By Sean Fenske, Editor-in-Chief
 
When 3D printing is mentioned, it is probably most often associated with plastic. While polymers do represent the bulk of the materials used with this fabrication process, metals are quickly becoming a preferred option for a number of applications. Within the medical technology space, metals are being used with 3D printing for orthopedic applications, such as implants and instruments. It is also being used to create small, yet strong, components in devices.
 
As 3D printing has matured and become much better understood, it’s become apparent that different additive manufacturing processes are better suited to achieve specific outcomes. One such technique that leverages metal powder is binder jet 3D printing. While comparable in some ways to metal injection molding (MIM), this process brings its own set of advantages.
 
To help explain those benefits and also address a number of common questions surrounding the use of 3D printing along with metal, Nicholas Eidem, director of business development at Advanced Powder Products Inc., took time to respond in the following Q&A. He addresses the use of metal, how binder jetting compares to MIM, and the challenges that must be considered.
 
Sean Fenske: How much is metal 3D printing being used in medical device development/manufacture? For what types of applications?
 
Nicholas Eidem: Due to the ability to produce complex geometries with minimal investment, metal 3D printing (also known as additive manufacturing) is growing in a wide range of medical device prototypes and production applications. Currently, the most common applications of metal 3D printing in medical devices are orthopedic implants and surgical instruments, including those used for robotic surgery.
 
Fenske: For those who are more familiar with 3D printing with plastic, how does working in metal differ?
 
Eidem: The metal 3D printing method most similar to plastic 3D printing is metal extrusion, where metal filament is heated through a nozzle and melted to the layer below. However, this method is not as common as direct metal laser sintering (DMLS) and binder jetting. DMLS uses a high-powered laser to selectively melt powdered metal layer by layer. Binder jetting differs in that it applies a liquid binder to powdered metal, which is then sintered to form the final geometry.
 
Fenske: What are the most common metals used for 3D printing for medical devices and what advantages/properties do they offer?
 
Eidem: The most common metals used for 3D printing for medical devices are titanium and stainless steel. Titanium, such as Ti6Al4V, is used for its excellent strength-to-weight ratio, corrosion resistance, and biocompatibility. Stainless steel, such as 17-4 and 316, is used for its excellent mechanical properties, corrosion resistance, and cost.
 
Fenske: How does binder jet 3D printing in metal compare to metal injection molding?
 
Eidem: Binder jet 3D printing uses identical powders and sintering equipment to those utilized in metal injection molding. Binder jet 3D printing does not rely on custom tooling, so 3D-printed part prototypes can be produced rapidly and delivered in days rather than months. This freedom from tooling along with rapid delivery enables engineers to test much sooner with functional MIM components.
 
In addition, powder sharing enables the binder jetting process to take advantage of the bulk buying power of the MIM operation to reduce material costs. Baseline properties and downstream processes are already defined and stable. Further, the MIM sintering profiles and infrastructure are in place to eliminate capital investment and development costs.
 
Fenske: What challenges are associated with binder jet metal 3D printing for medical device development/manufacture and how do you help resolve them?
 
Eidem: The biggest challenges for binder jet 3D printing are surface finish and feature resolution, especially with micro-components <1 gram. As medical devices continue to get smaller, 3D metal printing will need to continue to develop methodologies to produce components at this scale. As the layer of binder is applied to the bed of powder, it bleeds into the surrounding area. For larger components, the bleed does not typically impact the functionality; however, with small components, the bleed can drastically impact the feature’s design intent.
 
The surface finish of a MIM component is determined by the powder particle size and sintering process and, therefore, is highly controllable in the 32 to 40 Ra range. Binder jet 3D metal printing applies layers with an average layer height of 50 to 100 microns, producing a surface finish in the 70 to 125 Ra range without further processing. However, as with MIM, surface treatments can be applied to the 3D printed component.
 
Fenske: What are the most important considerations for companies looking to work with 3D printed metal components/devices?
 
Eidem: 3D metal printing excels at low-cost rapid prototyping of complex geometries. Binder jet 3D printing can be used to provide functional prototypes of geometries that will ultimately be scaled to metal injection molding. Therefore, many of the design considerations for metal injection molding apply to binder jet 3D printing. In some cases, the printed components may prompt a design change of the MIM process to aid in manufacturability, such as incorporating a flat surface to prevent distortion.
 
Fenske: Do you have additional comments you’d like to share based on any of the topics we discussed or something you’d like to tell medical device manufacturers?
 
Eidem: Binder jetting is a natural extension of metal injection molding as both processes use many of the same materials and equipment. Binder jet 3D metal printing is the ultimate bridge between prototype and production MIM parts. Metal 3D printing affords speed and design flexibility at a fraction of the cost of MIM and can save thousands of dollars.
 
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