3D Printing or RTV Casting?

3D printing has never been more accessible to product developers than it is today with the onset of high quality consumer grade printers and affordable printing services. While 3D printing is a powerful tool for product development, it should not be considered the only prototyping option. Often overlooked is RTV urethane and silicone casting, and for many projects it can fill gaps where 3D printing falls short.

3D printing, RTV Casting, Silicone molding, plastic part, urethane, form 2

Process Overview

RTV stands for room-temperature vulcanization. This is a process in which a two part resin (urethane or silicone) material is mixed together and injected into a plastic or rubber mold. As the material cures, it hardens into it's solid form. RTV casting is great option for accurately simulating injection molded materials and especially rubber parts.

3D printing is an additive process in which a material is combined layer by layer until a 3D object is created. This process is computer controlled and a CAD model of the object is required. Due to it's speed and low cost, 3D Printing is a powerful tool when beginning product development.

Material Options

3D printing can use a wide range of materials including nylon, ABS, PLA, a variety of photo-polymers ranging from rubber to rigid, a variety of metals, ceramics, gypsum powder, and others. You can use flexible materials designed to simulate polyethylene and others filled with carbon fiber. As this technology has matured, more and more materials have become available to the public, and we expect more to in the future.

Color

Generally speaking, most 3D printed materials are going to be a single color and in limited variety if any. There are a few exceptions to this, as the composite powder material can be printed in multiple colors. The highly advanced Connex printers by Stratasys can also print multi color parts using their Vero family of photo-polymers.

RTV materials can be dyed before being cast to achieve specific colors, and this will be significantly more durable than a painted part. Dying rubber materials is also a huge advantage, as painting rubbers can present feasibility and durability challenges.

Surface Finish

The type of 3D printer you use and it's resolution often drive the type of surface finish your part has. Typically you can see layer lines, or “striations” on the 3D printed part. Some companies also offer finishing services to sand your parts smooth for an additional cost. Of course, more advanced printers with higher resolution can create parts that require less finishing than others.

When you make a mold for RTV casting, that mold takes on the surface finish of whatever master pattern used to make it. So if you need several parts with a very specific surface finish, you can save significant time and money by getting a mold made and parts cast instead of hand finishing many 3D printed parts. The molding process is so accurate, that it can pick up finger prints accidentally left on the master pattern!

3D Printing, Prototyping, SLA

Functional Integrity

This is where RTV cast parts really shine. Since the part is cast, and not printed in layers, thin walls can stand up to more force before breaking. This is critical when working with small and precise components. Additionally, cast rubber parts behave much more similarly to a production material in terms of tear strength than 3D printed rubber materials. 3D printed parts are created in layers which can cause part failure on smaller geometries.

Geometry

3D printing can be used for geometries that would be impossible (or cost prohibitive) to cast and this is a major selling point for 3D printing. There may be requirements in some printing processes to create support structures, but with a little creativity these won't stand in your way.

RTV casting is very similar to injection molding in terms of form-able geometry and mold pull direction. Since the molds are made from flexible rubber instead of steel, they can handle small undercuts in the part. More advanced tools user inserts or cores to handle larger undercuts.

Both 3D printing and RTV casting have challenges when faced with forming large parts. For 3D printing, it's all about the build envelope and the cost of the material. For RTV casting, it's the all the challenges of designing and filling a large mold tool without machine aid.

Cost and Time

The cost of creating a prototype depends on a variety of factors including: fabrication method, material type, and aesthetic preferences like color and surface finish. So for making a few parts without any demanding functional or aesthetic requirements, 3D printing will nearly always be cheaper. If you're looking for a small run of parts, with specific functional or aesthetic qualities, RTV casting may be more cost effective.

Typically 3D printing has zero or minimal start up costs, depending on where you get your parts printed. However RTV casting requires the design and creation of a mold tool, which may cost hundreds to thousands of dollars.

Industry lead times for 3D printed parts typically range from 3-7 business days. Since RTV casting involves the creation of a mold tool, those lead times typically range from 5-12 business days, but are very dependent on order size. Many companies offer expedited printing and casting for an additional fee.

 

To learn more about these processes and figure out which is best suited for your project, contact us today at sales@touchstone3d.com.

Leave a Comment