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Figure 1: Quarter of a polymer rod; radius 100 μm; sharp cutting edges and smooth surfaces; the two cuts cross at the centre ridge.
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Figure 2: Oval windows in the silicate infusion sleeve; external diameter 1.66 mm; wall thickness 125 μm; no thermal damage and no melting.
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Figure 2: Oval windows in the silicate infusion sleeve; external diameter 1.66 mm; wall thickness 125 μm; no thermal damage and no melting.
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Figure 3: Polymer stent; external diameter 1.8 mm; wall thickness 0.2 mm; square and smooth cutting edges.
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Figure 4: One of the most compact, modular laser micro machining system in the world; floor space of 0.64 m2.
Eduard Fassbind, swisstec micromachining AG
Customised laser micro machining systems for tube machining in the production of medical implements and implants: the laser source has a major influence on the machining properties and quality, but it is the overall system, from system management and the numerous machining steps to the handling, that determines the machining properties and product quality.
Medical technology requires and is constantly developing complex products that provide ever-greater precision. The process of innovation is also taking major steps forward in the area of medical implements, such as needles, knives and hypotubes, and implants, such as stents and heart valves. As far as machine manufacturers are concerned, the production of these high-quality products in an efficient way is giving rise to new challenges on a daily basis. Manufacturers are now required to implement a never-ending stream of new requirements, particularly in areas such as laser sources, handling, automation and quality checks.
One System, One Setting, Many Processing Steps
In the case of a great many products, laser micro cutting is often the only manufacturing procedure that can be used. Many steps are needed, however, in order to manufacture a usable implement or implant that can be manufactured out of a tube.
Combining all machining steps to form a single system, and especially, a single setting, is highly precise and efficient. It is therefore useful to complement the laser cutting or welding stages with the addition of mechanical machining stages. The integration of shaping units or high-speed grinding spindles expands the field of application of the laser, which is already very wide. Combining several lasers within a single system, such as for welding, cutting, drilling, ablating and marking, also creates a particularly broad application spectrum.
Highly-dynamic and very flexible systems with up to 8 axes combine all of the necessary machining steps, enabling almost any desired cutting geometry to be manufactured. The precise, NC-driven linear axes operate to an accuracy of less than one micron.
Product and Quality Requirements
A high level of product quality is crucial, especially in the case of implants, such as stents. These very delicate and complex mesh- like structures are machined from thin-walled tubes. Implants may remain in the body for very long periods of time. Another type, known as ‘bioresorbable implants’, will actually dissolve inside the body. After insertion into the body, for example, stents expand and adjust their size to their respective application and position. As a result, the functional and quality characteristics must be respected for all implants. It is important that the cutting edges and surfaces are burr and slag-free. The material in the vicinity of the cut must be protected by minimising the size of the zone that is affected by heat. Micro cracks or other forms of material damage must not occur.
Using special and innovative types of materials also requires the development of systems to process them. The widely-used fibre laser will fail, if, for example, it is used in order to cut polymer, nitinol or magnesium.
Green Femtosecond Laser
In order to ensure that the vast range of materials used today is processed in the most effective possible way, ultrashort pulse (USP) lasers are required. Generally speaking, the cutting properties and the quality required can usually only be achieved by using what is known as ‘cold’ machining by means of picoseconds or femtoseconds. Here, the material is vaporised directly at the site of machining, without melting. The laser leaves behind burr and slag-free edges and surfaces in the machining area (figure 1).
Extensive skills and expertise are primarily available in the integration and use of typical USP lasers in the infrared (IR) domain, using a multitude of machines and applications. These lasers are perfectly suited to the machining of metals, however they are less suitable for the machining of many temperature-sensitive materials such as polymer, for example.
Application tests involving double frequency USP lasers have produced excellent results in that regard. Laser radiation in the green wavelength range firstly enables the laser to process a large number of materials, including temperature-sensitive materials. The reason for this is that many polymers that are more and more frequently used in medical technology demonstrate particularly good absorption properties in this wavelength spectrum (figure 2). This makes the machining of these products using a green USP laser a particularly attractive proposition and produces machining results of a very high quality. In fact, polymer stents can be produced in hardly any other way. Depending on the laser and optical instruments used, the very fine and complex structures with gap widths of5μmandwebwidthsof20μmcanonlybe manufactured in this way (figure 3).
The pulse and layered removal process commonly used in USP laser processing cannot compete with the processing speed of a fibre laser. High rates of repetition and effective process optimisation have enabled a cutting speed to be achieved that is cost-efficient for the industry. This application is rapidly becoming more efficient than conventional processes, especially in view of the fact that the product quality cannot be achieved in any other way and post-machining steps are no longer required.
Modular and Expandable
Their modular design enables micro machining systems to be expanded individually and this is not restricted to the mechanical machining stages, the laser sources and the linear axes. Automating the process through the addition of tube loading systems and the automatic removal of finished components now enables three shifts to operate 7 days a week. The expansion of wet cutting also improves the quality and speed by cooling the tube, protecting the material on the opposite side.
Thanks to its modular design, it has been possible to develop one of the world’s most compact laser micro machining systems that incorporates a whole wealth of functions. The robust granite machine framework contains all the components and requires a floor space of only 0.8 x 0.8 m2. The all-in-one laser micro machining systems (figure 4) from swisstec combine dynamics and precision with flexibility and compactness, thereby making a significant contribution to the improvement in quality of medical implements and implants.