An MD&DI May 1997 Column
A new way to make 3-D objects can help designers communicate better early in the product design and development cycle.
Engineers and designers conceptualize ideas in three dimensions, develop designs in three dimensions on computer-aided design (CAD) systems, but then print out a two-dimensional paper representation to communicate the design to others. In most medical device companies, the use of drawings is still the primary means of communicating early design concepts to other members of the product development team--marketing, engineering, and manufacturing. Most designers have experienced the communication failures that result from someone trying to visualize a 3-D design from a 2-D drawing, leaving much of the design intent to interpretation. Because of this, many design decisions are made and significant dollars are committed early in the product development process based on limited product and performance knowledge.
Because of the cost of rapid prototyping, device manufacturers historically have not built 3-D prototypes until the verification and test phase. Often, it is at this point that misconceptions and misinterpretations in the product development cycle come to light. For example, a designer of a socket for a prosthetic leg might use a CAD program to prepare the design, but print a 2-D drawing to present the concept to the design team. The team makes their recommendations based on their observations of these drawings. Many changes made to the original design result from misinterpretations of the drawings. Such a process is useful for a range of medical devices, including hip replacements, prostheses, catheters, and even diagnostic equipment.
The 3-D printer deposits plastic droplets in layers to produce a model of the device. Photo courtesy of BPM Technology.
To eliminate possible costly errors, companies are exploring methods for printing 3-D models instead of 2-D drawings. One technology that allows creation of 3-D concept models is known as 3-D object printing. This ink-jet technology, which jets ballistic particles, is more closely related to CAD printing than to other low-cost rapid prototyping systems. It uses a five-axis piezoelectric ink-jet head to deposit thermoplastic at up to 12,000 droplets per second. Each droplet begins to solidify on its way to the previous layer so that it adheres quickly, replicating the 3-D CAD image created by the designer (see photo above).
Designed to be a computer peripheral, 3-D object printers are similar to standard laser printers. No special training is necessary to use them. Users can scale or reorient the image, if needed. The printer produces a scaled object that fits within 10 x 8 x 6 in. BPM Technology (Greenville, SC), which has developed a system, says the printer has an accuracy of 0.015 in. and a surface finish of 250 µin. rms. Many devices cannot be printed actual size. Devices that are larger than the build envelope can be scaled. Objects can be constructed as hatch-fill or as a shell. Shell versions are usually produced for visual design verification only because they are not as durable as solid versions. Such 3-D object printing may represent a natural evolution in communication of design intent because it shifts design communication to the earliest stages of the concept.
With 3-D object printers, designers can create 3-D objects for about the same cost as a 2-D CAD color print or plot. Because 3-D object printing is less expensive than rapid prototyping, engineers and designers can create unlimited iterations of designs for just a few dollars per object. Producing a 3-D object instead of 2-D drawings provides definitive communication of design intent early in the design cycle.
However, 3-D printing is designed to produce a representation for visual verification and should not be used as a substitute for rapid prototyping. Once a company is ready to begin product testing, standard prototyping methods should be used to construct a physical model. As a result, 3-D object printing can provide a viable alternative to building prototypes late in the development process.