature distribution can be obtained using the Eq.1 [16].
T k x (T ) x x
T T T ( ) ( ) k T k T z Q C p (T ) y y z z t y
(1)
where T is the nodal temperature of the plate, k(T) and Cp are the temperature-dependent thermal conductivity and specific heat; ρ is the density of the material which is assumed constant in solid and liquid state; t is welding time; Q is the heat flux to base metal distributed by the double ellipsoidal heat source. The variation of thermal conductivity and specific heat with respect temperature can be obtained and incorporated by empirical relation given in Eq. 2 and 3 [17]. Thermal conductivity k(T) in W/m-0C k(T)= 8.116+0.1618T
(T<1427 0C)
k(T)= 12.29+0.003248T
(T >1427 0C)
(2)
Specific heats Cp(T) in J/Kg-0C Cp (T) = 465.4+0.1336T
(T<1427 0C)
Cp (T) = 788
(T >1427 0C)
(3)
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B. Singh et al./ Materials Today: Proceedings 18 (2019) 2962–2969
Initially, the temperature at t=0, is assumed 270C and Gaussian heat distribution is assumed for disbursement of heat flux on the plate. Double ellipsoidal type of heat source is used to model the welding torch. The combined effect of radiation and convection heat loss is used [18] in all region of the plate except the region below the heat source. Combined heat loss due to radiation and convection Ql= 24.1 x10-4 εT1.61, where ε is the emissivity (ε = 0.82). An in house FE code in MATLAB was generated to solve conduction Eq.1 with prescribed boundary conditions. 3. Melting or Thermal Efficiency In order to assess the performance of the process, melting efficiency is an important parameter to study. Melting efficiency quantifies the fraction of net heat input used to bring base metal to its melting point.In fusion welding process, an electrical arc is generated as a heat source to heat up and subsequent melting of material locally. The energy consumption in arc welding is influenced by welding input process parameters[14]. Eager [19] has observed the effect of thermal efficiency of the welding process on sound weld quality and environmental emissions. The thermal efficiency of the process can be described amount of heat absorbed by the metal to heat given to metal from heat source. The melting efficiency of the process for one root pass was proposed by [20], is given in Eq. 4.
m
QAw S VI
(4)
In Eq. 4 melting efficiency ηm, the melting enthalpy Q in J/mm3, Aw represents the molten weld bead cross-sectional area in mm2, arc voltage V, I the welding current in the amp, and S is the welding speed in mm/s. Based on the Box-Behnken design of experiment methodology, the different equation of melting efficiency was evaluated [5] and found that Eq. 5 describes the melting efficiency in a broader and complete way. Eq. 5 of melting efficiency provides better sensibility to the variation of welding input parameters for 2D and 3D domain.
m
EmaVma EmbVmb a .V .I .t
(5)
Where Ema and Emb are the fusion enthalpy of filler metal and base material respectively. Vma and Vmb are the volumes of deposited filler metal and volume of molten metal of base material respectively. a arc efficiency ( a =0.7). The values of fusion enthalpy for both Ema and Emb can be determined by the Eq. 6 proposed by [5, 20]
Ema orEmb
(Tm)2 300000
(6)
Where Tm is the melting point of the base metal or filler metal. The time taken in arc established is represented by t (sec). In the present study Eq. 5 is used to evaluate the melting efficiency of the process. Based on temperature distribution the volume of molten weld pool was evaluated. Consumption of filler rod, in terms of volume of cylindrical shape filler metal rod was estimated with respect to time t. 4. Results and discussion Experiments were performed on AISI 304L plates of dimensions 300mm X 70mm X 10 mm taking butt joint configuration. Specimen were cut from the large rolled sheet. A 308 L solid filler rod of 2 mm diameter was used to weld AISI 304L plates. The chemical compositions of base metal and filler rod are provided in table 1. Similar compositions of base and filler metal, are intended to reduce the effect of chemical in-homogeneities in joint. In order to avoid contamination inclusion in the weld pool, edges were cleaned mechanically before welding.
B. Singh et al./ Materials Today: Proceedings 18 (2019) 2962–2969
Table 1. The chemical composition of base metal and filler metal Composition C Cr Si P S Ti Mn (Wt %)
2965
Al
Co
Ni
Nb
Mo
Sn
Fe
Base Metal (AISI 304L)
0.019
18
0.34
0.028
0.001
0.004
1.6
0.003
0.2
8.1
0.006
0.38
0.008
70.60
Filler Rod
0.022
19.80
0.52
0.023
0.007
-
2.13
-
-
9.79
-
0.02
-
67.5
(SS 308L )
A manual GTAW process was used to carry out the welding. To minimize the manual operation error, three trials were taken to select the correct welding parameters and special care was taken to record the welding speed. The table 2 shows the selected welding parameters. Table 2. Input welding parameters Levels Parameters
Notations
Units
+1
0
-1
Welding Current
I
Amp.
160
180
200
Welding Voltage
V
Volt
35
37
40
Welding speed
S
mm/s
3
5
7
Shielding gas
-
-
Argon
Argon
Argon
A L9 orthogonal array experimental design matrix based on the chosen welding variables and their level, was used to conduct the experimental. Prepared design matrix is given in Table 3.Thermo physical properties of AISI 304 used for simulation, are given in Table 4. Table 3. Experimental orthogonal design matrix S.No
1 2 3 4 5 6 7 8 9
Welding Current (I)
Voltage (V)
Welding Speed (S)
160
35
3
160
37
5
160
40
7
180
35
5
180
37
7
180
40 35
7
200
37
3
40
Measured DOP (mm) 4.4
3.2
3.0
0.37
2.7
2.9
0.41
3.5
3.6
0.42
3.1
3.3
0.44
4.7
4.4
0.36
3.3
3.5
0.39
5.6
5.3
0.36
3.8
3.7
0.39
3
200 200
Numerical DOP (mm) 4.1
5
Melting Efficiency
Table 4. Thermo-physical Properties of AISI 304 [21] Properties Density(ρ) Convection Coefficient(h) Solidus Temperature (Ts) Liquidus Temperature(Tl) Latent Heat(L) Time step
Units 3
Value
Kg/m W/m2-0C
7900 10
0
C
1430
0
C
1480
J/Kg sec
2.74 x105 1
0.42
2966
B. Singh et al./ Materials Today: Proceedings 18 (2019) 2962–2969
Electric arc as a double ellipsoidal heat source is moving along x axis. Calculated nodal temperature over the symmetrical meshed plate of AISI 304L is shown in Fig. 1. It can be observed that nodal temperature decreases in the direction of thickness. Temperature of welded plate is recorded during weld run 1 at chosen strategic points P1(x=120, y=0, z=0), P2(x=120, y=3, z=0), P3(x=120, y=6, z=0), and P4(x=150 mm, y=2mm, z=0). The temperature data in Fig. 2 represent the average values obtained from four experiments performed under similar conditions to set up the repeatability of results. Temperature gradient near to weld centreline is higher and decreases away from the fusion zone.
Figure 1.Meshed symmetric plate for study and thermal field after 20 sec of start of welding
Figure 2. Temperature distribution at strategic points
Fig. 3 & 4 show the computed heat affected region and fusion zone for weld run1 using the proposed iso-volume method. The region of heat affected zone was estimated for a given temperature range in terms of iso-volume. Experimental measurement of weld bead dimensions was done as described by Ghosh et al. [22].
Figure 3. Temperature distribution and dimensions of heat affected zone (HAZ). Measured and calculated values of depth of penetration are tabulated in table 3. Figure 5 shows a better agreement in measured and predicted values of depth of penetration for weld run 1. It was observed the depth of penetration increased with welding current and voltage and a decrease in the increase in welding speed. The width of the weld pool or fusion zone is observed largely in X-Y and X-Z plane in comparison to width in the Y-Z plane as shown in Figure 4. Figure 6 shows the welded AISI 304L plate using the 308L filler rod.
B. Singh et al./ Materials Today: Proceedings 18 (2019) 2962–2969
(a)
2967
(b)
(c)
Figure 4. Temperature distribution and dimensions of fusion zone (FZ) a) X-Y plane, b) Y-Z plane and c) X-Z plane
Figure 5. Comparison of numerically calculated and measured the depth of penetration
Figure 6. Fusion and heat affected zone of welded AISI 304L plate with ER 308 Filler
The thermal efficiency of the process is calculated by using the iso-volume of the fusion zone. A small part of total energy used for melting the plate/substrate and the rest of the energy is transferred to the surrounding by means of conduction, convection, and radiation. The melting efficiency is significantly affected by welding input process parameters, the geometry of the plate to be weld, and thermo physical properties of the substrate. Distinct equations are available to calculate the melting efficiency of the of arc welding process. Estimation of accurate melted volume of substrate is still challenging. In present work melted portion of substrate was calculated from isovolume of fusion zone for any instant of time. Maximum calculated thermal efficiency of the process is 0.44 and shown in Fig. 7. The estimated efficiencies for all weld run found very close and with better agreement.
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B. Singh et al./ Materials Today: Proceedings 18 (2019) 2962–2969
Figure 7. Weld thermal efficiency for different weld run 5. Conclusion The important quantifiable parameter in the welding process is fusion and heat affected zone. It depends upon input operating parameters and process, thermophysical and chemical properties of the base material. The numerical approach presented in this paper has better agreement with measured and calculated temperature distributions. Based on the temperature profile over the welded plate calculated region of fusion and heat affected zone found good agreement with measured zones. Numerical calculations show that the peak temperature and the observed cooling rates were higher near to weld centerline. Proposed iso-volume approach provides the ease in the estimation of thermal efficiency with high accuracy. References 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13.
Desu, R.K., et al., Mechanical properties of Austenitic Stainless Steel 304L and 316L at elevated temperatures. Journal of Materials Research and Technology, 2016. 5(1): p. 13-20. Kumar, S. and A.S. Shahi, Effect of heat input on the microstructure and mechanical properties of gas tungsten arc welded AISI 304 stainless steel joints. Materials & Design, 2011. 32(6): p. 3617-3623. Wen, S.W., P. Hilton, and D.C.J. Farrugia, Finite element modelling of a submerged arc welding process. Journal of Materials Processing Technology, 2001. 119(1): p. 203-209. Singh, A.K., V. Dey, and R.N. Rai, A Study to Enhance the Depth of Penetration in Grade P91 Steel Plate Using Alumina as Flux in FBTIG Welding. Arabian Journal for Science and Engineering, 2017. Hackenhaar, W., et al., Welding parameters effect in GMAW fusion efficiency evaluation. The International Journal of Advanced Manufacturing Technology, 2018. 94(1): p. 497-507. Kant, R., et al., Fabrication and Characterization of Weldments AISI 304 and AISI 316 Used in Industrial Applications. Materials Today: Proceedings, 2018. 5(9, Part 3): p. 18475-18481. Vedrtnam, A., G. Singh, and A. Kumar, Optimizing submerged arc welding using response surface methodology, regression analysis, and genetic algorithm. Defence Technology, 2018. Bharat Singh, Piyush Singhal, and Avdhesh Sharma, Multiobjective Optimization of Submerged Arc Welding Parameters on AISI 5130 Alloy Steel using Taguchi Method. International Journal of Engineering and Advanced Technology, 2018(COMET 18): p. 2731. Yan, J., M. Gao, and X. Zeng, Study on microstructure and mechanical properties of 304 stainless steel joints by TIG, laser and laserTIG hybrid welding. Optics and Lasers in Engineering, 2010. 48(4): p. 512-517. Nakhaei, R., A. Khodabandeh, and H. Najafi, Effect of Active Gas on Weld Shape and Microstructure of Advanced A-TIG-Welded Stainless Steel. Acta Metallurgica Sinica (English Letters), 2016. 29(3): p. 295-300. Singh, A.K., V. Dey, and R.N. Rai, Techniques to improveweld penetration in TIG welding (A review). Materials Today: Proceedings, 2017. 4(2, Part A): p. 1252-1259. Unocic, R.R. and J.N. DuPont, Process efficiency measurements in the laser engineered net shaping process. Metallurgical and Materials Transactions B, 2004. 35(1): p. 143-152. Tadamalle, A.P., et al., Evaluation of Nd: YAG Laser Welding Efficiencies for 304L Stainless Steel. Procedia Materials Science, 2014. 6: p. 1731-1739.
B. Singh et al./ Materials Today: Proceedings 18 (2019) 2962–2969 14. 15. 16. 17. 18. 19. 20. 21. 22.
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Yan, W., et al., Multi-objective optimization of arc welding parameters: the trade-offs between energy and thermal efficiency. Journal of Cleaner Production, 2017. 140: p. 1842-1849. Magalhães, E.d.S., A.L.F.d. Lima e Silva, and S.M.M.d. Lima e Silva, A thermal efficiency analysis of a Gas Tungsten Arch Welding process using a temperature moving sensor. International Journal of Thermal Sciences, 2018. 129: p. 47-55. Goldak, J.A. and M. Akhlaghi, Computational Welding Mechanics, ed. S.-V. US. Vol. 321. 2005: Springer US. Choi, M., R. Greif, and M. Salcudean, A Study of the heat transfer during arc welding with application to the pure metal or alloys and low or high bioling temperature materials. Numerical Heat Transfer, 1987. 11(4): p. 477-489. Aissani, M., et al., Three-dimensional simulation of 304L steel TIG welding process: Contribution of the thermal flux. Applied Thermal Engineering, 2015. 89: p. 822-832. Eagar T W, An iconoclast’s view of the physics of welding rethinking old ideas. Recent trends in welding science and technology. ASM International, 1990: p. 341-346. Welding Handbook. 7(1976) ed. Vol. 1. 1976, Miami FL: American Welding Society,. de Moraes, D.A. and A. Czekanski, Thermal Modeling of 304L Stainless Steel for Selective Laser Melting: Laser Power Input Evaluation. 2017(58356): p. V002T02A033. Ghosh, A., A. Yadav, and A. Kumar, Modelling and experimental validation of moving tilted volumetric heat source in gas metal arc welding process. Journal of Materials Processing Technology, 2017. 239: p. 52-65.
ScienceDirect Materials Today: Proceedings 18 (2019) 2962–2969
www.materialstoday.com/proceedings
ICMPC-2019
Investigation of Thermal Efficiency and Depth of Penetration during GTAW Process Bharat Singha*, Piyush Singhala, Kuldeep Kumar Saxenaa a
Department of Mechanical Enggineering, Institute of Engineering & Technology, GLA University, Mathura, U.P., 281406, India.
Abstract A numerical and experimental investigation of gas tungsten arc welding (GTAW) of AISI 304L was carried out to obtain the thermal field, depth of penetration with varying input process parameters. A three-dimensional finite element model is developed to simulate the GTAW welding process considering double ellipsoidal heat source with Gaussian heat flux distribution. A novel iso-volume approach is used to estimate the melting efficiency of the process and calculated maximum melting efficiency of the process is found 44 %. Calculated results in terms of thermal histories and depth of penetration have compared with measured results and are in good agreement. © 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the 9th International Conference of Materials Processing and Characterization, ICMPC-2019
Keywords: AISI 304L; Thermal efficiency; GTAW.
1. Introduction Fusion welding is a commonly used joining method, which deals with material heating, subsequent phase transformation. The controlling of welding process variables plays a vital role to obtain the desired weld quality and joint strength. There has been a changing trend in increasing use of AISI 304L Austenitic Stainless Steel weldment since past decades due to wide applications. Austenitic stainless steel grade AISI 304L is a most commonly used stainless steels due to its excellent temperature, pitting and corrosive resistance property in an aggressive environment [1]. AISI 304L, in addition to iron, contains chromium and nickel as
* Corresponding author. Tel.: +91-8273113063; E-mail address: [email protected]
2214-7853© 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the 9th International Conference of Materials Processing and Characterization, ICMPC-2019
B. Singh et al./ Materials Today: Proceedings 18 (2019) 2962–2969
2963
principal alloying elements which lead to enhanced resistant to corrosion. There is the variousestablished application of these steels as in nuclear reactor coolant piping, food processing industries, chemical and petrochemical industries, dairy industries etc. [2]. Arc welding has been considered as a viable process in austenitic stainless steel for leak-proof fabrication. Arc welding deals with the mechanical, electrical and chemical phenomenon, which involves melting or thermal evolution, fluid dynamics of the molten weld pool, metal –flux/filler reaction, electromagnetic effects, the width of heat affected zone (HAZ), physics of phase transformation, depth of penetration, and welding process parameters [3]. Due to these complexities in welding, weld joint has a tendency of inhomogeneities in the weld, cold laps, hot cracks, microfissure, and porosity etc. In fusion welding process, welding input parameters play a vital role to obtain the high strength joint [4-8]. Kant et al. [6] has investigated the effect of GTAW and SMAW process parameters on tensile strength, hardness, and structure and found sound weld joint of AISI 304L and AISI 316 dissimilar metal by using ER-309L in terms of fine austenitic structure and less HAZ. A sound weld joint quality mainly depends upon heat input to the base metal, filler metal to be used, type of welding process, type of shielding used to joint, and cooling rate [9, 10]. Singh et.al [11] has made an overview of different inversions of the GTAW process and compared the depth of penetration with conventional GTAW process. Activated flux, flux bounded and pulse current GTAW processes provides the deeper penetration as compared to conventional GTAW process. Arc welding process characterized by high energy consumption and low thermal efficiency [12]. Where the large investment in existing equipment is not required, the parameter optimization of energy reduction continues to be the area of research for the researcher. Thermal efficiency plays a vital role in energy transfer efficiency and sound weld joint. The determination of fusion or melting efficiency in the welded joint is still controversial. Many equations are available in the literature to calculate the melting efficiency in welding and give distinct results [5, 12-15]. The thermal efficiency of process and depth of penetration can be calculated based on thermal histories of the plate. Sufficient fusion of faying surface is depended on the depth of penetration and base material properties. Accurate modeling of welding phenomenon can reduce the cost of trials and experiments. In order to understand the usefulness of AISI 304L austenitic stainless steel, GTAW process is used on rectangular plates by varying welding parameters. The evolution of the thermal cycle of the welded plate is predicted by using FEA (Finite Element Analysis). It sought to analysis influence of welding process parameters as welding current (I), arc voltage (V), and welding speed (S) on calculated and measured values of temperature field and depth of penetration (DOP). Additionally, iso-volume approach is used to calculate the thermal efficiency.
2. Numerical Model The welding is considered as 3D heat conduction and transient problem. Thermo physical properties are assumed dependent on temperature which makes the problem nonlinear transient. The transient temperature distribution can be obtained using the Eq.1 [16].
T k x (T ) x x
T T T ( ) ( ) k T k T z Q C p (T ) y y z z t y
(1)
where T is the nodal temperature of the plate, k(T) and Cp are the temperature-dependent thermal conductivity and specific heat; ρ is the density of the material which is assumed constant in solid and liquid state; t is welding time; Q is the heat flux to base metal distributed by the double ellipsoidal heat source. The variation of thermal conductivity and specific heat with respect temperature can be obtained and incorporated by empirical relation given in Eq. 2 and 3 [17]. Thermal conductivity k(T) in W/m-0C k(T)= 8.116+0.1618T
(T<1427 0C)
k(T)= 12.29+0.003248T
(T >1427 0C)
(2)
Specific heats Cp(T) in J/Kg-0C Cp (T) = 465.4+0.1336T
(T<1427 0C)
Cp (T) = 788
(T >1427 0C)
(3)
2964
B. Singh et al./ Materials Today: Proceedings 18 (2019) 2962–2969
Initially, the temperature at t=0, is assumed 270C and Gaussian heat distribution is assumed for disbursement of heat flux on the plate. Double ellipsoidal type of heat source is used to model the welding torch. The combined effect of radiation and convection heat loss is used [18] in all region of the plate except the region below the heat source. Combined heat loss due to radiation and convection Ql= 24.1 x10-4 εT1.61, where ε is the emissivity (ε = 0.82). An in house FE code in MATLAB was generated to solve conduction Eq.1 with prescribed boundary conditions. 3. Melting or Thermal Efficiency In order to assess the performance of the process, melting efficiency is an important parameter to study. Melting efficiency quantifies the fraction of net heat input used to bring base metal to its melting point.In fusion welding process, an electrical arc is generated as a heat source to heat up and subsequent melting of material locally. The energy consumption in arc welding is influenced by welding input process parameters[14]. Eager [19] has observed the effect of thermal efficiency of the welding process on sound weld quality and environmental emissions. The thermal efficiency of the process can be described amount of heat absorbed by the metal to heat given to metal from heat source. The melting efficiency of the process for one root pass was proposed by [20], is given in Eq. 4.
m
QAw S VI
(4)
In Eq. 4 melting efficiency ηm, the melting enthalpy Q in J/mm3, Aw represents the molten weld bead cross-sectional area in mm2, arc voltage V, I the welding current in the amp, and S is the welding speed in mm/s. Based on the Box-Behnken design of experiment methodology, the different equation of melting efficiency was evaluated [5] and found that Eq. 5 describes the melting efficiency in a broader and complete way. Eq. 5 of melting efficiency provides better sensibility to the variation of welding input parameters for 2D and 3D domain.
m
EmaVma EmbVmb a .V .I .t
(5)
Where Ema and Emb are the fusion enthalpy of filler metal and base material respectively. Vma and Vmb are the volumes of deposited filler metal and volume of molten metal of base material respectively. a arc efficiency ( a =0.7). The values of fusion enthalpy for both Ema and Emb can be determined by the Eq. 6 proposed by [5, 20]
Ema orEmb
(Tm)2 300000
(6)
Where Tm is the melting point of the base metal or filler metal. The time taken in arc established is represented by t (sec). In the present study Eq. 5 is used to evaluate the melting efficiency of the process. Based on temperature distribution the volume of molten weld pool was evaluated. Consumption of filler rod, in terms of volume of cylindrical shape filler metal rod was estimated with respect to time t. 4. Results and discussion Experiments were performed on AISI 304L plates of dimensions 300mm X 70mm X 10 mm taking butt joint configuration. Specimen were cut from the large rolled sheet. A 308 L solid filler rod of 2 mm diameter was used to weld AISI 304L plates. The chemical compositions of base metal and filler rod are provided in table 1. Similar compositions of base and filler metal, are intended to reduce the effect of chemical in-homogeneities in joint. In order to avoid contamination inclusion in the weld pool, edges were cleaned mechanically before welding.
B. Singh et al./ Materials Today: Proceedings 18 (2019) 2962–2969
Table 1. The chemical composition of base metal and filler metal Composition C Cr Si P S Ti Mn (Wt %)
2965
Al
Co
Ni
Nb
Mo
Sn
Fe
Base Metal (AISI 304L)
0.019
18
0.34
0.028
0.001
0.004
1.6
0.003
0.2
8.1
0.006
0.38
0.008
70.60
Filler Rod
0.022
19.80
0.52
0.023
0.007
-
2.13
-
-
9.79
-
0.02
-
67.5
(SS 308L )
A manual GTAW process was used to carry out the welding. To minimize the manual operation error, three trials were taken to select the correct welding parameters and special care was taken to record the welding speed. The table 2 shows the selected welding parameters. Table 2. Input welding parameters Levels Parameters
Notations
Units
+1
0
-1
Welding Current
I
Amp.
160
180
200
Welding Voltage
V
Volt
35
37
40
Welding speed
S
mm/s
3
5
7
Shielding gas
-
-
Argon
Argon
Argon
A L9 orthogonal array experimental design matrix based on the chosen welding variables and their level, was used to conduct the experimental. Prepared design matrix is given in Table 3.Thermo physical properties of AISI 304 used for simulation, are given in Table 4. Table 3. Experimental orthogonal design matrix S.No
1 2 3 4 5 6 7 8 9
Welding Current (I)
Voltage (V)
Welding Speed (S)
160
35
3
160
37
5
160
40
7
180
35
5
180
37
7
180
40 35
7
200
37
3
40
Measured DOP (mm) 4.4
3.2
3.0
0.37
2.7
2.9
0.41
3.5
3.6
0.42
3.1
3.3
0.44
4.7
4.4
0.36
3.3
3.5
0.39
5.6
5.3
0.36
3.8
3.7
0.39
3
200 200
Numerical DOP (mm) 4.1
5
Melting Efficiency
Table 4. Thermo-physical Properties of AISI 304 [21] Properties Density(ρ) Convection Coefficient(h) Solidus Temperature (Ts) Liquidus Temperature(Tl) Latent Heat(L) Time step
Units 3
Value
Kg/m W/m2-0C
7900 10
0
C
1430
0
C
1480
J/Kg sec
2.74 x105 1
0.42
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Electric arc as a double ellipsoidal heat source is moving along x axis. Calculated nodal temperature over the symmetrical meshed plate of AISI 304L is shown in Fig. 1. It can be observed that nodal temperature decreases in the direction of thickness. Temperature of welded plate is recorded during weld run 1 at chosen strategic points P1(x=120, y=0, z=0), P2(x=120, y=3, z=0), P3(x=120, y=6, z=0), and P4(x=150 mm, y=2mm, z=0). The temperature data in Fig. 2 represent the average values obtained from four experiments performed under similar conditions to set up the repeatability of results. Temperature gradient near to weld centreline is higher and decreases away from the fusion zone.
Figure 1.Meshed symmetric plate for study and thermal field after 20 sec of start of welding
Figure 2. Temperature distribution at strategic points
Fig. 3 & 4 show the computed heat affected region and fusion zone for weld run1 using the proposed iso-volume method. The region of heat affected zone was estimated for a given temperature range in terms of iso-volume. Experimental measurement of weld bead dimensions was done as described by Ghosh et al. [22].
Figure 3. Temperature distribution and dimensions of heat affected zone (HAZ). Measured and calculated values of depth of penetration are tabulated in table 3. Figure 5 shows a better agreement in measured and predicted values of depth of penetration for weld run 1. It was observed the depth of penetration increased with welding current and voltage and a decrease in the increase in welding speed. The width of the weld pool or fusion zone is observed largely in X-Y and X-Z plane in comparison to width in the Y-Z plane as shown in Figure 4. Figure 6 shows the welded AISI 304L plate using the 308L filler rod.
B. Singh et al./ Materials Today: Proceedings 18 (2019) 2962–2969
(a)
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(b)
(c)
Figure 4. Temperature distribution and dimensions of fusion zone (FZ) a) X-Y plane, b) Y-Z plane and c) X-Z plane
Figure 5. Comparison of numerically calculated and measured the depth of penetration
Figure 6. Fusion and heat affected zone of welded AISI 304L plate with ER 308 Filler
The thermal efficiency of the process is calculated by using the iso-volume of the fusion zone. A small part of total energy used for melting the plate/substrate and the rest of the energy is transferred to the surrounding by means of conduction, convection, and radiation. The melting efficiency is significantly affected by welding input process parameters, the geometry of the plate to be weld, and thermo physical properties of the substrate. Distinct equations are available to calculate the melting efficiency of the of arc welding process. Estimation of accurate melted volume of substrate is still challenging. In present work melted portion of substrate was calculated from isovolume of fusion zone for any instant of time. Maximum calculated thermal efficiency of the process is 0.44 and shown in Fig. 7. The estimated efficiencies for all weld run found very close and with better agreement.
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Figure 7. Weld thermal efficiency for different weld run 5. Conclusion The important quantifiable parameter in the welding process is fusion and heat affected zone. It depends upon input operating parameters and process, thermophysical and chemical properties of the base material. The numerical approach presented in this paper has better agreement with measured and calculated temperature distributions. Based on the temperature profile over the welded plate calculated region of fusion and heat affected zone found good agreement with measured zones. Numerical calculations show that the peak temperature and the observed cooling rates were higher near to weld centerline. Proposed iso-volume approach provides the ease in the estimation of thermal efficiency with high accuracy. References 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13.
Desu, R.K., et al., Mechanical properties of Austenitic Stainless Steel 304L and 316L at elevated temperatures. Journal of Materials Research and Technology, 2016. 5(1): p. 13-20. Kumar, S. and A.S. Shahi, Effect of heat input on the microstructure and mechanical properties of gas tungsten arc welded AISI 304 stainless steel joints. Materials & Design, 2011. 32(6): p. 3617-3623. Wen, S.W., P. Hilton, and D.C.J. Farrugia, Finite element modelling of a submerged arc welding process. Journal of Materials Processing Technology, 2001. 119(1): p. 203-209. Singh, A.K., V. Dey, and R.N. Rai, A Study to Enhance the Depth of Penetration in Grade P91 Steel Plate Using Alumina as Flux in FBTIG Welding. Arabian Journal for Science and Engineering, 2017. Hackenhaar, W., et al., Welding parameters effect in GMAW fusion efficiency evaluation. The International Journal of Advanced Manufacturing Technology, 2018. 94(1): p. 497-507. Kant, R., et al., Fabrication and Characterization of Weldments AISI 304 and AISI 316 Used in Industrial Applications. Materials Today: Proceedings, 2018. 5(9, Part 3): p. 18475-18481. Vedrtnam, A., G. Singh, and A. Kumar, Optimizing submerged arc welding using response surface methodology, regression analysis, and genetic algorithm. Defence Technology, 2018. Bharat Singh, Piyush Singhal, and Avdhesh Sharma, Multiobjective Optimization of Submerged Arc Welding Parameters on AISI 5130 Alloy Steel using Taguchi Method. International Journal of Engineering and Advanced Technology, 2018(COMET 18): p. 2731. Yan, J., M. Gao, and X. Zeng, Study on microstructure and mechanical properties of 304 stainless steel joints by TIG, laser and laserTIG hybrid welding. Optics and Lasers in Engineering, 2010. 48(4): p. 512-517. Nakhaei, R., A. Khodabandeh, and H. Najafi, Effect of Active Gas on Weld Shape and Microstructure of Advanced A-TIG-Welded Stainless Steel. Acta Metallurgica Sinica (English Letters), 2016. 29(3): p. 295-300. Singh, A.K., V. Dey, and R.N. Rai, Techniques to improveweld penetration in TIG welding (A review). Materials Today: Proceedings, 2017. 4(2, Part A): p. 1252-1259. Unocic, R.R. and J.N. DuPont, Process efficiency measurements in the laser engineered net shaping process. Metallurgical and Materials Transactions B, 2004. 35(1): p. 143-152. Tadamalle, A.P., et al., Evaluation of Nd: YAG Laser Welding Efficiencies for 304L Stainless Steel. Procedia Materials Science, 2014. 6: p. 1731-1739.
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