Verification of Tolerance Chains in Micro Manufacturing

The aim of this work is to define methodologies for the tolerance verification of injection moulded components with downscaled dimensions. In micro and nano metrology different challenges can be found: lack of calibration artefacts and available ISO standards, problematic uncertainty budget and tolerance verifications due to no proper measuring instruments.

In connection to the last issue, the characterization of optical components is often difficult to obtain using contact instruments which could damage the surface of the specimen, whereas optical measurements might be inaccurate due to scattered light. In this thesis a replica casting technique is proposed to overcome the problem: the workpiece is replicated and the replica is characterized instead of the part.

Different investigations are carried out on roughness specimens and deterministic structures (e.g. grooves) in order to define the replication degree and the replica stability. Moreover a new traceability procedure is studied and proposed when dealing with this methodology. The measuring instrument has to be calibrated on the same replica surface to ensure the traceability.

Therefore the aim of the procedure is to perform a replica on a calibrated standard artefact and to measure both in order to assure an unbroken chain of comparisons. The replica technique reveals to be a fast, cost-effective and reliable method. Regarding the tolerance verification of micro parts and nano-structured surfaces, a systematic approach is discussed based on dimensional and geometrical metrology.

If the measurements uncertainty is large compared to the tolerance interval, a small conformance zone is left for process variation. Therefore particular attention has to be paid to the instrument capabilities in order to reduce the measurement uncertainty. Different methods, such as the quality control approach and the measuring indices approach, are investigated in order to optimize and maximize the repeatability of the results.

Moreover a useful guideline is proposed to provide a viable method for the uncertainty calculation of measurements in the micro range (0.1 – 200 μm). Finally, an optical component is investigated with the purpose of suggesting a quality control approach for micro-manufacturing process through a control of the product.

It is a useful method to adopt when the aim is to detect and quantify inconsistency or incompatibilities during a process chain. In this way the process parameters can be adjusted in order to fulfil the requirements of the final micro-product.