• Bead weld
• Tack weld
• Fillet weld
• Groove weld
• Plug and slot weld

Bead Welds

Bead welds are single-pass deposits of weld material used to build up the surface of metal or to replace metal on worn surfaces. Bead welds used for this application are commonly called hardsurfacing or hardfacing.

Tack Welds

Tack welds are a series of short welds used to hold the joint assembly in place during the fit-up procedure (Figure 2). Each tack weld is a short (sometimes temporary) weld approximately 13 mm ([latex]\frac{1}{2} \text{"}[/latex]) in length. Tack welds are usually deposited at both ends of the joint and at approximately equal intervals along the length of the joint.

On tee joints, tack welds are often used along the opposite side of the weld to prevent the upright plate from leaning toward the weld (Figure 3).

Fillet Welds

Fillet welds are used extensively on lap, tee, and corner joints where they join two pieces of metal that are usually at right angles (90°) to each other. A fillet weld consists of one or more beads or layers that are roughly triangular in cross-section. The features of a typical fillet weld on a tee joint are shown in Figure 4.

The ideal fillet weld is characterized by:

• Joint faces at right angles (90°)
• Face that is flat or slightly convex
• Toes that merge smoothly with the surface of the joint members
• Legs of equal length

In many cases, fillet welds are more economical than groove welds, in that they are easier to assemble and require less edge preparation. They generally require more weld material and are less able to withstand high stress loads.

Fillet welds are not considered capable of carrying stress loads unless their length is at least four times the size of the weld. Stress-carrying fillet welds connecting material up to 25 mm (1″) thick should not be less than 10 mm ([latex]\frac{3}{8} \text{"}[/latex]) in size.

Groove Welds

Groove welds fill in the gap or groove between two pieces of metal. Groove welds are most commonly used on butt joints, although the weld on an open corner joint or on specially prepared lap and tee joints can sometimes be considered a groove weld.

Groove welds consist of a root bead, a hot pass, fill passes and a cap (Figure 5). The number of passes will vary, depending on the thickness of the material. On thinner metal, the hot pass and fill pass can be combined into one pass and, in some cases, a single pass is adequate for the entire weld.

The significant dimensions of groove welds are shown in Figure 6. These include the root opening, the root face (or landing), the included angle, the thickness and the throat. On bevelled joints, the bevel angle is important and, on joints with a J preparation, the root radius is significant.

The size of the root opening, the root face, the included angle, and the root radius all have bearing on the amount of weld material required and on the depth of penetration. For example, too large a root opening, face or included angle will result in excessive penetration and the deposition of unnecessary weld metal, while dimensions that are too narrow will make full penetration extremely difficult, if not impossible. If the root radius on a U-joint is too great, an excessive amount of weld material will be deposited and the possibility of uncontrollable distortion increases.

The selected dimensions for these dimensions will depend on the material thickness, electrode size and the welding process.

Groove Weld Size and Profile

The size of groove welds is determined by the depth of weld penetration in the groove or gap between the two pieces. In Figure 7, the weld size in A (where penetration is complete) is the same as the thickness of the plate. Where penetration is incomplete, as in B, the weld size is the depth of the penetration. In C (where the plates differ in thickness and there is complete penetration), the weld size is the thickness of the thinner plate.

Metal deposited above the surface of the plate is called reinforcement. Profiles of groove welds show the amount of reinforcement at the centre of the weld bead (Figure 8). This reinforcement must not exceed 3 mm ([latex]\frac{1}{8} \text{"}[/latex]) as excessive reinforcement is uneconomical and contributes nothing to the strength of the weld. It decreases the working strength of the joint because stresses concentrate at the toe of the weld.

Reinforcement may be removed by gouging or it must be built up uniformly from the surface of the parent metal to the maximum 3 mm ([latex]\frac{1}{8} \text{"}[/latex]) at the centre of the weld. There must be no valley or groove along the edge or in the centre of the weld.

The width of a groove weld should not extend more than 3 mm ([latex]\frac{1}{8} \text{"}[/latex]) beyond the shoulder or edge of the joint on either side. Extra deposit beyond this is uneconomical because there is no corresponding increase in joint strength.

If you’re unsure which weld to use, start by identifying the joint type first.

Five Basic Joint Types

There are five basic weld joints used in welding (Figures 9 and 10). Within these five, however, are many variations and the selection of a particular joint or variation is based on four important factors:

• The load applied to the weld (for example, compression, torsion, bending, or fatigue)
• The way the load is applied (for example, sudden, variable, or steady)
• The thickness of the base metal
• The cost of the joint preparation and welding time

The five basic weld joints are defined below:

Butt Joint: A joint that joins two pieces of metal in the same plane.

Corner Joint: A joint that joins two pieces of metal at right angles, formed at the ends of both pieces in an L shape.

Edge Joint: A joint that joins two pieces of metal that are turned up at the edges; also known as a flange joint.

Lap Joint: A joint that joins two pieces of metal that overlap one another.

Tee Joint: A joint that joins two pieces of metal at right angles, forming a “T” shape.

Variations in Joint Design

Variations in the five basic designs are a result of the different preparations that can be applied to the edges of the joint. Edge preparation is necessary on thicker material to ensure full penetration of the joint.

Tee Joints

The square tee joint requires no edge preparation and is widely used because it is relatively inexpensive and easy to fit. On thicker material, the edges may be prepared with a single bevel, double bevel, single J or double J (Figure 11).

Tee joints that are welded on only one side (single-welded) are satisfactory for only light static loads. For heavy or fluctuating loads, tee joints need to be welded on both sides (double-welded) to increase their strength.

Tee joints are relatively easy to design and they provide maximum access for welding, however, there is a high possibility of distortion. An additional drawback is the expense of tee joints in terms of the weld material, especially on larger tee joints and on joints that need to be welded from both sides.

Lap Joints

Lap joints require little or no edge preparation. On thicker material, a single bevel is all that is usually required. Lap joints are often selected for welds between two materials that have different thickness.

For welds that do not require great strength, a single lap joint may be selected to provide a “tight” joint. However, single lap joints must not be used for welds that will be subjected to fluctuating, bending or twisting loads. For these types of loads, the joint can be welded from both sides, or a double lap joint can be selected (Figure 12).

Lap joints have two significant drawbacks. As with tee joints, the material requirements are high, so maximum tensile strength can only be achieved when the overlap is five times the thickness of the thinner member. Also, under stress loading, the joint tends to lose its strength.

Corner Joints

There are two types of corner joints, the open corner and the closed corner (Figure 13).

The open corner joint is more frequently used than the closed corner. Penetration is usually excellent, resulting in a full strength weld. With the closed corner, penetration is impossible on all but light-gauge sheet metal. On thicker material, edge preparation is required (Figure 14). In addition to the edge preparation, a small opening is often left between the two pieces in order to ensure full penetration.

Although square corner joints are relatively easy to prepare and assemble, the variations using the bevel, the J and the U preparations require more skill and time to accurately fit the joint.

Corner joints are not satisfactory for heavy stress loading, particularly if welded from only one side. They are not normally used in construction, especially where the tension from bending is concentrated at the root of the weld. For some applications, corner joints may also be welded from the inside to increase their strength, a procedure that significantly increases the cost of the weld.

Edge Joints

Edge or flange joints are most commonly used on light-gauge material such as sheet metal. The edges of the sheet metal are turned up in a device called a brake. The turned-up edges reduce the danger of burn through on thin materials and at the same time help to prevent distortion. On thin materials, no additional filler metal is required. If selected for plate, the edges must be prepared with one of the variations shown in Figure 14 in order to ensure sufficient penetration.

Butt Joints

Butt joints are the most widely used of the five designs. Like tee joints, butt joints provide maximum accessibility for welding. They use a minimum of weld material and, with 100% penetration, they are effective for all types of stresses. They are the preferred joint for resisting fatigue stresses if complete penetration is assured. The strength of correctly prepared and welded butt joints compares very favourably with the strength of the parent metal.

On thin metal, complete penetration and full strength can be achieved using a square butt joint without extensive edge preparation. On thicker metal, edge preparation becomes increasingly extensive. Two basic designs are used (Figure 16), the bevel and the J. These edge preparations result in eight butt joint variations.

When joints are prepared and welded from both sides, they are called double joints. When welded from only one side, they are called single joints. To ensure complete penetration, a backing strip or plate is often required.

The drawbacks of the butt joint are primarily in the skill and accuracy required of the welder in fitting and welding the joint. Of the five joints, the butt joint is the most difficult to master. These joints require considerable experience to become proficient in preparing and welding because they often require extra time for back gouging or extra material for backing.

Welding Positions

There are four basic welding positions: flat, horizontal, vertical and overhead. Welding techniques for the four positions vary according to the ease of depositing the metal. Welding in the flat position is generally faster and less tiring than the other three positions and, whenever possible, you should try to place your workpiece in the flat position.

The term “position welding” refers to welding in the flat position. The term “welding out of position” refers to welding in any of the other three positions. Table 1 and Figure 17 show the four positions that are used.

Table 1: Welding Positions

Position of Weld	Groove	Tee-joint Fillet
Flat
Horizontal
Vertical
Overhead

Flat Position

In the flat position, the workpiece is positioned so that the joint is parallel to the floor and the electrode generally points downward. For butt joints on plate, the two pieces are simply placed on a flat surface. For lap and tee joints the two pieces of plate must be supported in an angled position so that the actual joint is parallel to the floor (Figure 18). With corner joints, the ends of the plate are positioned on a flat surface so that the two pieces meet at the top to form a small tent.