Rapid Prototyping Is About Tool Design, Process, Materials, Manufacturability and Costs

To have a high level of assurance that prototypes will simulate production output and production processes, they have to be formed using tool designs, materials and machines that approximate high-volume manufacturing.

Article From: 2/1/2005 MoldMaking Technology,

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A unique prototype process

A unique prototype process with tooling in mind for taillight assembly helped complete Mercury's latest generation mini-van, the Monterey, with style and safety as top priorities, though timing too, was critical to the Tier One supplier.

Many people today may not think of vehicle taillights as safety items, but then consider the days when there were no turn indicators or brake lights. Imagine that technology on today's roads and in current traffic volumes.

That, however, is one of the challenges designers and stylists face all of the time—making safety features like tail lamp assemblies an integral but unobtrusive component of the overall aesthetics. And, for the team of designers that worked on developing the new Mercury Monterey mini-van, that task was even more daunting as the automaker promotes the new vehicle as having "more available safety and security features than any other mini-van." But, as the 2004 model has rolled out to dealers and consumers, it's obvious that the design challenge was met through a rapid prototyping process that considered tool design, process, materials, manufacturability and costs.

The RP Challenge

Coming out with a pleasant appearance is just the first part of the battle ... the second part belongs to the manufacturer, and in this case, North American Lighting, Inc., (NAL) and its Technology Center in Farmington Hills, MI. The company is a premier Tier One supplier of lighting components. It was NAL that was charged with providing the tail lamp assembly and, for the firm's Technology Center, to develop the prototypes.

With time short, Scott Turner, NAL Prototype Manager at the Tech Center, needed to provide Monterey team members with production-quality parts for final review and approval. "Today, the prototype process involves proving design elements and verifying manufacturing intent. We also have to confirm that the lighting component will satisfy any and all federal government safety criteria.

"For us to have a high level of assurance that the prototypes would—as close as possible—simulate production output and production processes, they have to be produced using tool designs, materials and machines that approximate high-volume manufacturing. Because the development time schedule was tight, we also needed the parts done fast. For both of these reasons, we went to Urgent Plastic Services (UPS) of Rochester, MI, to have the prototypes made." UPS is a specialist in the rapid prototyping of injection molded plastic components.

The rapid part of the equation means that, in virtually all cases, through the use of advanced technologies, materials and creative thinking, prototype parts are completed 50 to 70 percent faster than traditional technologies and prototype manufacturing methods would allow.

"The main tail lamp components—not including any electrical parts—consists of three separate plastic components," explains Turner, "including the housing, a two-color lens and a grill-like overlay that would be given a satin chrome plate finish. We needed to be sure that the separate components would properly fit together; the assembly (with electrical parts) would fit correctly in the vehicle; and, the required illumination levels were reached.

"UPS' fast response, completing the prototypes in just eight weeks, gave us that necessary margin of time to review, test and approve the parts and still maintain our production schedules," Turner adds.

The RP Process

The fast turnaround was impressive to Turner and his Styling Department team at NAL, but Steve Kelly, Project Coordinator/Engineer for UPS, reports that the Monterey project was not extraordinary. "In the past, suppliers and OEMs would have expected prototype work for plastic components such as the tail light assemblies to take three, maybe four months or even longer," Kelly states. "The injection tooling would take most of that time and was expensive, and in many cases the molds would be jury-rigged to produce a few parts. So, the customer might get a prototype that approximated the appearance he was after, but he was not provided any indication of the part's true manu-facturability or insight into process alternatives and potential complications.

"The rapid prototype process that we've developed at UPS eliminates the wasted time of conventional prototype manufacture," Kelly continues. "Another important element is the fact that our parts, tooling and process all approximate production-like conditions, so customers know what to expect and can prepare accordingly."

The Design Step

A typical project begins with the customer's submission of part(s) design and a CAD file. At this initial stage, UPS engineers and injection mold process experts review the design, making their recommendations for any changes that would help the design and could ease manufacturing difficulties. After computer designs are approved and any engineering analysis required is completed, UPS may send the design file(s) to one of its stereolithography apparatus (SLA) systems available for producing 3-D models of parts—typically completing models in a few hours. SLAs use the CAD data file to generate a dimensional travel path for a laser light source that cures a photosensitive polymer into the size and shape of the part.

For the NAL/Monterey project, the resulting three models were used as a hands-on reference tool for checking fit and for aesthetic review by design and styling experts.

The Tooling Step

After model approval, the next step in UPS's rapid prototype process is usually building of injection molds. Using sophisticated CAM software, CAD data files are once again translated to machining language for use in machining centers, or by high-speed machining and grinding centers for processing carbide tooling for EDMs—depending upon the mold characteristics and manufacturing method required. For this Monterey light application, the molds were machined from aluminum alloy. Like the SLA system, the CAD files generated the path for the machining centers' cutting tools.

Kelly notes, "The aluminum alloy tooling is another of the time saving steps in the prototype process that we've experimented with and developed over time. The aluminum used is the right combination of machinability that allows us to fabricate molds at fast speeds and feeds yet with durability to mold hundreds of prototypes. The machining rates of the aluminum can save several weeks in the process and still duplicate production-like quality, rates and data.

"Also at this point, the CNC machining centers were used to cut the alternating prismatic facets into tooling to replicate the reflex pattern in the lens," continues Kelly. "Usually, this reflex tooling process consists of producing hundreds or thousand of individual pins that need to be highly polished on the ends to produce the surface finish required to get reflectivity. Our process is suitable for approximating reflex levels in most applications."

The Molding Step

Once the molds for the three parts were complete, the injection molding process began. UPS' multiple injection systems ranging from 75- to 1500-ton capacities played a significant role in the timely completion of the prototypes. The housing was shot using a tough, rugged polycarbonate-ABS material blend; the two-color lens was made from acrylic using insert-molding techniques; and, the grill was made of an ABS grade of material capable of being plated.

With the injection molding shots finished and the three individual parts formed, UPS used one of its quality-certified outside sources in completing the satin chrome metalized finish on the grill.

With the components completed, UPS then assisted NAL personnel with the coordination of the assembly process for the prototypes and in establishing efficient procedures for production volumes.

Completing the Project

Rapid prototyping is about more than parts—it's the process, the materials, the manufacturability, the costs and tool designs. From the start of the design approval stages, to final assembly, to implementing production processes, rapid prototyping should not only overcome time restraints, but also eliminate the questions and the variables that can halt production in its tracks.

Prototyping put all the pieces in place—the satin-chrome finish grill, the housing and the dual color lens—allowing North American Lighting to keep its production start up of the Monterey tail lamp assemblies on schedule.

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