Mass production

from wikipedia:

The slow print speed of 3D printers restricts their use for mass production. To reduce this overhead, several fused filament machines now offer multiple extruder heads. These can be used to print in multiple colours, with different polymers, or to make multiple prints simultaneously. This increases their overall print speed during multiple instance production, whilst requiring less capital cost than duplicate machines as they can share a single controller. Unlike using multiple machines, they are restricted to making identical copies of the same part, but then they can also offer the multi-colour and multi-material features, when this is needed. Their print speed increases proportionately to the number of heads and their energy cost rather less than this, as they can share the same heated print volume, both of which reduce their overhead costs. However the main cost is still the cost of the raw filament and this is unchanged.

Many printers now offer twin print heads.These are however used for manufacturing 1 part in multiple colors/materials.

In October 2012, CartesioLDMP was the first open source 3D printer to print 4 identical (set of) parts at the same time with 4 extruders.[citation needed]

Few studies have yet been done in this field, to see if conventional subtractive methods are comparable to additive methods.