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moldmakingtechnology.com 21 FOR MORE INFORMATION Cavaform International / 727-384-23676 / cavaform.com machine for cavities that, on first glance, don't lend themselves to the process. Consider a pen cavity with an undercut cre- ated by a logo on one portion of the ID. Although a split cavity design can release such an undercut during molding, rotary swaging cavities in the first place requires a consistent cross section. To get around this limitation, the shop might burn the logo into one half of a rotary-swaged cavity that's been cut in two lengthwise, then marry it to another half that has no logo. Cutting a cavity in two removes steel, he explains, so ensuring a perfect fit requires splitting two swaged cavities off-center so that one (usable) half of each is slightly oversized, and scrapping the two smaller halves. Nonetheless, exact size, consistency from cavity to cavity, less polishing, and less risk of damaging sharp edges make this solution more cost-effective than producing them conventionally. The shop has answers to other restrictions as well. All cavi- ties require some degree of draft to ensure they can be pulled back away from the mandrel when the process is complete (0.001 inch of draft per inch of stock is more than adequate, but the company has also worked with less, he adds). Material flowing from the larger, back end of the mandrel toward the smaller front end doesn't wrap perfectly over portions of the mandrel that step down at an angle of more than about 15 degrees, Hastick says. Instead, it tends to leave a rounded void. As a result, the Cavaform machine typically isn't a good fit when diameter changes create sharp corners and angles, at least not in its typical configuration. However, the rotary swaging machine isn't always in its typi- cal configuration, in which the mandrel and blank are held in the back-pressure rod for what Hastick calls a back-pressure hit. The shop has also developed another option: the pusher hit, which involves mounting mandrel and blank in the pusher rod instead. Although the direction of material flow is the same in either case (opposite the feed), reversing the setup ensures mate- rial forms toward the larger-diameter back end of the mandrel— and thus, directly into any sharp corner and angle geometries. Other limits aren't as restrictive as they might initially appear. For instance, blind cavities are usually not an option unless the blind end is rounded, Hastick says (test tubes are a common example). However, cavities without rounded ends can employ gate gaps and telescoping shutoffs instead. In addition to enabling the shop and its customer to reap the full benefits of Cavaforming, these components are easy to replace when worn. Driving Higher Standards Massie emphasizes that the impact of this niche process on the rest of the shop extends beyond improved workflow. It's shaped the company's identity as well, particularly its approach to quality control. When the shop got its start in the late '70s, ±0.0002-inch tolerances and 4-micron surface finishes far exceeded even the most stringent industry expectations, he says. The case was the same with the capability to consistently achieve process capability index (Cpk) values greater than 2, and some- times as great as 4 (most customers today expect only about 1.33, he says). Before long, however, customers naturally came to expect these levels of precision regardless of whether the job required it or was even suitable for Cavaforming. "Just by default, the quality of cold-formed cavities set a high benchmark for us over the years and really shaped our mentality," Massie says. For example, full volumetric cavity inspections have been "part of the culture" at this shop for decades, Massie says. Compared to measuring only "end to end"—that is, ensuring correct dimensions on both parting lines—Cavaform person- nel drop various-sized ball bearings into both Cavaformed and EDM'ed cavities, then polish as necessary to ensure consistency throughout the entire length. The shop also inspects first-arti- cle cavities and other components to serve as validated masters. This isn't a role played only by the quality control department, but also by every department on the floor, which checks part dimensions at dedicated stations after every stage of manufac- turing. Each inspection is conducted twice, by two different personnel, no matter how elementary the measurement. This "buddy" system helps avoid mistakes. More importantly, it helps eliminate distinctions between EDM-burned cavities and those formed via rotary swaging, and in Massie's view, that's the true measure of Cavaform's success. "We can't treat work any differently based on how it's processed," he says. "Everything is held to the same standards." As the spindle turns, the hammers contact surrounding rollers, driving the hardened dies simultaneously and repeatedly into the advancing tubestock to form the ID around the mandrel. Tube and mandrel travel together into the machine between the pusher rod, which provides the forward motion, and the opposing back-pressure rod, which prevents feeding too fast into the die set. Diagram courtesy of Cavaform International.