New generation of thread forming screws for light alloy
03 February 2015
In modern assembly lines cost saving and component optimisation are decisive competitive factors. EJOT® states that by omitting production steps such as drilling, thread cutting, cleaning – as well as optimisation in the field of tooling, warehousing and shorter cycle times – the total costs of a screw joint can be reduced by up to 30% with the use of a thread forming screw. For that reason thread forming in light metal will become more and more important for the market, especially with challenging designs.
In order to fulfil these increased technical demands for joints of high strength and dynamically loaded light metal components, EJOT® has optimised the ALtracs® screw. The objective of this improvement was to obtain a self-tapping fastener, with assembly parameters similar to a conventional metric 10.9 machine screw. The metric compatibility of the new EJOT ALtracs® Plus is still guaranteed.
The metric pitch and the specific 33° thread flank of the ALtracs® Plus leaves a larger thread root in the ‘weaker’ female thread of the light alloy. This geometry allows a higher loading of every single turn of thread and the new design of the fastener reaches the failure criterion screw fracture at clearly shorter insertion depths.
Lower installation and higher stripping torques offer a larger margin for the safe assembly with common pneumatic and electric screwdrivers. The circular cross section, in combination with various installation depths (1mm to 2.5mm x d), enables a high amount of flexibility in the choice of the appropriate fastening system. The use of other, for example torque/rotation angle controlled fastening methods, is also unproblematic. The even load distribution on the circular screw cross section of the new ALtracs® Plus promotes a high retention of the clamp load – even under thermal and dynamic stress.
Compared to self-tapping screws with a 60° flank angle, the ALtracs Plus screw’s low damage displacement of the light metal enables a low installation torque. This is realised with an optimised screw point design. The thread flanks in the screw point are smaller in diameter just like the previous ALtracs geometry, but the ‘Plus’ is also tapered to the front. EJOT® explains that this way the first threads can enter the female material much easier. This produces an improved ‘start’ to thread forming and a centred alignment, even in cast holes with handheld assembly tools.
The new ALtracs Plus also offers additional safety in the assembly process because of multiple repeat assemblies. In case of repair, a metric screw is completely interchangeable and can be fastened into the tapped hole.
