What are the surface roughness requirements for metal 3D printing in different industries?

一, The technical significance and industry influence of surface roughness.
Surface roughness (Ra) is a key measure of the surface's micro-geometric shape. The number that comes up for it directly influences how well the component resists wear, corrosion, fatigue, and sealing. When you 3D print with metal, the Ra value is affected by things like the size of the powder particles, the thickness of the layers, the power of the laser, and the scanning technique. For instance, fine powder (15–45 μ m) can have a Ra value as low as 3–5 μ m because it flows well and fills the melt pool evenly. On the other hand, coarse powders (53–105 μ m) usually have Ra values between 8 and 12 μ m because their particles are too big.
Most of the time, the Ra values of printed parts that haven't been optimised are between 7 and 20 μm. This level can suit most industrial needs, although there are big functional risks in the high-end industry.
Aerospace: Rough surfaces can readily cause stress to build up, which can make engine blades break too soon when they are under high temperature and pressure.
Medical implants: Ra levels higher than 3.2 μm raise the danger of microorganisms sticking to them and can cause infections after surgery;
Consumer electronics: Surface roughness can make it harder for optical parts to pass light through and lower the clarity of images.
二, The needs for and examples of industry differentiation
1. Aerospace: The ultimate goal of Ra ≤ 1.6 μ m
The aerospace sector has very strict standards for how reliable parts need to be. For example, turbine blades have to be able to handle a centrifugal force of 100,000 revolutions per minute at a high temperature of 1300 degrees Celsius. Even slight surface flaws might have terrible effects. In the business world, it has been established that:
Technical standard: To lower the risk of the high-temperature oxidation layer peeling, the Ra value of essential parts should be kept between 0.8 and 1.6 μm.
In a typical scenario, laser selective melting (SLM) technology was used to print single crystal blades for a certain type of aircraft engine. After that, vacuum electro polishing was used to make the surface smoother, lowering the roughness from Ra12 m to Ra0.8 m and increasing the fatigue life by 40%.
Process innovation: The Huashu High Tech FS200M machine has a 40 μ m fine light spot that can print Ra3.0 μ m parts directly. This meets the needs of the aerospace industry for mass production of small precision parts.
2. Medical implants: biocompatibility red line with Ra 3.2 m
The medical business needs rough surfaces because they are safer for people and work better with other things:
Orthopaedic implants: Titanium alloy joint prostheses must mimic the trabecular structure of bone, with surface roughness regulated at Ra1.5-2.5 μm to facilitate the adherence and proliferation of bone cells;
Dental implants: The Ra value of the threaded region must be ≤ 3.2 μm; otherwise, bacterial development could cause peri implantitis.
Yunyao Shenwei's whole process chain optimisation (ultra-fine powder spreading + high-precision optical path control) gives the surface a quality of Ra0.8–2.8 μ m. This means that implants can go straight to the operating room without any extra processing.
3. Electronics for consumers: Ra ≤ 0.8 μ m is the optical grade criterion.
The push towards smaller products and more functions in consumer electronics is what drives the search for smooth surfaces.
Optical parts: The mount for the mobile phone camera must have a Ra of 0.8 μ m or less to avoid blurry images produced by light scattering.
Structural parts: To keep laptop hinges from wearing down too quickly, they need to be treated with a surface that has a Ra of less than 1.6 μ m.
Industry practice: Zhongrui Technology iSLM80P equipment uses a 25 m spot and dynamic powder spreading technology to print micro antennas with Ra 3.2 m directly. This cuts down on post-processing time by 80% compared to standard methods.
4. Energy and mould: a good compromise between cost and Ra ≤ 6.3 μ m
In the making of energy equipment and moulds, surface roughness needs to be a good mix of cost and performance:
Gas turbine combustion chamber: It needs to be able to handle high temperatures of 1200 °C and gas erosion. The surface roughness needs to be kept between Ra3.2 and 6.3 μm to find a compromise between corrosion resistance and processing efficiency.
Injection mould: The Ra value of the conformal cooling channel's surface should be ≤ 6.3 μ m. If it isn't, the product may distort because it doesn't cool evenly.
For example, SLM technology was used to print a certain type of car mould. Chemical polishing brought the Ra value down from 15 μ m to 6.3 μ m, which made the mould last 30% longer.