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Laser drilling is a highly efficient method of machining holes. When the drilled hole diameter is in the range of 0.125 to 1.2 mm and the hole depth to hole ratio is <16, laser drilling is more economical and efficient than drilling methods such as mechanical, electrical corrosion, electrochemical and electron beam. However, the potential for widespread laser drilling has not been fully exploited. For example, with laser drilling, products with satisfactory geometry, conicity and other technical properties can only be obtained with a drilling aperture of >0.125 mm. In addition, the existing laser drilling equipment has a relatively low synthesis efficiency (<1%), because a small internal cavity diameter must be selected to obtain the TEM00 mode beam output, and the SBS-mirror has a large radiation loss. (about 30% to 50%), which is the main reason for increasing the cost of technology. The main problem with laser drilling deep holes is at the bottom of the hole. The laser energy density decreases as the hole depth increases, which is caused by the laser beam defocusing. Therefore, as the drilling depth increases, the drilling speed gradually decreases, and when the laser energy density falls below the energy density threshold required for the drilling material, the drilling stops. At present, the well-known method of dynamic beam focusing mostly moves the focus point into the sample as the depth of the hole increases, keeping the energy density of the beam at the bottom of the hole constant. However, due to the limitation of the waist width, the depth of the focus point moving into the sample cannot exceed 1.5 mm at most. In this connection, the single mode phase conjugate Nd:YAG velocity of a passive Q-switch (PQS) fabricated with LiF:F2-crystal.
1. the characteristics of laser drilling.
Laser drilling is the first practical laser processing technology and one of the main application areas of laser processing. With the rapid development of modern industry and science and technology, more and more materials with high hardness and high melting point are used, and the traditional processing methods can not meet certain process requirements. For example, processing micron-sized pores on high-melting-point metal molybdenum sheets, processing small holes of several tens of micrometers on hard tungsten carbide, processing deep holes of several tens of micrometers on red and sapphire, and jetting of diamond wire drawing dies and chemical fibers Silk head and so on. This type of machining task is difficult and sometimes impossible with conventional machining methods, and laser drilling is not difficult to achieve. The high concentration of the laser beam in space and time can reduce the spot diameter to the micron level to achieve high power density, and laser drilling can be performed on almost any material.
Laser drilling technology has significant advantages compared with conventional hole drilling methods such as mechanical drilling and EDM:
(1) The punching speed is fast, the efficiency is high, and the economic benefit is good.
(2) A large aspect ratio can be obtained.
(3) It can be carried out on various materials such as hard, brittle, and soft.
(4) No tool loss.
(5) Suitable for a large number of high-density group hole processing.
(6) Small holes can be machined on the inclined surface of materials that are difficult to machine.
2. Classification of laser drilling.
1, copy method.
The laser beam is repeatedly irradiated to a fixed point of the workpiece with a certain shape and precision, and there is no relative displacement of the beam and the workpiece in a direction perpendicular to the direction of propagation of the radiation. The copy method includes single pulse and multiple pulses. Multi-pulse methods are currently used, which are characterized by minimizing the lateral diffusion of energy on the workpiece and helping to control the size and shape of the holes. A pulse width of the order of milliseconds allows sufficient heat to diffuse along the axial direction of the hole, rather than being absorbed by the surface of the material. The shape of the laser beam can be obtained with an optical system. A shaped hole can be punched out, for example, in a focused beam or in the front of the lens with a hole of the desired shape.
2, contour roundabout method.
The shape of the machined surface is determined by the trajectory of the laser beam and the relative displacement of the workpiece being machined.
When machining with the contour roundabout method, the laser can operate in both pulsed and continuous states. In the pulse mode, since the holes are successively superposed on each other with a certain amount of displacement, a continuous contour is formed. With contour machining, the hole can be enlarged to have a cross section of any shape.
3. Laser drilling equipment.
1. Laser for laser drilling.
The laser is an important part of the laser drilling equipment. Its main function is to convert the power provided by the power system into laser energy with a certain conversion efficiency. According to the nature of the working substance of the laser, it can be divided into a gas laser and a solid laser. The gas lasers used for perforation mainly have carbon dioxide lasers, and the solid-state lasers used for perforation mainly include ruby lasers, neodymium glass lasers, and YAG lasers.
Carbon dioxide lasers have many unique advantages. They are more efficient than other lasers and can be absorbed by many non-metallic materials such as plexiglass, plastics, wood, multi-layer composite sheets, quartz glass, etc. More importantly, CO2 lasers can deliver high power output compared to other lasers. When combined with other technologies, high-speed drilling can be achieved with a maximum speed of 100 holes/second, which is difficult for other lasers.
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