3d printing vs injection moulding

3D printing is an exciting technological advance within the manufacturing industry.

Pioneers of this technology are regularly creating new materials and items that can be printed. This has led to assertions that 3D printing will soon replace traditional manufacturing methods such as plastic injection moulding.

These claims are definitely premature. Injection moulding is an incredibly reliable, efficient method of producing plastic parts that accounts for over 75% of plastic parts used in industry, according to Denny Scher of Manufacturing Tomorrow.

There are three key reasons why plastic injection moulding is here to stay:

Quantity

Injection moulding involves injecting liquid polymers into a mould, allowing it to adopt the shape of the mould before cooling it rapidly and removing the now-solid polymer. This process is significantly quicker than 3D printing that involves a liquid plastic filament being distributed in thin layers to create the object. Injection moulding is therefore significantly quicker than 3D printing.

Quality

Due to 3D printing’s method of producing items via layering, it cannot produce the same consistently smooth surface finishes that are possible using injection moulding. This layering method of production also leaves products with directional stress weaknesses that are not encountered by their injection moulded counterparts.

Although advances are occurring regularly, at the time of writing the range and complexity of shapes that 3D printing can produce is currently limited in comparison to the shapes that are achievable using injection moulding.
The relative infancy of the technology means that software issues are still prevalent within the technology. Fixing both software and hardware bugs in the new technology can prove to be costly and time consuming.

It is possible to combine the technologies and use 3D printing to create the moulds for the injection moulding process. However these moulds are normally created using photoreactive or thermoset resin, which breaks down faster than traditional metal moulds. Metal moulds are capable of producing hundreds of thousands of products in comparison to the 3D printed moulds. 3D-printing moulds is a viable solution for lower volume injection moulding projects, as it can help to reduce the high initial costs associated with injection moulding technology.

Price

The price of both 3D printing and injection moulding is dependent on the number of parts that are going to be produced. Injection moulding is considerably more expensive to produce prototypes and small patches due to the initial costs of creating a steel or aluminium mould. Any subsequent alterations which can require whole new tooling. In 3D printing, once the prototype has been developed, it is a case of pressing print.

There have recently been new software advances that permit any prototyping issues to be resolved in the initial CAD design phase. This has helped to eliminate the need for multiple mould iterations and prototypes.

3D printing therefore begins with lower startup costs. According to David Kazmer, Professor of Plastics Engineering at University of Massachusetts Lowell, 3D printing can typically prove to be cost effective for product runs of less than 50. However costs increase with quantity due to the risk of misprints. Injection moulding has higher initial costs, which drop rapidly with product volumes over approximately 60 items.

3D printing is a viable option for small volume batches, both to produce the product in its entirety, or to print the mould to reduce costs in the injection moulding process. For large businesses, such as Essentra Components, that regularly handle high-volume projects, injection moulding makes sense from a price, quality and speed perspective.