Laser welding is more and more widely used in various fields of medical devices because of its advantages of local heating, precision processing, and non-contact heating.
Compared with other commonly used welding techniques, laser welding technology produces almost no welding slag and debris, and no additional adhesive is added during the welding process, so that the entire welding work can be performed in a clean room. Laser welding technology has greatly promoted the development of medical devices. For example, the encapsulation of active implantable medical devices, the radiopaque markers of heart stents, ear wax protectors, and balloon catheters cannot be separated from the use of laser welding.
Plastic laser welding principle
Laser welding is a welding method that uses a high-energy-density laser beam as a heat source. That is, the laser radiation heats the surface of the workpiece, the surface heat is diffused into the interior through thermal conduction, and the workpiece is melted to form a specific molten pool. As shown in the figure below, the laser beam passes through the upper transparent material and is then absorbed by the lower layer material. The laser energy is absorbed and converted into heat energy. Since the two layers of material are pressed together, thermal energy is transmitted from the absorbing layer to the light transmitting layer, making the two The layer material melts and bonds.
At the same time, due to the thermal expansion of the material itself, internal pressure is generated and the internal pressure and the external pressure act together to ensure a solid welding of the two parts. The above two figures intuitively illustrate the principle and process of plastic laser welding.
Visible laser beam energy must be absorbed by the plastic in order to achieve a good welding effect, so plastic laser welding is generally used semiconductor laser. In addition, not all plastics can be laser welded. Plastics can be divided into two categories, thermosetting and thermoplastic. Thermosetting plastics do not have reproducibility, and they cannot be welded. Thermoplastics, on the other hand, remelt and then melt (ie, they can be heated and cooled to make them reversibly changeable). They are so-called physical changes and therefore have weldability.
Plastic laser welding process
Diode lasers or semiconductor lasers are commonly used in plastic welding. The light beam is in the near-infrared region, and the light beam has a wavelength of 400 to 1,100 μm, and can be transmitted through the optical fiber. In this range, the astronomy laser pointer beam can be absorbed by most plastics. The diode laser welding system is compact, and the laser can also achieve higher levels of power. The wavelength of the laser can be designed according to special requirements. The wavelength of a semiconductor laser is generally 808 to 980 μm. Semiconductor lasers have a low investment cost, small size, and high efficiency.
Thermoplastics contain amorphous plastics and semi-crystalline plastics. Plastics that can be laser welded are all thermoplastics. In theory, all thermoplastics can be laser welded.
Plastic laser welding technology requirements for welded plastics are: materials in the heat-affected zone require good absorption of laser light waves; materials that are not part of the heat-affected zone require good transmission of light waves, especially in This is especially true when welding two thin plastic parts. Adding an absorbent to the plastic in the heat-affected zone generally serves the purpose.
The use of absorbents is a very important process in the plastic laser welding process. The essence of plastic laser welding is to melt the plastic to be welded in the heat-affected zone, and then cooling naturally to join the plastic parts. Allowing the plastic to melt requires the plastic part to absorb enough laser energy.
The ideal absorber is usually carbon black. Carbon black can absorb almost all of the laser energy at infrared wavelengths, which greatly improves the heat absorption effect of plastics, making the material in the heat-affected zone melt faster and with better results. Some other color dyes can also have the same effect of absorbing light waves.
There are three ways to add absorbents:
One is to infiltrate the absorbent directly into the material to be welded, so that the plastic part that has penetrated the absorbent should be placed below, and the plastic part without the absorbent is placed on it so that the laser light wave passes through;
The second is the surface osmotic agent to be welded to the plastic parts, so that only a part of the plastic that has penetrated the sorbent will become the heat affected area and be melted;
The third is to spray or print the absorber on the contact parts of the two plastic parts to be welded.
Unlike metal welding, the laser power required for plastic laser welding is not as large as possible. The greater the power of the welding laser, the larger and deeper the heat-affected zone on the plastic part will cause the material to overheat, deform, and even damage. The laser power should be chosen according to the depth that needs to be melted.
Plastic laser welding speed is relatively fast, generally get 1mm thick welding speed of up to 20m/min; while using high power CO2 laser welding plastic film, the maximum speed can reach 750m/min.
Application in the field of medical devices
With the wide application of plastic materials in the field of medical devices, new types of plastics production and processing technologies have emerged one after another. Laser welding is one of them. Due to its advantages of non-pollution, non-contact, and seamless connection, it has attracted widespread attention in the industry.
The use of plastic laser welding technology in medical devices is far more than the above, plastic laser welding technology is being used by more and more medical device manufacturers, its application prospects will be very bright.
However, in order to achieve a satisfactory degree of welding effect, it is necessary to continuously adjust and test parameters such as welding power, welding speed, and welding frequency. In addition to the current laser welding technology applied to the production of medical equipment, there are many other innovative laser processing technologies also have great potential in the manufacture of medical equipment, such as laser surface modification, laser cutting, laser drilling and laser micromachining . It is believed that research and use of these advanced laser processing technologies will create more high-quality, high-demand medical equipment.