Is sandblasting suitable for all metal 3D printed parts?

一, The main job and limits of sandblasting technology
1. The main purpose of sandblasting
Sandblasting uses compressed air to push abrasives such quartz sand, diamond sand, glass beads, and others onto the surface of parts very quickly. This has the following effects:
Cleaning the surface: Get rid of dirt like oxide scale, oil spots, and powder that hasn't fused;
Control of roughness: Change the surface roughness (Ra 0.8–6.3 μ m) by changing the size of the abrasive particles (80–240 mesh) and the pressure of the jet (0.2–0.8MPa). Stress release: The impact can help get rid of some of the stress left over from printing and lower the chance of deformation.
Coating pretreatment: making the surface rougher so that the coating sticks better (for example, coating hydroxyapatite on the surface of titanium alloy implants).
2. What Sandblasting Can't Do
Risk of thin-walled structures: Jet pressure can change the shape of or make holes in thin-walled parts (thickness < 0.5 mm). Blind spots in complex cavity treatment: It is hard to get into holes or internal channels with a diameter of less than 2 mm, and leftover powder needs to be chemically cleaned.
Risk of surface damage: Hard abrasives like silicon carbide can scrape the surface of soft metals like aluminum alloys.
Loss of accuracy: Too much sandblasting can damage fine parts like threads and microstructures, which will need to be fixed by CNC machining later.
二, The Effect of Material Properties on the Usefulness of Sandblasting
The hardness, ductility, and inclination to oxidize of different metals directly affect the choice of sandblasting process parameters:
1. Titanium alloy (Ti6Al4V)
Applicability: It is the best material for aviation engine blades and orthopedic implants since it is very strong and doesn't rust. Sandblasting can get rid of surface oxide scale and make coatings stick better.
Optimizing the process:
Choosing an abrasive: Use glass beads or alumina sand instead of silicon carbide to avoid scratching the surface.
Pressure control: To keep thin-walled constructions from bending, the spray pressure should be less than 0.4MPa.
After sandblasting, acid washing (HF+HNO3) is needed to get rid of imbedded abrasives. Then, the surface is polished to get a medical-grade finish with Ra<0.8 μ m.
2. Aluminum alloy (AlSi10Mg)
Usefulness: Because it is light, it is often utilized in car parts. But the surface of aluminum alloy is easy to oxidize, and sandblasting needs to find a balance between being clean and smooth.
Improving the process:
Choosing an abrasive: white corundum or garnet sand with particles that are 120 to 180 mesh in size;
To keep the fatigue strength from going down, pressure regulation should be between 0.3 and 0.5 MPa to keep the coarsening from getting too bad.
To stop re-oxidation, do anodizing or coating treatment right after sandblasting.
3. Stainless steel (316L)
Use: Because it doesn't rust, it's a key material for food and chemical equipment. Sandblasting can make surfaces more even, but you need to be careful not to damage the surface underneath.
Improving the process:
Choosing an abrasive: stainless steel pellets or ceramic beads to keep ferrite from getting into the mix;
Control of pressure: 0.5–0.7 MPa, which keeps the inside wall of the deep hole clean.
Testing standard: Fluorescence penetrant testing (PT) must be done after sandblasting to make sure there are no cracks.
4. High-temperature alloy based on nickel (Inconel 718)
Applicability: Parts that work at high temperatures, like turbine discs in airplane engines, have to be able to handle very harsh conditions. Sandblasting can relieve stress during printing, however it is important to stop intergranular corrosion.
Improving the process:
Choose an abrasive: alumina sand or silicon carbide sand with a particle size of 80 to 120 mesh.
Control the pressure: 0.6 to 0.8 MPa to get the roughening effect;
After sandblasting, a solution treatment (1080 °C insulation for 1 hour) is needed to fix any damage that happened underneath the surface.
三, The problem that the structure of the parts poses for the sandblasting procedure
1. Structures that are thin-walled and light
Case: After sandblasting, a specific aviation bracket (with a wall thickness of 0.3mm) changed shape by 15%, which caused the assembly to fail.
Solution: Use low-pressure sandblasting (0.2–0.3 MPa) and spinning fixtures to spread the impact force uniformly.
To avoid mechanical damage, you can use chemical polishing (with nitric acid and hydrofluoric acid) or electrolytic polishing instead.
2. A complicated lumen and microporous structure
Case: After sandblasting, the residual powder blockage rate of a certain fuel nozzle (with an inner channel diameter of 1.5mm) is as high as 30%.
Solution: To get rid of big particle powders, vibration screening is performed;
To make sure that the inside of the cavity is clean to ISO 16232-10 Class 5, we use a combination of sandblasting and ultrasonic cleaning (40kHz frequency, 10 minutes).
3. Surface with precise function
For example, following sandblasting, the smoothness of an optical mold with a surface roughness of Ra<0.2 μ m was lowered to Ra 1.6 μ m, which does not match the standards for injection molding.
Solution: Use magneto rheological polishing (MRF) or fluid polishing to get sub-micron precision;
Segmented processing: Sandblasting is only used to roughen up sections that don't work, while manual polishing is only used to smooth out areas that do.
四, The future of sandblasting technology
1. Smart control
Development: A system that combines machine vision and force feedback, as well as the ability to change the spray pressure and angle in real time to avoid overspray or underspray.
The IEPCO sandblasting machine in Germany has reached closed-loop control, which can keep the deformation rate of thin-walled parts below 0.1%.
2. Green upgrade: Using recyclable abrasives (such ceramic beads) and dry ice sandblasting to cut down on dust pollution and the cost of getting rid of debris.
Data: Compared to typical methods, dry ice sandblasting uses 40% less energy and leaves no chemical residues, which is in line with REACH rules.
3. Integration of composite processes
Development: Using sandblasting, laser cleaning, plasma spraying, and other technologies together to provide a single treatment for "cleaning roughening coating."
Case: The "sandblasting+laser cladding" procedure is used on a certain aviation engine blade. This cuts the processing time from 72 hours to 24 hours.