User manual

Z406 System User Manual Z Corporation
www.zcorp-users.com 67
6.9 RTV MOLDING
Room Temperature Vulcanization (RTV) molding, also known
as Silicone Rubber Molding (SRM), is an inexpensive soft
molding solution for creating dozens of prototypes accurately.
The benefit of RTV molding is that anyone can do it because
of its simplicity. Factors such as draft
1
, complex parting
lines
2
and undercuts
3
are not factors in building effective
molds as they are when using hard tooling. Additionally, hard
tooling may not be practical during the design process due to
cost, production time, and likelihood of design changes. RTV
molding effectively bridges the gap between one off
prototypes and hard tooling in a fraction of the time.
RTV molding requires the production of a single master
pattern, which is encased in low durometer
4
silicone rubber.
Using a part printed on a Z Corporation 3D Printer is the
fastest and least expensive method for creating a pattern for
RTV molding. Once the silicone rubber, encasing the pattern, cures (2 – 48 hours depending on
chosen material) the master is cut out, leaving a cavity. The cavity is used as a soft rubber tool for
molding investment casting wax, epoxy, foam, or in most cases polyurethane or a similar thermoset
material that has physical properties similar to injection-molded themoplastics. Cast prototypes will
have the look and feel of a production piece.
Additional Resources for the Novice Mold Maker
www.build-stuff.com/002book.htm
www.bare-metal.com/articles/gremlins_how_to.htm
www.smooth-on.com/moldmaking.htm
www.eagerplastics.com/intro.htm
www.theminiaturespage.com/ref/fgmolds.html
www.micromark.com/part_mold.html
The quality of the pattern directly affects the quality of the part from the RTV mold because RTV
rubber molds will pick up details as fine as a fingerprint from the master pattern. Master patterns are
classically sanded and polished regardless of the method of their production. This makes parts
printed using Z Corporation technology a perfect fit due to the ease in which their surface finish can
be enhanced.
1 Draft Angle – A slight taper to the shape of a cast part to allow it to be easily removed from its mold. Draft angles should be
used on interior or exterior part walls in the direction of draw. A minimum 1° draft angle per side is recommended for parts
having no textured surfaces. Textured surfaces need additional draft to easily release the part, and eliminate drag marks or
scuffing of the part surface.
2 Parting Line – Line in which two halves of a mold will separate. Parting lines should be located to provide good part
appearance and function.
3 Undercut – A protuberance or indentation that impedes withdrawal from a two-piece rigid mold.
4
Durometer – The hardness of a material. RTV molds typically use a material with a Shore A hardness <50.