Subject 7 Butt welding of thin steel plate in flat position 1. Finished image 2. Materials (1) The size of materials 1 Back bead 5. Tack welding and its position (1) Tack welding condition Tack welding current 120 A Arc voltage 19~20 V CO 2 flow rate 15 L/min Crater-filler switch “OFF” (2) How to do tack welding and its position Do tack welding at the opposite side that file the material. Decide the root gap (G) of material. Do tack welding at both ends of material. After doing tack welding, check the deformation of the part of butt- welding joint. Do not set present distortion method. 6. Welding of the first layer by forehand welding (1) Welding condition Welding current 90~110A Crater-filler switch OFF ON Arc voltage 19~20V Crater-filler current A CO 2 flow rate 15 L/min Crater-filler voltage V 2 (2) Operating angle of the welding torch [Notes] 1. Molten pool 2. Arc 3. Roundness cut 3 ■ Start the arc at the end of material. Good Not Good 1■ Operating angle of the welding torch that see from the front of the welding direction. 2■ Aim the arc (wire tip) at the center of root gap of square (I) groove joint. [[Notes] 1. Molten pool 2. Arc 3. Roundness cut (4) Treatment of the end of welding Return to starting point about 5～ 10 mm at the welding end slowly then fill the crater by melting wire. 7. Self-check Adherence of slag Adherence of spatters Uniformity of bead appearance Uniformity of bead width Uniformity of reinforcement of weld Treatment at welding starting point Treatment at welding end Undercuts 4 If do welding with weaving motion, the width of weaving is the root gap or under. (2) In case undercuts occur after welding. 5 . Do not set present distortion method. 6. Welding of the first layer by forehand welding (1) Welding condition Welding current 90~110A Crater-filler switch