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The width of joined samples was 40 mm, length 40 mm and the length between clamps was 120 mm (Fig. 5). For tensile strength tests five samples were used for each type of joint. The basic geometry of tools used in the pressing technology was presented in Fig. 4. Strength tests were performed until complete separation of the joint by using Instron 3328 testing machine. The traverse speed of 10 mm/min of the tensile testing machine ensured constant conditions of the static test.

Figure 5 The width of joined samples was 40 mm, length 40 mm and the length between clamps was 120 mm (Fig. 5). For tensile strength tests five samples were used for each type of joint. The basic geometry of tools used in the pressing technology was presented in Fig. 4. Strength tests were performed until complete separation of the joint by using Instron 3328 testing machine. The traverse speed of 10 mm/min of the tensile testing machine ensured constant conditions of the static test.

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Figure 1 Example of pressed joint use in thin-walled structure of the industrial air conditioning duct
Figure 1 Example of pressed joint use in thin-walled structure of the industrial air conditioning duct
The joining tests were performed for steel sheets made of S350GD+Z275 (acc. to EN 10326 mat. number 1.0529) of the thickness of 140,05 mm, hot galvanized with coating of 275 g/m? of ~20 um thickness. The chemical composition was presented in Tab. 1, and the basic mechanical properties in Tab. 2.
The joining tests were performed for steel sheets made of S350GD+Z275 (acc. to EN 10326 mat. number 1.0529) of the thickness of 140,05 mm, hot galvanized with coating of 275 g/m? of ~20 um thickness. The chemical composition was presented in Tab. 1, and the basic mechanical properties in Tab. 2.
Figure 3 Examples of punch side embossments: round clinching joint (RCL), b) round clinching joint with additional rivet (CR), c) square clinching joint with material incision (SCL). Depending on the blind rivet type, different joint strength is obtained [24]. In the research only most commonly used rivet types for ventilation duct construction joining, were used. Steel blind rivets had the
Figure 3 Examples of punch side embossments: round clinching joint (RCL), b) round clinching joint with additional rivet (CR), c) square clinching joint with material incision (SCL). Depending on the blind rivet type, different joint strength is obtained [24]. In the research only most commonly used rivet types for ventilation duct construction joining, were used. Steel blind rivets had the
Figure 2 Lap joint: a) blind rivet, b) resistance spot welded
Figure 2 Lap joint: a) blind rivet, b) resistance spot welded
SERS RSE weer Stee Steere SD a I as Figure 7 Sheared weld nugget of lap joint of different values for welding current J (kA) Spot welded joint samples were separated in a tensile shearing test. Sheets did not separate (by cohesion loss) in the weld nugget for all values of the welding current (/=5, 5,5, 6, 6,5, 7 kA), but around the weld nugget (Fig. 7). Zinc coating, among others, has an influence on that joint destruction mechanism. The influence of the welding current on the sheet material macrostructure, for two values of the welding current, was illustrated in Fig. 8. In the case of 5 kA current the grain changing area and the intermediate area are visible. The area change is constant in a certain section. For J = 7 kA the grain grows significantly in the current flow direction, at the expense of the intermediate area. Changes of the welding current value caused differences in the maximum joints strength and the total dissipated energy (work or area under the load curve) — Fig. 9. Change of the welding current from 5 to 7 kA (40% increase) resulted in separation of the joined samples also in weld nuggets (the maximum joints strength increase of 47%).
SERS RSE weer Stee Steere SD a I as Figure 7 Sheared weld nugget of lap joint of different values for welding current J (kA) Spot welded joint samples were separated in a tensile shearing test. Sheets did not separate (by cohesion loss) in the weld nugget for all values of the welding current (/=5, 5,5, 6, 6,5, 7 kA), but around the weld nugget (Fig. 7). Zinc coating, among others, has an influence on that joint destruction mechanism. The influence of the welding current on the sheet material macrostructure, for two values of the welding current, was illustrated in Fig. 8. In the case of 5 kA current the grain changing area and the intermediate area are visible. The area change is constant in a certain section. For J = 7 kA the grain grows significantly in the current flow direction, at the expense of the intermediate area. Changes of the welding current value caused differences in the maximum joints strength and the total dissipated energy (work or area under the load curve) — Fig. 9. Change of the welding current from 5 to 7 kA (40% increase) resulted in separation of the joined samples also in weld nuggets (the maximum joints strength increase of 47%).
The increase of joint strength as a function of welding current (/) can be considered as linear (curve | in Fig. 10). However, if we specify the dependence between the relative increase of strength and the function of welding current increase, the optimum value can be determined Research related to the resistance spot welding process allowed to determine the influence of welding current on the joints strength of S350GD sheets. The welding current value affects creation of an appropriate weld nugget [25]. Sheets used in the experimental research had a zinc coating. Zinc and zinc compound vapours cause significant difficulties for a stable welding process. The main problem
The increase of joint strength as a function of welding current (/) can be considered as linear (curve | in Fig. 10). However, if we specify the dependence between the relative increase of strength and the function of welding current increase, the optimum value can be determined Research related to the resistance spot welding process allowed to determine the influence of welding current on the joints strength of S350GD sheets. The welding current value affects creation of an appropriate weld nugget [25]. Sheets used in the experimental research had a zinc coating. Zinc and zinc compound vapours cause significant difficulties for a stable welding process. The main problem
Figure 8 Microstructure of resistance spot welded joints for two different values of welding current J (kA)
Figure 8 Microstructure of resistance spot welded joints for two different values of welding current J (kA)
Figure 10 Dependence between welding current, joint strength and relative increase of shearing force value Figure 9 Long-elongation curves of resistance spot welded joint for different values of welding current
Figure 10 Dependence between welding current, joint strength and relative increase of shearing force value Figure 9 Long-elongation curves of resistance spot welded joint for different values of welding current
During the experimental research, the embossment thickness, for which the interlock is formed, was determined. For the forming force of the parameter X = 0,7 mm, the increase of forming force for X = 0,6 mm was compared. Then the forming forces were compared for X= 0,5 mm and X = 0,6 mm. For the remaining X values, relative changes of the forming force were calculated. Hence, relative increases of the forming force for all values of the X parameter were determined and compared with the average shearing force for the specified X parameter (Fig. 2). For these two parameters the optimum embossment hickness for Xis 0,5 mm (~25%-(t + t2)), when taking into account the value of the shearing force and maintaining a relatively low value of the forming force. When selecting he forming force value, also the increase of the forming ools pressure (punch and die) needs to be considered. High ool pressure load and high velocities of sheet material flow increase the tool wear [28, 29].
During the experimental research, the embossment thickness, for which the interlock is formed, was determined. For the forming force of the parameter X = 0,7 mm, the increase of forming force for X = 0,6 mm was compared. Then the forming forces were compared for X= 0,5 mm and X = 0,6 mm. For the remaining X values, relative changes of the forming force were calculated. Hence, relative increases of the forming force for all values of the X parameter were determined and compared with the average shearing force for the specified X parameter (Fig. 2). For these two parameters the optimum embossment hickness for Xis 0,5 mm (~25%-(t + t2)), when taking into account the value of the shearing force and maintaining a relatively low value of the forming force. When selecting he forming force value, also the increase of the forming ools pressure (punch and die) needs to be considered. High ool pressure load and high velocities of sheet material flow increase the tool wear [28, 29].
Figure 13 Joints cross-sections: a) RCL, b) SCL (t, = 0,11 mm, ¢,= 1 m 14 mm), c) CR (¢, = 0,12 mm, ¢, = 0,27 mm) Figure 12 Influence of minimum embossment thickness (X) on the shear strength (F max) of clinching joint
Figure 13 Joints cross-sections: a) RCL, b) SCL (t, = 0,11 mm, ¢,= 1 m 14 mm), c) CR (¢, = 0,12 mm, ¢, = 0,27 mm) Figure 12 Influence of minimum embossment thickness (X) on the shear strength (F max) of clinching joint
resistance spot welded joints, b) round clinching joint
resistance spot welded joints, b) round clinching joint
Figure 15 Average joints strength from shearing test Figure 16 Blind rivet lap joint after shearing test: a) fracture rivet surface, b) deformed part of the rivet head, c) sheet form the secondary rivet head, d) sheet form the rivet head
Figure 15 Average joints strength from shearing test Figure 16 Blind rivet lap joint after shearing test: a) fracture rivet surface, b) deformed part of the rivet head, c) sheet form the secondary rivet head, d) sheet form the rivet head
Figure 19 Round embossment view of ClinchRivet joint (CR) after shearing test: a) top sheet, b) bottom sheet
Figure 19 Round embossment view of ClinchRivet joint (CR) after shearing test: a) top sheet, b) bottom sheet
mw fe: Figure 18 Embossment view (CL joint) after shearing test for two values of X parameter: a) bottom sheet, b) top sheet
mw fe: Figure 18 Embossment view (CL joint) after shearing test for two values of X parameter: a) bottom sheet, b) top sheet
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