Overmolding accelerates into automotive

Two days before Ken Shaner, VP of manufacturing engineering for Lear Corp. (Southfield, MI), stood before trade press and automotive OEM reps at Husky''s Detroit Technical Center to unveil a technology he feels could radically alter the cost structure and design of interior systems, his own company announced it would enter the first phase of a restructuring process to eliminate excess capacity-a consolidation that will affect 7700 employees at five North American plants.

Wall Street reacted by sending Lear shares down 2.1% and Standard & Poors put the company''s debt on a negative credit watch, but two days later and 600 miles away from New York, in Novi, MI, Shaner stood together with Husky officials to launch a concept that could do more to address inefficiencies at Lear than any reduction in force might.

Dubbed the Quadloc-Tandem-Index (QTI) by Husky, and the One Step Manufacturing Process (OSMP) by Lear, the technology culminates in a multimaterial 3470-ton press producing a 10-lb instrument panel that consists of a polypropylene substrate and a TPE overmolding running across the entire top portion. A bid to introduce the tactile and visual appeal of TPE and multimaterial molding have brought other industries to large, automotive interiors parts; officials billed the process as a game changer.

Three machines become one

Pulling elements from three of its machine lines, the base system is Husky''s large machine line, the Quadloc, which ranges from 1500 to 8800 tons. The clamping system applies Husky''s Tandem technology where an intermediate center platen allows molders to place two standard molds in the press, duplicating a stack mold without special tooling, to create two distinct parts for double output. Finally, the center station actually rotates along a vertical axis the way Husky''s PET Index system does.

This last twist allows the machine to inject a substrate material into the first side, spin that part 180°, and overmold another material via a second injection unit that actually rides along linear bearings with the moving platen. While that overmolding occurs, the first injection unit can simultaneously mold another substrate in the first cavity.

Husky achieves all this in a package that it says isn''t much larger than a standard 3500-ton press, making it easier for automotive suppliers to integrate the system into their plants. By situating the second injection unit along the side at an angle, Husky was able to keep the overall length at 65 feet, versus the 80 to 85 feet it says other large multimaterial machines require, which locate the second unit behind the moving platen.

The QTI is able to hold a 50,000-lb mold on each side of the center turret, using an off-the-shelf hydraulic motor to spin the colossal mass, and pneumatic and hydraulic locks to hold it in place. The demonstration QTI had a 440-oz main injection unit shooting the 8 lb of polypropylene, and a 220-oz second injection unit for the nearly 2 lb of TPE, but it can also be fitted with dual 440-oz systems. Substrates 2.5 to 3.5 mm thick with 1.5 mm thick overmoldings have been created with flow-length-to-thickness ratios of 500:1. Lear declined to name names but said the TPE development work was done with several suppliers and resulted in a two-year exclusive agreement on the material. Lear itself has applied for patents covering certain aspects of OSMP system.

Why not automotive?

Looking at markets like personal care, where multimaterial molding is entrenched in toothbrushes, Lear and Husky began to wonder why not automotive. Attempts at transfer molding, or the creation of a substrate on one machine, which is removed, placed into another machine, and injected over with a second material, had been unsuccessful for multiple reasons, chief among them part shrinkage changing dimensional tolerances.

Reaction injection molding had been used to mold PUR substrates that were later overmolded, but the required 8 to 24 hours of curing this process requires limits its use. In addition, the fact that crosslinked PUR can''t be recycled, unlike two polyolefin family resins like TPE and PP, has also been a limiting factor.

This system also eliminates outside-the-press assembly, which can run from seven to 10 steps for complex parts that use multiple materials in processes like male or female vacuum forming, spray PUR, or slush/rotocast PVC skin.

Lear has played with the TPE grade to create "slip" or "grip" surfaces depending on customer spec; provided different levels of softness through manipulating TPE thickness; and reduced glare, which is key in interiors, especially along the top of the dashboard.

Beyond feel, by overmolding the instrument panel, Lear is able to hide sink marks on the substrate that form from the addition of structural ribs. Adding these ribs without worrying about their affect on surface appearance allows designers to eliminate some of metal and foam substructures currently used to fortify plastic instrument panels.

The future

While this part involves two materials and the use of two of the four sides of the index, Husky and Lear officials say this isn''t likely to be the only set up, with the possibility for more resins, more sides, and as has become common in other automotive interior trim applications, back molding of fabrics, woods, or other materials.

Lear, along with Tier One competitors, made a push to supply full automotive interiors, and by 1999, achieved what it called "total interior integration capability." In 2002, it won the first full interior supplier responsibility for the 2005 Buick Lucerne and Cadillac DTS from GM.

Lear will position the QTI machine as a tool to help it win such contracts in the future, and in the near term, use it for a TPO door panel as well as an instrument panel in 2006. For Rich Sieradzki, general manager of Husky''s Detroit Tech Center, it could be an answer to current pressures in the market.

"If you look outside," Sieradzki said, "the game is changing. There is a constant squeezing that''s going on throughout the industry. The idea is to stop the squeezing and change the rules of the game."

Tony Deligio [email protected]

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