Solenoid Coil

A precise distance between two ends of a bobbin assembly was maintained whilst the components were laser welded.

In this case study a nickel-iron Permendur alloy pin is first welded into the stainless sleeve tube by laser. This application shows the flexibility of laser welding, where using TIG welding would be too heavy-handed, and vacuum brazing would not be applicable. The high iron content of the nickel-iron alloy demands that the assembly is shielded by inert gas in order to avoid excessive oxidation and tarnishing.

Laser welding of similar alloys containing nickel tends to lead to good strong welds, whilst welding dissimilar alloys requires investigation and the possible use of fillers to ensure good welds. Similarly, titanium, stainless steel and other materials can be subject to good strong laser welds.

Like electron beam welding (EBW), laser welding has high power density, of the order of 1 megawatt/cm²(MW), resulting in small heat-affected zones and high heating and cooling rates. The spot size of the laser can be varied between 0.2 mm and 2.0 mm. The depth of penetration is proportional to the amount of power supplied, but is also dependent on the location of the focal point: penetration is maximized 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. Milliseconds long pulses are used to weld thin materials such as razor blades whilst continuous laser systems are employed for deep welds, which can take on a keyhole shape, down into the joint between the metals.

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Solenoid valve coil