The benefits of UV curable masking materials in orthopaedic implant manufacture
During the manufacture of orthopaedic implants, temporary masks are used to protect surfaces from metal finishing processes. Their tenacious adhesion seals and protects machined, ground, or polished surfaces during tumbling, peening, abrading, or cleaning processes, to help achieve the desired surface finish across different areas of the implant. However, masking can present a challenge to medical device manufacturers due to the properties of the masking materials themselves. Here Kevin Brownsill, Head of Technical: Learning and Development at Intertronics, discusses how temporary masking challenges can be overcome with UV curable materials.
Approximately 200,000 people receive hip or knee replacements in England and Wales every year, and these are typically highly effective. Research from the University of Bristol found that eight out of ten knee implants and six out of ten hip replacements last up to 25 years. To ensure long term success, orthopaedic implants must be precisely manufactured to specific surface finishes to achieve the required biological, chemical, and mechanical properties — for example, to reduce friction and wear.
Orthopaedic implant manufacturers typically achieve the desired surface finishes with multiple steps of processing. During these steps, maskants are applied to protect certain surfaces from processes like anodization, plasma treatment, or shot blasting, while applying them to the surfaces that remain exposed. Once the process has taken place, the mask is removed, typically via peeling, which may require soaking in water to soften the material, or incineration, and further masks can then be added where needed as the product moves through different processing steps.
Approaches to temporary masking
Traditional approaches to implant masking include tapes, boots, waxes, and lacquers. However, each of these techniques comes with benefits and challenges. Because orthopaedic implants are typically in complex geometries, masking accurately with boots and tapes is difficult and time consuming. Another challenge with boots and tapes is that they may deform — for example, if the edges of the tape lift, it can result in suboptimal edge definition. Applying these materials is typically done manually, which can be time consuming and subject to human error.
These challenges can be overcome by using a liquid mask, such as a lacquer or wax. If they have a low viscosity, they can be hard to accurately apply, and can drip or flow into additional areas of the implant, leading to poor edge definition. Alongside this, their cooling or curing time can take minutes to hours, and can create work in process, slowing down manufacturing.
If there is a problem during the masking process, such as the edges of the tape lifting, the mask being applied in the wrong place, or the mask not being tacked down correctly, there is the potential for rework or scrap. Implants are high value parts, and avoiding this is therefore of the utmost importance for manufacturing profitability.
Benefit