When injection molding and toolmaking company Reiter HG Geiger Kunststofftechnik GmbH (Hilpoltstein, Germany) sought to automate a delicate, precise assembly process, finding a partner proved to be daunting. The operation, which was being done manually, involved the insertion of 0.4-mm-diameter parts measuring 1.65 mm long into slides with injection cavities that are barely larger than the parts. Several companies Reiter approached did not consider their technology up to the task, given the miniaturization of the components and the precision required in their manipulation. It began to seem like the “task was not even solvable,” said Process Engineer Hans Kolb, but perseverance eventually paid off. A mechanical engineering firm partnered with Reiter to develop the right combination of vibratory feeding, vacuum suction and robotics to automate the process.
|Contacts, including pins less than 1 mm long, must be placed in a slide for overmolding.|
Reiter produces a thermoplastic part with overmolded contacts for a medical application. Slides with two injection cavities each hold four metal components. Manually inserting the tiny parts into the slides, which have a clearance of less than 0.01 mm, requires extreme concentration and poses a major challenge for consistent product quality. "In addition, the work as a whole is rather monotonous, which makes it hard to stay focused," said Kolb. Another disadvantage of the manual loading method is that if the surface coating is damaged, the parts are unusable.
Orders for the parts were steadily increasing, making it feasible to consider automating part of this process. After a rigorous and sometimes frustrating search, Reiter HG Geiger Kunststofftechnik GmbH partnered with a mechanical engineering specialist to develop a system that reliably separates and grips the pins and positions them in the slides.
The first hurdle in automating the process involved separating the contact pins for the subsequent pick-and-place operation. This was achieved with the use of a grooved vibratory bowl that feeds the part to a vacuum-based suction device. A robotic arm grips the pin and brings it to the slide.
Another challenge encountered by the engineers was ensuring accurate insertion of the pin in the tool cavity. Similar to the injection molding process, the slide is initially centred in the robotic cell with the aid of short-stroke cylinders and is then clamped to stop it from slipping. Each carrier is coded individually so that it can be identified by the system. "This is necessary because not all tool slides and holes can be made exactly the same in the 0.01-mm range,” said Kolb. “So that the robot finds the appropriate holes, it is specially trained on each slide. This allows the pin to be properly positioned, inserted and returned immediately.”