As part of ongoing optimization processes, every procedure in the BMW tool manufacturing plant in Munich, Germany, is examined and improved regularly. To manufacture precision parts for the large shaping and cutting tools used to shape body panels, two Mikron processing centers from GF Machining Solutions have been in continuous use since the beginning of 2012. This improved not just the quality of the parts, but increased the machine runtimes and doubled productivity within one year.
“The constant optimization of all processes has become second nature to us,” explains Herbert Winkler, manager of the mechanical tool manufacturing department at the Munich BMW plant. “The fact that we achieved such effects with the two new machines did come as a surprise to us, but it also served as an affirmation of our efforts.”
The two 5-axis Mikron HPM 1350U processing centers – equipped with tool changers, pallet magazines, and zero-point clamping systems – have made a decisive contribution to optimization measures since 2012.
BMW, Mini, Rolls Royce designs
As one of three sites of the BMW Group for tool manufacturing, the 220-employee Munich staff works closely with the development department to design and manufacture the tools for the car body exterior and structural parts of new models.
“We see ourselves as a partner and supplier for the technologies for shaping and constructing car bodies and virtually get the design into shape,” Winkler adds.
This includes the entire product manufacturing process with planning, prototype construction, engineering, mechanical manufacture, and toolmaking. Approximately 80 toolmakers use five large milling machines and several small- and medium-sized machines. Tools are tested on six test presses with up to 23,000kN pressing force before the Munich staff puts them in operation in stamping plants all across the world. Together with the Dingolfing, Germany, and Eisenach, Germany, sites, the Munich plant manufactures about half of all BMW tools themselves. The other half come from partner companies.
About 500 tools, with an average of four to five operating sequences per tool set, leave the manufacturing plants at the three sites every year. The manufacturing time of the tool sets has been drastically reduced in the last few years because all processes are interlinked with each other. Non-productive processes of mechanical manufacturing have been disentangled from the main processes and moved to units running in parallel. This affects setup and clamping processes, programming, and tool pre-sets.
While BMW was increasing productivity in toolmaking, quality improved as well. This is also necessary, Winkler says, since BMW doesn’t use intermediate assembly. All parts must be delivered installation-ready for tool assembly.
“The image of the machine operator has changed a great deal. The classical milling cutter has become a milling manager who is responsible for the result and all associated processes,” Winkler says.
During the manufacturing of small components, a tool can determine that some parts are too large for small machines and too small for the average machines. That is why suitable processing centers were sought for the manufacturing of components such as blades, shaping jaws, lifting devices, warm re-shaping bowls or sliders, and blank holders and stamps.
“We decided on the two Mikron HPM 1350U by GF Machining Solutions, because they promised the best values in the benchmarking for almost all important facts,” says Jürgen Heinzer, who is responsible for the technical planning and procurement of means of production.
Daniel Princip, mechanical manufacturing foreman of the Munich BMW plant who deals with the machines on a daily basis, agrees.
“We are much more flexible today, more precise and much more productive than we used to be. The Mikrons can be optimally adjusted to almost any manufacturing situation,” Princip says.
GF Machining Solutions employees build the 1350U models of the high-performance milling (HPM) type series using the moving column principle. Marked by the combination of many individual measurements, the manufacturing process results in a one-piece, molded machine bed standing on three feet for a stable basic structure. The table is symmetrical and the guides of the X-axis are arranged on two levels. This results in high torsion rigidity, especially if heavy workpieces are not clamped to the rotary table in a centered way.
At BMW, clamping towers often benefit from the increased rigidity. Beyond this, the linear guides have scraped supporting surfaces, which lead to very high geometric accuracy. The A- and C-axis can be clamped for roughing treatment, significantly increasing the stability and tool life.
“Machines with such basic properties can easily handle even the greatest precision requirements,” says GF Machining Solutions Project and Key Account Manager Michel Eder.
High-torque, high-tech components
High-performance high-tech motor spindles, made by the Swiss GF subsidiary Step-Tec, provide high torque even at a low rotational speed, rotating up to 24,000rpm with an HSK tool interface. The swivel arm, like the rotary axis, is powered directly by torque motors and is water-cooled – making simultaneous 5-axis milling processing possible. All axes are equipped with a direct measuring system.
Both machines are equipped with tool changers that contain 92 tools each. Pallet changing systems, with three pallets each, make parallel setups during the main production time possible.
“This turns auxiliary process times into production times,” Eder explains.
Princip adds, “Our machines now run around 22 hours a day, almost six times as much as five years ago.”
Due to the high rigidity of the machine, surface area finish of workpieces is close to 80% load carrying capacity and only requires half an hour of subsequent lapping work – reducing what had been a three to four hour manual post-process.
GF Machining Solutions adjusted the machines to use dry processing, a system used at BMW since 2002. Compressed air is brought to 12 bar pressure, and the processing zone is air-cooled from the inside via the cutter as well as from the outside. For dry processing chip removal, the conveyor chain is equipped with an active lubrication system because the cooling lubricant of the machine is not available.
With all these functionalities, these two machines by GF Machining Solutions make an important contribution to the productivity increase at the BMW tool manufacturing plant in Munich. Before 2012, 770 small parts were manufactured annually, in 2013 this increased to 1,550 components, with 1,900 parts expected for 2014.
Winkler concludes, “In the results achieved so far due to our entire optimization measures, the two Mikron HPM 1350U machines positively surprised us with their performance capacity, their precision, and their stability. They impressively confirmed our purchase decision.”
GF Machining Solutions