is considered to be an acceptable practice. But, there are no strict guidelines to correlate point cloud spacing and max edge length of surface meshes when holes appear in meshes due to a lack of data. Another point of interest can be the alignment of the data to a 3-D model. Unless specifically request- ed, the easiest method to compare the data to the model is to utilize the best fit. However, best fit data usually displays the least deviation of the casting when compared to the model. Te most useful align- ment technique is reference points (tooling points). A reference point alignment will display the condition of the part just as it will be setup to be machined. A quick evaluation can be made when determining whether a surface has enough material (stock) to machine the correct feature size. As seen in Figure 7, the best fit data can give the perception that all of the features are located correctly and they are the correct size. Figure 8 shows the part when bound to the tooling point locations. It gives the appearance that the fea- tures are undersized, but when look- ing at the two different alignment techniques, it can be determined that the features are just mislocated. Simply stated, the tooling point sur- face is plus material as shown in the best fit alignment image. If material could be removed from the B5 and A2 tooling points, then the surfaces shown out of location in Figure 8 would be as shown in Figure 7. If the opposite condition existed—the tooling point locations were minus material—the casting supplier could provide the exact surface deviation to the machinist, and he would shim the tooling point surfaces during machining to provide a dimension- ally compliant part.
Te other method of correcting the tooling point surface would be to take a measurement across the surface, weld the surface, then machine off the extra material to the nominal dimension plus the material deviation found in the best fit alignment. Tese methods for correcting the
Nov/Dec 2013 | METAL CASTING DESIGN & PURCHASING | 23
build, casting and inspection. Te most beneficial result of
Fig. 8. Tooling point alignment is shown.
surface condition of tooling point locations have proven extremely valu- able, especially when rapid prototypes are used. Both the cost of the pattern and all of the lead time for new rapid prototypes can be saved. Te lead time to reproduce patterns to a casting is typically three weeks, including gen- erating the patterns, shipment, shell
noncontact inspection is realized by the magnitude of efficiency due to the reduction in time required to perform inspection (data collection). In general, all of the exterior surface data for any casting can be collected in one eight-hour time period. Parts that need to be sectioned would only be cut after the outside data was obtained. Part size is not the deciding factor in the length of time to laser scan the surface; the number of scanner head angles is the driving factor. A conven- tional touch probe inspection of a
casting having 300 to 400 character- istics on the drawing would take an experienced inspector a minimum of three days. Tis being the case, every inspection that can be done using noncontact inspection will take less time and provide more data than any conventional inspection technique.
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