BASIC JOINTS

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BASIC JOINTS

INTRODUCTION

Welding is one the most widely used methods of permanently joining Structural Shapes used throughout the world. Generally engineers,

supervisors and technicians are charged with joint design and selection. Welders, however; need to be familiar with the most commonlyused joint shapes, their names, and the type of welds applied to them. Since there is a wide and varied list of possible joints to fabricate

structural shapes, this lesson will discuss only the most common joints used in Arc Welding.

When two pieces of structural steel are to be connected by welding, the way they are prepared for welding and placed together is known as

the Weld Joint.

KEY POINT: In other words the joint is the way they are joined.

EDGE PREPARATION

Preparation or edge shaping may be applied to each piece (joint member) in the same way, or combinations of the joint preparations may

be used. The edge preparation for welding these joints depends on the strength requirements and other design considerations. The Welder

needs to be aware of the most common edge preparations as shown below:

JOINT ARRANGEMENTS AND WELDS

The edge preparations are arranged to make the weld joint. The pieces to be welded may be connected or a gap between the pieces toensure penetration may be used. On most joints the gap is at the bottom of the joint and is referred to as the root of the joint.

The term root opening or open root is used to describe this condition. For example; Open root V groove, or V groove with an open root.When the joint design allows, a backing strip or insert may be used for easier welding.

Some joints may have a backing weld, or back weld applied. A back weld is applied after the groove is filled. A backing weld is appliedbefore the groove is filled.

See examples below:

THE FIVE BASIC JOINTS

There are five basicjoints in common use for assembling metal.

1. BUTT JOINTS

2. T JOINTS3. LAP JOINTS

4. CORNER JOINTS5. EDGE JOINTS

1. BUTT JOINTS

A butt joint is formed when the pieces to be welded are laid side by side and it is one of the most widely used types of joint.

C JOINTS http://deltaschooloftrades.com/basic_j

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KEY POINT: In other words, the pieces are butted together.

The names in the examples above are from the type of weld applied to the joint. Often the type of weld is used to fully describe the joint.

For example; this joint is a single bevel butt joint.The V groove and bevel grooves are easier to prepare and are used more than the J or U groves.

KEY POINT: If two imaginary lines are drawn parallel to the horizontal line in the above symbols they show the joint shape, this is truefor most of the symbols. This can be helpful to remember since symbols on a blueprint do not show the actual joint shape or edge

preparation.

2. T JOINTS

A T joint is formed when one piece of metal to be welded is placed vertically on another piece lying horizontally, to form the shape of aninverted T.

KEY POINT: The T shape resembles an overhead position T joint.

The vertical member is usually placed at 90 deg to the horizontal member.

One of the most widely used types of weld applied to a T joint is the fillet weld. When a single pass or multiple passes are made against the

joint, the weld resembles a Triangle when viewed from the side.

KEY POINT: Pronounce the T in fillet FILL-ET; not as FILL-AY a fish

The T joint and fillet weld are the most frequently used joint and type of weld.In the same way the edges of the butt joint may be prepared for welding, the tee joints vertical piece may be prepared using a Bevel, or J

shape. The preparation allows the Welder to penetrate into the root of the joint.

See examples below:


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3. LAP JOINTS

A Lap joint is formed when one piece to be welded is laid down and another piece is overlapped to form an edge for fillet welding or anarea to allow plug or slot welding.

Lap joints are often used when plug or slot welding thinner sections.

A plug weld is made by welding holes evenly spaced across the length of one or both sides of the joint. A slot weld is similar except slots aremade instead of holes.

Other welds may be applied to laps such as projection, or seam welding.

See examples below:

LAP JOINTS

4. CORNER JOINTSA corner joint is formed by placing one piece to be welded on the other so that a corner is formed. The corner may be Flush; Half Open;

or Fully Open.

An edge preparation may be applied to one, or both of the pieces of the joint for penetration and strength.

KEY POINT: The weld applied to the inside of many of the above is a fillet weld.

5. EDGE JOINT

An Edge joint is formed when the two edges of the pieces to be welded come together. This joint may be formed as a result of anotherstructural shape and is not as widely used as some of the other joints.

See examples below.

SUMMARY

Welders need to know the basic joint shapes and the type of welds most commonly applied to them.

The five basic joints are: Butt; T; Lap: Corner; and Edge.

The edge preparation may be: Square edge; Bevel edge; Double Bevel edge; Chamfer edge; J groove edge; and Double J groove edge.


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J and U grooves are more labor intensive to prepare and may not be seen as often in production.

Butt joints may be open root, have a backing, or be welded both sides.

The weld applied to a T joint is a called a Fillet weld.Fillet welds are the most commonly used welds.

Corner joints may be: Flush; Half open; or Full open.Corner joints may be simple or have edge preparation to increase penetration.

Lap joints are more likely to be used when welding thinner sections, or when plug and slot welding is called for.

Edge joints are usually seen as a result of an overall joint configuration.The Welding symbols used are for illustration, and will be discussed fully in another lesson.


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BASIC JOINTS

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