Fast to Market

April 14, 2009
An investment caster takes a functional approach to prototyping, speeding the route from casting designs to finished products.
Some cast components of the brushless DC motor structure, each one less than 6-in. in length.

In metalcasting, simulation and prototyping are a way of life: whether the work is conducted with wax or resin, or with nothing more than data points and pixels, prototype products and process simulations are the preliminary steps to successful production. The difficulty is that it’s never possible to compromise established production principles in order cast an ideal design.

To many foundries and diecasters, prototyping is more of an exercise in advanced engineering than in production planning. But, in the daily operations of some metalcasters, it’s really just a more functional approach to customer service. That is the experience at Aristo-Cast Inc. in Almont, MI.

Aristo-Cast is an investment caster that makes its design and production capabilities available to industries ranging from transportation to electronic equipment and military technology. One of its customers, Trico Products, has engaged Aristo-Cast in a successful design process, but one that did not necessarily develop according to expectations.

Trico develops and manufactures integrated automotive wiper systems and electronics. It approached Aristo-Cast with its new design for a windshield wiper motor device. The six main structural components for the brushless DC motor were to be manufactured in magnesium (AZ91E), to achieve space savings and reduce noise factors, and to lower overall component weight. But, the assembly’s internal parts were specified in steel, stainless steel, plastics, and rare-earth magnets.

While the final product had already been “designed,” these details presented a series of production challenges, as Aristo-Cast Larry Blum recalls. How to manufacture components with such narrow and precise dimensions? How to combine the different materials? How to manage the particular difficulties of casting magnesium?

All these concerns, and more, were to be worked out with prototypes. Aristo-Cast was chosen because of its rapid prototype and in-house tooling capabilities, and its ability to cast magnesium in ceramic molds was also important.

Once the motor structure is in full production, the magnesium components will be produced by Thixomolding — a semi-solid metalcasting process. Trico believed that investment casting would produce parts that most closely replicate Thixomolding, for form fit and function, and it is a cost-competitive process compared to machining from billet, diecasting, or prototyping Thixomold tooling. With that understanding, prototypes for the brushless DC motor and limited prototype production of the magnesium components had to approximate all the characteristics of a production thixomolded part, as nearly as possible.

Is prototyping always necessary on such complex designs? No, Blum advises, but it’s the only feasible way to achieve the look, feel, and structural integrity of the final design. Most such designs are the product of so many “decisionmakers” that finalizing the design involves multiple approaches and revisions. It’s not “trial and error,” he concludes, but rather “trial, and learn some more.”

This is where the functional approach to customer service is demonstrated. Aristo-Cast is able to incorporate in its products each of the iterations and varieties that are inherent to product development. But, they are able to do it quickly, and tangibly, while keeping Trico confident that the design is developing in a reliable manner.

Aristo-Cast’s thermojet wax imaging machines produced the initial casting designs, based on mathematical data. Trico’s design features some wall thicknesses as thin as 0.040 in., a weight-reducing detail that will be difficult to execute in full production.

Another anticipated difficulty is that the final structure will feature a magnesium casting surrounding a 303 stainless steel shaft. Aristo-Cast and Trico engineers developed a design for the over-cast shaft assembly that will positively lock into the magnesium casting.

Other changes were required to optimize cost and assembly issues before the motor design was ready for manufacturing. It was possible, thanks to rapid prototyping, to produce some parts even while the project’s prototyping phase proceeded. According to Aristo-Cast, it was simple to do this by modifying the mathematical data and casting the new designs as rapid prototypes.

As rapid prototyping helped to finalize certain parts, the parts to be Thixomolded were replicated by Aristo-Cast as semi-production wax injection dies. Then, semi-production castings were produced to match the final design, and machined and assembled. Trico then submitted the assembled prototypes to their customers for final evaluation.

The value of rapid prototyping in this case, and in innumerable similar cases, is that it links the component’s designers and manufacturers as they proceed through the critical stage of product development, the problem-solving stage. And, by anticipating production problems it speeds the effort to convert a design into a finished product.

Arena-flow 7.1 Runs Multiple Wares

For casting process simulation, a new version of Arena-flow sand core engineering software is available from Ashland Performance Materials, giving users the ability to run multiple software licenses on the same workstation. This allows additional calculations to queue automatically, maximizing computational resources while users are away.

“Today’s multi-CPU machines and multi-core processors put the processing power of many computers within a single workstation, and Arena-flow is now able to take advantage of that processing capability,” according to Peter Blaser, product manager for Arena-flow LLC. “Customers with multiple licenses benefit from reduced hardware costs and information technology hassles, and all customers benefit from maximum user efficiency.”

Alone among foundry engineering software suites, Arena-flow uses computational particle fluid dynamics (CPFD) technology to portray the entire coremaking process, including core filling, miss-fills, density variations, and curing. Users can produce consistent cores, examine core-related casting defects, reduce new tooling start-up costs, optimize cycle times, minimize consumable usage, minimize capital costs, minimize scrap, reduce machine downtime, and reduce tooling maintenance costs.