Mapal Highly precise machining of truck engine cylinder bores

Editor: Steffen Donath

Modern truck engines are produced at the Mercedes-Benz plant in Mannheim. The requirements for engine properties include extremely tight tolerances for the decisive dimensions.

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Machining these adapters for the cylinder liners requires highest levels of precision.
Machining these adapters for the cylinder liners requires highest levels of precision.
(Source: Mapal)

A first line for machining these engine blocks was commissioned in 2011. When planning a second line, the persons responsible drew on their experience with the first line. They identified the machining of the bores for the cylinder liner adapters as particularly challenging. The machining was divided into two stations: one for pre-machining and one for fine machining.

To this end, Mapal has developed complex actuating tools that are equipped with up to 20 indexable inserts, including ISO inserts and custom inserts. The actuating tools feature a tool body in monoblock design. The HSK-160 connection shows an enlarged face surface with a diameter of 200 mm. One tool weighs a total of up to 60 kg. Despite the connection and a tool length of 380 mm, it must be ensured that the tool has a radial run-out accuracy of 3 µm. The slides are actuated by a drawbar via an additional NC axis in the machine controller. It had to be integrated in the HSK connection and suitable for the automatic tool change. This challenge was solved with a high-precision bayonet coupling. It is used to couple the drawbar automatically during a tool change.

With machining operations like these, the cutting edges of such tools are usually replaced and adjusted in the working area of the machine. Due to the cooling lubricant, this is not only uncomfortable for the machine operator, the machine also cannot produce during this time. In three-shift operation and with three tools per machine, this downtime would amount to three to four hours per day.

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Together with the employees from Mercedes-Benz and the machine manufacturer, Mapal consequently developed a concept for an automatic tool change and for adjusting the tools outside of the machine. However, the dimensions of the tools alone indicate the extent of the challenge in this case. Given that a machine with an automatic tool change for this type of machining and these dimensions is a world first, the project required a great deal of innovative spirit and the courage to try out new things from all project partners.

In an effort to ensure that the external adjustment is as simple as possible, Mapal developed the corresponding devices for transporting, adjusting and maintaining the tools. This included a handling solution for inserting and replacing tools in the magazine, as the tools are inserted into the machining system while hanging, which is quite unusual. Due to the high tool weight of around 60 kg, the effort of just “turning over” the tool twice manually would have put the personnel under a lot of strain. When working with such a weight, the safety aspect also plays a major role. Furthermore, there would have been a risk that the tool could be damaged in the process. This is why Mapal realised two unique setting fixtures into which the tools are inserted in a hanging position. A cart for hanging transport between the machining system and the setting fixture was also developed. The tools are thus transported and adjusted in the same position in which they are used in the machining system.

Overall, the line was commissioned as planned. The tools fulfil their tasks in accordance with all specifications, and the engine blocks are now manufactured with great precision on the production line.

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