Generations of Americans learned to cook from the classic Betty Crocker Cookbook. It defined and refined the American palate. Marked-up and well-worn copies were handed down from mother to daughter.
Unfortunately, there is no equivalent to the Betty Crocker Cookbook for additive manufacturing (AM) processes. Most companies start their journey in additive manufacturing with one person who is “the 3D printer guy” for prototypes and design review. That one person knows all the tips and tricks needed to create the best possible part. Most of the learning was gained through trial and error. That one person’s experience exists as tacit knowledge which can be very hard to replace if lost.
Moving to an additive manufacturing workflow for production parts requires repeatable processes clearly understood and easily taught to other employees. For every type of additive process, right down to every brand, model, and material, there are specific procedures for taking a digital CAD model and producing a physical item. How to prepare CAD models, how to match requirements to printer capabilities, and which post-production operations are required is unique for each situation.
It often surprises people new to AM to learn that parts removed from a 3D printer may not necessarily be ready to ship. Post-processing is the modification of printed parts after they come off the printer. Knowing what post-processing steps to use can be particularly challenging. Depending on the creation process, one or more post-processing steps are required. Unlike traditional manufacturing, additive manufacturing processes frequently require post-processing — sometimes extensively — to meet desired specifications.
The basic 3D process creates objects layer by layer, which often results in a notched or rippled surface texture. Sometimes this is only observable by microscopic analysis, other times by simply touching or looking at the object. The lower the print resolution, the more pronounced the texture.
The use of support structures during the printing process may create additional flaws. Supports are generally easy to snap off, but even the best support processes will leave behind imperfections. It is often best in these situations to apply an appropriate post-production smoothing process to the whole part, not just where the supports were attached.
Three Stages of Post-Processing
Post-processing can be broadly categorized into three main stages: cleaning, surface finishing, and final treatments. Each stage plays a vital role in transforming a raw 3D printed object into a finished product that meets industry standards.
Post-processing starts with cleaning. Excess material such as support structure is removed. Cleaning also includes eliminating any residual powder (in powder bed fusion processes) or uncured resin (in stereolithography).
There are three primary categories of surface finishing used in post-processing:
Subtractive post-processing is the removal of material from the part surface, generally used to achieve uniformity and smoothness.
Additive post-processing adds additional material to a part, also generally for uniformity and smoothness.
Property Changing post-processing uses chemical or thermal treatment to make parts smoother or stronger.
Final treatments can include heat treatments like annealing to relieve internal stresses; coating or painting to protect against environmental factors; and even advanced techniques like electroplating to add a metallic finish.
[Editor’s Note: The author is Managing Director of Consilia Vektor. He was recently named an Associate at Wohlers Associates powered by ASTM International, the world’s leading Additive Manufacturing (AM) advisor and market intelligence consultancy. He will occasionally comment here on important AM topics and trends.]
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