KUKA Systems in the friction welding process – Technology part VII
The history of welding goes back to the Middle Ages. This joining method was once used for producing tools and weapons. Mostly, these were made by the hard work of forging from iron or copper. This welding process underwent little change until the early 19th century, but has developed remarkably since then.
Back in 1966, KUKA Systems developed friction welding as an industrial joining process. Since then, this sector has featured numerous innovations such as short-cycle welding or defined-angle friction welding. Many customers put their trust in the process because it guarantees a high degree of safety. As in the Magnetarc welding process, the friction welding machine guarantees the greatest possible quality in manufacturing safety-relevant components such as drives, engine components, axles or turbine rotors. In friction welding, unusual material combinations such as joining copper or aluminum to steel, and many other combinations, are the state of the art for KUKA. Such combinations are only possible with restrictions when other processes are used.
The friction welding process
In the starting situation, the two materials to be joined are firmly clamped and positioned in the machine. The second phase is the heating phase. The workpiece in the spindle is set rotating, and both workpieces are pressed against one another
KUKA Systems RS 300 – a powerful unit with 3000 kilonewtons forge force
with a defined force. The rotation and contact pressure generate friction, causing the welding surfaces to heat up. The third and last step is the actual welding process. At a defined moment in time, the rotating workpiece is braked and the contact pressure is increased. This creates the friction-welded joint.
The machinery involved
KUKA Systems places particular emphasis on dynamic properties, process control and, above all, precision. This is achieved by preloaded rolling-contact bearings in the slide guide, which do not permit play and also make it possible to achieve maintenance advantages because of the extremely long lubrication intervals. With long components, the floating slide acts like a highly sensitive fixture for automatic compensation of material elasticity, at the same time as evening out tolerances caused by manual loading of the components. Highly dynamic drives with frequency controllers are used for improved smooth running and welding quality. These permit variable spindle speeds, and also avoid peak current draws when the spindle is starting up. The machines are divided into force ranges with maximum forces between 20 and 3000 kilonewtons. The parameter monitoring facility PCD is an important system component. All parameters and machine sequences are monitored with cycle rates of one millisecond, and the values are displayed and documented at the end of the welding process.
Exact monitoring and precise control
Simultaneously with the process, the PCD system archives all the program and actual value data in an integrated database. An Ethernet interface is available for data exchange and connection to the network. The system runs under Windows, which means the user interface is very operator-friendly. In addition, the operator can choose between a numerical and a graphical mode when entering the welding parameters. The user receives an error message immediately in case of malfunctions. Thanks to the integrated ProAgent diagnostic software, it is possible to localize the fault quickly and easily, allowing it to be rectified immediately.
The KUKA Systems PCD feature is the high-end system for process control and monitoring. Eight parameters are evaluated and stored in real time and in parallel with the welding process. The documented parameters include not only the spindle speed and friction pressure/travel/time, but also the welding time, starting position and forge pressure. The parameters are additionally stored for tracking, which makes it possible to establish even years later when which part was produced with which parameters. If even one parameter in the process deviates from the defined lower or upper limits, then the system identifies the product as a reject and marks it accordingly. This ensures that machine- or component-related influences are detected. Only perfect components go on to further production.