Binder jetting is a fast, affordable method of metal 3D printing. The right debinding fluids can harmlessly remove wax binders from metal 3D-printed parts before they’re sintered.
Venesia Hurturbise, MicroCare Medical
Complex surgical instruments can be made of 3D-printed metals. (Image from MicroCare)
3D printing, a subset of additive manufacturing, has been in use since the 1970s. Originally limited to hobbyists to create plastic toys and figurines, the process intrigued medical device manufacturers who recognized 3D printing’s potential.
By the 1980s, medtech manufacturers were using 3D printing to create patient-specific devices. Today, hearing aids, orthodontics, contact lenses, artificial joints and prosthetic devices are 3D-printed and custom-made for each individual patient and their unique anatomy.
How is binder jetting used in 3D-printed medtech?
Historically, plastics were used to make the majority of 3D-printed medical devices and today, more than 80% of 3D-printed parts are still made using thermoplastic or thermoset polymers. Metals, ceramics and other composite materials comprise the other 20%.
However, metal 3D printing is rapidly moving to the forefront of medical device design. Metal 3D-printed parts are built much like plastic 3D parts, except that a metal powder feedstock is used instead of polymer or plastic for added strength and durability. A variety of metal powders, including stainless steel, low-alloy steels, carbon steels, nickel alloys, tool steels and tungsten alloys are all used to build small, precise and detailed geometries for all types of medical devices as well as complex surgical instruments.
Metal binder jetting – A quick overview
A number of methods may be used to make metal 3D-printed parts. Some, like selective laser melting (SLM) and electron beam melting (EBM), are advanced processes that require a significant investment in specialized equipment, complex safety procedures and very skilled operators. Binder jetting (BDJ) by comparison is faster and more affordable. It does not use lasers or electron beams to build parts, making it safer and easier to use with minimal training.
Binder jetting builds three-dimensional parts from a computer-aided design (CAD) file. Nozzles on the 3D printer head place an ultrafine layer of the metal powder on a build platform following a path determined by the CAD file. Then a liquid wax bonding agent, typically paraffin wax, carnauba wax or specialty polyethylene wax, is applied to bind the particles together. The print head continues to deposit alternating layers of the powdered material and the binding material, layer by layer, to form a “green” part.
Once the “green” parts are built, most of the wax binding agent is removed. Then the parts are placed in an oven and sintered at a very high heat to render their final, solid-mass state. The resulting high-quality dense metal parts have excellent dimensional repeatability and can be post-processed using standard metal finishing techniques such as grinding, cutting or coating.
Choosing the right debinding fluids and methods
Using metal binder jetting may seem straightforward, but it is important to get the details right for the best possible end product. This includes choosing the best fluids and methods for removing the wax binders from the parts.
The binding agents serve the important purpose of holding the “green” parts together, but they must be partially removed before the parts can be exposed to the high heat required for sintering. It is a balance of selectively removing enough of the binder from the “green” parts to allow fast sintering at a very high heat, but not so much that the fragile parts will lose their dimensional accuracy or fall apart during the process.
One successful method of removing binder is using a debinding fluid and a vapor degreaser. Debinding fluid vapors flow around the parts inside the vapor degreaser to dissolve the binding waxes. The lower viscosity of the debinding fluid allows it to penetrate the pores, blind holes and internal channels of the parts to effectively remove just the right amount of wax binders. After the debind cycle, the parts are cool and dry enough to be immediately placed into the sintering oven.
New, sustainable debinding fluid blends have been formulated without the use of solvents such as n-propyl bromide (nPB) or trichloroethylene (TCE), which may cause health and environmental problems. Most have a low global warming potential (GWP) and offer long-term compliance with global environmental regulations.
Companies looking for help with metal binder jetting and debinding should consult with a critical cleaning partner that specializes in vapor degreaser debinding. They can recommend the best debinding fluids and methods for any application.
Venesia Hurtubise is a technical chemist at MicroCare Medical, where she researches, develops and tests cleaning-related products that are used daily in medical and precision-cleaning applications. She holds an MS in Green Chemistry from Imperial College London.
The opinions expressed in this blog post are the author’s only and do not necessarily reflect those of Medical Design and Outsourcing or its employees.
