By Kip Hanson
We have many pioneers to thank for the laser. In 1917, Albert Einstein published a paper suggesting that atoms could be made to discharge photons through a process he called “stimulated emission.” Russian scientist Valentin Fabrikant’s research into optics and electromagnetic radiation over the coming decades helped validate that work. And while some attribute the laser’s invention to Charles Townes and Arthur Schawlow of Columbia University in 1958, most aficionados will tell you it was Hughes Research Laboratories’ Theodore Maiman who lit up the first working prototype two years later.
It was clearly a team effort, but whoever was most directly responsible, none could have foreseen how their actions would change the world. Lasers are ubiquitous today, used for everything from barcode readers and holographic imaging to liposuction and the hopeful annihilation of incoming ICBMs. Boom.
Not one size fits all
Doomsday discussions aside, laser technology plays an increasingly important role on the shop floor. Marking lasers provide accurate and exceedingly fast marks on parts of all shapes and sizes. If lasers were as inexpensive as welding guns, the latter would be out of business. And 3D printing? Much of it wouldn’t exist without lasers.
Brent Roeger, laser applications engineering manager at IPG Photonics in Minneapolis, knows all about it, and can suggest lasers for each of these processes. When asking him to recommend which one is right for micromachining, however, be prepared to answer a few questions.
“It’s very application specific,” he says. “If you’re processing metals, you would most likely use an infra-red (IR) laser, with a pulse duration determined by quality and throughput requirements. And then, depending on what feature size you’re going to create, you may need to change your optical configuration to match. If you’re processing many different types of materials such as polymers, metals, and ceramics, however, one laser source will generally not achieve all of the necessary quality and throughput requirements.”
Femtosecond and picosecond lasers change this equation somewhat. Roeger explains that the incredible peak power of these “ultra-fast” devices helps to overcome the low optical absorption coefficients of materials that would otherwise be difficult to machine. “These ultrafast lasers produce very high peak powers that lead to multiphoton absorption and significantly increase coupling into the material, thus allowing for high quality machining even across materials with very different optical properties.”
Time for a shout out
For those scratching their heads over the terms coefficient, absorption, and pulse duration, you’re not alone. Laser science is…well, deeply scientific, which is why it’s essential to speak with an expert or two before investing in the technology. For those needing to machine the ultra-small, though, doing so can reap big benefits.
A review of IPG Photonics’ websites offers dozens of examples of micromachined and drilled components made of polymer, glass, and metal. Most of these contain impossibly small channels, grooves, and cavities, each boasting sub-micron accuracy and virtually none of the “recast layer” that once plagued laser (and EDM) cutting systems.
Here again, which one to use depends on numerous factors. “That’s why IPG has a number of applications labs worldwide,” says Roeger. “Send us your requirements and we will configure the optics system and select the appropriate IPG laser to meet the desired results.”
So does Chicago-based GF Machining Solutions LLC – Microlution, where sales and marketing analyst Attila Farkas ticked off a handful of industries using laser micromachining. “One of Microlution’s first success stories was for the automotive market, machining high-precision holes with negative taper in gasoline direct injection (GDI) nozzles,” he says. “Before then, the customer was using EDM, but a five-axis laser simplified the process significantly. It was a great fit.”
Other great fits include laser drilling and shaping of engine blades and combustor linings for the aerospace industry, cutting out pinions, wheels, and other microparts
for watchmakers, and most recently, tube cutting on a machine that Farkas thinks of as a “laser lathe.”
“We recently introduced the Microlution Tube Cutter, or MLTC,” he says. “It’s a four-axis ultra-fast laser with a rotary spindle that supports off-centre cutting. It can be used to machine stents, but these are generally on the larger side and require nanosecond lasers, so probably the biggest application right now is for medical parts like guide wires and marker bands. Here again, these are often produced using EDM, but customers are finding that laser is frequently a more effective approach.”
Weighing the trade-offs
One reason that laser is sometimes preferred over EDM is conductivity. For example, many of the aerospace components just mentioned often have a thermal barrier coating (TBC) to reduce oxidation and thermal fatigue. Yet these coatings are non-conductive, immediately ejecting those parts from the EDM ballpark. Lasers have no such constraints and are able to ablate or “burn” virtually any material. A similar argument can be made for any polymer part and for those made of ceramic (excepting certain “doped” ceramics), each of which plays important roles in these and other industries.
A laser’s greatest downside, notes Farkas, is one that anyone who’s tried to shine a flashlight around a corner is well aware of—light doesn’t bend (except near black holes, another phenomenon that Einstein predicted). “A laser requires line of sight, whereas an EDM could use an offset electrode to reach hidden part features. Backwall strike is another concern, since lasers also tend to keep cutting once you’ve broken through a wall, so you need a way to protect the far side of a tube or similarly hollow feature. However, we’ve developed ways to mitigate this, and have also introduced the means to ‘shape’ the beam using a three-axis scan head. It’s a very powerful capability that’s opening the door to some previously impossible or at least impractical part geometries. When you add to that a laser’s great speed and flexibility, it’s understandable that so many in the manufacturing industry are taking a hard look at laser machining, micro or otherwise. SMT