Laser machine tools can help speed product development cycles for a range of materials.
Otherlab has developed ways of decomposing complex 3D shapes into strings and sheets that can be machined using 2.5D methods like laser cutting, and then reassembled. All photos: Otherlab
As product lifecycles shrink, there is increasing pressure on research and engineering personnel to speed the new product development cycle. A variety of technologies, from traditional CNC machining to waterjets and 3D printing, are now widely employed to enable the quick creation of 3D prototype parts directly from computer-aided design (CAD) files.
Laser machine tools are becoming another important tool in this arsenal, as they can process a wide variety of materials with high precision, repeatability, and speed, and are also relatively inexpensive to operate. Otherlab, San Francisco, is a small research and development firm that specializes in creating prototype solutions to problems that are computationally complex. One of the fabrication techniques they employ is a laser-based machine tool.
The Coherent MetaBeam 400 (Coherent, Santa Clara, Calif.) used by Otherlab mates a 400-W, sealed carbon dioxide laser with a motion system and control electronics. This platform can process most plastics up to about 1.25 in thick and metals of up to about 0.125 in thick, over a 4 ft by 4 ft working area. Importantly, it can cut with a dimensional precision of up to 0.001 in, at speeds up to 2,000 in/min. Cutting patterns are created in SolidWorks or some other application that produces files in DXF, DWG, AI, HPGL, Gerber, JPG, BMP, or TIF format.
Otherlab engages in a very diverse range of development tasks; the sealed carbon dioxide laser is capable of processing metals, such as mild steel, stainless steel, and aluminum. The long-wave infrared output (10.6-µm wavelength) of the carbon dioxide laser is also strongly absorbed by most organic materials, enabling processing of many plastics, wood, leather, paper, thin films, and foils. Most other industrial laser types, such as fiber lasers or Nd:YAG lasers, output in the near infrared (around 1 µm). Most organic materials (especially many transparent plastics) don’t absorb well at this wavelength, making it difficult to process them with these other lasers.
Techniques such as 3D printing and five-axis CNC routing are capable of producing parts having almost any arbitrary 3D shape. In contrast, laser machining is sometimes referred to as “2.5D” because it is limited to cutting parts having a fixed cross-sectional shape (as if they were extruded). Many users overcome this by cutting numerous pieces from a thin material, and then stacking these layers to form a more complex, 3D shape. Otherlab sometimes does this, but has also developed a more sophisticated “origami-like” technique. Here the 3D surface is computer modeled as a “mesh” of small, flat polygonal pieces. Then, the computer decomposes this 3D mesh into panels that are cut—and scribed—from flat sheets using the laser system, ready for folding, stitching, gluing, or welding.
Why laser cutting?
3D printing is best employed for creating very complex part geometries. Its major limitations are the high cost and very limited range of materials with which the technique can be applied. There also are limitations on tolerances, resolution, and maximum part size.
Traditional CNC routing is another way to create relatively complex part geometries, and can be applied to a wider range of materials than 3D printing. Thus, it is more directly competitive with the laser. The major disadvantage is cost; the CNC mill at Otherlab has operating costs in the $20 to $40 per hour range. In contrast, the operating cost for the laser system is only about $2 to $5 per hour.
Abrasive waterjet (AWJ) is another 2.5D technology that competes with laser processing. However, the AWJ machine at Otherlab costs about $160 per hour to operate, so it is only employed for processing metals over 3 mm thick, as well as certain materials, such as ceramics, that aren’t amenable to laser processing.
Otherlab used the laser system to cut and weld inflatable bladders for use as precision actuators in a two-axis mirror tracking system.
One area of interest at Otherlab is inflatable robotic structures. Robots consist of several separate inflatable pieces—for example, a body section and legs. Motion is achieved through the use of textile-based actuators—essentially bladders—which expand in one axis upon inflation.
Here the advantage of the laser cutter is that it can cut a stack of up to 10 layers of the thick, vinyl-coated fabric—typically nylon or polyester—that is used. This wouldn’t be possible with a knife plotter. Also, laser cutting delivers the sub-millimeter dimensional accuracy, even over large lengths of fabric.
Otherlab has also used this inflatable bladder approach to create precision actuators for two-axis mirror tracking. These components were used in a heliostat—a device to track the movement of the sun—in a solar power application. In this case, the material was polyurethane. Two layers of the material were stacked in the laser machine, and high power was used to cut the required shapes. Then, a second pass was made at lower laser power to weld the edges of the two pieces together.
The laser is a faster, more accurate, and more flexible way of performing plastic welding than traditional techniques, such as ultrasonic or traditional thermal welding. Furthermore, these other methods typically require some sort of purpose-built jig, which involves greater cost and time.
Otherlab also regularly uses the laser machine to cut metal. A prototype bicycle frame was constructed of several pieces of 16-gauge mild steel. When welded together, these thin pieces curved out of their flat plane to form a rigid, but light, 3D structure. Small locating notches were machined into the parts to ensure the required sub-millimeter dimensional accuracy when assembling and welding these pieces.
This same level of dimensional accuracy would have been difficult to achieve using waterjet cutting. It could be attained using the CNC router, but that machine imparts some pressure on parts during processing, which can deform delicate or small parts.
Otherlab has found that the laser machine tool offers greater economy, speed, and versatility than most other prototyping techniques. While it certainly cannot do everything, it has become a premiere method used at Otherlab.