Flat shoulder tool welded plate

Flat shoulder tool welded plate - Welding defects

Figure 1: Appearance of flat shoulder tool welded plate.

Figure 2: Flat shoulder tool welded plate (a) C scan (b) A scan (c) B scan (d) Radiography.

Figure 3: Appearance of concave shoulder tool welded plate.

Figure 4: Concave shoulder tool welded plate (a) C scan (b) A scan (c) B scan (d) Radiography.

Figure 5: Appearance of Sub shoulder welded plate.

Figure 6: Sub shoulder tool welded plate (a) C scan (b) A scan (c) B scan (d) Radiography.

Defect name: Voids
Record No.: 1914
Type of defect (Internal/Surface): Internal, surface
Defect classification: Welding defects
Steel name: Steel
Steel composition in weight %: See the text bellow.
Note: Tool design in Friction stir welding (FSW) of steel is a critical problem and hence experiments were carried on with three combinations of tool profiles having tapered pin, concave and flat shoulders. The study of tool wear resulted in a new finding of Sub shoulder tool and gave reduced tool wear. The tool wear is indirectly being reduced by using a shorter pin length of 2.6mm. Rupture of material surfaces which were in contact created reduction in the tool geometry and defect on welds were obtained. Based on the tool shape corresponding to its weld length, defects were occurred in the weld zone. This study is concentrated on finding the possible defects during welding by using different tool profiles using ultrasonic, radiography and thermography techniques. It was observed from the weld that the flat shoulder gave improper joining defects while the concave shoulder gave reduced defects when compared to flat shoulder, and the Sub shoulder is defect free.

Friction stir butt weld was conducted using IS: 3039, grade II (0.204 wt% C, 0.129 wt% Si, 1.10 wt% Mn, 0.309 wt% Cr) low alloy steel plates, having dimensions of 100 x 50 x 3 mm. A modified vertical milling machine was used to perform this Friction Stir Welding (FSW) processes. In this investigation Tungsten alloy tool (W-5.7908Ni- 3.2318Fe-0.2228Mo-0.1214Co-0.0709O2 wt-%) was used to perform the tool wear study. Shorter pin length of 2.6 mm, shoulder diameter of 25 mm, and pin diameter of 12mm at the root and 4 mm at the tip were maintained as constant.

Flat shoulder tool: The surface of flat shoulder will be completely been in contact with the work piece surface. The frictional contact of this flat surface might produce higher temperature, which makes the material to its plastic material flow quickly. In terms of tool wear for steel plates, this flat surface rubs over the interface surface and results in higher tool wear rate when compared to other profiles. Defective Weld is formed by using this flat shoulder. Appearance of welded sample is shown in Fig. 1.

The surface of the welded sample found to have voids on the upper surface itself. At the bottom of the welded plate, there is a root defect. The marked region opposite to the exit hole shows higher attenuation, which represents the defect in the particular region as shown in Fig.2 (a) and this, is the C – scan image of flat shoulder. The defect is a void shown in a circle. The defect is at a depth of 2.8 mm which is shown in the A – scan image of Fig.2 (b). In the weld length, at 25mm cross section as shown in Fig.2(c) indicates the defect region with a variation in the signals. The B – scan image shows the defect is at a depth of 2.8 mm and size of the defect is 11 x 5mm. The radiograph reveals that there is void at the marked position as shown in the Fig.2 (d).

Sub shoulder tool: During the experiments conducted on concave shoulders, a step like formation was naturally occurred and this was developed as a new tool design tool and has been named as sub shoulder. It was found that the tool could produce 1200 mm length of weld, which was the highest weld length among the other tools that could travel. The welded plate by sub shoulder tool is shown in Fig.3 and found with defect free.
Concentric circles can be seen over the plate surface. This is the metal flow because of first mode of metal transfer, as shown in Fig.4 (a) and roughness in surface is clearly seen in A-scan image of Fig.4 (b). However, the welded plates are found to befree from defects along the thickness of the weld, and this is assured from the B-scan image as shown in Fig.4(c). Ultrasonic images show that there is no defect along the weld length. Exit hole is visible on the radiograph as shown in Fig.4 (d). Except the initial plunge impression of tool From the results of NDT techniques, Sub shoulder tool is found to be free from defects. Flash on welded plates cannot be considered as defect, if it is in allowable limits and this does not affect the weld formation. All the welded plates of flat shoulder were found with tunnel defect and surface irregularities. Lack of material flow and poor tool design are the reasons for such defect. Among the tool profiles, flat shoulder tool is found to give maximum number of defects.
Reference: Not shown in this demonstration version.