Achieving low deformation in workpiece clamping

Related Vendors

AMPCO METAL Deutschland GbmH

Renishaw plc

DIPROFIL Diamantprodukter AB

SCHUNK GmbH & Co. KG Spann- und Greiftechnik

Oscillating mounted 6-jaw chuck ensures high repeat accuracy

The smaller the tolerances on the workpiece and the higher the required repeat accuracy, the more speaks in favor of oscillating balancing 6-jaw chucks. They consist of a central chuck piston carrying three inner pendulums aligned at 120°. Each pendulum is connected to two base jaws. This ensures workpiece centering between six contact points, which can be adjusted in pairs. As the clamping forces are directed towards the chuck center, optimal centering is achieved without distortion of the workpiece even for raw parts. Workpieces are aligned and clamped in the 6-jaw chucks in no time at all.

The chucks are perfectly adapted to the raw part with their oscillating jaws. For finish machining or for clamping pre-turned surfaces, the pendulums can be clamped similar to the pendulum jaws in the center positions, meaning all six jaws can move concentrically. Because of its high precision, it is possible to eliminate entire production steps, for example, by reaching tolerances during the finishing process that would otherwise only be reached in complex grinding operations.

Radial pole technology for interfering contour-free machining

Magnetic chucks with electrically activated permanent magnets are a real set-up time killer for low-deformation workpiece clamping. These are used in different versions for low-deformation workpiece clamping. The most common are radial pole plates for which the magnetic elements are arranged radially around the center. With them, bearing rings for instance can be machined in a single set-up on the outer and inner diameter and on the front side. As the magnetic field acts into the outermost peripheral zone, even large workpieces are clamped securely and without any deformations. Due to the two-dimensional holding force, the machining takes place largely without any vibrations. The protects the cutting edges of the tools and improves the quality of the workpiece surface.

To align the workpieces, the holding force can be adjusted using the control system or the holding force regulation. In order to ensure optimum stability, radial pole plates up to a diameter of 4,000 mm should be produced from a single piece. For larger plate diameters, plates in segmental design may be advantageous as these can be transported more easily. To suit the respective application, there are standardized radial pole plates in three versions: for grinding operations, as an AlNiCo single magnet system; for turning operations as an AlNiCo double magnet system with high holding forces. And finally for demanding volume machining with milling and turning as an extra strong AlNiCo neodymium magnet system.

Square pole technology increases flexibility

Users wishing to act flexibly on mill/turn centers combine magnetic chucks with square pole technology with an efficient pair: they use the magnetic chucks both on top for clamping workpieces and downwards for flexibly placing the clamping solution on the machine table. Such a solution can be set up and loaded with a workpiece in just a few minutes. Here, variable pole extensions ensure a safe and at the same time deformation-free workpiece clamping. Without additional set-up effort, workpieces of varying sizes can be machined alternately with a high level of precision on the quadratic pole plates from three or five sides.

With the aid of a multi-level holding force control system, the parts can be aligned within seconds and clamped without any deformations by means of a short current pulse. Like with the radial pole plates, no additional energy feeding is required for square pole technology after having activated the permanent magnet. Compared to conventional clamping solutions, the set-up time is reduced by 30 to 80 percent.

Hybrid chucks combine radial pole technology and a centering chuck

The peaks of the low-deformation workpiece clamping are formed by hybrid chucks, for which the technology of a classic 3 or 6-jaw centering chuck is combined with the technology of a radial pole plate. The clamping process is designed extremely easily: the workpiece can be manually inserted into the chuck, which will be centered by three chuck jaws, and then securely clamped by electropermanent magnets. Particularly for large rings it is worthwhile that vibrations are eliminated, which has an effect both on the workpiece quality and the tool costs. The parts are simply pre-roughed. Then the magnet is temporarily deactivated in order to release workpiece warpings, and then the part can be finish turned. The hybrid chucks can also be activated at varying power levels. They are suitable for use on revolving lathes, mill/turn machines, vertical pick-up lathes and special machines.

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