Metrics for high-volume, accurate micromoldmakingMetrics for high-volume, accurate micromoldmaking

Mcromolding is a specialty of custom molder/moldmaker Empire Plastics Inc. (Rochester, NY). Micromolding requires more accuracy than macromolding jobs. That's why Empire pays special attention to minimizing as many manufacturing variables as possible, especially in mold manufacturing.

Neal P. Elli, president, offered a number of important micromoldmaking metrics during his Molding 2002 presentation in New Orleans, LA earlier this year, including the following. (To obtain reprints of Molding 2002 presentations, visit Executive Conference Management Inc.'s website, www.executive-conference.com.)

Sprues and Runners
Since part weight is minimal, all the material cost really is in scrap—in the runner and, mostly, in the sprue. What's worse, Elli says that the runner can slow down the cycle since it's the thickest wall cross-section in the tool. He suggests using full-round runners wherever possible to obtain an optimum flow-to-weight ratio.

Gating
Elli says micromolds are typically two-plate molds with tunnel or tab gates, or three-plate molds with pinpoint gating. Best practices should include a good parts-containment system and a good cavity identification and control strategy. Parts spraying all over the floor, or part jam-ups and the mold damage they cause, can have an expensive impact on manufacturing costs and on parts pricing.

Cavitation
Run time should be a metric playing into cavitation considerations. As a high-volume injection molder, Empire uses a parts/day guideline when determining run sizes. That's because the parts use very little storage space, and a significant amount of material gets scrapped during startup and teardown.

Capacity planning also comes into play. Understanding peak demand periods of high-volume applications makes it easier to synchronize output to match the downstream manufacturing processes.

Moldbuilding
EDM still is the most commonly used method in micromoldmaking. Hand polishing, and the damage it can cause to cavity impressions and parting lines, should be minimized. Elli says it's better to creep up on better precision by leaving the steel in the mold, measuring trial parts, and making adjustments.

A good micromold temperature control strategy also is very important. Empire uses a moldmaking practice it calls Hybrid Tooling, which combines lightweight, thermally conductive, easy-to-handle aluminum bases with tool steel cavity inserts. Its Hybrid Tools reach temperature equilibrium faster, which decreases scrap at mold startup. (See "Beefed Up Aluminum Challenges Steel," February 2001 IMM, p. 64 for details).