Inspection investment
Major improvements to the inspection process at Alcoa Howmet’s foundry have been enabled by the introduction of a GOM ATOS II optical measurement system and Geomagic Qualify computer-aided inspection software. ‘What used to take us a week or more we can now complete in one day’ says Steven Edwards, layout and tool room manager. He’s referring to the proof inspection of newly-cast turbine blades and other airfoil components, a process which has been transformed with the introduction of digital shape sampling and processing (DSSP) and computer-aided inspection software from Geomagic.
Alcoa Howmet’s products include castings of superalloy, titanium and aluminium alloys - components such as turbine blades and vanes - for companies such as Siemens, Alstom, Rolls-Royce and ABB. The lost-wax, or investment casting process, is favoured for these products. Castings can be manufactured with complex features, such as 3D contours, thin walls and undercuts, while control of the process variables enables closer tolerances. It is also an economical process for both prototype and production run quantities.
Nevertheless distortions of the cast parts can occur, so inspection is critical in ensuring parts that meet all geometric tolerance and quality standards. Thet inspection process, both for first-article and for changed parts inspection, relies mainly on new digital shape sampling and processing (DSSP) technology.
DSSP encompasses the convergence of multiple technologies, and 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 for design, engineering, inspection and custom manufacturing.
At Alcoa Howmet the DSSP technology used comprises a GOM ATOS II optical measurement system, which captures part geometry as a dense ‘point cloud’ or polygon mesh that precisely describes an object’s surface and primitives, and Geomagic Qualify computer-aided inspection software.
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 Geomagic 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 three-dimensional 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 (GD&T) 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 Geomagic Qualify. Geomagic Blade focuses on the turbine machinery industry, providing specific functionality to enable the analysis of rotors, stators, impellers and specific internal blade features.
‘With the Blade extension we can readily undertake multiple airfoil analysis by analysing and reporting on dimensions related to turbine segments, such as minimum opening, or throat, and minimum distance blade to blade, as well as other turbine-specific inspection requirements such as twist analysis and cross section and chord length measurements,’ says Matt Willacy, Alcoa Howmet layout engineer and Geomagic Qualify user.
‘What’s more, the software is easier to use and faster than our earlier system and Geomagic is always willing to listen to our needs and to come up with new capabilities.’
