PRODUCT REVIEWS
Left : Use of Polysoude Smart Welding Stations in a clean room . Above : Semiconductor silicon wafer produced in ultra-high purity area . Right : Closed chamber welding tools used in UHP industry .
TIG welding in the Ultra High Purity ( UHP ) industry
By
DR . – Ing . Jürgen Krüger , Engineer
Whenever high-quality joints are required , GTAW ( Gas Tungsten Arc Welding ) or TIG ( Tungsten Inert Gas ) welding , as it is commonly called , will offer a solution . A wide range of products need to be manufactured under white room or clean room conditions . These products may be susceptible to microbes , as is the case with pharmaceutical ingredients , to contamination ( as seen in micro-electronics ) and to foreign objects , which must be kept out of optical devices and precision mechanics .
In many cases , the components for equipment which is intended to be operated inside clean rooms must be produced and assembled under controlled atmosphere as well . Tube network , for example , is frequently used to supply clean room installations with ultra-pure gases and liquids , which serve for inertisation , etching , rinsing , diluting and injection purposes .
To minimise the effort on-site , as many as possible of the connections for the tube network installation of a clean room supply are pre-fabricated . In the factory , standard pieces ( like micro-fittings , Tees , elbows and valves ) are welded together with matching tube segments . Here , the use of orbital TIG welding can provide significant advantages . Complete weld cycles are carried out automatically and lead to consistent highquality results .
To keep contamination inside a clean room as low as possible , any generation or emission of particles has to be avoided . Manufacturing processes can also be the origin of significant particle emissions . Each
electric arc which is struck during a TIG welding procedure is accompanied by clouds of vaporising metal and streams of welding and backing gas . Additionally , the released heat provokes turbulences between inert gas and surrounding air and entrains undesired pollutants .
However , the adverse side-effects of an open arc can be avoided . Closed orbital welding heads have initially been invented as fast and efficient tools for the numerous
Super clean tube to be welded .
butt weld connections of aircraft hydraulics . Ease of use , productivity and outstanding weld quality had been the targets of the development . The advantages of an arc burning inside a closed chamber have also been exploited for clean room purposes . Hot surfaces , turbulences , radiation , uncontrollable particle emission provoked by an open electric discharge could be eliminated . Today , closed orbital TIG welding heads have become indispensable tools whenever tubes and accessories must be welded together under clean room conditions .
The welding equipment should be developed and designed for various clean room requirements . A smart welding station should be able to supply and control the entire range of closed orbital welding heads for micro-fittings and important tube diameters . Due to its very low weight , it can be moved by the operator without any hoisting equipment , which is important to keep the clean room clean . The operating elements should be independent from the power source , so the device can be kept somewhere outside the work bench . If a liquid cooling circuit becomes necessary for larger tube diameters or improved productivity , the cooling device should be independent from the power source .
The OPC-UA protocol delivers the interface to the Industry 4.0 process . With a barcode scanner , which may be used plugged or unplugged , the operator can read the QR-code on his working suit to introduce himself , in the same manner that he can identify welding head , welding gas and workpiece . The matching welding programme is then calculated on the tablet ( data input can be done even if the operator is wearing gloves ).
Weld preparation is divided into two parts : fixing the workpiece in the clamping unit , where it is also possible to use clamping devices from other companies , and final positioning of the welding head including motor , gear , supply hose etc . The real-time progress of the weld cycle can be viewed on the tablet , where welding parameter values are also displayed . These data are transmitted to the factory network at the same time .
Finally , after visual inspection of the completed weld , the operator can confirm the successful production of the joint . n
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64 | sheetmetalplus . com | ISMR April 2021