How to avoid damaging the surface of the parts during the support process?

一, To back up the process's possible damage mechanism
1. Damage from mechanical tension
Dents and scratches: When typical grinding wheels or wire brushes take off supports, hard particles can leave scratches on the surface of parts, especially on delicate materials like titanium alloys and cobalt chromium alloys.

Deformation and cracking: When milling or turning, stress can build up at the point where the support meets the part. This can produce local deformation and even microcracks, like in areas with thin walls or cantilever beams.
2. Problems in the heat-affected zone (HAZ)
Cutting with a laser: When cutting support, high-energy laser beams can cause parts to get too hot in certain areas. This can lead to surface oxidation, changes in hardness, or grain coarsening (as with Inconel 718 high-temperature alloy).
Electric discharge machining (EDM): The discharge creates a very high temperature (up to 8000–12000 °C) that can remelt the surface layer and raise the residual tension.
3. The possibility of chemical pollution
Corrosive substance: When chemical etching is used to remove support, not controlling the concentration of the solution properly might cause the surface of the part to corrode evenly or develop pits (as when aluminum alloy reacts with acidic solution).
Cross contamination: When supporting materials (like stainless steel) are mixed with component materials (like titanium alloy) for recycling, impurities can get into the mix and change the characteristics of the materials.
二, Process optimization: full control of the process from design to processing
1. Improving the design of the supporting structure
Make the contact area smaller: To lessen the mechanical force when taking off support, use point support or line support instead of surface support. For instance, the support design of medical implants, like acetabular cups, can make the contact diameter smaller than 0.5mm.
Design that is easy to break: Make weak spots in the connection between the support and the parts, like V-shaped grooves or pre-drilled holes, to make it easier to break them by hand or cut them with low pressure later.
Soluble support material: For complicated interior structures, water-soluble or hot-melt support materials like polyvinyl alcohol (PVA) are utilized. These materials are removed by dissolving or heating them to avoid mechanical contact.
2. Precise control of processing parameters
Cutting with low stress:
Cutting wire (WEDM): Using parameters with a pulse width of less than 10 μs and a peak current of less than 5A to keep the heat input low and stop the surface from melting again.
Water jet cutting: To cut cold and avoid thermal impacts, the pressure is kept between 200 and 400 MPa. This is done with pure water or a water jet with abrasives like garnet added.
Layered milling: For thick support systems, a layered milling technique with a short cutting depth (<0.2mm) and a high feed rate (>500mm/min) is used to spread out the cutting force and lower the risk of deformation.
3. Application of many processes together
Laser mechanical composite support: First, use a low-power laser (less than 100W) to melt the connection between the part and the support. Then, use hand tools to break it to lower the mechanical stress. GE Additive's Concept Laser M2 machine, for instance, uses this technology to work with titanium alloy parts.
Chemical mechanical synergistic treatment: For pieces made of aluminum alloy, first use an alkaline solution (like NaOH) to dissolve some of the support. Then, to avoid scratches, polish the rest of the structure with a soft polishing cloth (like nylon).
三, Choosing Tools and Materials: Barrier for Protection of the Surface
1. Tools that don't touch
Support for ultrasonic: Using high-frequency vibration (20–40 kHz) to break down the support structure, which is good for precision parts like microchannel systems. For instance, Sonic Mill's ultrasonic support system can hold supports that are less than 1mm in diameter.
Plasma etching is the process of selectively removing supporting materials using low-temperature plasma, like Ar/O2 mixed gas, to keep them from touching each other. This approach has been applied for cobalt chromium alloy supports that don't have any support, with a surface roughness of Ra<0.8 μm.
2. Tools that are soft or bendable
Silicone polishing head: A Shore A 30–50 hardness silicone polishing head that spins slowly (less than 500 rpm) can be used to clean curved parts and make scratches less visible.
Magnetic polishing solution: putting ferromagnetic particles (like silicon carbide) in oil- or water-based carriers and using a magnetic field to move the particles around to polish blind spots. Magnalux's magnetic polishing solution, for instance, has been utilized to treat aircraft engine blades without any support.
3. Technology for processing at low temperatures
Liquid nitrogen cooling milling: During the milling operation, spray liquid nitrogen (-196 °C) on the supporting material to make it brittle, lower the cutting force, and keep the pieces from being too hot. This method has been employed on unsupported nickel-based high-temperature alloy parts that have surface hardness changes of less than 5%.
Cleaning with dry ice blasting: To spray dry ice particles (-78 °C), high-pressure airflow (0.5–0.7MPa) is employed. This makes the supporting structure brittle and fall off, which is good for intricate internal pathways.
四, Protection after processing: two guarantees of repair and strengthening
1. Technology for fixing surfaces
Laser cladding: The same material is used to fix micro scratches or pits that happen after removing support. You can select the thickness of the cladding layer from 10 to 50 μm, and the binding strength with the substrate is over 400MPa.
Electrochemical polishing: using electrolytes (such a mixture of phosphoric acid and sulfuric acid) to selectively dissolve bits that stick out on the surface of objects to get a smooth finish. For instance, electrochemical polishing may lower the surface roughness Ra of titanium alloy parts from 3.2 μm to 0.2 μm.
2. Protection from coatings
Physical Vapor Deposition (PVD): Putting hard coatings like TiN and CrN on the surface of items, with a thickness of 1–3 μm, can make them much more resistant to wear and corrosion. After TiN coating treatment, for instance, the surface hardness of medical implants becomes up by three times and the friction coefficient goes down by 50%.
Chemical conversion coating: Chemical treatment, like chromate passivation, makes a thick oxide deposit on the surface of the part. This stops secondary contamination during the unsupported process. After chromate treatment, for instance, aluminum alloy parts can resist salt spray corrosion for more than 1000 hours.