The use of 3D printing for injection mold inserts is rising for many reasons. Perhaps the most significant reason is the quick turnaround of parts. The example shown above could conceivably be machined but the lead time for such parts can be measured in months. A 3D printed one can be measured in days or weeks. That is valuable even if the parts come in perfect on the first try, but it becomes even more valuable when considering that so many molds require adjustment after learning lessons from the first shots or if the design changes.
Plastic 3D printing is gaining a lot of ground for this application. They are cheaper to produce because they take less time than metal prints and they can withstand a hand full of shots. Quite often that is all that is needed. However, if the temperature and strength limitations of a plastic mold insert is not good enough for your application, then DMLS is the natural upgrade.
Not only is DMLS stronger, but it draws heat away as you would normally expect from a metal mold. For very high production molds, temperature control becomes even more important for reducing stresses and decreasing cycle time. That is where metal additive manufacturing shines because of the ability to add cooling channels exactly where needed to get the temperature distribution you are looking for. This is why DMLS is used for inserts even if the mold surface is machined and processed conventionally afterwards.
In the case above, the natural surface finish in the mold cavity was exactly what the customer was looking for. It was not etched or treated in any other way than a typical bead blast. The critical interface surfaces were machined on a simple 3-axis mill to ensure the insert fit into the injection system but that was much easier to do than typical machining on a mold insert.
Mold inserts is already a huge segment of the 3D printing industry. In fact, Concept Laser has its roots the mold tooling industry. However, the benefits of DMLS are still under-recognized among design engineers and we predict its use will continue to expand.