When EDAG, a global design engineering firm for vehicles and the production plants that manufacture them, was faced with the task of designing a new production concept for small-lot production of vehicle components, it wanted a more efficient system. The rectangular index tables common to most automotive manufacturing cells let humans or robots work from only one side. But a ring-style table with a robot in the middle has 360 degrees of workspace and reach.
The challenge was EDAG wanted a system that could not only bear the weight of car body tools weighing up to 4 tons, but also provide sufficient room at its center for handling systems and a heavy-duty robot.
EDAG’s Managing Director/COO Manfred Hahl commissioned Weiss North America (www.weissna.com) and its German parent Weiss (Buchen, Germany) because they are specialists in rotary tables and automation. EDAG knew what its automotive customers wanted: While production is underway at one or two positions, the free positions must then be either manually or automatically equipped with new tools, ensuring fast availability. The table should also feature sufficient space in the center for a robot to carry out both machining and logistics functions—thus permitting space saving while enhancing the flexibility and productivity of the system.
According to Bill Eppich, vice president for Weiss N.A., his company started designing a rotary table that could accommodate four tools and the largest ABB robot available. The result was the CR 2600—a unique-for-its-size combination of a classic rotary table and a shuttle system, in which robots can access the workpiece from both sides.
Says Stanislav Cafuta, a Weiss system developer, “ The key was designing the ring’s central opening with a diameter of 2 meters, tool weights of up to 20 tons, and a reach of up to 2.5 meters—demands which even our largest heavy-duty rings were unable to meet at the time.”
One of these critical parts of the ring design was the very large bearing. The development of a so-called YRT bearing, a combination of two axial bearings and a radial bearing, is a time-consuming matter, Eppich says, and “such large parts are not easy to come by.” To overcome this issue, Weiss engineers assumed responsibility for development of the bearing cages themselves and they compressed total development time and delivery to six months.
Another important choice was the use of SEW servo motors to move the heavy table. “There are only a couple of good motors that large with enough torque for that kind of load,” Eppich says. “Customers often want the same motor used in both the robot and the table, because they think they’re saving on spare parts. But EDAG let us spec the best motor for the job.”
The WAS software overlay lets anybody who can use a computer and Excel program the servo parameters of the index table. “Anyone with mechanical or electrical experience can configure the system,” Eppich says. “You don’t have to write code for the servo.” The parameters of the table are held in the servo drive. EDAG will integrate the servo and robot controls with its choice of PLC once the table is on-site.
The system is currently running with two tools for two components, so that the rear hatches and bonnets of a major automotive OEM can be manufactured in a combined process. Eppich says the CR 2600’s unique configuration “opens up other possibilities for the installation that sparks the imagination.” This is due to the user-programmability of the table, as well as savings in floor space brought about by the option of positioning even large robots at its center.
EDAG’s Hahl expands on the possibilities: “For example, if an opening of 2 meters can accommodate one large robot, then there is, of course, room for two or more small robots. In addition, four or more different tools can be used instead of the current 2+2. As a result, it is possible to either produce four different door types for small lots on one installation, or provide four different tools in quick succession in a similar manner as a turret on a machining center.”
Hahl adds, “The free positions can also naturally be used for logistics and equipping the tools. Therefore, the heavy-duty ring’s low height of only 300 mm is very convenient, enabling ergonomically favorable, stepless manual loading alongside automatic loading."
>> For a video demonstration of the Weiss CR 2600 visit: http://www.Weissna.com/Type-CR.509.0.html
>> Renee R. Bassett, firstname.lastname@example.org is Deputy Editor of Automation World.