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RKT Rodinger Kunststoff- Technik GmbH

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Design Differences in 3D Printing and Injection Molding

In the construction of a plastic part, guidelines must be observed that differ for the 3D printing process compared to injection molding. In injection molding, attention must be paid to wall thicknesses and wall thickness-flow ratios, among other things. Additionally, a component must be designed in such a way that it can be easily removed from the mold, which can also be supported by the geometry of the cavity. In 3D printing, it may also be necessary to create support structures to produce certain geometries, which must be removed from the finished part. This means more or less—usually manual—elaborate post-processing, which is not needed with injection molded parts. They are usually immediately usable or mountable.

Differences in Mechanical Strength

A part produced layer by layer in 3D printing also does not have the same mechanical properties as an injection molded part made from a melt in one piece. The adhesion of the layers applied to each other in 3D printing is generally weaker than the strength of a part created entirely from a melt because the molten layer applied to a printed layer essentially only "adheres."

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This Should be Considered in Material Selection

But not all plastics that can be injection molded can be easily processed in 3D printing. For example, when fiber-reinforced plastics are processed, the orientation of the fibers in 3D printing is different from that in an injection molded part, where in the cavity, the melt still flows and the fibers orient in the flow direction. Conversely, not all plastics used in 3D printing can be easily processed in injection molding—consider unfilled resins that are cured by UV light. However, there are also resin-like plastics (thermosets) filled with mineral powders or glass fibers that can be injection molded, provided the injection mold is not cooled but heated. The thermoset in the cavity is then thermally cured.