With sales of folding bikes booming, it has often been tough for Brompton to keep up with demand. But that hasn't stopped incremental improvements being made to Andrew Ritchie's 20-year old design. The all-important hinge has now been upgraded, with 25 of Brompton's in-house jigs redesigned to accommodate the change.

Brompton overhauls hinge; spends £100k on boosting manufacturing capacity

"All the effort and investment to develop and improve our product is driven by our aim to remain the producer of the finest folding bicycle in the world," said Brompton’s marketing manager, Edward Donald.

The new socket braze hinge has double the fatigue life of the existing butt braze. And the design of the new hinge allowed the London-based company to increase the length of the wheel base on the Brompton by 30mm, improving comfort and ride quality.

"With the existing work force and workflow management, Brompton Bicycle Ltd was approaching maximum capacity. The introduction of the new hinge has increased capacity by 10 percent across the company," said Donald.

"The capital investment in design, machinery and training has been high, but the new method for manufacturing and brazing is more cost effective. This improved efficiency is estimated to pay back costs within three years."

The hinge was designed using AutoCAD Mechanical Desktop 6, resulting in two 3D solid models for each side of the hinge. The models were then sent to a rapid prototyping facility, to generate resin models built up from 0.1mm layers, using laser technology. These models could then be sent to the iron foundry to make up aluminium patterns for production castings.

To make the new hinges, Brompton invested in a HAAS VF-1 CNC machine with integrated 4th axis. The castings need to have an accuracy of +/-0.3mm, on 4 axes, including boring, drilling, reaming, tapping and special cutters.

The new CNC fixture is an aluminium cube, holding a hinge on each face, light enough to handle, designed to give access for the different tools and based on a three-pin arrangement for solid positioning.

"The ‘hinge project’ has touched all aspects of the company," said Donald.

"Twenty-five jigs have been redesigned on CAD, over 250 frame parts have been tested, 500 transportation boxes modified, a CNC machine, hydraulic press and shot blaster purchased, all of which has required planning, training and commitment."

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