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Tiebar-free hybrid micromolding machine

The Sesame .020 is a new tabletop, U.S.-built micromolding machine. This small, tiebar-free, electro-pneumatic hybrid press was introduced at the most recent Medical Device & Manufacturing show (Nov. 2?5 1998, St. Paul, MN). It can mold 20 sesame-seed-sized parts, each measuring 2 cu mm and weighing .0022g, from a single plastic pellet. At MD&M, the machine?s originator molded such parts with its company logo in .3-mm-high molded-in letters legible only under a microscope.

In development for 21/2 years, the Sesame?s design is based on two key concepts: extremely fast, controlled injection and short material residence time. The injection cylinder is driven by an all-electric Trilogy brushless linear servomotor. The Trilogy provides excellent accuracy, repeatability, acceleration, stiffness, and life, and it is suitable for operation in cleanrooms. The machine is lubrication-free.

Total injection time can be as short as .020 second (1250 mm/second with a 25-mm stroke) with two profile speeds and two holding pressures. This allows filling of extremely thin wall sections, approaching .025 mm thick, at injection pressures up to 50,000 psi. Position control feedback is through a linear pot with a 50-mm stroke. Patents are pending on the machine?s design concepts.

Residence-time degradation problems can occur even when screws are 12 mm in diameter. That is because, with micromolding shot sizes, some 1000 or so shots can be held in the barrel for several hours. To solve this problem, the Sesame uses a pneumatically driven vertical plunger for plasticizing and the linear servomotor-driven needle plunger for injection. A high-pressure valve is positioned between them.

Material loading is automated on the Sesame with a special spiral feeder. It is designed to feed down to one pellet each reload cycle, if necessary. When combined with the reloading controls for the plasticizing plunger, residence time can be precisely matched to the part and the material it is molded in.

The tiebarless clamping unit is driven by a pneumatic cylinder with force and speed control. Standard clamp force is 600 lb; 4000-lb clamping is optional. Ejection is pneumatic. Clamp motion and injection unit alignment are achieved through precision THK linear bearings running the full length of the machine. Vertical clamping is an option.

The Sesame is built with stainless steel and anodized aluminum for use in cleanrooms and is controlled with an LED touchscreen capable of setup storage and temperature control through Eurotherm PIDs.

In addition to the Sesame, its developer, Murray Inc., offers process development and mold construction services. Standard 90-by-95-mm mold bases are from D-M-E.

The Sesame?s footprint is 20 by 42 inches, and it is 16 inches high. Utilities include 15A, 115-volt a-c power, and 90-psi air. Targeted applications include inline molding of tips or luer fittings onto catheters, in-line plastic and metal assembly, electronic components, and other small precision parts. The Sesame costs $30,000 to $40,000, depending on options.?Carl Kirkland

Murray Inc.
Buffalo Grove, IL
Phone: (847) 419-0090
Fax: (847) 419-9861
http://www.murrayeng.com

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