Metal 3D printing (SLM): stainless steel 316L and titanium TC4

For a long time metal 3D printing was considered a technology for the aerospace and medical industries. Today it is also accessible for single parts and small series: for a custom bracket, flange or sensor housing you send an inquiry online just as easily as for a plastic part. In this article we explain how the SLM process works, what stainless steel 316L and titanium TC4 (Ti6Al4V) can do, which design rules apply and when metal printing is a smarter choice than CNC machining.

How SLM works

Selective laser melting (SLM, also DMLS or LPBF) takes place in a chamber filled with an inert gas (argon or nitrogen). A layer of metal powder 20 to 50 µm thick is spread onto the build plate, and a powerful laser fully melts the powder wherever it belongs to the cross-section of the model. The plate is lowered, a new layer is spread and the process repeats. After several thousand layers, a fully dense metal part has been created, fused to the build plate.

Unlike nylon printing (MJF, SLS), a metal part needs supports during printing. They not only hold the overhangs but also conduct heat away and prevent the part from warping or tearing off the plate due to internal stresses. After printing, the part is heat-treated together with the plate to relieve stresses, then cut off the plate; the supports are removed mechanically and the surface is bead-blasted.

The result is metal with a density above 99.5 %, mechanically comparable to cast and, in some properties, even to wrought materials.

Material properties

The values are indicative for the heat-treated condition and vary slightly between batches.

Choose 316L when corrosion resistance, toughness or high temperature matter: brackets in humid environments, parts in contact with liquids, tooling, threaded elements and anything that must withstand impacts. It can also be polished very well.

Choose titanium TC4 when you need high strength at low weight or exceptional corrosion resistance: brackets for electronics in drones and vehicles, parts exposed to seawater or chemicals, and light but heavily loaded elements. It is almost half the weight of steel and stronger at the same time. It conducts heat poorly, so it is not suitable for heat sinks; it is also more expensive and more demanding to machine afterwards.

We do not offer aluminium in metal printing. For heat sinks and aluminium enclosures, CNC machining is the better choice.

Design rules for SLM

Metal printing has its own rules, which are worth following already when modelling:

• Wall thickness: at least 0.8 mm, 1.0 mm or more recommended. Thinner walls warp during printing.
• Overhangs: surfaces inclined less than 45 degrees from the horizontal need supports. Where possible, design overhangs at 45 degrees or more, or replace them with arched shapes.
• Horizontal holes: up to a diameter of 6 to 8 mm they print without supports; design larger ones as a teardrop or diamond so that the top of the hole supports itself.
• Vertical holes: minimum diameter 1 mm; model holes for threads as plain holes at the core diameter and cut the thread after printing.
• Internal channels: minimum diameter 1.5 mm, with chamfered or teardrop cross-sections; long channels need openings for powder removal.
• Sharp internal corners: round them with a radius of at least 0.5 mm, as they concentrate stresses.
• Large flat surfaces parallel to the build plate tend to warp; add ribs or tilt the surface.
• Massive blocks: metal is expensive by volume, so hollow out massive parts or design them with a lattice structure where it makes sense; powder removal openings are mandatory.
• Tolerances: expect ±0.1 mm or ±0.2 % after printing. Plan functional dimensions (bearing seats, sealing faces, holes with a tight fit) with an allowance of 0.3 to 0.5 mm for subsequent machining.

For metal printing always export a STEP file, because it preserves the exact cylinders and planes needed to prepare the machining.

Supports and orientation

With SLM, supports are the most important factor for price and quality. They are removed mechanically (cutting, grinding) and leave a rough surface behind. When designing, therefore:

• decide which surfaces are visible or functional, and model the part so that they can face upwards or be vertical during printing,
• avoid supports in internal cavities that no tool can reach,
• for parts where a good surface matters, write this in the note for the model.

The orientation of the part is determined by our manufacturing partner based on the geometry, but a better model means fewer supports and a lower price.

Post-processing

As standard, the part is bead-blasted after printing, which evens out the surface to a matte grey. Additional options:

• Machining of functional surfaces (CNC milling, drilling, thread cutting) for tolerances of ±0.02 mm.
• Polishing for a glossy surface on 316L.
• Tumbling for rounded edges and an even surface on smaller parts.

When metal printing beats CNC machining

CNC milling remains the best choice for simple, prismatic parts made from bar or plate stock, when a smooth surface and high accuracy over the whole part matter. SLM is better when:

• the part has internal channels (cooling paths, fluid routing) that cannot be milled,
• the geometry is organic or topology-optimised and milling would require several set-ups or five axes,
• CNC machining would remove more than 80 % of the material from the blank,
• it is one or a few parts with a complex shape, where preparing the CNC program and fixtures costs more than the print itself,
• weight matters and can be reduced by a third or more with lattice structures and optimisation.

For series of more than a few dozen simple parts, CNC or casting remains cheaper. It is good practice to finish a printed metal part on a CNC machine only where the accuracy is really needed.

Typical uses in electronics

When developing electronic devices, we most often use metal printing for:

• Lightweight titanium brackets for drones, vehicles and portable devices, where every gram counts.
• Brackets and mounts for fastening boards, sensors and antennas in vehicles, machines or enclosures, where plastic is too weak or gets too hot.
• Metal enclosures with EMC shielding for sensitive measurement modules and radio assemblies.
• Flanges and adapters for sensors, cable glands and connectors in industrial equipment.
• Tooling and fixtures for testing boards: test needle holders, clamping fixtures and assembly aids.
• 316L parts for humid or chemical environments: probes, sensor housings, brackets in the food industry.

How to get a quote

The process is the same as for plastic: upload a STEP or STL file to the 3D printing configurator and choose the SLM technology, the material and the quantity. A price estimate per part appears immediately, and we prepare a quote with the final price after reviewing the model. The lead time for metal is longer than for plastic, usually two to three weeks, because of the heat treatment and support removal.

Need help?

If you are considering a metal part, upload it to the 3D printing configurator and check the price estimate. If you still need the model – for example a bracket or flange adapted to your board – we create it as part of our 3D design service, taking into account all the rules for SLM, including orientation and machining allowances.