Small or not, this fan has to be balanced

When the marketing department of IMC Magnetics Corp. (Tempe, AZ), a Mineba Group Company, identified a niche for a smaller, high-performance fan that offered better air flow for business equipment and telecommunications, the easy part was done.

The real challenge was building a fan with a blade configuration that would operate quietly and efficiently while still getting enough air flow in a 1-inch-wide frame. IMC enlisted the help of Mastercraft Companies (Phoenix).

Mastercraft Companies is Mastercraft Mold, a designer and builder of precision injection molds, and Polycraft Industries, a custom molder with 21 presses ranging from 40 to 400 tons clamping force. IMC specializes in manufacturing 6-inch d-c brushless fans for the telecommunications and office automation products markets.

IMC adapted technology developed for the aerospace industry into the new fan product. As a late entrant into the fan market, IMC knew it had to come up with a superior product. The 1-inch fan, called the Sunflower, proved to be the answer. It is the only 1-inch-thick, 172-mm fan on the market that delivers 240 cu ft/min.

Design ChallengesThe in-house engineering staff originally believed it couldn't be done, saying they needed 11/8-inches to achieve an optimum fit. But, 1 inch was the absolute acceptable limit.

"Our team of engineers met the challenge," says Joe Smith, general manager for IMC, of the project's success. "They did an excellent job of overcoming design challenges to produce a fan that is technically superior to others on the market."

The fan's superior performance is the result of a new, 13-blade impeller design, on which a patent is pending. The first fans have been shipped and are "having terrific acceptance in the market," says Smith. However, this blade configuration also presented some challenges. For the fan blade alone, IMC went through three different prototype iterations using stereolithography (SLA) to assess the design and evaluate the fan's function. "It's the only way we'll prototype," says Smith.

Using Pro/E files, an SLA prototype can be made in three days. That's crucial with the extremely narrow market window for new products. From concept to actual delivery of a working sample to IMC took 90 days. Smith admits IMC put pressure on Mastercraft Mold to build a fan blade mold with complex geometry, close tolerances, and little spacing between the blades, making for tight machining conditions.

IMC provided Mastercraft Mold with an SLA part for reference and a Pro/E file with a solid model. Mastercraft took the solid model and put it into TekSoft to develop the program for machining the electrodes.

Mastercraft worked concurrently with IMC's engineering staff to update the design as changes were made. One issue was the distance between the blades. From the trailing edge on one to the leading edge of the next, the space was too narrow to allow for a proper shut-off angle. Because additional spacing was not possible, a creative way to solve this problem had to be developed.

"We took our cavity and made electrodes that would burn alternate blades," explains Bob Larson, engineering manager for Mastercraft. "We then made other electrodes-which were key to machining the 3-D features of the blade-and went back and burned the remaining blades." Mastercraft machined the electrodes on a Fadal CNC 3-axis machining center. Moldmakers then took those electrodes and burned the A and B mold halves in the company's Charmilles Roboform 20 EDM.

The ResultThe mold is a three-plate mold that uses drops to ensure even filling of the feathered-edge blades. Larson points out complex contours such as an airfoil of a fan blade using an old-fashioned 2-D system version required a moldmaker to work from coordinates, a much slower method. Using a Pro/E solid model saved time and permitted engineering changes to be completed quickly and more accurately.

The profile and thickness of the individual blades are two critical considerations to the overall function to ensure optimum balance of the fan and to reduce noise when the fan is rotating. The fan also requires a molded-in metal hub. Mastercraft's custom molding division, Polycraft Industries, took on the challenge of insert molding the parts, which are molded from 33 percent glass-filled, flame retardant nylon from RTP Corp. Steve Wiedenbacher, molding operations manager, says proper gating was critical to successful molding.

The complex part geometry of the fan blades necessitates a very consistent molding cycle. Location of the insert during molding is also critical to maintaining the concentricity of the area surrounding the hub for optimum performance. Polycraft is looking at automating the insert-loading phase of the molding cycle to ensure greater accuracy of placement and improved cycle consistency.

The fan mold runs in a Kawaguchi injection molding machine with 180 tons of clamp force equipped with closed loop process controls to monitor critical process parameters and ensure shot-to-shot consistency.