NEW-AGE WELDING TECHNOLOGIES
QUICK TAKE Often high precision plastic moulding dies, e.g. those used for making tiny but dimensionally precise parts for camera, computers and other such applications – especially when such dies are dented or chipped off – calls for a MPW technique, also referred to as needle arc welding (since the arc is so thin, it can pass through the eye of a needle).
Plasma welded products used in architecture and paper processing
Hence, the longer PAW arc is more stable and tolerant of unsteady torch manipulation by novice welders. PAW requires relatively expensive and complex equipment as compared to GTAW; meticulous and timely torch maintenance is critical. Welding procedures tend to be more complex and less tolerant to variations in fitup. Automation is desirable. All this is worth the trouble as impossible-seeming welds can be performed. There are various process variables when it comes to PAW. One of them include gases. At least two separate (and possibly three) flows of gas are used in PAW: Plasma gas that flows through the orifice and becomes ionised Shielding gas that flows through the outer nozzle and shields the molten weld from the atmosphere Back-purge and trailing gas required for certain materials and applications, e.g. titanium/alloy welding. These gases can all be same or of differing composition. argon, hydrogen and helium gases are most commonly used. Some other important variables include: Current type (pure DC or square wave/ pulsed) Polarity is another factor. Direct current electrode negative (DCEN) from a constant current (CC) power source is a standard requirement. AC square-wave is common in aluminium and magnesium, which provides better cleaning of the nearly transparent surface oxide films that can hamper welding. Welding current and pulsing current can vary from 0.5 A to 1200 A; Current can be constant or pulsed at frequencies up to 20 kHz.
Gas flow rate (this is a critical variable). These days high precision welding of 0.01 mm thick sheets is also carried out, for instance in filter fabrication, welding of stainless steel bellows, or wire-mesh grids, etc. Automated welding units are usually employed for various applications. However, aerospace & nuclear engineering, and biomedical engineering are some areas where micro-plasma welding is a mandatory solution to tricky welding configurations. Sheets as thin as 0.076 mm have been welded reliably. Given below are a few welding techniques employed across industries:
LASER BEAM WELDING (LBW) It is a welding technique used to join multiple pieces of metal through the use of a laser. The beam provides a concentrated heat source, allowing for narrow, deep welds and high welding rates. The process is frequently used in high volume applications, such as in the automotive industry. Like electron beam welding (EBW), LBW has high power density (in the order of 1 megawatt/cm²) resulting in small heataffected zones and high heating and cooling
Milliseconds long pulses are used to weld thin materials such as razor blades while continuous laser systems are employed for deep welds. LBW is a versatile process, capable of welding carbon steels, high-strength lowalloy (HSLA) steels, stainless steel, aluminium and titanium. Due to high cooling rates, cracking is a concern while welding high carbon steels. Proper pre-heat and postheat can eliminate this problem. The weld quality is high, similar to that of electron beam welding. The speed of welding is proportional to the amount of power supplied and depends on the type and thickness of the workpieces. The high power capability of gas lasers make them, especially suitable for high volume applications. LBW is particularly dominant in the automotive industry. Some of the advantages of LBW over EBW are : The laser beam can be transmitted through air rather than requiring a vacuum The process is easily automated with robotic machinery X-rays are not generated LBW results in high quality welds.
LBW EQUIPMENT The two types of lasers commonly used are solid-state lasers and gas lasers (especially carbon dioxide lasers and Nd:YAG lasers). The first type uses one of the several solid media, including synthetic ruby and chromium in aluminium oxide, neodymium in glass, and the most common type, crystal composed of yttrium aluminium garnet Micro-plasma welded Palladium strips
rates. The spot size of the laser can vary between 0.2 mm and 13 mm, though only smaller sizes are used for welding. The depth of penetration is proportional to the amount of power supplied, also dependent on the location of the focal point: penetration is maximised when the focal point is slightly below the surface of the workpiece. A continuous or pulsed laser beam may be used depending upon the application.
High precision plasma welded s.s. bellows
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