Fracktal Works

3D Printing for Silicone Molding

INTRO

Currently among all the 3D printing technologies FDM is the most commonly used technology for the prototyping. We can use 3D printing for making 2-3 parts but if we want to make a small quantity production of 15-20 parts then 3D printing would be a costly and time consuming task. Thus for reducing the cost and time for small scale production a suitable option Is silicone moulding.

OVERVIEW

Silicone moulding — also known as room temperature vulcanizing (RTV) moulding — creates finished products for prototyping, functional testing and short-run production. Considering tool life and cycletimes, it is ideal for small quantities (15 – 60 castings) because it offers lead times and costs that are well below that of machining or injection moulding.

Silicone moulds are made by pouring silicone rubber over a pattern. After curing, the resulting firm but flexible mould can produce parts with extremely complex geometry, intricate detail and tight tolerances. The parts are cast from a silicone mould made with thermoset materials (commonly urethanes) that are available with a vast array of mechanical, thermal and electrical properties.

The traditional silicone mould-making process uses a machined pattern made of plastic, wood or other materials. This method is often expensive and time consuming, and as pattern complexity rises, lead time and cost also increase.

SLA and FDM – 3D printing technologies are an innovative alternative to machining patterns for silicone mould making. These are built by laying patterns layer by layer, using data from computer-aided design (CAD) files. Pattern generated with these process require post processing for getting smooth surfaces.

REQUIREMENT FOR SILICONE MOULDING

Master part or 3D printed model of master part used as pattern
3D printed mold box
Mould Release
Silicone Rubber Material
Latex Gloves and protective glasses
Surgical blade
Container for preparing the silicone mixture
Fasteners for holding the mould box

STEPS FOR CREATING SILICONE MOULD

3D printing of master part
Sanding, Polishing and cleaning of master part for smooth surface
Volume calculation for mold box, silicone mixture and Urethane casting material
Designing and printing of mold box
Placement of master part in the mould box
Adding Sprue
Mix and pour silicone
Mold Complete

CAD DESIGNS AND 3D PRINTING OF MOLD BOX

The purpose of a mold box is to contain the liquid rubber (after it is poured over and around a model) until the liquid turns to a solid.

PLACEMENT OF MASTER PART IN MOLD BOX

The master pattern is placed in such a way that it makes no contact with the mould box. Suitable
spacers are inserted in a way so as to not interfere with the cast part.ADDING THE SPRUE
We create a sprue or sprues on our part. These will become funnel shaped holes in the mold. We need
them so we can get our casting material into the mold.
Keep in mind when we are molding a part, if something looks like it will trap bubbles, try to orient things
to avoid it. Our goal is to create a mold that will produce the best quality parts with the least amount of
work and fiddling.

MIX AND POUR SILICONE

Initially put mold release over the master part and the inner surface of mold box which held in easy demolding.
Combine equal amount of liquid part A and B (1A:1B) of silicone rubber material and mix these liquid rubber
contents thoroughly. Pour this mixture over prepared model and let it cure to a solid, flexible rubber mold.
After that demold it to get mold cavity that further used for casting the duplicates of the master part.REFERENCES
1. http://www.stratasys.com/~/media/Main/Secure/Applications/RTV%20Molding/PolyJet/SSYSTA
GSiliconeMolding%202314%20FINAL.pdf
2. http://www.instructables.com/id/Two-Part-Silicone-Casting/?ALLSTEPS

 

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