Lasers are HELPing medical manufacturers

Focusing only on orthopedic implants in the U.S. in 2012, more than 1 million Americans had a joint replaced for an estimated $22 billion, according to the Centers for Disease Control and Prevention (CDC). This is a significant increase from the 720,000 replacements performed in 2009. Analysts forecast global orthopedic implants to reach $41.8 billion by 2016. With the growth of the aging population around the world, the numbers of medical implants is expected to grow at an annual rate of 7% to 8%.

With growth comes challenges. Manufacturers of components and surgical tools continuously face expectations to improve the quality and life of their products. At the same time, they aim to reduce production costs and waste while still working to meet the changes in FDA regulations – such as the newly introduced Unique Device Identifier (UDI) 1D/2D code.
 

Stringent requirements

Producing medical devices is a complex process requiring tight control of each manufacturing step. For example, making a femoral stem – the largest component of a hip replacement – includes several key steps: forging, trimming, drilling and cone finishing, bead blasting, and then plasma etching, which creates microporous surfaces essential to the osseointegration (growth of the bone in the implant).

During the manufacturing process, continuous validation of each component is required for part dimension and surface finish through visual and metrology inspection tools. Once machining of the part is complete, it has reached its peak-manufactured cost. The last step in the process, before cleaning and packaging, is laser marking.

Because laser marking occurs at the end of an expensive and extensive list of manufacturing steps, there is no margin for error. In contrast to other laser-marked commercial components, such as the control buttons of a car radio, where parts are laser-etched well before assembly, a medical component can reach a manufacturing cost of several hundred dollars by the time it reaches the laser marking station. Dismissing or simply putting improperly marked components into a reject bin is not an option. For these reasons, laser marking requires extreme precaution to avoid partial or incorrect marking on ready-to-ship devices.

Despite many safety measures at laser marking stations, glitches do happen; they are generally caused by machine performance, flaws in fixture designs, hardware failures, or, most often, a second of operator inattention. The type of defect can range from simple to complex; it can be a misaligned bone screw with a partial mark, a mark from a laser with a significant drop of power, or a part mistakenly processed twice. Correcting some of these defects is never easy and requires craftsman skills.

To overcome these challenges, manufacturers rely on complex tooling and fixtures to minimize errors. Also incorporated into the process are dedicated inspection stations to provide 100% part inspection to catch possible slipups. These solutions work but tend to require costly designs, extensive engineering resources, and premium factory space.

Unfortunately, because the majority of the current processes handle parts in batches, part inspection occurs as a batch, and flagging defective components only happens after a full batch has been processed. By this point, the damage may have been done, and the batch may go to waste.
 

Overcoming challenges

To support manufacturers needing to laser-mark implants, FOBA engineers developed a software process called Holistic Enhanced Laser Process (HELP), to overcome many of the daily laser-marking challenges medical device manufacturers face. The process, which includes built-in automatic inspection, alignment, and validation tools, helps reduce waste and defects from existing laser marking processes.

With HELP, the focus is not on the hardware or the operator’s attention but the medical implant itself. HELP’s built-in part validation technique – where authentication of a part comes from inspecting its shape and dimensions – will automatically notify the operator of part mismatches. The laser will not initiate any mark on an incorrect part even if the proper fixture is used and the wrong part fits in. This is a common challenge when handling a family of parts that come in different lengths and sizes. Femoral stems are a good example. To fit varying human sizes and shapes, femoral stems are produced is in size increments of 1mm or 2mm. For an operator to discern between two successive sizes is a clear challenge. As an example, the photos on page 24 depict femoral stems of different lengths where, although the bottom one looks significantly longer, it is shorter than the one above by 2.5mm (0.1").

Mismatching sizes is not the only challenge manufacturers face during production. In some instances, because of a moment of inattention or the lack of appropriate tools, some parts may be processed twice, resulting in a double mark. Double marking parts is more likely to happen on small components where the laser mark is too small to be visible to the naked eye. Bone screws, with marked characters ranging from 0.3mm to 0.15mm, are likely candidates. To address this issue, HELP comes with is pre-inspection tool that will flag already marked parts and stop the laser from double marking components.

After identifying components as correct and confirming them as blank, they are ready to be laser marked. HELP’s Intelligent Mark Positioning (IMP), the next layer of intelligence in the marking process, works so parts do not require precise alignment and fixtures do not require an accurate design. The IMP function, still focused on the part, can track the part’s location to realign the laser mark. Parts can fit loosely into the fixture and IMP will track their positions. Fixtures do not have to be accurate and the same fixture can be used for similar parts. If a part is missing, because it was forgotten or a tray is partially filled, IMP will only mark parts that are present and will only count the ones that have been marked.

With bone screws, for example, where the laser marks have to use characters that are 0.2mm (0.008") in height, these marks must align to an arc segment and be placed on a curved surface. Marking screws at this small size with high accuracy is practically impossible without such technology.

Another benefit, HELP’s tracking feature allows manufacturers to move to fixtures that are lower in cost. Fixtures made from stereolithography (SLA) can be designed on site, produced overnight, and manufactured at a fraction of the cost of metal counterparts. This represents a significant saving as fixture cost can grow exponentially with part varieties. The graph above shows the significant reduction in the cost of fixtures when using IMP technology.
 

Small space, small marks

Laser marking is the preferred identification process for medical components. It can provide permanent, high-quality, and high-precision marks that overcome harsh environments, but most importantly, a laser can mark or engrave text smaller than the eye can see. Data matrix codes are generally preferred over human-readable contents for their data storage capability and their built-in redundancy and error correction. Laser-marked 2D codes can fit 30 characters in a data matrix smaller than a millimeter square.

Often, and particularly with small medical implants, the space available for laser marking is limited, making 2D code technology highly desirable. The photos on page 27 show a 0.3mm 2D code marked on the quadrant of the drive of a scrwew. However, even though today’s laser markers are able to mark data matrix codes accurately on the top of the head of a pin, no commercial technology exists to read them.

In the two examples, where the text and the 2D data matrix codes are too small to be easily readable, HELP will check the presence of the laser marks and validate their content. For the human readable content, HELP will validate the location and contrast of each character. Parts with a partial mark or poor contrast are flagged for an immediate investigation or corrective action. Similarly, for the 0.3mm size of 2D code on the screw head, HELP will check the 2D data matrix for content, contrast, error correction, and other qualification parameters.
 

Addressing needs

The improvement of advanced laser marking processes, driven by many industries from medical to aerospace, has been the main reason for the success and growth of direct marking in the medical industry. Today’s laser marking systems provide key technologies that support manufacturing’s constantly evolving requirements. Turnkey laser systems are highly powerful and more intelligent than their predecessors. They come with developments and technology that significantly reduce waste, increase efficiency, and are user friendly. HELP is an example of the adaptation of unique and affordable technology to address specific industry needs. HELP focuses on augmenting productivity and lowering production costs while providing unique traceability of laser marking processes. With its direct feedback and immediate warnings on process deviation, HELP can help improve manufacturers’ existing production processes, delivering a rapid return on investment.

FOBA
www.fobalaser.com

About the author: Dr. Faycal Benayad-Cherif, product manager, FOBA Products, can be reached at faycal@fobalaser.com.