Injection moulding vs 3D printing: which pays off when

How the two methods differ

In injection moulding, plastic is melted and injected under pressure into a metal mould, where it sets. The mould first has to be made from steel or aluminium, which often costs thousands to tens of thousands of euros and takes weeks. After that, though, one part comes out every few seconds and costs a few cents.

FDM 3D printing has no mould. The part is prepared on a computer and the printer builds it from filament layer by layer. Zero upfront investment is its main advantage, at the price of every part taking tens of minutes to hours.

At what quantity each one pays off

What decides it is the number of parts over which the cost of the mould is spread. Roughly speaking, at tens to hundreds of parts, 3D printing is almost always cheaper, because the mould never pays for itself. At thousands and tens of thousands of parts, injection moulding usually pays off, because the price per part is many times lower.

In between there is a grey zone where it depends on the size and shape of the part. That is why it is worth comparing prices on your actual part. With us you see the 3D printing price per part straight after uploading your model, for quantities from 1 to 5,000, so working out the break-even point against a mould quote is simple.

What differs on the finished part

• Strength. An injection moulded part is one solid piece. A printed part is made of layers and is weaker across the layers, so it can split under overload (delamination).
• Surface and accuracy. Injection moulding gives a smooth surface and tight tolerances. On a printed part the layers are visible, especially on sloped faces.
• Design. An injection moulded part needs draft angles and an even wall thickness. In printing the shape can be almost anything, including cavities that could not be made in a mould.
• Materials. Hundreds of plastics are injection moulded. We print in PLA and PETG, which are enough for ordinary boxes, holders and covers.

Prototype, small batch and the move to a mould

A common approach is to print a prototype first, check the shape and function on it, and only then pay for a mould. A mistake found on a printed part costs a few euros, and one found in a finished mould costs thousands. Small-batch production from printing works just as well until demand is large enough to justify a mould.

If your batch is bigger than it makes sense to print, we will tell you straight. You upload the model, the price and lead time appear immediately, and nothing commits you.

A part meant for injection moulding is designed differently from one for printing. It needs draft on the walls so it can be released from the mould, an even wall thickness and rounded transitions, otherwise sink marks and warping appear. A part you designed for printing therefore has to be adapted before the mould is made. A printed prototype, though, catches most functional errors before that adaptation.

When deciding, work out three numbers: the price of the mould, the price per part when injection moulding and the price per part when printing. The break-even point is the mould price divided by the difference in price per part. If it comes out higher than the number of parts you plan per year, the mould will not pay for itself. With printing you also do not have to hold stock, as you order exactly as many as you need.