Solvent debinding: A proven method for improved parts fabricating
Venesia Hurtubise, technical chemist at MicroCare, writes about why specialised debinding fluids are so important to today’s 3D printed medical components and how they can help to enable the innovation in state-of-the-art medical device design and manufacturing.
Using Additive Manufacturing (AM) methods to produce parts is gaining momentum in the medical device manufacturing industry. As the process becomes faster, more stable and more affordable it is a viable alternative to other more traditional, subtractive machining methods like milling, cutting or turning.
The most common use for AM within the medical device manufacturing industry is to build simple manufacturing support items like jigs, fixtures and other machine tooling. But it is also used for small volume runs of very complex parts and intricate surgical instruments. Or to fabricate highly customised models used as surgical guides. 3D printing is also used to make biomedical devices such as dental implants, hearing aids, contact lenses, personalised orthotics and prosthetic limbs for individual patients.
AM also appeals to device makers when security is a concern. Since 3D printing is typically done in-house, device designs are never publicly shared with outside service providers like mould or die makers. This helps protect patents, trademarks and intellectual property.
How AM Works
There are many types of metal 3D printing methods used today. However, many designers choose binder jetting (BDJ) for their parts. It is typically less expensive, faster and easier-to-use than other AM methods. Binder jetting builds a part out of a feedstock made up of fine metal powders and binders. It deposits alternating layers of metal powder and binders in thin horizontally progressive layers, until it reaches its final shape.
The powdered metals can include medical-grade stainless steel, titanium and other alloys to produce high-performance precision parts that meet both FDA regulations and customers’ exacting standards.
Binders are typically made of wax, stearic acid or polymers, such as polyethylene or polypropylene. The bindershold the powdered metals together to build “green” parts using the AM layering process.
The binders help form the metal powder into a specific shape. However, the binders are only temporary. The green parts must be debound before they can be sintered. During debinding, some of the binders are selectively removed to form interconnected open pores within the parts with only enough binder staying behind to help the parts retain their structural integrity. Successful part debinding is a fine balance of selectively removing the right amount of binder as quickly as possible without damaging the fragile part.
The part is then thermally sintered at near melting temperature. This burns off any remaining binders and bonds the metal powder to its solid mass state, typically 96-99.8% density. After that, the part is post-processed using standard finishing techniques like sanding, painting or coating.
Debinding for success
Parts debinding is typically done using one of four different methods. Thermal, catalytic, aqueous or solvent debinding. All have their pros and cons, but solvent debinding inside a vapour degreaser is growing in popularity because it provides both operational efficiencies and environmental advantages.
Thermal debinding: Thermal debinding happens at very high temperatures inside an oven. It is typically slower and more time-consuming than other methods. In some instances, a thermal debinding cycle can take up to 24 hours since it takes time to heat the oven, debind the parts and then allow enough cool-down time before processing the parts inside. The longer debinding cycle typically requires longer production schedules and takt time.
Catalytic debinding: Catalytic debinding happens in a gaseous environment using oxalic or nitric acid. The acids debind the parts by decomposing the binders. Catalytic debinding is faster than thermal debinding, but still takes about 3-4 hours to complete the process.
Aqueous Debinding: In some instances, parts fabricators choose to use water-soluble binders because they feel working with aqueous debinding is better for the environment. However, what they don’t consider is the power consumption and extra time used to rinse and dry the part. Also, after debinding, the wastewater must be filtered and prepped for proper disposal.
Solvent debinding
In some shops, part debinding typically happens inside a vapour degreaser using a specialty debinding fluid. Depending on the part’s material and the binders used, the binders are removed from the part by either immersing it in the boiling debinding fluid, by holding it inside the vapour blanket inside the vapour degreaser, or a combination of both. The low-boiling debinding fluid melts the wax binder and creates porosity within the green part to allow the fluid to evaporate quickly before sintering.
Some fabricators still use heptane or acetone for solvent debinding, but those options are flammable and are not recommended. A better option is to use a new, modern debinding fluid inside a vapour degreaser.
Modern debinding fluids – better for the environment
Modern debinding fluids used inside the vapour degreaser are recycled and reused for hundreds of hours before it needs refreshing or replacement. The vapor degreaser concentrates the binders and other contaminants, minimising the amount, frequency and cost of your hazardous waste disposal.
Reduced energy consumption
Solvent debinding happens at a very low-boiling temperature that still melts the wax binders but does not damage the non-soluble fragile parts. Plus, it reduces energy consumption and cost, and requires less heat input to operate to help reduce your environmental footprint.
Contaminant and bioburden-free debinding
Solvent-based debinding fluids are hostile to bioburden and don’t harbour pyrogens. They do not use water, which helps maintain an environment free of bacteria, viruses, or other pathogens and provide a convenient way to validate a cleanroom compatible, bioburden-free debinding process.
A more controlled work environment
Vapour degreasers typically have a smaller footprint while sustaining high output, allowing for lower overall operating costs in the expensive production or cleanroom floor space. Vapour degreasers don’t generate dust, fumes, heat, or moisture, so they do not require special blowers and fans or any special climate controls to maintain air quality or ambient temperature and humidity.
Consistent, fast debinding with little monitoring
The vapour degreaser debinding process, once established and tested, remains constant with little variation. The debinding fluid remains consistent and stable and does not require daily monitoring or testing. This means debinding outcomes remain consistent, complying with product and process validation specifications.
Solvent debinding is a well-engineered process that is simple, predictable and repeatable, making it easy to qualify and validate for medical device manufacturing.
In addition, vapour degreasing allows the green part to come out clean, dry, and cool enough to immediately transfer to the sintering oven. This translates into shorter debinding cycles and faster production runs overall.
Work with a debinding expert
Debinding fluid is an important tool for successful AM manufacturing. Fabricators looking for help choosing the right debinding fluid or method should consult with a company that specialises in medical device parts debinding. They can recommend which debinding methods and fluids will work best.