New Assembly Technologies Slash Costs

Innovations in automotive assembly introduced at K 2010 in Düsseldorf, Germany last month reduce component weight and increase functionality.

Two of the technologies are used in the new lightweight Audi A8, which also features an aluminum space frame.

A display by Bayer MaterialScience featured LED used in fiber optics for daytime running lights in the front headlamps of the Audi A8.

The components were developed in collaboration with Audi AG and Hella. The ten plastic lenses used in the headlamp are made from Makrolon LED 2245, which offers high transmission for long light paths, high thermal resistance and excellent yellowing stability to LED light.

"Our material meets the high optical requirements for exposed headlamp parts and is within the narrow color tolerance range. It also enables enhanced design freedom and a considerable weight reduction," says Martin Döbler, an expert in optical polycarbonate applications at Bayer MaterialScience. LED lenses are around 50 percent lighter than their glass counterparts.

The polycarbonate headlamps are expected to be particularly attractive to manufacturers of electric vehicles, who are leading the fight against vehicle weight.

The rectangular, slightly curved LED headlamp lenses for the Audi A8 are 4 cm long, 2 cm wide and 1 cm thick. They cannot be produced via standard injection molding because of the complex shape and thick walls of the optical components.

A new multi-layer injection molding process offers sophisticated mold temperature control to provide dimensional stability and fast cycle times for high-precision LED lenses with walls of greatly varying thickness.

"The design of the LED lenses shows that, compared with glass, polycarbonates offer much greater design freedom for precision optical parts," says Klaus Reinartz, head of the global LED project for general lighting at Bayer MaterialScience.

Other advantages of polycarbonate include its high heat resistance and high break and shatter resistance, which protects the LED lamps against vandalism.

Expanded use of polycarbonate in lighting fits into plans by resin producers to find new markets to replace packaging applications that have been cut back because of concerns about bisphenol A in the transparent, high-impact plastic.

Organic Sheets

Three exhibitors showed a new technology in which hybrid front end structures can be made with specially reinforced, very rigid plastic sheets in place of aluminum.

At the heart of the technology are sheets developed by Bond-Laminates, of Brilon, Germany, that consist of special fabrics embedded in a defined orientation in a glass-reinforced polyamide 6 matrix. In different versions of the technology the sheets can be made with different resins and different fibers: glass, Kevlar or carbon. The original technology was developed by DuPont and acquired by Bond-Laminates.

A front end for the Audi A8 made with the material was displayed by Lanxess, a German resin producer that provided specially formulated polyamide 6 for the project.

Semi-finished sheet for the Audi project is preformed and then inserted into an injection mold with three sheets of aluminum. The sheets are then overmolded with reinforcements and ribbing with Durethan BKV 30EV. The original prototype developed by Magna Decoma Exterior Systems GmbH was made solely of aluminum.

The lightweight organic sheet is used to create a 1.0 mm thin U section on the lower beam of the hybrid front end that will be used in the Audi A8. Weight savings are estimated at 20 percent.

"For quite some time, we have been developing concepts designed to harness the potential of lightweight organic sheets in the series production of structural bodywork components," says Gottfried Sailer, head of the Front End Systems Development Center at Magna Decoma in Altbach, Germany.  "Our accumulated findings and experience persuaded Audi AG to replace the aluminum sheet in its lower beam with an organic sheet."

The stringent demands in terms of strength and stiffness proved particularly challenging. The new structural concept incorporates a double torsion ring that increases the stiffness of the front end of the vehicle significantly. In the event of a head-on collision, the resulting forces are distributed across three load planes and four load paths, maximizing safety.

The technology may be going through rapid change. In one version, thin organic sheet precuts (0.5 to 2.0 mm wall thickness) may be heated for a brief period in an infrared radiation field to prevent oxidative degradation of the thermoplastic matrix. The sheet would then be pre-shaped by a robot head en route from the preheating station to the mold and then shaped by the insert-placing process in the mold.

In a demonstration at the Engel booth, flat sheets of four-layer, 40 percent glass-reinforced polyamide are heated with infrared energy to 280C and then robotically inserted into a 500-ton injection molding machine. There are nine partners, including Bond-Laminates, in the Engel project. Engel is working on the technology for a Mercedes application that was not disclosed.

The Engel technology, called "Organomelt", is particularly interested for design engineers. It shows how structural parts can be made from plastic in one automated production cell even though the parts have deep-draw sections.

The organic sheet hybrid technology can be used in frame components for panoramic roofs. Another promising field of application could be reinforcing functional modules for doors and hatches with integrated mounts for locks and grips, guides for electric windows and various fasteners. Kurt Knoll, an Engel project engineer, says the technology may also be used to make components for white goods.

Die-Cast Metal

Another interesting approach to hybrid assembles was demonstrated by IKV Aachen, a German research group. The technology was demonstrated on a molding cell producing sports glasses, but the process has significant potential for automotive applications that could benefit from use of a structural housing that is made conductive by a metal alloy.

In a demonstration at K 2010, a low-viscosity metal alloy is shot into a K-Tec 200 S/2F injection molding machine from Ferromatik Milacron GmbH, Malterdingen, Germany.

Based on technologies for multi-component injection molding IKV has developed a three-station index plate mold. Sport glasses are produced in a compact production cell with only one mold and one machine.

The temperature of the cavity inserts in the individual stations of the index plate mold is controlled with water via separate circuits. To enable processing of the extremely fast solidifying low-melting metal alloy in the area of an electrically conductive track, the mold is equipped with a variothermal temperature control system.

For the production of the glasses, the IKV team used polyamides CX 7323 (lens) and CX 9704 (frame) from Evonik Industries AG, Essen, Germany.

The inserted metal alloy has a melt point below 200C and has an electrical conductivity in the range of 8 x 106 S/m. This makes it particularly suitable for the production of conductive tracks with a high ampacity, the maximum amount of current a track or cable can carry before sustaining deterioration.

Lighter PP

In another K 2010 development, lighter polypropylene (PP) auto parts are possible with new synthetic mineral fibers from Milliken Hyperform HPR grades that increase stiffness, temperature resistance

"We envisage HPR-803 being used mainly in automotive applications, but are not limiting our project scope," says Adam Watson, who is in charge of marketing for the Hyperform HPR range. "It enables the production of polypropylene compounds that have mechanical performance similar to or better than mineral filled compounds, but at lower weight."

HPR-803 fibers have a high aspect ratio of around 40:1. "We expect PP compounds containing HPR-803 to replace talc-filled types and possibly other non-PP-based materials too," says Watson. "Tests have also demonstrated that HPR-803 works very well in combination with talc, giving processors and end users the opportunity to convert to the new technology in a step-by-step fashion."

Plastic Bullets

One of the most novel automotive technologies introduced at K 2010 is called "projectile injection technology", in which a plastic "bullet" powered by a burst of inert gas is shot through molten plastic.

Röchling, a German molder, developed the technology to improve uniformity of wall thicknesses created in the gas injection process.

"The inner diameter is defined by the projectile," says Fabrizio Chini, advanced projects manager,

Röchling Automotive. "The process enables us to inject in the same process step additional features, such as lips and brackets."

One of the new applications is integrated bi-material tubular sealing used for a cowling grille on the Ford C-Max, a seven-seat car built in Europe. The C-Max is being introduced in the North American market next year.

"The function of the cowling grille is to carry in air for climate-control in the car, drain water and to stop the hood from fluttering," says Chini. "Steel hoods are getting thinner and thinner for pedestrian safety, and as a result they are beginning to flutter."

TPE Plus PP

The PIT process starts by partially or completely filling a mold cavity with plastic. The bullet-like projectile is then shot through the cavity forcing polymer melt against the walls. In the Ford cowling grille, polypropylene is first injected into the cavity. A second cavity opens for injection of thermoplastic elastomer. The projectile is then fired. The result is a part with a bulb-shaped hollow seal.

The cowling grille made for a new Ford model features an innovative injection process.

Traditionally, the same type of part would be made with an extruded EPDM (ethylene propylene diene monomer) rubber seal attached to a hard plastic section. Chini says the PIT process cuts cost by 10 percent compared to the traditional process, which requires manual assembly of the parts. Expensive foamed EPDM rubber is also eliminated. The TPE is recyclable while the vulcanized rubber is not.

A projectile designed with protruding ribs creates notches in the elastomeric material that reduce permanent deformation and can precisely control the compression force. Wall thicknesses in the notched areas are 1 mm compared to 2 mm in other sections.

The bulb seal created by the projectile creates pressure between the hood and the cowling grille to damp hood fluttering. Changing dimensions of the seal allows tuning of the pressure. "The force can also be tuned without any tool modification just by changing material hardness or the projectile shape," says Chini.

In an interesting innovation, Röchling engineers developed a chamber that recovers the melted core pushed out of the mold cavity by the projectile. The melt is stored in the chamber and pushed back into the cavity in the following injection cycle. "This avoids regrinding the purged materials," says Chini.

Currently the projectile, which is made of polyimide, is not re-used. Polyimide polymers are expensive, but very strong and resistant to heat.