In a classic machining process, the parts after machining are taken out of the machine tool to be checked. In the event of a deviation from the specifications, and if a rework is possible, the part must be re-mounted on the machine, which generates positioning uncertainties, which can lead to the impossibility of producing a compliant or acceptable part without having analysed the correlation between the specified product characteristics beforehand, thus resulting in the rejection of the part produced.

Metrologically assisted machining consists in integrating measurement as early as possible in the process of machining parts using a machine tool.

Metrologically assisted machining can take on different aspects, integrating into the machining process:

• Hardness (surface resistance to deformation / wear, in Rockwell HRC).
• Tool path corrections related to the measurement of the machine geometry, (measurement on machine tool).
• Touch-up corrections integrating interactions between the characteristics described in the product specifications (measurement after machining and dismantling of the part from the machine tool).
• Measuring sensors to monitor the stability of the machining process and, in the event of instability (not necessarily failure), to consider maintenance.
• Measurements in the machining cycle, in order to be able to react without dismantling the workpiece from the machine tool (measurement integrated in the machining cycle).

In the context of this note, the third and fourth path will be considered: integration on machine tools of means for measuring parts in the course of manufacture, in order to reduce the rejects. These measuring means can be dedicated to surface measurements, vibration spectra, and determination of cutting forces. In all cases, the results of these observed characteristics are intended to allow intervention on the operating parameters of the machine tool to improve the quality of the part. The data collected is therefore processed to provide information to the machining centre's control system. Depending on the case, this information is used to rectify the positioning of the tool and/or the part, modify the machining conditions or implement active vibration compensation.

Access to the full watch note (in French version) is provided below : https://www.cetim.fr/mecatheque/Veille-technologique/note-de-veille-usinage-metrologiquement-assiste

After the presentation of three systems, participating in the implementation of metrologically assisted machining and put on the market in 2020.

• On the road to smart machining - Automation of metrology data on machining centres. Metrology data is the driving force behind the Smart Factory. Advanced measurement software, such as CappsNC from Applied Automated Technology (AAT), enables machine tools to take measurements and use them immediately to make adjustments, adapting various parameters such as tool offsets for example.
• CEA Valduc has joined forces with two French companies, SOMAB and I-MC, to robotize a turn-milling centre and integrate AI into it. SOMAB wishes to market I-MC's robotic control solutions on its machines from 2021.
• DMG MORI will integrate a laser scanner on the machine tools. DMG MORI will install Nikon's LC15Dx non-contact measuring system on its original machine tool and will start selling the machine tools with the new optional measuring system this autumn.

A synthesis of some recent scientific publications is presented.

• Review of hybrid methods and advanced technologies for in-process metrology in the field of very high precision single point diamond turning.
• Photogrammetric measurement process capability for metrology-assisted robotic machining.
• Features of metrology-assisted robotic machining on large nuclear power plant components.
• A stand-alone multi-sensor in-situ metrology system for high-dynamic measurement of 3D surfaces on precision machine tools.
• Surface metrology on machine and in-process for precision manufacturing.
• Robotic automation assisted by metrology.