Which is Better: Injection Molding or 3D Printing?

Silicone rubber products can be processed in several ways. In this blog, injection molding and 3D printing will be compared. But first, both processes are explained.

What Is Injection Molding?

Injection molding is a process to produce high volumes of parts. In contrast to thermoplastics, silicone injection molding requires special treatments; an intensive distributive mixing must be done and a low temperature must be maintained in the plastification unit, while high temperatures are needed in the mold to promote the vulcanization. An injection molding machine is used to mix the components of the silicone rubber and an injection mold is used to form the final product.

What Is 3D Printing?

3D printing, or additive manufacturing, is a group of processes which generate pro-ducts from a three dimensional digital model (CAD).

 

The deposition of material (powder or liquid) to form layers using “printer heads” is the same in all groups of  3D printing processing. The first processes were developed in the early 1980s and are now some of the most popular processes in polymers. But the use of silicone in 3D printing is pretty new. Companies, such as Stratasys, Structur3D and Essential Dynamics, presented their processes as recently as two years ago because there are already some photopolymers that can simulate rubber and silicone behavior (even of different hardness) well.

 

Which Is Better For Your Company?

There are many factors that come into play when determining which method to use for silicone production.  One of the main factors is cost. Although the initial investment for both processes is high, 3D printing is cheaper than injection molding in many other instances. In injection molding, the mold is the most expensive part and its cost increases with the complexity of the part. For example, if the geometry of the part is not regular or symmetrical, the expulsion system and the gate locations are more expensive. In injection molding, different products require different molds, which need to be changed out for different shapes, sizes, and perhaps even materials, all of which cost additional time and money. In 3D printing, a simple change in the computer’s CAD file and maybe a simple configuration in the machine is all that is needed. As a result, a custom product is more expensive in injection molding. Another issue with the cost of injection molding is that the flow behavior of the material needs to be considered. If the mold is not designed adequately, the knitting lines will generate problems during the application, making the process even less economical.

The final properties of the product are another important component when processes are compared. Injection molding does have some advantages over 3D printing, in this aspect.  Injection molding, for example, makes parts quicker and with better tolerances than 3D printing.  The automatization of the production process is important because it accelerates the production, decreasing costs. Using injection molding, this system is simpler to implement than in 3D printing.  Furthermore, 3sourceful recently compared the cost of manufacturing a small part and a large part using both injection molding and 3D printing. They found that for a small part, 3D printing is cheaper over 1000 units, while for the large part, injection molding was cheaper over 100 units.

Initially, the objective of the 3D printing was to create prototypes of a product but, at present, most of the companies are working to improve the mechanical behavior of the products produced with this process. So, for now, the injection molding product has better performance in application.

The surface finish is also acritical characteristic in silicone products.  Depending on the application, the surface should favor the adhesion or improve the movement (low friction coefficient). Different textures can be obtained using injection molding, while the textures in 3D printing depend on the layer thickness. All of the info can be summarized as follows:

injection molding vs 3d printing

In conclusion, according to the needs of the manufacturer, either injection molding or 3D printing can be used. To determine which is best, many factors must be taken into consideration: cost, delivery, quality, production volume and complexity and application of the product.  It is necessary to conduct a comprehensive analysis of all components in order to make the best decision from economic, design and implementation points of view. For now, things evolve quickly, especially for medical devices, as a new process is being implemented: 3D-printed injection molding.

This process combines the economic advantages of the 3D printing process with the accuracy of injection molding. Additionally, there are no constraints with FDA materials. The molds used in the process are made using 3D printing technology and can hold temperatures as high as 500°F. The process, for now, has two disadvantages: the molds can produce only 100 parts before degradation and the surface finish of the product must be improved using metallic inserts, which increases the cost of the mold.

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This entry was posted in Liquid Silicone Rubber on by SIMTEC.