System supplier AutomationsRobotic has opened up a whole new dimension with its fully-automatic grinding cell for chassis components that offers 99.65 percent system availability.
The robotic cell with two Yaskawa six-axis robots also sets benchmarks in terms of autonomy, output and flexibility.
When AutomationsRobotic directors Walter Schaffhauser and Alexander Steiger and their team closely examined the requirements specification of a renowned automotive supplier for a planned robotic grinding system, they found themselves increasingly questioning the feasibility of the project. The task seemed simple enough: the grinding, in defined areas, of structural components made of die-cast aluminum.
What initially appeared to the experienced system integrators to be a standard application quickly became a genuine challenge due to a whole host of restrictions and special requirements. Walter Schaffhauser recalls: “Even taken in isolation, the specified maximum cycle time of 30 seconds for the complex grinding operations is very difficult to achieve. What made us actually doubt the feasibility of the entire application, however, were the maximum requirements with regard to flexibility and availability. Despite having great confidence in our know-how, it takes a certain amount of courage to guarantee 99.65 percent overall system availability in three-shift operation under the harshest of operating conditions.”
Demonstrating this courage, and the motivation of an ambitious young company with ample confidence in its capabilities, the AR team took up the grinding challenge. In close cooperation with the automotive supplier specialists, a pioneering system concept was developed step by step that perfectly meets the requirements profile. A glance at the system reveals convincing detailed solutions that testify to the great automation expertise of the partners involved.
Details of the robotic grinding cell
The fully-automatic grinding cell is divided into two robot sections with a total of three grinding areas. The varied grinding tasks on the chassis components are shared between the two Yaskawa 6-axis robots, with the larger MS 80W in charge of operations in the cell while the smaller MH 50 performs the tool-guided grinding tasks.
Thanks to its considerable reach of over 2.2 meters and payload capacity of 80 kilograms, the MS 80W is able to perform the complete handling of the components and the workpiece-guided grinding tasks. The details of the sequence of operations are as follows. The structural chassis components are transported to the robotic cell on a conveyor belt. Once a part has reached the defined unloading position, a window in the robotic cell automatically opens, allowing the large 6-axis robot to reach out to the conveyor and fetch it into the cell for machining. The door then closes, hermetically sealing the cell, and the grinding operations can begin.
For this, the large 6-axis robot moves to the stationary grinding station and carries out various workpiece-guided work steps. It then transfers the part to a clamping fixture where the streamlined MH 50 executes further tool-guided grinding processes. In order to achieve the specified cycle times, AutomationsRobotic has coordinated the processes in such a way that the robots can work at their respective stations simultaneously and there are always two structural components in the cell at any one time. Once all the grinding is complete, the MS 80W removes the part from the clamping fixture and sets it back down on the conveyor belt. Alternatively, the parts can also be offloaded via a service drawer to enable integrated quality inspections.
More than 800 possible machining variants
Two technical highlights underscore the amount of know-how that has gone into the system. One of these is the automatic compensation for wear of the grinding materials. The state of the abrasives is permanently monitored by means of sensors. The motion paths of the robots are then automatically adjusted on the basis of this data. Only in this way is it possible to meet the strict requirements of the automotive manufacturer with regard to consistent machining quality and guaranteed process reliability with all steps fully documented.
Walter Schaffhauser is also particularly proud of the programming options which include an impressive range of stored machining variants: “Five surfaces that are always to be machined are defined for the structural components. In addition to this, there are 29 further surfaces for optional grinding, depending on the degree of wear to the tools in the upstream aluminum die-casting process. The operator can directly select or deselect each of these surfaces individually on the visualization display of the system. Theoretically, freely combining these surfaces results in more than 800 machining variants, each of which had to be completely programmed in the robot with meticulous attention to detail.”
Yaskawa robots take grinding dust in their stride
Without a doubt, however, the major difficulty presented by the requirements specification was compliance with the specified system availability of 99.65 percent in such extreme operating conditions. At the on-site photo shoot it became apparent just how harsh these conditions really are. Extremely fine grinding dust settled everywhere in the cell and all over the robots. Once the six-axis robots start their grinding operations, it is simply impossible to take photographs. The cell is now on “fine dust alert” and visibility is down to that of the densest London smog.
Although AutomationsRobotic pulled out all the stops with regard to dust removal by installing the most powerful extraction systems, the strain placed on the robots by the grinding dust is enormous. Furthermore, in the 1,440 minutes of a complete working day, the maximum daily downtime allowed for cleaning the system or replacing worn abrasives is just five minutes. “The fact that we were nonetheless able to achieve this incredible availability is primarily due to the proverbial quality of the Yaskawa robots that serve uncomplainingly, even when exposed to massive quantities of grinding dust. For these six-axis robots, failure is an unknown concept - even in three-shift operation under such extreme conditions,” says Alexander Steiger.
The automotive supplier that mass-produces the aluminum structural components for one of Germany’s leading automotive manufacturers is clearly satisfied by AutomationsRobotic’s pioneering robotic grinding cell, as is shown by the recent follow-up orders. “We have received an order to build more grinding systems in 2015. Our minor gamble in accepting such a challenging project has fully paid off. To our immense relief, we managed to complete it to the full satisfaction of our customer. With this motivation to spur us on, we are now embarking on the construction of the new robotic cells,” agree Walter Schaffhauser and Alexander Steiger.