Which rapid prototyping technique works best for micromolded components? To find out, we presented a test part to several RP service bureaus. We designed the part to include many of the dimensions and features that medical, optic, and micro electronics industries require. Thus, the part’s overall dimensions were 0.200 × 0.200 × 0.125 in. Features included 0.010 and 0.020-in.-diameter through holes; 0.015 × 0.006 in. and 0.005 × 0.0025-in. thin wall sections, and a highly polished surface embedded with twelve 0.009846-in.-diameter lenses. Delicate features and embossed details completed the component. Our results with various RP technologies follow:

Stereolithography (STL) uses liquid UV-curable photopolymer resin subjected to a UV laser beam. The UV laser traces a cross-section of the part, hardening the resin and bonding it to the just-completed layer below. This process continues until the machine builds the complete 3D component. Excess resin is drained and the model placed in a UV oven for final curing. The model is finished by smoothing the “stair-step” surface.

Capabilities: Tolerances are +/-0.005 in. for the initial inch, and 0.0015 in. for each additional inch; layer thicknesses are 0.002 in.; resins can be made to mimic a wide array of production plastics such as ABS, polypropylene, and polycarbonate. Some materials are soft and flexible, ranging from 45 Shore A to 80 Shore A.

Pros: Can produce parts quickly; no tooling required; inexpensive for low volumes.

Cons: Limited materials and colors; generally Considered brittle; might not produce all fine features; parts often limited to dimensional representation and not actual functional intent.

Conclusion: STL is not the best way to get prototypes for micromolded parts.

3D printing (inkjet printing). This method is similar to the ink jet printers many of us have on our desks today. But instead of dropping tiny spots of ink on paper, this process uses tiny droplets of thermoplastic and wax. It also forms cross-sections layer-by-layer into complete and complex 3D parts.

Capabilities: 0.0010-in. accuracy; 0.005 in. minimum feature size; 0.0005 in. minimum layer thickness; smooth surface finish.

Pros: Can produce parts reasonably quickly when compared to hard tooling; no tooling required; inexpensive for low volumes.

Cons: Limited material availability; might not produce all micro features; parts often limited to dimensional representation and not actual functional intent; generally Considered brittle.

Conclusion: Despite decent accuracy and smooth surface finish, the limited material choice may make this a poor option. We could not find a vendor that felt confident its process would be successful with our test part.

3D printing (3DP — Z Corp). The other common use of “3D printing” is similar to the inkjet technique. An MIT-developed process, 3DP distributes a powder and binder to form prototypes.

Capabilities: 0.0035 in. layer thickness.

Pros: Can produce parts quickly; no tooling required; can print in color; inexpensive for low volumes.

Cons: Surface finish not as smooth as with other methods; micro features are lost; brittle parts.

Conclusion: Depending on what features are needed, this process may or may not work.

PolyJet is similar to SLA, but it produces much thinner layers and cures parts in-line while layering. A jetting head accurately builds each layer 0.0006-in.-thick (about 1/5 that of STL layers).

Capabilities: A variety of photosensitive resins are available; 0.004 to 0.01-in. accuracy (varies according to geometry, part orientation, and print size); layer thickness as small as 16 micron.

Pros: Can produce parts quickly; high resolutions; no tooling required; inexpensive for low volumes.

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