In 2016, Audi replaced manual radial drills with an innovative robotic system built into the production process. A giant step towards Industry 4.0 in mold making. After a comprehensive review of all conceivable machining options, Audi has opted for an unprecedented solution involving the use of a Stäubli TX200 industrial robot to drill deep holes and, at a later stage of the project, to ensure bore and precision thread in the molds. Precision and rigidity were immediately recorded. For Audi, the robotic machining center meets all its expectations for drilling ventilation holes. This good experience really encourages the manufacturer to integrate other machining processes in the near future.
One thing you won’t find at the highly advanced Audi Competence Center for Plant Equipment and Forming Technology is any sort of process that is not somehow digitally linked. Thus, a robotic machining center now replaces four radial drilling machines in the manufacture of molds. A sophisticated project which yields decisive benefits.
Back in 2015, when Audi yet again won the Werkzeugbau des Jahres (Toolmaker of the Year) award, the panel of judges were complementary in their praise of the outstanding development and partial realization of a continuous digital process chain. Almost one year later, the Ingolstadt-based automotive giant is taking another giant leap towards Industry 4.0 in mold manufacture. They are replacing manually operated radial drilling machines with an innovative robotic system that is integrated into the production process.
Gereon Heidrich, Head of Machine Technology at the Competence Center, explains: « To date, we have been using radial drilling machines to make the vent holes in our molds. The disadvantages of this are that the process cannot be automated with the existing machines, that it is time-intensive and that it entails high labor costs. Furthermore, it is inconsistent with the concept of Industry 4.0, in which the digital linking of all process steps is essential. »
After thorough analysis of all conceivable machining alternatives, Audi opted for a pioneering solution involving the use of an industrial robot to perform deep hole drilling and, in the later course of the project, precision boring as well as thread-cutting in molds.
Audi officials had no doubts about implementing this advanced project. Juliane Kollecker, project manager in the Department of New Business Areas for Automation Technology at the Competence Center: « Since 2011, we have had positive experiences with a robot solution developed in-house for the machining of vent holes in molds cast in gray iron. This persuaded us of the feasibility of our idea. »
When the equipment manufacturers were consulted, however, they did not share this view. The requirements were too demanding for machining by robot and would involve too many uncertainties, they said. Eventually, an experienced equipment manufacturer was found – robot-machining GmbH in Seligenstadt – who were willing to take on the exploratory work and subsequent realization. The company specializes in the development, design and production of turnkey robotic machining centers. Working in close collaboration with the Competence Center, they developed a system concept complete with process technology, clamping mechanism and machining technology. The proposal met with the approval of Audi senior management, and the vision became a reality. Since the fourth quarter of 2016, the plant has been fully integrated into production.
The sheer level of expertise that went into the robotic machining center is immediately apparent during an on-site tour of inspection in Ingolstadt. On the 8-meter-long and seven-meter-wide robotic machining center, molds made of steel or gray cast iron can be machined. The dimensions of the molds can be anything up to 4500 x 2500 x 1000 millimeters, and they can weigh up to 20,000 kilos. An elegant solution has been found for maneuvering molds weighing many tons into the cell. They arrive and depart via the roof of the safety enclosure, which can be opened at the push of a button.
Controlling all activity within the cell is a precision robot from Stäubli, which has a 37kW machining spindle with a maximum speed of 16,000 rpm. The large six-axis TX200 has a nominal load of 100 kg and a range of 2,194 millimeters. These are impressive statistics, but they are still not enough to access all machining positions, which is why the robot has been mounted on a traversing rail.
Bernd Luckas, sales engineer at robot-machining GmbH explains why this robot was selected: « With the Stäubli TX200, we were able to achieve the required level of precision as early as the process testing stage. We also deliberately excluded the TX200L with its arm extension but instead chose the TX200, because it is even more precise and structurally rigid with a repeatability of ±0.06 millimeters. That’s why we were willing to settle for a shorter range. » A constraint that requires the realignment of very large molds, since the robot cannot reach all machining positions, even via the traversing rail.
When a mold is realigned, it often requires re-dimensioning, which increases throughput times. This could soon be a thing of the past. In the plant layout, there are already plans for the use of a second Stäubli TX200 within the robotic machining center. Robot 2 will operate on the opposite side to Robot 1 and will be mounted on a track. This means that each tool can be completely machined in a single clamping, thereby significantly reducing throughput times. According to Gereon Heidrich, the decision on if or when the second robot comes into operation will be based on number crunching: « Here, we are looking at the economic arguments, and they depend on how busy our robotic machining center gets. »
Before the robot begins drilling a deep hole, the exact calibration of the mold must be performed. For this purpose, the TX200 uses a 3D probe from the tool magazine and measures the exact position of the mold. After the offline reconciliation with the calculated drilling positions, a final simulation of all steps in the process is carried out by the operator before the actual drilling commences.
Between 70 and 80 vent holes are required for each half of the mold. Drilling a vent hole is in three stages, the first of which is called ‘mirroring’, secondly the drilling of a 30mm-deep pilot hole and finally of the actual hole, the diameter of which ranges from four to eight millimeters. The special feature is that the linear advance of the drill bit is controlled by the robot.
An automatic tool changing system allows the robot to supply itself with all necessary tools from the magazine. The TX200 can even exchange the complete machining spindle for another end effector at a changing station. This solution ensures maximum flexibility and automation.
« The robot actively drills the vent holes which may be up to 120 millimeters in depth. It requires excellent motion control and rigidity which only the Stäubli robot with its proprietary drive technology is capable of. »Juliane Kollecker, project manager in the Department of New Business Areas for Automation Technology
A further decisive advantage is that the positions for the vent holes are predefined during the mold design stage in the CAD system and can be transferred to the offline programming system of the robot machining center without additional effort. Digital networking is a key factor in 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 drill them with manually operated rigs. The digital process completely eliminates all of this effort, with the result that we achieve a reduction in throughput time of around 60 percent. »
Gereon Heidrich is equally enthusiastic about the innovative plant: « The robot machining center fully lives up to our expectations with regard to the drilling of the vent holes. Our positive practical experience with the robot fills us with confidence that the integration of further machining processes will be realized in the near future. »
Once these processes have been integrated, the gaps that currently exist in the digital networking of all process steps will be largely closed. For the Competence Center, the overarching objective of being able to fully simulate entire process chains is tantalizingly within reach. The intention is that networked systems will in future facilitate the adaptive fine-tuning of capacity and thus lead to even more efficient production.