PSI - Issue 22

Xiaoteng Wang et al. / Procedia Structural Integrity 22 (2019) 59–63 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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Fig. 1. The HPAW system, SuperMIG, patented by Weldobot, was utilized for keyhole welding. The following elements detail the process: (1) workpiece; (2) plasma jet; (3) plasma nozzle; (4) melting metal; (5) plasma arc electrode axis; (6) wire axis; (7) angle betw een electrode’s axes; (8) tungsten electrode; (9) consumable electrode (wire); (10) GMAW arc; (11) plasma; (12) wire current (Iw) direction; (13) plasma current (Ip) direction; (14) magnetic forces (F) applied to plasma arc; (15) magnetic forces (F) applied to GMAW arc [1] Figure 1 shows the schematic drawing of HPAW. The ER50-6 welding wire with the diameter of 1.2mm was used in these experiments. Both plasma torch and MAG torch are aligned with welding direction, and the former is plasma arc. Besides, the hybrid type of plasma and MAG is paraxial. The plasma arc is compressed by the argon with the purity of 99.99% pouring from plasma torch at the flow rate of 6L/min. The molten pool was shielded by 80% argon-20% CO2 at the flow rate of 15L/min. The distance between the MAG arc and plasma arc is 4mm. To get the fatigue life of welding joints, the plates were cut into standard test pieces according to GB/T 13816 1992. The fatigue life of welding joints is measured by QBG-400 high-frequency fatigue testing machine with the static loading of -400~+400kN, dynamic loading of 0~200kN and test frequency of 60~300Hz. The sample is clamped along with the axial direction, and stress of 340MPa in this paper is applied. When the crack is occurred, the fatigue life test is finished. However, to find out the reason, the sample with a fatigue crack is clamped with stress of 170MPa until the sample breaking apart. Moreover, the sample with the fracture surface is cut with the dimension of 60mm × 40mm × 12mm, and the fracture surface is observed with optical microscope and electron microscope in order to get fracture mechanism. 3. Results and discussion

Table3. The experimental results of fatigue life tests (Stress ratio R=0.1, test stress= 340MPa)

Welding method

Sample number

Fatigue life (N)/kC

Test time/min

LgN

Average fatigue life/kC

G-1 G-2 G-3 G-4 G-5 H-1 H-2 H-3 H-4 H-5

158.9 173.2 210.5 145.8 136.9 253.9 272.8 223.2 286.2 264.7

28 31 39 25 22 45 54 42 58 51

5.2011 5.2385 5.3233 5.1638 5.1364 5.4047 5.4358 5.3487 5.4567

GMAW

165.06

HPAW

260.16

5.4228 As shown in Table3, the fatigue life of welding joints with HPAW and GMAW are measured. It can be seen from Table3 that with the same geometric dimensioning and the same stress of 340MPa, the average fatigue life of HPAW welding joint with 260.16 thousand is 57.62% longer than those of GMAW with 165.06 thousand. Furthermore, the maximum fatigue life of sample G-3with GMAW is 210.5 thousand, which is shorter than the