Additive manufacturing processes have opened up new design possibilities for components. Due to the layer-by-layer structure, components with almost any geometry can be manufactured. During construction, components can be optimally designed for their intended use. Additive manufacturing processes are therefore particularly widespread in the production of lightweight structures.
One challenge of additive manufacturing processes is the production of functional surfaces and low tolerances. Additively manufactured components are therefore machined. For machining, the components must be securely clamped in the machine tool using suitable clamping devices. Common clamping devices such as clamping claws can often not be used. The reason for this is that due to the high geometric complexity of the components, suitable planar or cylindrical clamping surfaces are usually not available. So-called shaped clamping jaws are therefore often used to clamp the workpiece. These clamping jaws form a negative shape of the workpiece to be machined on the clamping surface and must be individually manufactured for the respective workpiece.
The production of the shape clamping jaws thus represents an additional, non-value-added manufacturing step. In addition, the shape clamping jaws can often only be used for one specific workpiece and cannot be reused for other workpieces. In addition, several clamping set-ups are usually required to machine all functional surfaces. In addition, time-intensive measuring processes of the workpiece are often associated with each clamping set-up in order to precisely determine the position and orientation of the workpiece in the working area of the machine tool and thus also to comply with narrow manufacturing tolerances. With existing clamping systems, there is also the deficit that the contact surface of the workpiece on the clamping surface can only be machined in a additional clamping set-up. A clamping system that enables workpiece machining on all clamping and functional surfaces in just one set-up without individual clamping jaws thus offers particularly high potential for significantly reducing non-productive times. Such a clamping system is described in the following section.
Concept enables machining of the clamping surfaces without reclamping
The picture above shows a schematic of the new clamping concept for additively manufactured components. In this approach, the workpiece is fixed with the help of several clamping modules. Each clamping module consists of several pins that are arranged in a grid pattern (figure detail a). The pins are mounted on sliding bearings and can be locked in a specific position. In combination, the pins form a negative shape of the workpiece to be clamped, analogous to existing shape clamping jaws. Such clamping modules are already available on the market. In the "AllSpann" research project, the clamping module is combined with a linear unit. This allows the clamping module to be positioned in the X-direction in each case. The advantage of this approach is shown in figure detail b). With a retraction of the clamping module, the clamping surface becomes accessible for milling. The workpiece is securely fixed by the remaining clamping modules. After machining at this point, the clamping module is again brought into contact with the workpiece and thus contributes to secure clamping. With this procedure, clamping and functional surfaces can thus also be machined. This also eliminates additional reclamping processes and the associated non-productive times.
The clamping system is currently being prototyped at IFW. The first results on the application behaviour of the system are expected in Q4/2023.
Contact:
For further information, please contact Eike Wnendt, Institute of Production Engineering and Machine Tools at Leibniz Universität Hannover, via telephone +49 511 762 18257 or by e-mail (wnendt@ifw.uni-hannover.de).
