Prototipado rapido

HISTORICAL PERSPECTIVE
Joseph J. Beaman
TECHNOLOGY
The early roots of rapid mechanical prototyping technology can be traced to at least two technical areas:
Topography and photosculpture.

Topography
As early as 1890, Blanther (1892) suggested a layered method for making a mold for topographical relief maps. The method consists of impressing topographical contour lines on a series of waxplates, cutting the wax plates on the contour lines, and then stacking and smoothing the wax sections. This produces both positive and negative three-dimensional surfaces that correspond to the terrain indicated by the contour lines.
After suitable backing of these surfaces, a printed paper map is then pressed between the positive and negative forms to create a raised relief map. This is shown inFig. 3.1.

Perera (1940) proposed a similar method for making a relief map by cutting contour lines on cardboard sheets and then stacking and pasting these sheets to form a three-dimensional map. Further refinements of this approach were made by Zang (1964), who suggested using transparent plates with topographical detail inscribed on each plate, and Gaskin (1973), who described athree-dimensional geological teaching device.
In 1972, Matsubara of Mitsubishi Motors (1974) proposed a topographical process that uses photo-hardening materials. In this process, a photopolymer resin is coated onto refractory particles (e.g., graphite powder or sand), which are then spread into a layer and heated to form a coherent sheet. Light (e.g., from a mercury vapor lamp) is selectively projected orscanned onto this sheet to harden a defined portion of it. The unscanned, unhardened portion is dissolved away by a solvent. The thin layers formed in this way are subsequently stacked together to form a casting mold. In 1974, DiMatteo (1976) recognized that these same stacking techniques could be used to produce surfaces that are particularly difficult to fabricate by standard machining operations.Examples he mentions include propellers, air foils, three-dimensional cams, and forming of dies for punch presses. In one embodiment (Fig. 3.2), contoured metallic sheets are formed by a milling cutter, then joined in layered fashion by adhesion, bolts, or tapered rods. This process has obvious similarity to the earlier 19th century work.

In 1979, Professor Nakagawa of Tokyo University began touse lamination techniques to produce actual tools such as blanking tools (Nakagawa et al. 1979), press forming tools (Kunieda and Nakagawa 1984), and injection molding tools (Nakagawa, Kunieda, and Liu 1985). Of particular note, Nakagawa mentions the possibility of complex cooling channels in injection molds (Nakagawa, Kunieda, and Liu 1985).

Photosculpture

Photosculpture arose in the 19thcentury in attempts to create exact three-dimensional replicas of objects, including human forms (Bogart 1979). One somewhat successful realization of this technology was designed by Frenchman François Willème in 1860. In his method, shown in Fig. 3.3, a subject or object was placed in a circular room and simultaneously photographed by 24 cameras placed equally about the circumference of theroom. The silhouette of each photograph was then used by an artisan in Willème’s studio (Fig. 3.4) to carve out 1/24th of a cylindrical portion of the figure.
In an attempt to alleviate the labor-intensive carving step of Willème’s photosculpture, Baese (1904) described a technique using graduated light to expose photosensitive gelatin, which expands in proportion to exposure when treated with water.Annular rings of the treated gelatin are then fixed on a support to make a replica of an object, as shown in Fig. 3.5. Similar techniques and improvements were developed by Monteah (1924).

In some of the earliest work in Japan, Morioka (1935, 1944) developed a hybrid process combining aspects of photosculpture and topography. This method (Fig. 3.6) uses structured light (black and white...