Section III. TYPES OF WELDS AND WELDED JOINTS
a. Welding is a materials joining process used in making welds. A weld is a localized coalescence of metals or nonmetals produced either by heating the materials to a suitable temperate with or without the application of pressure, or by the application of pressure alone, with or without the use of filler metal. Coalescence is a growing together or a growing into one body, and is used in all of the welding process definitions. A weldment is an assembly of component parts joined by welding, which can be made of many or few metal parts. A weldment may contain metals of different compositions, and the pieces may be in the form of rolled shapes, sheet, plate, pipe, forgings, or castings. To produce a usable structure or weldment, there must be weld joints between the various pieces that make the weldment. The joint is the junction of members or the edges of members which are to be joined or have been joined. Filler metal is the material to be added in making a welded, brazed, or soldered joint. Base metal is the material to be welded, soldered, or cut.
b. The properties of a welded joint depend partly on the correct preparation of the edges being welded. All mill scale, rust, oxides, and other impurities must be removed from the joint edges or surfaces to prevent their inclusion in the weld metal. The edges should be prepared to permit fusion without excessive melting. Care must be taken to keep heat loss due to radiation into the base metal from the weld to a minimum. A properly prepared joint will keep both expansion on heating and contraction on cooling to a minimum.
c. Preparation of the metal for welding depends upon the form, thickness, and kind of metal, the load the weld will be required to support, and the available means for preparing the edges to be joined.
d. There are five basic types of joints for bringing two members together for welding. These joint types or designs are also used by other skilled trades. The five basic types of joints are described below and shown in figure 6-16.
(1) B, Butt joint – parts in approximately the same plane.
(2) C, Corner joint – parts at approximately right angles and at the edge of both parts.
(3) E, Edge joint – an edge of two or more parallel parts.
(4) L, Lap joint – between overlapping parts.
(5) T, T joint – parts at approximately right angles, not at the edge of one part.
6-11. BUTT JOINT
a. This type of joint is used to join the edges of two plates or surfaces located in approximately the same plane. Plane square butt joints in light sections are shown in figure 6-17. Grooved butt joints for heavy sections with several types of edge preparation are shown in figure 6-18. These edges can be prepared by flame cutting, shearing, flame grooving, machining, chipping, or carbon arc air cutting or gouging. The edge surfaces in each case must be free of oxides, scales, dirt, grease, or other foreign matter.
b. The square butt joints shown in figure 6-16 are used for butt welding light sheet metal. Plate thicknesses 3/8 to 1/2 in. (0.95 to 1.27 cm) can be welded using the single V or single U joints as shown in views A and C, figure 6-18. The edges of heavier sections (1/2 to 2 in. (1.27 to 5.08 cm)) are prepared as shown in view B, figure 6-18. Thickness of 3/4 in. (1.91 cm) and up are prepared as shown in view D, figure 6-18. The edges of heavier sections should be prepared as shown in views B and D, figure 6-18. The single U groove (view C, fig. 6-18) is more satisfactory and requires less filler metal than the single V groove when welding heavy sections and when welding in deep grooves. The double V groove joint requires approximately one-half the amount of filler metal used to produce the single V groove joint for the same plate thickness. In general, butt joints prepared from both sides permit easier welding, produce less distortion, and insure better weld metal qualities in heavy sections than joints prepared from one side only.
6-12. CORNER JOINT
a. The common corner joints are classified as flush or closed, half open, and full open.
b. This type of joint is used to join two members located at approximately right angles to each other in the form of an L. The fillet weld corner joint (view A, fig. 6-19) is used in the construction of boxes, box frames, tanks, and similar fabrications.
c. The closed corner joint (view B, fig. 6-19) is used on light sheet metal, usually 20 gage or less, and on lighter sheets when high strength is not required at the joint. In making the joint by oxyacetylene welding, the overlapping edge is melted down, and little or no filler metal is added. In arc welding, only a very light bead is required to make the joint. When the closed joint is used for heavy sections, the lapped plate is V beveled or U grooved to permit penetration to root of the joint.
d. Half open comer joints are suitable for material 12 gage and heavier. This joint is used when welding can only be performed on one side and when loads will not be severe.
e. The open corner joint (view C, fig. 6-19) is used on heavier sheets and plates. The two edges are melted down and filler metal is added to fill up the corner. This type of joint is the strongest of the corner joints.
f. Corner joints on heavy plates are welded from both sides as shown in view D, figure 6-19. The joint is first welded from the outside, then reinforced from the back side with a seal bead.
6-13. EDGE JOINT
This type of joint is used to join two or more parallel or nearly parallel members. It is not very strong and is used to join edges of sheet metal, reinforcing plates in flanges of I beams, edges of angles, mufflers, tanks for liquids, housing, etc. Two parallel plates are joined together as shown in view A, figure 6-20. On heavy plates, sufficient filler metal is added to fuse or melt each plate edge completely and to reinforce the joint.
b. Light sheets are welded as shown in view B, figure 6-20. No preparation is necessary other than to clean the edges and tack weld them in position. The edges are fused together so no filler metal is required. The heavy plate joint as shown in view C, figure 6-20, requires that the edges be beveled in order to secure good penetration and fusion of the side walls. Filler metal is used in this joint.
6-14. LAP JOINT
This type of joint is used to join two overlapping members. A single lap joint where welding must be done from one side is shown in view A, figure 6-21. The double lap joint is welded on both sides and develops the full strength of the welded members (view B, fig. 6-21). An offset lap joint (view C, fig. 6-21) is used where two overlapping plates must be joined and welded in the same plane. This type of joint is stronger than the single lap type, but is more difficult to prepare.
6-15. TEE JOINT
a. Tee joints are used to weld two plates or section with surfaces located approximately 90 degrees to each others at the joint, but the surface of one plate or section is not in the same plane as the end of the other surface. A plain tee joint welded from both sides is shown in view B, figure 6-22. The included angle of bevel in the preparation of tee joints is approximately half that required for butt joints.
b. Other edge preparations used in tee joints are shown in figure 6-23. A plain tee joint, which requires no preparation other than cleaning the end of the vertical plate and the surface of the horizontal plate, is shown in view A, figure 6-23. The single beveled joint (view B, fig. 6-23) is used on heavy plates that can be welded from both sides. The double beveled joint (view C, fig. 6-23) is used heavy plates that can be welded from both sides. The single J joint (view D, fig. 6-23) used for welding plates 1 in. thick or heavier where welding is done from one side. The double J joint (view E, fig. 6-23) is used for welding very heavy plates form both sides.
c. Care must be taken to insure penetration into the root of the weld. This penetration is promoted by root openings between the ends of the vertical members and the horizontal surfaces.
6-16. TYPES OF WELDS
a. General. It is important to distinguish between the joint and the weld. Each must be described to completely describe the weld joint. There are many different types of welds, which are best described by their shape when shown in cross section. The most popular weld is the fillet weld, named after its cross-sectional shape. Fillet welds are shown by figure 6-24. The second most popular is the groove weld. There are seven basic types of groove welds, which are shown in figure 6-25. Other types of welds include flange welds, plug welds, slot welds, seam welds, surfacing welds, and backing welds. Joints are combined with welds to make weld joints. Examples are shown in figure 6-26. The type of weld used will determine the manner in which the seam, joint, or surface is prepared.
b. Groove Weld. These are beads deposited in a groove between two members to be joined. See figure 6-27 for the standard types of groove welds.
c. Surfacing weld (fig. 6-28). These are welds composed of one or more strings or weave beads deposited on an unbroken surface to obtain desired properties or dimensions. This type of weld is used to build up surfaces or replace metal on worn surfaces. It is also used with square butt joints.
d. Plug Weld (fig. 6-28). Plug welds are circular welds made through one member of a lap or tee joint joining that member to the other. The weld may or may not be made through a hole in the first member; if a hole is used, the walls may or may not be parallel and the hole may be partially or completely filled with weld metal. Such welds are often used in place of rivets.
A fillet welded hole or a spot weld does not conform to this definition.
e. Slot Weld (fig. 6-28). This is a weld made in an elongated hole in one member of a lap or tee joint joining that member to the surface of the other member that is exposed through the hole. This hole may be open at one end and may be partially or completely filled with weld metal.
A fillet welded slot does not conform to this definition.
f. Fillet Weld (top, fig. 6-28). This is a weld of approximately triangular cross section joining two surfaces at approximately right angles to each other, as in a lap or tee joint.
g. Flash Weld (fig. 6-29). A weld made by flash welding (para 6-5 d).
h. Seam Weld (fig. 6-29). A weld made by arc seam or resistance seam welding (para 6-5 b). Where the welding process is not specified, this term infers resistance seam welding.
i. Spot Weld (fig. 6-29). A weld made by arc spot or resistance spot welding (para 6-5 a). Where the welding process is not specified, this term infers a resistance spot weld.
j. Upset Weld (fig. 6-29). A weld made by upset welding (para 6-5 e).No tags for this post.