Make the model, make the part

Make the model, make the part

Service bureaus for rapid prototyping find they must expand into moldmaking, metal casting, forming, and test-production runs just to stay competitive.

Service bureaus for rapid prototyping find they must expand into moldmaking, metal casting, forming, and test-production runs just to stay competitive.

Starting with the latest CAD software and rapid prototyping machines, 3-Dimensional Services creates part models it then uses to provide downstream services such as injection molding, metal casting, stamping, and forming.

Producing models in the intended engineered material meant 3-Dimensional Services had to expand its operations to include forming and fabricating, CNC machining, ram and wire EDMing, and plastic-injection molding.

In-house pattern makers produce foundry tooling in days instead of weeks using rapid-prototyped models.

Pilot production of a stamped component can involve laser cutting or welding— operations not usually associated with a rapid prototyping company.


The stock and trade of prototyping service bureaus are geometric models done in a day, using processes such as SLA, LOM, and SLS. But increasingly, having a concept model to hold is not enough. Manufacturing companies now want a real prototype component made from the intended, engineered material. Moreover, they want it fast and supplied by their prototyping service bureau.

The market has become saturated with firms producing models. Rapid prototyping companies are finding it more difficult to compete without offering such downstream services as mold-making, metal casting, and forming. They must even be prepared to make test-production runs. According to Alan Peterson, vice president of 3-Dimensional Services (3-DS), this is the trend. And he emphasizes the point by mentioning that five rapid prototyping firms he knows of have folded within the last six months because they didn't provide the extras. Downstream services tend to determine who sinks or swims in the rapid prototyping business. "Companies that don't plan to offer the extras," advises Peterson, "might want to reconsider entering the field."

There is another reason rapid prototypers are getting into downstream services: Their stock and trade concept model work is dwindling.

Though 3-DS once did a great deal of CAD solid modeling for its customers, manufacturers are handling more of this work themselves. Many larger firms are buying their own rapid prototype machines, sending out less work to service bureaus. "Most of the master models we build," says Peterson, "are for our own use and don't go to the customer. Four or five years ago, they all went to customers."

The extras
At 3-DS in Rochester Hills, Mich., the extras, besides rapid prototyping, can include tooling for an injection mold or stamping die, pattern making for metal castings, complete CNC machining along with laser cutting and EDMing, or working the bugs out of a 20,000-piece test-production run.

Typical projects begin with a product concept sketched, blueprinted, or in a CAD file. The service bureau imports the information into its software packages. The CAD part file then may undergo finite-element analysis on one of the firm's 20-plus CAD terminals. The FEA helps verify the integrity of mechanical properties and structural prints.

When a physical model is required, an SLA (stereolithography apparatus), LOM (laminated object manufacturing) system, or an SLS (selective laser sintering) process will create one to within thousandths of actual part size. Customers can test the model for fit in an assembly, machine it for tooling and fixturing tryouts, or simply judge its aesthetic appeal. But today's customers are asking service bureaus for help answering questions that go beyond physical models, questions pertaining to such things as material suitability and production methods.

For example, 3-DS might machine prototype injection-mold tooling from aluminum or cast molds in zinc alloy, then injection mold a few parts in the desired material. As a result, the company may help design tooling to get the best molding conditions.

Typical activities in this area include finding the best locations for gates and determining the correct melt flows for a specific material. Peterson mentions that gating in the wrong spot or molding at too high a temperature for such materials as glass-filled nylon can weaken the part, perhaps cutting its strength by half. Frequent consultations with materials suppliers help keep service bureau personnel current on how to maintain material integrity. This sort of legwork, says Peterson, in turn saves the customer tooling design time.

For instances that call for stamped or formed metal prototypes, 3-DS has in-house presses ranging from a 7,000-ton hydraulic to an 800-ton mechanical. Tool and die machinists fabricate dies with either tercite tooling or machined aluminum alloys.

The company's pattern shop is inhabited by a model maker with 35 years experience in metal casting. But he no longer makes mahogany models for foundry tooling. What once took weeks is now complete in days.

Pattern makers work from a master physical model produced on a rapid prototype machine. They pull positive and negative patterns and cores for urethane, sand, investment, and plaster casting applications.

No matter what the prototyping process, 3-DS will make short test production runs—Peterson defines them as any quantity below 20,000 pieces/year.

From these test runs, 3- DS gives customers advice about manufacturability of the proposed design. For instance, personnel there might examine an injection mold to minimize the number of slides, ensure flow is good, or check for too many thin wall sections. Conversely, in a stamping situation, technicians might point out that a customer is trying to draw the shape at too severe a radius and suggest a less demanding angle.

Customers are invited to see the test manufacturing process. They witness, firsthand, any problems and hear suggestions or critiques from 3-DS shop personnel. Peterson says these typically relate to issues that would have stalled actual production. In this setting, the customer can address them before they cause trouble.

One job, an automotive gas tank shield, ran the full gambit. Engineers at 3-DS started by creating a rapid prototype and 'pulled' the tools from it. Pattern makers then rammed an epoxy negative of the model into sand for casting the injection-mold tooling. Peterson boasts that this was the company's first prototype with cast tools.

After injection molding the prototype, the customer wanted engineering changes. The problem was tooling size—the part to be molded measured approximately five feet across and two feet tall. Scrapping the tooling and starting over would have been expensive. So, welders added material in one spot and machinists milled another. Both departments refer-enced the original electronic data used to build the rapid prototype, and machining centers actually ran on it. Because the part had to be stamped, the forming department assisted the customer in refining the production molding process.

Prototype tooling that lasts longer than steel

The Rapid Manufacturing Center at the University of Rhode Island wants to skip the models and go right to producing actual injection-mold and die-cast tooling on its rapid prototype machine. The development that makes this possible is ceramic/metal composites.

Instead of the usual materials—paper, polymers, or powders—the Center loads its rapid prototype machines with Zyrkon (zirconium diboride/copper). The key is the ceramic part of the composite. It lets researchers tailor the wear properties to produce tooling that lasts a long time—quite possibly longer than steel tooling, says Dr. Brent Stucker, URI assistant professor and head of research at the Center.

Stucker's first success with Zyrkon was in creating an EDM electrode on a rapid prototyping machine. This electrode, while machining a mold, displayed wear ratios as low as tungsten/copper and better than copper or graphite— today's common electrode materials. Zyrkon, he says, is the optimum material for the EDM process and a good first step for injection molding and die casting. But, he foresees even better engineered composites in the future.

Technology, according to Stucker, has been available for short runs using silicone rubber mold transfer techniques and SLS nylon or a SLA part it-self as an injection-mold tool for certain low-melting-point polymers. There has also been a steel/copper composite for bridge tooling or short-run tooling 10 to 50,000-part jobs. But, he adds, a lot of companies don't consider that full production.

Because of the composite Stucker developed, he can manipulate the metal side to reduce cycle times. A high-conductivity metal in the mix (copper, for instance) dissipates heat better to cool the mold faster, so parts can come out sooner. Stucker wants the process to both increase production and be accurate.

At present, Zyrkon parts are as accurate as others from today's rapid prototype machines, within thousandths. Stucker believes that automated, novel finishing processes, such as CNC machining, can finish cut the tooling fast enough. He envisions a turnkey-type operation starting with a rapid prototyped or cast near-net shape which then moves to a simple finishing operation for final dimensions.

"All the pieces are there, the hardware and software. It's just a matter of combining them in a single efficient line," says Stucker. The Center wants help with this, which is why it invites outside companies to become members. The goal is to form a link between university research and industry.

Current members include a casting company, a rapid prototype machine manufacturer, a tooling provider, a die casting and injection-molding company, a large plastics firm, a maker of computer chip cooling equipment, and others. These and future members will have distinct competitive advantages.

Members will receive updates on progress and results, review all articles and presentations, have access to university faculty, and work with students who could be recruited as employees. They can also attend all Center seminars, sit on the Industrial Advisory Board, and license developed technology. Interested parties can call Dr. Stucker at 401-874-5187 or E-mail him at [email protected]

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