Perks of fiber lasers

Machine shops don’t have to be experts with fiber laser cutting technology to know that if they can cut a 6.35 mm (0.25″) plate with a 4-kW laser, they can cut faster with an 8-kW laser power source, let alone a 12-kW or 15-kW fiber laser cutting machine.

The main benefit of high-powered fiber laser technology is decreased process time for laser cutting. That’s often why a shop buys a high-powered laser cutting machine to replace two or even three old lasers. Parts can come off a laser bed more quickly and, accordingly, cheaply than before. But those are not the only perks.

“Pulsed fiber lasers offer numerous advantages compared with traditional fabrication methods, such as mechanical cutting, stamping and electrical discharge machining,” said Thomas Schreiner, product line manager for Coherent Munich GmbH & Co. KG, Gilching, Germany. (Coherent Inc. is in Santa Clara, California.) “The laser can be extremely spatially selective. It can be focused to a spot diameter much smaller than the width of a mechanical blade or saw, enabling the creation of finer details with greater precision.”

He said a fiber laser typically produces a high-quality edge that requires no post-processing, reducing overall costs. Also, unlike with a drill or an EDM tool, noncontact laser processing involves no tool wear, so consistent, uniform results are delivered.

Lasers in Use

Schreiner gave an example of an application that illustrates the advantages of laser cutters. Bone drill bits, such as craniotomes, now are made routinely by laser cutting. These stainless steel devices have small, sharp edges. The use of pulsed fiber laser cutting avoids heating the bulk of the material, virtually eliminating thermal transformation, which otherwise could render these edges prone to break off. Also, the correct function of the drill depends on the precise geometry of various features — like the cutting edge, rake face and flank face — so the superior spatial accuracy of laser cutting is ideal for creating these instruments.

Laser cutting is ideal for creating tools like craniotomes and other drill bits. Image courtesy Coherent

In terms of the laser technology, Coherent offers a comprehensive range of lasers with pulse widths from milliseconds to femtoseconds, output power from tens of watts to multikilowatts and wavelengths from deep ultraviolet to midinfrared. For medical devices, many applications are well served by near infrared lasers in the tens-of-watts power range with adjustable pulse widths, such as the fiber laser technology in Coherent’s StarFiber 100-600 fiber laser machine.

Common Composites

Composites are structures in which two or more materials combine to produce a material whose properties would not be attainable by conventional means. An example is carbon fiber-reinforced polymer, which is constructed by two materials — carbon fiber and polymer matrix — that have significantly different properties.

Ronald Schaeffer, CEO of HH Photonics, New Ipswich, New Hampshire, said numerous laser job shops are familiar with the challenges of machining FR-4, which is glass-reinforced epoxy laminate material. An overwhelming proportion of the composite dielectric material used in the interconnect industry remains FR-4, though a lot of other materials, including CFRP, are used extensively in the aerospace industry. CFRP is finding its way into a host of new applications and is amenable to laser processing, cutting, drilling and structuring.

He is former CEO of a laser materials processing company, Pelham, New Hampshire-based PhotoMachining Inc., which has an array of laser tools ranging in wavelength from 248 nm in UV to 10 µ (0.0004″) CO₂ in infrared and with pulse lengths ranging from milliseconds to femtoseconds. This includes fiber lasers that operate in infrared with pulse lengths in the hundreds of nanoseconds.

Schaeffer said how these laser tools are used depends on the application and the power of a laser. High-energy lasers can “punch” through many materials in one pulse, which effects faster processing but results in losing some control. Lower-energy beams can be rapidly multipassed, which usually results in better cut quality and smaller feature sizes — if a small kerf is used — but at the sacrifice of processing speed. To enhance cut cleanliness, laser contract manufacturers like PhotoMachining typically design laser machines with the smallest usable kerf.

“If we squeeze that energy per pulse down into a very small spot and keep the pulse length as short as possible,” he said, “it results in high peak power intensity, which is the key to clean processing.”

The use of a granite-based motion module ensures dimensional accuracy and repeatability with the ExactCut system. Image courtesy of Coherent

PhotoMachining uses a Lumera UV laser with a 12-picosecond pulse and 20-W to 100-W Q-switched fiber lasers with pulses of 100 nanoseconds and shorter for micromachining composites. Even so, PhotoMachining often laser-machines composites in multiple passes to allow heat to dissipate between them, Schaeffer said. He said cutting a feature, such as a hole, in a single pass is quicker, but the quality isn’t as high.

“The ability to tailor properties, combined with the inherent low density of the composite and its relative ease of fabrication, makes this material an extremely attractive alternative for many different industrial sectors but primarily the aerospace sector,” said Mohammed Naeem, director of business development and special projects at Prima Power Laserdyne LLC, Brooklyn Park, Minnesota.

Delamination, fiber pulling out, matrix chipping, heat damage and tool wear generally represent the main concerns when machining composites. These materials require processing like cutting, drilling and milling, typically using traditional machine tools.

Laser Versus Water

Aerospace companies recently have been investing in waterjet technology for cutting CFRP.

“Waterjet can give a high-quality cut,” Naeem said, “but this has associated problems of causing delamination and requires a pilot hole to be drilled mechanically if the cutting process starts anywhere other than at the edge of the sheet.”

“Waterjet cutting is a subtractive manufacturing technique, but it uses pressurized water focused in a very small point to cut the material,” said Alexei Markevitch, market development manager at IPG Photonics Corp., Oxford, Massachusetts.

The pressure can be as high as 27,216 kg per square inch (60,000 psi). Water may be mixed with an abrasive, such as garnet, which increases cutting possibilities by allowing more materials or closer tolerances.

Waterjet cutting is ideal for stone, ceramics and thicker metals, which are more difficult to process by laser cutting or other methods. Unlike other material removal processes, waterjet systems can cut extremely hard, reflective and nonconductive materials, making waterjet an efficient, productive method.

Composites machine differently from metals and therefore can be challenging to cut. Although shops have applied traditional cutting tools and alternatives like waterjetting to cut composites, interest in using lasers is growing for some applications.

Lasers cut a wide range of materials: all plastics, woods and metals, excluding highly reflective metals. Lasers also process ceramics, sapphire, silicon, glass, diamond, polymers, epoxy and composites but often require different wavelengths or modes of operation, Markevitch said.