Due to the unique properties of materials such as nickel-titanium (NiTi), platinum (Pt) and stainless steel (SS), the connection of dissimilar materials is a key issue in the continued development of advanced medical devices . The requirement to connect special biocompatible materials may result from the unique function of using shape memory alloys such as NiTi and SS or to reduce the cost while maintaining the special corrosion protection properties of Pt and SS joints. To meet these requirements, a new laser joining process is being developed to form a self-generated (no filler material) joint between two heterogeneous biocompatible metals. The auto-laser joining process will enable seamless connection of these components without the use of special adhesives and filler materials.
Due to the small heat affected zone and small spot size, the laser-based joining process has become the primary connection mechanism for metal components in medical devices such as pacemakers. The advantages of lasers in the joining process (such as minimal heat affected zone and controlled energy supply) are important for medical device manufacturing processes due to the thermal sensitivity of the components and their continued miniaturization compared to conventional heat sources. However, specialty metal joints are often complicated by the formation of new phases, such as intermetallic brittleness that results in low strength and premature failure in the joint.
Autogenous laser brazing
While most laser-based joining processes use laser input to directly melt the substrate or filler material of the joint, the design of the auto-laser joining process is substantially lower than the spot of the laser beam due to the advantages of thermal accumulation at the joint interface. size. This joining process for scanning a special metal interface is to irradiate one of the substrates with a laser.
Laser parameters such as power and rate are selected such that the equilibrium temperature of the illuminated component does not exceed its melting temperature. The thermal accumulation due to the heat resistance of the interface causes the temperature rise to be higher than the melting temperature of a substrate, thereby forming a molten layer when the laser beam approaches. Upon reaching the interface, the laser beam is turned off and the molten layer is quenched upon contact with adjacent cooling elements to form a self-welding joint. See Figure 1 for a schematic of this joining process.
The autogenous laser brazing process is designed to minimize mixing of the two materials because of the small melt volume, high quenching rate, and partial melting of one end of the welded joint to reduce intermetallic brittleness. Another advantage of localized heat is the ability to join two materials at similar melting temperatures with minimal mixing. Figure 2 shows the temperature profile of a laser beam scanning thermal model for the wire-to-wire interface. Due to the accumulation of heat, an increase in temperature is observed as the laser beam reaches the interface.
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