Text Meinolf Droege ––– Photography
Hidden from view and virtually inaudible, they perform their duties reliably for years. These drive units do the heavy work for you, gently opening and closing the boot lid of your car at the touch of a button or via a proximity sensor. Behind this technology are amazingly complex plastic components that have to meet a raft of requirements – a challenge that is just perfect for LKH Kunststoffwerk.
A global market leader for automotive applications needed excellent mechanical performance in a tight installation space for its electromagnetic spindle drives. This is where LKH came on board as a partner, despite massive competition from Asia. “Which brings us to the point,” says Project Leader Markus Sandmann. “Projects are usually awarded based on price. Nevertheless, we won this project from the international OEM thanks to our attractive overall package. Advantages such as speaking the same language and being in the same time zone were of course a bonus.”
COHERENT COMPLETE PACKAGE DEVELOPED
Materials account for around 50 percent of the product costs in this project. LKH can offer certain cost advantages due to high purchasing volumes for various polyamide grades from different sources. However, there is limited scope for optimisation. Sandmann explains: “In this market, which is both price-sensitive and technically demanding, it is important to work with the customer to develop the optimum service package, from the design of the injection mould through to series production. We can usually work to a tight schedule.”
The feasibility study that LKH proactively carries out as standard before a contract is awarded has proven to be particularly effective at safeguarding the start of series production. This is supplemented by up-front quality planning meetings with the customer to identify key issues. Problems that would typically not be encountered until mould-making or subsequent production operations are systematically identified and dealt with at this stage, reducing the risks in terms of costs and scheduling.
Relatively small design changes helped to deliver significant cost and quality improvements for the two components of the spindle drive. The low runout tolerance of less than 0.1 millimetre over the entire length of the spindle – despite variations in wall thickness – and the part’s high fibre content presented a major challenge.
12-CAVITY MOULD DEVELOPED
Mould design determines a high proportion of process costs. LKH decided to develop 12-cavity hot runner moulds instead of the 8-cavity moulds originally envisaged. These promised the best value for money in terms of mould costs against production outlay over the medium to long term. The aim was to design and build the mould to enable unattended production during “ghost shifts”.
Another challenge was that the spindle drive components required a high-temperature mould with a special cooling system. On top of that, the carbon fibre content in conjunction with the intricate internal and external serration required stringent process control with little margin for error.
To ensure series production started as it should despite the demanding processes in the 12-cavity mould, LKH used the “Design of Experiments” (DoE) statistical method. Stasa QC software from Kistler was used, which helps with selecting the optimum settings so that stable processes and the ideal operating point can be quickly identified.
Mould design and construction also delivered significant potential cost savings for another project associated with the drive for the liftgate. LKH developed a “family mould” for the two components of a connector, which are made from a polyamide 6.6 with 60 percent glass fibre fill and need to meet tight tolerances. The two different components are formed in a single mould and in one shot, but are removed and stored separately. The carefully balanced injection technology ensures consistently high quality and low material stress despite the different weights and high glass fibre content.
Projects like the drive for the liftgate may not have a high profile – given that the components in question are virtually invisible – but they can certainly pose a tough challenge. All the same, even in a globalised market with varying cost structures, fast and cost-effective solutions for precisely this kind of challenge can still be developed right here in Germany.