A Material Argument: Ceramic Injection Molding
Ceramic injection molded products are increasingly being used in the manufacture of innovative medical components and devices, thanks to the unique range of material and performance attributes. In this article, the material, its key features, and the growing range of applications for which it is suited are highlighted.
It is an established fact that people are living longer, thanks mainly to advances in medicine and medical procedures. Alongside advances in drug technologies, one of the most important contributors to increasing human longevity is the use of advanced ceramics, enabling scientists, engineers, and doctors to challenge the limits of what is possible with medical components and devices.
One of the most widely known applications is in hip replacements. While these are not produced by injection molding, they are an excellent example of the use of ceramics in a medical application. But what is it about ceramics that makes them particularly suitable for medical use?
One of the key features of ceramics is its biocompatibility, or bio-inertness, meaning it does not adversely react with other substances found within the human body.
Some of the medical and clinical applications where ceramic products are particularly appropriate include dental abutments, ablation components for the treatment of soft tissue, oxygen concentrator systems, and seals used within blood apheresis devices. Ceramic components are also used in diagnostic applications, such as blood and cellular analysis systems, mass spectrometry, and gas chromatography.
The unique properties of ceramics allow for them to be increasingly used in surgical applications too. Zirconia RF endoscopic tumor ablating tips are formed using ceramic injection molding. While these tips are sharp enough to enable surgeons to make the necessary incisions, the use of ceramic material avoids instances of toxic shock syndrome or the likelihood of an allergic reaction in patients.
Cost is an important consideration and ceramic injection molding (CIM) offers virtually endless solutions for delivering repeatable, high-precision components. Medical engineers require considerable versatility and flexibility when designing advanced components. One of the main benefits of CIM is that it allows for designs that previously may have been too difficult or expensive to manufacture to become commercially viable. CIM also enables the production of complex features, including re-entrant angles, multi-shaped blind holes, screw threads, surface profiles, perpendicular holes, undercuts, and intricate cavities. Further, ceramics lend themselves very well to sterilization processes, where the heat and presence of chemicals could seriously affect the shape and performance of other materials, such as polymers.
CIM has extensive capabilities that provide an ideal process for the engineering of intricate features on small components, surgical instruments, diagnostic equipment, and surgical implants. The process begins with very fine ceramic powders, which are then mixed with thermoplastic binders using sophisticated techniques to produce a homogeneous pelletized feedstock. These binders form a liquid medium which carries the ceramic powders into the mold during the injection stage. An injection molding machine is used, similar to those used for conventional plastic molding, and the molten feedstock is forced into a cavity forming a net shape part. The molds can be single- or multi-cavity configurations. After the part is formed, it goes through two thermal processes—pyrolysis, which removes the binder, and then sintering in a high temperature kiln to form the final ceramic component. During sintering, the component shrinks uniformly by up to 20% while retaining its complex shape.
This technique enables even highly complex components to be molded to extraordinarily tight tolerances of typically ±0.5% of the stated dimension, with exceptional process control achievable over multiple dimensional tolerances. This level of control enables the required geometry and surface finish to be achieved without the need for further processing steps, such as grinding, lapping, or polishing, which would increase both cost and lead times. CIM delivers a homogenous and consistent product with excellent dimensional stability, whether the manufacturing volumes are one thousand or one million pieces.
A range of high performance materials have been formulated specifically for CIM processing use. High-purity alumina offer high density, good conductivity, and wear resistance, as well as resistance to chemical attack. Yttria-stabilized Zirconia, which combines high mechanical strength and density, has been used in the manufacture of clinical products for more than 20 years. Zirconia toughened alumina is a high-purity material offering enhanced mechanical properties compared with standard alumina. Silicon nitrides are particularly appropriate for applications where high temperatures are involved as their porosity and low density ensures exceptional thermal shock resistance. This material also offers excellent resistance to wetting and attack by molten, non-ferrous alloys. The unique properties of silicon nitride also assist with cooling control and preventing cracking during the production of dental restorations.
More recently, technological developments enable the production of materials with almost any combination of characteristics to meet customer requirements for increasingly challenging applications. This flexibility, alongside the capabilities of the leading players in the marketplace to deliver a complete service in close collaboration with the customer from concept to development, commercialization, and finally, production-scale manufacturing, is continuing to push the boundaries in the medical device development for ever more diverse applications.