In injection moulding, the mould is a fixed investment that only pays for itself at high volumes, and any design change means modifying the mould. SLS needs no tooling, and the cost of a part depends on its volume, the space it takes up in the build chamber and the material. For this reason SLS makes sense for runs from a few dozen to a few thousand pieces, depending on the size of the part.
Because the powder supports the parts, they can be stacked on top of each other through the full height of the build chamber. A full chamber is more efficient than a chamber holding a single part, since heating, printing and cooling happen for the whole build anyway. The Fuse X1 (330 × 330 × 565 mm) fits many more parts in a single build than the Fuse 1+ 30W (165 × 165 × 300 mm). Unsintered powder is recovered in the Fuse Sift and mixed with fresh powder, and the Fuse Blast cleans the parts automatically, which matters when you have hundreds of parts to blast.
A common case is bridge production, when you need parts now and the injection mould will arrive in a few months, or the design is still changing. You print the first batches in SLS, collect feedback from assembly and from customers, then freeze the geometry for injection moulding. Sometimes it turns out that the annual volume does not justify a mould at all.
Why SLS
- There is no mould and no fixed tooling cost, so a design change only needs a new file.
- Parts are also stacked through the height of the chamber, so the cost per part drops when the build is full.
- Each part in the build can be different, for example with another geometry variant, another serial number or another engraved batch code.
- Formlabs reports stable X and Y dimensions between builds and between positions in the chamber, which matters for repeat batches.
- Unsintered powder is recovered and partly reused, so you don't pay for the whole chamber volume.
Parts we often print
- Enclosures and covers for equipment made in a few hundred units a year
- Spare parts for machines whose supplier no longer exists
- Clips, spacers and guides for cable harnesses
- Buttons, handles and interface parts for small appliances
- Pilot batches before the injection mould is ready
- Products customised per unit, with different engravings or dimensions
- Adapters and parts for laboratory equipment
Design tips
- Keep wall thickness as uniform as possible. Thick sections next to thin ones distort more during cooling, and hollowing out thick sections reduces both distortion and material use.
- If the part will move to injection moulding later, keep draft angles and constant wall thicknesses from the start. SLS does not need them, but the move to a mould will be simpler.
- Add a batch code or an engraved number to the model. For engraved text, Formlabs gives a minimum character height of 3 mm and a depth of 0.3 mm.
- Send the estimated annual volume as well as the quantity for the first order, because the price per part depends heavily on how well the chamber is filled.
- Design holes that have to be accurate slightly undersize and ream them after printing, as Formlabs recommends.
The full rules are in the SLS design guide.