Today’s rapid prototyping technologies offer more choices in materials, pricing, and model quality, yet the basics remain the same.
While still far removed from being able to produce the proverbial cup of Earl Grey from Star Trek fame, RP systems are undergoing a degree of change. No longer in their infancy, the group of technologies covered under the RP umbrella is pushing the envelope in several categories. At the same time, the underlying principles and reasons for using the systems are essentially identical. Before evaluating the cutting edge, it pays to examine the basics as a baseline.
Building Fundamentals
Definitions of rapid technologies vary, but all agree that these processes create a physical representation of three-dimensional digital data. Data can come from 3-D CAD solid models, CT scans, MRI scans, or scanners and digitizers.
Creating a rapid prototype for molded parts, such as this housing for an Electrolux vacuum, helps to eliminate errors that might otherwise require costly tool rework.
To produce a model or part, digital 3-D data is converted to an STL file, a neutral file format that all RP systems accept. Triangular elements in the STL file represent the object’s surface. The number and size of the elements can be adjusted for greater precision in defining the surface, reducing the so-called “stair stepping” effect.
Prior to building, the STL file must be sliced into layers using a preprocessing program, which also allows users to modify size, location, and build orientation. Programs are typically supplied by the RP equipment manufacturer, and include a means for generating support structures needed to prevent shifting and sagging during the build process and to support any overhanging features. Sliced STL files are then used by the systems to build objects. While RP systems use different materials and technologies, they all build models in an additive process, layer by layer. Materials can be in liquid, powder, or sheet form, and run the gamut from plastic and paper to metal and ceramic.
Rationale for RP
Why do manufacturers and designers continue to create physical prototypes when virtual techniques are now on the rise? The answer lies in the ability of a physical prototype to communicate, unequivocally, the design concept for a part or product.
3-D printers, or concept modelers, offer smaller footprints and lower costs. The Dimension SST (Stratasys), a recent entrant in this category, sells for $24,900.
In addition, physical models help reduce product development cycles and decrease costs by eliminating downstream engineering changes and by optimizing designs. RP models can be approved by a team of marketing, manufacturing, purchasing, and engineering personnel early in the design process, when changes do not require reworking tools or modifying manufacturing processes, both costly endeavors.
Todd Grimm, author of a recent guide on the subject (see “Catching up with Rapid Technology,” opposite), says rapid prototypes have other uses beyond the concept model phase. These include form and fit checking, ergonomic studies, functional testing, RFQs, CAD data verification, presentations, DFM analysis, and pattern fabrication.
Systems Overview
According to Grimm, RP systems can be grouped into four classes: 3-D printers (also known as concept modelers), enterprise prototyping centers, direct digital tooling, and direct digital manufacturing. The first two categories, described below, directly relate to RP rather than rapid tooling or manufacturing.
Enterprise systems use various technologies to produce models. The main technologies in existence today are stereolithography (SLA), selective laser sintering (SLS), fused deposition modeling (FDM), and laminated object manufacturing (LOM). Concept modelers rely on powder-binder printing, multiple jet systems, and FDM. Manufacturers supplying these systems include the following: SLA and SLS—3D Systems, EOS; FDM—Stratasys, Dimension; LOM—Cubic Technologies; powder-binder printing—Z Corp.
While this list is brief, RP equipment suppliers are many and varied. For a full listing, visit www.wohlersassociates.com or www.immalmanac.com.
Catching up with rapid technology
How do you stay informed about the advances in RP/RT? Manufacturers’ websites always provide news about new systems and/or materials offered. Industry consultant firm Wohlers Assoc. publishes a yearly report detailing the status of the industry. In addition, the Society of Manufacturing Engineers’ Rapid Prototyping Assn. published a book earlier this year entitled User’s Guide to Rapid Prototyping by Todd Grimm, which serves as a technical reference.
There are also research-oriented and association websites that span a broader range of technical updates. IMM reviewed several of the latter, which provide information ranging from primers and process details to industry trends and instant quotes on RP models:
Penn State Learning Factory: Applications, techniques, and a step-by-step tutorial for building rapid prototypes. www.me.psu.edu/lamancusa/rapidpro/index.htm
Castle Island’s Worldwide Guide to RP: Extensive data on both commercial systems and industry/government research, info sources, and FAQs; includes an online marketplace. home.att.net/~castleisland
Rapid Prototyping Forum: Discussion forums, industry news, and a buy/sell/trade forum for machines, materials, and software along with service bureau provider information. www.rapidprototyping.net
Engineering Fundamentals: Detailed information about each RP technology, along with a section for instant quotes. www.efunda.com/processes/rapid_prototyping/intro.cfm
Wohlers Assoc.: Articles, technical papers, reports, and documents on rapid prototyping, rapid tooling, rapid manufacturing, 3-D printing, CAD/CAM, 3-D digitizing, and reverse engineering. www.wohlersassociates.com
CADCAMNet: Includes the monthly newsletter, Rapid Prototyping Report, with reviews, summaries of new developments, and independent investigation, i.e., Consumer Reports for RP. www.cadcamnet.com
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