CMI-Wabash Uses Direct Pouring System to Cast Aluminum Intake Manifolds.

CMI-Wabash Cast, a 280-employee aluminum green sand foundry in Wabash, Indiana, was established in 1978 as one of the first suppliers of aluminum intake manifolds to the auto industry. As with most aluminum foundries, its largest problem has been the formation of oxide films and inclusions (up to 2 in. in length) on the surface of its castings due to turbulence in the gating system.

The 120,000-sq-ft foundry has used screens, sieves and strainers to prevent large inclusions from entering the mold cavity. In addition, reticulated foam filters have been used to remove even the small inclusions while smoothing metal flow and eliminating turbulence. These conventional gating systems, however, were not achieving the desired results as a prototype intake manifold produced using these methods was not of acceptable quality.

CMI-Wabash decided to try the Kalpur direct pour system from Foseco, Inc., Cleveland. Direct pouring involves the introduction of molten aluminum into the mold cavity through an assembly of a foam filter and a low-density insulating sleeve. The sleeve locates the filter in the desired location in the mold and acts as an insulated riser when full of aluminum. Flow modifications ensure the laminar flow of molten metal into the mold cavity, thus reducing turbulence, oxide formation and gas entrapment that are detrimental to the internal soundness of the casting. In addition, this reduction in the metal flow allows for the reduction or total elimination of the gating system and improvements in casting yield, cleaning/finishing and flask utilization.

By using a filter to replace conventional gating, reductions in turbulence and improvements in metal cleanliness are performed as close to the casting activity as possible--maximizing the likelihood of an oxide-free casting.

The direct pour method also improves the thermal gradients during pouring. With this method, the bottom of the mold doesn't become superheated because the hottest metal remains at the top of the casting. This provides improvements in directional solidification throughout the casting, resulting in an optimized thermal gradient and a reduction in shrinkage defects and improved feeding efficiency.

CMI-Wabash pours molten 319 and 356 alloy aluminum from two 140,000lb reverberatory furnaces. The metal is poured directly into the direct pour unit--on a pad on top of the casting--which distributes the metal to the mold cavity. Due to mold height restriction, the aluminum pouring unit was cut down to 2 in. in height. The unit had a 1.75-in. diameter exit hole from the filter and the downsprue diameter below the unit was 1.63 in.

During testing of the direct pouring system, the foundry performed extensive tests to verify results before they were implemented. One improvement made as a result of testing was the change from a ceramic-based to a graphite-based foam filter. The new filter simplifies separation at remelt while minimizing potential ceramic inclusions. The potential also exists for more efficient priming due to lower thermal capacity of the graphite-based filter.

"At first try we had a lot of leakers that we had to scrap," said Jim Bohlen, quality manager for CMI-Wabash. "But as we fine-tuned the system, we reduced scrap to an exceptional level."

Bohlen continued, "By performing careful analysis of the pouring system and running a series of tests, we were able to prove out any changes before they were made permanent. This has helped to improve our operations by lowering scrap and rework."

Initially, casting yield improved for the intake manifold from 55% to 77%. However, as the foundry continued to refine its processes, the yield lowered to 59%. Scrap, however, was reduced from more than 10% to just below 2%

According to Pat Meredith, CMI-Wabash tooling engineer, the foundry also reaped the benefit of increased mold utilization. "Some large parts that take up a lot of room in the mold may leave little room for conventional gating, potentially making these parts non-manufacturable because of mold size," he said. "The direct pour system requires less mold area for gating, therefore more parts can be designed to fit a particular mold size. This increases the potential job possibilities for a given mold size."