The recent introduction of a rapid prototyping machine that leverages consumer technology in the form of Digital Light Processing (DLP) may challenge the dominance of lasers for curing resins.
For some photopolymer curing applications, lasers have several drawbacks, two of which are cost and complexity of operation and installation. You need special input power, cooling systems and ventilation, and other overhead for the system. You also usually must calibrate the laser, and some systems require specific expertise to operate.
DLP technology cures parts a layer at a time rather than tracing individual parts on a build tray. This approach to curing enables DLP systems to build parts faster than all but the higher end SLA systems.
Selective light modulation using a technology known as Digital Light Processing (DLP) offers an easier to use and less expensive form of photo-polymer curing; it is about one-third the price of laser based rapid prototyping equipment. Plus, parts made from equipment using this technology deliver resolutions to 138 microns, accuracy on par with those made from laser based equipment, and a vertical build speed of ½ in. per hour.
DLP was first used by envisionTEC, a developer of rapid prototyping equipment out of Germany, for use in mCAD, jewelry, dental and hearing aid markets. Through a strategic OEM partnership with Z Corp., the two companies have created the ZBuilder Ultra, a DLP based system with modifications that suit the industrial rapid prototyping market.
DLP Technology starts with a small imaging chip with millions of tiny mirrors that make a picture amazing.
DLP is based on a special chip developed by Dr. Larry Hornbeck of Texas Instruments in 1987. The chip is used in most conference room projector systems. Often viewed as “the world’s most sophisticated light switch,” it is made of a rectangular array of more than 2 million hinge-mounted microscopic mirrors. Each of these micromirrors measures less than one-fifth the width of a human hair. Combined with advanced electronics, the chip is said to produce images and video that have “redefined picture quality.”
DLP can even be used to project color, primarily used in cinema and large display applications. Such applications use a three-chip system. The white light generated by the lamp passes through a prism that divides it into red, green and blue. Each DLP chip is identified for each of these three colors; the colored light that the micromirrors reflect is then combined and passed through the projection lens to form an image.
Light from the DLP system’s light source hits the entire chip. Each mirror can be viewed as an On or Off “pixel.” If a mirror is pointed in one direction with the light, then that mirror is “On.” If the mirror is pointed away from the light, then it is “Off.” The “Off” light will not hit the build area but will hit a light absorber. Each mirror can be switched on and off several thousand times per second. The number of mirrors determines the build area as well as the resolution.
The envisionTEC and Z Corp rapid prototyping systems use a modified version of this chip, with some of the modifications being proprietary. These systems use the highest resolution DLP chip available; 1920 by 1200 total pixels, which is twice the resolution of a standard HDTV.
As Joe Titlow, Director of Product Management noted, “Our focus was not on the image clarity the chip delivers. The modifications we were interested in involved getting as much energy as possible, as accurately and purely as possible, from its source into the build area.”
The build size of the ZBuilder is 10.2 x 6.3 x 7.5 in. (260 x 160 x 190 mm). According to Z Corp., this printer is competitive with stereolithography, FDM, and photopolymer-jetting technologies, offering comparable quality in part accuracy, resolution, and material properties but at one-third the price. Compared with low-end FDM systems, it shares a similar price point but delivers true plastic parts with surface finish that rivals injection molding.
The chip’s mirrors focus the energy of the UV light source to cure in one step. Because of this exposure, the equipment only needs to move in the Z direction. Thus, it can expose a number of parts simultaneously, as opposed to a laser beam tracing parts on a build tray individually. The simultaneous exposure makes DLP based systems about two to five times faster than SLA equipment.
When it comes to materials, lasers have higher energy density so they can be used with more materials. With DLP, the main material is a resin with ABS like performance. According to Titlow, other materials will be coming later, including the possibilities of clear resins and casting waxes.
Parts made from the liquid photo-polymer mimic injection molding on accuracy, material properties, detail, and surface finish. The parts do not display a stair-stepping effect common with layer-build 3D printing. In addition, these DPL systems give you precise control over each volumetric pixel, or voxel.