Expert compares rapid-tooling choices.

Not so long ago, molders wanting to use a rapid-tooling method had few choices. But now the field has grown to around a dozen different processes. All of them slash tooling lead times and costs to a fraction of what's usually required. And all are based on rapid-prototyping technologies to produce a master model or the tool itself. How do you know which method best meets your needs?

The accompanying table compares five of the available rapid-tooling techniques. The table is based on the experience of an acknowledged expert on the subject, Drew Santin of Santin Engineering Inc. His firm in Peabody, Mass., specializes in rapid prototyping and prototype injection molding. The table's final column, "Overall Performance," reflects Santin's judgment of each method's capabilities compared with traditional tooling.

FIVE RAPID-TOOLING METHODS

Here are brief descriptions of the five processes that are compared with traditional machining in the table:

* Nickel composite tooling starts with a stereolithography (SLA) master, [TABULAR DATA OMITTED] which is then plated with nickel, mounted in a frame, and backed up with a cast ceramic. This type of tooling was developed by Pitney-Bowes of Shelton, Conn., and by Cemcom Corp., Baltimore, which has proprietary ceramic tooling technology.

* The Keltool process from SLA supplier 3D Systems, Valencia, Calif., starts with an SLA model as the basis for a silicone rubber mold of the core-and-cavity set. A powdered-metal mixture goes into the silicone mold, and the part is then sintered and infused with copper.

* Cast tooling also starts from an SLA model around which a rubber mold is poured. A ceramic impression of the mold is created, and molten metal is poured into the impression, producing the mold cavity and core in aluminum or other alloy.

* Albright is a relatively new method from Albright Technologies Inc., Sterling, Mass. An SLA master is placed in an aluminum backing that has been roughly machined to match the finished core-and-cavity set. Silicone rubber is then poured between the SLA master and the backing to create a more accurate final version of the core and cavity.

* Direct SLA tooling involves making a polymer core and cavity directly by stereolithography.

A WORD OF CAUTION

Some specifications cited in the table may differ from what vendors of rapid-tooling technology say about their systems. Remember that the table is based on a molder's real-world experiences.

Much of the data in this table - especially the tolerance information - was based on a benchmark part Santin created earlier this year. It's a small box with ribs, bosses, and various draft angles. One part, however, cannot represent all parts, Santin cautions. "When you're trying to do better than traditional tooling on time and cost, you're going to have to make compromises," he says. Those compromises change with the part geometry, no matter what tooling technology is used. "So don't pigeon-hole these systems," Santin warns. "Each one has its place."