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GENERAL PROCESS - REF. #GP009 | View PDF
THE CHALLENGE
In a typical gas shielding application, different shield gases are used to keep the weld area clean, control plasma, and control surface tension or prevent oxidation, depending on the application. Flow control of shielding gas in the laser welding process has a dramatic affect on the quality of the weld. In a dual shield gas application, helium may be used at the point of welding since it reduces the volume of plasma under the laser and promotes deep penetration. Argon is used to protect the weld bead as it cools. Argon is heavier and lays on the part, and it is also less expensive than helium. This type of set-up is common for long welds such as pipe forming.
CO2, air and O2 are used to widen the toe of the weld via surface tension effects. O2 can be used to promote coupling into difficult-to-weld materials like copper and aluminum. The oxide promotes coupling by reducing reflection on the surface, resulting in successful welding at lower power densities. Helium promotes penetration since it retards the formation of a plasma over the weld which can reduce thepower to the weld.
Often, inexpensive flow meters are installed on original equipment, resulting in inconsistent gas flow and weld quality, and in the case of a flow interruption, these meters do not typically provide alarms to alert the operator, which can result in very costly waste and/or rework.
 THE BROOKS SOLUTION
Brooks variable area flow meters (rotameters) are perfect for critical purge and cooling flows. They use a precision glass measurement tube, with superior tolerances and stability to the more common plastic models. A Brooks Model 1355 with 2-5% accuracy can be supplied with direct reading scales for any gas. Equipped with an integral Model 8800 flow controller, the Model 1355 is optimized to hold flow constant with changes in feed pressure. Brooks VA meters can also be equipped with alarms and transmitters to alert an operator of a loss of flow.
 If the process gas flow is very critical, a Brooks thermal mass flow controller (MFC) is a better choice. This device consists of an electronic flow meter, control valve and control electronics in a compact, integrated package. It will maintain the flow at the desired setpoint to better than 1% accuracy and it will alert the operator when gas flow is not present. Brooks MFCs are available in a wide range of flow rates and price ranges, in analog or digital configurations. |
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