How do smoothing fluids work?

Today over 80% of 3D printed parts are made using thermoplastic or thermoset polymers. Metals, ceramics and other composite materials comprise the other 20%.  Plastic 3DP parts are manufactured using any variety of 3D printing methods including FFF, DLP, SLA or material jetting processes. Common to all these methods is that the parts are created from a computer aided design (CAD) file and all are fabricated using a polymer construction material. The construction material is either powder-deposited or extruded through a nozzle in progressive layers, level-by-level, until the parts reach their final shape. The quality and the precision of the items made using 3DP processes result in parts requiring minimal post-processing and with excellent dimensional repeatability. However, building the parts is just the beginning of the 3DP process. Choosing the smoothing fluid also plays a key role in the successful construction of the 3DP components.

Fluid Finishing for Plastic Parts

The layered 3DP process leaves some plastic printed parts with a tiered or stepped surface, requiring smoothing to get a finished part. Traditional methods of smoothing the tiers, such as sandblasting, buffing or grinding, are manual, time-consuming, and often leave particles behind.  A more efficient method for smoothing parts to their finished state is to use a specialty smoothing  fluid inside a vapor degreaser to chemically even them out.  Immersing the unfinished parts in a fast-evaporating fluid vapor inside the degreaser slightly melts the surface of the plastic parts, levelling out any irregularities and removing the tiers. It leaves a smooth finish without any leftover particles or damage to the finished parts. The quality of the finished parts is comparable in quality to parts using more traditional injection molding processes.

For smoothing to be effective, it is necessary to understand the chemical composition of the polymer parts.  For instance, ABS, acrylic, polycarbonate and highly basic materials with a pH of 10 or above need to be approached carefully due to potential softening and swelling of the materials.  Finding the best smoothing fluid can often be a delicate balance between selecting one with a high enough solvency to effectively level out the parts, but not so strong that it damages them or compromises their structural integrity.  Trained vapor degreasing experts have experience selecting smoothing fluids for specific types of 3DP polymers and can guide part designers through this process.

In addition to smoothing the parts, the fluid must also be effective at removing soils or particulate left behind from any other manufacturing processes. The fluid, when used in a modern vapor degreaser can be used to dissolve and clean a variety of oils, greases and waxes. Any stray particulate like dust or shavings are typically non-soluble and will not dissolve in the cleaning fluid. Therefore, the particulate must be removed using displacement cleaning where the cleaning fluid gets under the particulate, dissipates any static charge and lifts it off the surface.  The key to effective displacement cleaning is to use a dense, heavy fluid that floats the particles of dust and dirt off the substrate surfaces. Today’s modern fluids are typically 20% heavier than water and 50% heavier than alcohol, making them an ideal choice for displacement cleaning of 3DP polymer parts.

An added advantage of using a fluid for smoothing and cleaning 3D printed parts is that they dry very quickly and completely, leave no residue on parts and are cool after they exit the vapor degreaser. This allows parts to be packaged or post-processed immediately, speeding production and overall throughput.

In addition, modern-day 3DP post-processing fluids are nonflammable and safe for use in cold operations, heated machines or in ambient temperatures.  They have also been formulated without the use of n-propyl bromide, methyl pyrrolidone, polyethylene glycol, heptane, or trichloroethane, all which can create groundwater and air quality issues.

Venesia Hurtubise is a Technical Project Chemist at MicroCare Corporation, which offers precision cleaning solutions.  She has been in the industry more than 5 years and holds a MS in Green Chemistry from Imperial College, London.  Hurtubise researches, develops and tests cleaning-related products that are used on a daily basis in precision cleaning and medical applications.