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GENERAL PROCESS - REF. #GP010 | View PDF
THE CHALLENGE
In a CNC laser welding application, the laser beam is often directed over the assembly via servo-controlled mirrors. In this arrangement, the shield gas does not travel with the laser head. Automotive seats and body components are often welded with this technique. Shielding gas is directed to each joint to be welded. The supply flow must be matched to the size of the area to be welded. Flow control of shielding gas in CNC laser welding processes has a dramatic affect on the quality of the weld.
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 the power 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. This is an application that can benefit significantly from a more precise and versatile flow control device.
 THE BROOKS SOLUTION
Brooks variable area (rotameter) flow meters 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.
 Brooks thermal mass flow controllers (MFC) are also an excellent 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. A Brooks MFC will also economize flow by shutting off between parts or after a section is welded. Brooks MFCs are available in a wide range of flow rates and price ranges, in analog or digital configurations. |
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