The surface coating of high-strength lock bolts for use in automobile construction called for the short-term development of a high-performance solution that could handle low annealing temperatures in particular. A zinc flake coating was able to satisfy these and other requirements and, in combination with a black top coat, also enables the premium appearance required.
Gebr. Titgemeyer GmbH & Co KG, Osnabrück, is one of the leading international companies in the field of fastening technology and vehicle components. Its customers include firms in the automotive and railed vehicle industries, vehicle and chassis construction, shipbuilders and the aerospace sector. The focus of collaboration lies upon engineering co-operation with the customer with the aim of achieving best-possible implementation of the respective specifications. In the field of fastening technology the range of products supplied includes blind rivets, threaded components and rapid assembly systems, together with the associated processing technology.
With the new HS lock bolts the company offers a complete system of fastener, tool and assembly equipment, with the fastener already registered for patent. A lock bolt system such as this consists of a fastening collar and a lock pin, with the fastening collar pressed into the grooving surrounding the lock bolt. In the process the components are also tightened using the assembly tool. Once the pretension has been achieved, the protruded end of the lock bolt is removed. The entire procedure takes approximately 1.5 seconds. The tightness of the fastening is comparable to a screwed connection of the same quality. The system also offers key advantages compared to standard welding procedures. As the process is a cold joining one, the disadvantages of an adhesive procedure, such as the risk of heat generation, are avoided.
The lock bolt system is employed, for example, in securing the rails for the height adjuster of car seats. These are safety components that are not permitted to fail, even in the event of a crash. For this reason, amongst others, the automotive industry places particularly high requirements on the stability of the material. The HS lock bolts are therefore produced from steel with a relatively high C content, hardened to a particularly high level in the shearing zone using a special procedure. The aspect of corrosion protection also plays a role in the interior of the vehicle. In this case 72 hours of salt spray testing were required. Also important is the ductility of the coating, as the parts may be moulded in installation. However, what is truly decisive is that the partially inductively hardened steel components are no longer exposed to high temperatures in the coating process in order to avoid loss of stability. As the fasteners are at least partially located in visible areas, a black appearance is also required.
Rapid problem solving
Titgemeyer supplies the standard lock bolt system to Johnson Controls Automotive Experience, a global leader in the field of car seats, roof liner systems, door cladding, instrument panels and electronics for vehicle interiors. The programme includes, for example, modular metal structures for seating systems and various mechanisms for items such as locks, seat rails and height or rest adjusters. In this project the specifications of the OEM with regard to the stability of the rails for the height adjuster and their securing were increased due to a change in the framework conditions, leading to the short-term requirement for presentation of an alternative with higher performance.
In collaboration with Dörken MKS-Systeme GmbH & Co KG a viable solution was developed in just one week. The market leader in the field of zinc flake coating systems created various sample coatings in its Herdecke technology centre, testing them before proposing the use of the zinc flake coating Delta-Tone. The most important criteria in this was that the base coat would be annealed for approximately 30 minutes at a material temperature of below 200°C. This low annealing temperature enables renewed tempering of the hardened peripheral areas of the lock bolt to be avoided.
The required corrosion resistance remains nonetheless. The coating is suitable for all standard application procedures and in this case is applied using the dip-spin procedure. As no hydrogen is involved in the coating process, the risk of hydrogen brittling of the high-strength component as a result of the coating procedure can be safely excluded. The additional organic topcoat with Delta-Seal GZ gives the lock bolt the desired black surface whilst also optimising the sliding properties vital to the closing process.
The close co-operation between coating, fastener and car seat manufacturers meant that it proved possible to present the OEM with a prototype for the new rails for the seat height adjuster in the shortest of times - including secure fastening via the HS lock bolts with new surface coating.
Enter √ at www.engineerlive.com/ede
Dipl-Ing Peter Kalkenings is Head of Product Management Fastening Technology Gebr. Titgemeyer GmbH & Co. KG, Osnabrück, Germany, www.titgemeyer.de, and Dr Gerhard Reusmann is Managing Director, Dörken MKS-Systeme GmbH & Co. KG, Herdecke, Germany, www.doerken-mks.de