Dogan Basic, product marketing manager, GF Machining Solutions
There have been great advances in medical devices over the last two centuries; Alexander Wood invented the first hypodermic needle in 1853, Rune Elmqvist invented the first implantable cardiac pacemaker in 1958 and Dr Melvin Scheinman performed the first catheter ablation on a human in 1981, all impossible without micromanufacturing processes.
Implantable medical devices have a strong trend towards miniaturisation to reduce invasiveness and increase effectiveness. This requires the manufacturers to constantly expand their capabilities, be it through advances in process engineering, purchase of newer capital or changeover to new technologies. One of the technologies that OEMs and job shops have been utilising to keep up with new medical device designs is ultra-short pulsed (USP) lasers, or lasers with pulse widths ranging from tens of femtoseconds to hundreds of picoseconds.
Challenges
There are numerous challenges faced by medical device manufacturers. Devices implanted into the human body, whether temporarily or permanently, receive a high level of scrutiny to ensure the best patient prognosis possible. Two big questions are asked before a new design is to be manufactured: “What will the cost per part be?” and “Will the part be produced at the required quality?”
Understanding the cost per part before production starts is critical for each manufacturer. Contributors to the cost per part are the costs of equipment, maintenance and consumables such as electrodes or grinding wheels. The cycle time per part is another critical constituent.
The topic of whether or not a new part design can be produced at the required quality is not at all trivial. The trend of miniaturisation pushes manufacturers to either expand the capabilities of their current process or invest in new equipment to achieve the required results. For micromachining of medical parts, the manufacturing difficulties include defects such as heat affected zone (HAZ), burrs, machining debris and recast layer, as well as accurate and repeatable positioning.
Fortunately for parts manufacturers, providers of manufacturing equipment have evolved to work closely with their customers and take many of the risks out of purchasing capital through providing turnkey solutions that address both the productivity and process sides of the equation.
Solutions
Many solutions have been developed over the years to address the manufacturing need for smaller and higher quality medical devices. The change in tooling required to accommodate this trend of miniaturisation is exemplified at GF Microlution, which started as a mechanical micromachining solutions provider and evolved into an USP laser micromachining solutions provider. GF Microlution's USP laser machines incorporate femtosecond lasers, solid granite bases, high-precision motion platforms, built-in vision systems, automation and high-end optics.
Large-series production
In the case of producing parts in large series, particularly in the medical industry, beyond the notion of cost is the notion of repeatability, which is critical. It is therefore important to design equipment that ensures very high stability of quality across production batches. GF Microlution prioritised this in its development of the ML-5 laser micromachining platform and MLTC laser tube cutting platform. A feature of these platforms that is conducive to the aforementioned is a solid granite base, which allows for high acceleration without detriment to quality. Another important feature of the ML-5 and MLTC systems as regards large series production is the use of linear axes.
Then there are optional features for the avoidance of part damage and loss, such as the MLTC’s sealed cut box for capturing and draining water, an important part of the closed-loop wet cutting system, which creates minimal mist and keeps the rest of the machine dry, an especially important factor in the manufacture of very small tubes.
The spindle on the MLTC platform, which is designed for very small, delicate tubing.
Femtosecond lasers
Medical parts require tight process control to ensure the safety of patients. Oftentimes, this requires complex post processing of parts to remove burrs, machining debris and recast layer. Even with precautions in place to prevent defects, the scrap rates are often high. Because of this, many producers of these parts have implemented 100 percent inspection. Using USP lasers greatly increases the quality of the features and therefore removes many of the downstream processes that add significant costs for manufacturers.
The beam delivery utilised in laser machines is important for both productivity and quality. The MLTC laser tube cutting platform is 4 axis and uses an adjustable beam expander through a fixed optics delivery system to allow for controlling of the laser kerf and divergence.
The ML-5 laser micromachining platform is 3 or 5 axis and is often used to machine thicker materials that require taper control. Manufacturers can use the 5-axis scanning unit to leverage advanced micromachining capabilities that can produce negative tapered holes and slots, drill arbitrarily shaped through-holes and contour with exceptionally small inside radii. Moreover, shops can easily achieve near-perfect machining quality, even for complex geometric features that were all but impossible to cut only a few years ago.
Both the MLTC and ML-5 platforms are optimised for their respective use cases to give process engineers the flexibility they need to achieve their quality of parts and reduce cycle times.
Built-in vision systems
Visual checks have been a mainstay in verifying that the machined medical parts pass the required standards. Not only is the cost of visual inspection expensive but it is alsoprone to human error, which is especially exacerbated in small medical parts. Vision systems have become an essential tool for offloading some of the inspection workload and therefore reducing overall costs. Both the MLTC and the ML-5 have built-in vision systems to set up the parts and machine as well as to provide an additional layer of inspection.
The MLTC has a programmable camera through the optics and an end-on camera trained on the end of the tube to be machined. The cameras provide the process engineer with quick feedback on the machine and stock positions through the changeover process (whether the laser is on the centreline of the stock, for example). They also allow the process engineer to check the outer and inner diameters of tubing before each part is machined to ensure that the correct stock is loaded and that there is no damage to the material.
The ML-5 also comes with a fully integrated vision system. A common use case on this platform is for initial part setup relative to the fixture or other features on the incomingpart. The machine is programmed to identify certain features and compensate locations to ensure that errors in part loading or sizing does not affect the machined features' locations.
Automation
The cost per part is greatly reduced with the use of automation throughout a part's manufacturing and verification processes. Loading/unloading parts, cleaning processes, verifying flow rate and measuring features are examples of commonly automated processes that bookend an operation. Equipment providers have become adept at working with manufacturers on providing either flexible interfaces for connecting to automation or automated solutions directly with the equipment.
One of the most commonly automated processes is bar feeding. Bar feeders allow lights out production by drastically increasing the amount of time between operator interventions for loading new material. However, in the past, these bar feeders were unable to handle small diameter tubing, which is often required by medical device manufacturers.
In 2021, GF Microlution developed its first bar feeder for tubingdiameters as small as 254 μm. Tubes of this diameter are often about as flexible ascooked spaghetti. Small diameter tubing automation has allowed manufacturers of small parts to more quickly realise their return on investment (ROI) through lights out production and reduced workload per operator per machine.
Conclusion
Over the last two decades, USP lasers have diversified from the optical R&D benches and matured into an integral tool for the medical and other industries requiring micromanufacturing capabilities. These advances in manufacturing equipment help reduce cost per part (and ultimately cost per medical intervention) as well as give design engineers more flexibility to create the next generation of medical components.
GF Machining Solutions