- - AGRICULTURE CORE CURRICULUM - - (CLF2000) Advanced Core Cluster: AGRICULTURAL MECHANICS (CLF2300) Unit Title: Arc Welding ___________________________________________________________________________ (CLF2302) Topic: STRIKING AND Time Year(s) MAINTAINING AN ARC 5 Hours 1 / 2 / 3 / 4 ___________________________________________________________________________ Topic Objectives: Upon completion of this lesson, the students will be able to: Learning Outcome #: (G-2) - Strike and maintian an arc correctly. Special Material and Equipment: Electrode 1.8" or 5/32", E6010 or E6011 or E6013 References: Burke, Stanley R., & Wakeman, T. J. (1990). MODERN AGRICULTURAL MECHANICS (2nd ed.). Danville, IL: Interstate Publishers. Cooper, Elmer L. (1987). AGRICULTURAL MECHANICS: FUNDAMENTALS AND APPLICATIONS. Albany, NY: Delmar Publishers. Phipps, Lloyd J., & Reynolds, Carl L. (1990). MECHANICS IN AGRICULTURE (4th ed.). Danville, IL: Interstate Publishers. Resources: Deere & Company. (1987). WELDING (6th ed.) (Fundamentals of Service (FOS) Series). Available from: John Deere Technical Services, Dept. F, John Deere Road, Moline, IL 61265 (Available in Spanish) Giachino, Joseph W., & Weeks, William (1976). WELDING SKILLS AND PRACTICES (5th ed.). Available from: American Technical Society, Chicago, IL 60637 Hobart Brothers Company. (1978). TECHNICAL GUIDE FOR SHIELDED METAL ARC WELDING. Available from: Hobart Brothers Company, Troy, OH 45373 Evaluations: Tests, quizzes and practical welding test. TOPIC PRESENTATION: STRIKING AND MAINTAINING AN ARC A. Setting, Checking, and Adjusting the Equipment 1. Equipment adjustment for proper amperage is vital for arc establishment. a. To start the welding operation make sure that the electrode holder and ground clamps are clean and in good condition. Inspect the cable connection to make sure they are tight and that no exposed wires are present. b. The welding bench should be clean and dry. c. The ground clamp should be attached to the welding bench in a secure manner. d. If using D.C. polarity, it is important that the machine is set for straight or reversed current e. The next step is to select the proper amperage. Tentatively determine the recommended current setting for the type and size of electrode to be used; make the final adjustment after the actual welding operation has been started. The electrode selection chart gives both a low and a high setting choice. A current value midway between the two limits is recommended. The following electrodes are recommended for this exercise: E6010, E6011, E6012, E6013 or E7014. NOTE: Some instructors like to use E-6013 and E-7014 rods because they strike and hold an arc easily and beginning welders build confidence. However, others feel that changing back to a E-6011 type rod is more difficult and they prefer to start with a fast-freeze rod of E-6011 type. It is also suggested that you use 1/8" or 5/32" electrodes for this exercise (see electrode selection chart in the addendum). B. Striking an arc 1. Select a plate or coupon of steel 1/4" thick, 3" to 5" wide, and 6" to 10" long. a. There are two methods that can be used to start or strike the arc: a tapping or a scratching motion. The tapping method is the one that experienced welders use, whereas the scratching motion method is generally easier for the beginner. 1) The scratching motion method requires that the electrode be brought down at an angle to the plate very similar to scratching a match. When the arc is started (flashes) the electrode must be quickly raised so that it will not stick to the base metal. 2) The tapping method requires that the rod be held directly above the work. The rod is brought down and touches on the base metal. As the arc strikes, the rod must be quickly brought up to approximately the thickness of the electrode or the rod will stick to the base metal. 3) If the rod sticks to the base metal, the current flow will cause the rod to become very hot. To remove a stuck electrode from the work, use a quick twisting or striking motion of the electrode holder. If this does not break the electrode loose, remove the electrode holder from the grip end of the electrode. Since this electrode is red hot, use pliers to twist it loose. b. Practice striking and stopping the arc until this action can be completed quickly and easily. 1) A good practice coupon can be laid out in a grid pattern with center punch mark 1/2" apart. Practice starting the arc on each of these marks. 2. Practice running beads after the skill of striking and maintaining an arc has been mastered. a. Stringer beads are an excellent bead for beginning welders to make. The beads will not be consistant but should improve with practice. b. The beginning welder can practice with different electrode settings, arc lengths, electrode angles, and speeds until a smooth, strong weld is produced. 1. Welding done with proper amperage, voltage, and speed displays a) Good penetration b) No undercut or overlay c) Smooth appearance 2. If the arc is too long, there is: a) Poor penetration, overlap, spatter b) Leaves weld puddle exposed to oxidizing air 3. If the welding current setting is too high, there is: a) Spatter and undercutting b) A deep crater 4. If the welding current setting is too low, there is: a) Poor penetration with high narrow bead b) Not enough current to fuse weld to metal 5. If the welding speed too fast, there is: a) Irregular bead with skips 6. If the welding speed too slow, there is: a) Bead too high, somewhat irregular and porous b) Builds up too much metal and metal stays melted too long 5. After mastery of the stringer bead, practice oscillation, which entails keeping the tip of the rod weaving back and forth across the molten weld pool. a. The weaving motion of the electrode keeps the molten metal pool agitated; this helps float the slag and impurities to the top so they can be removed by chipping and brushing and it also helps to reduce porosity within the weld bead area. b. The weave bead also can be used to give a wide coverage (cover pass) for the weld joint. c. The weave bead will improve penetration and thicken pieces of weld plate. d. The basic weave bead is a crescent-shaped zig-zag. 1) Hesitate at sides to prevent undercutting and to allow the bead to build. 2) Be sure to bond the weave to the material on each side. 6. There are various other welding patterns, for example, whipping motion, semicircular motion, circular motion, V-shaped motion, back and forth or N-shaped motion, U-shaped motion, figure-8 motion, and rotary motion. 7. Metal Preparation a. Cut a plate approximately 4" X 5" X 1/2" b. Brush and clean plate c. Mark 4 lines 1/2" apart down the 5" length d. Run a stringer bead down each line with 1/8" rod e. Chip and clean stringer beads 8. Weaving Exercise a. Weave beads between stringers to cover plate with smooth weld b. Fuse the weave into the stringers c. Chip, clean, and evaluate work _________________________________________________________ ACTIVITY: 1. Strike and maintain an arc by building up a small boss on each center punch mark on coupon 2. Explain what happens when an arc is being maintained. 3. Start and restart the electrode at different places on the coupon. 4. Run and evaluate stringer bead for correctness. 5. Run and evaluate weave beads. _________________________________________________________ 7/24/91 DF/RRE/tf #%&C