Working on a two-day, art-to-part turnaround time for many projects, Vantage Tool and Engineering (VTE), Fort Wayne, Indiana, is redefining the concept of rapid manufacturing. The company satisfies its customers'' needs for fast delivery of prototype parts that exhibit high-quality, accurate surfaces using CAD/CAM technology, high-speed mills, and easy-to-machine Ren Shape® 450 boards from Vantico, Inc., Ren Shape Tooling Systems, East Lansing, MI.
VTE President Ken Brosch explains, "We formed our company three years ago with a group of experienced engineers, toolmakers, and machinists. Our objective was to provide customers with a full spectrum of services from design to tooling to thermoformed parts...in record time and at competitive prices. Supporting these goals was our investment in state-of-the-art computers and software as well as advanced materials."
Typical Project Profile
The large majority of VTE''s thermoforming projects call for molding food trays, bowls, and other highly contoured containers in quantities of up to 5,000. Materials formed include polypropylene, polystyrene, polyvinyl chloride, and polyethylene. To quickly cut prototype tooling that can be used for up to 500 molding cycles, VTE has found that Ren Shape 450 boards are ideal.
"Our toolmakers have the equipment and expertise to mill aluminum, but we can cut a Ren Shape mold in half the time needed to machine metal. The board helps us significantly reduce delivery times and costs on initial parts while hard tooling is being made," reports Sam Geiger, general manager at VTE. "The completed Ren Shape prototype molds also generate trays and bowls with a production-quality surface and intricate detail."
After VTE receives the data for a part, or designs a container based on client requirements, the CAD file is downloaded to the CAM program, which adds cutter and tool paths. At the same time, VTE moldmakers begin building up a machinable block by laminating together Ren Shape 450 boards. Individual boards measure 16 in. wide x 60 in. long x 4 in. high; they are bonded using Ren Weld™ 103 adhesive. After the block is built up, pieces are clamped for 48 hours until the adhesive cures.
"The key to good adhesion between board pieces is accurate measuring and weighing of the adhesive components," Geiger explains. "Once the boards are joined properly, the bondlines are really tough. In fact, during testing, we''ve found that the board shears before the bondline breaks."
To cut a mold cavity, the Ren Shape 450 block is installed in one of VTE''s high-speed, 3-axis mills. Machining typically begins with a 1/2-in. depth of cut, followed by 1-in. and then 1-1/2 in. cuts to produce the deep cavities that characterize many of the trays and containers formed by VTE. Two-flute, hardened steel ball-end mills are used to machine the board at 3,500 revolutions per minute (RPM) and 120 in. per minute (IPM) for roughing. Finishing cuts are made with 1/4-in. tapered, fluted-end mills at 4,500 to 5,000 RPM and 150 to 160 IPM using a 0.007-in. stepover to produce mold surfaces that require no secondary finishing.
Completed molds exhibit the strength and thermal properties needed to withstand numerous thermoforming cycles, including a glass transition temperature of 205°F (96°C), Shore hardness of 65D and tensile strength of 2,300 psi.
To mold a container, the machined Ren Shape tool is mounted in a standard base and installed in the thermoforming machine. Plastic sheet is inserted in a frame over the mold, heated until soft, and then formed into the mold cavity. The completed container is demolded immediately and preparations are made to produce another part.
"Thin-walled parts, run at temperatures up to 450°F (232°C), are typically the most difficult to form because the Ren Shape molds hold the heat. When we''re running multiple parts, heat build-up has the potential to damage mold surfaces. To prevent this, we reduce the cycle time to allow the heat to dissipate," says Geiger. He concludes, "Ren Shape boards meet our needs for an easy-to-handle, durable moldmaking material for initial part production."