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Injection molded or RP? Hard to tell on these plastic models

May 24, 2010

Leslie Gordon

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A new rapid prototyping machine additively builds parts that appear as if they have been injection molded and let users verify designs for form, fit, and function. The ZBuilder Ultra (available in July) from Z-Corp., Burlington, Mass., creates components using a high-resolution digital light processor (DLP) projector to solidify liquid photopolymer. According to the developer, the machine builds functional plastic prototypes two times faster than other RP technologies and at one-third of the price of stereolithography machines. The machine builds parts to tolerances of +/- 0.008 in. with feature sizes down to 0.005 in. and a smooth surface finish. The photopolymer’s material properties are similar to those of ABS.

Sources: Z-Corp.www.zcorp.com

Comments

RP vs injection molded

One of the pitfalls of non molded prototypes is the morphology of injection molded parts is very different from that of the base material. Injection molded parts have highly anisotropic properties in the flow versus cross flow directions due to the long chain molecule nature of polymers.

Also, RP parts cannot simulate knit lines and other molding anomalies which effect the functionality of a part,

If the part is always in compression only, no worries, but if there are tension, shear, or torsion forces, watch out!

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