The new printing station was incorporated into an existing production
line, where it replaced a single-colour printing machine. It prints multiple guide bars simultaneously in order to achieve the required cycle times. It now takes only a few seconds to print both sides of a guide bar – and that includes drying and laser marking. The machine is fully enclosed; filtered air streams into the system from the top and exits at the bottom. This clean “print island” approach avoids possible quality problems caused by factors such as dust from the production environment.
The material handling is fully automated as well. Handling robots and servo drives supply, remove, transport and rotate guide bars of different lengths (from 300 to 1300 mm). High-precision linear motors move the substrates up and down all the print axes.
THIEME developed different machine designs for STIHL’s Light and Strong product lines: Two printing stations were placed in series in order to coat the shorter Light bars (300 to 700 mm in length), while a two-tier system was built for the 1.30-meter-long Strong bars. Once the first side is printed, the bars pass through the upper tier and then return to the same printing station, which then prints the second side. This approach made it possible to design a highly compact machine with a small footprint.
Automatic data transfer
The printing system is controlled by a Siemens PLC. It is operated using touch panels, with users receiving different authorisation levels (for workers, maintenance, etc.). When a print job is selected, the THIEME digital printing system retrieves the associated image right from the STIHL print data server. That way, different designs can be quickly and easily implemented for specific batches, such as special editions for specialty retailers. Set-up times are minimal since settings such as bar size do not have to be manually configured. However, it takes different knowledge to operate this system than the previous printing process – knowledge that THIEME teaches in intensive courses.
Once the print job has been selected and the image imported, the system automatically sets itself up on its own. In fact, after changing
products, all the operators have to do is restart the process. If necessary, they can request sample bars for a visual check. The system then ejects one set of guide bars onto a roller conveyor for inspection. In all other respects, the printing process is fully operational without requiring any additional intervention. The machine even cleans the printheads autonomously as needed. It automatically stops, flushes the printheads and restarts at the end of the cleaning process – no start command is needed.
The printing system is also connected to a master production control system that can pass on production information such as system status, error messages, printing mode, productivity, etc. This information allows rapid responses to departures from the normal production process. The printing machines used at STIHL offer a high level of technical availability on par with the remainder of the automated production line. In addition, THIEME provides different after-sales service packages, including 24/7 service with threehour response times.