Grimm Brothers Processes

Processes

THERMOFORMING PROCESS

Thermoforming is a means of shaping thermoplastic sheet to conform to the contour of a mold through the use of heat and pressure, either positive or vacuum. Plastic is heated to predetermined temperature at which the plastic softens but is below its melt temperature. It is stretched to cover the contours of a mold with the use of vacuum and cooled to a temperature at which the thermoplastic becomes rigid, thus retaining the shape of the mold. The formed part is then trimmed to eliminate edges, decorated and/or fabricated into an end use article.

Pressure Forming: The 10% solution.

Pressure forming means startup tooling costs as low as 10% of that required for the same injection molded project!

That's more than a claim; it's documented fact. 10% of the cost...a 90% savings. Any way you look at it, it's a strong argument for considering pressure forming for your next molding project. Add to that enormous cost savings a turnaround time of just 20% of injection molding...together with quality that rivals injection molding for finite detail and crispness...and it's easy to see why pressure forming has become one of the hottest molding processes of the nineties.

As with other thermoforming processes, pressure forming begins by heating a sheet of material to a point that's malleable enough to be shaped. The process accepts almost any thermoform-rated material, and we can work with sheets up to 6 X 16 feet. Therefore, we can shape components of virtually any size.

After the material is heated to the correct degree of flexibility, it's formed to the desired shape over a high quality, precision-tooled mold which can be designed with incredible detail, including undercuts and reverse drafts. When the material is in place, air is evacuated from the sealed space between the sheet and the mold. At the same time, extremely high air pressure is applied to the outside of the material as it is formed to the mold. Not a centimeter of material nor a single detail of the mold escapes that high pressure treatment. That ultra high pressure applied to the soft material is what helps the pressure forming process deliver such extremely accurate, detailed molding completely faithful to the original design.

When the formed part is removed from the mold, it progresses through a series of fully automated secondary operations. Edges and trim are smoothed to perfection with precise CNC routers; slots and grille work are added as needed; bosses, ribs and special fastening devices are permanently bonded; silk screened logos and other accouterments are added. But the most demanding step in the process is left till last: A rigorous inspection in Grimm Brothers' own Quality Control department, an uncompromising process which accepts nothing less than absolute perfection.

Pressure forming provides a manufacturer with these benefits:

Startup tooling costs typically as little as 10% of comparable injection molding tooling.
Extremely fast turnaround time, with production tooling commonly completed in six to eight weeks and the first completed parts ready to ship within one to two weeks following approval of the finished tooling.
Easily modified tooling to accommodate revisions to part specifications.
Highly cost efficient production runs of 50 to 5,000 units, or higher, depending on the size and complexity of the component part. The cost and affordability of running these small quantities also allows the manufacturer to maintain a leaner inventory and schedule more frequent runs.
Broad material flexibility which allows the use of several different thermoformable materials from .060 to .500 gauge with virtually unlimited size restrictions.
Complete aesthetic integrity. Properly pressure formed materials look as good or better than injection molded items with sharp edges, tight corner radii and ultra-fine detail.

Twin Sheet Pressure Thermoforming: Double your options.

For all the honors heaped on single sheet pressure forming, no conventional thermoforming can make a hollow part unless two halves are made separately and bonded together. Twin Sheet Pressure Thermoforming can make that same part in a single operation. Depending on part size and quantities, it can actually do the job much more economically than blow molding.

At Grimm Brothers, two separate processes are employed to Twin Sheet Pressure Thermoform. In the "SST" (Single Station Twin Sheet Thermoforming) process, two material sheets are simultaneously clamped into one frame. A metered air probe is inserted between the two sheets to prevent them from sticking together during the heating cycle to come. The frame is shuttled into an oven so the material can be heated to the proper forming temperature. Then it's shuttled back out of the oven and positioned between two mold halves which are mounted on a top and bottom plate that come together, sandwiching the two halves close, a powerful vacuum literally "sucks" each sheet into their respective mold half and high pressure is applied through additional air probes. The high pressure along with a special pinch off design and high heat effectively "welds" the two pieces together into a single hollow, molded part. The final product advances through an appropriate series of fully automated secondary operations, delivering an end result as polished, refined and sophisticated looking as any blow molded or injection molded part. And to add either rigidity, insulation or sound deadening qualities, SST parts can be urethane foam filled.

We call the other process Sequential Twin Sheet Pressure Forming. This process requires a specifically designed four station rotary thermoforming machine. Rather than starting with two plastic sheets, one sheet is heated and formed in one half of the mold. Then a second sheet is heated and formed in the other half of the mold. The two tool halves are then closed to bond the two sheets together. The same "pressurizing and welding" that happens in the SST also happens with this process. The time lapse of the first sheet to the forming and mating of the second sheet, about 15 to 20 seconds, allows enough time to insert a metal, wood, foam or other structure between the two sheets. This insert gives a designer opportunity for a super structural part. CAD-assisted design services are available to help make sure costs are kept to a minimum and your finished parts do exactly what you want them to do.

Vacuum Forming: When cost is critical.

Vacuum forming is characterized by extremely low tooling and parts costs. Like pressure forming, vacuum forming features sheets of virtually unlimited size heated to a point of maximum flexibility, then formed to a mold. Also like pressure forming, the air between the mold and the material is removed by a powerful vacuum as the heated plastic melds to the mold and takes on its new shape. Although vacuum forming lacks some of the refined detail of pressure formed parts, its dramatic economies make vacuum forming a sensible alternative for many simple designs, large parts, small to high quantity production runs and molded components that need to progress from concept to tooling to finished product in a big hurry.


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