Titanium metal injection molding (TiMIM) is a method for high volume, precision manufacturing of small parts. TiMIM is performed by mixing titanium powder with a binding agent to form a thermoplastic compound. The compound is injected into a mold using an automated injection molding machine. The part is then removed from the mold and heated to remove the binder and densify the part, leaving behind a pore-free, dense part made to very tight tolerances and delivering excellent mechanical properties.
TiMIM is best suited for titanium parts that require one or more of the following characteristics:
- Small and complex
- High volume
- Corrosion resistance & biocompatibility
The titanium alloys used in TiMIM are biocompatible, making them suitable for implants. The process is suitable for high production volumes and can be used to make very tiny, complex parts, much more economically than other manufacturing techniques. The high precision of this method also makes tight tolerances components possible. The high integrity, pore-free nature of the final product makes hermetic seals possible
While there are many other characteristics that set TiMIM apart and make it well suited for particular applications, these four are some of the most important for medical use. Let’s take a look at each one.
TiMIM is the Solution for Design Flexibility and Strict Requirements
Titanium is a preferred material for medical implants and devices for many reasons, but most importantly for its biocompatibility. The titanium materials used in this process, such as Ti-6Al-4V or Commercially Pure titanium, are suitable for implanting in the harsh environment of the human body. Because of their high corrosion resistance titanium alloys also exhibit excellent biocompatibility.
Ti-6Al-4V is the most common choice for medical devices and implants, more suitable for biomedical applications than stainless steel alloys in terms of strength-to-weight ratio, corrosion resistance and modulus. Medical-grade titanium alloys, including Ti-6Al-4V, meet all associated standards for use in the human body. They will not corrode or react with the body, will not generate harmful byproducts, and will last for many years.
Meeting the demanding chemical requirements of titanium materials is key to delivering their corrosion resistance. In powder metallurgy, a small contaminant in a commonly-shared processing tool can affect biocompatibility. At Praxis, we only work with titanium alloys, which eliminates the risk of contamination by other metals. Because of this, we’re the only company on the market to produce medical devices certified to ASTM F2885.
High Volumes Through Careful Design
TiMIM can be used to produce high production volumes (>10,000 parts/year). Once the initial injection molds are designed and tested, they can be loaded into an automated injection machine and the molded parts are batch processed in furnaces. With most of the design and time commitment at the beginning of the process, the scale up to high volumes is not as challenging or costly as it would be with other production methods. If higher volumes are anticipated in the future, this can be taken into consideration by designing tooling that can be expanded to more cavities as the requirements increase.
The design process begins with careful planning of the injection molds. These molds are designed to account for shrinkage during molding and densification and for the strategic placement of gates and parting lines to minimize post-processing. Mold flow simulation modeling can be used to estimate how the tool will perform before the molds are constructed.
Once the mold is designed, they can be used on an automated injection line to produce many identical parts. With more parts, there is only the added expense of additional material and machine time. In additive manufacturing, this machine time can be very expensive in comparison, putting TiMIM at a distinct advantage for high production volumes. In many cases the TiMIM molding output can be increased greatly by simply increasing the cavities in a tool, with no need for more molding time or an additional molding machine.
Small, Complex Parts
TiMIM can be used to make very tiny parts, some weighing less than 20 milligrams. Other manufacturing methods cannot be relied upon to repeatably produce parts at this scale. For example, investment casting is limited in the minimum size of parts that can be created, as the wax, investment ceramic, burnout, and pouring of molten metal must have enough room for thermal expansion, gas release, and other process considerations.
Small parts still require all of the same support and technical structures, such as runners and sprues, to allow for material to reach the mold. The real advantage to TiMIM over other methods is that it can meet much tighter design tolerances with much smoother surface finish. The technique simply has better feature resolution than investment casting or additive manufacturing in the realm of small parts.
Some biomedical assemblies require parts to fit tightly together to form a hermetic seal. The most typical example of this is a glass-to-metal seal for electrical feedthroughs. These seals may protect delicate electronics or other components that would not be biocompatible and would be affected by the environment of the human body.
One advantage of TiMIM processing is the ability to make small parts to very tight tolerances. TiMIM makes hermetic seals possible, as the tight tolerances (within 0.1-0.3%) ensure a perfect fit between mating or matching components in a biomedical assembly.
Tight tolerances are not enough to form a hermetic seal, however. Another key component is absence of porosity. TiMIM can produce 99.9% dense components due to the combination of tailored sintering conditions and a post-sintering hot isostatic pressing (HIP) step. When compared to investment casting, TiMIM parts are extremely uniform and pore-free.
The surface finish of TiMIM components also helps create a hermetic seal. Because of the high quality of the surface finish TiMIM material is compatible with glass-to-metal seal processes. Additive manufacturing and investment casting do not have the same smooth surface finish, requiring more post-processing time to ensure a good seal.
TiMIM is the Solution for Design Flexibility and Strict Requirements
The design flexibility of TiMIM enables the large-scale production of complex and highly precise parts. With the added capabilities of biocompatibility and hermetic seals, TiMIM is suitable for producing medical implants. If your part has strict design and medical requirements, TiMIM can help you meet them.
Titanium metal injection molding (TiMIM) is a cost-effective way to transform titanium metal powder into serviceable parts, especially those with small dimensions and those requiring tight tolerances, such as parts that must be hermetically sealed. When compared to CNC machining or investment casting, TiMIM can produce a net shape with minimal waste and post-processing, all at high production volumes.