What Is a Galvanometer? | Understanding Laser Powder Bed Fusion

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In a laser powder bed fusion (LPBF) additive manufacturing machine, the galvanometer, or “galvo,” is the hardware element using coordinated mirror motion to precisely steer the laser beam. The laser itself is fixed, but its beam is in motion thanks to the galvo. A laser beam following a seemingly simple and continuous path through a powder bed, to melt the metal along that path, is probably in fact responding to complex set of precise angular moves of multiple mirrors reflecting the beam from one mirror to another.

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At the Technical University of Denmark (DTU), where researchers have developed an open-source laser powder bed fusion system built from standard third-party hardware, we filmed a series of videos on fundamental elements of laser powder bed fusion — including this video that takes a look at the galvanometer and the important role it plays.

Transcript

I'm at the Technical University of Denmark in Copenhagen, where researchers have developed an open source laser powder bed fusion machine, and among other things, it gives us a chance to look at and explain fundamental elements of a laser powder bed fusion system. A Galvo, or galvanometer, is fundamental to the operation of laser powder bed fusion.

The galvo moves the laser beam, moves the beam through the bed of powder metal. The laser itself is stationary in the machine, but the laser beam passes through the galvo, which moves it using a set of coordinated moving mirrors. In its most simple form, one mirror moves the beam in the X direction, another mirror moves it in the Y direction, and together these coordinated moving mirrors in the galvo create the path the laser beam follows to 3D print precisely the part profile needed at a given layer.

One issue, the galvo locates in the center of the top of the build chamber and this means that the angle of the beam changes as it traces its path through the powder bed. And so you would expect that the shape of the laser spot would also change with that changing beam angle.

A perfect circle directly below the galvo becoming an increasingly more distorted oval as the angle of the beam increases. To compensate for that is the purpose of this f-theta lens.

The lens geometry overcomes exactly that distortion resulting from the angle of the beam. It's not perfect. There is still some spot size discrepancy that users of laser powder bed fusion need to understand, but in general, the combination of galvo plus the right lens geometry allows for consistent laser beam intensity as the beam traces the precise path it needs to trace through the powder bed. We are doing other videos like this that look at other components of laser powder bed fusion. Find these other videos in links in the description.

Also find a link to our report about the development of this open source laser powder bed fusion system. And if you're interested in much more on the basics of additive manufacturing, check out GBM.Media/AM101.