Materials manufacturer Covestro relies on a dynamic temperature control solution from technotrans for the production of a highly integrated LED low-beam module including a thermoplastic heat sink.
Pioneering functional concept: At the K 2022 trade fair for plastics and rubber, Covestro Deutschland AG presented the prototype of an innovative LED low-beam module that significantly reduces costs, weight and complexity. The highly integrated manufacturing process consists of two-component injection moulding (2K) and the direct integration of an LED module by means of In-Mould-Electronics (IME). The reflector surface is then metallised in a separate step. This novel 2K low-beam module is the result of a complex development cooperation between Covestro and Lumileds Germany GmbH from Aachen. The fully automated production process was set up together with the injection moulding machine manufacturer Engel and the temperature control unit manufacturer technotrans. One of the central parameters of this process is temperature control: The injection-moulding process is conducted on an Engel SGM system with variotherm mould temperature control from technotrans SE. This is essential for the process, as it ensures the surface quality and therefore the functionality of the reflector by means of precise temperature control.
When it comes to vehicle headlight design, manufacturers are faced with the challenge of, among other things, optimally combining brand identity, aesthetics, performance and safety. At the same time, manufacturers must always keep cost optimisation in mind, as the choice of materials, components and manufacturing processes has a significant influence on the overall costs. A look at the modules commonly used in the automotive industry shows that the optimisation potential is far from exhausted. Nowadays, low-beam headlights with reflectors made of a BMC duromer (Bulk Moulding Compound) in combination with a die-cast aluminium heat sink are often used. The advantages of such systems lie primarily in good and stable light output, due to the extremely low thermal expansion of duromers in active headlight operation. However, the disadvantage is an elaborate production process. For example, the reflector and aluminium heat sink have to be manufactured separately and then assembled with the LED module to form a single unit. Another disadvantage is the rework usually required when processing duromers, such as deburring and cleaning the parts before they can be transferred to the next step. "We have addressed these points to be able to offer headlight manufacturers a cost- and weight-optimised thermoplastic solution with an innovative new concept," says Rainer Protte, Head of Advanced Injection Moulding at Covestro.
Two core questions arose at the beginning of the development process: Firstly, is it possible to back-inject the LED module as part of the injection moulding process without affecting the functionality of the LED? Secondly, can the reflector be moulded onto the heat sink with the appropriate surface finish and precision so that the overall system ultimately meets low-beam requirements? Another challenge was to find a solution that would remain stable in its geometry even under high thermal load. "In a previous project, we had developed our dimensionally stable Makrolon® DS in the form of a 1K reflector specifically for this purpose and proved that we could basically implement a low beam," Protte explains. "The new 2K module is a consistent development with a further integration stage – the connection of the heat sink consisting of our thermally conductive Makrolon® TC including a directly integrated LED."
Dynamic thermal management for injection moulding
Specifically, this development comprises a highly integrative manufacturing process for producing the low-beam module, which consists of only one part and essentially requires only three different materials: Covestro Makrolon® TC and Makrolon® DS polycarbonates, LEDs and aluminium for the required metallisation step. "The combination of these two types of polycarbonate provides the necessary dimensional stability, as they have a lower coefficient of thermal expansion and lower processing shrinkage compared to unfilled polycarbonate," Protte explains. The new process also eliminates the need to manufacture individual components and the tools required for this, as well as rework and assembly steps. Only two production steps are necessary: Two-component injection moulding with IME, i.e. the integration of the LEDs during the injection-moulding process, as well as metallisation of the reflector surface to improve its reflective properties. Thanks to the new concept, this can be done without additional surface preparation after injection moulding.
For this to be possible, temperature control must be optimally matched to the process. "With conventional tempering solutions, highly filled materials, as were used here with the reflector, create a dull, uneven surface due to the filler showing on the surface," says Protte. This is where technotrans' dynamic tempering solution comes into play, helping to achieve the desired glossy, highly reflective surface. The injection-moulding process follows a variothermal mode: First, the mould cavity is heated to glass transition level and higher before injection and then the material is injected. Once the cavity is completely filled with the material, it is cooled to the necessary demoulding temperature so that the part can be removed from the mould - which starts the next cycle. In this regard, precise temperature control is crucial to achieve consistently high-quality mould surface reproduction.
Innovation meets solution competence
technotrans developed a system solution tailored to this process and the associated requirements, with hot-water temperature control in close proximity to the mould. By using a highly efficient energy storage and control unit (ESR) with a flow temperature of up to 200 °C, the technotrans solution enables significant energy savings compared to conventional products. The ESR stores the amount of heat that changes in the course of the cooling and heating cycle and returns it to the process when the temperature level is switched. However, this is not the only component for greater energy efficiency, explains Carsten Schmidt, Sales Manager Temperature Control at technotrans solutions GmbH: "Thanks to the ESR and the use of speed-controlled pumps with an efficiency module (PEM), it has been possible to make the energy-intensive variothermal process more efficient as a whole. Our system operates with the lowest possible energy input at all times." To ensure a high level of operating convenience and flexibility, technotrans also equipped the temperature control solution with a 7-inch multi-touch display and PLC control system that offers the option of programming variothermal process curves.
The thermal management specialist is not only responsible for dynamic temperature control, but also for the remaining temperature control of the master mould. Two units from the technotrans eco.line series – one of the most energy-efficient solutions on the market – are in operation here. These are used in combination with the control-integrated multiple distribution system itd evo and are also equipped with speed-controlled pumps. "Effective thermal management must always be thought of holistically to achieve the greatest possible process stability, precision and efficiency," Schmidt emphasises. The company is making an important contribution to the production of the low-beam module, which not only consists of fewer parts, but is also around 40 percent lighter than conventional units.
A joint project on equal footing
One of the project's success factors was the close and trusted cooperation between the companies. "We have already been working with technotrans for several years and particularly appreciate the joint development in which the company always contributes its technological solution expertise," says Protte. Schmidt iterated that the presentation of the 2K injection moulding process at the technotrans stand during the K 2022 not only underpinned this good cooperation, but also highlighted technotrans' role again as a strong partner in thermal management. "After several joint projects, this innovative concept was a real highlight. We were able to make full use of our expertise and many years of experience and help shape part of tomorrow's automotive manufacturing."