A completely automated process for overmoulding 72,000 pieces a day
Lautertal Plastic began life as a company manufacturing injection-moulded plastic pieces for the mobility sector. This German firm, which specialises in high volume production, has chosen to keep its labour force small – it employs just 24 people – and enhance its production capacity by means of work shifts and above all completely automated processes. The company persisted in its strategy even when it was awarded a large contract to supply internal leads with Fakra pin connectors, the type of connectors used, for example in GPS, GSM and radio cables.
A well-considered choice
«Our absolute priority was to produce the inserts, or gilt finish brass pins, in two different lengths for use in a 16-cavity mould supplied by Erz, in a cycle time of approximately 20 seconds – says Wolfgang Goller, general manager of Lautertal Plastic –. Another priority was the production of large quantities of high quality pieces. This forced us to operate using a highly efficient process. For this reason we spoke to a number of injection machine manufacturers and worked with them on the design right from the very beginning. This brought about a number of different solutions from which we chose the best».
«Arburg came up with the most convincing solution – says company CEO Ingo Schöllhammer–. As well as the machinery, Arburg also supplied the peripherals and took care of integrating them into the system. This was a great help because we were working with just one supplier for maintenance and any follow up problems that might arise».
Speed and precision
The production cell is built around a hybrid injection Allrounder 370 H, the electric clamping unit of which permits short cycle times. Precise injection is assured by a position-regulated screw and electro-mechanical dosage drive.
A shortened 15 millimetre screw minimises material dwell times. The pins, in versions with a length of 10 or 16 millimetres, are overmoulded with 0.07 grams of a special polypropylene. The PP is cross-linkable in order to increase its temperature resistance. This is because the internal conductors are subsequently irradiated and soldered onto circuit boards at a temperature of around 260 degrees centigrade. In addition to the vertical Multilift V robotic system, the peripherals are also integrated in the central Selogica machine control system. «The complex system is simple to operate – says Ingo Schöllhammer –. Arburg programmed the sequences for us and then trained the machine operators on our application».
Gripper performs simultaneous removal and insertion
The key challenge here is the reliable and positionally accurate insertion of 16 pins per cycle into the mould. The feeding device was designed by Hörmle: two vibrating spiral conveyors separate the bulk goods and feed the pins to a Scara robotic system, which transfers them one-by-one to a provisioning device. The part length is optically checked in a fraction of a second during the process. As soon as all the pins are in a horizontal position, the vertical Multilift V robotic system docks onto the insertion module of the gripper (made by Kiki). The pins are pressed into the bores provided and held in place by vacuum. The robotic system then moves vertically into the open 16-cavity mould, where it is centred. Forked photoelectric sensors ensure that no pins are left on the nozzle side.
On the ejector side, the finished parts are first pushed into the 16 cavities of the robotic removal module and held in place via a locking plate. Simultaneously, the insertion module on the opposite, nozzle side, inserts the pins into the bores. A vacuum applied to the mould ensures that the pins remain in position.
During vertical extension of the robotic system, photoelectric sensors check that all 16 pins are inserted and, if the number is correct, transmits an OK signal to the Selogica control system. The injection moulding process can then begin. In the meantime, the finished parts are ejected according to the cavity pattern via a tubular distribution system and the next 16 pins are provided. This process allows Lautertal Plastic to produce up to 72,000 parts a day.
Version changeover in 15 minutes
The same system and mould are used for both part versions. «When switching to a different length, all that has to be changed are two flat bars. After around 15 minutes, the system is running smoothly again», explains Ingo Schöllhammer. As it is very difficult to distinguish between the two pin versions with the naked eye, the correct lengths are verified via a camera system during the ongoing injection moulding process.
Lautertal Plastic generally places great emphasis on preventive maintenance and service. The responsible service technician makes regular visits and also keeps up-to-date by regularly attending training courses at Arburg.
«The fully automated system of internal conductor production is in permanent use here and operates in a very stable manner», says Wolfgang Goller. For 2013, Lautertal Plastic is planning a total production volume of 12 million units.