One of the unresolved challenges of additive manufacturing is the surface treatment and finishing. In theory, additive manufacturing allows complete freedom to create complex shapes, but in practice, surface finishing usually requires design constraints. Although improving the quality of metal powder, optimizing the manufacturing direction and process parameters can improve the surface quality of additive manufacturing parts to a certain extent, the problem of surface roughness of the parts additive manufacturing cannot be completely solved. Therefore, it is necessary to perform the post-processing of additive manufacturing parts. At present, the main post-processing methods include finishing and mechanical processing. Below, we take a closer look at Adaptive Grinding (SAG), Laser Polishing, Chemical Polishing, and Abrasive Flow Machining (AFM).
Surface treatment: effect after post-treatment
Finishing methods mainly include hand polishing, sandblasting or CNC grinding. The quality of manual polishing largely depends on the experience of the operator, which has poor repeatability and consistency, high labor and time costs, and the dust produced during the polishing process is harmful to human health. Additionally, CNC sandblasting and grinding have poor processing accessibility for parts with complex internal surfaces and porous structures, so they are generally used to clean and polish the external surfaces of parts and remove the oxide layer.
For complex structural parts with high surface quality requirements (0.8μm
Adaptive shape grinding
Adaptive Shape Grinding (SAG) is a new process for freeform machining of difficult materials such as ceramics and hard metals. Despite the low rigidity of the equipment of the machining equipment, due to the semi-elasticity of the tools, ductile mode grinding can be carried out with a high surface finish. A foreign researcher used the adaptive shape grinding method with a spherical flexible grinding head to polish the freeform surface of titanium AM parts. The defect layer on the additive manufacturing surface was removed by coarse polishing and fine polishing, and the final surface roughness Ra reached less than 10nm.
Laser polishing is a new polishing method that uses a high energy laser beam to remelt the surface material of parts to reduce surface roughness. At present, the surface roughness of laser polished parts Ra is about 2-3 m. Due to the high cost of laser polishing equipment, it has not been widely used in practical 3D printing post-processing processes.
The direct result of chemical polishing is the smoothing of micro-roughness and the formation of polish as well as the parallel dissolution of a top layer. It has a remarkable effect in removing the spheroidal layer which is loose and easily falls on the surface of hollow structures or parts with hollow structures in small additive manufacturing. Through chemical polishing and electrochemical polishing, the surface roughness of the above porous implant has been reduced from 6 ~ 12μm to 0.2 ~ 1μm.
Abrasive flow machining
Abrasive Flow Machining (AFM) is an interior surface finishing process characterized by the flow of an abrasive-laden fluid through a workpiece. This fluid is generally very viscous, having the consistency of a putty or paste. AFM smooths and finishes rough surfaces and is specifically used for removing burrs, polishing surfaces, forming radii and even removing material. The nature of AFM makes it ideal for interior surfaces, crevices, holes, cavities and other areas that may be difficult to reach with other polishing or grinding processes.
Powder bed fusion technology provides the best surface quality of any metal additive manufacturing process. In addition to the above finishing methods, sometimes critical parts need to be machined. These two kinds of post-processing means are widely used in the application of 3D printing molds. Welcome to contact us to explore more post processing methods for metal 3D printing.