Aluminum extrusion is a very popular technique in the metalworking industry, construction industry and more to easily fabricate rods and prismatic profiles. Due to the increasing importance of lightweight design, the demand on especially hollow extrusion profiles will grow. The fabrication of closed hollow profiles requires several die parts with highly precise mandrels to form the cavities. The hardness and wear resistance of the tool steel is not sufficient for operation condition, therefore an additional nitration step is implemented afterwards. The main drawback of nitration is its brittleness, causing crack initiation and eventually spalling of the surface layers during service.
Conventionally, the mandrel of extrusion dies is fabricated by eroding and machining from a massive tool steel part, producing a huge amount of waste. Laser Metal Deposition as an additive manufacturing technique is more time- and resource-saving compared to conventional production. DIN 1.2343 / H11 hot work tool steel is standardly used in industry to manufacture dies for aluminum extrusion. So it was chosen to use it in conventional cast, wrought and machined condition for the lower part of the die on which the mandrels will be additively manufactured. Due to higher commercial availability in powder form DIN 1.2344 / H13 was used as the standard material for the additive parts, combined with DIN 1.3343 / M2 high speed tool steel or Stellite 6 Co-based hard facing alloy for especially wear critical parts.
Tensile and bending test samples were manufactured out of conventional DIN 1.2343 / H11 and used as a benchmark in tempered condition and additionally nitrated condition. Specimens were additively manufactured in monolithic or multi material fashion and tested in the as-built or tempered condition. Also specimens consisting out of conventional DIN 1.2343 / H11 and different additively manufactured alloys were used to determine the influence of the material transition and intermixing zone.
As the process and wear conditions during aluminum extrusion is hardly recreatable in the lab, real dies were manufactured. First test pressings on a full scale extrusion press in industry were successful. No deformation of the mandrels could be detected, also no differences in surface quality on the profiles could be measured, so the more martensitic additively manufactured mandrel surface did not change the aluminum adhesion compared to the nitrided conventional surface. The tool is now cleared for further tonnage.