- - AGRICULTURE CORE CURRICULUM - - (CLF2000) Advanced Core Cluster: AGRICULTURAL MECHANICS (CLF2250) Unit Title: OXYACETYLENE WELDING ____________________________________________________________________________ (CLF2254) Topic: FOUR BASIC OXYACETYLENE Time Year(s) FUSION WELDS 5 Hours 1 / 2 / 3 / 4 ____________________________________________________________________________ Topic Objectives: Upon completion of this lesson, the students will be able to: Learning Outcome #: (F-6) - Use the oxyacetylene equipment to perform four basic welds other than a bead. (F-16 - Describe how materials behave under applied stress Special Material and Equipment: Oxygen and acetylene cylinders, regulators and hoses, torch, tips, open-end wrench, filler rods, 1/8 & 1/16 inch mild steel, protective gear, and striker References: 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) Evaluation: Quiz by instructor. TOPIC PRESENTATION: Four Basic Oxyacetylene Fusion Welds A. Corner Weld Without Filler Rod 1. Place two pieces of mild steel (1/16 inch thick) so that their edges form a 90 degree angle with their inside corners touching. 2. Select the appropriate tip by consulting a tip chart. 3. Adjust the working pressures to about 10 psi for oxygen and 5 psi for acetylene or according to manufacturer's recommendation for tip. 4. Wear appropriate protective gear, then light and adjust the torch to a neutral flame. 5. Tack weld the two pieces together: a. Hold the torch at a 90 degree work angle and a 45 degree lead angle with the inner cone of the flame 1/16 to 1/8 inch above the base metal. b. Play the torch over the two edges of the joint just inside the right corners of the base metals until a single molten puddle is established. d. Remove the flame to allow the puddle to solidify. e. Make another tack weld at the opposite end of the joint. 6. Play the flame on the right-hand tack weld to remelt a puddle on its surface, then advance the puddle from right to left along the joint at a speed that will maintain a uniform puddle size and shape. B. Butt weld with filler rod: 1. Prepare two pieces of mild steel 1/8 inch thick. 2. Select the appropriate tip by consulting a tip chart. 3. Adjust the working pressures to about 10 psi for oxygen and 5 psi for acetylene or according to manufacturer's recommendation for tip. 4. Wear appropriate protective gear, then light and adjust the torch to a neutral flame. 5. Tack weld the two pieces together so that they are spaced about 1/8 inch at the left and 1/16 inch at the right to allow for normal expansion from heating. a. Hold the torch at a 90 degree work angle and a 45 degree lead angle with the inner cone of the flame 1/16 to 1/8 inch above the base metal. b. Play the torch over the two edges of the joint just inside the right edges of the base metals until a molten puddle is established. c. Hold the filler rod in the outer part of the flame away from the joint until two tiny molten puddles begin to form on the corners, then add some filler metal from the rod to bridge the two puddles. d. Continue to heat the puddle and add filler metal until the puddle is about 1/4 inch in diameter, then remove the flame to allow the puddle to solidify. e. Make another tack weld at the opposite end of the joint. 6. Play the flame on the narrower, right-hand tack weld to remelt a puddle on its surface, then add metal from the filler rod. 7. Using a forehand technique, advance the puddle from right to left along the joint at a speed that will maintain a uniform puddle size and shape. a. Make sure that the puddle melts into both pieces of metal at all times. b. Make sure that the filler rod is added only to the puddle, not just melting onto the pieces. C. Lap Weld with Filler Rod 1. Overlap two pieces of 1/8 inch thick mild steel. 2. Select the appropriate tip by consulting a tip chart. 3. Adjust the working pressures to about 10 psi for oxygen and 5 psi for acetylene or according to manufacturer's recommendation for the tip selected. 4. Wear appropriate protective gear, then light and adjust the torch to a neutral flame. 5. Tack weld both overlapping edges together at each end of the workpiece. 6. Hold the torch at a 45 degree lead angle and a 75 degree work angle with the inner cone of the flame 1/16 to 1/8 inch above the base metal and directed more towards the overlapped metal surface. a. Metal edges conduct heat faster than metal surfaces. b. Direct the flame more towards the metal surface to prevent the edge piece from being melted away before the surface piece reaches the proper welding temperature. 7. Play the flame on the right-hand tack weld to remelt a puddle on its surface, then add metal from the filler rod. 8. Using a forehand technique, advance the puddle from right to left along the joint at a speed that will maintain a uniform puddle size and shape. 9. Add filler rod to the front edge of the puddle and withdraw the rod as the puddle is advanced. 10. Turn the metal over and weld the other overlapping edge. D. Fillet weld with filler rod: 1. Position two pieces of 1/8 inch mild steel so that one joins the other to form a T, and support the vertical piece with a fire brick until tacked. 2. Select the appropriate tip by consulting a tip chart. 3. Adjust the working pressures to about 10 psi for oxygen and 5 psi for acetylene or according to manufacturer's recommendation for tip. 4. Wear appropriate protective gear, then light and adjust the torch to a neutral flame. 5. Tack weld the two pieces together, then remove the support. 6. Hold the torch at a 45 degree work angle and a 30 degree to 45 degree lead angle with the inner cone of the flame 1/16 to 1/8 inch above the base metal. a. Metal edges conduct heat faster than metal surfaces. b. Direct the flame, therefore, more towards the horizontal metal surface to prevent the vertical edge piece from being melted away before the horizontal surface piece reaches the proper welding temperature. 7. Play the flame on the right-hand tack weld to remelt a puddle on its surface, then add metal from the filler rod. 8. Using a forehand technique, advance the puddle from right to left along the joint at a speed that will maintain a uniform puddle size and shape. 9. Add filler rod to the front edge of the puddle and withdraw the rod as the puddle is advanced. 10. Weld the other side of the fillet joint in similar fashion. E. Metal Behavior Under Applied Stress 1. Stresses are internal forces set up in the welded pieces due to heating and cooling. 2. Two types of stresses result from the welding process: a. Stresses that develop while the weld is being made but which disappear on cooling. b. Stresses that remain after the weld has cooled off (residual stresses). 3. There are several factors that affect distortion and residual stresses: a. Distortion (warping of the welded part) occurs if the expansion due to heating is resisted. b. A residual stress results if the contraction due to cooling is resisted. Residual stresses can result in cracking of the welded part. 4. Methods of Reducing Distortion: a. Decrease the welding speed and use the smallest flame possible to obtain the correct penetration and fusion of metals. b. Line up the work at a slight angle opposite the direction of distortion during cooling to ensure correct alignment. c. Use skip or step-back method of welding. d. Use clamps to prevent movement. 5. Methods of Reducing or Relieving Stress a. Run the weld bead from the fixed end to free end. b. Use the round end of a ball peen hammer to peen the weld lightly as it cools. c. Heat treat the welded material and then allow slow cooling _________________________________________________________ ACTIVITY: 1. Perform a corner weld without filler rod. 2. Perform a butt weld, lap weld, and fillet weld with a filler rod. _________________________________________________________ 7/24/91 OLR/tf #%&C