Cost-effective production of lightweight decorative components
Elegant design and styling elements in the interiors of premium vehicles ensure a distinctive feel and a comfortable environment. Buyers of small and mid-sized cars are also increasingly looking for greater individuality in interiors. In its “SurfaceTechnologies” project, Covestro, formerly Bayer MaterialScience, has developed an integrated polycarbonate-based material and process concept suitable for series production
It is the perfect response to the trend among buyers and enables cost-effective production of decorative components. Automakers can thus use customized design and styling elements in interiors, ranging from standard models to the premium segment.
At the Fakuma trade fair in Friedrichshafen from October 13 to 17, 2015, the company will be showing various products including prototypes of components produced in an injection mold with dynamic temperature control using the MuCell® foaming process. These will include glove box covers made from the polycarbonate ABS blend Bayblend®, and whose surfaces have high-gloss and structured areas.
Dynamic temperature control and this new material, which is tailored specifically for these purposes, ensure outstanding surface quality, including when using physical foaming. Manufacturers can therefore dispense with an additional coating step.
The sensitive high gloss areas are protected against scratches and contact-related soiling by being embedded more deeply in the structure. However, the surface is well-prepared if the component is to be coated in some way.
Lightweight components thanks to physical foaming
“We used a combination of various technologies to produce the prototypes,” said Rainer Protte, who is responsible for the development of special injection molding processes at the Polycarbonates Business Unit of Covestro. “This makes it possible to manufacture high-quality molded parts that weigh less while also saving money.”
For example, physical foaming (MuCell®, Trexel, Wilmington, MA, United States) enables the production of microcellular foams. This involves using injectors to inject supercritical nitrogen into the injection molding cylinder and thus directly into the melt. Compared with conventional injection molding, quality features such as flatness, roundness and distortion are enhanced significantly thanks to lower and more uniform internal stresses and more consistent shrinkage, while sink marks are reduced or eliminated. Holding pressure can also be omitted with this method.
“Physical foaming also improves the flowability of the melt, which enables a reduction in the wall thickness of molded parts without the injection pressure becoming inadmissibly high,” Protte said. “Compared to conventional methods, this solution reduces weight and saves fuel, in part also due to the lower density of the foams compared with solid plastics. We’re currently working on reducing the wall thickness further.”
Outstanding surfaces thanks to dynamic mold temperature control
A disadvantage of foaming is the usually inferior surface quality, which manifests itself in the form of streaks. However, this problem can be resolved using dynamic mould temperature control. When processing amorphous thermoplastics, the cavity surface of the mould is heated before the shot to the level of the plastic’s glass transition temperature. Once the melt has been injected, this is followed immediately by cooling to the demoulding temperature. The process leads to outstanding surface quality, including for filled or reinforced plastics. As a result of the high wall temperature, the mould surface is smoothed out to an exceptional degree. Structures can also be moulded highly effectively.
During the project, Covestro worked closely with a range of partners – gwk Gesellschaft Wärme Kältetechnik in Meinerzhagen (temperature control processes), Hiddenhausen-based mold manufacturer Krallmann, and J. & F. Krüth in Solingen, which specializes in mould surface grains, with the focus in this case being on a 3D laser structure.
The strengths of the Covestro interior concept lie in the countless design possibilities it offers in terms of shape, colour, surface structure and gloss. Components can also be further enhanced by finishing if, for example, chrome, leather, real wood or soft-touch surfaces are required. Lighting effects such as ambient lighting are also possible with transparent and translucent polycarbonate grades.
Polycarbonates and blends under the Makrolon®, Bayblend® and Makroblend® brands and Makrofol® and Bayfol® films have a proven track record in the interiors of premium automobiles. This is due in no small part to their excellent crash properties and high surface quality.
With 2014 sales of EUR 11.7 billion, Covestro is among the world’s largest polymer companies. Business activities are focused on the manufacture of high-tech polymer materials and the development of innovative solutions for products used in many areas of daily life. The main segments served are the automotive, electrical and electronics, construction and sports and leisure industries. The Covestro group has 30 production sites around the globe and employed approximately 14200 people at the end of 2014. Covestro, formerly Bayer MaterialScience, is a Bayer Group company.