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A new form of long-fiber thermoplastic (LFT) injection molding can rapidly produce large, complex parts with intricate design features at low shear and clamping pressures while also maintaining post-mold fiber lengths typically only seen in compression molding. Those claims from LOMOLD Group (Cape Town, South Africa), which utilized the process to create an LFT pallet injection molded in 17% fiberglass-reinforced polypropylene (PP) that won in the Transportation category of the JEC's (Paris) annual Innovation Awards Program.

IMM Staff

March 22, 2010

2 Min Read
IM tech takes on compression molding, promises fiber-length retention

LOMOLD and its partners, Chuan Lih Fa Machinery Works Co. Ltd. (Tainan, Taiwan), KHS Consulting cc (Johannesburg, South Africa), and Addcomp Holland BV (Nijverdal, Netherlands) say the pallet provides proof-of-concept for the new form of LFT injection molding.

Depending on part, LOMOLD says its process allows fiber lengths of 10-50 mm (0.4-2.0 inches) compared to 3.0-4.0 mm (0.1-0.2 inches) for conventional LFT injection molding. The company reports that the main difference between conventional injection molding and its process is the modified melt-delivery system, which uses a large piston as a plunger to force melt into the tool through a single 100-mm (3.94-inch) gate. The fill portion of the molding cycle is 60% faster than straight injection molding of a comparably sized part, coming in at 7 seconds for a 16-kg (35-lb) pallet, and the melt is delivered at far lower shear, filling at less than one-twentieth the melt velocity of injection molding. This helps preserve fiber length and reduce shear heating and post-mold warpage, while nearly cutting clamp tonnage required in half.

The plunger/piston face closes off the mold's bounding wall during the end of stroke, sealing the tool, and during the pack-and-hold portion of the cycle, a second piston meters out the next shot so there is no lag between finished part ejection during mold open and recharging for the next shot once the mold closes again.

LOMOLD says its process offers the ability to maintain fiber lengths in intricate, three-dimensional designs, allowing components with high mechanical properties at thinner walls and lower mass. Parts with longer reinforcing fibers can provide better low-temperature impact strength, higher mechanical properties at elevated temperatures, better dimensional stability at any wall thickness, and enhanced creep and fatigue resistance.

These benefits come from the combination of injection and compression moldings' strengths, according to its developer. Like conventional injection molding, the LOMOLD process is automated, fast-cycling, and repeatable. Like compression molding, it is a cost-effective method of producing large, low-shear, low-warpage parts on lower tonnage machines, while maintaining much higher post-mold fiber lengths and avoiding the design limitations of that process. —[email protected]

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