For engineers interested in functional prototypes of plastic parts, the models produced on 3D printing machines may not have much to offer at first glance. These rapid prototyping machines create models by depositing successive layers of a build material through computer-controlled nozzles, much like the ink jets used in paper printers. Depending on the machine, the build material can range from special plasters to acrylic polymers, but none of them really mimic the mechanical properties of common engineering thermoplastics. Nor do they approximate the part attributes imparted by the molding process itself-like molded-in stresses. They don't even offer the production finishes typical of a molded plastic part, at least not without lots of handwork and a coat of paint. So why bother with them?

With product development cycles tightening up, the main reason comes down to speed. Running in an office environment as a CAD peripheral, a 3D printer can turn out physical representations of design concepts in a flash. "We could do an iteration of a phone every hour and a half if we wanted to," says Michael Jahnke, global prototyping manager for Motorola Inc.'s Personal Communications Sector and a user of Z Corporation's 3D printing system. Not only is this ink-jet-based machine fast, its plaster feedstock and low overhead costs allow it to make models on the cheap. Jahnke notes the models typically cost around $5.00 in material and finishing costs. "It's not a big deal to use them for five minutes and throw them away," he says.

These fast, inexpensive models come in handy as Motorola develops new mobile phones and communication devices. According to Jahnke, the relatively fragile models from a 3D printer may not pass muster for heavy-duty mechanical testing, but they do support design decisions related to format, form, and ergonomics. On any given project, Jahnke says, Motorola prints a multitude of these 3D models early in the design process.

Head Start

Some of these early models help disqualify poorer design concepts. Others models help the industrial design team, which includes engineers for early technical input, refine the successful designs. "We sand and mark up models all the time," he says, explaining that these modified physical models sometimes drive changes to the solid CAD geometry that ultimately represents the design as it reaches the tooling stage.

This ability to quickly zero in on and improve winning design concepts shouldn't be discounted in a quick moving business like consumer electronics, and may alone justify having a 3D printer on hand. But Motorola has also pushed its 3D printing further into the realm of mechanical engineering and design for assembly-what Jahnke calls "early mechanical proof of concepts." And in this use, the company stands alone. "I don't know of anyone else using our machine the way they do," says Marina Hatsopoulos, CEO of Z Corporation.

Pushing the Envelope

The earlier engineers weed out designs with the potential for assembly or manufacturing difficulties, the better from a cost standpoint. And there are plenty of computer-driven tools to help with the whacking. Most 3D CAD systems, including the Pro/ENGINEER software that Motorola uses, can highlight interferences between components and help identify stack-up problems. Sometimes, though, computer screens fall short. "Designs that look fine on screen often don't work in the real world," Jahnke says. He notes that computer models can obscure fine details that are readily apparent in three dimensions, and they don't help with parts that must "feel" a certain way when they move-like a battery latch. With the help of 3D printing, Motorola has taken a clever approach to identifying these situations early in its design process.

In addition to working on the external surfaces of a proposed design, engineers attached to the industrial design now also create representations of the internal component package. Jahnke and his team then model these component packages as a single piece that represents the phone's battery, circuit board, display, and other internal parts. "We don't bother to model every little capacitor separately," he says.

These packages are then dropped into simple "wall-thickness" housing models of proposed designs, giving engineers an idea of how well everything fits together. "We use these models very early in the design process to check the component stack-up," Jahnke says. And he adds that this process flags many subtle problems long before the initial industrial design team hands off the product to "Motorola's larger engineering collective" for the nitty-gritty mechanical and electrical design work.

Slice, Dice, Even Test

In a related effort, the company also produces cross sectional models of promising housing and component configurations. They do so by splitting a solid CAD model and letting it drive the 3D printer. These models help flag spacing difficulties and give the engineers a tool for adding or removing volume as necessary-or as Jahnke puts it, "looking for extra cc's."

Motorola may even take some of these 3D printed models even further into the realm of real engineering. He points out that Z Corp. has come out with infiltrants that make the models stronger (see chart), perhaps enabling some simple mechanical tests in the future. Epoxy-filled models, for example, have already allowed Motorola to tap screw bosses in its phone models. Jahnke also believes that Z Corp.'s more recent ability to produce color models could make 3D printing a more valuable engineering tool (see sidebar on page 74).

Cost Cutter

Motorola's use of 3D printing has started to pay off for a variety of new design projects. Jahnke reports that 3D printing cuts development time significantly on high-end phone programs-mostly by slashing the number of sketch pad, rendering software, and CAD iterations. And saved time means saved money. "We've seen substantial savings on development costs," he says, though he declines to say exactly how much.

Nowhere are these benefits more noticeable than on last year's V70 phone, a model whose faceplate rotates open. According to Jahnke, the 3D printer got a workout on this project, which started with a desire to create an "iconic, groundbreaking product." Before the design team had even committed to the phone's unique form, it used 3D printing models to evaluate between 15 and 20 initial concepts-including side open and various flip styles. "The rotating form quickly rose to the top, though some of the other ideas were good, too, and could become future products," he says.

Then, once the design team had settled on the rotating form, it began to model the interior component package and further refine the housing. This work helped speed the V70's development time to about one-third that of other high-end phone projects, Jahnke says. "Not all of that was because of 3D printing. But some of it was," he notes.

Limits

For all its value, though, 3D printing has certainly not replaced other prototyping methods or prototypes molded in soft tooling. As designs go into production, engineering teams responsible for testing have standards that a 3D printed model just won't meet. Even the industrial design team still has to make solid visual models by machining blocks of plastic. "At some point we want a model in production materials with production colors and production finishes," Jahnke says.

What's more, 3D printing can't produce all the detail that Motorola's designers want to see. For example, Jahnke says, the Z Corp. models don't adequately represent keypad height, power and earphone jacks, radii under 0.5 mm, and other fine details. "Some details simply don't translate to Z Corp models," he says.

But then again, those details don't have to translate for the machine to be of value. "People have to be taught to read these models," Jahnke says. "They're not supposed to be a finished part. They're more like a rough draft."

And starting with a rough draft has worked for Motorola's designers and engineers. Bookings for the company's Z Corp. machine doubled in 2002, Jahnke reports. And though 3D printing remains optional, Jahnke says "every new phone program now uses it in early stages of development."

Senior Editor Joseph Ogando can be reached at[email protected].