Additive manufacturing has the freedom to create complex shapes, but in practice, surface finish often requires design constraints. Although improving the quality of the metal powder, optimizing the build direction and process parameters can improve the surface quality of additively manufactured parts to a certain extent, the problem of part surface roughness cannot be completely solved. Therefore, post-processing of 3D printed parts is necessary. The current main post-processing methods include finishing and machining. Let's take a closer look at these methods.
Finishing process
Finishing methods mainly include manual polishing, sandblasting, or CNC grinding. The quality of manual polishing depends largely on the operator's experience, with poor repeatability and consistency, high labor and time costs, and the dust generated during polishing is harmful to human health. In addition, sandblasting and CNC grinding have poor machining accessibility for parts with complex inner surfaces and porous structures, so they are generally used for cleaning and polishing the outer surface of parts and removing oxide layers.
For complex structural parts with high surface quality requirements: Ra is 0.8μm~1.6μm, the finishing process faces great challenges. In addition to the above methods, there are shape-adaptive grinding, laser polishing, chemical polishing, and abrasive flow machining.
Shape Adaptive Grinding
Shape Adaptive Grinding (SAG) is a new process for free-form machining of difficult-to-machine materials such as ceramics and hard metals. The semi-elasticity of the tool enables ductile mode grinding with a high surface finish despite the lower equipment stiffness of the machining equipment. It is reported that some researchers use the shape adaptive grinding method of spherical flexible grinding head to polish the free surface of titanium alloy 3D printed parts. The defect layer on the additive manufacturing surface is removed by rough polishing and fine polishing, and the final surface roughness Ra is less than 10 nm.
Laser polishing
Laser polishing uses a high-energy laser beam to re-melt the surface material of the part to reduce surface roughness. At present, the surface roughness Ra of laser polished parts is about 2~3μm. Due to the high cost of laser polishing equipment, it has not been widely used in the actual 3D printing post-processing process.
Chemical polishing
A direct result of chemical polishing is micro-roughness smoothing and polishing formation, as well as parallel dissolution of the upper layer. In small-scale additive manufacturing, the removal of hollow structures or loose spherical layers on the surface of parts with hollow structures has a significant effect. By chemical polishing and electrochemical polishing, the surface roughness of porous implants was reduced from 6~12 μm to 0.2~1 μm.
Abrasive Flow Machining
Abrasive Flow Machining (AFM) is an internal surface finishing process characterized by flowing an abrasive-laden fluid through a workpiece. This fluid is usually very viscous and has the consistency of putty or dough. AFM can smooth and polish rough surfaces and is designed for deburring, polishing surfaces, forming radii, and even removing material. The properties of AFM make it ideal for interior surfaces, grooves, holes, cavities, and other areas that are difficult to reach by other polishing or grinding processes.
Powder bed fusion technology enables the best surface quality of any metal additive manufacturing process. In addition to the above finishing methods, it is sometimes necessary to machine critical parts. These two post-processing methods have been widely used in 3D printing mold applications. Let us look forward to more simple and effective surface machining processes in the future!
JR can not only provide metal 3D printing, we also have a professional CNC processing factory, which can provide post-processing of metal printing.
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