Can metal 3D printed parts achieve mirror effect?

1. Technical principle: How can 3D printing meet the needs of mirrors?
The main benefit of metal 3D printing is that it can immediately make complicated shapes. However, its initial surface roughness (Ra10-50 μ m) is very different from the mirror standard (Ra<0.01 μ m). To get the mirror effect, you need to work together on "printing+post-processing":
Basics of High-Precision Printing
Selective Laser Melting (SLM) technology, for example, combines a thin layer of 20–60 μm powder and a laser spot that is only a few micrometers wide to obtain a dimensional precision of ± 20–50 μm. This makes a sturdy base for polishing later. The full process center for metal additive manufacturing that Hanbang Laser and Zhongnan Zhicheng worked on together has lowered the initial roughness of turbine blades to Ra12 μ m by improving scanning strategies and controlling layer thickness. This makes it possible to process mirrors.
Impact of material characteristics
Due to their low coefficient of thermal expansion and high resistance to corrosion, titanium alloy, stainless steel, and other materials have become the best choices for mirror processing. For instance, the TC4 titanium alloy that is often used in the aerospace industry can get rid of pores using hot isostatic pressing (HIP) following SLM printing. This makes the material density 99.9% and makes polishing much more even.
2. Process Path: A look at the whole process, from printing to mirroring
For a mirror appearance, you need to go through four main steps: rough grinding, fine grinding, polishing, and coating. Each step needs careful control:
Removing layers and flaws through coarse and fine grinding
Mechanical grinding: Use diamond grinding wheels or silicon carbide sandpaper to slowly get rid of printed layer patterns. For instance, Jialichuang 3D printing uses automated grinding equipment to make BJ process parts less rough, going from Ra2.4 μ m to Ra0.8 μ m, while keeping the same level of accuracy.
Chemical etching: Acidic solutions are utilized to selectively dissolve surface protrusions on complex internal cavity geometries, which makes the material removal even. For instance, one aviation company used an etching solution based on phosphoric acid to make engine blades less abrasive, going from Ra15 μ m to Ra3 μ m.
Polishing: The jump from sub-mirror to mirror
Mechanical polishing: The WENDT three-step polishing method uses a coarse polishing wheel to get rid of grinding marks, a medium polishing wheel to smooth the surface, and a fine polishing wheel to get a mirror finish. For instance, Johnson & Johnson's hip implants have a surface roughness of Ra0.05 μm after this treatment, which meets biocompatibility criteria.
Stress-free polishing is possible with electrolytic polishing, which dissolves small bumps on the surface using electricity. For instance, a certain brand of watch employs nitric acid-based electrolyte to make the 316L stainless steel case less rough, going from Ra0.8 μ m to Ra0.02 μ m, and at the same time, it makes the case more resistant to corrosion.
Coating: a dual improvement of function and decoration
Physical Vapor Deposition (PVD): This process puts hard coatings like TiN and CrN on mirror substrates. The thickness can be regulated between 0.5 and 2 μm. This makes the coatings more resistant to wear and gives them beautiful effects like gold and black. For instance, one automotive maker has used PVD technology to make shift paddles last more than 500,000 times.
Chemical nickel plating: Electroless deposition process generates a consistent layer of nickel on complex curved surfaces that is 10 to 20 μm thick. For instance, an aircraft manufacturer has made fuel nozzles three times more resistant to corrosion by using electroless nickel plating, while yet keeping the dimensions accurate to within ± 0.01mm.
3. Use in business: Common uses for mirror 3D printing
Field of aerospace
Turbine blades, combustion chambers, and other parts must be able to handle both high temperatures and good aerodynamics at the same time. For instance, GE Aviation used the SLM+electrolytic polishing method to make the surface of LEAP engine blades less rough, going from Ra10 μ m to Ra0.2 μ m. This made the engine 2% more fuel efficient.
Field of medical devices
Orthopedic implants, surgical tools, and other things need to be biocompatible and fight bacteria. For instance, a certain company made a 3D-printed titanium alloy acetabular cup that has a surface roughness of Ra0.03 μm after electrolytic polishing. This means that germs are less likely to stick to it, and the risk of infection following surgery is much lower.
In the area of consumer electronics
Hinges for folding screens, high-end watch casings, and other things need to be both light and strong. For instance, Hanbang Laser made a titanium alloy hinge for a certain brand of mobile phone. It was 0.3mm thick and had a surface hardness of HV1200, which met the requirements of 200,000 fold tests.