High-precision aspherical mirrors are produced solely on electric Alldrive machines and the whole process, including packaging, is fully automated and takes place in a cleanroom
Dr Sebastian Wiebel, Head of Production HUD-Spiegel, is highly satisfied with the quality of the moulded parts. Photo courtesy of Arburg
Arburg, a global manufacturer of plastic processing machines, has delivered the tenth Allrounder injection moulding machine to Continental for the production of aspherical mirrors for head-up displays (HUDs).
The company has been cooperating with Arburg on an exclusive basis in this highly demanding segment since 2010, for which it solely uses specially equipped electric machines from the Alldrive series.
Demand for head-up displays is growing steadily: annual production increased by 70% to around 600,000 parts between 2015 and 2016 alone.
Head-up displays from Continental are installed in cars of various brands throughout the world. These use aspherical mirrors to project all driving-related information (such as the current road speed) onto the windscreen, and thus directly into the driver's line of vision – an important contribution towards greater driver safety.
Displaying this information on the screen without distortion requires moulds with accurate contours and high-precision surfaces. When producing the mirrors, it is essential to accurately reproduce the different curvatures of a wide variety of car windscreens.
Continental has been using Allrounders in plastics processing since 1970. In 2010, cooperation intensified in the field of head-up displays, as the production of aspherical mirrors makes extremely stringent demands in terms of precision. In the case of the injected part, the permissible deviation from the target geometry is less than five micrometres, in other words the diameter of a human hair.
Accordingly, technological cooperation between the two companies covers not only machine design, but also joint process optimisation in terms of sequencing and programming.
To mould the mirrors from cycloolefin-copolymer (COC), a special transparent thermoplastic, the electric Allrounders of the Alldrive machine series feature injection compression moulding equipment.
A sensor in the mould detects the coining gap and the internal mould pressure during injection compression moulding.
The Selogica machine control system monitors these measurement signals. Near-contour temperature control is implemented in up to 12 individual mould temperature control zones. The sprue is removed immediately in the mould.
After the injection moulding process, a six-axis robot with specially adapted gripper removes the mirrors without bending them and transfers them to a laser station.
Here, each part is marked with its own individual production data, so that it can be identified directly and tracked through production.
This step is in line with the requirements of Industry 4.0.
Next, the mirrors are set down onto a cooling station, where they are cooled from below with ionised air.
This is followed by 100% measurement and vacuum deposition of highly-reflective aluminium on the front side.
The whole process, including packaging, is fully automated and takes place in a cleanroom to prevent contamination from dust particles.
Continental is now producing its third generation of head-up displays. While the first-generation moulded parts still required downstream assembly operations, the optical and mechanical functions are now directly integrated in the current versions.
They can be installed directly in the housing, which enhances production efficiency. HUD development is moving in the direction of larger mirrors, better image quality, integration of assist systems and augmented reality applications.