PROCESSING AND FINAL APPEARANCE

FDM printing is the most efficient for prototype production. An important step in this printing process is the processing of the printed 3D model. Some finishing processes can add strength to the printed object. Some finishing processes of the model include removal of material that served as support during the printing of the main object, cold welding, filling gaps created after printing, grinding, dyeing, epoxy coating.

Removal of the filament that supports the main object during printing

Removing the material is the first step in processing the model in any 3D technology that requires support to produce the correct parts. Support can be divided into two categories: standard and soluble. Unlike other post-press processing methods, the removal of support material is an essential requirement and does not produce an improved surface finish. The material that serves as a support during printing can be removed with a little effort, and cleaned with the help of a needle with the help of which places that cannot be easily cleaned are reached.
The advantages of this type of machining are that it does not change the geometry of the object and is a speedy machining process.
The disadvantage is that if the support structure leaves behind excess material or marking, the accuracy and appearance of the print is reduced.

Removing excess material by dissolving

Conventional soluble materials used as a support during printing are removed by lowering them into a vessel with a suitable solvent until the material dissolves. Support is usually printed in combination:

  • HIPS (in combination with ABS),
  • PVA (in combination with PLA)

The advantages of this type of removal are the application in more complex geometric shapes where the removal of standard additional material would be difficult and the results in the form of a smooth surface where the structure of other material is in contact with the main printing object.
The disadvantages are the appearance of holes in the object if the soluble material leaked into the object during printing.

Sandblasting

After the printing support material has been removed, sandblasting can be done to make the surface of the object smooth and to remove any remaining defects in the form of redundant lines, etc. The starting point of the sandpaper depends on the height of the layer and the quality of the print. For layers, 200 microns and less, or flawlessly printed objects, sandblasting can be started with 150 grit. If there are obvious flaws, or the object is printed with a height of 300 microns or more, sandblasting will start with 100 grit. After the process, the object should be cleaned with a brush and soapy water.

The advantage of this processing method is the incredibly smooth finish and makes the subsequent painting or polishing process more comfortable. It is impractical to apply to more complex surfaces and objects with small details. Print accuracy can be affected if blasting is performed too aggressively, and too much material is removed from the object.

Cold welding

When the size of the object exceeds the maximum size of the printer, the design of the object is often divided into several parts and assembled after printing. For PLA and other materials, bonding can be done with glue. For ABS, bonding can be done with acetone. The surfaces to be joined must be cleaned, then coated with acetone, and firmly adhered to adhere to each other. In this way, the chemical connection between two parts of the building is performed.
The advantage of this treatment of the object is that acetone will not damage the surface paint as much as other adhesives do.
The disadvantage of this process is that joining parts of the object with acetone will not make the object stronger than it would be by printing from one part.

Filling in the blanks

After blasting or removing excess material by dissolving, it is no wonder that voids in the printed object appear. During printing, gaps are formed when the layers are incomplete due to the failure to release enough filaments. Small gaps can be filled with epoxy lacquer, and they do not require any additional process. Larger voids, or holes due to the joining of the two parts, can be repaired by fillers that require additional sanding after drying. These filler materials are very strong and do not reduce the strength of the plastic. When an error is made due to the merging of an object, that part is usually stronger than the natural plastic used for printing.

Gaps while printing with ABS can be filled by creating a mixture of ABS and plastic, which chemically react with the ABS print and are inserted into any part of the defect when printing.


Polishing

After sandblasting the object, plastic polishing can be applied to give the object a visual effect of glass. One of the ways of polishing is the application of a polishing composition (Blue Rouge) or microfiber material. Blue Rouge is used for polishing jewelry, specifically jewelry made of plastic and synthetics, and produces a long-lasting shine effect. The use of other polishing components (vehicle polishes) must take into account the potential damage to the building.

The advantage of applying this processing method is to achieve a glass effect without using solvents that can damage the surface of the object. The disadvantage is that the object must be sandblasted before polishing if the glass effect is to be achieved, and it can affect the printing tolerance. Another problem is that the paint may not adhere to the object after polishing.