Visit the Product Innovations Archive at
www.moderncasting.com
Simulation Aids in Impeller Redesign J. Walter Miller Co., Lancaster, Pa.,
Case Study
produces brass and bronze castings for the fire protection, pumping and valve industries. When the company converted from manual green sand molding to fully automated molding, many of the casting jobs required de- sign changes. Impellers represent a particular challenge because of the wide varia- tion between their heavy and thin sections. The metalcaster was expe- riencing problems with one part in particular, and the conversion was becoming costly. “This part was becoming a serious
problem,” said Dan Rudolph, quality engineer for J. Walter Miller. “We had spent about eight weeks and $5,000 trying to fix the problem and did not seem to be making progress.” The metalcasting facility turned to
the QuikCast software from ESI Group, Farmington Hills, Mich., to perform solidification modeling. The difficult impeller was pro-
duced in a squeezer mold using an open riser fed by a large overhead mass of molten metal. This configura- tion was not possible with the auto-
PRODUCT INNOVATIONS
Prior to the use of QuikCast simulation, J. Walter Miller Co. used a closed riser and cored hub design, which produced a shrink pocket in the wear ring (left). Using solidification simulation, the metalcaster determined that a design incorporating a solid hub and open riser would eliminate the shrink pocket in the wear ring.
matic molding machine, which uses fixed riser or sprue locations with a maximum contact diameter of 1 in. The open riser was replaced by a 1-in. sprue, reducing the contact area. When the new configuration was tried on the automatic machine, the impeller castings exhibited voids in the hub caused by the contraction of metal. These voids were discovered when the parts were machined. Prior to the use of QuikCast soft-
ware, the metalcasters added a core in the hub to reduce the amount of liquid metal required to feed it dur- ing solidification. The open riser was replaced by a tall closed riser. After casting and boring, the hub of the impeller exhibited no defects, but a new shrink defect began to appear in the wear ring section, a heavy circular rib about an inch from the hub. “By viewing the [QuikCast] simula-
tion results, I was able to determine that the new shrink defect resulted because the hub section was now solidifying much more quickly,” Rudolph said. J. Walter Miller applied design
changes to the CAD model of the casting that included removing the core in the hub to allow a feed path to the wear ring. Subsequent simulation showed the new design eliminated the shrink in the wear ring, while the shrink porosity in the hub was confined to the center-most region that was removed during the machining process. “This problem would have taken
about 12 weeks and $6,000 in pat- tern changes plus countless hours of machine time to solve using conven- tional trial and error methods,” Ru- dolph said. “With casting simulation, we can easily solve similar problems in two weeks and produce a good pattern the first time.”
MC Shown is the impeller casting based on the new design. No shrinkage defects are present. MODERN CASTING / February 2010 Visit
www.esi-group.com for more information. 53
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68