Fig. 5a. An unedited image of the merged polygons is shown.
Fig. 5b. An example of FAI Data is shown.
of each scan pass either by manual adjustment or a software control based on overlap. Each laser line stripe captures 6,400 points per second (pts/s) for a total 19,200 pts/s. When performing a sphere fit, the scanner’s accuracy is guaranteed to be 0.0008 in. It cap- tures all 3-D details of features, edges, pockets, ribs and free-form surfaces in a single scan. Inspection software enables the
user to process and analyze the point cloud data. Its strength lies in its ability to manage large amounts of data and do complicated translations and manipulations. Large workspace files typically contain a gigabyte’s worth of information. Tese files can be compressed to fit on a CD along with a free viewer. Te software allows for
full calibration of each lens, point-to-point spacing along the line stripe, and stripe spacing. Typical set- ting for first article inspec- tion data is a line stripe spacing of 0.04 in. and a point-to-point spacing of 0.02 in., as seen in Figures 2 and 3. Te number of points within the point cloud varies with the size of the casting. Typically, parts
at O’Fallon fall within a 12 x 12 x 12-in. bounding box with a normal point cloud density of approximately 2 million points.
Data Processing and Analysis
After scanning is complete, the next step of inspection is to import the point cloud data into the software for review. Once all of the point clouds are oriented with respect to the normal vector (which side is the outside and which is the inside), a surface mesh of
data points can be created. Te surface mesh of each scan pass is represented by unique colors (see Fig. 4), and all of the meshes can be merged into a continuous polygonal surface model. Tis allows the created polygonal model of the casting to be modified or edited within the software, as shown in Figure 5. Any fixturing that appears in the final polygonal model can be deleted, holes can be filed, surfaces can be smoothed and sharp edges can be corrected. After all editing of the polygonal model is com- plete, it is now ready for digital comparison to the customer’s 3-D model. Scanning software al-
Fig. 6 Here is an additional view of FAI data.
lows the direct comparison of the 3-D model to either a point cloud or a meshed polygonal model. Te cus- tomer supplied model can be imported in many for- mats, such as IGES, STP, Parasolid, and CATIA. All of the standard geometric dimensioning and toler- ancing can be done within the software, but the most powerful tool is the surface- to-surface comparison using a profile color scale. Te profile color scale can quickly display the surface condition of any feature and the scale can be created to provide simple accept/reject
Nov/Dec 2013 | METAL CASTING DESIGN & PURCHASING | 21
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