Joint success story with Fanuc
The automation of plastics machines is one of those things: it costs money, which has to be added to the price of the parts. The market for injection molded parts is also highly competitive - every tenth cent counts. So other criteria must be decisive for automation.
Hans Arnold Kunststofftechnik, Mühlhausen, has long since made the decision to do so, and now also for complex tasks and production stages.
The company, which was founded a good 40 years ago, now has around 170 employees, including a joint venture in Hungary. Petra Arnold-Herpertz, an industrial engineer, manages the company together with her father and founder Hans Arnold: "We are in the process of making the company fit for the future. Therefore we automate not least out of our own interest".
The criteria are not at all industry- or company-specific. Wage costs are not decreasing, skilled personnel is not readily available and the quality demands of customers are increasing. First experiences have manifested themselves in the realization: Once the process is up and running, I get 100% quality directly from the machine. Especially for injection molding processes with inserts, the experienced automator can't do without a robot, as Production Manager Kevin Lützkendorf says: "Manual inserts are subject to errors and I can cover complicated processes better with a robot. In addition, manual insertion work ties up personnel in three shifts. In the meantime, Hans Arnold even goes so far as to insist on automation for quality reasons when a customer inquiry is received.
The automated future at Hans Arnold Kunststofftechnik has already begun with the production of the handle for a Bosch angle grinder.
The special thing: The cell was planned and realized by the company itself, partly for cost reasons and partly because it was hoped that it would be possible to implement the cell quickly by building it in-house. To make a long story short: Both goals were achieved.
Clues were provided by the production of the predecessor handle. The tool was getting on in years, the design of the handle should be renewed. Together with the customer Bosch, Hans Arnold Kunststofftechnik then implemented the new handle and its production. To ensure that the handle fits well in the hand, it has a strongly structured surface, which in turn was a challenge for the toolmaker. Kevin Lützkendorf: "We have our own tool shop with many years of experience. For the Bosch handle, we were supported by the toolmaker Foboha from Haslach". They had already built the tool for an older 2K version of the handle. "That's why we wanted to stay with the known quality."
Four handles are injected in a four-cavity mold, each of which is hollow on the inside and closed on the screw-on side. A robot removes the plastic handles at a demoulding temperature of 80 to 90°C and places them in sleeves of the press-in station. The robot then positions one screw in each hollow handle, which is then pressed down through the still soft plastic so that exactly 12 mm of the thread protrudes on the screw-on side. All four screws are pressed in simultaneously. The finished handles are then subjected to two test procedures and then put down.
The structure of the cell is quickly described: the all-electric injection molding machine Roboshot α-S 150iA and an M-20iA robot from Fanuc, feeding technology from Grimm with separation technology for screws, vision system from Fanuc with Sony camera enclosed by a protective fence.
"We didn't look at an existing modular system, but concentrated on the system," says Lützkendorf. "The system was ready at the first attempt. There was no correction loop. The project team also made use of the FANUC Roboguide software, with which the plant construction can be simulated in advance. Since the design was done completely in-house, all 3D data was available, which naturally facilitated offline programming and simulation of the cell. All data for the removal cycles and pressing could be transferred 1:1 into the programming. The cornerstones were thus set, the basic position and reference marks laid out with Roboguide - and that was it. Only for the actual removal process was the fine adjustment made on the machine.
All processes are initiated and controlled by the robot controller. The system was deliberately built without PLC. When switched on, the robot makes a reference run, everything is reset to the initial state and the system can be started from the injection molding machine. "Via the I/O Link interface, we have a perfect connection between the robot and the robot shot," says the production manager - including peripherals such as the control of pneumatic valves, the screw feed or the press fixture. "Everything is kept user-friendly and also simple because the central components from Fanuc come from a single source". In fact, the system is operated by a single button.
A process visualization system was subsequently installed. Since the cell is located in an "unmanned" hall, it should always be possible to have a look at the status of the cell from the existing production hall.
What was originally intended as a tool for displaying production data for the management has in practice developed into a real support for the employees. On the one hand, a glance at the status monitor saves unnecessary walking distances to the adjacent hall, on the other hand it immediately signals whether a helping hand is required.
For quality assurance, standard systems and mechanisms are integrated into the cell. In the process itself, a sensor system monitors whether the screws are correctly seated after the pressing process and whether the required 12 mm threads are protruding from the plastic handle. In addition, a 100% visual inspection of the handles is performed with a vision system from FANUC. Then the robot places the four handles evenly in the pallet cage.
The robot cycles upwards in steps of a few millimeters, so that the parts fall to a maximum height of 10 mm. Damage to the polyamide handles is virtually impossible. At the start of the production process, the robot scans the floor and then layers 135 layers upwards at five depositing positions. The mesh box holds a total of 2,600 components - the production quantity of one shift.
The cell runs from early assembly until early Saturday morning, or one shift longer depending on the order situation. Screws have to be refilled every three or four hours. Otherwise, the cell runs autonomously. According to Kevin Lützkendorf, "tuning measures" are out of the question: "Of course, we still have a bit of air in the process. But I do not have to produce more parts than I need. He is more interested in ensuring that the machine is used to its full capacity: "It is better to have a predictable, constant process than the shortest cycle times, which could endanger process reliability. In the end, that doesn't help."
A robot S-150i in a loaded version with 180 tons clamping force and a larger mold opening is in use. Daniel Armbruster, plastics expert at Fanuc: "Here we have two interesting alternatives. The 150-tonne version is ideal for continuous operation with high volumes and short cycle times. The 180 t version offers more flexibility, provided that the cycle time is not the first selection criterion".
The demoulding is done with an index mould. This means that the parts do not fall down during ejection, but are removed by the robot. The machine's drive-up distance is therefore important in order to get into the mold easily with the quadruple gripper.
Hans Arnold Kunststofftechnik has been using all-electric Roboshot injection moulding machines for over a decade and they now fill almost half of the machine park. Petra Arnold-Herpertz, together with her father, the company's managing director, pursues a consistent strategy: "It is important for us to break new ground in technical equipment as well and to signal to our customers our efficiency and willingness to perform". The main arguments in favor of Roboshot are its precision and energy efficiency. "Both criteria are important." For Production Manager Kevin Lützkendorf, maintenance and service is also an issue: "We recently serviced our oldest robot, a 50-ton machine purchased in 2007. There was nothing, nothing at all. The machine is still in perfect condition, actually unchanged. If I hadn't insisted on preventive maintenance, the machine would probably continue to run for another ten years without any problems. Was there really nothing at all? A little grease had accumulated and a fan was replaced - just in case. Otherwise: low-maintenance and easy to service, no comparison to hydraulic machines.
Experiences like this are inspiring, also with regard to cooperation: "Fanuc shines when it comes to advice, support and service," says Lützkendorf in praise of his supplier. Daniel Armbruster, his contact person at Fanuc, gives back: "In our application support, we also get completely involved with the customer, and at Arnold we also had discussion partners with precise ideas and an eye for the whole.
The next project is already in the constructive phase. Lützkendorf: "For the new project, too, we will again do everything ourselves. This has the advantage that we have no frictional losses in the coordination of the individual areas. Together with the customer, the decision was made in favor of automation. Hans Arnold's equipment construction department is still responsible for such a project and is focusing its activities on its own production.
Petra Arnold-Herpertz can certainly accept the idea of realizing projects outside the company with a "Hans Arnold Systemtechnik": "We believe that we can offer automated cells in the current constellation so inexpensively that it is also interesting for other plastics manufacturers who want to implement automation with a smaller budget".
Lützkendorf: "We are not talking about systems with 20 robots. We are talking about a complete package from the idea to the falling plastic part". But until we get there, "let's practice a bit more," laughs the boss.
f. l. t. r. Daniel Armbruster(Fanuc Sales), Kevin Lützkendorf(Production Management Hans Arnold), Thomas Alt(Plant Engineering Hans Arnold), Petra Arnold(Management Hans Arnold), Andreas Foissner(Electrical Foissner&Abt GmbH), Tariq Nass(Construction tqn engineering)