Car companies welcome back their flexible friend

Flexible manufacturing systems, the production-line concept conceived in the early 1980s to handle small batches of components, is back.

Automotive companies fighting to gain market share are introducing more products more frequently than ever before. Having identified niche products and more ‘personalised’ vehicles as ways to satisfy consumer demand and increase competitiveness, the industry is offering increasing numbers of variants and options.

It is a trend that is bringing back the FMS, or flexible manufacturing systems. FMS, the acronym the machine tool world coined in the early 1980s, was a concept that aimed to combine the productivity of a transfer line with the flexibility of a machining centre, providing the market with small batches of products. Lean ideas were already starting to be introduced and companies were beginning to reduce their component and product stocks.

Many FMS systems were installed but few were operated successfully. British Leyland and the 600 Group invested in the concept, for engine and machine tool parts respectively. Not only was the concept very ambitious for the time, but their designers became a little carried away with the technology.

The systems were highly complex, incorporating rows of machining centres, washing and measuring stations, with automated guided vehicles to deliver palletised parts to and from the machines and a pallet storage system. Managing such a system proved difficult, as did keeping individual components in working order.

For the past 12 years or so, talk of FMS has been quiet, if not non-existent. That is now changing, as automotive manufacturing companies again seek to increase the flexibility of the production lines.

For Renault, the key driver for flexibility is the short lifespan of engine products. Instead of 15-20 years, an engine is now in production for two to five years, according to Jean-Loup Huet, director of engine products. ‘It is out of the question to purchase new facilities so frequently. What we need is equipment that can easily be converted and adapted for new models.

This is particularly the case for the machining of cylinder heads, as these are the components that undergo the greatest evolution,’ he says.

With increasing legal pressures to reduce emissions and fuel consumption, the trend for shorter product life cycles is set to intensify, adds Bernard Le Meaux, industrialisation manager at Renault’s FASA engine plant in Valladolid, Spain. The company’s first FMS has been operating there for more than a year, to produce cylinder heads for at least two families of diesel engine.

BMW’s powertrain division director Dr Lutz Kuhne places a slightly different emphasis on flexible production. His vision is to build all engine families at all assembly plants, using systems that can produce any engine in the range in any order. ‘The degree of flexibility this provides in terms of production volumes is very important in meeting fluctuating market demand,’ he says.

Also important, according to Kuhne, is the flexibility to modify production equipment when major design changes have to be introduced. Changes normally happen two or three times in the life of an engine, and a conventional transfer line is then down for several weeks while costly modifications are made. ‘With the new flexible system, we can reduce the cost of those changes significantly,’ he says. ‘We are now able to use the computer controls on the machines to make the necessary changes within a few days.’

Advanced features

The FMS of the new millennium is not as flexible as its predecessors. It is highly dedicated to specific, and very similar, groups of components. All the systems installed so far are for cylinder heads for car engines, but they incorporate some highly advanced features.

The past five years has seen a major technological breakthrough in machining centre technology that has improved the economic viability of FMS installations. The latest generation of machining centres has linear motors to drive the machine axes, rather than the ballscrews previously used. This considerably increases the speed and therefore the productivity.

Renault Automation Comau, one of the first to bring the new technology on to the market, claims that independent comparative studies have indicated a 30-40% productivity increase, without loss of accuracy, for the company’s Urane linear motor machine compared to a conventional model with ballscrews.

The FMS systems now operating at Renault and BMW are similar, with castings passing from one machining cell to the next, undergoing a series of operations. Each cell incorporates two or three, or even four machines, depending on the cycle time of the operation, and all the machines within a cell are identically set up and tooled to perform the same machining operation. When a cylinder head arrives at a cell, it is simply directed to the first available machining centre.

Automated handling equipment, to match the productivity and flexibility of the machine tools, is used to take workpieces from one cell to the next, and for loading and unloading the individual machine tools. Rather that the complex automated guided vehicle systems used in many of the early FMS installations, the latest generation employs more simple forms of transport such as conveyors and gantry loaders.

An adapter plate, on which each cylinder head casting is mounted at the start of the machining operations, acts as a common interface between the different designs of cylinder head being manufactured and the handling system and machine tools. It is a flexible solution that allows almost any design of head to be machined. As long as the dimensions of the design fit within the envelope of the machine tools, the new part can be introduced by simply changing – or maybe even adjusting – the adapter plate.

At Renault’s FASA engine plant, an FMS incorporating 28 of Renault Automation Comau’s Urane high-speed machining centres has been operating for more than a year. Although the initial investment was 20% higher than it would have been for a transfer line of an equivalent capacity, the new FMS will start to become economic when a second engine family is brought into production. Le Meaux says that while adapting a transfer line for a new product requires up to 40% of the initial investment, the additional cost for an FMS is just 5%.

BMW’s newly-installed DM1bn FMS in its Munich engine plant was built by German company Ex-cell-o and incorporates 41 of the company’s XHC 241 high-speed machining centres to provide a capacity of 160,000 cylinder heads annually, on three shifts. The space is available to add a further 20 machines to increase capacity by about 50%.

No extra cost

According to Kuhne, the flexible facility did not incur more investment than a transfer line would for the same production output. This, he says, was due to the supplier’s strong interest in introducing the innovative technology to the market.

Adopting such technology is risky, but not overly so, says Kuhne. ‘We don’t know all the facts yet. The key question is how the machines will behave in the long term: what will their mechanical stability and accuracy be over 10 or 15 years? Right now we are convinced this is the right technology for us. We have had very good results with the engines we have produced so far.’