Designs that incorporate grips, soft touch surfaces or other features for compatibility with manual use (or when incorporating inserts directly into a part), traditionally use over-mold manufacturing via injection molding. This form of manufacturing typically requires larger volumes to account for traditional two-shot molding processes which significantly increase costs. Prototyping over-mold designs are therefore not usually practical given the cost. However, today, 3D printing over-molded parts is possible for prototyping and even low volume needs. By eliminating tooling, and subsequent two-shot molding processes, over-mold 3D printing with PolyJet delivers a cost effective prototyping solution.
PolyJet is one of the only 3D printing technologies capable of manufacturing parts in multiple durometers and colors. It is most significantly used for high-fidelity prototypes and models, but its move towards more rugged short-term applications has strengthened in recent years thanks to material developments which include biocompatible options and materials with higher tensile and higher heat deflection mechanical properties.
PolyJet can 3D print in rigid and flexible in a single build directly from a 3D CAD file to create over-molded parts. Through dozens of material combinations, PolyJet delivers parts with shore hardness ranging from 40-90A in multiple colors and opacities. Designers often turn to PolyJet because it can print a design within hours, providing immediacy to a project without increasing the project’s overall cost. Because PolyJet doesn’t require tooling to deliver an over-molded part, it is frequently used during early concept prototyping for designs requiring an elastomeric surface, such as grips or buttons, before moving into final product development stages.
PolyJet is the only rapid prototyping technology available that delivers immediate over-mold concept realizations that incorporate all material deviations in a single part without tooling or any manual application.
Injection molding becomes the most cost-effective choice when part volume is high. Because over-molding with injection molding requires more than one tool, the cost for over-molding can quickly become a barrier to part production. Testing out the prototype using PolyJet over-molding, which simulates injection molding without hard tooling – provides for the best design readiness when finally moving into large volume production with injection molding.
Common Multi-Shot Mold Applications:
Multi-shot molding is still the go-to manufacturing solution for large-volume manufacturing.
At Stratasys Direct, we’ve found the best way to begin a new over-mold project is to start small. Experiment with material thickness and durometer using PolyJet before moving into injection mold plastics. If you’re unfamiliar with how material thickness relates to softness when it comes to more flexible materials, testing out the rubber-like PolyJet materials is an inexpensive way to get familiar with durometers and determine what your product really needs.
