Rapid Prototyping

e3k utilise a range of rapid prototyping technologies including our own technology "TruSurf" used for prototyping large objects.

True Surface System (TruSurf)

e3k offer a service to produce physical 3-D prototypes, using the TruSurf system, and is able to ship them anywhere in the world. Prototypes can be shipped fully constructed, partially constructed, or in layers ready for assembly. Please contact us for a quotation if we can be of assistance. (ray@gilmore-engineers.com)

TruSurf is a system designed to produce physical parts from layers of sheet material. Most layered manufacturing systems use layers which have constant (two dimensional) cross-sections and fixed thickness. This often results in an undesirable “stair-case effect” on the surface of the finished parts. Although the effect, and its associated errors, can be minimised by using very thin layers, this approach is only fast enough and cost effective for small parts. For large parts, an alternative approach to reducing the stair-case effect is desirable.

TruSurf uses a unique method to slice CAD models and output surface cutting data so that individual layers can be cut with sloping side surfaces from stock material. To make the process more efficient, each individual layer's thickness can be automatically selected from a range of stock material thicknesses to optimise the build speed and accuracy.

TruSurf obtains the definition of the required part from Non-Uniform Rational B-Spline (NURBS) surfaces. TruSurf uses these NURBS surfaces because they enable direct calculation of surface slope and curvature. NURBS surfaces use the same geometric definitions for surfaces as the original CAD model, thus accuracy is maintained, unlike the faceted approximations used by most Rapid Prototyping systems.

In TruSurf, the cutting information for each layer is obtained by sampling points, at a user specified spacing, around the mid contour curves of the layer. At each point the surface normal, curvature, and tangent to the contour curve are calculated directly from the NURBS surface. This information is used to establish a linear approximation of the local surface curve, and calculate the error caused by approximating a curved surface with a straight line tool. The maximum error for each layer is used to select the layer thickness, based on user specified tolerances.

TruSurf can use two different measures of error, cusp height, and maximum difference in the layer plane. These errors are calculated at each sampling point by approximating the local surface section as a circle and using the radius of surface curvature and angle of the surface normal to the layer plane. To cater for different manufacturing requirements, a method to produce parts with either an inside or outside tolerance, or a combination of both, is also available in TruSurf.

Other methods of producing sloping layer side surfaces have problems with pairing curves, loops and points, and branching geometry, where the number of curves in one cross section is different to the number in the next. These problems stem from the use of more than one cross section to reconstruct a sloping layer side surface. TruSurf uses a single cross section and additional surface information to define a layer. The direct calculation of surface information from NURBS surfaces eliminates the need for additional cross sections to define a layer, and avoids the associated problems.

TruSurf has been used to produce several physical parts. The most significant was a life size dolphin measuring 1692 mm x 660 mm x 1274 mm, built from 10 mm, 20 mm and 30 mm thick layers, with maximum allowable cusp height set to 1 mm. To produce the dolphin and an extra tail, one hundred and forty two layers were cut from sheet material with a five-axis waterjet cutter. Actual cutting time was approximately four hours, and assembly by one person by hand took about three hours. This represents a significant time saving over current Rapid Prototyping systems. It was estimated by the Queensland Manufacturing Institute that the build time for the same size dolphin, split into a number of parts, in an SLA-500 would be ten days.

Click here for a dolphin model, measuring 1692 mm x 660 mm x 1274 mm, that was built from 10, 20, and 30 mm thick sections of polystyrene foam. The layers were cut in four hours using the five-axis waterjet cutter at the Queensland Manufacturing Institute. The photos show the dolphin after assembling the layers by hand and without any finishing.

This photograph shows the dolphin finished and painted.

Some publications relating to TruSurf are:

Hope, R.L., Roth, R.N., Riek, A.T. "Rapid Generation of Large Objects", Proc. First Asia/ Pacific Conference on Rapid Product Development, QMI, Brisbane, 1995.

Hope, R.L., Roth, R.N., Riek, A.T. "Layer Building With Sloping Edges For Rapid Prototyping Of Large Objects", Proc. 5th European Conference on Rapid Prototyping and Manufacturing, Helsinki, Finland. 4-6 June 1996.

Hope, R.L., Jacobs, P.A, Roth, R.N. (1997) "Rapid prototyping with sloping surfaces", Rapid Prototyping Journal, vol 3, no.1. pp 12-19. (Awarded most outstanding paper in the Rapid Prototyping Journal in 1997)

Hope, R.L., Roth, R.N., Jacobs, P.A (1997) "Adaptive slicing with sloping layer surfaces", Rapid Prototyping Journal, vol 3, no.3. pp 89-98.