How small is micro molding? Less than a milligram!

* A new all-electric molding system for the very tiniest parts may give a new definition to "micro molding" when it's introduced this fall by Germany's Battenfeld GmbH. The MicroSystem 50/2 SE is designed to mold parts weighing less than 20 milligrams (0.020 g) - some even less than 1 milligram. Meeting that challenge required development of a proprietary, three-stage injection unit, accompanied by a tiebarless horizontal clamp and a variety of custom downstream equipment, all within a compact clean-room enclosure.

Three possible applications for the system will be demonstrated at the upcoming K'98 Show in Dusseldorf. One is a 0.8-mg acetal watch gear. Another is a 2-mg polycarbonate housing for a hearing-aid implant. And the third is a 16-mg, glass-reinforced LCP automotive microswitch actuator pin.

Battenfeld's previous micro-injection unit, introduced in 1995, was suitable for parts of about 3 g. According to Wolfgang Meyer, president of Battenfeld of America in West Warwick, R.I., the MicroSystem overcomes limitations of previous micro-parts molding technology. These include inadequate pressure control and long cooling times that result from the weight discrepancies between the tiny parts and relatively massive sprues and runners, which can constitute more than 90% of the shot. Meyer says previous micro-molding efforts also lacked the quality-control and parts-handling systems suitable for the smallest parts.

New type of injector

The new three-stage injection unit consists of a 14:1 plasticating screw slanted on a 45 [degrees] angle; a vertical, pneumatically powered dosing unit; and a horizontal injection plunger. The nozzle reaches inside the mold right up to the parting line, eliminating the sprue altogether. Plungers of 3-5 mm diam. can provide shot sizes of 0.45 to 1.25 g and injection pressures as great as 61,500 psi. Injection rates are 9.2 to 25.5 cc/sec, roughly twice the rate of a standard precision-molding press, Meyer says.

The servo-driven, 5.5-ton clamp (with 392 x 170 mm platens) reportedly achieves position resolution around 40 times finer than that of a standard machine. Even without tiebars, clamp parallelism stays within 0.05 mm, Battenfeld claims.

A servo-driven rotary table allows molding to overlap with cooling and parts removal so that cycle times can be less than 5 sec. Battenfeld says that's more than 50% shorter than cycles of previous micro-molders.

Clean-room cell

A Class 100 clean-room enclosure houses the press, a new two-axis robot, and other handling, orienting, and packaging systems customized for the application. An optical quality-control system uses CCD cameras to verify part dimensions before packaging.

After field testing in Europe, the Microsystem will become available here early next year.