Making a mark
For companies that manufacture medical devices, it has always been important to offer a means of tracking precisely which devices have been distributed to a hospital or implanted in a patient. However, it is no longer an option to simply print and attach a label to a medical device.
The US Food and Drug Administration (FDA) is gradually phasing in new requirements for medical device manufacturers to place unique device identifiers (UDIs) on all of their components. In 2015, the first major milestone meant that all Class III implantable, life-supporting, and life-sustaining devices displayed UDIs on parts and packaging. Fast approaching is the September 2016 deadline, by which Class III device manufacturers are required to have a permanent mark on the device itself, if intended for multiple uses. And Class II moderate risk devices, which require the UDI, have to submit information to the Global UDI database. They must bear the correct marking by 2018.
Part of the challenge for meeting increasingly stringent traceability requirements is the need to identify and log parts throughout the production and marking process. These challenges are driving forward a new wave of integrated system laser marking technology. The Medtec Europe conference in Stuttgart, Germany in April highlighted some of these systems.
Turning to laser marking
Traditionally, medical devices were marked for identification either with ink, or with an engraving tool or etching pen. Etching posed the problem of requiring full-contact between tool and device, and offered limited resolution or repeatability. Ink posed the problem of requiring FDA approval, and by the time approval was achieved, in many cases the ink had gone out of production.
Laser marking came into its own in the mid- to late-1980s, offering a repeatable process with good contrast, clarity, and resolution that did not introduce impurities to the medical device.
Of course, laser marking as a concept is nothing new, but ‘the main thing to consider is that 20 years ago, a laser would have been a pump flash Nd:YAG laser with a separate chiller. Its yearly power consumption was massive,’ said Andy Toms, director of TLM-Laser, a UK-based distributor of integrated laser systems.
Now, fibre lasers provide a stable, low power consumption option small enough to use in integrated systems and that require no service intervention. New short-pulse lasers can mark different types of materials, producing better contrast and well-controlled marks. They also reduce peripheral damage caused by heat, which can lead to long term mechanical defects and corrosion.
‘Lasers have helped create chemical-free markings that ensure long-lasting marks with contrast that matches solvent-based ink printings,’ said Faycal Benayad-Cherif, business manager for vision and software of Germany-based Foba laser marking and engraving solutions.
Vital to medical device marking is ensuring that the correct part gets marked with the correct information. TLM-Laser distributes a system developed by Foba, which not only marks the varied and challenging surfaces of myriad medical devices, but also checks the part before and after marking.
Before, laser marking was ‘a nuisance that was required for getting the product out the door, but it never gave value. Now, we can assist with scrap reduction and improve throughput,’ said Toms. Previously, separate systems would be required for pre-marking verification, laser marking, and post-marking confirmation. Now, state-of-the-art systems combine these steps in a simple, fully integrated user interface.
If a part is laser marked at the end of an expensive manufacturing process, it has already reached its maximum manufacturing cost. Correcting defective markings is cost- and labour-intensive, and can affect the mechanical performance of the device. Avoiding error in the first place is critical.
Foba’s M1000 and M2000 work stations combine a rotary table with a camera system and laser to supply the ‘mark accuracy the medical market demands, with the shortest processing time’, according to Benayad-Cherif. The machine combines an intelligent marking positioning vision system and a point-and-shoot camera, with state-of-the-art fibre lasers.
‘Traditionally, you placed a part under the laser and then marked it. But you had to use a scrap piece during each set-up,’ said Toms. ‘With the point-and-shoot system, you can place the part under the laser in real time and view an image.’ The operator can then place the mark exactly where required on the part via a drag-and-drop function based on the camera images. This removes the need for expensive tooling, increases precision, and reduces scrap for one-off marking jobs.
As a step further, single-platform software makes the mark accurately. Foba’s intelligent marking positioning system views the part through a camera, and confirms that it matches the expected part in the correct position. It compensates for skewed positioning so that even if the part is misaligned, it can be marked correctly. Equally important, it avoids assigning a mark to non-existent parts that might be absent from a production line, and can reject incorrect parts. ‘What’s unique about it is that it looks directly through the same lens that the laser looks through. That offers very high accuracy, ±25µm,’ said Toms.
In another example, Germany- and Netherlands-based Amada Miyachi offers a laser marking workstation with a specialised user interface that interacts with both the production system and laser marking tools. ‘In this way, customers can get information into the marking file from their production database, mark the part, and create a logged record of the mark,’ said laser product engineer Mark Boyle. The operator initiates the marking sequence by scanning barcodes containing information about the positioning and template, along with UDI serial identification information. Integrated barcode readers verify that a part has been properly marked, and operators confirm accuracy throughout the process via displayed images.
Without careful checks, parts may be marked twice or serial numbers repeated. Before integrated laser systems, marking too often relied on checking the parts at the end of the process, at which point correcting errors was too late. Intelligent vision further reduces costs, improves quality, and reduces waste.
Lasers and challenges
‘The UDI requires both a 2D matrix code and an alpha-numeric code when possible,’ noted Toms. ‘It’s a challenge with small parts, and quite often, is not necessarily human-eye readable. But with machine vision, it’s going to be right every time.’
Device manufacturers have to find sufficient physical space on a small device to place the 2D matrix code and human-readable content. In many cases, that space is not available and the physical size of the mark has to be reduced. Here, accuracy becomes significantly more demanding, with laser marking equipment needing a precision of 0.1mm for inscribing content limited to a tightly defined area like the outer surface of a screw, according to Benayad-Cherif.
‘Validating the quality of the mark is as critical as its placement,’ said Benayad-Cherif. Mark contrast is critical for performing optical character verification, where every character is checked for presence and correctness.
Laser quality and optical configuration help to overcome these challenges. Foba’s new Y-series fibre laser marker product line offers nine different laser sources, which create the flexibility to find the best solution for any application.
‘Some sources are able to generate short laser pulses that help minimise heat zone effects on certain materials, providing less damage to the area surrounding the mark,’ said Benayad-Cherif. This allows significantly better contrast for marking a variety of materials. Further, users can choose from different lasers equipped with a standard customer interface.
The new CP10 scan head of Foba’s Y-series product line is faster and more accurate than previous lasers, which increases marking quality and speed. Including it with the fully integrated vision system ensures a much easier handling of multi-component projects.
Amada Miyachi’s system includes tooling plates set up to ensure consistent positioning of the part for marking with an integrated pulsed fibre laser. The correct configuration for a particular material and process is tailored by selecting the optical configuration, including laser, collimator, and focal lens, and optimising the laser parameters such as power, frequency, and mark speed. For example, a 100mm lens produces a very small marked spot size, critical to small features on the order of 50µm. ‘But this comes at the cost of a shallow depth of focus,’ added Boyle.
Tricks of the trade
‘Worldwide, we’ve probably sold 75 to 100 [Foba] systems to the medical industry in the last year,’ said Toms. Clients have used the marking system on hip replacements, knee replacements, and bone screws; indeed, anything that could be inserted or used in surgery requires traceability and serial numbering. How this is best achieved depends on the part and the material.
Fibre lasers are well suited for corrosion resistant marking of stainless steel surgical tools, banding various diameter tubes and cylindrical devices for depth measurements during surgery, and laser marking UDI codes on titanium implantable devices including pacemakers or anodised aluminium placards.
Laser annealing generates a colour change on metal surfaces, and is the preferred process for materials like stainless steel. The heat effect of the laser beam causes a change in the material characteristics underneath the top surface, resulting in a black mark. ‘The mark is long lasting as well as texture and corrosion free,’ said Benayad-Cherif.
The most commonly used materials for medical parts are stainless steels, which have a natural, passive, corrosion-resistant layer that resists repeated sterilisation cycles, according to Boyle. Machining during the manufacturing process, however, can remove or degrade this passive surface. So the passive layer must be rebuilt, in a process that removes iron and thus potential corrosion sites from a part’s surface. Unfortunately, the process also tends to remove laser marks.
‘There is no universal solution for every part and mark,’ added Boyle. Amada Miyachi’s system capabilities allow users to achieve a dark mark that is resistant to both passivation and repeated sterilisation cycles using nanosecond fibre, nanosecond ultraviolet, and infrared picosecond lasers.
The right choice is dictated by the material, surface finish, and speed of the required mark. ‘For example, the fibre laser marker can be used on 300 series stainless, and some 17-4 steels; however, as the material and surface finish increase in difficulty and cycle times, nanosecond UV, and picosecond IR solutions might be the best choice,’ said Boyle.
Indeed, laser marking on plastic materials, without the use of chemical additives, has always posed a challenge. Many medical device manufacturers shy away from added chemicals that can affect the performance of their devices and have possible adverse health effects. The introduction of UV lasers has helped to address this limitation by producing clearly visible marks, without the need for additive chemicals.
Laser systems have increased their role in meeting medical device traceability requirements, and it can be easy to forget their already-prominent role in the medical industry for welding, cutting, and additive manufacturing. For example, TLM-Laser supports laser additive printing for bone implants and laser micromachining for coronary stents.
Most recently, Amada Miyachi has worked with leading medical device manufacturers on advanced processing of their parts with the same laser used for marking. This includes cutting or trimming of stainless steel tubes, surface roughening of implantable devices for increased adhesion, and laser welding of small components of various metals.
With advances in machine vision and laser technology, further efforts toward system integration are poised to add new value and ease of production to medical devices.