Effect of resistance spot welding parameters on mechancial behavior of thin sheet
BENACHOUR Mustapha1,2
1Department of Mechanical Engineering, Faculty of Technology
2Ingeniery of Mechanical Systems and Materials Laboratory, University of Tlemcen, 13000, Tlemcen,
Algeria,bmf_12002@yahoo.fr
LARBI CHERIF Mohamed1
1Department of Mechanical Engineering, Faculty of Technology
University of Tlemcen, 13000, Tlemcen, Algeria
Abstract— Different welding methods have been developed for joining stainless steels; however, resistance spot welding is the promising method for welding of thin sheets of these steels.
Resistance spot welding is a non-solder process that uses the combined effect of mechanical pressure and an electric current passing through the parts. In this study, commercially 304L stainless steel sheets were welded by resistance spot welding at various welding parameters (welding effort, welding times and intensity of current welding. The results showed that the parameters, effort and welding time have little effect on mechanical properties compared with respect to the effect of the intensity of the current welding. The experimental results show also that the welding current is an important parameter for joining structures and its mechanical strength. The hardness and external aspects of spot were carried out in order to examine the influence of welding parameters on the welded joints. Hardness measurement results indicated that welding nugget had the highest hardness and this was followed by the heat-affected zone and the base metal.
Keywords— resistance spot welding ; hardness ; mechanical strength, stainless steel; electric current; welding time;
I. INTRODUCTION
Resistance welding is a welding process widely used in manufacturing industry for joining metal sheets and components. Spot welding is the predominant joining process in several industries especially in assembling automobile component. However, in other products such as in the aerospace industry, furniture and domestic equipment are joined using resistance spot welding [1]. Stainless steel in special case is used in furniture and domestic equipments.
The resistance spot welding process can be described by a number of parameters. The weld process can be described by a time, current and welding force. The welding current is the most effective and common parameter to influence welding result of a given material configuration. The welding time is of importance when calculating heat generation and resulting welds formation. Additionally, the force magnitude is another variable which will affect the outcome of the weld.
Several researchers have shown that the formation of nugget in any material by resistance spot welding depends on optimised combination of spot welding parameters [2 - 5]. The
weld quality is affected by several welding parameters: the current intensity, welding time, the force applied by electrodes, contact resistance, the size of electrodes [6].
Charde and Rajkumar [5] have investigated the effect of current and weld time with constant force on the nuggets growth in RSW of austenitic stainless steel 304.
The effects of welding parameters on the tensile shear strength of the joints were investigated by Qui et al. [7]. Qiu et al. have developed and reported the technology of resistance spot welding with cover plate, which has been used to weld magnesium alloy sheets, Al-alloy to steel and applied also in jointing 5052 Al-alloy [7]. In the study conducted by Kianersi et al. [8] an attempt was made to optimize the welding parameters namely welding current and time in resistance spot welding of the austenitic stainless steel sheets grade AISI 316L. Effect of welding current at constant welding time is considered in the evaluation of nugget size, tensile-shear load bearing capacity of materials. For the same materials (stainless steel 316), Jagadeesha and Jothi [9] have studied the influence of process parameters of resistance spot welding
The effects of welding current in the range 3–9 kA on the structure and mechanical properties of welded joint were investigated by Shawon et al. [10]. An increase in tensile strength of the weld coupon was shown in increasing of welding current. Otherwise, the variation in welding current has no significant effect on the hardness value. It mainly affects size of the fusion zone and heat affected zone. Also Hasanbasoglu and Kacar [11] found that the tensile shear load bearing capacity of welded material increased with an increase in peak welding current due to enlargement of the nugget size in resistance spot welding of dissimilar materials ((AISI 316L- DIN EN 10130-99 steel). Behulova and Nagy [12] have studied numerically the resistance of 304 stainless steel plates assembled by resistance spot welding and the formation of the nugget under the effect of welding parameter in a DP600 dual- phase steel. In recent research conducted by Shamsul and Hisyam [13], the relation between the nugget diameter and welding current and also Hardness along welding zone for austenitic stainless steel 304. Results have shown that the weld nugget increases with the increasing of welding current. In the investigation conducted by Thakur et al. [14] in assembled AISI-1008 Steel Sheets by RSW, they had shown that welding
current is most effective parameter controlling the weld tensile strength as well as the nugget diameter.
II. MATERIAL AND EXPERIMENTAL INVESTIGATION Stainless steel 304 L sheet with thickness of 2.0 mm was used in this study. Table 1 shows its chemical composition.
Figure 1 shows the shape of specimens. Specimens were prepared with a size of 115 mm (length) × 30 mm (width) × 2 mm (thickness) as shown in the Fig. 1. The dimension “A=30 mm” presents the overlap distance. Mechanical properties are given in Table 2 and load/displacement curves for receive material 304 L is shown on Fig. 2.
It is difficult to give a precise adjustment of the welding parameters. The settings of these parameters are directly depending on the application and are usually determined by testing. Welding conditions used in this investigation recommended for 304 L stainless steel are given in Table 3 with diameter of electrode is equal to 7 mm.
TABLE I. CHEMICALCOMPOSITION OF304 L STAINLESSSTEEL
C Si Mn P S Cr Ni
< 0.03 < 1.00 < 2.00 < 0.045 < 0.015 17.5-19.5 8-10
Fig. 1. Welding specimen by RSW
TABLE II. MECHANICAL CHARACTERISTICS OF304 LSTAINLESS STEEL
E (GPa) e (MPa) UTS (MPa) A% HRB
Provider
data 200 310 520-670 45 80 max
Tested
specimens 190 336 655 43.2 60
Fig. 2. Load/displacement curves for receive material
TABLE III. WELDING SCHEDULE
III. RESULTS AND DISCUSSION
The welded zone is affected by parameters of welding process (RSW). The hardeness at weld zone is affected.
Hardness test was carried out by using Rockwell hardness (B Scale) machine with 20 kg of pressing forces according to welding schedule on the upper surface of the welded assembly (Fig. 3)
Fig. 3. Load/displacement curves for receive material
Hardness variation along the vertical axis of the weld area to the free side is shown in figures 4a and 4b at welding current I= 10 KA. As shown by these figures, a significant difference is observed on the distribution of hardness in the base metal compared with respect to the hardness at the welded area. The maximum hardness at the weld point justified the presence of residual stresses due to thermal process.
A weak effect of the welding force and welding time is observed at different positions. Away from positions 1 and 2, the time effect is significant compared with respect to the central position of the welding point (figure 5a and 5b).
(a)
(b) Fig. 4. Evolution of Hardness for welding current I=10 KA and welding
force (a) F = 7 bar (b) F = 8 bar
(a)
(b) Fig. 5. Effect of welding current on hardness at central zone for welding
force (a) F = 7 bar, (b) F = 8 bar
The effects of the welding parameters on the welding geometry and the hardness at the welding point studied show the need to investigate its effects on behavior in shear strength of the assembly by overlay. The curves 6 and 7 show respectively the variation of the load versus displacement until fracture of the welded assembly by RSW for welding loads 8 and 7 bar at t = 10 cycles. The increasing in current intensity increases the area of the plastic deformation but random. The curves Load/displacement present several areas. Positions A present little distorted points. At positions B, rotation of point to align the sheets in the direction of loading and starts necking. Positions C give the maximum breaking loads and D positions represent the maximum effort achieved when the fracture propagated in the thickness in the necked region of one of the sheets and propagation of fracture in the base metal MB and tear around the point of the specimen to the final rupture. The effect of welding current on the maximum breaking load (points C) for both welding load is given by figures 8 and 9. The general appearance shows an increase in the breaking load with increasing welding current. To better understand some interactions of welding parameters and random phenomena, statistical tests are necessary and accompanied by analyzes of fracture surfaces at the interfaces.
Fracture of assembled of sheet plate by RSW under tension/shear load are given in Figure 9. Fracture is initiated heat affected zone and propagates in the base metal. This propagation is made according to the mode I of fracture.
Fig. 6. Effect of welding current on mechanical behavior of the welded assembly by RSW at welding force F=8 bar and time welding t=10 cycles
Fig. 7. Effect of welding current on mechanical behavior of the welded assembly by RSW at load welding F=7 bar and time welding t=10 cycles
Fig. 8. Effet of welding current on max breaking load at welding force 8 bar
Fig. 9. Effet of welding current on max breaking load at welding force 8 bar
(21) I=10 KA, T=10 cycles, F=7bar (22) I=10 KA, T=11 cycles, F=7bar (23 I=10 KA,T=11 cycles, F=7bar
(24) I=10 KA, T=10 cycles, F = 8 bar (20) I=10 KA, T=11 cycles F=8bar (19) I=10 KA,T=11 cycles, F=8bar
Fig. 10. Effect of welding parameters on frature modes in RSW IV. CONCLUSION
In this study, stainless steel 304 L sheets were welded using the resistance spot welding. The effects of welding parameters on the tensile shear strength of joint and hardness were investigated. The conclusions obtained in this investigation are summarized as follows:
Welding time and welding force have little effect on variation of hardness on free surface of spot weld.
Increasing of welding current allows to increases the hardness at spot weld.
Tensile/shear tests show that the welding current is dominant parameter over welding time and welding force on the evolution of the load/displacement curves.
Increasing in welding intensity increases the plastic deformation zone and the breaking load.
Acknowledgment
SORMEP Society was acknowledge for supporting assembly of sheet by resistance spot welding.
References
[1] CMW,http://www.cmwinc.com/resistance-welding-materials.html 2016.
[2] G. Farizah Adliza, H.P. Yupiter, “Manurung, Mohamed Ackiel Mohamed, Siti Khadijah Alias, Shahrum Abdullah. “Effect of process parameters on the mechanical properties and failure behavior of spot welded low carbon steel”. Journal of Mechanical Engineering and Sciences, Volume 8, pp. 1489-1497, June 2015
[3] M.R.A. Shawon, F. Gulshan, A.S.W. Kurny, “Effect of welding current on the structure and properties of resistance spot welded dissimilar (austenitic stainless steel and low carbon steel) metal joints”, J. Inst.
Eng. India Ser. D, 96(1), pp 29–36, January–June 2015.
[4] Oscar Andersson1, Arne Melander. “Prediction and Verification of Resistance Spot Welding Results of Ultra-High Strength Steels through FE Simulations”. Modeling and Numerical Simulation of Material Science, Vol. 5, pp 26-37, 2015.
[5] Nachimani Charde, Rajprasaad Rajkumar. “Investigating spot weld growth on 304 austenitic stainless steel (2 mm) sheets”. Journal of Engineering Science and Technology. Vol. 8, No. 1, pp 69 – 76, 2013.
[6] Mohsen Eshraghia, Mark A. Tschoppa, Mohsen Asle Zaeemd, Sergio D. Felicellia. “Effect of resistance spot welding parameters on weld pool properties in a DP600 dual-phase steel: A parametric study using thermomechanically-coupled finite element analysis”. Materials and Design, Vol. 56, pp 387–397, 2014.
[7] Ranfeng Qiu, Zhanling Zhang, Keke Zhang, Hongxin Shi, and Gaojian Ding. “Influence of welding parameters on the tensile shear strength of aluminum alloy joint welded by resistance spot welding”. JMEPEG, Vol. 20, pp 355–358, (2011).
[8] D. Kianersi, A. Mostafaei, AA. Amadeh, “Resistance spot welding joints of AISI 316L austenitic stainless steel sheets: phase transformations, mechanical properties and microstructure characterizations”, Mater Des Vol. 61, pp 251–263, 2014.
[9] T. Jagadeesha, T.J. Sarvoththama Jothi, “Studies on the influence of process parameters on the AISI 316L resistance spot-welded specimens”, Int. J. Adv. Manuf. Technol. DOI 10.1007/s00170-015- 7693-y.
[10] M.R.A. Shawon, F. Gulshan, A.S.W. Kurny, “Effect of welding current on the structure and properties of resistance spot welded dissimilar (austenitic stainless steel and low carbon steel) metal joints”, J. Inst.
Eng. India Ser. D, Vol. 96 (1), pp 29–36, 2015.
[11] A. Hasanbasoglu, R. Kacar, “Resistance spot weldability of dissimilar materials, (AISI 316L-DIN EN 10130-99 steel)”, Mater. Des., vol 28, pp 1794–1800, 2007.
[12] Maria Behulova, Máté Nagy, “Numerical simulation of the resistance spot welding of parts from the AISI 304 steel”.
[13] J.B. Shamsul and M.M. Hisyam. “Study of Spot Welding of Austenitic Stainless Steel Type 304” School of Materials Engineering, University Malaysia Perlis, Journal of Applied Sciences Research, 2007, INSI net Publication.
[14] A.G.Thakur, T.E.Rao, M.S.Mukhedkar, V.M.Nandedkar, “Application of Taguchi method for resistance spot welding of galvenized steel”, Journal of Engineering and Applied Sciences, vol.5 november-2010.
