Is the recycling rate of metal printing materials high?

一,Technical principle: the main idea behind choosing materials and controlling the interface.
The main goal of multi-metal 3D printing is to get two or more metals to fuse together metallurgically. There are two main ways to do this: powder bed melting (SLM/L-PBF) and directed energy deposition (DED). Using SLM technology as an example, three fundamental technological problems must be solved in order to make multi-metal printing possible:
Controlling material compatibility
Pick a metal combination that has a difference in thermal expansion coefficient of less than 10% and a difference in melting point of less than 200 °C. NASA uses a combination of GRCop-42 copper alloy (melting point 1083 °C) and HR-1 nickel-based high-temperature alloy (melting point 1390 °C) to make rocket engine combustion chambers. They do this by controlling the laser energy density (120-150 J/mm ³) and scanning speed (800-1200 mm/s) to create a 0.3mm transition layer that bonds the two materials together. The tensile strength at the interface is 420 MPa, which is 60% higher than that of typical brazing methods.
Renovation of the powder spreading system
The conventional single-material powder spreading process is inadequate for the requirements of multi-metal alternating deposition. The Fraunhofer IGCV laboratory's electrostatic adsorption powder spreading device can selectively adsorb different metal powders by delivering a -5000V electrostatic field to the construction platform. The system spreads CW106C copper alloy powder (the inner layer) and 1.2709 steel powder (the outer layer) very accurately while making the copper steel jacket thrust chamber. It also recovers 98% of the powder, which is three times more efficient than typical mechanical scraper powder spreading.
Controlling process parameters in real time
When printing with multiple metals, the laser strength, scanning method, and other settings must be changed in real time for each material region. Meltio's 3E metal deposition technology uses smart sensors to keep an eye on the temperature of the molten pool in real time (with an error of ± 5 ℃). It also automatically matches the deposition parameters of titanium alloy (laser power of 400W) and aluminium alloy (laser power of 250W). When making brackets for aviation engines, this technology makes the titanium alloy area 38% harder and the aluminium alloy area 18% longer, which is 25% better than the printing performance of single materials.
二, Common Use: Moving from the lab to the factory Practice
1. Aerospace: Making the combustion chamber lighter and better at managing heat
The combustion chamber of a rocket engine has to be able to handle gas flushing at 3000 °C and liquid oxygen cooling at -180 °C. To link the copper alloy lining and nickel-based alloy shell in traditional manufacturing, they have to be welded together with explosives. This procedure can take up to six months. After using multi-metal 3D printing technology, the German Safran Group's copper-steel bimetallic combustion chamber made using the SLM technique has cut the manufacturing time in half and made it 40% lighter. The main innovation is the use of functionally graded material design. There is a 0.5mm thick NiCrAlY transition layer between copper alloy (GRCop-84) and steel (316L). This layer smoothly changes the thermal expansion coefficient from 16.5 × 10 ⁻⁶/℃ to 12.8 × 10 ⁻⁶/℃, which gets rid of stress concentration at the interface.
2. Energy equipment: The conformal cooling channels revolution in manufacturing
In the making of injection moulds, traditional cooling water channels are mostly straight because of processing limits. This makes the temperature fields in the mould uneven (with variances of up to 30 °C), which lowers the quality of the moulded products. Aerosint's bimetallic SLM technique prints copper alloy (CuCr1Zr) cooling channels inside the mould inserts, which makes cooling three times more effective. This method cuts the cooling time for making automobile bumper moulds from 45 seconds to 18 seconds, cuts energy use for single-piece production by 60%, and makes the mould last more than 2 million times longer.
3. Biomedical: Customising the performance of personalised implants
It takes 6 to 12 months for traditional titanium alloy prosthetic joints to fully integrate with the bone. Researchers at Northwestern Polytechnical University have come up with a new way to 3D print titanium tantalum bimetallic implants. They do this by putting tantalum (Ta) porous structures (65% porosity, 500 μm pore size) on the surface of titanium alloy (Ti6Al4V). This makes the bond between the implants and bone tissue three times stronger. Clinical evidence demonstrates that this technology's hip joint implant has a bone integration rate of 92% three months following surgery. This is 50% shorter than the recovery time for typical titanium alloy implants.