Retrofit with a vision

In the manufacture of high-quality sunglasses by Silhouette, a modernized multi-spindle manufacturing plant accurately cuts the polycarbonate glasses, while an articulated-arm robot precisely feeds the blanks - both with Sinumerik CNC.

Silhouette International Schmied AG

Under the Silhouette brand name, the world’s lightest sunglasses are manufactured in Austria and then exported to approximately 100 countries worldwide. The glasses are produced with a significant amount of handcraftsmanship, a distinct design language, the best materials and the latest technologies. In both the elegant Silhouette sunglasses and the sporty sunglasses from the Adidas eyewear brand, a special glass design ensures a clear perspective without creating fatigue. Herbert Flattinger, head of special-purpose machine development at Silhouette International, explains: "Especially for glasses inclined toward the eye, as is often the case with sporty glasses, the eye needs to compensate the small amount of light refraction arising. This results in long-term strain and sometimes causes headaches. We have succeeded in balancing this effect already in the glass manufacture."

The foundation is built during injection molding of the polycarbonate glasses, but the subsequent production processes need to follow through. This means that the outer cutting of the individual sunprotection lenses must take place in an exact position and within several steps. In the Silhouette production line, this task is performed by multi-spindle milling machines from Anger. Until a few years ago, the individual lenses were inserted into the machine by hand. The integration of a gantry robot meant that the operation could be automated - though not fully at first.

Extensive retrofit

Thanks to an extensive retrofit of the entire machine, robot and CNC system, manual intervention is no longer necessary. Originally, the decisive factor for the complete modernization in 2013 was the age-related wear, along with the associated rising maintenance costs. From today’s perspective, however, the redesign has also delivered benefits for the productivity, reliability and user-friendliness of the plant. “We expect the complete investment to have paid off within only 18 months,” the project team at Silhouette International reports.

Because, according to Silhouette, there are no fully automated manufacturing plants on the market that are suitable for continuous production throughout the complete production process, it was already clear in 2011 that the existing equipment needed to be given a general overhaul. Accordingly, the company needed to supplement the expertise of its production personnel with a knowledge of drive, control and robot technology from external partners. After extensive studies and comparison tests, the company determined that Siemens and KUKA best fulfilled the technical requirements. Following the project launch, the entire system was completely disassembled within four months, mechanically optimized, equipped with a new drive and control system and supplemented with a KUKA KR 5 arc articulated-arm robot.

Consistency from programming to machine and robot

A special feature of the new plant is that both the multi-channel milling machine and the six-axis robot are controlled centrally via the high-end Sinumerik 840D sl CNC. Engineers from both Siemens and KUKA worked closely together to develop a consistent, standard solution - an important aspect for Silhouette, because although the machining technicians knew exactly how to operate machine tools, they were not familiar with handling a multi-axis articulated-arm robot. Controlling the robot with the CNC, and thereby reducing the technicians’ fear of using the robot, was made possible with the Run MyRobot (RMR) software interface. As confirmed by Silhouette’s production workers: “Being able to control the mechanical KUKA arm with our normal operator panel makes us very happy with the entire plant. To be honest, we actually enjoy being in charge of such complex movements every now and then.” These complex movements are transferred to the robot control system in real-time via the mxAutomation command interface and are then performed by the robot with typical KUKA precision. In the process, the safety functions in the SafeOperation robot option ensure that the robot does not leave the designated operating range.

The NC technicians use the operating terminal primarily when setting up the machine and when teaching or retracting the robot. They are as enthusiastic about the touchpanel as they are about the intuitive Sinumerik Operate user interface. Above all, they like the brilliant resolution and the quick-response touchpanels on the industrial display as well as the PC-typical design of Sinumerik Operate. They already know several of the keyboard shortcuts from their PCs, such as Ctrl+A for “select all,” which is one reason the employees find working with Sinumerik easy, even though some of them have worked with a different CNC for several years.

The milling machine and robot programs are generally written using Silhouette’s own CAD/CAM workstations, which are equipped with NX CAM. Here too, consistency is a priority. “Once our lenses are developed, the data is made available to every department involved in the process. Even the robot and machine operators can access NC programs as well as tool data,” explains the head of special-purpose machine development. After graphical simulation on the CAD/ CAM workstation and any possible optimization, the NX program can be transmitted directly into the NC code using a post-processor optimized for Sinumerik and then transferred to the 840D sl. The production technician can then set up the system without further delay, equip it and start the production process.

Smooth production process

The fully modernized production plant has been in operation and running smoothly in three shifts since mid-2013. In order for the night shift to function unmanned, the late-shift worker fills the workpiece storage with the appropriate blanks and loads the relevant NC program before the end of work. After this, even various product changeovers are possible. The six-axis articulated-arm robot takes the corresponding raw lenses out of the stacking magazine with its vacuum grippers and inserts them into a centering station, where it is positioned precisely and transferred to the milling machine. The machine then mills and drills the contours of the polycarbonate lenses in several steps. Here, thanks to the stable design and the high-quality Sinumerik 840D sl CNC, the multi-spindle center is able to observe tolerances of +/-0.015 mm and to reach surface qualities with an average roughness of Ra = 0.1 μm.

The Sinumerik MDynamics technology package, along with the corresponding Advanced Surface intelligent path control, plays an important role for the high-quality machining taking place here, as highlighted by Siemens sales consultant Thomas Waltschek: “In this latest software version, our developers have optimized the look-ahead function once again and integrated a high-performance data compressor. Now, our control system achieves a perfect ratio of cutting efficiency to surface quality and precision.” At the end of the machining process, the vacuum grippers are used once more to store the completed sunglasses in transport boxes.

Correct lenses in less time

“With our completely overhauled plant, we can constantly manufacture optically correct lenses without any human intervention - and around 20% faster than before. For us as a premium eyewear manufacturer, these arguments are compelling,” summarizes Flattinger. Currently, a second production line is going through the same retrofit with the same partners. “And our third production line, out of a total of eight, is already being planned,” reveals the head of special purpose machine development.