Geomagic helps cuts turbine blade inspection time

The proof inspection of newly cast turbine blades has been improved by the introduction of a GOM ATOS II optical-measurement system and Geomagic Qualify computer-aided inspection software.

Alcoa Howmet's UK foundry layout department have cut turbine blade inspection times by up to 70 per cent.

The foundry casts turbine blades and vanes for companies such as Siemens, Alstom, Rolls Royce and ABB.

The components it produces are cast using the lost-wax, or investment casting process.

Metals that are difficult to machine or to fabricate make good candidates for the process.

Turbine blades that have complex shapes or aircraft parts that have to withstand high temperatures are some examples.

Patterns of the castings to be made are moulded by injecting a special wax into a metal die.

These dies are produced by external tooling suppliers using digital 3D solid models supplied by the customer and evaluated by product engineers.

Cores of pre-formed ceramic, to create special voids within a cast part, may be incorporated into the wax patterns as they are moulded.

Individual patterns are then assembled into a cluster around a wax runner system.

This 'tree' of patterns is then coated with several layers of a refractory material, each layer being dried or chemically cured before the next layer is applied.

The assembly tree is heated to remove the wax and is then fired at high temperature to bond the refractory mould strongly.

The hot mould is then filled with molten metal.

When cool, the mould material is removed leaving the castings, which are then removed from the runner system.

As with any other manufacturing process, distortions of the cast parts can occur.

Therefore, the inspection process is key to Alcoa Howmet's ability to produce parts that are of high quality and meet all geometric tolerance conditions.

This process, both for first-article and for changed parts inspection, relies mainly on new digital shape sampling and processing (DSSP) technology.

DSSP describes the ability to use scanning hardware and processing software to digitally capture physical objects and automatically create accurate 3D digital models with associated structural properties.

At Alcoa Howmet's Exeter facility, the DSSP technology used comprises a GOM ATOS II optical measurement system and Geomagic Qualify computer-aided inspection software.

The ATOS II system will digitise a physical part by projecting different fringe patterns of white light onto the object's surface.

These patterns are captured by two cameras located at either side of the projector.

As the object is scanned, the areas in which measurements have been recorded are displayed on a computer screen.

The system monitors its calibration and the effects of the environment to ensure reliable measurement in rough industrial conditions.

The captured data is then imported into Geomagic Qualify for the inspection process.

Geomagic Qualify takes advantage of DSSP to enable fast, easy-to-understand graphical comparisons between CAD models and as-built parts.

It saves time and increases accuracy for first-article inspection, trend analysis, 2D and 3D dimensioning and automated reporting.

The inspection process relies on two inputs: the 3D scan data of the part to be inspected and the original 3D CAD model of the part.

Both are read into Qualify using industry-standard data transfer methods, or directly in the case of the data from Alcoa Howmet's Unigraphics CAD system.

Datums and features upon which the inspection is going to be based are then created on the CAD model.

The scan data is then aligned with the nominal CAD model using both the manual and the automatic alignment facilities provided by Geomagic Qualify.

Once the scan data and the CAD model are aligned correctly the inspection process starts.

This includes overall 3D analysis of any deviation between the physical part and the nominal CAD model, with the results being presented as a colour-shaded plot of the part, showing deviation values.

Areas of the part that fall outside assigned geometric tolerances are also displayed for easy identification, along with geometric dimensioning and tolerance (GDandT) call-outs, whisker plots of cross-sections and wall thickness analysis results.

Alcoa Howmet also takes advantage of the specialised inspection capabilities offered with Geomagic Blade, an optional extension to Qualify.

Geomagic Blade focuses on turbine machinery, providing specific functionality to enable the analysis of rotors, stators, impellers and specific internal blade features.

Results are reported to the product engineers so that any required changes to the wax patterns that the inspection process might have identified can be carried out.

Images for the reports are created by saving required views during the inspection set-up procedure.

Reports are then output automatically and can be in a number of standard formats, including HTML, PDF and Microsoft Word.

The Alcoa Howmet team in Exeter outputs PDF documents, which are then printed off for use by the product engineers.

However, plans have been made to install the free Geomagic Review software on all engineers' PCs to give them easy access to reports - by downloading over the network.

This will enable the engineers to further analyze the part and interrogate the results.

The ability to produce inspection templates within Geomagic Qualify also speeds up the process.

These templates are customer-specific and are produced by saving the inspection workflow created the first time a part is inspected.

The same workflow is then applied to subsequent inspections at the touch of a button and a separate report for the new part is produced automatically.

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