Who needs tooling anyway?

A guide to going tool-less

Tool-Less production methods won't work for every job. Functional requirements—most notably impact resistance—can push enclosures into traditional processes. "I sometimes have to steer people into injection molding or structural foam," says Jim Fowler, president of Tool-less Technologies.

Cost and production volumes also define the suitability for tool-less production—which seemingly defies conventional wisdom about economies of scale by offering the biggest savings at low volumes. According to Fowler, tool-less production potentially shaves 50% or more from the overall cost of injection molded parts, 30% from thermoformed or structural foam costs, and 15% from RIM costs. And what are the volumes needed to reap these cost advantages? For smaller enclosures, appropriate volumes range from 50 to 500 per month. For larger enclosures, such as Eko's housings, the volumes should fall between 25 and 100 per month. "At high volumes, injection molding start to make more sense," Fowler says. Intermediate volumes can favor thermoforming, structural foam, or RIM.

Finally, successful tool-less production means designing for the process right out of the box—as soon as electronics have been chosen. "We can't just take a design for injection molding or thermoforming and make it work on our equipment," Fowler says, "If the design has been completed for another process, we usually have to re-design it."

Here's a brief guide to designing those Tool-Less parts:

• Material choices. The standard materials line-up includes ABS, PC/ABS, PC, and acrylic, but Fowler says the tool-less process can work with any thermoplastic that comes in sheet form and supports solvent bonding. Typical sheet thickness range from 2 to 10 mm, with bends possible on sheets under 6 mm.

• Dimensional capabilities. The CNC equipment can handle bend lengths up to 1,000 mm and machine components up to 1,050 mm. Larger structures can be assembled using joints between sheets—though this method leaves a visible seam. The largest enclosures to date measure 32×16×8 inches and 24×20×30 inches, Fowler reports.

• Tolerances. Machining tolerances are ±0.008 inches on dimensions up to ten inches, and±0.016 inches for dimensions from 10 to 40 inches. Angular tolerances are ±0.5 degrees for fixed bends and ±2 degrees for freestanding bends. Thickness tolerances vary with the sheet material but are typically around ±0.15 mm. Bending tolerances are ±0.33 mm single, or L-shaped, bend and ±0.5 mm for a double, or U-shaped, bend.

• Geometry considerations. The Tool-less process will not produce compound bends, which rules out spherical structures but lets the process tackle just about any enclosure shapes. The standard bend radius for the outer corner equals one material thickness. All Tool-Less housings have zero draft.

• Features. According to Fowler, the process handles all standard enclosure features—including vents, fans, snap-fit doors, latches, threaded inserts, stand-offs for circuit board, light pipes, clear windows, and membrane keypads. It also supports secondary features like silkscreen decorations. Fowler notes that the company locates important features, such as bosses, in pockets that have been machined into the sheet. "Bosses and other features snap in like Lego, and we also use solvent to bond them to the housing" he explains.

• Functional capabilities. Tool-less doesn't perform any destructive testing, so Fowler doesn't have data on impact resistance. Yet he notes that the process has created two-lb enclosures that can survive a four-foot drop onto vinyl-covered concrete without catastrophic failure. "Our enclosures aren't as durable as the most robust injection molded housings," he acknowledges, "But we get close enough for most applications." As for environmental resistance, the enclosures meet NEMA 4 requirements. Tool-less also offers two RFI/EMI shielding options: It can spray the sheet stock with conductive paint prior to any machining. Or for a higher level of shielding, it can treat the finished housings with a conductive paint after assembly. When made from flame retardant sheet materials such as 0.125-inch-thick PVC/acrylic blends, Tool-less enclosures can achieve a UL 94 V-0 rating, says Fowler.

• Aesthetics. In addition to the thermal bending for sharp transitions, the process allows single-axis cold bends for curved, sculptural surfaces. Color and texture choices correspond to the wide range found on commercially available sheet stock. And Fowler notes that Tool-less produces multi-colored enclosures by simply joining different-colored sheets.

• Applications. Nearly all of Tool-less Technologies' applications have been for enclosures. "We specialize in electronics packaging," says Fowler. Still, he does report a handful of other applications, including an internal component for a medical imaging system, a bezel for an ATM machine, and a package-drop box for UPS. "We specialize in electronics packaging," says Fowler, "But we can make just about any part whose geometry lends itself to machining and bending."