Teamwork reduces development time

The development of components together and devoid of flow lines visible surfaces only have been possible through the close collaboration between a supplier of systems, a supplier of raw materials and an automobile manufacturer. "Metal plastics" Alcom give an aspect of aluminium components in the engine compartment and introduce color in your design.

Acoustic screen

Finding new applications for plastics has always been part of the activity of suppliers of raw materials. The only consumption of plastic above-average growth can be explained through the opening of new markets or by the substitution of traditional materials. For example, the content in the plastic of a car in 1998 was of around 12 per cent of the weight, and currently is around 14 per cent. In 2008 it is estimated that that content will be between 17 and 18 per cent. This growth is partly driven by compounds of high quality with reproducible properties with tight specification limits. Only a supplier that can provide them on time with the necessary properties and at a favourable price will remain competitive. In addition, the supplier of raw materials plays an increasingly important role in the development of products.

This situation can be illustrated through the collaboration between the BMW, the systems Faist Automotive supplier Group GmbH & Co. KG, Kulmbach, Germany, and the supplier of raw materials Albis Plastic GmbH, Hamburg, Germany. All of them came to the conclusion that only could occur the optimal components at a favorable price through the close collaboration of a team as soon as possible in the phase of the project. The case specific question had to do with an acoustic screen and a cover of air to the current series 3 BMW with diesel engine four-cylinder direct injection power of 110 kW (330 n·m). The underlying philosophy was to introduce the functionality and design sophisticated in the engine compartment. The demands of components were beyond an elegant design of the engine compartment. Functions such as noise attenuation, decoupling of components and specific routes are taken into account in the design and development of these components of the air intakes to allow that the vehicle can drive through high water levels.

Air intake cover

The sets of components produces Faist modular systems provider. Specific functions such as design and acoustics and, consequently, are manufactured in different plastics. Acoustic screen consists of two parts of polyamide 6 filled with glass/mineral fiber molded by injection: a black outer part in PA6 GF10 MR20 standard and a central part in metallic silver color of aluminum on the basis of Alcom 6 PA 900/8 GF10 MR20 12-778. The logo and the bars of the design were later printed in silver in a single operation. The two parties are joined together using ultrasonic welding. To meet the acoustic requirements, mounts a part molded foam PUR to the bottom of the acoustic screen.

For design reasons, the middle section of the cover of air intake also is moulded by injection in the polyamide of color aluminum silver metal supplied by Albis. This is produced by moulding by injection of two components: in the frontal region shapes a flange of PP/EPDM to provide a function of fixing and decoupled with the body. Both components are delivered preacabados to the automaker production lines.

Previous engine covers were uniformly black and were manufactured in PA6 GF10 MR20 standard with printed silver bars.

BMW logo and bands of the design in a single operation (image: BMW)

Other developments in the design of the compartment of the motor required new approaches. The available possibilities were: partial painting using masks, decorative films on the template, or the use of precoloreados materials. In addition to the cost-benefit analysis, the plausible processes were evaluated considering their merits individual and inconvenient: painting plastics offers greater freedom in the design and a high quality, but is associated with expensive equipment and high processing costs. Decorated in the mold parts are also more expensive than injection-molded parts of metallic and tend to restrict the freedom of design. In addition, in the case of roofs painted or decorated in the mold, any scratch will reveal the underlying color of the part. Taking into account these considerations, the automaker decided to use a metallic compound. The top layer should resemble as much as possible to a surface of aluminium. With the use of scales of aluminium and colour pigments, Alcom product should continue meeting the characteristics required of standard materials. This has required a special technology of preparation of compounds. Mechanical properties such as resistance to tensile, elongation at rupture, modulus of elasticity and resistance to the impact of the standard black plastic were taken as reference values. Other criteria were good properties of Union, ultrasonic welding, printing capacity, consistency of colour and resistance to ageing in an ambient temperature of 110 ° C for a period of 3,000 h.

Mechanical properties of the standard black material in comparison with the material of aluminum metallic silver color.

The goal was to develop a reproducible surface appearance. Other requirements to the plastic were: continuously good properties of the material and consistency of colour, without visible joints or flow lines. It should also be little tendency to suffer from distortions and a high resistance to thermal ageing, dimensional stability.

On the basis of the characteristics required of the materials addressed product development in the area of metal plastic color for use in the attenuation of noise and air cover. ALBIS developed a technology of process which allowed the complex composition of a hybrid plastic achieving the desired metal effect introducing aluminium flakes and the appropriate color. The results presented a significant improvement on the homogenous appearance of the surface compared with the metal plastics used so far.

Were preliminary experiments with 6PA GF10 MR20 material specified by the manufacturer of the car; However, this plastic required greater optimization in regard to his appearance. The sequences of correction consisted of vary the shape and size of the scales with a simultaneous control of color during the preparation of the compound until obtaining the desired appearance and the necessary thermal stability to ageing. After this series of experiments, the product had to be able to play the laboratory to production. A fundamental problem in this context is the consistency and reproducibility of the color as a result of the use of extrusion machines of different sizes. In order to guarantee the quality characteristics, Albis developed a special for the molding mold injection of this material. Incorporated in this mold geometries enabled evaluation continued visibility of joints and lines of flow during production.

Interpretation reológica of the best possible casting hole (image: Albis)

To achieve short system times of development, organized a team of development of the BMW Group with the Albis company as a supplier of raw materials and the company Faist as a systems supplier during an early phase of the project.

According to Albert Fendt, responsible for authorized company and director of key accounts for Faist: "the corresponding specialized departments were involved in an initial stage of the development of the product." We had intensive discussions and discuss the possibilities and risks. Faist has a line of data especially for the car manufacturer. Exchange CAD data, there are drawings, our design engineers have to transform the designs into tools and functions of the components should validate. Another task is to develop reliable sets of parties and individual components that conform to the specifications of the client. We updated the CAD data of the system to avoid the collision between interconnected parts and to ensure a direct and logical sequence of mounting in production lines. Cost-effective production of the two covered only could be achieved by injection by moulding. Only problems can occur when there are openings in one piece; which lead to unions, which may be visible as flow lines on the surface. "It is necessary to have a great experience in the design of molds and the injection moulding to produce a visible components and design with an appearance of such high quality".

At the preliminary stage of the construction of the mold is invested considerable effort to ensure that the demands of quality of the components met with the help of a presentation by computer and simulation of delay by Moldflow carried out by the Department of falls from Albis. The sets were produced with the help of six individual moulds, designed and produced by Faist Tooling. The sets were built in Faist in Ziemetshausen, Germany facilities, machines of injection moulding with up to 10,000 kN clamping forces. Assembly workshops were prepared for the ultrasonic welding process and the final assembly of sets.

The selection of materials is not only critical to achieve the necessary properties, but it also has economic implications. The BMW Group established the maximum expenses for raw materials of aluminum metallic silver color. The work of development with the supplier of raw materials started during this phase. Since that could not meet the requirements with the standard materials, developed a plastic with specific properties. Technical knowledge in the preparation of compounds of Albis proved a great advantage.