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Casting redesign reduces scrap, saves space.

Space constraints in a large, V-6 outboard motor with up to 225 hp was a critical design point for a customer of Watry Industries, Sheboygan, Wis. The customer's goal for the central component of the motor was to avoid any external plumbing to eliminate the chance for fluid leaks.

The part houses a high pressure hydraulic pump, reservoir and all hydraulic passageways for double-acting hydraulic cylinders, and functions as the housing for two of these cylinders. The power trim cylinders are an integral part of the casting and machined to fine surface finish. The power tilt cylinder is a separate component that is supported and controlled by this casting.

Because the trim cylinders are an integral part of the casting, strength and casting quality were important to ensure product performance and long life. The piston seals of the trim cylinders run directly on the machined surfaces inside the bores of the casting, so density was a given.

In addition, the high-pressure passageways operate at up to 4,000 psi, so pressure tightness was important. And because the propulsion forces of the V-6 engine are transferred through this part to the transom of the boat, mechanical strength was critical. This strength had to be maintained for the life of the engine, and many of these castings would be used in saltwater applications.

Previously, the part was produced in low-pressure permanent mold. That part required sand cores to form the cast inner diameter for the cylinders, and additional features were required that could not be part of the main casting. Mating faces for these features on the main casting had to be machined for mounting purposes. Assembly of these features was required.

Unfortunately, failures at leak testing were a common problem, resulting in a 100% x-ray requirement and leading to 18% scrap during production.

Watry's engineers worked closely with the customer's engineering group to redesign the part for the tilt-pour permanent mold process, which would eliminate the sand cores that formed the inside of the cylinder bores. The additional features that previously had to be assembled were now designed as an integral part of the redesigned permanent mold casting, which eliminated the extra machining, assembly and fasteners. The new design used metal cores with 7 in. of travel and eliminated several components of the assembly by casting part of the reservoir integral to the part. One sand core formed both reservoirs located on each side of the casting. Molds for the casting incorporated core pulls, a sand core and five sliding sections.

Several part features required changes to allow adequate gating access and reduce the cost of gating removal. As a result, scrap due to leakage was effectively eliminated, x-ray testing requirements were reduced to a metalcasting facility control level, and the part met all life cycle test requirements.

[ILLUSTRATION OMITTED]

Additional operations for the part consist of T6 heat treatment and a grit blast to clean the surface in preparation for black anodizing after machining. Because the casting is in view of the end-user, a nice-looking part was required.

The final design resulted in a more compact part, measuring 5 x 9 x 9.4 in. and weighing 10.5 lbs., with a reduction in scrap and required assembly that translated into a better part at a better price.

Visit www.watry.com for more information.
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Title Annotation:Case History
Publication:Modern Casting
Date:Sep 1, 2007
Words:555
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