(TLE 70)Metalworks and Welding

Welding

- is a fabrication process that joins materials, usually metals or thermoplastics, by causing coalescence. This is often done by melting theworkpieces and adding a filler material to form a pool of molten material that cools to become a strong joint, but sometimes pressure is used in conjunction with heat, or by itself, to produce the weld.

- is a joining process in which a filler metal is melted and drawn into a capillary formed by the assembly of two or more work pieces. The filler metal reacts metallurgically with theworkpiece (s) and solidifies in the capillary, forming a strong joint.

- a printed circuit board. Soldering is a joining process that occurs at temperatures below 450 °C (842 °F). It is similar to brazing in the fact that a filler is melted and drawn into a capillary to form a join, although at a lower temperature. Because of this lower temperature and different alloys used as fillers, the metallurgical reaction between filler and work piece is minimal, resulting in a weaker joint. In a correctly made deposit the ripples produced on the bead will be uniform and the bead will be smooth no overlaps or undercuts.

1. CORRECT ELECTRODE SIZE

The correct choice of electrode size involves consideration of a variety of factors, such as the type, position, preparation of the joint, the ability of the electrode to carry high current values without injury to the weld metal or loss of deposition efficiency, the mass of work metal and its ability to maintain its original properties after welding, the characteristics of the assembly with reference to effect stresses set up by heat application, the practicability to heat treatment before and / or after welding, the specific requirement before and / or after welding, the specific requirements as to welding quality and cost of achieving the desired results.

2. CORRECT CURRENT

If current on equipment is too high or too low, you are certain to be disappointed in your weld. If too high, the electrode melts too fast and your molten pool is large and irregular, if too low, there is nor enough heat to melt the base metal and your molten pool will be small, will pile up, look irregular.

3. CORRECT ARC LENGTH

If the arc is too long or voltage too high the metal melts off the electrode is large globules which wobble from side to side as the arc wavers, giving a wide, spattered and irregular bead-with poor fusion between original metal and deposited metal. If the arc is too short, or voltage too low, there is not enough heat to melt the base metal properly and the electrode quite often sticks to the work, giving a high, uneven bead, having irregular ripples with poor fusion.

4. CORRECTTRAVEL SPEED

When your speed is too fast your pool does not last long enough, impurities an gas locked in. The bead in narrow and ripples pointed. When speed is too slow the metal piles up, the bead is high and wide with a rather straight ripple.

5. CORRECT ELECTRODE ANGLE

The electrode angle is of particular importance in fillet welding and deep groove welding. Generally speaking, when making a fillet weld, the electrode should be held so that ir bisects the angle between the plates (as shown at right) and is perpendicular to the line of weld, if under cut occurs in the verticle member, lower the angle of the arc and direct the arc toward the vertical member.

In arc welding an electrode is used to conduct current through a workpiece to fuse two pieces together. For an alternating current arc welder the welding electrode would not be considered an anode or cathode.

Correct and safe arc welding station.Welding can be a dangerous and unhealthy practice without the proper precautions; however, with the use of new technology and proper protection the risks of injury or death associated with welding can be greatly reduced.

Because many common welding procedures involve an open electric arc or flame, the risk of burns is significant. To prevent them, welders wear protective clothing in the form of heavy leather gloves and protective long sleeve jackets to avoid exposure to extreme heat, flames, and sparks.

The brightness of the weld area leads to a condition called arc eye in which ultraviolet light causes inflammation of the cornea and can burn the retinas of the eyes. Welding goggles and helmets with dark face plates are worn to prevent this exposure and, in recent years, new helmet models have been produced featuring a face plate that self-darkens upon exposure to high amounts of UV light.

Welders are also often exposed to dangerous gases and particulate matter. Processes like flux-cored arc welding and shielded metal arc welding produce smoke containing particles of various types of oxides. The size of the particles in question tends to influence the toxicity of the fumes, with smaller particles presenting a greater danger. Additionally, many processes produce various gases (most commonly carbon dioxide and ozone, but others as well) that can prove dangerous if ventilation is inadequate. Furthermore, the use of compressed gases and flames in many welding processes pose an explosion and fire risk; some common precautions include limiting the amount of oxygen in the air and keeping combustible materials away from the workplace.

Certain welding machines which use a high frequency AC current component have been found to affect pacemaker operation when within 2 meters of the power unit and 1 meter of the weld site.