The International Journal of Advanced Manufacturing Technology https://doi.org/10.1007/s00170-018-2779-y
ORIGINAL ARTICLE
Optimization of friction stir spot welding process parameters for Al-Cu dissimilar joints using the energy of the vibration signals Alberto Nacer Colmenero 1 & Mario Sánchez Orozco 1 & Emilio Jiménez Macías 2 & Julio Blanco Fernández 3 & Juan Carlos Sáenz-Diez Muro 2 & Hipólito Carvajal Fals 1 & Angel Sánchez Roca 1 Received: 7 June 2018 / Accepted: 25 September 2018 # Springer-Verlag London Ltd., part of Springer Nature 2018
Abstract A friction stir spot welding (FSSW) process for dissimilar aluminum alloy AA1050 and pure copper sheets of 3-mm thickness at different tool rotation speeds between 710 and 1800 rpm and dwell time levels of 0, 5, and 10 s were performed in this study. Empirical relationships were developed to predict the shear failure load (joint strength) and the energy of the vibration signals incorporating two of the most important process parameters, tool rotation speed and dwell time. Process parameters were optimized by using the response surface method (RSM); the optimal values of tool rotation speed and dwell time were 1255 rpm and 4 s, respectively. The parameters optimization results were used in a confirmation test; the dissimilar Al/Cu FSSW joints made with optimal parameters exhibit a good shear failure load. The close relationship between the shear failure load (SFL) of the welded joint and the energy of the vibration signals (EVS) generated during FSSW process was demonstrated. This model can be used to develop and optimize the parameters for automatic control of the FSSW process, based on the vibration signal generated. Keywords friction stir spot welding . dissimilar Cu/Al joints . parameters optimization . energy of vibration signal
1 Introduction The use of welding for dissimilar materials in different industrial sectors has been experiencing a significant increase due to its technical and economic advantages. Joining dissimilar materials by means of welding processes leads to enormous difficulties because of the difference between the mechanical and metallurgic properties. This is the case of the process of dissimilar welding copper (Cu) and aluminum (Al) [1]. Cu and Al are materials with good electrical and thermal conductivity, which makes them useful in applications such as
electrical conductors, conductors for transformers and condensers, and heat exchangers. Conventional welding techniques by fusion are not recommended to join these materials (Cu-Al) due to the marked difference between their fusion temperatures and the tendency to form too hard or fragile intermetallic compounds, thus causing flaws [1, 2]. Alternative solid-state metal joining techniques, such as the process of friction stir welding (FSW), have proven to be viable for dissimilar joints of Cu-Al with excellent mechanical properties [3]. The process of friction stir spot welding (FSSW) is a variant of FSW with great potential to substitute
* Mario Sánchez Orozco
[email protected]
Hipólito Carvajal Fals
[email protected] Angel Sánchez Roca
[email protected]
Alberto Nacer Colmenero
[email protected] Emilio Jiménez Macías
[email protected]
1
Faculty of Mechanical Engineering, Universidad de Oriente, Ave. Las Américas s/n, CP 90900 Santiago de Cuba, Cuba
Julio Blanco Fernández
[email protected]
2
Electrical Engineering Department, Universidad de La Rioja, Logroño, La Rioja, Spain
Juan Carlos Sáenz-Diez Muro
[email protected]
3
Mechanical Engineering Department, Universidad La Rioja, Logroño, La Rioja, Spain
Int J Adv Manuf Technol
the resistant spot welding process. This method allows joining metal sheets without displacement of the tool and has been consolidated as a feasible option for automotive and airspace industries [4]. There are few reports available on obtaining dissimilar welded joints of Cu-Al by FSSW. Significant results have been achieved in the development of this technique [2, 5–9]; however, the scientific community researching into these topics continues to pay special attention and interest to the optimization of the parameters of the process for its direct relation with the resistance of the produced welded joints. Heideman et al. [5] obtained dissimilar welded joints between the 6061 Al-T6 and Cu by means of FSSW. These authors conducted metallurgic analyses to study the effect of the parameters: longitude of the pin, shoulder plunge depth, dwell time, and tool rotation speed in the resistance of the resulting welded joint. They managed to produce welded joints free of intermetallic compounds and of high resistance. Özdemir et al. [6] used three different tool plunge depths, 2.8 mm, 4 mm, and 5 mm respectively, to obtain dissimilar welded joints between the AA1050 and pure Cu by means of FSSW. The authors produced welded joints free of flaws and with good resistance in two of the three conditions (4 mm and 5 mm). The results of the resistance tests demonstrated that for a 4-mm plunge depth the higher resistance values were obtained; for 2.8 mm, the resistance values were very low. In 2014, Shiraly et al. [7] conducted welds by FSSW of compounds of Al/Cu produced by the accumulative rollbonding process at different tool rotation speeds. These authors found that the maximum values of shear failure load (SFL) were incremented with the increase of the rotation speed and came to the conclusion that the intermetallic compounds present in the stirred zone augment the hardness of the zone. Manickam and Balasubramanian [8] analyzed the effect of four parameters, tool rotation speed, plunge rate, dwell time, and tool diameter ratio, in the resistance of dissimilar welded joints between AA6061 sheets and pure commercial copper. The authors developed an empirical relation to predict the resistance of welds, by applying the response surface method (RSM), incorporating the aforementioned parameters. Based on the model obtained, the optimal parameters of the FSSW process were identified. Abbas et al. [9] produced dissimilar welds between AA2024T3 and pure commercial copper by means of FSSW at different rotation speeds and plunge times with three different tools. The process parameters were optimized with the use of the Taguchi technique. Furthermore, a Pareto chart was made, which allowed concluding that the plunge time was the most influential parameter in the resistance of the welded joints. Recently, Effertz et al. [10] investigated the effect of the FSSW process parameters, such as plunge depth, plunge time,
and rotational speed, in order to obtain the highest lap shear force. The authors used the Taguchi method as well as analysis of variance to study the influence of process parameters on the mechanical behavior of welding joints. They demonstrated that the plunge depth was the leading parameter in order to obtain the best lap shear force. An analytical model was used to predict the optimum performance of the design. Babu et al. [11] carried out the parameter optimization of FSW of cryorolled AA2219 alloy to obtain defect free weld joint with maximum weld strength. The authors used an artificial neural network to model the relationship between the input parameters and the mechanical and corrosion properties of the weld joints. The optimal FSW parameters were determined by genetic algorithm. The feasible input parameters were rotational speed of 1005 rpm, tool travel speed of 20 mm/min, and tool tilt angle of 3°. The FSW joint made with feasible solution exhibits good tensile strength, microhardness, and corrosion resistance. As it was possible to corroborate, several studies have been conducted to optimize the parameters of the FSW/FSSW process [8–12]. The techniques commonly applied to that end are the RSM, the Taguchi technique, or even the application of neural networks, among others. In all cases, the objective was to obtain a model that relates process parameters with the resulting resistance of the weld. However, studies about the application of non-invasive techniques, such as the monitoring of vibration signals, in the optimization of the FSSW process parameters are limited. In 2013, Orozco et al. [13] obtained welded joints with AA1050 by means of the FSW. These authors presented a model that allows predicting the resistance of welds based on the vibro-acoustic signals generated during the process. They also determined the optimal parameters of the process by means of the method of optimization by multiple responses. This study validated that the vibro-acoustic signals generated during the FSW process have a high sensitivity to any change in parameters, which corroborates the results of other published studies [2, 14, 15]. This paper aims the parameters optimization of the FSSW process for dissimilar welds of Cu/Al, applying the multiple response optimization method. The model obtained will allow predicting the optimal parameters of the process and the maximum SFL of dissimilar welded joints of Cu/Al, based on the energy of the envelope of the vibration signals generated during the FSSW process.
2 Experimental procedure To perform the experiments, the materials used were 3-mmthick sheets of aluminum alloy AA1050-H24 and commercially pure copper in annealed conditions, both with the
