MAKING VARIOUS WELDED JOINTS

Types of Weld Joints

There are two major classes of weld ‑ fillet and butt.

1. Fillet welds. These welds are roughly triangular in cross section and between two surfaces not in the same plane and the weld metal is substantially placed alongside the components being joined.

2. Butt welds. A butt weld is made between two pieces of metal usually in the same plane, the weld metal maintaining continuity between the sections.

In addition there are lap welds, corner welds and edge welds, which are to some extent special variations of the fillet and butt welds. The various weld joints and some associated terms are illustrated on page 7.

Making a Welded Joint in the Flat Position

Take two pieces of 250 x 75 x 10mm plate and tack (a small or temporary holding weld) them together at each end to form a right angle section and set it in the V position between two bricks, as shown in Fig 15. Using your 3.2mm o electrode at 130 amps, run your first pass into the joint, bisecting the angle with your electrode and making sure that you obtain complete penetration to the corner with no lateral movement of the electrode. Remove the slag and your weld should be flat with a good flow into each side and probably have a 8mm wide surface. Deposit you next layer using a weaving motion, remembering to pause slightly at each edge.

This fillet weld could probably have a face width of 12mm (and a leg length of 10mm) and of maximum desirable size for this thickness material. However, in using the specimen for practice it could be assumed that the material was thicker and a larger weld required.

A larger electrode could be employed (4mm or 5mm) and/or it may be found necessary to restrict the width of weaving to where there are two or three passes (weld beads) in each layer of weld material as indicated in Fig. 17.

The same technique and procedure would apply for single Vee butt welds, although of course the included angle is usually restricted to 70° max. Where a single vee butt weld is employed, the first run should achieve full penetration, with a cover weld placed on the reverse side. Alternatively, the gap between the two plates is widened and a backing bar that become part of the structure is employed.

It should of course be remembered that it is not essential to use other than a square butt joint for material less than 6mm thick. Light sheet (2.Omm and under) should be tightly butted together while heavier sheet should be gapped up to half the material thickness to assist in full penetration by a weld from each side.

Source : aussieweld.com.au

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Welding Test

Welding only is not enough, many step should be performed after welding process to make sure weld quality in good condition. One of critical process after welding is welding test, which commonly use Nondestructive Testing (NDT).

Nondestructive Testing (NDT) is the method used to examine or inspect a part or material or system without affected future usefulness. Nondestructive Testing (NDT) is utilized to investigate specifically, and it’s concerned in particular way with the performance of the test piece, how long the piece may be utilized and when it is necessary to be checked again. This is the main advantage of Nondestructive Testing (NDT), we can examine without destroying speciment and of course it is saving cost. There are several type of Nondestructive Testing (NDT) type, but commonly used are Magnetic Test(MT), Penetrant Test (PT) , Ultrasonic Test ( UT), and Radiography Test (RT).

Modern Nondestructive Testing (NDT) used by manufacturer for several purposes.

• Ensuring the Integrity/Reliability of a Product
  The users of a fabricated product have high expectation that it will give no trouble happen during service for a reason-able period of usefulness. Few of today’s products are expected to deliver decades of service but they are required to give reasonable unfailing value. Public has learned to expect better service and longer life, despite the increasing complexity of our everyday electrical and mechanical appliances.
• Preventing Accidents and Saving Lives
  To make sure product reliability is very important because of the general increase in performance expectancy of the public. But reliability merely for convenience and profit is not enough. Reliability to protect human lives is a valuable end it itself. The railroad axle must not fail at high speed. The front spindle of the intercity but must not break on the curve.
• Ensuring Customer Satisfaction
  While it is true that the most laudable reason for the use of nondestructive tests is that of safety, it is probably also true that the most common reason is that of making a profit for the user. The sources of this profit are both tangible and intangible.
  
• Aiding in Product Design
  Nondestructive testing aids significantly in better product design. For example, the state of physical soundness as revealed by such nondestructive tests as radiography, magnetic particle or penetrant inspection of a pilot run of castings often shows the designer that design changes are needed to produce a sounder casting in an important section. The design may then be improved and the pattern modified to increase the quality of the product. This example is not academic; it occurs almost daily in many plants.
  
• Controlling Manufacturing Processes
  Almost every nondestructive testing methods is applied in one way or another to assist in process control and so ensure a direct profit for the manufacturer.
  
• Lowering Manufacturing Costs
  Most manufacturers could cut manufacturing costs by deciding where to apply the following cost reduction principle: A nondestructive test can reduce manufacturing cost when it locates undesirable characteristics of a material or component at an early stage, thus eliminating costs of further processing or assembly.
  
• Maintaining Uniform Quality Level
  Once the quality level has been established, production and testing personnel should aim to maintain this level and not to depart from it excessively either toward lower or higher quality. In blunt language, a non destructive test does not improve quality. It can help to establish the quality level but only management sets the quality standard.

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