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March 8, 1999

6 Min Read
The Nearly All-Plastic Dashboard

By combining various plastic technologies (structural plastic moulding, foam, slush-moulded skins), a dashboard designed for the Audi A4 meets the requirements of the car manufacturer and satisfies the comfort needs of the buyer. IMI talked with Alfred Wagner, of automotive moulder Peguform, headquartered in Bötzingen, Germany, about the company's success in reducing the dashboard's metal components to a minimum. We visited the company's manufacturing facility in Neustadt/ Donau, Germany to see how it was done.

In the previous model, the instrument panel support beam was based on metal. Replacing the metal with reinforced plastics allowed a substantial weight reduction. However, it was not possible to eliminate metal altogether. A reinforcing metal frame as well as bolts, screws, nuts, and springs necessary to attach and secure the instrument panel remained, making the design one that had to accommodate both materials.

The dashboard has to fulfill various needs. It has to hold in place air ducts, instruments, and part of the airbag, and at the same time be able to absorb the high-impact energy in case of a crash. In addition, it has to be visually appealing and pleasant to the touch. When designing the instrument panel and selecting the material, the manufacturer has to consider the environmental demands, such as exposure to sunlight and temperatures up to 130°C. The car manufacturer also demands weight and cost savings.

The instrument panel made by Peguform today for the Audi A4 consists of three plastic components: a glass-fiber-reinforced PC/ABS support beam, polyurethane foam (PUR), and a PVC skin. The plastic support beam alone weighs 2,500g; in the previous model it was metal and weighed 4,000g. This structure was the primary source of weight reduction. The new concept also permitted economical production by reducing the number of components, and at the same time increased the design possibilities.

However, metal parts continue to play an important role. Metal frames for air vents and airbags as well as nuts, bolts, and screws serve to absorb impact energy and to attach the panel to the car frame. Here is how they become integrated in the individual manufacturing steps.

Design of the Instrument Panel

The instrument panel, as part of the front cockpit, has to meet in its design and functionality certain technical requirements provided in the form of specifications and drawings by the car manufacturer.

The slush-moulded PVC skin, in combination with the PC/ABS structure and the foam, substantially expands the design possibilities. It allows the manufacturer to achieve unusual shapes with a leather-like surface. Its form is attached to the glass-fiber-reinforced PC/ABS support beam with the PUR foam, which acts as an adhesive and also absorbs noise and impact energy, and is soft to the touch.

The structural material was selected during the development stage of the instrument panel for optimum design possibilities and to meet the various technical requirements. Experience from working with similar units in the past led designers to choose a PC/

ABS blend reinforced with 10 percent glass fiber. Mould flow calculations performed at this stage simulated the resin flow inside the mould for this 2.2-mm-thick part.

This component has to support the attachments for the main frame. it holds, in addition to the skin and the foam, the air vents, the defroster units, and part of the airbag. The defroster duct made from the same material is attached under the instrument panel and handles the air flow to the air vents. It contributes strongly to the stability of the instrument panel.

During product development, test units are used to determine where the instrument panel needs to be reinforced with metal. To meet the low weight requirements, aluminum is the metal of choice. The necessary reinforcement cannot be achieved at the same price and cost by using any type of plastic.

Integration of the Manufacturing Process

Using three dissimilar plastic components for the dashboard requires three different manufacturing processes that need to be coordinated. In addition, the metal attachments have to be effectively integrated into this process.

The structural elements and the defrosting vents made from the PC/ABS (Pulse 979, Dow Plastics) are injection moulded on a 2,700-ton Krauss-Maffei moulding machine. The moulded part is automatically placed on a conveyer belt, and after the seams have been deflashed, transported to the foaming unit. Moulds and material have been planned for the car's six-year life expectancy plus four years for replacement parts.

The slush method of rotational moulding, allows the manufacturer to achieve the complex shape of the instrument panel surface that would not be possible by vacuum forming. By covering the surface of the tool cavity with the PVC powder (Marvyflo, LVM) and melting it at 210°C while rotating the mould, a 1-mm-thick skin is formed. The exact thickness of the skin is controlled by the dwell time in the mould and its rotational speed. After cooling the mould to 40°C, the skin is removed without deformation and is directly transported to the foam unit.

The first assembly step of the instrument panel takes place at a rotary table. The support elements are attached to the upper part of the foam mould. The skin is held in place in the lower part of the mould by vacuum. At this point, aluminum reinforcement rods are placed in the mould to give the necessary stability once the air vents are carved out.

The PUR foam (Bayfill PUR 51 IF 02, Bayer) injected by a robot evenly fills the closed mould, encapsulating the aluminum rods. After 5 minutes the mould opens automatically and the foamed portion of the panel can be removed. It continues to harden on the cooling belt for at least 30 minutes. At that point the air vents and required channels are carved out in a two-step process by which the final form of the instrument panel is achieved, giving it a perfect fit. The defrosting vent is attached to the foam in 3 seconds by high-frequency welding and 60-bar pressure.

Peguform plans to make the process even more economical by introducing a one-component process in which the skin, the foam, and the panel support beam are of the same material. Development work is going on using either PP or PUR as the basic material.

Safety Requirements for Metal Parts

During installation of the blowmoulded air ducts, the air vents, the airbag unit, and its lid, a variety of metal bolts, nuts, screws, and springs are responsible for holding the panel and its instruments in place. These metal parts, called D-parts, have to meet stringent safety requirements. For example, the screws are always tightened with the same amount of torque.

The compliance with safety requirements has to be documented on special forms. Peguform is planning to increase the safety controls further by introducing electronically controlled screwdrivers, which test the tightening of each screw, document it, and feed the results back for adjustment.

Lightweight plastic instrument panels cannot totally do without metal reinforcements and attachment units, mainly for safety reasons. The primary aim of manufacturers is to integrate these metal parts into the manufacturing process of the individual building blocks as efficiently and economically as possible.

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