In the late 1980s, the automated grinding and polishing of mass-produced parts was typically carried out by special cam-operated or CNC-controlled machines. As fixtures, fittings, and components from the medical technology and automobile manufacturing industries became more complicated, the use of freeform surfaces began to increase and economic solutions needed to be found for the growing product variety and smaller series.
Whereas robots provided the degree of flexibility required for this operation, they have their limits when faced with highly complex geometries. In order to reach the farthest corner and the deepest radius, the grinding and polishing machines, to which the robot holds the work pieces, needed to be able to swivel into specific positions.
Karl-Heinz Oberkampf, production manager at SHL, (Böttingen, Germany), recalled the early years of this dilemma stating, “In the first installations, we mounted our grinding and polishing robots on a construction we put together ourselves from gears, transducers, and locking mechanisms which involved a lot of work. In the mean time we were looking for a standard, yet flexible solution.”
SHL consulted with Weiss North America, Inc. (Willoughby, OH). Using the same dimensions and load data, Weiss offered both fixed-position and user-programmable tables, both with and without their own drive as required. Thus Weiss was able to offer SHL not only a high degree of standardization in design and construction, but also flexibility when it came to the drive and control system.
In a typical robot cell, several grinding and polishing machines are mounted on a rotary indexing table or arranged in a fixed constellation around a robot. The articulated arm grips a component and guides it along the polishing disks and grinding belts. The Weiss rotary indexing tables allow processing at various angles and even enable travel during processing.
Notably, SHL selected the rotary indexing tables for their swivelling and positioning units, and rotary indexing rings and heavy-duty tables for special solutions without drives.
The lightweight design has both of the smaller SHL grinding and polishing machines mounted to a fixed-position WeissS TC220 rotary indexing table. The table rotates in 15-degree steps and swivels the machine a maximum of 90 degrees from the central axis.
For the heavy grinding and polishing machines, Oberkampf chose the user-programmable Weiss NR750 rotary indexing ring.
SHL also increased use of the Weiss rotary indexing tables for special machines and feeding systems. One such case is the polishing robot, in which a user-programmable Weiss CR750 heavy-duty table takes care of changing the work piece carrier.
Weiss supported SHL in selecting a drive to go along with the rotary index table. The drive and control system are selected in accordance with the customer‘s requirements, which means many different motors are used. In some cases, the rotary indexing table is even controlled by the robotic control system as an additional robot axis.
Weiss’ first step is to define the size of the rotary indexing table in line with the specified volumes and dimensions in the concept phase. As soon as detailed construction data and information on the desired drive are available, they contact the drive manufacturer in order to find the optimal motor size and transmission ratio for the application and the table used.
Finally, the SHL robot heaves an enormous polishing unit over the work pieces that the heavy duty rotary indexing tables from Weiss replaces with a fresh batch once processing is complete. To date, more than 1,100 SHL robotic grinding and polishing systems have been implemented worldwide.
WEISS North America, Inc.