information. Te program allows for several alignment techniques, including best fit, point pairs, reference points, feature based and manual alignment. Te most complicated concept is the method of aligning the surfaces. Te easiest and more commonly used is the best fit alignment, which utilizes mini- mum deviation using the least squared deviation method. Te other type of fitting technique frequently used is the reference point alignment. Reference points are created on the 3-D model, planes are created on the poly- gonal model and the correlating locations are bound together. Tis usually is done when the drawing requires tooling point locations to define the primary, secondary and tertiary axes. Once the models are fitted together, a surface comparison color scale can be generated to show
different views to display all the sides of the casting. Te software has an internal report generator, but O’Fallon uses the standard AS9102 report, forms 1, 2 and 3. Typically, a drawing callout is
Fig. 7. The best fit alignment shows the part to be within +/- 0.030 in. of nominal to the customer sup- plied 3-D model. The two text boxes in red are show- ing the bound tooling points B5 and A1, which are respectively 0.013 in. and 0.011 in. out of location.
for an overall profile of the surface (to A, B and C datums). To keep the presentation of such a large amount of data simple, very few colors are used to illustrate the condition of the surface. As seen in Figure 5b, the portion of the casting within 75% of the total tolerance from nominal is shaded in green. Te surfaces that use the last 25% of the negative side are colored yellow, and surfaces that are out of tolerance on the negative side are shown in red. Te same holds true for positive
areas of the casting that are in or out of tolerance. After the data color map has been created, a snapshot can be taken at
variations from nominal as seen in the light blue and magenta. Any method of choosing colors and delineations can be used. Te color scale as shown in Figures 5b and 6 allows for an easy review of the inspection and pro- vides a quick assessment of whether the casting is mostly in tolerance or out of tolerance. If out-of-tolerance conditions exist, deviation balloons are added to the image to show the exact value of the surface deviation.
Items for Discussion
In most situations, the software’s editing module tools are used to cos- metically correct a surface irregular- ity. Small holes in the surface mesh can be created when the max edge length is smaller than the point- to-point spacing of the point cloud in local areas. Te max edge length might need to be very close to the point-to-point spacing to prevent a mesh from completely removing small holes that are supposed to be in the casting. Conversely, sometimes small holes appear because the scan passes of the laser had to make an odd move around a feature in an attempt to cover the entire surface, thus leaving the points within the cloud further apart than the max edge length for meshing. In these situations, a hole filled in during editing is an interpolation rather than an extrapolation. Tis generally
22 | METAL CASTING DESIGN & PURCHASING | Nov/Dec 2013
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