Re-design and Additive Manufacturing (AM) of Cab Handsets

Overview

We worked for Transport for London (TfL) on a Proof of Concept to re-engineer a cab handset for the S-stock fleet of London Underground trains; a complex multi-part assembly that was repeatedly breaking. We modified the design to remove the common failure mode, making it stronger and better suited for the environment. Manufactured using SLS (Selective Laser Sintering) technology with PA12 Nylon material then dyed black and chemically smoothed, the final revised part was very well received, demonstrating increased strength, reduced costs and allowing manufacturing on demand.

This demonstrates that parts can be designed to meet requirements, rather than be limited by specific, or traditional, manufacturing methods.

Work Undertaken by DB ESG

• London Underground provided DB ESG with original handset assemblies; including all internal components, the handset cradle and information about the failures that they kept experiencing with the handsets. The parts were 3D scanned and then converted into a CAD model.
• The CAD model was further developed by DB ESG to incorporate design changes that would make the handset stronger; including a thickened back shell and walls, and a stronger spring clip. The design was also refined for production by AM. All design changes were approved by TfL.
• DB ESG provided TfL with a list of possible materials and finishing methods, together with the different fire performances and surface textures to allow them to determine the best manufacturing option. These materials included SLS (Selective Laser Sintering), FR (Flame-Retardant) Nylon and PA12 Nylon FDM (Fused Deposition Modelling), Ultem™ 9085 Black and Clariant FR (Flame-Retardant) Nylon. The finishing options included dyeing, painting, chemical smoothing and manual post processing. A structural and materials assessment was completed, together with any design changes mandated by the manufacturing method.
• On completion of the design work, DB ESG provided an assurance document that included a fire and structural performance assessment as well as a risk assessment.
• Once the design was approved by TfL, DB ESG had three prototype handsets produced, which were sent to TfL for assessment.
• After this assessment, the handsets were returned to DB ESG for inspection, together with feedback from TfL engineers and operators.
• The design was refined based on the trial results and the final handsets were manufactured using SLS technology with PA12 Nylon material then dyed black and chemically smoothed. These were quality inspected before dispatching to TfL.