- - AGRICULTURE CORE CURRICULUM - - (CLF2000) Advanced Core Cluster: AGRICULTURAL MECHANICS (CLF2300) Unit Title: Arc Welding ___________________________________________________________________________ (CLF2304) Topic: FOUR BASIC Time Year(s) WELD JOINTS 5 Hours 1 / 2 / 3 / 4 ___________________________________________________________________________ Topic Objectives: Upon completion of this lesson, the students will be able to: Learning Outcome #: (G-5) - Identify four basic weld joints and demonstrate the application of each in the flat position, using AC and DC equipment. (G-8) - Construct a project requiring at least three different welds. Special Materials and Equipment: Samples of different weld joints, coupons of clean 1/4" metal 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 TOPIC PRESENTATION: FOUR BASIC WELD JOINTS Introduction: There are four basic joints used in arc welding: butt joints, tee joints, lap joints, and corner joints. Each welding joint has several variations to provide for different needs. Two different types of welds are used when welding these joints. The fillet-type weld fills in space on the outside of pieces of metal that are positioned at an angle to each other. The groove-type weld fills in grooves that are cut on the inside of two pieces of metal that are positioned next to each other. A. Butt Joints 1. The butt joint is one of the most frequently used weld joints. a. A butt joint consists of placing the edges of two pieces of metal together. 2. The butt joint is used when structural pieces have flat surfaces, for example, tanks or flat decks, and when laminating pieces for machine parts. 3. There are three types of butt joints: closed, open, and when laminating pieces for machine parts. 4. The closed butt should be used only if the material to be welded does not exceed 1/8" to 3/16" in thickness. 5. When using the open butt, the joints are spaced 3/32" to 1/8" apart. 6. When the material to be welded exceeds 3/16" in thickness, the butt joint should be beveled. There are three types of bevel or V joint designs: a. In the feather edge, the material is 1/8" to 3/16" thick, the bevel is 60 degrees and the bottom edges of the material are placed together. b. The shoulder edge is used for materials 1/4" or more thick; 1/16" to 1/8" of the bottom of the material is not beveled and a gap of 1/8" is allowed for the root pass. c. The double V is used for material over 3/8" thick. This V joint has a 60 degree bevel; however, a 3/32" to 1/8" face is left in the lower 1/3 of the weld joint. This root face is generally spaced 1/8" apart for proper root pass operation. 7. If the bevel on any groove joint is greater than 60 degrees, it is difficult to limit and control the amount of contraction when the metal cools. 8. A backup strip should be used in an open butt joint in order to prevent excessive burn-through. 9. A round stock weld is a variation of the butt joint weld. a. In order to weld rods or round solid shaft material, both ends of the stock must first be beveled, leaving a shoulder in the center. The edges should be ground so they have the same angle.B. Lap Joints 1. The lap-joint is another of the most frequently used joints in welding. When the metal is lapped it provides great strength. a. Both surfaces of the lapped area must be clean in order to ensure evenly aligned surfaces. b. The amount of lap depends on the thickness of the material. Generally, the thicker the material the more lap. c. If the joint will be subjected to heavy bending stresses, both edges should be welded. d. The lap weld joint will greatly stiffen the object where the material is lapped. This makes a good joint, particularly when large flat sides are part of the structure, as in tanks and bins. It is also an excellent method for making many types of repairs such as fish plating for strengthening other members of a structure or frame. 2. The lap joint is a fillet-type weld. a. Both the amount of lap and number of passes required to fill the joint face must be considered. b. Material that is 3/16" or 1/4" should be used for this practice weld. This thickness of material will require a single pass which is one layer of weld to a bead. A 1/8" or 5/32" electrode should be used for this. c. After the material is lapped, you should tack each end before starting the main weld. d. The angle of electrode is very important. The best results are obtained by holding the electrode at 45 degrees with the tip of the electrode pointed toward the weld area. The direction of travel will have a 60 degree angle in the traveling direction. This first single pass bead should be 1/4" fillet. C. Tee Joints 1. The tee joint is formed by placing one plate at a 90 degree angle to another to form a letter T. A tee joint is a fillet-type weld. a. The tee joint is weak and should not be used if heavy pressure will be applied from the opposite direction of the welded joint. b. There are several types of fillet joints. The basic fillet welds for tee joints are classified as square, single bevel, double bevel, single J and double J. 1) The square tee is used where the material can welded on one or both sides. Considerable weld metal is required for maximum strength. 2) The single bevel tee is used on material that is less than 1/2" thick. This joint will withstand more severe loading than the square tee, where welding can be done from one side only. 3) The double bevel tee is used where heavy loads are applied in all directions and where welding can be done on both sides. 4) The single J joint is used on material 1 1/2" and thicker and can be welded from both sides. c. To start a practice fillet, use 3/16" to 1/4" thick material. Set the vertical plate on the middle of the flat plate and tack weld each end. Then start the main weld. On material of this thickness, a single pass (which is one layer of a weld bead) should be sufficient. d. The angle of electrode is very important. The best results are obtained by holding the electrode at 45 degrees between the vertical bottom flat plate with the tip pointed toward the weld area. The direction of travel will have an 80 degree angle in the traveling direction. This first single pass bead should be a 1/4" fillet. e. Some key points are: 1) Beads should penetrate the metal to get a strong bond. 2) If a multi-pass weld is done, clean the weld by chipping and brushing between passes. 3) On multi-pass welds the beads should tie in with one another. D. Corner Joints a. These joints are often used in the construction of rectangular- shaped objects and where outside corners must have a smooth radius. b. Position the pieces in a 90 degree angle and tack both outside corners. c. The angle of the electrode is very important. The best results are obtained by holding the electrode at 45 degrees with the tip of the electrode pointed at the weld area. The direction of travel will have a 30 degree angle in the traveling direction. On light stock, one bead is usually enough. However, the corner should contain enough weld material to create a smooth radius. This smooth radius will ensure a strong weld and leave the desired finish for the outside corner weld. _______________________________________________________________ ACTIVITY: 1. Prepare and weld each of the major joint types. 2. Design and build a project utilizing at least three different types of welds. _______________________________________________________________ 7/23/91 DF/RRE/tf #%&C