ADDITIVE MANUFACTURINGSECTION TITLE
In many cases, debinding is done using a speciality fluid inside a modern vapour degreaser
Some plastic parts have a stepped or terraced surface that requires smoothing
due to the potential softening and swelling of the polymer 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. In addition to smoothing, the
vapour degreaser fluid also removes any soils or particulate left behind during manufacturing. Te fluid dissolves and rinses a variety of oils, greases and waxes. For stray particulate such as dust or shavings that are non-soluble they are removed through displacement. Te cleaning fluid gets under the particulate, dissipates any static charge and lifts it off the surface. Te key to effective displacement cleaning is to use a dense, heavy fluid that undercuts and lifts the particles of dust and dirt off the substrate. Today’s modern fluids are typically 20% heavier than water and 50% heavier than alcohol, making them the ideal choice for displacement cleaning of AM polymer parts.
DEBINDING METAL PARTS Although plastic is still widely used for AM, using metals, ceramics and other composite materials is rapidly gaining momentum. Metal 3D printing employs the same layered-build process as plastic AM, but uses fine metal powders and a binding agent, typically paraffin wax, carnauba wax, or speciality polyethylene waxes, to create green-state parts. After layering, the green parts are sintered in an oven to make fully dense metal parts.
Te binding agents help form the green
parts but must be partially removed before the parts are exposed to the high heat of sintering. Too much binder left behind in the parts could result in cracking, deformation of the backbone, or part expansion during the sintering stage. Too little binder could cause the parts to lose their dimensional stability and collapse upon themselves. In many cases, the binders are extracted using a speciality fluid inside a modern vapour degreaser. Te fluid is engineered for selectivity, so the right amount of binder is removed without damage to the part structure. Some, but not all, of the binder is removed to avoid contamination of the metal during sintering, but not so much that it affects the parts dimensional accuracy during sintering. Due to their low viscosity and surface tension ratings modern metal debinding fluids penetrate complex part structures including inside blind holes and end holes to ensure thorough debinding. Once the select amount of binder is removed, the parts are thermally sintered
under high heat to bond the metal powder into its finished solid mass state. After sintering, the parts are post-processed using standard metal finishing techniques such as grinding, cutting or coating.
FINISHING FLUIDS FOR A CLEANER ENVIRONMENT Today’s finishing fluids meet strict global environmental regulations and can help manufacturers replace chlorinated solvents such as trichlorethylene (TCE) that if not used properly can contribute to groundwater and air quality problems. Most modern finishing fluids have a low global warming potential (GWP) under 10 and a zero ozone depleting potential (ODP). In addition, modern finishing fluids, when used in a vapour degreaser can also be distilled and reused in the smoothing or debinding processes, saving time and disposal costs.
Companies looking for help in determining the correct finishing fluid or method to use should consult with a critical cleaning partner that specialises in vapor degreaser smoothing and debinding. Some fluid manufacturers have field engineers that conduct on-site audits to evaluate methods. Tey can also perform comprehensive in-lab tests with sample parts to ensure smoothing or debinding success.
Elizabeth Norwood is a senior chemist at MicroCare.
www.microcare.com
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