When demand for the brand grew at an extraordinary pace Mini could have been a victim of its own success, but intelligent production management and an enthusiastic workforce have managed to maintan quality

The Mini production triangle covers the Swindon Pressings operation, the Hams Hall engine plant and the Oxford BIW, paintshop and assembly plant. While these operations are separated by a total of 127 miles (200km) they are united by a remarkable dedication to maintaining BMW levels of quality under the pressure of extraordinary demand.

At Plant Oxford, even the buildings have had to respond to the doubling of orders; the three original halls have been merged into one to help smooth production flow, what is called a major ‘flex re-think’.

This will further help to manage the ever-expanding range that now includes the new Coupe, Clubman, Cabriolet and the forthcoming Roadster, and original Hatch. The only Mini model not produced at Oxford is the Countryman; built at Magna Steyr’s Graz, Austria plant, it is based on a unique platform that could not be easily integrated into the lines at Oxford.

Flexible thinking

Part of the system for handling so many variants, which includes 750 combinations of colour and LHD/ RHD in the painted body stage alone, has led to a remarkable change in the vehicle production management system.

Instead of the traditional ‘broadcast sheet’ being assigned to each BIW at the framing stage of production, Mini bodies remain ‘unidentified’ until they enter the assembly hall, where they receive their VIN (vehicle identification number) marking. Prior to this, they are identified by an RFID tag and later, a metal tag is fixed to one of two front and rear ‘paint bars’ – lighter and simpler alternatives to the traditional skid. Nigel Dickens, Production Group Leader explains how the bodyshop lines came into being: “The planning of the lines was carried out by the overall planning department in Munich, to [BMW] group-wide standards and production process methods.” Mezzanine levels are used to ease the space pressures on the ground floor areas. The ground level extensively uses robots to move parts within cells. Conveyors move front-end, floor and bodyside pressings into position for the framing stations.

Body-in-white starts from the front of each vehicle; this is the datum assembly from which the whole car takes its measurements. In total, 108 robots work on the front-end assembly over 12 operations. A Perceptron measuring cell checks the accuracy of every front end assembly, after which these are transported upstairs to a mezzanine level for distribution to dedicated framing stations serving each of the various models.

Each has an RFID tag to direct them to the correct station and the tag remains as the ID carrier until the body is finished and an IGEF serial number is stamped on one suspension turret; the VIN is engraved on the other turret in assembly. As well as traditional spot welding, there are several manual MIG weld stations, where roof panels are joined to the A-pillars – accessibility issues make re-spot impossible in these areas.

Closing the doors

After passing through a Perceptron laser measurement station, the bodies are then ready for their closures. In a dramatic departure from the traditional, doors are ‘offered up’ by robots, using the measurements relayed from the previous station. The robots move the closures around until they find the correct position, after which the hinges are welded to the door and body. As Nigel Dickens says: “Once those welds are done, that is the position of the doors no matter what, the doors are removed by pushing out the hinge pins but they will always go back in the same place, there is no further adjustment necessary.”

Bonnets and front wings are bolted on automatically using the same datum system but tailgates, boot lids, and the rear side door of the Clubman are fitted by hand.

Stores and doors – final assembly

After paintshop, a detailed review of which is included in Automotive Paintshop Solutions magazine, bodies are moved to the Painted Body Storage area, where careful production planning is needed as the store has capacity for just 600 bodies. Doors are removed and dressed on an upper floor before they are returned for glass fitting, carried out by teams using reference templates that also add window and door sealants.

These operators are managed and paid by the BIW unit, giving them a ‘through production’ responsibility for seeing their bodyshop creations achieve correct fit in assembly. All painted bodies pass through a ‘roof tunnel’ where cars requiring roof bars are automatically identified and a high-speed laser cuts the necessary holes through the painted metal before bodies continue on to trim and final. Customisation has really caught on with Mini buyers.

To carry out accurate applications of roof decals, Mini engineers have devised an ingenious yet logical solution. Cars requiring such extras are driven onto a ramp-type rig that tilts the car towards a gantry. This allows the operator to apply the decals accurately and in a safer and more ergonomically-efficient way than by standing on a ladder or platform and stretching over the roof.

Interview: Dr. Jürgen Hedrich

Jürgen Hedrich is Managing Director of Production for Mini. In addition to overseeing operations at Oxford, he is also in charge of Swindon Pressings, which manufactures all panels for Mini, including doors and bonnets, which essentially makes the facility a combined press and body shop. Additionally, he is in charge of Hams Hall, which produces the ‘Prince’ range of petrol engines in a joint venture with PSA.

Mini can be considered one of the great success stories of modern European auto manufacturing with output rising from an initial production forecast of 120,000 cars per year to an annual figure of almost 240,000 units after six years. How can BMW effectively and economically produce cars in the UK when many other OEMs are moving to areas offering labour costs and - some might say - more efficient practices?

As it turns out, Hedrich is quite the evangelist for the British workforce: “As the Mini is such an iconic brand, there was no doubt that BMW would decide to produce the cars here. There was no actual ‘strategic’ decision necessary on where to establish production.

The key issues are not the UK union situation or goverment legislation; it is the supply base that has ‘hollowed out’ over the last 15-20 years. The suppliers which remain here are vital and they support us really well.” Hedrich continues: “At the part number level, the proportion of parts sourced in the UK is relatively low. It is the large parts and modules, due to the logistics considerations, that remain in the UK. These tend to be more expensive and, as a result the Tier One spend in the UK is still significant. The key point however is that much of the value is added in the subcomponents and most of that takes place in the Tier Two areas outside the UK.” With regards to labour relations, Hedrich is confident, and happy with the Mini team: “We have a really good relationship with our workforce and their shop stewards [union representatives]. I don’t know if we work differently to other OEMs in the UK.”

Apprenticeships and meisters

In Germany, technical education is often put forward as the benchmark of vocational training, a model followed by many countries. With that in mind, Hedrich is impressed with the UK labour drafted in to cope with the massively increased production levels. “The skill level is different to what you would find in Germany, we are working with the NVQ (UK National Vocation Qualification) system and our objective is to bring in more people with NVQ Level 2 at the operator level. We can then further develop our people internally, and with external education and training. In leadership positions, the traditional German ‘meister’ qualification just does not exist here.

“My team leader role model is a ‘small plant leader’, responsible for delivering product from his section, training his teams and maintaining equipment in his area.” Hedrich is keen to create this role: “We really want to standardise this model, not only giving the team leaders more responsibility, but more power and more resources to acquire staff and equipment for their unit.”

As such, what specific educational programmes is the company involved in, both inside the plant and at local colleges? Hedrich: “We take 30 to 40 apprentices each year, they are working here and we are working closely with local colleges to help them understand what we want from our people. We have run this model since we started the plant. Leadership training is more specifically BMW-aligned in its thinking; we use external companies to help with training. This is for what we call ‘Group Leader’ level positions and upwards.”

Shift patterns for shifting demand

The BMW system of ‘time banking’, where employees use accrued hours that they have built up in addition to their contractual term for holiday during slower production periods is very effective in giving both operators and the employer added flexibility. Has the system proved popular with the British workforce? Hedrich confirms he was pleased to find out that the system has been well-accepted at the Oxford plant: “When there is a longer shutdown, we can give the workforce the time off, using time they have built up during the very busy uptimes. At the moment people are a little bit ‘under’, they have some time banked that they can take off, but we are quite well balanced.”

There is an agreed suite of shift models that allow for between 80 and 130 hours per week. Plant Oxford is currently working 9.25 hour shifts (two in every 24 hours), which then allows for night-time and weekend (Saturday and Sunday) maintenance work.

New models, growing demand

With demand for Mini vehicles increasing with the introduction of each new model, will Hedrich look to outsource more production, as in the case of the Countryman, or does the rapid ramp-up of the new Coupe model show that Oxford will be able to handle more volume and variation in the future? “With the mainly shared architecture and the commonality of parts, we can cope with more volume and variation in the future. Countryman is of course different, as it has a different platform. If we tried to integrate its production here, it would be more a case of adding it to the line, with many line modifications, rather than actually integrating it.” Overall, Hedrich is impressed with the quality of Countryman production: “[Magna Steyr] really is a great partner, they showed [BMW] that they could do a great job when they set up and produced the X3 so well.”

Would Oxford offer adequate space for the seemingly constant range and continued volume growth, bearing in mind that the new bodyshop will take up quite a large area? “We are looking at up to 260,000 units per year in the long term. This is an educated guess based on what we are capable of with a higher shift model after we have integrated the new bodyshop and swapped over from existing BIW to the new shop.”

While Oxford may have the capacity, the age of the equipment at Swindon and the fairly old premises might identify the pressing operation as the weak link in a higher-capacity future, but Hedrich is confident about the stamping plant. “We have spent and will spend a lot more of our £500 million ($800m) investment on building refurbishments and new equipment at Swindon.

We are moving a complete press line over from Munich to help us meet capacity and this means we have no plans to outsource any body parts, closures, etc. Also, we have an extremely motivated and efficient workforce at Swindon, a lot of really experienced and highly-skilled guys.”

Automation levels stable

While customer perception views the Mini as a thoroughly modern car, it is built using several manual weld operations in BIW. This is due to the car’s design, which makes some sections inaccessible for robot weld guns, so manual MIG welding is used in these areas. Hedrich: “The automation level in the bodyshop is comparable with other plants in the BMW Group. All spot welding is done by robots; we recently implemented a highly-automated line to fit the doors, bonnet and fenders in a so-called ‘best fit’ process, which means there is always a best match between the hangon parts and the specific body. In this line the MIG welding process is also automated and done by robots.

“Looking to the future, we will implement an ‘adaptive welding process’, which ensures an automated adjustment of the welding parameters and causes fewer sparks, for all spot welding cells. We have implemented this in a dedicated testing cell already, and it will be the new standard for the new body shop.”

Parallel lines

Although the new bodyshop structure is now under construction, Hedrich refuses to be drawn on the exact timeline – with this in mind, where would the previouslyannounced £500 million investment be targeted? “The main big expenditure will be on new buildings, and of course the bodyshop.

“This will be an online system with a ‘fish bone’ shapedesigned by the central BMW planning engineers as a standard BMW type of bodyshop, maybe a bit more compact and customised towards the specific needs of the Mini.” The company plans to run parallel lines for special models, the present convertible and coupe line alongside the new bodyshop as the new shop ramps up. It is planned that the new shop will be able to deal with foreseeable demand, benefiting from a sophisticated system of buffers at various stages of process completion.

As for incorporation of future Mini variants with a longer or wider wheelbase like the Countryman, Hedrich says the line will have that flexibility. “The one-line system is needed to give us the flexibility for taking something bigger or very different in the range of future vehicles, and it is planned to go up to 260,000 units per year.”

Exporting expertise

In terms of process sharing, has Mini delivered anything new to its parent company, particularly the integrated primerless paint and the automated door fitting system? “The primerless paint process uses up to 20% less paint depending on colour. We [BMW] are using it in America now, and there are plans to start using it in Germany soon. Other things we are very proud of include the ‘roof ’ laser, where all the fully-painted cars go through a laser ‘tunnel’ and the ones that require holes in the roof for luggage bars are automatically identified and the holes are cut by a high speed laser.”

One of the main areas that is very specific to Mini is in the management of the enormous variety of models and specifications. There 750 body and colour combinations, before powertrain or trim is considered. Mini management has taken some variants out of the mix, but this has been countered by the introduction of the Coupe model.

Hedrich points out why painted body sequence and expert management of the assembly-ready shells is vital: “As the VIN stamp is not put onto the body until assembly starts, the car does not become a customer car until this point. There are six days of lead time between the order coming into the system and the car leaving the plant. So you must have really efficient order across body-in-white and painted body volume and supplier management. If the right painted body variant is not available, all JIT sequenced parts have to go into backlog.”

Individuality across the range

Out of all the elements that have come together to create the Mini production setup, which has made Hedrich the most proud? “To go from 120,000 to 240,000 cars per year with all the individuality ‘embedded’ in every car; using one plant for almost all of the production; the flexibility of the workforce responding to market demand on one hand but also their ability and enthusiasm to accommodate all the variants. The new Coupe is a good example of this. We brought the car to market in record time, on time with every part of the ramp-up.”

The success of the Mini operation is also remarkable when considering its extended planning history, which involved BMW helping Rover to relocate production of the Rover 75 from Oxford to Longbridge before installation of the Mini line. Hedrich sums up a great success story: “We not only got the car out on time but also we ‘harmonised’ more and more of the production process, some of it grew organically but much was carefully planned. I am delighted with the way it has all turned out.”

MINI metrology matters

BMW Swindon employs a range of non-contact measuring systems for three-dimensional co-ordinate measurement and deformation analysis, including three ATOS 3D CMMs delivered by GOM, which are used for panel shape and dimension inspection covering form, trim and springback.

While the toolroom runs a mobile, manually-operated ATOS system, the metrology department has set up two robotic measuring cells for automated inspection of sheet metal parts. These 3D systems are also used in the Tool and Die shop, where they can scan tooling to help fi x or replace damaged tools. Using the 3D surface scan data, representative tooling is reverse-engineered using the CAD data to ensure it is representative of the original, enabling a CNC-copy of the tool to be produced without having to go through a full try-out phase.

AMS visited the Metrology department at Mini and spoke with Kevin Titcombe, Geometry Tech Manager/Quality Manager and Nick Horwat, Geometry Technician, about the advantages of optical metrology in terms of the reduced measuring times and how this can still provide full-fi eld data – using this technology, parts can be inspected up to six times faster than with CMMs using tactile solutions. Additionally, the full surface data offers other important advantages. Since it allows a deviation colour plot-to-CAD data, reading the results is that much easier to interpret. Where warm colours present excess material and cold colours show less material, it is easy to understand bend, springback, dents, and other part deformations.

Sharing the information has also become a lot easier as hundreds of spread sheet pages have been reduced to two pages with images and data covering important assembly points. Many tool makers (EBZ, KUKA, TK, Batz, etc.) supplying tools to BMW Swindon are using GOMs optical metrology to keep pace with their OEM customers’ requirements and Kevin Titcombe expects the rest to follow suit in the near future. He and Horwat further cover how the VMR (Virtual Measuring Room) is used as part of GOM´s professional ATOS and GOM Inspect software packages.

Besides implementing measurement plans, CAD data of parts, fixtures, walls, light fences, and sensors with measuring volume etc., it also allows data to be imported to almost any type of robot, including kinematics. Thus the programming can be done offline, without using the robot control panel, by simply moving the robot within the software or simply clicking on an object’s surface. The robot, with the sensor on top, will automatically find the best position to measure the respective inspection feature (surface, hole or trim).

After a short offline/online control of the automated measuring system, the program is ready to start. The VMR has speeded up inspection procedures at BMW Swindon, just in time to help with the Roadster project. “For this project we had an extremely narrow time frame, only three days for some parts. Without the VMR, we would not have been able to meet these conditions,” states Titcombe.