Back in 2015, when Audi once again received the 'Toolmaking of the Year' award, which is presented by the Machine Tool Laboratory (WZL) at RWTH Aachen University and the Fraunhofer Institute for Production Technology (IPT), the jury highlighted the outstanding development and partial implementation of an end-to-end digital process chain. Almost exactly one year later, Audi has taken another decisive step towards Toolmaking 4.0. The Ingolstadt-based company is replacing manually operated radial boring machines with a robot system that is fully integrated into the production process.

Gereon Heidrich, Head of Machine Technology at the Competence Center, explains what this is all about: "Radial boring mills were previously used to insert the vent holes in forming tools. The disadvantages of this are that the process cannot be automated with the existing machines, is time-consuming and requires a lot of manpower. And it doesn't fit in with the Toolmaking 4.0 concept, in which the digital networking of all process steps is the order of the day."

After a thorough analysis of all possible machining alternatives, Audi opted for a concept in which an industrial robot would carry out the deep-hole drilling and, in the later course of the project, also fit drilling and thread cutting processes on the forming tools. The Audi managers had no doubts about the realization of this forward-looking project: "We have already had positive experience with an in-house developed robotic solution for machining vent holes in grey cast iron tools since 2011. This convinced us of the feasibility of our idea," says Juliane Kollecker, Project Manager, New Business Areas Automation Technology department at the Competence Center.

However, the plant manufacturers initially approached did not share this view. They said that the requirements were too demanding for robot processing and involved too many uncertainties. In the end, Robot-Machining from Seligenstadt was found to be an experienced system manufacturer that was confident enough to test and then implement the task. The company specializes in the development, design and production of turnkey robot machining centers and worked closely with the competence center to create a system concept including process technology, clamping device and machining technology.

Just how much know-how is contained in the robot machining center was demonstrated during the on-site visit in Ingolstadt. The system, which is around eight meters long and seven meters wide, can be used to machine forming tools made of steel or grey cast iron. The tool dimensions can be up to 4500 mm × 2500 mm × 1000 mm with a weight of up to 20,000 kg. The elegant solution is to load the tools, which weigh several tons, into the cell: they are transported in and out via the roof of the safety housing, which can be opened at the touch of a button.

The 'master' in the cell is a robot from Stäubli, which has a 37 kW machining spindle with a maximum speed of 16,000 revolutions. The load capacity of the six-axis robot is a nominal 100 kg with a reach of 2194 mm. This is a considerable value, but it is still not enough to be able to move to all machining positions, which is why the robot was positioned on a traversing axis.

Bernd Luckas, Sales Engineer at Robot-Machining, sums up why this particular robot is being used: "With the Stäubli TX200, we were able to achieve the required precision straight away during process testing. We deliberately chose the TX200L with arm extension rather than the TX200 because it is even more precise and rigid with a repeat accuracy of ±0.06 millimeters. We therefore accepted the disadvantage of the shorter reach." This is a circumstance that makes it necessary to reorient tools when processing particularly large pressing tools, as the robot cannot reach all processing positions even via the traversing axis.

What increases throughput times today in the case of tool reorientation with remeasurement could be the opposite tomorrow. The system layout already provides for the use of a second Stäubli TX200 within the machining center. This robot is to be used on the opposite side of robot 1 - also mounted on a traversing rail. This would allow each tool to be completely machined in a single clamping operation and further reduce throughput times.

Calibration before drilling

Before the robot starts drilling the deep holes, the forming tool needs to be calibrated precisely. To do this, the robot picks up a 3D measuring probe from the tool magazine and measures the exact position of the pressing tool. After offline comparison with the calculated drilling positions, the operator performs a final simulation of all work steps before drilling begins.

When deep hole drilling, the six-axis robot impresses with its precise path behavior and high rigidity. A traversing axis considerably extends the robot's working range.

© Audi

Between 70 and 80 vent holes are required per tool half. The execution of a deep-hole drilling consists of three phases, the so-called mirroring, a 30 mm deep pilot hole and the final deep-hole drilling with diameters of 4 to 8 mm. The special feature here is that the linear feed in the deep-hole drilling process is performed by the robot. "This means that the robot actively drills the vent holes, which are up to 120 millimetres deep. This requires excellent path behavior and corresponding rigidity," says Juliane Kollecker.

An automatic tool changing system allows the robot to supply itself with all the tools it needs from the tool magazine. It can even swap the complete machining spindle for other end effectors at a change station if required. This solution ensures maximum flexibility and automation.

End-to-end digital process chain

Maximum precision required: the robot during a measuring bore.

© Audi

Another decisive advantage is that the positions for the vent holes are now already defined in the CAD system during tool design and can be transferred to the offline programming system of the robot machining center without any additional effort. Digital networking makes a decisive contribution to reducing throughput times, as Lisa Dilg, Project Manager for Machine Technology, explains: "In the past, we had to define the positions for the vent holes on site and insert them using the manually operated boring mills. The digital process completely eliminates this effort, meaning that we achieve an overall reduction in throughput times of around 60 %."

Following the integration of these processes, the remaining gaps with regard to the digital networking of all process steps have largely been closed. For the Competence Center, the overarching goal of complete simulation of entire process chains is now within reach. In future, networked systems should enable adaptive fine-tuning of capacities and thus even more efficient production.

Author:
Ralf Högel is a freelance author from Stadtbergen.