BMW’s Mini plant in Oxford is receiving the bulk of a 2012-2015 spend of GBP750m – also shared with the pressings factory in Swindon and engine facility at Hams Hall – primarily to produce the redesigned hatchback and Clubman versions.
Countryman and Paceman models are contracted out to Magna Steyr in Austria and there is also some kit assembly of those models in India and Malaysia. What models will be built at the former Mitsubishi/Nedcar plant in the Netherlands has not been announced.
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Meanwhile, the one-time Pressed Steel plant at Cowley (the original Morris works is long gone, replaced by commercial redevelopment) which BMW bills as Plant Oxford, has received a new body shop and upgrades to quality processes and the paint shop.
Plant Swindon – also a former Pressed Steel factory – has introduced three new body manufacturing tricks and generally improved productivity.
Pressings
Tactile laser welding is used to make the bonnet from eight pressed parts. The bonnet’s outer panel is bent to touch the mating flange on the inner panel and joining uses a fine weld wire on the laser. Panels were previously roller-hemmed together with adhesive and seam sealer but there was always the possibility of a void forming that could allow condensation to develop.
A remote laser can produce long continuous joints of greater precision, a process quicker than spot welding and a group first.
Up to five different door designs can now be produced in the same production cell by the same set of robots using a new fixture holding system. A new linear change system for switching the tooling from one model to another has also increased efficiency.
Body
At Oxford 1,000 new robots – with a new, power caving sleep mode – work in a new 100,000 sq m body shop, now arranged around three framing stages rather than the usual two, to boost flexibility. BMW’s flexible platform requires a higher number of smaller panels than before so more spot welds are needed – between 4,000 and 6,000. Up to eight robots work on a single body simultaneously, on three levels. Assembly is measured using perceptron cameras accurate to 0.05mm across 502 points at five stations.
BMW claims the new shop is unusual for its single common finished process line, rather than two identical lines in parallel, and claims more consistent quality and greater efficiency.
The shop also has 1,000 grippers for tool changes and panel handling with enough intelligence allowing them to pick components from a part-empty box.
Paint
A new seam sealing system automatically protects against water entry with a flexible mastic material applied by 12 robots. Automation ensures that the application of the mastic is performed to a consistently high quality and with less material waste.
The previous electrocoat system with three stage bath has been replaced by 12 stages catering for the different shapes of each body variant.
Automation has also been introduced to the application of top coat to the door, tailgate and bonnet openings, ensuring a consistently high standard and less paint wastage. Productivity also improves with the introduction of the nine robots that perform these tasks while the energy efficiency of the paint shop has also been improved by the introduction of a new oven temperature control system requiring less gas.
Robots inject two chemicals into the new double skin front bulkhead which combine to form a foam that rapidly expands into the available space.
Quality
Quality and engineering tools now include a geometric optical measurement cell with 8m megapixel cameras with an aluminium master buck built to a tolerance of one fifth of a millimetre as a reference point.
Assembly
Height-adjustable skillets on two production lines ease the assembly process and 44 automated guided vehicles (AGVs) carry pre-assembled cockpits to the line. Of six new robots in the glass fit cell, two have cameras to identify derivatives and sunroof installation is now fully automated. Cameras help with engine installation.
