برنامه های کاربردی از اندازه گیری دقیق ابعاد میکرو برای محصول و کنترل کیفیت فرآیند ساخت دقیق قطعات میکرو پلیمر

Precision manufacturing of micro injection moulded (μIM) components presents challenges in terms of quality control due to the miniaturization of product dimensions and tolerances. This paper addresses product compliance with specifications, focusing on tolerances of dimensions and position on μIM components selected from industrial production. Two systems were analysed: a tactile coordinate measuring machine (CMM) with sub-micrometer uncertainty and an optical CMM allowing fast measurements suitable for in-line quality control. Product quality control capability, measuring uncertainty and calibration guidelines are discussed for both systems. Finally, a new approach for the manufacturing of hybrid micro polymer–metal calibrated objects is proposed.

A micro product can be defined as having at least two critical dimensions in the sub-mm range [1]. Micro products can be two-dimensional structures (2D) (such as optical gratings), 2D structures with a third dimension View the MathML source(212D) (for example micro fluidic sensors [2]) and real three-dimensional structures (3D) (for example components for hearing aids). The specification of a micro mechanical component is usually defined on the basis of the desired function of the part, e.g. mating and assembly capability. The specifications are given in terms of maximum deviations from an ideal geometric form, but a downscaling below the defined lower borders of ISO GPS standards may prove to be problematic [3] and [4]. Compliance with tolerances is described in [5]. In the case of micro mechanical parts the absolute dimensions are small and so are the tolerances [3]. These facts result in at least two challenges: (a) finding a suitable measurement method to actually measure the components; (b) ensuring that the measurement uncertainty is sufficiently small to actually be able to verify the tolerance (see Fig. 1). The consequence in all cases usually is that the measurement uncertainty becomes larger compared to the tolerance interval leaving a much smaller conformance zone for process variations.The relationship between tolerance, processing capability and metrology methods is particularly challenging in micro technology. References [6] and [7] describe a categorization of tolerancing based on the type of micro product. One category deals with a downscaling of macro scale principles, and here the use of tolerances is necessary to ensure functionality. A monolithic approach is based on the use of a single substrate, e.g. semiconductor processing, and it is based on the calculated performance deviations during the various process steps. If they are larger than the product tolerances, the parameters of the currently active manufacturing step will be corrected, so that the final product will be situated within the expected product tolerances as defined by the functional behaviour. For micro mechanical components based on a non-monolithic approach (i.e. assemblies of components, usually manufactured in different ways and locations as seen in macro scale manufacturing) detailed knowledge of not only absolute dimensions and geometrical quantities, but also about the uncertainty of measurement is necessary in order to apply [5]. A viable and standardized procedure for uncertainty assessment of CMM measurements at micro dimensional scale is not available yet, especially when the focus is on actual micro products and complex measurements. To this respect, research work has been recently carried out in the field of dimensional metrology using CMMs for micro systems quality control. The uncertainty was calculated on a reference object for a one-dimensional measurand (i.e. flatness) in [8]. The accuracy and precision were calculated for on diameter measurements on a calibrated ring in [9]. Finally, diameter measurements of micro gears were investigated in [10] and the study focused on measuring repeatability. The computation of all the relevant uncertainty contributors of complex micro dimensional measurements on micro products is clearly a challenging task. This paper addresses product compliance with specifications, focusing on tolerance of dimensions and position on micro injection moulded components selected from industrial production. In particular, methods to assess and to subsequently lower the measurement uncertainty based on ISO 15530-3 [11] are presented.

The micro injection moulding process and polymer micro product quality control were analysed and investigated in this paper. Firstly, the verification of dimensional tolerances in the micro dimensional range was considered with particular attention to the challenge of obtaining low measuring uncertainties. Secondly, the tolerance verification of a micro injection moulded component selected from the actual production was presented. Both a tactile and optical coordinate measuring machine (TCMM and OCMM respectively) were investigated. Uncertainty assessment of both systems based on ISO standards was performed and an application of the substitution method to correct measuring results and decrease the OCMM's uncertainty was described and validate. Uncertainty to tolerance ratio and conformance zone available for verification was sensibly improved for the optical system using this approach. Suitability of the OCMM for an in-line implementation on the production floor was demonstrated and a typical configuration suggested. Finally, the manufacturing of hybrid polymer/metal micro component based on batch metallization process was analysed. The hybrid micro components were calibrated using the previously described methods with both systems (TCMM and OCMM) and the possibility of using such micro components as reference metallic objects was investigated. Due to the different surface characteristics between the reference object (nickel) and the item to be measured (polymer), the uncertainties of the OCMM measurements were rather large. On the other hand, the deposited metal layer provided long term stability to the micro polymer objects which could be used as calibrated reference objects for TCMM measurements.