was found to result in a 38% yield. By contrast, for an application that did not need as stringent a porosity require- ment, accepting some porosity resulted in an 82% yield and a 15% cost savings. Reducing iron casting weight can shave a little off the cost. Running castings through a trim press rather than manual grinding also can reduce costs, if it is a job of high enough volume.
Time Is Money Scheduling happens when a job order
Figure 3. An X-ray inspected E357 aluminum casting has many risers (orange and pink areas) and chills (blue) at every ingate to achieve the required mechanical properties, due to the alloy’s sensitivity to the cooling rate.
as ASTM or ASM, you can expect to pay more for that casting,” said Weiss, “especially with aluminum.”
Bye’s example of an iron casting that was specified to be 100% porosity free took 50 simulation trials to achieve and
is accepted, but there are many steps in the process of completing the work that can impact on-time delivery. “A lot of time the only setup people think of is at the mold machine, but it takes place at each step in the process,” Bye noted. “Starting with the person at order entry, the time can vary based on the complexity. If we’re going to make 1,000 castings, 10 orders of 100 each, setup takes less time than if it’s 100 or- ders of 10 each.” Setup varies at the core machine, where some products require an additive and some don’t. “Te pattern for the track pad (see
p. 19) takes date tags to show when it was made, so you’ve got to put those tags on and take them off again,” said Bye. “It isn’t a big deal on this job, with two impressions in the mold, but if you have a pattern that has 30 impressions and the customer is ordering 50 pieces, you’re now taking date tags on and off 30 impressions to run two molds. Tey order that every other month, and think about what the costs are associated with getting that pattern ready to run.” Manual finishing doesn’t require
much setup, but automated finishing equipment’s setup time offsets its faster, more accurate throughput. “Te more automation you have, the more setup [cost] you might have to spread across the quantity,” said Bye. Shipping is the last step where
scheduling impacts cost. As in Bye’s order entry example, shipping costs vary based on whether there are 10 or 100 orders being processed to ship those 1,000 castings. “We’re all rushing to get castings
qualified on the front end, but sometimes that gives us insufficient time to build and develop the casting,” Weiss added. “And sometimes when you don’t have
24 | METAL CASTING DESIGN & PURCHASING | Mar/Apr 2014
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