Cutting the perfect tread

TASK

Automated carving of prototype tires

Prototype tires generally have their tread carved by hand. But at tire giant Continental, they like to do things differently. High-precision Stäubli robots handle the difficult task of carving with a hot blade, achieving maximum accuracy and reproducibility, and working faster than ever before. A hi-tech solution based on a wealth of expertise.

The engineers at Continental in Hanover are constantly designing new tire models for cars and trucks, which they produce in short runs for testing purposes. The profiles of the first prototypes are traditionally carved by hand from slicks using hot-wire tools. A time-consuming process that can take up to 40 hours. It starts with dimensioning and marking before the actual carving process can begin.

Continental is therefore striving to automate the various steps in prototyping. Working in close collaboration with the tire manufacturer, the expert team at system integrator Preccon Robotics in Bayreuth have developed a highly innovative robot cell for tire carving.

SOLUTION

The robot as dimensioning and machining tool

On the sophisticated Preccon production line, a high-precision Stäubli RX160 industrial robot is in complete charge of the dimensioning, marking, carving and drilling of automobile and truck tires. At the same time, the robot acts as a totally reliable measuring device. Thanks to its superior drive technology and above-average rigidity, the RX160 meets the stringent requirements of this application for accuracy.

The slick to be processed is clamped onto an external seventh axis which is configured as a turntable. The robot controller directs not only the three-dimensional pathway of the carving tool in the gripper but also the fully synchronized rotation of the tire by means of the seventh axis during the dimensioning and carving. In order to determine the depth to which the tool will cut, the robot always starts by sizing up the contour of the tire blank. For this purpose, the laser is picked up by the gripper and calibrated on a ceramic ball before making multiple passes over the rotating tire. On the basis of the data secured in this way, the tracks generated in the CAD model of the offline programming system are automatically adjusted before they are fed into the robot controller.

The carving begins with the robot picking up the cutting tool from the knife station. This has been parameterized for the respective process path. After determining the Tool Center Point (TCP) via the image processing system, the carving process begins. Control of the cutting process is a fully automatic function of cutting force and blade temperature as measured in the gripper. The main job of the operator is to observe and intervene as and when necessary. Live data is displayed on a process monitor. The representation of the carving tool in the parameterized CAD graphic allows visual tracking and rapid assessment.

CUSTOMER USAGE

Significantly enhanced reproduction accuracy and productivity

The plant named RACE (Robot Accuracy Carving Efficiency) has been in active service for more than a year now, meeting the highest standards of reproductive accuracy and productivity. The associated offline programming system also offers a high level of flexibility. The Stäubli robot is currently carving many prototype tires in batches of more than six. In the first year after commissioning, total output had already reached around 1,500 units. And this upwards trend has continued.

Compared to the previous semi-automated solution, the new system makes time savings of around 50 percent in 3D programming and setup alone. A further 15 percent is saved by the robot cell during production, including contour dimensioning and automatic temperature control. RACE thereby makes an important contribution to shortening response times to the requirements of tire development. In addition, it has been possible to further increase the reproduction accuracy of the profiles – an important prerequisite for ensuring that all tests of a prototype series are conducted under exactly the same conditions.