Automation tooth by tooth
30. November 2017
The plant was installed at Weißer & Grießhaber GmbH in Mönchweiler, near the county town of Villingen-Schwenningen in the Schwarzwald-Baar district. At present almost 300 employees are turning out over 850 million plastic parts per year on about 100 injection moulding machines with clamping forces varying between 15 and 280 tonnes. With in-house mould construction as a basis, precise solutions for the automotive, building and sanitary industry, as well as for the fields of industrial and consumer goods, are being developed and produced together with the customers. The company’s competence embraces the areas of gearing and drive technology, hybrid and multi-component technology, microfilters and thin-wall technology, lenses and optical parts, including assembly and automation technology. The injection moulding automation described in the following was developed and realised by EGS Automatisierungstechnik GmbH. EGS was founded in 1996 and is headquartered in Donaueschingen. In its first 20 years the company installed over 1,200 industrial robots, mainly in the sphere of injection moulding and machine tools automation.
This system also includes three industrial robots manufactured by Yaskawa, at the time of installation still being marketed under the product name Motoman: a four-axis SCARA robot with a reach of 850mm and two six-axis robots with 6 kg and 20kg payloads and reaches of 1.4m and 1.7m. Uniform operation and programming across all the different kinematics is thus assured. The metal inserts are separated via two vibrating spiral conveyors from bulk material and positioned for picking up by the SCARA robot. One feed system is responsible for the provision of each insert variant. At this point a changeover procedure is thus unnecessary when a change is made between the two part variants.
The SCARA robot picks up the inserts individually from the feed system and deposits them already in the correct cavity spacing of the injection mould at a preheating station. In the case of the gear housing, the components are injected in four cavity moulds; in the case of the gear wheels, six cavities. With the gear wheels the SCARA robot also takes care of the radial orientation of the inserts before positioning them for preheating. The preheating station likewise has a universal configuration for both component versions and reproduces both transfer moulds and mould cavity geometries in parallel.
The larger of the two six-axis robots, a Motoman HP20, picks up the inserts at the correct insertion temperature from the preheating station and moves to the Arburg injection moulding machine with a clamping force of 250 tonnes. Following the injection process, the finished parts are removed on the ejection side and the inserts inserted on the nozzle side. Retooling to the two workpiece variants takes place here through a complete change of gripper head. With a manual tool changing system, this is done in next to no time. The media supply is plugged and unplugged tool-free with the respective quick-change coupling. With the appropriate coding, the robot recognizes whether the suitable gripper tool is already mounted for the selected programme. Whereas the process was identical up until now for both parts variants, it differs after removal. The gear housing is examined by optical sensor for core breakage and then deposited by the HP20 on a conveyor belt in rows of four. The latter carries the finished parts from the robot cell and drops them into two bins at the end of the belt. Positioned packaging for these components is not required by the customer. Following removal, the gear wheel is transferred to the third robot, a Motoman SSF2000. This takes place by direct handover, part-by-part in a star-shaped gripper tool. Now the finished parts are inspected one after the other for possible overfeeding or missing inserts by rotating the hand axis on a camera system. The robot then deposits the good parts one-by-one in mould cavities of the customer’s packaging, a deep draw tray. The empty trays are fed in stacks by a conveyor system, and the stacks of filled trays taken away on a second conveyor belt system. Following an automatic gripper change, the 6-axis robot performs the stacking work with a second gripper tool for handling the trays. No elaborate pallet system is thus required and the robot can demonstrate its full flexibility. The system offers autonomy for four stacks of 20 trays, each of which holds 39 finished parts. The system has been in three-shift operation since 2012, on 5-7 days per week depending on the customer’s need for parts.
Michael Späth, responsible for the TSA 20 area at Weißer & Grießhaber, praises the reliability and flexibility of the system: “Right from the beginning, the system was working reliably and accurately. Thanks to fast and simple retooling, a product change is easy, despite the different tools and packaging. Since their installation, the robots have easily proven their reliability in three-shift operation.”
Text: Heiko Röhrig, EGS Automatisierungstechnik GmbH
Tel. +49 (0) 771 185 90 80-0
Fax +49 (0) 771 185 90 80-99
Contact Weißer + Grießhaber:
78087 Mönchweiler / Germany
Tel. +49 7721 9487 0
Fax +49 7721 9487 50
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