By Jan H. Schut
Two unusual new concepts for cube molds for multi-material injection molding were introduced at the Kunststoff Show (K Show) in Düsseldorf, October 16-23 this year (www.k-online.com). Both alter the normal role of cube molds to move and assemble parts by creating unusual new non-cube structures to transport molded parts for assembly. Separating part transport from the cube neatly allows secondary automation without adding cycle time providing for significantly faster production. Servo-driven rotating molds also cycled faster with more automation than ever before on the show floor, demonstrating new possibilities for durable and medical applications.
Rotating molds with two, three and four sides have been used since the 1950s to mold multi-material parts, sequentially injecting two to as many as six different materials or colors. Four-sided cubes offer much higher automation and output than two-sided rotary stack molds. Cubes are typically dedicated to in-house molding millions of parts a year of small disposables like toothpaste tube shoulders, re-closable lids and soft-touch toothbrushes. Two-sided rotary molds produce lower volumes of larger multi-material parts in the tens and hundreds of thousands for durables like tools, automotive, appliance and electronic parts.
ON TRACK FOR MORE FLEXIBILITY
One of the two new cube concepts is Flexi-Cube launched by G. B. Boucherie N.V., Izegem, Belgium (www.boucherie.com), which has a fixed cube around which light-weight mold inserts or carriers travel on a track. Parts are molded with different material shots on the stationary cube. Because the cube doesn’t turn, it doesn’t have to be square, but can be rectangular, allowing more stations to be added for molding, cooling, and other functions.
Inserts carry parts from station to station around the cube. Boucherie’s K Show announcement describes a solid track “around the cube on which holders with molded parts are traveling. These holders are moved by servo motors, allowing [them] to travel over different distances.” The patent application (U.S. Pat. Applic. # 20110117233) describes mold inserts that “serve as holders and can be lifted out of partial cavities,” pulling back from the cube just enough to travel freely around it.
The first commercial Flexi-Cube mold, which took seven months to build, was installed in July 2012, in the U.S. It has 24 cavities molding three-component solid razor handles for a snap-fitting razor. There are four sets of molds on the stationary cube and five sets of inserts to move parts around the cube. The extra insert allows a fifth station on the non-operator side for robotic part removal without adding cycle time. The first parting line of the mold has two sets of cavities for the first and second shots of PP. The second parting line has cavities for contact cooling and a third shot of soft-grip TPE. Cycle time for the 10-gram razor handle is only 17 seconds. “Typically a solid razor handle like that would take 25 seconds,” says John Williams, president of Boucherie USA Inc., Knoxville, TN. Boucherie showed a two-cavity prototype in motion at K without molds.
The other unusual new cube molding concept comes from Zahoransky Formenbau GmbH, Freiburg, Germany (www.zahoransky-group.com) and combines multi-component indexing mold plates with a “TURN-stack” rotating assembly cube. The propeller-like indexing mold plates carry either two or three molds, depending on how many materials are being injected. A single-component part uses two plate molds and indexes 180 degrees with one plate always in the molding machine and the other plate transferring parts to the assembly cube. A two-component part uses three mold plates and indexes 120 degrees with two plates always in the molding machine and the third plate transferring parts to the assembly cube. The assembly cube rotates on either a vertical axis, mounted outside the machine base, or a horizontal axis, mounted off the machine platen. The cube can also do other things besides assembly like leak testing or vision inspection.
The “indexing plate/assembly cube” concept was presented January 2013 by Zahoransky managing director Michael Schmidt at the Molding 2013 conference in New Orleans, sponsored by Executive Conference Management in Dearborn Heights, MI (www.executive-conference.com). The schematic shows two-component parts made on three 120-degree-indexing plate molds and one-component parts made on two 180-degree indexing plate molds. The two parts are transferred to the cube, which indexes and assembles them. Cycle time is determined by the longest time to mold either part. Zahoransky has built a prototype to demonstrate the new technology.
FASTER CUBES, MORE AUTOMATION
Foboha GmbH in Haslach, Germany (www.advaltech.com), set a speed record at K with its patent-applied-for (U.S. Pat. Applic.# 20120328730) all-electric cube, first launched at the Fakuma Show in 2012 in Germany. Arburg GmbH, Lossburg, Germany (www.arburg.com), ran a pilot Foboha mold at K making two-component (HDPE and PP) caps for juice packs with 12 caps per side (4 x 12 + 12) on an Allrounder 720A press with 3200 kN of clamp force.
“It molded in under six second cycles,” says Hansjoerg Keusgen, head of sales and marketing at Foboha. “That’s a record for sure for cubes.” A servo drive and servo motor allow the cube to turn as the mold opens, for cycle times at the show of 5.6 to 5.7 seconds.
Last year Zahoransky showed a 6.5-second cycle molding three-component drink caps at NPE 2012 in Orlando, FL, using a pilot total integrated manufacturing (TIM) cube with servo drive and servo motor rotation on a press from KraussMaffei Technologies GmbH in Munich, Germany (www.krauss-maffei.com). Cycles for commercial cubes have been reported as short as 7 seconds for two-component toothpaste tube shoulders.
At the K Show Foboha also demonstrated patent-applied-for new technology (U.S. Pat. Applic. # 2012/0088000) to screw two-part drink caps together automatically in the mold for the first time. The demo ran on a standard F-270 all-electric press from Ferromatik Milacron GmbH, Malterdingen, Germany (www.ferromatik.com). The molds have eight bottoms and eight tops per side (4 x 8 + 8) and inject two PPs of similar shrinkage. Caps are automatically unscrewed from the mold and screwed onto the bottoms while the bottoms are still in the mold. Assembled caps are then removed robotically. Cycle time is 10 seconds because the caps are relatively thick.
Reflecting increased interest in rotating molds for durable automotive, appliance and electronics applications, KraussMaffei showed a GX series machine for the first time with a SpinForm swivel plate. It used a two-sided mold to make a demo part with upper and lower PC/ABS blend shells, combining colored and optical grade transparent materials. Then two different polyurea coatings were flowed onto the finished surface in the mold for high gloss finished coat. Finally the parts were assembled robotically with an LED light inside. KraussMaffei introduced its ColorForm PU in-mold coating at K 2010, but says it has reengineered the RIM process since with wear-resistant pumps and more accurate metering.
Engel Austria GmbH, Schwertberg, Austria (www.engelglobal.com), demonstrated servo-driven rotating index plates, without a tiebar or conventional turntable. Engel molded three component drip chambers for blood transfusions at the show on an Engel e-victory hybrid injection molding machine. The molds index 180 degrees, making two parts, one PS and the other PP, assembling them with a filter between, and overmolding them with PP. The complex molds were built by Hack Formenbau Gmbh in Kirchheim, Germany (www.hack-formenbau.de), accommodating 14 separate moving axes driven by servo motors. “It is by far the most movement we have ever integrated into a production cell,” says Georg Steinbichler, vice president of R&D technologies at Engel.
At the K show Zahoransky showed a TIM Light mold for the first time, which adds external assembly automation to single-component parts for lower volumes. The two-platen mold doesn’t rotate or require a tie bar support structure. “Two assembly plates enter the dual-platen mold when open, remove parts from their respective platens, and then slide back out from the mold, where they mate and assemble the parts,” explains Frank Kigyos, CEO of Zahoransky USA Inc., Sugar Grove, IL (www.zahoransky-usa.com). The system takes slightly longer cycle time than Zahoransky’s original TIM cube technology, but costs significantly less. Zahoransky also showed its TIM cube with a central rotating cube to mold and carry parts and two flat external assembly platens in 90-degree positions beside the cube. The external assembly platens included servo-slide pick-and-place units and rotated 180 degrees, providing up to four assembly functions. Outside assembly platens with servo motion can be retooled for different parts.
Ermo Group, Marcille-La-Ville, France (www.ermo-group.com), introduced a one-sided mold for two components with its in-mold assembly system (IMAS) automation. Three other makers of two- and three-component rotating molds also exhibited at K: Braunform GmbH in Bahlingen am Kaiserstuhl, Germany (www.braunform.com); Ferbe Tools AB, Gislaved, Sweden (www.ferbe.se), with “SpinStack” molds licensed from Gram; and Caco Pacific Corp., Covina, CA (www.cacopacific.com) with low inertia technology (LIT).