Fig. 4. To convert this part from investment casting to shell mold casting, Eagle Alloy added a load and feed pad.
size had to be maintained to hold the quoted price. Eagle Alloy used solidifi- cation simulation to develop the design. Duplicating the fabrication design was
not practical because the handles were not large enough to act as feed paths to the body of the casting. Making the handles thicker proved ineffective due to a step at the front of the part. Moving the handles to the front of the part helped feeding but proved to hinder the number of castings per mold. By angling a corner on the handles, the casting per mold count could remain as-quoted. Eagle Alloy used solidification simu-
lation results to convince the customer of the design’s validity. Tooling was produced for all five sizes, samples passed x-ray and pressure testing, and production started in both carbon and stainless steel. The customer’s market- ing department promoted the angled
feed pads as a design enhancement. An added benefit to the design was that the new parts did not get caught in the brush when dragged into place, unlike the fabrications.
5
Communicating Castability Issues
Even when parts are designed
as castings originally, instances may arise where a change to the design is needed, particularly when changing from one cast- ing process to another. In one instance, a part originally designed for investment casting was converted to the shell process. Due to delays in the product launch, the customer had little time to wait for re- rigging or a change in the design after the first samples were cast. Due to mold space limitations, the rigging options were limited. The customer was willing to change the part but required justifica-
tion. The metalcaster used solidification simulation to show before and after results from incorporating a load pad to create a feed path (Fig. 4). The customer agreed to the change, and the first castings were produced to satisfaction.
6
Solving Defects
Even when parts seem to be
cast successfully, issues can arise. In one instance, a valve body part had been caus- ing significant problems for a customer, despite passing analysis, simulation, sampling and x-ray testing. Small mi- croshrinkage on a sealing face was being revealed after machining and fluorescent penetrant inspection. Subsequent review of the simulations using more sensitive criteria duplicated the microshrinkage found in the part (Fig. 5). To eliminate the defect, casting engineers suggested adding a load in a pocket area, which significantly reduced but did not eliminate the defect. Next, Eagle Alloy examined using an external chill to promote di- rectional solidification, but due to the casting design, the risers appeared to be fighting each other for feeding. By adding a chill to the flange face and moving the riser to the opposite side, the solidification pattern was changed significantly and the defect indication in the solidification simulation disap- peared. Twenty-five sample castings were made, machined and passed fluorescent penetrant inspection. MC This article was adapted from a paper pre- sented at the 2010 SFSA T&O Conference.
About the Author
Fig. 5. Originally, this valve body casting was suffering from microshrinkage originally undetected in simulation and x-ray testing. By using more sensitive simulation criteria, Eagle Alloy was able to pinpoint the cause of the defect and ultimately solve it.
42
Jim Smith is engineering manager for Eagle Alloy Inc., Muskegon, Mich. For More Information
“Casting Layouts Become Self-Optimizing,” C. Heisser, MODERN CASTING, September 2009.
MODERN CASTING / February 2011
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