Plastics Engineering - May 2014 - (Page 10)

" Injection Molding's Wild Side __________________________________ In situ polymerized glass-filled PA6 is a thermoplastic, not a thermoset, so scrap can be reused. " Auxiliary Injection Units Get Mobile Multi-shot machines for packaging markets are typically built new as dedicated systems, often for in-house molding. Multi-shot machines for durable applications are more commonly built by adding auxiliary injection units onto an existing press, often at custom molders. Mold builder Mgs Mfg. group, germantown, Wisconsin, UsA, a mold and equipment builder specializing in multi-shot conversions, has installed auxiliary injection units for two-, three-, and four-shot conversions including rotary molds. Mgs works primarily with non-automotive industrial applications. Mold Masters ltd. of georgetown, Ontario, canada, which was acquired last year by Milacron llc in Batavia, Ohio, builds small E-Multi auxiliary injection units, multi-shot runners, and multi-component conversions. "We've done a lot of work recently on automotive key fobs with up to five shots for different colors. From a hot runner point of view, they are very difficult to do because they are close pitched," explains Bruce catoen, Mold Masters' chief technical officer and VP of business development. The company's iFlow technology specializes in hot runners for multiple small shots. It was used recently to convert a six-injection-unit Engel machine for multi-shot toothbrushes to seven units, using a multi-component linear mold from Zahoransky Formenbau in Freiburg, germany. Hybrid Co-Injection And finally, don't forget regrind. co-injection (a.k.a. sandwich molding) is also growing, spurred by high resin prices. "The goal is to save 20% to 30% on material," says Paul caprio, president of KraussMaffei corp. (Florence, Kentucky, UsA). 10 "All molders should be evaluating co-injection if they can take advantage of it." co-injection injects two materials through one injection point using a sandwich head. First the skin material is injected, then the core material, followed by the skin material again. Historically, the two materials are a virgin surface layer and an inner regrind or recycled layer in a comparatively thickwalled part. The technology was promoted for over 20 years by Bemis company Inc. in sheboygan Falls, Wisconsin, for a variety of injection molded parts. However, since 2004 Bemis has combined sandwich molding with multi-shot molding-for example, co-injecting a steering wheel part with a glass-filled recycled PP core and a virgin PP skin without glass, then over-molding the part with a different color and material for a soft-touch surface. For three-shot molding, Bemis typically moves portable injection units from one two-barrel machine to another. How Multi-Shot Conversion Works "converting a single-shot press into a multi-shot press involves the integration of several pieces of additional equipment, based on the tooling technique as dictated by part geometry," explains John Berg, director of marketing at Mgs. "An additional injection unit is required, obviously, to supply the second shot of resin. "This unit can be mounted vertical to the press, generally on the stationary platen. The vertical vs. horizontal decision is based on [the] second shot size, size of the base molding machine, and molding facility limitations. The secondary injection unit can also be mounted directly on the injection mold, providing the mold is large enough and the shot size is small enough. support mechanisms can be employed for stability. "The servo or hydraulic injection unit (depending on customer preference and project needs) requires its own power supply, operator interface, and controller and is integrated into the base machine via standard sPI robotic or Euromap 67 interface. A rotary platen or rotary stack structural system may need to be added to the base machine to enable transition between the first and second shot. The secondary system may require an independent support system for cores and valve gates along with a connection for a rotary platen interface and other required operations, like a vision inspection system, for example." | PlAsTIcs EngInEERIng | MAY 2014 | www.4spe.org | www.plasticsengineering.org http://www.4spe.org http://www.plasticsengineering.org

Plastics Engineering - May 2014

Table of Contents for the Digital Edition of Plastics Engineering - May 2014