Long Fiber Technology
LFT is a new production technology, similar to SRIM* processing, that automates the two-step process into a single operation performed by a robot. A glass chopper gun is attached to the mixhead, which is mounted to a robot. The robot is pattern programmed to move over the mold cavity while dispensing the polyurethane infused with the chopped long glass fibers** in an open-pour method. At the end of the pour, the mold is closed to compression form the part. The product benefits that result from the LFT process include high stiffness, thermal stability, density and low weight.
Romeo RIM, Inc. was the first company in North America to install a Long Fiber Technology (LFT) RIM system for serial production. The inaugural product was sixteen different interior trim panels for the sleeper cab of Freightliner LLC's Century Class™ truck in which Romeo RIM applies a soft touch, two-component, in-mold paint to the tool, yielding a painted part after each cycle. This LFT process displaced conventional FRP processing for these parts as a result of its lower cost and weight savings.
The LFT process offers the following design advantages:
- Variable Wall Thickness - LFT allows wall thickness as low as 2.5 millimeters to 5 millimeters (or more) in the same part.
- Vertical Walls - LFT can produce parts with nearly vertical walls.
- Strength and Lightweight - Flexural modulus can range from 250,000 psi to 1.1 million psi. with very thin walls. This property will vary depending on the amount and the length of the glass fiber used and whether the polyurethane RIM system is foamed or a solid.
- Large Parts - LFT can produce parts weighing more than 30 lbs., depending on the polyurethane system used.
- Variety of Finishes - LFT parts can be finished inside the mold using a number of options: polyurethane elastomer skin, in-mold paints, polycarbonate films, and fabric or vinyl skins. These techniques allow production of high quality parts out of the mold, and often offer significant cost savings compared with secondary painting and decorating options.
Specific advantages of LFT are:
- Lower Tooling Costs - LFT RIM Molds do not require gating or other requirements for a closed mold injection process. Existing mold tools can in many cases continue to be used.
- Lower Production Costs - With LFT, chopped glass-fiber strands and polyurethane are poured into the open mold simultaneously, during a single working cycle. No mat-blanks or preforms are required.
- Optimized Weight - Through a precisely defined pour pattern of variable wall thicknesses, optimized for part loading, the parts can be 'slimmed-down' considerably. The simultaneous mixture discharge enables structural components of thinner wall thickness to be produced, than would be possible with saturated mats or preforms.
- Dimensional Stability - Optimum pouring-pattern coverage of the mold cavity in combination with the closed mold curing of the part reduces warping propensity, compared to other composite processes, thus ensuring accurate dimensional stability and precise fits.
- Optimized Strength - The Quantity and length of the chopped glass fiber strands can precisely be matched to suit the part's specifications. Changing the glass content and the polyurethane volume permits reinforcement to be made exactly where it is required.
- Reduced Material Waste - Specified openings in the part can be accommodated within the pouring-pattern and will not have to be trimmed in a separate operation, with the consequent waste of material.
- Stable and Repeatable Process - The simultaneous discharge of the polyurethane and glass fiber blend insures an isotropic arrangement and thorough wetting of the glass. The robotic pouring precision ensures accurate production repeatability.
* SRIM is a traditional two-step process based on fiberglass mats or preforms produced in one manufacturing cell then transported to the polyurethane-molding cell where the final part is produced.
** Natural fibers (e.g. sisal, hemp and flax) can be substituted for the glass fiber.