The Lowdown on Lost Cores

Mark Battista, vice president at Electrovert's Metal Dispensing Div. (Providence, RI), has seen many lost-core applications succeed-his company makes the core molding and melt out equipment essential to the process and offers turnkey service in setting up a fully automated molding cell. IMM asked Battista to comment on the notion that lost-core molding may not be suitable for every molder or every part. "Contrary to some opinions," Battista explains, there is a time and place to use what his company tradenames metal-core technology (MCT). But when and where?

"There is an extensive range of automotive parts that benefit from the MCT technique, including water pumps, impellers, thermostat housings, and power steering fluid reservoirs," says Battista. "Years ago, DuPont did a study that identified some 40 components underhood that can advantageously use the metal-core process. BMW has been using it for impellers, pumps, and manifolds for quite some time. Some time ago, Ford and General Motors proved a 1-mpg savings with plastic manifolds from greater engine efficiency based on part quality. In the non-automotive area, a bicycle company now offers a range of hollow, lost-core molded bicycle wheels that span the gamut from racing to mountain bikes."

When you look at the cost of implementing this technology, you realize that it's not suited to making hollow ashtrays, with costs ranging from $4 to $5 million to put a fully automated cell in place. According to Battista, molders can justify the cost if production volumes are relatively high, as in automotive, and/or the added value that the process brings to the part warrants the cost. "We have customers in the aerospace market who produce low volumes for whom the technology gives unlimited design flexibility and this justifies the cost." Cores have been used to form external geometry also, eliminating the need for side actions.

Design flexibility and accurate part-to-part repeatability are the number one values that lost-core design offers. There have been other matrix materials like sand, salt, or wax used to form internal geometries, but the problem has always been making the core dimensionally accurate each cycle and at the same rate at which you're molding parts. Manifold cores are generally made in 60-to 70-second cycle times. Also, you need a core with a quality surface-this is the art of the technology.

Core molding equipment is similar to an injection molding process, except that the mold isn't filled under pressure due to the highly viscous molten metal. Core tools must be designed carefully to support the process, Battista notes.