Emuge-Franken offers a case study of the development of MQL tooling at Volkswagen’s Salzgitter engine factory

The Salzgitter plant produces 7,000 petrol and diesel engines a day for the entire VW group. These cover more than 370 versions – ranging from three to 16-cylinders. Minimum quantity lubrication (MQL) is used exclusively in the production of cylinder heads for the latest EA 211 engine generation. The Softsynchro Modular tap holder newly developed by Emuge-Franken has meanwhile established itself as one of the main players in the production of threads.

Minimum quantity lubrication

“We started to introduce MQL ten years ago in the Salzgitter plant and since then have integrated the use of this technology step by step into large-series production”, explains VW’s Hayri Aydin from the technology and work planning division. A good example of the very high level of development, achieved with MQL, is the new production line of the cylinder head of the 1.2-litre petrol engine for the EA 211 unit, which started operation in the course of the 2010. “We rely on MQL in all machining processes using a defined cutting edge,”,” says Aydin. “The consumption of approximately four litres of coolant lubricant emulsion per cylinder head produced can be reduced this way to less than 20 millilitres of MQL oil.”

As head of the tool management department, together with his team of 12 members, Aydin is focused on solving the problems and challenges associated with this topic every day. “Our area of responsibility includes the testing of the newest technology developed by our suppliers and the implementation into series production.” For example, this was also the case with the newly-developed tap holder series Softsynchro Modular / MQL with minimum length compensation. These tap holders, particularly designed for the requirements of Volkswagen with regard to modularity and MQL, have been in use for a couple of months in the cylinder head production line of the EA 211 series in Salzgitter. They provide an even higher productivity in thread production while at same time maintaining a very high process reliability and lowest consumption of resources.

Cold-forming threads

To reduce the quantity of coolant lubricant emulsion used, the Salzgitter plant started initial tests of MQL production technology ten years ago – at that point they had been researched very little. One of the first practical applications was tap production. Since cylinder heads, crankcases and most of the add-on components for the EA 211 and also for the predecessor model EA 111 consist of aluminium, the threads are not cut but cold-formed. “Cold–forming of threads does not produce chips which could become stuck between tool and thread profile. This fact is important for MQL. In addition, tool life is longer and the quality of the threads is higher because the microstructure of the material is not interrupted,” explains Heiko Dormann, specialist for MQL at Volkswagen Salzgitter. These are good basic conditions in order to replace coolant lubricant by aerosol, even though the heat to be dissipated is higher compared to thread cutting.

The term MQL is used when the consumption of oil is less than 50 millilitres per hour. The mixture of oil with air (aerosol) is transferred to the processing area either externally via a nozzle or internally through the spindle, the clamping system and the tool. The Emuge-Franken Softsynchro /MQL tap holder used in the MQL tests, relied on internal transfer of aerosol to the cutting edge.

The Softsynchro tap holder ensures a very high thread quality and a long tool life in thread production because process-related differences in thread pitch are compensated by the minimum length compensation (+/- 0.5mm) patented by the company. Any remaining inaccuracies caused by influencing factors such as computing speed of the CNC, resolution of the axis sensors, condition of the machine kinematics, temperature response or tolerance of the thread pitch are compensated this way, resulting in a stable thread production process.

The MQL tests conducted by Aydin and his team under serial production conditions with the first generation of the Softsynchro tap holder were successful with regard to thread quality. However, some weak points were also detected. One of them was the transport of aerosol between HSK interface, tap holder and tool. “The leakage loss did not become apparent in the beginning because we had fully turned on the oil tap, so to speak, for security reasons and therefore oil consumption was just little below 50 millilitres per hour”, remembers Dormann. When the tool goes into operation and the coolant-lubricant supply does not work accurately, the breakage of the tools is the inevitable result, says Dormann of his own experience. “Nowadays we work with approximately seven millilitres and have an absolutely reliable process.”

Demand for modularity

An additional point of criticism was the missing modularity of the tap holder. The product range of Softsynchro tap holders tested at that time had different types of aerosol supplies depending on tool diameter and tool type, which could not be exchanged by the customer and therefore required different tap holders for various sizes of tools. But the technical specification sheet of Volkswagen required that the supply of aerosol through the tap holder could be adapted to different tools while at the same time ensuring absolute leak-tightness.

The variety of the minimum quantity lubrication systems used in practical terms and the variety of associated MQL interface elements for one-channel- or two-channel systems therefore required a modular construction of the system. This also concerned the variable design of the interface on the tool, because the different individual diameters of the taps had to be taken into account.

New development

In June 2011, the newly developed tap holder was presented to Volkswagen. The advantages of the new development had convinced Aydin and his team, and after an intensive testing period the system was approved for tap production. The new system now has exchangeable MQL interface elements for HSK-A and HSK-C on the spindle and also supports onechannel and two-channel MQL systems.

In one-channel systems the oil-air mixture is created directly in the MQL device. In two-channel systems, the mixture of both media is generated only at the rotary feedthrough of the tool holder. Since at Salzgitter two-channel systems are predominant but one-channel systems can also be found there, the requirement also included variability of the tap holder in this regard. Furthermore the new development is now leak-tight during aerosol transport and has an exchangeable length adjustment screw for tool shanks, with internal or external centre.

Extended tool life

Currently Volkswagen has approved Emuge-Franken’s Softsynchro Modular tap holder and two holder systems of another German manufacturer for tap production under MQL conditions. The introduction of the new Softsynchro development was accompanied by a series of tool life tests conducted against a competitor’s tap holder used at the Salzgitter plant. The result? The Softsynchro Modular tap holder enabled machining of 32% more work pieces using an identical tap. “The newest generation of the Synchro tap holders has achieved a very high technological level and works really well, in particular under MQL conditions”, said Dormann, adding: “Actually MQL is very simple – once you understand the process thoroughly.”