Here are some of the latest developments in magnetic clamping technology. Article by Schunk.
The electrically activated permanent magnetic clamping technology is considered an insider tip when it comes to reducing set-up time and low-deformation clamping of workpieces. With a bit of design finesse, even large-sized components can be clamped deformation-free in a matter of seconds and machined from five sides. Even in the field of standard modules, development is not standing still: Modern magnetic chucks allow visual or automated monitoring of the clamping process.
The secret of deformation-free workpiece clamping by means of a magnet lies, on the one hand, in the movable pole extensions and, on the other, in the optimized interfering contours. Comparable with a waterbed, the movable pole extensions flexibly attach to the workpiece in the case of electrically activated square pole plates and compensate for workpiece unevenness in the first set-up. Ferromagnetic raw parts can be clamped in this way deformation-free and machined in a single operation from five sides.
In the second set-up, workpiece smoothness that cannot be achieved with any mechanical clamping device is possible: plane parallelism of up to 0.02 mm is not uncommon in practice. Unlike conventional set-ups with chuck jaws or clamping claws, punctiform damage and workpiece deformation are avoided. Instead, users benefit from maximum clamping precision and achievable workpiece smoothness. This advantage comes into play especially with large-area steel plates or other deformation-sensitive workpieces.
Clamping over a large surface area minimizes vibrations, and protects the machine spindle as well as the cutting edges. Operation is very simple: the ferromagnetic workpiece is placed on top and the magnetic chuck is activated by a short current pulse. Within a few seconds, the permanent magnet ensures a long-lasting secure hold, without the need of further energy input.
Magnetic Chucks Report the Clamping Status
On such technology is SCHUNK’s MAGNOS square pole plates, which are now equipped with a patented status display that permanently signals the current clamping state—even if the magnetic chuck has been decoupled from the control system. This leads to zero operating errors and increased process reliability. With this technology, the machine operator always has full control no matter if the magnetic chuck on the machine table has been activated.
Another aspect is that the higher the degree of automation, the more frequently magnetic chucks are now pre-equipped, and stored like pallets in workpiece storages. Using the display, machine operators can now check at any time whether all magnetic chucks in the tool rack are properly activated.
Automated Clamping Procedure
SCHUNK also pursues the idea of simple control and monitoring of the clamping state in the modular control unit SCHUNK KEH plus. Depending on the basic version, one, two, four, or eight square or radial pole plates can be controlled with it—either directly or by using connection boxes via the control unit. The control unit provides information about the current clamping status of the magnetic chucks at any time. A 16-step holding force regulation process facilitates the alignment of the workpieces and allows the clamping of thin components.
In addition, the magnetic chucks can be operated in automated applications via 78-pin PLC connection directly from the machine control system. To ensure process reliability, a detailed monitoring of each magnetic chuck is possible. To do this, the individual clamping state is transmitted via a PLC interface to the higher level plant control. The hand remote control SCHUNK MAGNOS HABE KEH plus, in turn, allows convenient manual control of up to eight magnetic chucks as well as their individual, 16-step holding force regulation. The control continuously provides information to the operator on the individual clamping status of the connected magnet chucks via LCD display and LED. Faults are shown on the display in the form of error codes.
App for Simulating the Clamping
Via an app that SCHUNK will soon provide for iOS and Android, registered users can simulate different clamping situations on SCHUNK MAGNOS square pole or radial pole plates free of charge. For this, only the basic data on the workpiece, the cutting parameters and the type of magnetic chuck have to be entered; the app already determines whether the holding forces are sufficient for machining. With the digital tool, SCHUNK enables a very fast assessment of machining operations. In addition, users can fully use the potential reserves of magnetic clamping technology.
Intelligent Magnetic Chuck with Force Measuring System
The SCHUNK MAGNOS force measuring system takes a significant step towards smart manufacturing. The intelligent magnetic clamping solution automatically records the respective position and size of the workpieces placed on the magnetic chuck, and determines the precise individual clamping force, thus, creating the precondition for continuous process monitoring as well as for automatic adaptation of the machining parameters to the size and quality of the individual workpieces. This means that in the future, the feed rate or the cutting speed can be increased on an individual basis with a large pole cover and high clamping force, or, in the case of low pole covers or low-ferromagnetic workpieces, can be reduced in such a way that process-reliable machining is ensured.
Potential fields of application of the system include the processing of small and medium batches with automated parts handling, as well as machining operations where extensive process monitoring is required. The system paves the way for first-class, highly transparent, and flexible networked processes for Industry 4.0.
Magnetic Gripper for Machine Loading
When it comes to automated loading and unloading of machine tools, the importance of magnetic grippers with electro-permanent magnets has significantly increased. Reasons for this are the high power density and energy efficiency as well as the decidedly favourable interfering contour for handling.
The SCHUNK EGM series is designed for systems with a voltage range of > 400 V. Even the smallest size (26 mm x 98 mm) of the compact SCHUNK EGM-M monopole gripper is suitable for handling parts up to 7 kg. As the magnetic surface reaches right to the outer edge, no interfering contour needs to be taken into account. The SCHUNK Bipol grippers EGM-B, meanwhile, is designed for handling heavy and complex ferromagnetic parts, which are available with either one, two or four pairs of poles in different arrangements.
Under ideal conditions, the EGM has gripping forces between 1.2 and 22.5 kN, depending on equipment, and is designed for maximum part weights up to 147 kg and material thicknesses from 3.5 mm. The compact SCHUNK EMH magnetic gripper is designed for systems on 24 V basis: as the electronics are completely installed in the gripper and it is actuated extremely easily via the digital I/O, the components require neither space in the electrical cabinet nor an external control electronics system. In order to increase process reliability, the gripper reports both the magnetization status and the workpiece presence. At the same time, errors are signalized via an LED display on the housing. Unlike magnetic grippers, no maintenance time between activations is required, meaning high cycle times can be achieved. The SCHUNK EMH magnetic gripper is available in four sizes for workpiece weights of up to 3.5 kg, 9 kg, 35 kg, and 70 kg. For handling thin components and sheets, the magnetic holding force can be adjusted in four stages.
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