Modern, more modern – production cell 3

Developing a toolmaking system that is expressly intended to be a model for others, is a demanding task. Only the most modern machines with intelligent control technology can be considered. At such a high level, a significant amount of engineering is required. 

In order to secure the Mercedes-Benz plant in Sindelfingen as a site for development, technology and expertise, Daimler AG is also investing in this equipment centre with an additional building on Tübinger Allee, which is known internally by the abbreviation "TübA". It was here that in 2015 the new "production cell 3" was created – as a try-out centre, where sheet metal forming tools for the outer shell of vehicles can not only be manufactured but also tested straight away.

In addition to the fundamental requirements of Daimler for maximum accuracy, reliable processes, environmental protection and energy efficiency, Centre Manager Günter Sprecher set clear objectives for the project: "The new technology factory is intended to serve as a model for other toolmakers. And the equipment centre will in turn play a key role in the technology factory, because toolmaking and systems engineering skills can be bundled here." To implement all the requirements, all the project participants had to break new ground, as many new functions relating to the machine and control technology had to be developed in the process.

A strong team

With its brand Droop+Rein, Dörries Scharmann, part of the Starrag Group, is well known for large, special-purpose toolmaking machines with interchangeable milling heads. It was awarded the contract to fit the system with the appropriate protection machinery including accessories. To be able to fully simulate the machining process, it was established in advance that the machines would have to be fitted with Sinumerik 840D sl CNCs from Siemens AG. "Because this control system fits seamlessly into the Siemens NX process chain that is planned for the future and is therefore one of the factors that contribute to process reliability", explains Ali Fidankök, Project Manager for Large Machines at Daimler. To ensure that the details in the technical specifications could also be fulfilled, the machine engineers required full access to the control technology. Consequently, this job marked the start of a close project partnership between Droop+Rein and Siemens. 


Reduced machining time

The equipment

The system, which became operational in mid-July 2015 as planned, comprises two T 30 55 PT R75 C portal machining centres and two FOGS 50 68 PT M40 C multi-functional, high-speed centres with high gantry design. Supplemented with a pallet transport system for a workpiece weight of up to 40 tonnes and robotic workstations etc., these linked large machines can completely machine the sheet metal forming tools in one clamping position.

The machining process of the cast unmachined parts starts at the portal machining centre. This machine delivers drive power of up to 75 kW and a torque of up to 5500 Nm for the heavy-duty cutting. It has six milling heads with an automatic milling head changer, plus a tool magazine based on a seven-axis robot. This machine does the tough work – this is where roughing is performed. The fine machining and finishing, such as of the active surfaces that are in direct contact with the sheet metal when pressing, then takes place on the FOGS series high gantry machines. They are each fitted with four automatically interchangeable milling heads, including a fork head for various motor milling spindles.

The process and technology used are designed to ensure that the parts can move to the next step on the try-out press with the least possible or even no rework at all. "We implemented this and at the same time reduced the machining time of the defined acceptance part from 36 to 25 minutes", says Ulrich Wiehagen, Head of Sales and Plant Manager at Droop+Rein. "The surface features of the CNC make an important contribution to this." Use is made of the Sinumerik MDynamics milling technology package, which enables high machining speeds with excellent and visually attractive milling performance by means of improved web run. Support is also provided by the latest mechatronic motion control highlights, such as the model-based feedforward control Engineered Motion Control (EMC).

Kinematic measurement increases process reliability

Machines with interchangeable milling heads have complex kinematics. If, due to a temperature difference for example, there is uncertainty regarding the machine accuracy, or if particularly delicate or high-precision machining is planned, the automatic kinematic measurement of the milling heads provides the necessary process reliability. Based on the new C9960 measuring cycle made by Siemens, Droop+Rein developed a measuring and checking cycle for all milling heads available on the machine, which is easy and safe for the machine operator to use. The measurement of the machine kinematics is performed quickly, precisely and without a service call-out or special equipment. With the machine's standard measuring probe and a high-precision ceramic calibration ball, the machine operator is able to reproducibly qualify a milling head in less than an hour. Change the measuring probe, put on the calibration ball, call up the program, execute the automated process, check the results, adopt the correction values if necessary – and it's finished! For new system applications, such as the implementation of this extended kinematic measurement, what are called kinematic chains are required in the control system. These are a standardised declaration of the kinematic structure. Although they sound abstract and remain in the background for the user, they facilitate the realisation of other future functionalities, therefore making the machines future-proof.


Easy handling: moving in tool orientation

The ability to move the milling cutter together with the milling head into a wide variety of operating situations in tool orientation makes life much easier for machine operators. For the implementation of this virtual Z-axis in the tool direction, the newly available Tool Coordinate System (TCS) within the control system was used for the first time. According to the orientation of the tool and the milling head in the working area, when they are moved, the respective portions of the displacement are then distributed across the linear geometry axes. 

Environmental protection and energy efficiency

The equipment of the new production cell 3 should not only ensure faultless and highly productive performance of the actual machining tasks; environmental protection and energy efficiency were other important issues in project implementation. The high requirement of the Daimler overall project management led by Ulrich Funk that energy consumption should be reduced by 40 percent was successfully achieved through intensive project work on the part of all the participants. Everything had been thought of from the LED lighting on the machine and the fitting of the machines with Siemens high-efficiency asynchronous motors of energy efficiency class IE3, right through to the idle power compensation. The latter is not simply a conventional, one-off, predefined idle power compensation. Instead, it automatically responds to different load statuses of the machine, which are produced with each activation or deactivation of swarf conveyors, units, etc. The idle power is therefore compensated automatically, permanently and almost completely. Ulrich Wiehagen: "In this way, the electricity consumption is optimised and the energy costs are limited to almost the active power."


Modern service and maintenance concept supports process reliability

Droop+Rein has also implemented a modern and forward-looking service and maintenance concept here. The state and quality of the machine tools are continuously monitored based on Analyze MyCondition from the Sinumerik Integrate software suite, which supports smooth machine operation and keeps unplanned downtime to a minimum. This is another, not insignificant piece of the puzzle, which supports the process reliability of the system.

Up to three in no time at all

After production cell 3 became operational in July, three-shift operation was introduced as early as the beginning of August 2015. All the participants are extremely proud of the result. In accordance with the Starrag Group claim "Engineering precisely what you value", the exact requirements stipulated were implemented for Daimler AG in the most modern manufacturing system for sheet metal forming tools. The proof of this success can be seen in the technology factory on TübA: as an exemplary toolmaking system.


Electricity consumption reduced