Additively manufactured components are available with almost any complex geometry. This has the advantage that the geometry can be optimally adapted to the intended use of the component. Due to the lower production accuracy and surface quality achievable with additive manufacturing, post-machining of the functional surfaces is usually still necessary. However, clamping the complex-shaped components is a challenge. Conventional clamping systems often cannot be used or can only be used with a high set-up effort. For this reason, the Institute of Production Engineering and Machine Tools (IFW) at Leibniz Universität Hannover is researching a new clamping system together with Lauscher Präzisionstechnik and the company Spreitzer.

Challenge: clamping additively manufactured components

Additively manufactured components can be designed in such a way that they achieve optimum utilization of the material used. As a result, they are significantly lighter than conventionally manufactured components - with the same rigidity, service life and function. In times of dwindling resources, this advantage is becoming increasingly important. In combination with the increasing price erosion of additive manufacturing processes, there has been steady growth in this sector in recent years. Compared to machining production processes, however, the shape and positional accuracy and surface quality achievable with additive processes is still considerably lower. For this reason, post-processing of the functional surfaces is necessary. However, clamping the components is a challenge. Typically, form clamping jaws with a geometry specifically adapted to the workpiece are used for this purpose. Consequently, specific form clamping jaws must be available for different workpieces - this has a negative impact on non-productive times and production costs. Another disadvantage of form clamping jaws is that the clamping surfaces of the workpiece used for clamping cannot be machined without reclamping; this results in additional production costs.

A new approach for clamping additively manufactured components is being developed as part of the funded research project "AllSpann". The project is researching the use of several flexible ram clamping jaws. These jaws clamp the workpiece from several sides and can be moved forwards and backwards. The idea is that the clamping jaws automatically retract when the tool approaches and release the workpiece surface to be machined. By using at least four clamping jaws, secure clamping is still guaranteed by the remaining three clamping jaws even after one jaw has retracted. The biggest advantage of the system is that non-productive times are reduced.

Flexible clamping jaw with automatic workpiece release

A first prototype of the flexible clamping jaw was developed as part of the research project. It has form-flexible clamping surfaces that are based on individual clamping pins and emboss the contour of the workpiece. The pins of the clamping jaws can be clamped after the contour has been stamped in order to absorb the forces that occur during machining. The clamping jaw is also equipped with a linear feed unit that enables a retraction path of 35 mm so that the clamping surfaces can be released for machining. The feed unit is based on a Harmonic Drive FHA-11C-50-D200 servo motor with integrated gearbox and a self-locking spindle drive. The combination of the servomotor with the spindle enables high feed forces and therefore also high clamping forces of up to 3 kN to be achieved.