 |
3D Tool for Modeling
|
||||||
|
|
|
T ZCorp's |
|
|
The allure of a convenient method to quickly produce low-cost concept models is powerful. Such a method could not only replace existing modeling techniques but would offer a means to make many more models than ever before and thus would foster creativity and innovation. The problem is that most of the conventional methods as well as the so-called "rapid prototyping" tools do not address the needs of the early stages of the product development process. A 3D modeling tool should be useful at the earliest stages of design and allow for many "rough draft" designs. Many iterations of any proposed design will ideally be seen only by the designer, before he or she is ready to have the design critiqued by others. In order for this tool to be practical, it must be easy enough to use that the designer has the luxury of making a model just for a quick look. It must be fast enough to fit within the existing design process -- for example, a designer must be able to print a model during a one-hour lunch. To deliver on speed, the system must also be easily accessible to the designer. If the part can be produced in one hour, but must be made at a remote location and delivered, the first advantage does little good. The models must be cheap: the majority may have extremely short lives before ending up in the trash. This means that the total cost per model, including capital cost, materials, and maintenance, must be low enough that the designer is not inhibited from making twenty or so iterative design models on a given project. Finally, if this model is to serve as the basis for a decision, it must also accurately represent the design. The importance of the ability to build complex geometries, such as undercuts, overhangs, cores, and inner passages, is obvious. The designer needs to evaluate the actual design, not a simplification resulting from the limitations of the fabrication method. Based on these criteria -- speed, cost, ease of use, and the ability to fabricate complex geometries -- nearly every modeling technique fails the test. Conventional model-making methods such as cutting of foam core, molding of clay, or handwork of wood are very time-consuming, especially when the communication with their remote location is taken into account. They are labor-intensive and hence inherently expensive. Finally, all these methods are limited in the types of geometries that can be made. CNC machining is neither simple to use nor fast enough to be practical for early-stage concept models; it also requires the designer to interface with a shop group in a distant location with its own backlog of work. In addition, the types of geometries that can be made via CNC are extremely limited. Most rapid prototyping systems are not rapid at all. Furthermore, the equipment and materials are generally exceedingly expensive, while the systems are difficult to use and most are not office-compatible. While rapid prototyping provides true CAD design verification, since the digital data is used directly to fabricate the model, many techniques use support structures which render true model representation impossible. While the gap between the potential of iterative modeling and the reality of the tools available seems daunting, there is a new technology that is able to cross this chasm. It is a very fast, inexpensive, and surprisingly simple tool which can build complex three-dimensional objects directly from a CAD file. Z Corporation has commercialized a technology that radically streamlines the process of building three-dimensional models automatically from CAD files. The Z402TM system, based on the Massachusetts Institute of Technology's patented 3DPTM technology, is an affordable 3D printer. The system builds parts out of a starch-based powder and aqueous binder in an office environment, thereby providing engineers, marketers, and manufacturers a means to communicate and improve designs in three dimensions instead of on a flat screen or paper. The Z402 system is about 10-20 times faster than any competing rapid prototyping technology, making it a powerful tool for reducing the time required to bring a new product from conceptualization to market. For example, the build time for a part with dimensions of 8" x 4" x 1.5" is about 45 minutes. In addition to its speed, which has set a new standard in the rapid prototyping industry, the Z402 system is surprisingly inexpensive to operate: the equipment (with software) sells for $59,000, and the materials generally total less than a dollar per cubic inch of part, and often as little as 50 cents. Finally, the Z402 system has the ability to produce complex geometries with no supports, since all stressed elements have support from unbound powder until fully cured. This allows for the building of parts that would be impossible on other systems. The maximum part size is 8" x 10" x 8". The machine size is 29" x 36" x 42" high, and it weighs 300 pounds. The designer must first export the design from the 3D CAD system into the STL file format. STL is the de facto standard file format for all rapid prototyping equipment and approximates the surface of the solid model by covering it with a multitude of small triangles. Ideally, to make a good rapid prototyping model, the STL file must be made from a watertight solid model. The biggest drawback of the STL format is the magnitude of the file sizes generated, which slows down computer time and uses a lot of memory and disk space. This can be minimized by reducing the number of triangles generated, i.e., increasing their size and therefore reducing the accuracy of the STL file. File-size reduction can be achieved by saving the file as Binary STL instead of ASCII STL. Binary STL is the recommended file format, although either type file can be read by the Z402 system software. Ready to Print The user is now ready to 3D-print the part on the Z402 system, which produces the part layer by layer from powder that is bound by a proprietary liquid binder. Minimal training on hardware and software is needed to operate the system. The user first fills the machine with powder, and then imports the STL file into the Z402 system software, a Windows-based application that can run on a standard ($1500) Pentium PC. The Z402 system software slices the STL file into cross-sections that can be anywhere between 0.005" and 0.010" thick. The user, in selecting the layer thickness, makes a tradeoff between resolution (stair-stepping) and print speed. The Z402 system then prints these cross-sections one after another from the bottom of the design to the top. Inside the Z402 machine there are two pistons, as shown in the diagram below. The feed piston is on the left and is shown in the 'down' position filled with powder. The build piston is the piston on the right, shown in the 'up' position. Also represented in the diagram is the roller (drawn as a circle) and the print assembly (drawn as a square.)
Click here for a larger diagram... To begin the 3D printing process, the print assembly moves to the right and spreads a layer of powder in the same thickness as the cross section to be printed. Then, as the print assembly returns to the left, the 128 jets in the Z402 binder cartridge apply a binder solution to the powder, causing the powder particles to bind to one another in the shape of the cross-section of the layer. The feed piston comes up one layer of thickness and the build piston drops one more layer of the thickness. The Z402 system then spreads a new layer of powder and repeats the process until the part is completely printed. At this point the build box is filled with powder, some of which is loose and some of which is bonded to form the part. The excess powder is removed with a vacuum hose and then the part is picked out from the loose powder and depowdered in a post-processing unit. The part can be infiltrated with various materials to improve its strength and surface finish. The standard method of infiltration is a quick dip in wax; however, Z Corporation recently released a new materials system that makes concept models so strong that they can support the weight of a person. Parts made with the new materials can be sanded, painted, drilled, tapped, and finished in a number of ways for even higher-quality models. The key to the new materials system is the use of ZR10 resin for infiltrating the part. The resin, which is applied by using a simple hand-held applicator, cures in 20-40 minutes, depending on the size of the part. Very fast 3D printing allows for design verification by the designer. It also provides a means for communication between the designer and the design supervisor, or other designers working on products which will interface with each other. By providing almost instantaneous feedback on each proposed design change, the Z402 system allows the designer to make more iterations of a design at a faster rate. Carefree 3D printing improves communication with the marketing department and can provide feedback from potential customers at a stage in the design cycle when changes are inexpensive and easy to implement. Finally, 3D printing early in the design cycle also provides improved communication with the manufacturing group, which results in early detection of flaws and improved design for manufacturing. The Z402 system can transform 3D modeling into an indispensable, everyday adjunct to the inherently limited 2D visualization provided by computer screens and printouts. The Z402 system will improve part visualization and communications while enhancing creativity and reducing the number of design flaws. For more information, please contact the author of this brief,
Marina Hatsopoulos, at
|
