Can the hardness of metal 3D printing molds meet the requirements for high-strength production?

1. Choosing the right material: Bottom support made of metal powder with a high toughness
The material itself determines how hard metal 3D printing moulds are. Tool steel, stainless steel, hard alloys, and special alloys are the most common materials for 3D printing moulds right now. They have a hardness range of HRC 20 to 70, which means they can be used in a variety of situations.
Tool steel, like H13 and A2, has a hardness of HRC 40–60 after heat treatment. It is robust and resistant to wear, making it good for high-stress situations like die-casting moulds and hot forging moulds. For instance, a company that makes car parts employs 3D printed H13 steel moulds that are HRC 52 hard after heat treatment. These moulds work just as well as traditional forging moulds and last three times longer.
316L stainless steel has a hardness of about HRC 20–30, but by adjusting the printing settings and post-processing, its hardness can be raised to over HRC 40 while still being very resistant to corrosion. This makes it good for areas where hygiene is very important, like food packaging and medical devices.
Hard alloy: WC Co (tungsten carbide cobalt) is a typical material for extreme wear situations like punching dies and drawing dies. It has a hardness of up to HRC 55–70 and is more than 10 times more wear-resistant than tool steel. A certain company that makes electrical parts employs 3D-printed strong alloy moulds to double the punching frequency, from 500,000 times to 2 million times.
3D printing can make fine-grained structures in special alloys like Inconel 718 nickel-based alloy. These structures are 20% harder than those made by traditional casting. They also stay strong at high temperatures (strength retention rate>90% at 650 ℃), which is why they are used a lot in moulds for aviation engine turbine discs.
2. Process optimisation: precise control from "printing" to "forming"
The hardness of metal Not just the material but also the exact management of process parameters are important for 3D printing. For example, selective laser melting (SLM) technology increases hardness by optimising the following important parameters:
Control of energy density: The quality of the molten pool is directly affected by the strength of the laser, the speed of the scan, and the size of the spot. When the energy density is low, the material may become more porous (15% less hard when>1%), and when it is high, it may crack. A study demonstrates that when printing 316L stainless steel with a laser power of 150W and a scanning speed of 800mm/s, the porosity stays below 0.3% and the hardness reaches HRC 38, which is almost the same as that of forgings.
Interlayer bonding strength: A strong metallurgical bond between layers can be made by changing the scanning procedures (such chequerboard scanning and island scanning) and the layer thickness (20–50 μ m). For instance, a certain aviation business prints Ti6Al4V turbine blade moulds with a layer thickness of 30 μm and an interlayer bonding strength of 450MPa, which is 20% stronger than previous methods.
Setting the cooling rate: Rapid cooling (>10 ^ 4 ℃/s) can create a fine-grained structure (like martensite) that makes the material much harder. Using L-PBF technology, the City University of Hong Kong team printed an Al Mg Mn Sc Zr alloy. They used the nano twin strengthening mechanism to raise the yield strength to 656MPa while keeping the ductility at 12%.
3. Post-processing technology: the last step in making hardness better
3D printing isn't the end; post-processing technology is the most important part of making moulds harder.
Heat treatment: changing the lattice structure by annealing, quenching, or ageing. For instance, after being aged at 480 ℃, the hardness of a 3D printed 18Ni300 martensitic ageing steel mould went from HRC 38 to HRC 52. This got rid of residual stress and made it less likely to shatter.
To make the surface harder, you can use shot peening, nitriding, or laser cladding. A certain die-casting mould maker employed shot peening to 3D print H13 steel moulds. This made the surface harder (from HRC 50 to HRC 58) and made them 40% more resistant to wear.
Hot isostatic pressing (HIP): Using high pressure (100–200 MPa) and high temperature (900–1200 ℃) to get rid of internal pores and get the material density near to 100%. The Inconel 718 mould that was treated with HIP is 30% harder and lasts five times longer than the mould that wasn't treated.
4. Industry use: testing from the lab to the manufacturing line
The hardness benefit of metal 3D printing moulds has been confirmed in several areas:
GE Aviation uses 3D-printed Inconel 718 fuel nozzle moulds with a hardness of HRC 45. These moulds are 15% lighter than standard castings and can handle high temperatures and pressures.
Making cars: BMW Group makes aluminium alloy engine cylinder blocks using steel moulds and 3D printing tools. The mould hardness is HRC 50, and it lasts more than 100,000 times, which lowers the cost of each piece by 40%.
Johnson & Johnson employs 3D-printed cobalt chromium alloy orthopaedic implant moulds that are HRC 60 hard and Ra<0.2 μ m rough on the surface. These moulds meet both biocompatibility and wear resistance standards.