MOLDMAKING REPORT: Perfecting protoyping
A recent project undertaken by Reko International in Oldcastle, ON tested the limits of Vantico Inc.'s Parts-In-Minutes epoxy- and polyurethane-based prototyping system. The project required Reko to p...
A recent project undertaken by Reko International in Oldcastle, ON tested the limits of Vantico Inc.’s Parts-In-Minutes epoxy- and polyurethane-based prototyping system. The project required Reko to produce 30 tractor roofs, each weighing 89 lb. and measuring nearly 7 ft. in length by 6 ft. in width. In addition to the prototype part’s large size, another challenge was roof’s design, which incorporated multiple, hard-to-mold bosses.
As a first step, Reko model shop and prototype manager Rick Stone met with Vantico’s RenShape Solutions Tooling Group based in East Lansing, MI. Because of the roof’s large size, Stone needed a material with a work life longer than the two minutes afforded by the standard RP 6455 R/H Part-In-Minutes polyurethane resin. Technicians at RenShape experimented with different hardeners, finding one that would slow the pot life of the polyurethane to seven minutes.
To initiate the tool build, Reko used CAD data to cut a tool from Ren Shape 450 urethane boardstock. Several layers of a surface coat, followed by a laminating paste was applied to the core half of the tool. Next, 1/4 in. thick copper water lines were installed and covered with three layers of epoxy/fiberglass, building a tool wall thickness of 3/8 in. Once the tool cured, silicone rubber inserts were cast, vents drilled and square block ejectors were added. Finally, the core side of the tool was waxed out for wall thickness of the part. The cavity was formed using the identical process.
To cast the parts, two meter/mix dispensing machines were used to shoot each roof through multiple injection holes. After an experimental first shot, toolmakers determined that the mold needed more ejectors and venting. The mold was prepared, closed and filled with 89 lb. of RP 6455 R/H polyurethane and RP 6470 hardener. Resulting parts showed good accuracy and no warpage; however on the basis of the initial prototypes minor additional changes were made to both the mold and part. Additional prototype parts were made before proceeding to production parts molded from structural foam.
FORD LICENSING ADVANCED RAPID TOOLING TECHNOLOGY
Metal spraying methods to make dies and molds have been around for years but Ford Motor Company believes it may have perfected the technique with its Sprayforming technology. Sprayforming is a method of making tools and other objects by thermal spraying metal onto patterns made from ceramics, sand and other substrates. However, whereas other metal spraying technologies will produce a metal layer only a few thousandths of an inch thick, Sprayforming can produce dies and molds up to three inches thick.
“We have one die for a turbine blade made from Sprayforming that has taken over a million hits,” says Damian Porcari, Ford’s licensing manager for the technology. Porcari says the process can produce production-ready injection, blow and thermoforming molds for less cost than CNC-machined tools, with tolerance and hardness equal to tools made from conventional metals
Ford acquired the Sprayforming process when it purchased UK-based Sprayform Holding, Ltd. in 1999. According to Porcari, the process begins with a master model prepared from stereolithography, 3-D printing, CNC machined REN board or other methods. A ceramic substrate is cast off the master; then the substrate is placed in a Sprayforming cell where spray metal is deposited to the required thickness. In some applications no further finishing is required.
The breakthrough with this process is its ability to deposit carbon steel with little or neutral internal stresses, says Porcari. “We’ve made 44 production tools with this process so far for many different applications.” He notes that the price advantage offered by Sprayforming tools especially comes into play for complex types of injection molds.
Ford is licensing the process and Porcari reports that two plastics-related companies, General Plastics, based in Blaine, MN, and an unspecified Magna division in Ontario, have become Sprayforming licensees. Generally, the licensee will provide Ford with a master model and then lease time on Ford’s spray cell. Once a ceramic substrate is made, spraying usually only takes a few hours.
“This process can produce a production tool or mold in a matter of weeks,” Porcari says, reporting that Ford is continuing to develop the technology to find ways to make it even more cost-effective.