Graham Warwick/FORT WORTH

BELL HELICOPTER Textron is using stereo-lithography (SL) and rapid casting to meet its schedule for production of the Model 407 light helicopter, deliveries of which begin early in 1996. The manufacturer estimates that it has saved six months by using QuickCast technology developed by 3D Systems.

SL is a photochemical process for producing plastic models of parts direct from computer- design data. QuickCast is used to take those models as patterns for investment casting of production parts, avoiding the expensive and lengthy process of machining the hard tooling required to produce the wax patterns used in conventional investment casting.

In SL, a laser scans the surface of a liquid polymer, which solidifies when exposed to light. Each scan represents a slice through the part being produced, and a three-dimensional model is built up layer by layer.

Bell has so far used SL QuickCast to produce over 30 different parts for the 407. The most critical of these is the hydraulic power-boost support fitting, the heart of the primary flight-control system, which had to be produced within 60 days.

Using SL QuickCast, the unit was produced in 50 days, with greater accuracy and better mechanical properties than expected from a conventionally cast part, Bell says.

The manufacturer used SL solid models, to fit check the flight-control system, in the first production 407. This "virtual installation" allowed operation of the system to be verified in advance of assembly.

Bell says that SL Quickcast has proved to be at least four times cheaper than the traditional method of machining initial production parts from solid metal.

Valencia, California-based 3D Systems says that it is looking at improvements, including a lower-cost SL system which would act as a "three-dimensional" printer for designers, enabling them to convert computer data into physical models to visualise and verify designs.

Source: Flight International