Stack-mold builders in the West are making strides in supplying the high-output tools to meet North American demands.
A highly engineered stack mold includes a heavy center section with a manifold system and both cavity plates. Two side sections can dispense similar or dissimilar resins. Developers specify volume thermoplastics and avoid heat-sensitive resins.
As knowledge about stack molds grows, mold makers and customers look to them more often when applications justify their use, as opposed to conventional, single-parting-line molds.
``There is no one answer for every molding need, just as there is no one perfect steel for every mold build,'' said Vince Lomax, vice president of Tech Mold Inc. in Tempe, Ariz. ``Stack molds should be considered when you need to make more parts competitively.''
Demand for stack molds ``seems to be increasing every year,'' said John Catalano, business manager for Fairway Molds Inc. in Walnut, Calif. ``Folks want more out of their footprint,'' and they want to realize energy savings, especially in the West.
The potential for lower costs and higher volumes pushes manufacturers to consider stack molds, said John Thirlwell, vice president of sales and marketing for Caco Pacific Corp. in Covina, Calif. Stack molds can operate with eight cavities at four per side up to 128 cavities at 64 per side.
Caco Pacific, Tech Mold and Fairway Molds have years of experience with stack molds and are committed to technology advances. Stack-mold production accounts for 25-35 percent of Caco's annual sales, about 20 percent at Tech Mold and 10 percent at Fairway. But they are aware that stack molds present a unique set of demands.
Industry consultant John Bozzelli of Midland, Mich., recognizes their value, ``provided good parts can be run at the estimated cycle time.'' But he has concerns.
``Put in money for extra [temperature control] Thermolators and more plant cooling capacity. Take into account the flow differential that favors the filling of the front cavities first,'' and use a press with the correct clamp tonnage, barrel size and plastic pressure capability, he said.
In the largest available configuration, a basic 128-cavity stack mold with hot runners for a round cap costs at least $450,000 and, with more complexity, more than $1 million. The time from order to delivery may take 18-28 weeks.
North American injection molders generally use stack molds with more than 32 or 48 cavities to make product for local end uses.
Caco is adapting a proprietary Low Inertia Technology for conventional stack molds. It began building the configuration for single-face tools in 2000. A servomotor-driven, rotating horizontal bar is attached with two core sets to half of each mold and creates a simple multishot system, of interest for clean-room medical applications.
Caco began building stack molds in 1963. Early applications of multicavity stack molds included film packs for Polaroid Corp., packaging lids and containers, various closures and cassette cases for magnetic audiotapes and videotapes.
Later, medical companies saw value in using stack molds. Applications include Petri dishes, well plates, inhaler parts, vials and specialized closures and intravenous devices.
Consumer products include razor handles, barrier packages and mold-in closure liners. Other possibilities include soft-touch toothbrushes and cellular telephone housings. Stack molds lend themselves to family molds, in which a body and lid are molded in the same cycle. Complex cores and cavities become the lead item.
``Our industry has gotten more complex and sophisticated, pushing us to innovate continually,'' said Thirlwell, who retires May 31 after 14 years with the company. During certain times, it's ``all stack molds.'' Most include a full hot-runner system and, in many cases, valve gates.
Tech Mold delivered a 128-cavity stack tool for molding 38-millimeter, nonthreaded closures with custom locking features for packaging in late November. It built its first stack mold in the mid-1990s and has invested heavily in equipment.
``If we don't differentiate ourselves, we will have a tough time,'' said President Bill Kushmaul. ``We started preaching automation 10 years ago.'' Mold makers that invested during those ``10 years of prosperity'' were positioned to withstand the recession. ``Those not spending are not keeping up,'' he said.
Stack molds are ``more expensive, harder to take in and out of the press and harder to understand,'' Kushmaul said.
Tech Mold works largely ``for customers who dominate their marketplace,'' he said. ``If appropriate for volume and part, [a stack mold] keeps a company in the arena with lowest cost.''
Fairway is building 64-cavity stack molds for plastic cutlery. It designs each system to mold knife, fork and spoon components using full-blown hot runners and no tab gates. It can produce a mold in 14 weeks ``if we use the StackTeck hot-runner system and the design is not different,'' Catalano said.
The firm was formed in 1977 and began making stack molds in the mid-1980s. In 1998, Fairway became a division of Rexdale, Ontario-based StackTeck Systems Inc. Castle Harlan Inc., a New York merchant bank, formed StackTeck as a holding company.
Fairway and sister businesses Tradesco Mold Ltd. and Unique Mold Makers Ltd. in Brampton, Ontario, share intellectual property, sales leads and overflow production, which he said leads to better molds, more business and higher production rates.
``We at Fairway have been fortunate to stay as busy as we have been during a pretty aggressive slowdown,'' Catalano said.
Fairway has succeeded with high-volume family molds for optical media packaging. ``We have a great design'' and cut cycle times to eight or nine seconds using eight-cavity stacks, he said. Fairway is exploring higher-cavitation stack molds, Catalano said.