Two Beam, or not Two Beam

[TECH]

Ok, I admit to being a bit cheeky with the title, since there's already a growing concensus that multi-beam tehnologies can take AM processes to another level of productivity, and there's already been a number of successful technology platforms that have demonstrated this.

What I'm introducing here is the types of beam that can be used together, not just more of the same, or more powerful versions of the same. And I'm doing this now because I recently read about some clever research students that have achieved something similiar. In truth, it's been a long time curiosity of mine to consider mixing and matching laser technologies to take care of the different aspects of the additive manufacturing process. My greatest curiosity thought has been, why haven't others at least given it some thought as well?

Perhaps they have, and perhaps they've always considered that it just doesn't make sense, or possibly even that it's just plain dumb to try. Well, not being one to shy away from considering dumb ideas, or even sharing them, here we go.

When there's only darkness, there's no such thing as a light that is too dim..

Let's start with something that is really outside of the box first. Many of you have seen this type of thing; walking into an event, or snazzy disco where lasers are being used to project images onto walls, the ceiling or other surfaces. It never ceases to make me stop and think, wow! Well it takes a certain type of scanning technology to do this reliably, and I just can't help but think that a similar scanning strategy could be used to maintain heat in a build, or pre-heat a metal powder bed. Using lower powered lasers to simply pre-heat a build plane, build plate, or build volume, or to maintain a specific temperature over the progression of the build; to add in extra heat when and where it might be required, to relieve the build up of internal stresses, or to aid in the transformation on a metal. The reasons for wanting to try this are many and varied.

Could it even be possible to slowly increase the heat over an entire 2D slice of 3D data, by repeatedly scanning that slice with ever increasing laser energy to the point that it caused almost simultaneous melting, or sintering over the required area?

This could have the potential of releiving many issues associated with uneven heating. I mean, the common result of having variable scan path lengths associated with stripe pattern scanning to in-fill large areas.

So where does the dual, or multi-beam factor come into it?

Well, now imagine one type of laser that takes care of a stable border/contour area, and another that does the larger in-fill areas, whilst a third could be synchronously laser re-melting/machining the surface profiles or other critical areas. Each one of the scanning strategies may benefit from subtly different optimum type of laser, due to the change in process conditions, or the particular laser/materials interaction.

I hope by now you are already seeing some more possibilities, and up to now, you may have been thinking that I've only been considering fibre lasers (afterall, these are the most commonly used in metal-LPBF systems), but that is not so. What if it were possible to use a bank of pulsed diode lasers, or surface emitting lasers, utilising different wavelengths, and/or combinations of these, used in a single head (much like a multi-nozzle inkjet printhead) to somehow "print" parts?

Shh, don't go telling anyone, but I think the World isn't flat.

But wait, powder bed isn't the only popular type of laser based system. So what if the same logic is applied to DED, or Laser Metal Deposition systems?

It would be entirely reasonable to conceive of a multi-head system for simultaneously building with different alloys, carrying out laser micro-machining, surface modifications (it's no secret that laser re-melting can enhance corrosion resistance, for instance), or in-line inspection processes, or laser welding to join smaller parts together, and all on the end of clever robotic arms.

And whilst we journey on in our non-flat world, where there is no end to the Earth, laser based AM doesn't have to stop there either. In other industries, and in other applications, lasers are used for imaging devices, audio/listening devices, sensors, safety switches, and plain old measurement devices. Imagine what could be achieved if all of this pre-existing knowledge could be combined in an AM machine. Imagine further where AM could go with the addition of new things like machine learning, AI, and computed simulation.

The inherent beauty of using lasers is that they can be configured for all sorts of non-contact measurements.

• Laser based optical scanning systems, to accurately measure the 2D contour of a melted layer, or the exact height of a melted layer (sometimes the layer shrinks more than expected, and sometimes it starts to lift more - hot things do like to expand). Or even 3D scanning semi-finished parts whislt still in a machine.
• Laser based thermal analysis systems, used to constantly monitor the build temperature, both at the melt pool and in the previously formed/melted material. Systems with direct feedback to process parameters to ensure unform input energy, an prevent over-heating, or large residual stresses building up.
• Laser based systems for in-line analysis, of process gases (the composition or the pressure) at various stages within an AM machine, of powder particles (even at sub-micron levels) in the gas stream, or other part of a powder recirculation system.

So there you have it, just some of the musings that have filled up my other-times vacuous mind. Nothing too clever, and certainly no detail.

"I don't know where you get your delusions, laser brain!" - Star Wars (just love it!)