Flexibility first

Automotive Engineer report, März 2006

 

by William Kimberly

In the new world of make-to-order and faster time-to-market, increased flexibility on the production line is the true test of manufacturing efficiency. William Kimberly went to Germany to find out how BMW does it through “breathing structures”

Along with cost, weight and cost again, one of the principal challenges facing carmakers is time to market. Over the past few years there have been enormous advances in reducing the time from concept to job one, with development and production co-operating from the start of process. Together, they share responsibility for the successful implementation of every vehicle project as well as the quality and reliability of the cars. A further advantage of this close co-operation from an early stage is that each new car can be quickly integrated into the local production process, series production starting smoothly without friction. Virtual tools play an essential part in the development of a new car and its production facilities, with digital data in the vehicle crucial in securing the right layout for production. Leaner production methods have also played a part so that a three- to four-years process has now been reduces to a two- to three-year one, the timescale depending on the car company and how it measures it. Just when it seemed no further big improvements could be made, along comes another solution that is already making an impact on some car companies. BMW has always been at the forefront of lean production methods, although it tends not to shout about them too much as it does not want to give too much away on what it believes to be its competitive edge. Now it has developed what it calls “breathing structures”. This is a slogan that denotes a fast and flexible response to changes in the market and individual customer requirements. An important part of this breathing process is its customer-oriented sales and production process (COSP) that optimises the entire process chain from ordering all the way to the actual delivery of cars and motorcycles, following the specific wishes and preferences of each and every customer.

Across all models

The COSP principle has been applied to all BMW and Mini brand models, shortening the period from this inclusion of a specific model in the production schedule, through the distribution process, all the way to the actual delivery of the car to the dealer in the same country to just 10 days. Prior to the introduction of COSP, the time required for this process was up to 28 days. The online ordering system that was introduced in 1998 enables the dealer to show the customer a “dream car” on the screen and to provide binding confirmation of both production date and time of delivery. Once the order has been made, a slot is immediately reserved in the production process and the production logistics division is informed. A major advantage of this is that it offers customers very high flexibility in modifying the order with changes to the body variant and colour, the engine or equipment available up to just six days before the start of assembly. This not only ensures customer satisfaction even before the start of ownership but also BMW is happy since it usually means a higher level of equipment is specified, with obvious price implications. COSP also guarantees stable processes in logistics and production, not only within the BMW Group, but also with suppliers. It therefore ensures a high level of transparency as well as a stable supply and production process both for internal network partners and for external suppliers. Another important prerequisite for COSP is the standardised process in body construction which has led to a drastic reduction in the number of body variants. While the predecessor to the current 3 Series had up to 100 different floorpans, depending on the engine and the level of equipment, the current model comes with only four different body variants: left-hand drive, right-hand drive, with sliding roof and without sliding roof. The painted bodyshell is then regarded in terms of logistics as an internal component supplied within the company.

Allocating specific numbers

Following the painting process, the car bodies are kept in intermediate storage and fed into assembly as soon as an order comes in for that body. It is not until this point that the car is given a specific customer order. Shifting the process of customisation in this way to the assembly period allows any changes desired by the customer to be made until shortly before the actual start of production. A significant feature in this flexible production is the “all-in-one” main assembly line that includes test and finish areas. The individual assembly operations specific to different customers and involving a large number of body variants are grouped in specific modules and pre-assembled at supply centres and delivered just-in-sequence to the main line in assembly. This not only reduces the sometime large fluctuation of assembly periods on the main line but also allows even more flexible production of several models on the main assembly line. This enables production plants to work even more efficiently and with higher capacity. Over the past few months, the BMW Group, which also includes the Mini plant at BMW Oxford and the Rolls-Royce plant at Goodwood, has gone a step further in implementing its “pull” philosophy rather than the more traditional “push” one. For quite some time it has used the fuzzy logic software tool Qualicision, devised and developed by FLS (Fuzzy Logik Systeme) of Dortmund, Germany in its production process. This is a planning and control program that helps smooth out and balance the flow of cars on an assembly line. For example, it is used to adjust body shop and paint shop operations on a continuous basis to keep their output as far as possible in line with the planned assembly schedule. A permanent and continuous exchange of operation takes place between the control systems and Qualicision´s production control system.

As a planning tool it is used to create the optimum sequence of assembly. This is the stable assembly schedule that is frozen six days ahead of start of assembly which is passed onto the suppliers. “Qualicision is different to other programs by applying analysis techniques as well as algebra and fuzzy set theory,” says Dr Rudolf Felix, managing director of FLS. “It detects conflicts and resolves them in an optimum manner through fuzzy logic compared to the analytical approach normally taken.” FLS has now developed a further refinement of this program with Qualicision-Opti-Zaus. While Qualicison generates the optimal production plan for the flow of cars on an assembly line, the new program devises the “logistical pull” into the storage and supply system. It saves process time and time used on movements by optimising the assignation of storage location and the way racks are filled. It also recognises if there is a problem in the supply system. If, for example, a lane in the storage area becomes blocked for any reason, such as an elevator breaking down, Opti-Zaus instantly re-optimises the access to an identical part or component stored in another place so that there is no disruption to the assembly line. What it does is to re-calculate the filling strategy so that the lane with the defect is circumvented. This ability for dynamic planning is not limited to the operation of one single high stock system, but can also combine two or more that can be switched to a kind of “collaborative” mode. In effect, by increasing the system adaptability, it makes existing and new storage systems more flexible. Another advantage of this new tool, says Felix, is that it avoids additional costs due to disruptions in the storage system while instantly reacting to disruptions of the hardware systems. It leads to a more stable production process by getting closer to the ideal of the “optimal batch” in logistics. “Qualicision-Opti-Zaus seamlessly connects the world of production with the world of logistics,” says Felix. “It increases the complete facility’s efficiency ratio by combining and smoothing both process lines from the storage of parts to the end of the line where the car is finished."