License-Free Magnesium Molding

NisseiPlastic Industrial Co. Ltd., the largest injection molding machinemanufacturer in Japan, has developed a press for molding magnesiumalloys that it will sell with neither license fees nor royalties.Tsukasa Yoda, president, says, "Nissei believes its machinedoes not infringe on the patented Thixomat technique. From thebeginning of the design, we made sure we did not break any ofthe Thixomat concepts."

Nissei's machine is a 140-metric-ton (1372-kN) direct-hydraulic.It is based on the company's existing UH Series machine platform,specially designed for the ultrahigh-speed filling of extremelythin-wall parts. The magnesium molding version, designated FMg3000, will sell for ¥43 million ($396,000)-about twice thecost of a similarly sized UH Series machine for plastics, but,again, license- and royalty-free.

Unlike Thixomat's semisolid, thixotropic injection moldingprocess, Nissei's machine is designed for the argon-blanketedinjection of completely molten AZ-91-D magnesium alloy, as previouslydiscussed (seeJune 1999 IMMC). Nissei has yet to test other grades and othermetals.

Magnesium chips are automatically transferred into an on-demandhopper with level sensors, and then to a preheating station equippedwith oxygen sensors. An electrically driven fixed-screw augerin the preheating station precisely delivers preheated magnesiuminto the melting section of the main barrel, which is configuredat an angle to the machine base, taking advantage of gravity toensure full-shot feeding of the melting section.

The injection unit is made from special alloys capable of resisting700C temperatures. It is also equipped with ceramic heaterbandsthroughout. Several shots' worth of the preheated chips are fullymelted at 650C.

Back to the Future

Injection is via a closed loop controlled plunger, rather thana reciprocating screw. Following precise metering by a specialaction of the plunger, the melt is injected into the mold at pressuresup to 1000 kg/sq cm and speeds up to 2000 mm/sec. Maximum injectioncapacity of the 140-metric-tonner is 76 cu cm. The plunger isaccumulator assisted and hydraulically driven. Since a reciprocatingscrew is not used, there is no problem with material backflowover a check ring, which can clog screw flights and cause downtime.

The FMg 3000's hydraulic pump motor is driven by a servomotor,reducing energy consumption and noise. Mold temperature is controlledat 250C. The sensor and cylinder sections of the direct-hydraulicclamping unit have a special cooling circuit to maintain durabilityand reliability.

To accommodate fast-cooling magnesium, Nissei uses its UH Seriescontrol technology. It is designed to ensure quick response forfast injection speed acceleration, and good braking characteristicsfor controlling changing speeds during injection and hold-pressureswitchover. The technology's braking characteristics complementthe system's back-to-the-future plunger to help stabilize shotvolume repeatability for near flash-free molding, thereby providingsubstantially reduced part costs.

Nissei uses its 32-bit model NC9300T touch-screen machine controlleron the FMg 3000. It is designed to slide into the machine basewhen not in use and is equipped with a large, thin, 10.4-inchTFT color LCD screen that is easy to read. The company alreadybuilds its own robots for its machines, and plans to build a lubricant-dispensingmodel.

Commercialization Plans

Nissei began receiving orders for its FMg 3000 in June. Whilein the final stages of long-range cycling tests, Nissei is nowsearching for adequate sources of the special alloys required.It already has enough to make 10 machines, but it has announcedto the Japanese press that its goal is a 200 machine/year capacity.Nissei's Yoda says a 60 to 70 machine/year capacity may be morerealistic near-term numbers.

He adds that Nissei's magnesium molding machines may go onsale in Japan early next year, to be followed shortly thereafterby global sales to strategically selected areas throughout Nissei'sexisting sales and service network. Plans presently call for asequential release of a series of FMg machines with clamping forcesranging from 40 metric tons (400 kN) to 360 metric tons (3500kN), with injection capacities of 20 to 500 cu cm. A 220-metric-tonmodel may be next, according to Yoda.

He presently has no plans to exhibit the FMg machine at anyof the upcoming trade fairs around the world, and says "interestedparties can come to Nagano to see it."

When asked if he was concerned about his competitors copyingthe machine's design, President Yoda smiled and shook his headno. Nissei has enjoyed its best year of sales in its 50-plus years,shipping 4100 molding machines by its fiscal year's end. It introducedthe world's first commercial all-electric molding machine in 1983and many others have since followed suit, yet the company is stillon top.