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Dimensional measurement

CT measurement of interior and exterior component geometry

Apart from defect detection (pores, cavities, cracks), three-dimensional measuring is the second fundamental range of application for computed tomography. At Microvista, the dimensional measurement service includes amongst others a CAD comparison of actual versus target values, measurement of drawing positions, wall thickness measurement and first article inspection. Microvista digitalises components of different sizes and materials in an NDT process and also carries out dimensional measurements.

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In dimensional measuring, all (internal and external) component geometries can be precisely measured by means of specific measuring software (e.g. GOM Inspect Professional). The measurement report, some parts of which are generated automatically, provide the required actual dimensions of the scanned components and indicate all dimensional deviations (in dependence of the relevant component-specific tolerances) in a manner that is easy to understand. Due to its comprehensive information (measured values), dimensional measurement via CT is an advantageous and cost-effective alternative in the field of measuring services.

CT measuring of actual component geometry and comparison with nominal dimensions.

CAD comparisons of actual versus target values are a common standard in quality assurance of components or assemblies. In addition to optical measurement with 3D laser scanner, 3D computed tomography is particularly suited for CAD comparisons of actual versus nominal values, because all component contours can be scanned and digitalised in a single pass. This is followed by CAD comparison of actual versus nominal values, in which a component-specific CAD model (target) provided by the client is compared with the CT dataset (STL). Orientation (e.g. best-fit or contact points / zero tolerances) is defined by the client. During CAD comparison of actual versus nominal values, both datasets are virtually pushed into each other.

The deviations or differences generated by this step are visualised in so-called false-colour image. Already at first glance, the scaled images convey a clear impression and unambiguous statement on significant deviations of actual geometry from nominal geometry, so that the client can immediately identify critical areas under consideration of component-specific tolerances. Thus, the CAD comparison of actual versus nominal values, which Microvista can deliver within hours in the form of a concise test report, is an excellent decision basis for assuring the dimensional stability parameter.

Checking of drawing dimensions by means of CT.

Apart from classical CAD comparison of actual versus target values, Microvista also offers measuring of drawing positions, i.e. checking of individual dimensions against drawings. In this case, the client provides both the component and a 2D drawing defining all positions to be measured. When measuring drawing positions, the CT evaluation software for example checks significant functional dimensions. Compliance with these dimensions is often decisive in ensuring a component’s functionality. Examples for these dimensions are the diameter and position of bearing seats and liners.

In general it can be said that measurement of drawing positions involves precise measuring of all distances between two points of the geometry as well as measuring of radii, angles and virtual centres. Therefore, this Microvista service offer is a perfect complement to a CAD comparison of actual versus nominal values, which mainly provides general information on dimensional stability.

Measuring wall thickness via CT.

Measuring wall thicknesses is an integral part of quality assurance of industrially manufactured components. Measurement of wall thickness in parts requires very diverse measuring equipment and methods. In many cases, however, the features to be measured are inaccessible and/or have a rough surface, which prevents use of conventional measuring methods. An innovative and trend-setting method is industrial computed tomography, which captures all details of component geography with all wall thicknesses in 3D. The dataset generated this way is a precise digital representation of the real component. Then a professional, tried and tested CT evaluation software is used to measure wall thickness at any given point and to visualise the recorded measuring values.

The user-friendly representation features colour-coding for different wall thicknesses. Colour gradients and measuring value scaling can be individually adjusted to provide measuring results not only in the mm range, but also in the µm range. In addition, it is also possible to precisely measure and visualise flat and point wall thicknesses measurements. This way, the customer obtains important information on the actual values of his component’s wall thicknesses that are not possible to this extend in any other measuring method. Convinced users of CT wall thickness measurement are well aware of the advantages this measurement method offers. A key benefit is that individual points or whole areas with critical wall thickness can be reliably located, depicted and measured – in a non-destructive manner and in 3D. This cutting-edge wall thickness measurement method facilitates important and production-specific decisions and minimises risks.

Visualisation and measurement of cavities by means of CT.

In manufacturing of cast metal components, it is common to use individual cores or whole core packages made from different materials (sand core, salt cores or ceramic cores), which provide for the cast component’s cavities specified by its constructive design. These cavities for example could be turbocharger channels or inlet or outlet ports or oil and water chambers of cylinder heads. When extracting cores by means of CT, these areas are closed by the program. The resulting cavity (the negative of the core used for casting) can then be extracted from the component and viewed independent of the rest of the CT dataset.

This, core extraction provides information on the nature and position of interior surfaces, which enables the customer to draw conclusions on the current core status or core box wear. Moreover, core extraction based on CT scanning provides for better 3D high-resolution visualisation and measurement of combustion chamber volumes or of the results of core ruptures or cracking (casting burrs / veining). Within a very brief time, the client is provided not only with important data required for comparisons in the form of fluid dynamics analyses and calculations, but also with the type of information that enable the client in case of unforeseeable manufacturing problems to act promptly and to make the right decisions. Due to the mentioned advantages, extraction of cores is one of Microvista GmbH ‘s highly innovative services.

Execution of first article inspection and preparation of first article inspection report.

If a supplier is commissioned by his client with the manufacturing of a new component, the client has to verify series maturity according to the requirement specifications by means of a so-called first article before series production starts. This test is called first article inspection. The test results are documented in a first article inspection report. If the results obtained during first article inspection are consistent with the agreed specification and are within tolerance limits, the supplier is given approval by the client to start series production. Therefore, first article inspection reports are of crucial importance for the supplier’s quality assurance. Some suppliers provide proof of series maturity themselves, others use the whole or parts of the services of external measuring and testing service providers for first article inspection of their components. Microvista provides such evidence by subjecting the client’s sample components to NDT testing in accordance with specifications.

Apart from dimensional checks (e.g. CAD comparison of nominal versus actual values, measurement of drawing dimensions, wall thickness measurements etc.) customer requirements may also include execution of testing for existing material defects such as pores, cavities or cracks, which are then documented in the first article inspection report. The decisive advantage: Microvista’s first article inspection reports contain all supporting data (pictures and numerical data) and are therefore reliable and independent evidence of the quality of the components manufactured under series-production conditions as required by the specification – in a non-destructive manner and within a short time. This way, sectioning components for measuring is now a thing of the past! While maintaining an attractive cost-benefit-ratio, we are also able to minimise risks and optimise quality standards.