Equipment + Materials Add Up to Success
Time-saving technologies and products redefine the concept of rapid prototyping.
Optimizing efficiency is the key to remaining competitive in the rapid prototyping field. In a tough economic environment, Metro Plastics Technologies, Inc. - Metro RP (Noblesville, IN) - a company specializing in thermoplastic injection molding, decorating, assembly and packaging - is thriving by applying this principle to all aspects of its operations - from automated silicone rubber moldmaking equipment to fast-setting, high-performance polyurethanes.
"We've perfected our ability to produce parts in as little as four hours on many prototyping projects, including three hours to make a silicone rubber mold from a master pattern and an hour to cast and demold a fast-setting polyurethane part," explains Todd Wetz, rapid prototyping manager at Metro RP. Among the polyurethane prototyping materials Metro RP prefers are RP 6450 R/H medium flexural modulus polyurethane and RP 6486 R/H fast ultra-high impact polyurethanes supplied by Ren Shape Tooling Systems (East Lansing, MI) - a polyurethanes manufacturer.
As a rapid prototyping service bureau, Metro RP has been working with technologies that can increase efficiency and reduce part production time since it was founded in 1975. Today, the company has Pro-E and AutoCAD software to receive digital files and four stereolithography (SL) machines in-house along with fully automated silicone rubber and polyurethane mixing/dispensing equipment and pressure vessels large enough to accommodate castings up to 36" wide x 24" high x 72" long. Equipment capabilities are backed by a staff of 11 that has long-term experience in quickly producing high-quality, functional prototypes. Among Metro RP customers are appliance, automotive, electronic, medical and consumer goods manufacturers.
RTV Moldmaking
The majority of Metro RP projects are supplied digitally and then
manipulated to develop a database for downloading to a SL system. The
resulting master model, built from a SL material such as Cibatool® 7450
SL photopolymer, is then used to cast a silicone rubber mold.
Metro RP has realized significant timesavings by building reusable containment boxes in which silicone rubber can be cast. Each box is coated with Ren Shape Tooling Systems' Pro-Cast® 10 fast-setting polyurethane, which produces a super-smooth surface that facilitates demolding of cured silicone.
What also increases moldmaking speed is a proprietary, three-part, platinum-catalyzed silicone rubber that cures quickly and an advanced, fully automated system for mixing and dispensing silicone. The system maintains silicone rubber resin and catalyst under pressure, allowing technicians to shoot molds at a moment's notice.
To make a mold, workers simply suspend an SL master in a pre-built, polyurethane-lined box and inject silicone rubber. The mold is then cured under pressure, as an added precaution against void formation, and demolded after about two hours. To remove the model, the silicone rubber is cut in half, forming a parting line. Mold surfaces are then released and prepared for casting prototypes.
"We find we get cleaner parting lines and better quality parts with a one-shot pour than we did when we made two mold halves," Wetz explains.
Prototyping
For prototypes, Metro RP uses a variety of different polyurethanes,
enabling the company to select a resin system that offers the ideal
combination of viscosity, gel time, flexural modulus, impact strength
and heat deflection temperature for each project. For a battery box
used on Indy 500 cars, for example, RP 6450 R/H was the material of
choice because it features a 55-second gel time, flexural modulus of
184,000 psi and a heat deflection temperature of 252°F (122°C) to
withstand exposure to under-the-hood heat. Other benefits of the RP
6450 R/H system are its 15- to 30-minute demold time and its ability to
produce numerous parts without degrading silicone rubber surfaces
better than more rigid, high-temperature polyurethanes. Extended mold
life is particularly important on the battery boxes because about 300
of the parts are produced each year.
To make tougher prototypes of a series of 16 different blades for an industrial fruit juice separator that process berries at 1,500 revolutions per minute, Metro RP turned to RP 6486 R/H fast ultra-high impact polyurethane. The advanced polyurethane cures slower than other materials, with a demold time of 60 minutes, but produces parts that have a thermoplastic-like notched Izod impact strength of 6.3 ft. lb./in. to perform in applications like the separator blades. It also exhibits good elongation of 170 percent for added flexibility.
Parts-In-Minutes polyurethanes are dispensed from an automated meter/mixing machine. The static mixing nozzle is inserted in a silicone rubber mold and it is filled until material flows from vents. The completed mold is then placed in a pressure vessel and cured between 30 minutes and several hours, depending upon the polyurethane being used. Cured prototypes are demolded, flash is removed and parts are painted and textured, if necessary, before being shipped to customers.
"Most of our customers ask for accurate, functional prototypes in quantities of about 20, rather than injection molded production-intent parts. Metro RP has its own production injection molding facility, but for fast, initial parts and making multiple design iterations, we've found that the Parts-In-Minutes polyurethanes are ideal," Wetz concludes.
For more information contact Ren Shape Tooling Systems (East Lansing, MI) at (800) 955-5509 or Todd Wetz, rapid prototyping manager for Metro RP (Noblesville, IN) at (800) 676-6904.
