Schwab CNC-Metallbearbeitung manufactures high-quality milled and turned parts for various industries - from prototypes to larger series in the field of aluminum and magnesium die casting. The company is now planning to link and automate two machines for magnesium machining. The 'Actuator Housing' workpiece is a magnesium housing component for steering gears in motor vehicles; the annual output is up to 250,000 units.
Both sides of the workpiece are machined in succession on two machines: four times on the first machining center and individually on the second machine. At the same time, the machining area of the machines is to be manually accessible for set-up processes and start-up parts. As an additional process, the marking of the workpieces with a data matrix code after machining is to be integrated into the automation process. The automation with robots was developed and implemented as a turnkey system by EGS Automatisierungstechnik.

Robots automate the machining process

Eight components are stored and securely positioned in the workpiece carriers using workpiece-specific holders.

© Zimmer Group / EGS

The starting point for the automation process was the existing Brother Speedio S1000 machining center, in which one side of the workpieces is machined in a quadruple clamping. The existing clamping device, into which the components were previously inserted manually, was to be loaded automatically with as few modifications as possible. The machining time and workpiece changeover total around six minutes for four parts, which was also the cycle time determining specification for the automation. A side loading hatch was retrofitted to the machine, which was integrated into both the safety circuit of the machine and the safety circuit of the robot cell.

Reach played a decisive role in the selection of the robot. In order to reach all positions on the fixture, the robot has to plunge relatively far into the machine. Combined with the required precision when handling and inserting the parts and the necessary high traversing speed, the choice fell on the Yaskawa GP25 industrial robot with a YRC1000 controller.
The second important requirement was the autonomy of the automation system. The system had to be able to produce autonomously for as many as twelve production hours. To achieve this, a storage capacity for 480 raw parts and 480 finished parts must be available. The component dimensions of the geometrically complex workpiece are roughly 145 mm x 135 mm x 50 mm, and the weight is around 200 g. The Sumo Ecoplex2 from EGS was used for this parts storage and provision. This is a palletizing system for workpiece carriers up to a size of 600 mm x 400 mm. The workpiece carriers are stored stacked, depalletized and made available to the robot for parts removal and palletized back after being filled with finished parts. In the version with infeed and outfeed conveyors, the capacity is six workpiece carrier stacks for raw and finished parts.

Commercially available and stackable plastic containers were selected as workpiece carriers. The workpiece-specific inlays, in which the components are precisely positioned, were designed by EGS and manufactured by Schwab using its own production capacities. The correct design of workpiece carriers is essential for the reliability of the subsequent automation.

Gripper for optimum positioning

Another important core component is gripping technology. Gripping modules from the Zimmer Group are used here. A pneumatic three-jaw gripper from the GD300-C series was used for the system.
The three-jaw grippers consist of a robust housing made of a hard-coated aluminum alloy. They are driven by a double-acting pneumatic cylinder with round pistons. A characteristic feature is the power transmission via a synchronous positively driven wedge hook gearbox; this enables high gripping forces through optimum deflection of the drive force. The three-jaw grippers concentrate on the essentials - on the most economical way of gripping in order to reduce production costs. The T-slot guide of the GD300-C grippers ensures high force and torque absorption. It guarantees high rigidity and combines this with a long service life in a compact design.

An end effector with specially designed, workpiece-specific gripper jaws ensures that the components are held securely. The gripper modules also do their job under adverse ambient conditions, in cooling lubricant mist and in constant contact with chips. The blow-out nozzle can be used to remove coarse dirt from parts and fixtures in the machine.

© Zimmer Group / EGS

The second side of the workpieces is processed in a second machine, a Brother Speedio S700. Here too, automatic loading takes place from the side through a special loading hatch. Processing of the second side is much less extensive, therefore takes considerably less time and is carried out individually.
As the first machine determines the system cycle, the four processed workpieces must always be removed from it immediately after the end of processing and four new blanks inserted. A combined depositing and turning station with four workpiece holders is used for the intermediate storage of the semi-finished parts. The robot places the components here and picks them up again, turned, to load the second machine.
In both machines, the components are largely freed of cooling lubricant after machining and before removal by means of a blow nozzle attached to the robot tool.