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Automotive molder sees untapped potential for multicomponent molding.

Automotive Molder Sees Untapped Potential for Multicomponent Molding

Multicolor, multimaterial injection molding has much wider potential than just automotive headlamps and taillamps. That's the conviction at Keeler Brass Automotive Group, a custom molder located in Kentwood, Mich. Keeler has been molding automotive lighting for Chrysler and other car makers on a 2000-ton, four-barrel Krauss-Maffei injection machine since 1989.

Keeler v.p. of sales and engineering John Jula is so happy with what he calls "multiscrew molding" that the company plans to purchase additional multibarrel machines and branch out into markets other than automotive. "Multiscrew molding provides capabilities that no other process can," according to Jula.

Jula says the technology can provide complex parts with nearly perfectly aligned edges between different colors or materials, while also reducing assembly, scrap, and providing more consistent quality. "Some people see multiscrew molding as an alternative to insert molding," says Jula, "but it's more important to consider multiscrew molding's own unique potential. With multiscrew molding you can provide more varied styling and structural combinations of different materials or colors. We want to offer cost-effective designs that cannot be produced by any other means."

Multicomponent molding generally allows for much more complex parts than insert molding. "An example is a striped lens with alternating colors," says Jula. "More than two colors or materials can't effectively or economically be manufactured with insert molding. And single-screw injection would require multiple presses and secondary assembly that multiscrew molding doesn't."


Elimination of secondary operations such as assembly leads to improvements in part quality. For example, molding the three-color, two-material lens pictured on the previous page resulted in close to perfect alignment of the different colors because alignment in multibarrel molding is a function of a common core and/or cavity. Of equal importance, part-to-part consistency is significantly improved because no secondary fixtures are utilized. To produce a lens requiring four colors--red, amber, clear, and black--either multiple assembly and/or injection operations are required. These are eliminated with the multibarrel machine. The parts are molded in four colors, untouched by human hands.

A multicomponent machine can also eliminate the adhesion problems frequently encountered in assembling parts molded discretely. Three- or four-color parts molded with a multibarrel machine also suffer less warpage, according to Jula. Scrap is reduced as a result of the decrease in the number of manufacturing operations. And there is less opportunity for bad parts due to misalignment and in-process damage.

Furthermore, when a styling change or structural shape change is necessary, they can sometimes be implemented using removable metal inserts in the core or cavity. Thus, a different look or product differentiation can be achieved without need for secondary molding or assembly. For example, automotive lenses can be molded with different ornamental emblems, or with no emblem at all, on the same basic tool.


The accompanying artist's renderings illustrate Jula's vision of what can be accomplished with multiscrew molding from a styling and/or structural aspect in markets beyond automotive. Jula says, "We are beginning to capitalize on the unique capabilities of the multiscrew process in the furniture and appliance markets. We are attempting to answer the question of what can be accomplished with its expanded manufacturing and design freedom."

In office equipment, the pedestal base for a swivel chair exemplifies the capability to mold a highly glass-reinforced material for the inner portion of the base in order to meet the high-load requirements of a swivel chair base. The second screw would then inject an unfilled covering material in order to produce a Class-A as-molded surface finish. While it might be possible to produce the part with a single material, Jula believes that would sacrifice styling and design flexibility. For instance, an unfilled material alone would require a larger cross-section to achieve the same stiffness, while a filled material alone would have surface-finish limitations.

Jula is also looking to the appliance industry for business. Among the many applications he has up his sleeve is the refrigerator crisper tray illustrated on p. 23. The slide areas are the focal point for localized high stress during high loads or impacts. These could be molded in a high-impact material while the remainder could be molded in multiple colors and offer significant improvement in durability compared with the hot stamping and/or painting operations that would be required with single-material molding.

Jula believes the multibarrel configuration also has application in automotive under-the-hood applications such as valve covers and air-filter housings. Mounting or gasket areas could be molded in a high-strength or high-modulus material, he says. The overall surface could incorporate stylized logos and striping in order to capitalize on the trend toward neater, more ornamental engine compartments without sacrificing any durability.

In fact, compared with hot stamping or most paints, a multimaterial molded part has greater appearance durability because the color is molded through the part ("through-color molding") rather than applied as a thin surface coating.

Furthermore, elastomeric gaskets can be molded directly and integrally onto rigid plastic valve covers, access doors, pump housings, etc., improving assembly efficiency and design flexibility.


Keeler's four-barrel press (supplied by Krauss-Maffei Corp., Plastics Machinery Div., Florence, Ky.) costs $4-5 million totally installed. While it depends upon the specifics, a multicomponent molding machine is generally a somewhat larger investment than multiple single-barrel machines. But when you consider the cost of a total manufacturing system--including injection machines, secondary assembly equipment, materials-handling equipment, and multiple tools--multicomponent molding reportedly appears competitive for higher volume applications.

Jula thinks the process' potential is limited only by the imagination. "We've proved the capability exists. The limiting factor is our creativity in envisioning and incorporating multiple materials and colors to meet unique requirements."

PHOTO : The four-barrel, 2000-ton Krauss-Maffei press has capabilities that haven't yet been fully exploited for making multicolor or multimaterial structures.

PHOTO : Assembly was eliminated and quality improved by multibarrel molding this three-color, two-material auto light. Color alignment is nearly perfect and part-to-part consistency improved, as it's made without secondary operations and untouched by human hands.

PHOTO : The four injection units sit in a semi-circle on the shop floor rather than being stacked. The clamping unit is vertical rather than horizontal.

PHOTO : The slide areas of a refrigerator crisper tray, a focal point for stress, can be molded in a high-impact resin, while the remainder can be molded in multiple colors, offering improvements in durability and styling over single-barrel molding with secondary operations.

PHOTO : One concept for multicomponent molding: The interior of a pedestal base for an office chair can use a core of reinforced material for stiffness, overmolded with a material that provides a Class-A finish.

PHOTO : Under-the-hood automotive parts are going to more attractive styling than in the past, creating a fertile market for multibarrel molding. This four-color valve cover capitalizes on the trend.
COPYRIGHT 1991 Gardner Publications, Inc.
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 1991, Gale Group. All rights reserved. Gale Group is a Thomson Corporation Company.

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Title Annotation:Babcock Industries Inc. Keeler Brass Co.
Author:Fallon, Michael R.
Publication:Plastics Technology
Date:Apr 1, 1991
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