BMW gives customer orders top priority and brings in fuzzy logic to help

World Automotive Manufacturing, March 2003

BMW gives customer orders top priority and brings in fuzzy logic to help

 

by Anna Kochan

BMW is revolutionising the way it schedules ist assembly lines by using a combination of clever mathematics and fuzzy logic. designed to give total stability of the final assembly sequenz despite the thousands of late changes customers make to the order specifications they have chosen, the nex system is to be progressively applied throughout BMW assembly plants. Anna Kochan reports

In a typical month, BMW's customers request 120,000 changes to the vehicle that they specified when they placed their order. On average, that is more than one change per order. It is a planner's nightmare. To add to the challenge, there are the inevitable disruptions to the schedule arising from incidents such as suppliers goods arriving damaged or specific parts just being unavailable. In an attempt to streamline the customer ordering and vehicle assembly processes, BMW has started implementing a new initiative that it has termed 'customer-oriented sales and production'. The initiative has several aims. BMW is stiving not only to deliver customers their chosen vehicle with a minimum dely, but also to offer them the chance to change specifications as late as possible in the production cycle without the slightest disruption or incident.

In practice, the new customer-oriented approach implies wide-ranging changes to the sales and production processes. Until recently, BMW associated a particular customer order with a specific car body at the moment that the body panels started to be assembled in the body shop. Now, with the new approach, the early body assembly and paint stages of car prduction follow a sequence that is termed 'virtual'. This virtual sequence is esentially a guideline. The body and paint shops make every effort to adhere to it but the probability is that, when the painted body moves onto the final assembly lline, the sequence is a different one. With the new initiative, it is at the moment that the painted body shop starts moving down the final assembly line that it becomes firmly associated with a specific customer order. The bodies then progress down the line in a fixed sequence that BMW has determined six days earlier. This is what is most important for a stable assembly process. The fixed sequence is frozen. customers can make changes up to six days before start of final assembly but not later. These six days constitute the time that BMW considers necessary for suppliers to make the exact right parts available at the assembly line with unfailing accuracy. To create the firm schedule, BMW was forced to look for new planning software. The main challenge is to convert the virtual sequence into a fixed sequence by taking into account incidents that have occurred during body assembly and paint processes. The existing planning tools could not support the new strategy, says Johann Köppl, group logistics director, customer process and IT. "We needed a more flexible software, one that would enable us to allocate the customer order to the body shell in the most flexible manner."

The tool that Köppl and his team selected for the application is based on Qualicision, the product of a small German company FLS. The first full implementation is at Dingolfing an was introduced with the launch of the 7-series in 2001. As new models are introduced in the coming years, in BMW plants in Germany, the US, the UK and South Africa, their launches too will be accompanied by the implementation of Qualicision for planning. According to Köppl, it is critical to introduce the new planning procedure alongside a model launch. "Firstly, in the new supplier contracts that we negotiate for a launch we can include the supply conditions relating to six-day frozen schedule. And we have to ensure that the supplier is flexible enough to handle the last-minute specification changes. Secondly, we are progressively designing our models to use a significantly smaller number of body shells. This simplifies the sequencing task," he comments. With the 7-series, the number of bodyshell variants has been cut from around 100 to just 8, Köppl reports. BMW uses Qualicision in two main roles. In one instance it plays a controlling role, In the other, it is mainly planning.

As a control tool, Qualicision 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. The software is in permanent operation, and a continuous exchange of information takes place between the machine control systems and the Qualicision production control system. As Köppl explains, "in the body shop, parts are joined together to make small-assemblies. At a number of points in the process, there are decision cross-roads where the sub-assembly changes form being a general sub-assembly to being more model-specific.

Via its continuous exchange of information with the machine control system, the Qualicision software is able to monitor production, in terms of bodyshell variants and colours, and to compare the actual output with the planned schedule. If the software identifies that not enough of a specific body variant is in the output then it can intervene directly in the production control process and automatically send a signal to increase production of a particular variant."

In its planning role, the Qualicision software is a tool that BMW uses on a daily basis to create the optimum sequence of assembly. This is the stable assembly. And it is the schedule that is passed onto suppliers and which they us to plan their own internal processes.

Starting from a list of vehicle specifications and their delivery dates, BMW has to create a smooth schedule for each day of production. Navigation systems, for example, are a sophisticated optional extra that take time for the operator to fit and have to be spread out. A smooth schedule is one that not only meets the criteria for a balanced assembly line from the vehicle manufacturer's point of view. Other criteria also have to be taken into account, those of Tier One suppliers, for example. According to Köppl, the optimum supply conditions for many Tier Ones is to create an even distribution throughout the day of vehicles with specific equipment. It gives them an even workload. since the build schedule is used to derive schedules for the paint and body shops, colour grouping is another factor. In total around 100 criteria have to be respected to achieve an optimum schedule.

Qualicision is the core of the optimisation module. It comes with a graphical user interface for defining the criteria to be used in the decision-making process. Although most of the criteria are stable, there is a continuous process of adjustment. "Combinations of variants can bring in other criteria. So every day, the criteria have to get re-interpreted," says Köppl.

The sequencing process is done under the supervision of a specialist planner. It is a job that maybe takes two or three hours a day, not longer. In this time, the planner may want to try out a number of different scheduling criteria According to Köppl, it takes just two or three minutes to run the scheduling process. For any one day of production, the planner may run the process five to ten times until he is satisfied that he has achieved the best schedule possible for the mix of orders that are to be produced on the day concerned. The output of the scheduling process is a printout showing a sequence of lines, each line representing an order. Any order that does not meet the criteria are shown in red; the others in black. "As long as there are no more than five ton ten criteria violations in one day's schedule, about 1,000 cars, that is acceptable. the schedule is then optimised and fixed. The goal is not to change it at a later time.

Being able to fix the schedule at such a late date so that customer changes can be accommodated until the last possible moment is an achievement that places BMW ahead of its competitors, claims Köppl. !Other OEMs can't do it," he says. In the best possible case, BMW's re-engineered car production process provides a delivery time of just ten days. As a result of implementing the 'customer-oriented sales and production' process, the dealer taking a customer order can use the online ordering process to check available production capacity and see if there is a slot in the production schedule that he can reserve for the customer's vehicle. While it may be possible to quote a 10-day delivery at this time, in the majority of cases delays will be longer. The BMW dealer will be able to indicate the week during which the customer can expect delivery. Then, six days before the start of assembly, once the firm schedule is created, the customer will be told the precise day of delivery. The Qualicision software kernel that is at the heart of BMW's new scheduling process combines fuzzy logic with decision support and optimisation techniques. According to Köppl, it is considerably superior to the other products on the market. "We did a benchmarking exercise. There were a number of solutions to investigate. The Qualicision product came out ahead because of its speed. It achieves the same quality of result but does so in only a couple of minutes whereas other take hours." What makes Qualicision different is that it applies analysis techniques as well as algebra and fuzzy set theory, says Dr. Rudolf Felix, founder and managing director of FLS, the company that developed it. "All the other approaches are just analytical." he comments. In simple terms, the fuzzy logic is the means of expressing the criteria which can be the cause of conflict. Detecting the conflicts and resolving them in an optimum manner is where Qualicision mathematics and analytical tools are required. The challenge of scheduling a car assembly line is that the choice of equipment offered is so great, the number of options is huge and there are large numbers of criteria to take into account. Some criteria partially conflict. Some don not conflict at all and some criteria are interdependent. As Dr. Felix explains, "it is a complex problem. Different options demand different spacings in the sequence. And then you have the situation where one feature can only be fitted in a car if a certain other feature is also included - and both features have different spacings. To calculate the best sequence you have to resolve all these conflicts. It is a computation challenge of huge complexity. With Qualicision, however, it is possible to obtain an optimal sequence in a very short time and after only one or two tries," he claims.

The planner who uses the Qualicision scheduling tool is not aware of the complexity of the computation. The user interface enables him to define different scenarios and to change parameters and priorities, in the search for the optimum result. The spin-off from a PhD thesis, Qualicision is the brainchild of Dr. Rudolf Felix. He set up the company FLS in Dortmund in 1992 to exploit the Qualicision software. FLS has since grown to a workforce of 30 and now supplies Qualicision to customers worldwide as a decision support tool in varied applications. The automotive industry is the major user segment. However, no other car manufacturer is using the tool in the same way as BMW, according to Dr. Felix, although there are discussions under way. The customer reference list includes Audi, Ford and Volkswagen. Machine vision is a common application. Ford, for example, uses the Qualicision software as the decision support tool for the recognition of tyres and wheel rims to ensure that matching tyres and rims are put together to create the right wheel. FLS also has a strong relationship with the tyre manufacturer Continental that uses Qualicision for monitoring the extrusion process.