InFocus Corp. is an Oregon company that makes digital data and video projectors and, under orders from top management, is learning how to operate in an atmosphere of cross-functional cooperation. This change in corporate culture is recent, but it already has resulted in a new projector made with a trio of cast-magnesium parts that were prototyped in Colorado and now are being purchased in production quantities from a supplier in Taiwan.

These next-generation cast magnesium parts are thinner yet stiffer, weigh less and can be machined to tighter tolerances than the castings they replaced. Two are housings for a new LP 130 business projector, while the third is a critical component for the interior lamp module that helps provide high-resolution XGA (extended graphics array) video display of 1024x768 pixels. These cast parts are being sourced by Rock Kent, InFocus purchasing professional, from Waffer Technology Corp. of Taiwan, the largest producer of net-shape magnesium parts made by the thixotropic injection molding, or thixomolding, process (see "VA guide to molding", PUR: Oct. 4, '01; p.27)

Kent went to Waffer because the company's two main customer groups are projector manufacturers and makers of notebook computers, and has produced parts for InFocus in the past. "They also understand the importance that cast metal components play within our products," Kent says.

He says the InFocus purchasing/design team decided to use magnesium over plastic because of better thermal conductivity, EMI/electrical grounding and rigidity in a high-temperature operating environment. "Overall, we felt that magnesium castings would provide the lowest total cost to meet the product's working requirements," he adds.

The new magnesium castings are considered electronic enclosure parts, which typically are produced by plastic injection molding of polycrystalline silicon (polysilicon) resin. However, InFocus designers had experimented with traditional hot-chamber die casting technology to make the magnesium alloy internal parts for an older and heavier (4.8 lb) mobile projector model. When it came time to lighten the projector to a 3-lb model, Brian Heintz, the principal product design engineer, decided to try thixomolding of a magnesium alloy that becomes semi-solid when it is heated near the melting point.

To help overcome what Heintz calls "numerous design challenges," the InFocus design team at Wilsonville, Ore., headquarters worked with Prototype Casting, Inc., Denver, Colo., to make castings in a rubber plaster molding process (similar to investment casting) using AZ91D-grade magnesium, an alloy of magnesium containing 9% aluminum and 1% zinc. "The thixotropic semi-solid behavior allows this alloy to be injection molded into a part with walls as thin as 0.0003-inch," says Heintz, although the typical wall section on these parts is 0.05-inch (1.2 millimeter).

Thin-wall casting generates cost savings mostly by reducing the weight of the cast parts. The projector housings, which measure 8.5 x 6.25-inch and weigh just 0.22 lb (100 grams), while the 4.5 x 3-inch interior interface casting weighs only 0.05 lb (23 grams). "Weight is of no small consequence in the new LP 130 notebook-sized data/video projector," says a corporate spokesperson. "After all, the unique selling proposition of InFocus' is that at only 3 lb, it's a 'no-compromise' portable projector offering 1100 lumens of brightness."

The American Foundry Society recently honored the InFocus cast-magnesium parts as the "Casting of the Year" for 2002 mostly because new cast design offers improved durability and rigidity, high heat tolerance and electromagnetic (EM) shielding benefits. EMI plating requirements were also eliminated. The society's judges also noted that, when compared to plastics, the cast design provides a significant weight reduction and stiffness improvement. The equivalent plastic design would have required 0.08-inch (2-millimeter) wall sections. And, by converting to magnesium casting from plastics, a dimensional improvement was achieved, as critical areas are post-machined to tighter (±0.002-inch) tolerances.

The cast-magnesium components "clearly illustrate the flexibility and versatility of cast metals and how the process can benefit virtually any industry," says Brett Peak sales manager at Prototype Casting. "While state-of-the-art compact electronic devices typically aren't considered as casting candidates, new advances in casting technology and rapid prototyping offer engineers significant design freedom and time-to-market advantages."

John Harker, chief executive of the $390 million (2001 sales) projector maker, says development of the part is a radically transformation in internal operations for the firm "whose departments used to operate in silence." He explains that: "Engineers once thought manufacturing guys were stiffs; manufacturing guys knew the engineers were never liked; nobody liked marketing; and the cops from finance were never liked, let alone the auditors; purchasing wasn't even on the radar screen." But, after a three-day offsite session with an outside quality facilitator, "managers decided we had to work better cross-functionally, and if we were ever going to succeed cross-functionally, we had to change our behavior and internal culture."

That cultural change filtered down to the InFocus designers' decision to choose Prototype Casting because of the Denver firm's ability to cast and machine thin wall and tight tolerance magnesium parts. "Up front dialogue between the engineers at InFocus and the molders at Prototype Casting was paramount to the success of this development program," says Heintz. "Tradeoffs and shortcuts were discussed to enable optimal molding and finishing so that the fresh casting process is more cost effective than machining prototypes from stock," notes tooling engineer Greg Sample Sr.

He adds that the two firms' close relationship allowed design modifications that reduced potential difficulties—a key concern on such thin-wall, highly angled magnesium components—well before manufacturing commenced. Sample says the engineers learned to cooperate with the prototype supplier to minimize design and fabrication risk of the complex part, adding: "I can't imagine the mess we would have been in, if we bypassed this phase of the program."

Heintz suggests that's why the prototype cast parts behaved in test production very similarly to the way they have when the process switched to production casting at Waffer Technology in Taiwan.