“
Normally it takes three to five weeks to develop a new pattern. With this method we lowered the leadtime to no more than 1.5 weeks. —JAVIAR GARZA
tooling at the Matamoros casting facility, it was met with apprehension. “Te biggest challenge was to
deliver a smooth surface to the ABS plastic part,” said Javiar Garza, a cast- ing engineer at the Matamoros facility. After a few attempts, it was clear the plastic pattern was not providing the desired results. Garza suggested using the printer to make a pattern for the tool, including matchplate, which the metalcasting facility then polishes to achieve the required surface finish. “It was great, because normally it takes three to five weeks to develop a
new pattern,” Garza said. “With this method we lowered the leadtime to no more than 1.5 weeks.” Acuity designers draw the part, whether it is adding a logo to an exist- ing design or creating a completely different style, in 3D and scale it in the model based off pattern shrink- age, which is an allowance made on patterns to compensate for the change in dimensions as the solidified casting cools in the mold. “I consult with the factory in Mat-
amoros because shrink is not linear,” Davis said. “I rely on their knowledge
and expertise to guide us.” Acuity scales the model for two
shrink sizes since the plastic pattern will be used to cast the tool, which will then cast the part. “Te first aluminum part we get off the plastic tool is one shrink big, and that becomes the tool for production,” Davis said. “We take the ABS plastic pattern and label it master.” When a new tool is needed for an existing product, the casting facil- ity makes it from the master ABS plastic pattern. “We go to the shelf, use the master and an hour later, we have a brand new tool,” Davis said. “There is no downtime.” If the required pattern is too big for
the printer envelope, the model may be produced in sections and assembled together to make the finished pattern. Davis used this method to produce a custom scroll measuring 3 x 5 ft. Since the first 3D printer, Acuity also has added a couple more machines to its model shop to accommodate larger parts and the increased usage of the rapid tooling method. “After I got my printer, of course
every brand wanted one,” Davis said. Te rapid tooling method is more than a time saver. “For every custom opportunity,
new tooling is required. Who’s going to absorb that?” Davis said. “A lot of times we would do it ourselves to get the job for the payoffs later. [With the new method] the tooling cost went from the standard $10,000 to basically the cost of the plastic.”
Illuminating In-House Casting The choice between sand or per-
manent mold casting depends on the design, Davis said. Some design ele- ments are less expensive and easier to achieve in sand casting, where mold aids such as floating inserts can be used. Historic designs based on the early 1900s often feature sur- face finishes that are not as smooth and thicker, heavier elements that are more cost effectively produced in sand casting. But permanent mold offers better dimensional accuracy and is more cost effective for larger volumes.
24 | METAL CASTING DESIGN & PURCHASING | Nov/Dec 2012
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