Around 30 different types of worm gear screw jacks - electromechanical drives that convert a rotary motion into a linear motion - are manufactured by the Austrian company Zimm. Previously, the components were clamped onto plates manually, but the company has automated this process with the help of Vischer & Bolli. Together with other cooperation partners, they developed a flexible production cell consisting of a five-axis milling machine from Grob and two robots from Kuka. The latter take over the fully automated loading and unloading of the fixtures and workpieces in the production cell with their subsequent post-processing. Specially coordinated clamping technology and sensors from Vischer & Bolli ensure reliable processing in the cell and the machine.

Special gripper solution for the robots

A special gripper from the Zimmer Group on a Kuka KR Quantec robot removes a pallet of blanks. It loads the milling machine with the components, removes them after machining and automatically places them for post-processing.

© Kuka

For the special gripping tasks in the robot cell, those responsible called in the systems engineering department of the Zimmer Group. The department developed a special version of a double gripper with servo technology for the production system at Zimmer. This can grip components of all types and different geometries. It has a stroke of 150 mm and a holding force of 5000 Nm or 3000 Nm with a secure hold via a trapezoidal threaded spindle in the event of an unforeseen power failure. In addition, the clamping pressure on the gripper can be variably programmed depending on the workpiece.

Almost all tasks that previously had to be carried out manually are now performed fully automatically by a KR Quantec and a KR Agilus from Kuka. The five-axis milling machine is supplied with raw material via a lift system. To do this, employees load trays within a 4 m high lift system. In addition to raw material and finished parts, the clamping devices and, if necessary, tools are also stored here.
The subsequent processes are fully automated: A special gripper, which is docked to the KR-Quantec robot via the zero-point clamping system, first removes the trays filled with raw parts (aluminum and cast cubes) in various sizes from the lift system in the robot cell and places them on an attachment table. The robot then uses the gripper to automatically position four blanks in the fixture and places them in the milling machine. The machine can produce around 30 different components in batch sizes between 1 and 200 from aluminum and cast iron. Loading the quadruple fixture outside the machine avoids unnecessary downtimes on a table machine.

Automatically correct tolerance deviations

While the milling machine processes the four workpieces, the Zimmer gripper on the KR Quantec loads another fixture. Once the components have been machined from both sides - the turning process is also automated - the gripper places them on the workstation for post-processing. There, a KR Agilus type KR 10 R900-2 deburrs and cleans the aluminum and cast parts, while the Procam master computer of the modular robot cell takes over the entire logistics. The next stage of automation involves checking all measurement parameters in a further process step. Tolerance deviations can then be transmitted and automatically corrected via a feedback loop to the milling machine.

Flexibility through modular cell design

The modular design of the robot cell opens up a wide range of possible applications. All project participants see automated machine tools as the future in machine and mold construction as well as in the automotive and medical technology sectors. Particularly in the field of parts handling, there will be no other option in the future due to economic efficiency.

Sebastian Schuster
is Global PR and Content Manager at Kuka.

Gregor Neumann
is responsible for media and communication at Zimmer Group.