What are the main 3D printing technologies available for custom prototyping services?

The short answer

Seven families, five that matter

Additive manufacturing is not one technology. The international process categories divide it into seven families, grouped by the physical event that joins one layer to the next, and every capability difference a buyer sees is a consequence of that grouping. For custom prototype work, five of the seven are commercially routine and two are specialised.

The two families missing from most prototype quotations are the two that do not suit single parts: binder jetting, which becomes economic in batches because the whole build is sintered together afterwards, and directed energy deposition, which trades accuracy for deposition rate on parts measured in metres. Both are real production routes and poor prototype routes.

What separates them on the floor

Three variables explain almost every difference a buyer notices. The first is what the machine does with material: melting a filament, curing a liquid, fusing a powder bed, or gluing then sintering. The second is whether supports are needed, because a support is a labour step and a contact mark that has to be removed. The third is the energy source and its control, because that is what sets both the accuracy and the material properties a part can reach.

Powder bed fusion is the family that removes supports from the equation, since the surrounding powder holds the part. That is why it dominates functional prototype work: internal channels, undercuts and interlocking assemblies that need support in the other families can be printed in one piece. Vat photopolymerisation removes seams instead, curing the part from liquid into one solid, which is why it holds the finest detail and the smoothest surface of any family while remaining brittle in impact. Material extrusion is the only family that builds with genuine engineering thermoplastics, and the only one where the bond between layers is a measurable weak point, at 50 to 75 percent of bulk strength.

How a prototype is routed to a family

Bureaus do not start from the process list. They start from the geometry and work outwards, and the order of the four steps below is deliberate: the first two eliminate families on engineering grounds, and only then does price enter.

1. Read the geometry. Internal channels, lattice cores, undercuts, thin walls and part size each eliminate families before anything else is discussed. A part with an internal channel that must be free of support material is a powder bed part; a part 1.5 metres long is a material extrusion part or a directed energy deposition part.
2. Name the requirement. Detail, strength, heat resistance, chemical resistance, electrical properties, appearance or unit volume - one of these usually dominates, and it points at a family rather than a machine.
3. Match the family. The output of the first two steps is a shortlist of two families with an accuracy figure and a material attached to each, which is the point at which the decision becomes a comparison rather than a choice.
4. Print and finish. Post-processing is part of the process, not an extra: support removal and ultraviolet cure for resin, depowdering and bead blasting for nylon, stress relief, support removal and often machining for metal. A route that does not name its finishing steps has not been costed properly.

Where each family stops working

• Material extrusion: stops at fine detail, at fluid-tight parts and at loads crossing the layer direction. It is the cheapest and the fastest, and it is the wrong answer for a customer-facing appearance part.
• Vat photopolymerisation: stops at impact loading, at sustained ultraviolet exposure and at temperatures above roughly 60 to 90 degrees Celsius depending on the resin grade. Resins also shrink and can distort on thin, high-aspect geometry.
• Polymer powder bed fusion: stops at surface appearance and at fluid-tightness. As-built texture is matte and grainy, the parts are slightly porous, and reused powder changes crystallinity unless the refresh ratio is controlled.
• Metal powder bed fusion: stops at the build envelope, at geometry that needs no internal detail, and at cost. It also needs a post-processing route, because sealing faces, bores and threads are machined afterwards rather than printed to size.
• Material and binder jetting: stop at structural loading. Jetting gives colour, multi-material and smooth surfaces rather than strength, and binder jetted metal depends on a sintering step that shrinks the part and leaves it porous unless it is infiltrated.
• Directed energy deposition: stops at accuracy and finish. It builds large metal forms at a high deposition rate, which makes it a near-net-shape process that expects to be machined afterwards.
• None of them is a production process at volume. Above a few hundred parts the economics move to moulding, casting or stamping, and a prototype validated for one of these families is not validated for the process that will make the production units.

Choosing a supplier by what it runs

The practical test for a prototyping supplier is not the length of its machine list but whether the process that suits your part is under the same roof as the processes around it. A part that is printed and then needs a sealing face machined, a surface blasted, a thread cut or a dye applied should not have to travel between three companies, because the tolerance stack and the accountability both get lost in the post. Ask which families are run in house, which are subcontracted, what the accuracy figure is for each, and how the finishing route is costed.

Send the model, the governing requirement and the quantity, and the process shortlist can be produced against your part rather than against a comparison chart. See SLA 3D printing for fine-detail resin parts, FDM 3D printing for economical large parts and SLM metal 3D printing for dense metal components, then send a file for a free engineering review.