Precision components must be produced with an accuracy of a few microns. This requires a level of accuracy during manufacture that even cutting-edge processing machines are often unable to reliably deliver. Unfavorable trajectories or light wear to tools can lead to component geometries which do not conform to the specifications. Quality control thus involves precise measurement of the machined components.
Typically, Coordinate Measuring Machines (CMM) in special measuring rooms outside of the machine tool are used for this purpose. The process is slow and complicated, and only random sample measurements are possible.
Measuring Part In The Machine
The digital holography measurement systems HoloCut and HoloPort, developed by Fraunhofer Institute For Physical Measurement Techniques (IPM), make true 100 percent quality control within the manufacturing process possible. The systems map up to 20 mm x 20 mm of the processed component surface with a single measurement. Deviations of a few microns can thus be reworked directly in the machine tool without the need to first reposition the workpiece. In its HoloPort version the system operates without the need for cables.
The incorporated sensors use multi-wavelength digital holography for inline 3D measurement. The systems map the topography of even rough object surfaces with interferometric accuracy. HoloCut and HoloPort provide contactless, highly accurate measurements of component surfaces and operate so quickly and robustly that they can be integrated directly into the machine tool making it possible to detect rejects at an early manufacturing stage. In addition, process errors can be identified and corrected directly in the manufacturing process. This means that both the milling parameters (e.g. infeed, cutting speed) and the trajectory of the milling head can be optimized and tool wear can be detected precisely. HoloCut and HoloPort can be integrated into various types of machine tool (Fig.1). This makes it possible to remachine components while they are still in the workpiece holder. Measuring macroscopic topography with microscopic accuracy The tactile measurements or optical probes, which are currently commonplace, are severely limited by the number of measuring points and the significant measuring time that this entails. Furthermore, these methods have a very limited capacity to measure complex structures such as gradients, deep grooves, high edges or holes. Optical alternatives generally require an expensive separate measurement system, meaning that workpieces must be repeatedly set up after inspection. HoloCut and HoloPort set new standards here – they are fully integrable and boast a very large working distance, a large measuring range and high measuring accuracy. The accuracy is better than 1 µm.
For more information: www.ipm.fraunhofer.de