Cable harnesses are among the few parts that still have to be manufactured or processed by hand, especially in automobile production. They are among the first components to be installed in the body-in-white. Due to the high number of variants in today’s vehicles, they are usually manufactured in “quantity 1” – each one is unique. If this centrally important part is not available at the beginning of the assembly of a car, the car cannot be manufactured. When the Ukraine war recently forced several wire harness manufacturers to suspend their operations in Ukraine and the supply of these parts stopped, this failure sent shockwaves through the entire industry – many automotive OEMs had to stop all production because of it.
The wiring harnesses of today’s vehicles are highly complex wiring harnesses weighing up to 60 kg and with a total length of several kilometres. Due to the increasing use of microelectronic assemblies, the cables as well as the connections and plugs are becoming smaller and smaller and manual processing is becoming more and more difficult. The requirements in the field of electric cars or, for example, future developments in self-driving systems will intensify this issue of having to accommodate more and more electronics in as small a space and with as little weight as possible.
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Up to now, the individual cables have been laid on a cable board and bent or plugged together in certain directions. Automation is difficult because previous gripping systems have not been able to grip cables that have not been precisely placed in a bendable manner or to connect plugs. At the same time, more advanced automation would make it easier to quickly relocate a manufacturing operation if necessary.
The pressure for automation in manufacturing is becoming increasingly relevant not only because of the current supply problems: On the one hand, the cable harnesses could be adapted more individually to the respective requirements by a robot system on site. For another, the cable cross-sections, the plugs and the connections have become so small that manual processing is difficult and time-consuming. Quality control, which has so far been carried out optically or by pulling on the cable, is also hardly possible with very small components.
Prof. Dr.-Ing. Bernd Langer and Prof. Dr.-Ing. Martin Kipfmüller have now developed a process for the automated production and assembly of cable harnesses at Karlsruhe University of Applied Sciences. This process will make it possible to use industrial robots flexibly and economically for the production of cable harnesses.
The relationship between force and deformation is clearly defined and linear in the flexurally rigid state. After the bending-resistant state is reached by freezing the cables, they are formed by industrial robots and fixed on laying arrangements, which are characterised by controllable movable and temperature-controlled pins. Cooling can take place in a cooling area or by means of cooling jaws – i.e. a microclimate. Thus, it is conceivable that heating and cooling elements are contained in the gripper of the industrial robot.
The cables are heated locally at the bending point so that the insulation is not irreversibly damaged during deformation. The cable is then immediately cooled again to stabilise the bending. The robot arms can then align the next cable section with predefined force. It is particularly interesting that cables can now also be inserted through connector walls during assembly without snapping off.
The foundations for a prototypical implementation have been laid, and now the focus is on industrial applications.
Through cooling, the process enables automation in the area of cable harness production with a high degree of customer-specific variance and flexibility. The wiring harness can be produced shortly beforehand in the desired finish and is then ready exactly at the time of installation. This means that weeks of delivery time no longer have to be planned, as was previously the case.
This means that the method also fits into manufacturing processes that are to be optimised with regard to lean production. The advantages of the process are a significant reduction in production times as well as better plannability and shortening of the supply chain, as production can be relocated back to industrialised countries due to cost optimisation through automation. According to the Karlsruhe researchers, this in turn also has a positive effect on quality assurance. In addition, the lead time can be reduced because required wiring harnesses do not have to be ordered long in advance.
If the wiring harness can be produced within the production run through automation, the so-called one-piece flow also becomes possible, which in turn increases flexibility.
The process has already been patented. Commercialisation is taking place via Technologie-Lizenz-Büro (TLB) GmbH – it operates on behalf of the university and offers interested parties opportunities to license or purchase the patents.