At the same time, however, the requirements for preload forces and the reliability of the connections are increasing. And the lowest possible overall connection costs are also important. A new thread-forming screw for direct metal fastening has been developed to meet precisely these challenges.

Arnold Umformtechnik spent more than three years in an intensive development process designing, optimizing and adapting the “Powertite” to meet requirements always with a view to specific applications. It was presented to the public for the first time at the end of June 2024 at the Industrial Screwdriving Assembly Workshop in Dresden.

 “We used the development time to take on board all of our customers' suggestions and implement them in the best possible way,” says Thomas Jakob, Application Sales Engineer. The product, which has already been patented, is now set to be launched on the market in October.

 Potential customers will then be able to draw on the complex product knowledge of the Forchtenberg-based fastener manufacturer in the usual way, as well as a comprehensive understanding of the product's performance in the various applications and application areas. This is complemented by the corresponding calculation tools and extensive manufacturing expertise. Arnold Umformtechnik has developed a completely new manufacturing process specifically for Powertite in collaboration with development partners from the tool manufacturing sector.

Light metal screw connections

 With light metal screw connections, the focus is on optimizing installation space, performance compression and cost optimization. A very important point against this background is the load-bearing capacity optimization of the connection. With regard to thread-grooving metal screw connections or light metal screw connections, this means that better utilization of the nut material must be achieved through a higher thread overlap of the thread flanks of the screw and grooved nut thread.

“The thread-grooving Powertite is characterized by a higher load-bearing capacity of the screw itself compared to conventional products on the market. Thanks to a slightly increased stress cross-section, which corresponds to the level of the standardized stress cross-section of a metric screw, the Powertite can generate higher tensile breaking forces,” explains Thomas Jakob.

 Thanks to the special geometry of the fastener, relatively high assembly preload forces can be achieved during screw assembly in conjunction with adapted surface systems. These are generally on a par with metric screws, both for elastic and overelastic assembly.

Geometry plays a decisive role in the function of the fastener

The Powertite screw is a round thread-forming screw with a trilobular forming zone. This means that where the forming work is carried out, the screw has a slightly triangular cross-section (with rounded corners) to reduce the forming torque. The forming zone length is optimized with a length of 3 x p (p = thread pitch) installation space and enables the forming work to be distributed over several threads during the thread forming process as well as optimum positioning and centring of the screw. The round load-bearing cross-section has a defined oversize; the outer diameter of the screw is always larger than the nominal dimension. This ensures greater overlap between the thread flanks of the screw and the grooved nut thread.

 Basically, this special geometry ensures that the screw achieves a higher stress cross-section and therefore slightly higher tensile breaking forces than conventional metric screws. The combination of trilobular cross-section in the grooving zone and round cross-section in the load-bearing area significantly optimizes thread-grooving screw connections because, on the one hand, the grooving torques are low and, on the other hand, the overtorques and load-bearing capacity of the grooved nut thread are significantly increased.

The focus of Powertite applications is on electromobility in particular. It offers great potential, from the battery area to the engine and axle steering area as well as the transmission. This applies in particular to light metal screw connections, but also in combination with cast components.

Calculation of weight and CO2 savings

Powertite thread-forming is a fundamental further development of thread-forming technology. By replacing conventional M8x40 thread-rolling screws (nominal diameter x length) with M7x40 screws from the Powertite series, significant CO2 savings can be achieved. This is demonstrated by two specific examples.

 Since June 2022, the Powertite M7x40 has been used in a load transfer gearbox, which is currently still used in conjunction with a combustion engine. This alone can achieve a weight saving of around 42 g per gearbox and therefore a CO2 saving of around 72 g per gearbox. With 13 screws per gearbox and a requirement of around 6 million screws per year, this results in a weight saving of around 19,400 kg or a CO2 reduction of 33.1 tons per year for this gearbox alone.

 The savings are even greater for an electric motor gearbox unit, in which 33 screws are used per gearbox unit. Of the 50,000 vehicles planned per year, 30,000 are expected to be equipped with two e-motor transmission units per car. In this case, the weight saving through the use of Powertite is around 213 g per vehicle and the CO2 saving is around 364 g. Extrapolated to all 50,000 vehicles and the 80,000 gearboxes required, this results in a total requirement of around 2.64 million screws per year. The use of Powertite alone can then achieve a weight saving of around 8,519 kg or a CO2 reduction of 33.1 tons per year in the production of these vehicles. This means a CO2 saving of 17% per vehicle for the fasteners replaced by Powertite.

Info

The ARNOLD GROUP, internationally renowned for innovative fastening technology, has developed into a leading supplier and development partner for complex fastening systems thanks to its extensive expertise in the production of intelligent fasteners. Under the umbrella of “BlueFastening Systems”, the company positions itself as a comprehensive provider of engineering, fasteners, functional parts, feeding systems and processing technology. This holistic combination of experience and know-how offers efficient, sustainable solutions on an international level. Arnold has been part of the Würth Group since 1994.

www.arnold-fastening.com