Accuracy in The Micron Realm

Blum´s Laser measuring systems measure micro tools down to Ø 5 µm and provide superior absolute accuracy

Miniaturization of tools and cutting sizes, faster machining speeds and contact sensitive coatings, provide an ever-increasing challenge in terms of tool monitoring. As a result, machines used for micro manufacturing now feature almost exclusively non-contact laser measuring systems, since they are the only way to detect and compensate for all factors influencing tools while machining. An important aspect to consider when choosing the right tool monitoring system is to ensure that it can demonstrate maximum possible absolute accuracy in the harsh conditions of a machining center.

The accuracy of a laser measuring system is defined by its repeatability on one hand, and by its absolute measuring accuracy on the other. For the user, the latter is more important since it defines how precise the measured results are when workpieces with extremely diverse characteristics are measured. The reason for this lies in the functioning principle of the system. Simply put, a laser measuring system uses a light barrier that operates as a simple switch. When a rotating tool breaks the beam, a skip signal is generated and transmitted to the control to record the machine’s axis positions. Standard software integrated into the machine control compares a calibrated reference value to the tool’s measured values and then calculates the tool’s length and radius and automatically enters this data in the tool table.

No matter the brand of laser, a skip signal is only generated after a certain percentage of the beam is shaded. For this reason, when measuring tools with varying characteristics (e.g. diameter, shape, cutting radius etc.) the beam is shaded in differing ways and can result in inaccuracies, particularly in laser systems with simpler optics. When measuring smaller tools, it is primarily the cutting edge geometry that exerts an influence on the measured result. Different cutting edge geometries protrude to unequal depths into the beam before the corresponding shading percentage is reached. For this reason, a beam with a smaller diameter minimizes the shading error for every blade. Based on this relationship, large beam diameters have a correspondingly higher shading error. What this means for the machining process is that, when using different tools, dimension deviations occur on the workpiece. Systems with larger beam diameters will measure small tools to be longer than they actually are because the tool needed to protrude further through the beam to cause a skip signal.

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