Sami Sayer

Effect of Pin Penetration Depth on the Mechanical Properties of Friction Stir Spot Welded Aluminum and Copper

Abstract The effect of pin penetration depth on the mechanical properties of friction stir spot welded (FSSW) aluminum alloy 1050 and pure copper has been investigated. For a certian tool geometry, constant tool rotation speed and penetration time, the materials have been friction stir spot welded in three different penetration depths, namely 2.8 mm, 4 mm and 5 mm. Tensile shear tests, microhardness measurements and micostructural investigation have been carried out on the welded specimens in order to investigate the effect of penetration depth. 2.8 mm plunge depth has resulted in a weak joint, whereas 4 mm and 5 mm plunge depths offer acceptable tensile shear results. Presence of intermetallic phases had an influence on the tensile shear and hardness values.

Application of the Taguchi method for the optimization of the strength of polyamide 6 composite hot plate welds

Abstract The purpose of this study is to investigate the influence of the welding parameters in the hot plate welding process of polymer composites, polyamide 6 glass fiber reinforcement 15 wt.-%, by using the Taguchi method. Four welding parameters, namely the plate temperature, heating time, welding displacement and welding time, were optimized under the consideration of the joint strength. The Taguchi approach of the parameter design was used as a statistical procedure to set the optimal welding parameters. For hot plate welding of the specimens, the combination of process parameters based on three levels of the L9 orthogonal array was utilized. The signal to noise and the analysis of variance were employed to find the optimum levels and to indicate the impact of the welding parameters on joint strength by tensile tests of welded joints. It was shown that choosing 270 °C as plate temperature, 1.0 mm of weld displacement and 25 s of heating time, reveals an improved joint strength. For the optimized parameters it was verified that the welding time does not have a significant influence and the most effective factor on joint strength is the plate temperature. The weld displacement and heating time only slightly influenced the joint strength. A confirmation run was also performed to prove the effectiveness of the Taguchi method after determination of the optimum levels of the process parameters. The results showed that the joint strength was improved by about 27 % as compared to the initial welding parameters and the joint efficiency increased from 56 % to 71 %.

Influence of Pin Structure on Microstructure and Mechanical Properties of Friction Stir Welded AA 6063 (AlMgSi 0.5) Aluminum Alloy

Abstract In this study, AA 6063 (AlMgSi0.5) Aluminum alloy plates were welded by a solid state welding procedure, friction stir welding (FSW). The influence of pin structure on the microstructure of the weld region and the mechanical properties of the joints were studied. It has been seen that the helical structure on pinscrew has an effective role on the formation of a zigzag line in the weld region. While rather long and uninterrupted zigzag lines in the weld region are obtained when right helical pinscrew is used, left helical pinscrew gave rise to shorter zigzag lines. While the zigzag line has no effect on the mechanical properties of the as-welded joint, heat treatment after the welding (PWHT) procedure seriously affects the strength of the joint due to the zigzag line formed in the weld region. The mechanical strength decreases with right helical pinscrew in PWHT, whereas, left helical pinscrew causes an increase in mechanical strength.

Influence of Tool Geometry on Microstructure and Mechanical Properties of a Friction Stir Welded 7075 Aluminum Alloy

Abstract The effectiveness of a friction stir welded joint is strongly dependent on several process parameters such as the tool geometry, including the height and the shape of the pin and the shoulder surface of the tool. In this study, two pin parameters, namely the pitch dimension (1.25 and 0.75 mm) and the helix angle (right and left helices), are varied in order to study their influence on the micro-structural, hardness, and tensile properties of friction stir welded 6 mm thick aluminum alloy 7075. The results reveal that the best combination has been obtained when welding with a pitch dimension of 0.75 mm using a right helix pin.

Welding parameters and joint strength optimization during friction stir welding of high density polyethylene (HDPE) using the Taguchi method

Abstract The aim of this study is to investigate the effect of important process parameters and tool parameters on joint strength in fiction stir welding process of high density polyethylene (HDPE) using the Taguchi experimental design method. The tool rotation, feed rate and tool shoulder diameter were considered as varying parameter and used to fabricate the joints. The quality of the joint was evaluated by examining the characteristics of the joint as a result of ultimate tensile strength. For friction stir welding of the plates, the experiments were arranged by using Taguchis L9 orthogonal array in randomized way. From the analysis of variance and the signal-to-noise response graphs, the significant parameters and the optimal combination level of the parameters were obtained. It was found that using a tool rotation of 1600 rpm, a feed rate of 20 mm·mm−1 and a shoulder diameter of 20 mm, an improved joint strength can be obtained. A confirmation run is also performed to prove the effectiveness of the Taguchi method. The results show that joint strength was improved by about 25% compared with the initial welding parameters.

Mechanical Performance of Polyamid 66 and Influence of Glass Fiber Content on Moisture Absorption

Abstract This study investigates the determination of the mechanical performance of polyamid 66 and the influence of moisture and short glass fiber content (15 wt.-% and 30 wt.-%) at six different conditioning times (1, 2, 4, 8, 16, 32 minutes) in 105 °C water vapor. It was determined that as the glass fiber content increases, moisture absorption decreases. While the moisture absorption increases, tensile strength decreases and the percental elongation and toughness increases. It can also be derived that continuation of moisture absorption after 16 minutes is not effective and beneficial. The moisture absorption values observed in this study are equivalent to the amount of moisture that can be absorbed at 50 % relative humidity and 23 °C room temperature in the air for four months.

Effects of Post Weld Aging on the Mechanical Properties and Microstructure of TIG and MIG Welded AA 7075

Abstract In this study, the effect of post-weld artificial aging has been investigated on Tungsten Inert Gas (TIG) and Metal Inert Gas (MIG) welds of Aluminum Alloy 7075 (AA 7075). Artificial aging has been carried out for several durations at a temperature of 125 °C. In order to study the effect of post-weld aging, microstructural examination, hardness measurements and room temperature tensile tests have been carried out. The results show that TIG and MIG welding caused an increase in grain size in the HAZ and the weld metal as compared to the base material. After post-weld aging, it turned out that the mechanical properties of MIG welds increased while those of TIG welds decreased for the same aging conditions, compared to as-welded joints, while the grain sizes are not significantly affected from the aging process.

Optimization of welding parameters of hot plate welded PC/ABS blends by using the Taguchi experimental design method

This study aims to investigate the influence of welding parameters in hot plate welding (HPW) process of polycarbonate (PC)/acrylonitrile-butadiene-styrene (ABS) blends using Taguchi method. Three welding parameters, namely the plate temperature, heating time, and welding displacement, were optimized in terms of joint strength using the results of tensile tests. Taguchi experimental design method is implemented as a statistical design of experiment technique so as to set the optimum welding parameters and determine the optimal levels. For HPW of the specimens, the combination of process parameters based on three levels of L9 orthogonal array was utilized. The signal to noise ratio and the analysis of variance were employed to find the optimum levels and to indicate the impact of the welding parameters on joint strength after tensile tests of the welded joints were carried out. It was shown that it might achieve the improved joint strength using 290 °C of plate temperature, 1.25 mm of welding displacement, and 25 s of heating time. For the optimized parameters, it was verified that the most effective factor on joint strength is plate temperature and second effective factor is welding displacement and heating time only slightly influenced on joint strength. After the optimum levels of process parameters are set, in order to demonstrate the effectiveness of Taguchi method, a confirmation run is also performed. An improvement by about 70% from initial welding parameters was observed, and joint efficiency has increased from 22.5% to 38.2% regarding base material properties.

Mathematical Modelling of Vibration Response Characteristics for Dissimilar Hot Plate Welded Polyamide 6 Composite Beams

Abstract This study is concerned with the mathematical modelling of the vibration response characteristic of a special dissimilar composite beam based on experimental modal analysis. Here, experimental modal analyses of three different dissimilar polyamide 6 composite beams, which are connected to each other by hot plate welding are performed. The measured natural frequencies are compared with finite element predictions for verification purposes. Modal information obtained by experiments is used to construct a mathematical model representing vibration response characteristic of beams by applying multi degree of freedom curve fitting method. The model showing modal characteristics of dissimilar beams is now ready to be used in different kinds of excitations to predict the frequency response of vibration.

Mechanical and Microstructural Behaviour of Dissimilar Aluminum Alloys Joined by Friction Stir Welding

Abstract In this study, joining of dissimilar aluminum alloys 5059-H111 and 7075-T651 was carried out using friction stir welding. The joint has been investigated in terms of microstructure, hardness and mechanical properties. Optical microscopy was used to characterize the microstructure of the weld area. Seven different zones of the microstructure in the joint can be distinguished. It has been observed that a fine grain structure is formed in the nugget zone as a result of recrystallization. Although there is a general hardness decrease throughout the weld region compared to both base metals, the lowest hardness values are seen at the heat affected and thermo mechanically affected zones of aluminum alloy 5059. The mechanical strength of the dissimilar joint was found to be varying between 56 % to 68 % those of the base metal ultimate tensile strength values. The results show that friction stir welding can be successfully applied for the joining of dissimilar aluminums alloys.