Thermoplastics have been key to enabling the creation of lighter weight, stronger and more durable products of all kinds over the past 50 years. One major facilitator of this growth in the range of possible applications has been continuous innovation in fastener technology
Thermoplastics have become an obvious material consideration in new product development because of the performance, weight and safety advantages they can offer versus other materials. Without the continuous innovation of fasteners, however, the potential of thermoplastics may not have been realised quite so rapidly or extensively.
The rise of thermoplastics
Rewind to the 1970s. It was a decade that saw major advances in manufacturing technology and the increased deployment of computer technology and automation. Social, political and economic pressures were impacting productivity and environmental issues were becoming an increasingly important consideration in any new product design or manufacturing process.
Thermoplastics ticked many boxes but the challenges of how to use them to meet demanding performance standards in an efficient and cost effective way persisted. Rising to the challenge, EJOT developed the PT, a new type of self-tapping screw that would enable direct assembly into thermoplastics with no requirement for metal inserts. It was a tiny component that enabled a massive step forward.
Universal Joining
PT made universal joining of plastics possible for the first time. Prior to its development, whilst there was the opportunity to join plastics together, no one screw serviced the whole range of plastics that were available. Hence, PT offered a pick and mix screw for pick and mix plastics
Dynamically and thermally stressed components could be fastened directly thanks to an innovative flank angle and thread pitch suitable for use with thin walled and flat designs. It made an immediate impact on the market because it offered the potential to deliver material savings and reduced cycle times during injection moulding.
Nearly half a century later, the same basic principles of the PT are still benefiting manufacturers, and that is largely due to the fact that it was created as a continuously evolving fastening platform. This has enabled EJOT’s R&D team to create new screw designs which respond to ever greater performance demands from design engineers, and develop completely new generations of the PT.
New generations
The second generation came with the launch at the dawn of the new millennium of the EJOT DELTA PT. This extended the capabilities of the PT screw by incorporating a special thread forming zone which makes it suitable for use with thermoset plastics too. The thread geometry was optimised through a well-balanced ratio of the highest possible pre-tensioning force and small contact pressure on the plastic to ensure DELTA PT would offer a secure joint, even under difficult conditions and in challenging designs.
Further innovation came in the way EJOT supported engineers to deploy the DELTA PT. As technology was playing a more significant role at concept stage, EJOT created the DELTA CALC prognosis program which would give designers the parameters for the screw’s applications according to the material and pre-hole dimension. It was a tool that immediately helped customers to save valuable time during the design phase.
Whilst the PT and DELTA PT continue to provide effective jointing solutions to customer challenges across the world, the performance bar continues to be raised. For this reason, fastener evolution has continued in parallel. And with fastener costs amounting to only around 20% of the total joint cost, meaning that the system costs make up the remaining 80%, there is significant scope for further development of screw design.
Hence the latest generation of the PT, the EVO PT. This enables system costs to be reduced with the benefits of higher efficiency and greater productivity. It is a fastening solution which successfully integrates manufacturing and application knowledge with new methods based on computer simulations into the development process. The result of this cross-disciplinary approach is a screw with excellent connection properties.
EVO PT features a forming thread that creates a torque curve during the installation phase, almost independently of the screw-in depth. As a result, a uniform tightening torque can be used in the production at different screw lengths. A special lead-in feature of the screw creates a uniform load on the thread flanks when completely fastened, thanks to its automatic centring in the pilot hole during the installation.
Supported by software
Like the DELTA PT, EVO PT is supported by a digital calculation service in the form of EJOT EVO CALC. With this software tool, EJOT is able to offer a prediction of the torques and preload forces according to component requirements, aided by individual FEM-supported component optimisation, which can result in valuable time and cost savings in the design phase.
All three generations of the PT screw continue to offer design engineers a solution for thermoplastics that is supporting product and process innovation in many industries around the world. It is an excellent example of how important fastener innovation has been in enabling change, and the next generation of the PT, as well as other advanced screw designs, will undoubtedly play a key role in overcoming as yet unknown design challenges.
Dan Lunn is an Application Engineer at Ejot UK
