The times when brachial roughing was normal are over. Those who want to produce a lot of chips in a short space of time now take advantage of high-quality cutting and intelligent toolholding systems that transmit high torques and, at the same time, reliably absorb any occurring vibrations. Modern toolholders protect the cutting edges, the machine spindle, and the workpiece surface and allow you to work with high metal removal rates even when using challenging materials.

With large volume cutting, you need maximum productivity; that is to say high feeding and infeed rates. As much material as possible needs to be cut within a short period of time. At the same time, the whole system consisting of the headstock, spindle, toolholder, tool and workpiece is subjected to very high loads. Cutting materials specially designed for the procedure such as carbide, cermet or cubic boron nitride withstand the enormous alternating loads on the cutting edge particularly well. In some cases, fibre-reinforced tools are also used to minimize the risk of fracture.

Toolholders are also exposed to extreme loads. When dismantling from the front side, very high radial forces can develop which can cause the toolholder and tool system to be deflected. The deflection behaviours are influenced by the toolholder's design, by the toolholder and tool system's projecting length and by the cutting parameters. Also having an effect - depending on the angle of twist on the cutting edge of the tool - are, in some cases, enormous axial pull-out forces which will pull the tool out of the toolholder in the worst-case scenario.

Four Factors are Decisive when Selecting a Toolholder Suitable for Volume Cutting:

Run-out Accuracy: If the clamped tool does not turn centrically to the toolholder axis, then the tools start to bang during machining, which leads to micro blowouts on the cutting edge and accelerates wear on it. The run-out accuracy also crucially affects whether the dimensions and tolerances are observed. The combination of these factors is the reason why - even in volume cutting - precision toolholders with run-out accuracies of less than 0.003 mm, measured at 2.5 x D, are being used more and more frequently.

Clamping Force: This decides whether the torque at the interface between toolholder and tool can be controlled. If the clamping force is sufficient, the tool's cutting edge cuts evenly into the material. If the clamping force is sufficient, the tool begins to turn in the holder and the cut will be unsteady. In extreme cases, the tool may even be pulled completely out of the toolholder. In order to prevent this from happening, toolholding systems with form-fit clamping, which frequently exhibited deficiencies in concentricity however, were mostly used in the past for volume cutting. Owing to technological progress, toolholders with force-fit gripping today also ensure high clamping forces, which means process-stable volume cutting is possible when using them.

Radial Stiffness: This determines how high the cutting forces may be. Important factors here are the material properties of the toolholder (E-module), the geometry of the toolholder (size and shape, wall thickness) and the integration of the toolholder in the overall system for the machine tool. As the radial stiffness increases, the shorter the toolholder, the greater its diameter; the more homogenous the unit consisting of tool and tool mounting the thicker the wall of the tool mounting and the more extensive the support for the holder on the machine spindle.

Vibration Damping: Vibrations will inevitably occur during milling, and will not only result in the varying chip thicknesses during the machining process and from the interrupted cut of the individual teeth due to the process, but also from imbalances, for example. Toolholders can absorb vibrations in a similar way as the shock absorber and ensure a smooth and even cutting action. This allows noise emissions to be minimized, the quality of the workpiece surface is improved, tool life is prolonged, and the spindle can be protected.

Only Very Few Tool Clamping Systems Meet all the Requirements

Marked differences are revealed if one compares the tool clamping technologies currently on the market with regard to these four characteristics. Weldon chucks exhibit deficiencies in the run-out accuracy and have a tendency to judder. Conventional collet-style holders have shortcomings in the run-out and repeat accuracy as well as in the clamping force.

Heat shrinking holders have a good run-out accuracy, high clamping forces, and high radial stiffness. However, due to the one-piece clamping system, they can hardly absorb vibrations occurring during volume cutting. So precision holders specially designed for volume cutting were viewed for a long time as the first choice in the field of volume cutting on the basis of a polygonal clamping technology.

A framework-like chamber design guarantees you an especially high rigidity. In addition, cast inserts made of a copper alloy ensure excellent vibration damping that is around four times higher than of heat shrinking toolholders.

Hydraulic Expansion Toolholders and Polygonal Clamping Technology

A leap in technology has now ensured that polygonal clamping technology must share the foremost rank with hydraulic expansion toolholders. Among other things, the transmittable torques of the hydraulically expanded precision toolholders could be greatly increased with the help of reinforced expansion sleeves.Thus modern hydraulic expansion toolholders with 20 mm