Additive manufacturing of tool steel (H13 / 1.2709)
Conformal cooling in injection molds for extremely shortened cycle times.
1. Introduction: Tool making in the next dimension
Tooling for plastic injection molding or die casting is a billion-dollar industry. The massive steel molds not only have to withstand the extreme pressure of the plastic or aluminum being injected, but they also have to cool the melt as quickly as possible. The faster the mold cools, the shorter the cycle time per component, saving millions.
Traditionally, cooling channels are drilled straight into the steel. They often do not reach the edges of the tool properly (hot spots arise). 3D printing of hot-work steel (e.g. 1.2709 / Maraging Steel or H13) is revolutionizing this area through conformal cooling.
What is conformal cooling?
In 3D printing, cooling channels can be curved, spiral or contoured to exactly follow the complex 3D shape of the tool surface. The cooling water flows just a few millimeters below the hot tool surface and cools the component absolutely evenly. This prevents warping in the plastic part and often reduces cycle times by 20 to 40%.
2. The PBF-LB pressure of tool steel
Processing carbon-containing tool steels (such as H13) using the Laser Powder Bed Fusion (PBF-LB) process is demanding but extremely rewarding.
- Crack prevention: High-carbon steels such as H13 (1.2344) are extremely susceptible to cold and hot cracks due to the rapid temperature changes during laser melting. To prevent this, modern printers heat the build plate to over 200 °C (sometimes up to 500 °C). This reduces the temperature gradient and prevents cracks.
- Maraging Steel (1.2709): This nickel-alloyed martensite steel (without much carbon) is extremely easy to print. When printed (as-built), it is relatively soft (good for re-milling) and only develops its extreme hardness (up to 54 HRC) through subsequent aging at approx. 500 °C.
3. Hybrid production: milling and printing combined
Printing a tool mold entirely out of steel often takes weeks and costs an enormous amount of powder. Therefore, the industry usually uses a hybrid approach.
The solid base of the shape is classically and inexpensively CNC milled. This block is then clamped into the 3D printer as a building plate. The laser then prints only the top, highly complex centimeters of the shape (including the fine cooling channels) exactly onto the milled base block. This combines the speed of CNC technology with the freedom of 3D printing.
4. Longevity and repair
Tools wear out. The sharp edges of injection molds round off over time. Instead of throwing away half a ton of steel, the industry uses laser deposition welding (DED/LMD).
A robot arm with a laser powder head moves over the damaged edge of the tool mold and precisely applies a new layer of ultra-hard tool steel. The repaired area is lightly milled over and the mold is ready for use again. This "in-situ repair" process saves massive amounts of time and material.
5. Conclusion: A no-brainer for series production
3D printing of steel tool inserts is no longer research, but rather an industrial standard. Anyone who produces injection molding series of several million parts has often recouped the high costs of using a 3D printed tool after just a few weeks thanks to the cycle time saved (reduction in cycle time through conformal cooling).