Laser processing refers to the use of laser beam projection to the surface of the material produced by the thermal effect to complete the processing, including laser welding, laser cutting, surface modification, laser marking, laser drilling and microprocessing.
Use a laser beam to perform various materials such as punching, cutting, scribing, welding, heat treatment, etc.
The laser can adapt to the processing of any material, especially in some special precision and requirements, special occasions and special materials processing and manufacturing play an irreplaceable role.
I. The principle and characteristics of a laser processing
The principle of laser processing
Laser processing is the laser beam irradiation to the surface of the workpiece to remove, melt material and change the surface properties of the object by laser’s high energy.
As the laser processing is non-contact processing, the tool will not directly generate resistance by grinding with the surface of the workpiece, so the laser processing in very high speed, affected by a smaller range of heating when processing objects and will not make noise.
Since the energy of the laser beam and the speed of movement of the beam can be adjusted, laser processing can be applied to different levels and ranges.
Laser processing features
The precious features of the laser determine the advantages of the laser in the field of processing:
① because it is non-contact processing, and high-energy laser beam energy and its moving speed are adjustable, so you can achieve a variety of processing purposes.
② it can be used for a variety of metal, non-metallic processing, in particular, can be processed the material with high hardness, high brittleness, and high melting point.
③ laser processing without “tool” wear, no “cutting force” on the workpiece.
④ the laser beam energy density is very high during laser processing, processing speed is fast, and is the local processing, non-laser irradiation site has no effect or minimal impact. Therefore, the heat affected zone is small, the workpiece thermal deformation is small, the subsequent processing capacity is small.
⑤ It can be used for a variety of processing through a transparent medium to the workpiece within the sealed container.
⑥ As the laser beam is easy to guide, gather to achieve the transformation of direction, easily work with the CNC system for processing complex parts, it is a very flexible processing methods.
⑦ laser processing featured high production efficiency, reliable quality, good economic returns. For example ① US General Electric Company adopts slab laser processing the shaped slot on the aircraft engine, complete with high quality in less than 4 hours, and the original use of EDM processing needs more than 9H. Only this one, the cost of each engine can save $ 50,000.
② work efficiency of steel cutting by the laser can increase 8-20 times, the material can save 15-30%, a significant reduction in production costs, and high precision machining, product quality is stable and reliable. Although laser processing has many advantages, the inadequacies are also very obvious.
II. Laser technology
Use a laser beam to perform various materials such as punching, cutting, scribing, welding, heat treatment, etc.
Laser processing has many advantages:
① high laser power density, the workpiece absorbs the laser after the rapid rise in temperature and melting or vaporization, even if the materials with high melting point, high hardness and brittle property (such as ceramics, diamonds, etc.) can also be used laser processing;
② laser head and the workpiece does not touch, there are no processing wear problems;
③ the workpiece free from forces, not easy to pollution;
④ can process the workpiece on the movement or sealed in the glass shell;
⑤ laser beam divergence angle can be less than 1 million arc, spot diameter can be as small as the order of microns, the action time can be shortened to nanoseconds and picoseconds, while high-power laser continuous output power can reach kilowatts to ten kilowatts, so the laser is suitable for precision micro-processing, but also for large-scale material processing;
⑥ laser beam is easy to be controlled, easy work with precision machinery, precision measurement technology, and electronic computer, to achieve a high degree of automation of processing and achieve high processing accuracy;
⑦ in harsh environments or places difficult to get close to human, the robot can be used for laser processing.
Pulsed laser can be used for drilling, the pulse width is 0.1 to 1 millisecond, especially suitable for playing holes and shaped holes, the aperture is about 0.005 to 1 mm.
Laser drilling has been widely used in watches and clocks and gemstone bearings, diamond drawing die, chemical fiber spinneret and other parts.
Laser cutting, scribing, and lettering
In the shipbuilding, automobile manufacturing industries, often use the continuous CO2 laser with hundred kilowatts to million watts to cut large parts, both to ensure the accurate shape of the space curve, but also a higher processing efficiency.
Cutting small workpieces commonly used in medium and small power solid-state lasers or CO2 lasers.
In microelectronics, commonly used laser cutting silicon or cut slits, fast, heat affected area is small.
The laser can be used on the assembly line of the workpiece lettering or marking, does not affect the speed of the assembly line, carved characters can be permanently maintained.
The use of medium and low power lasers to remove part of the electronic components on the material to achieve changes in electrical parameters (such as resistance, capacitance, and resonant frequency, etc.) purposes.
Laser fine-tuning featured high precision, fast, suitable for large-scale production.
The use of similar principles can repair defective integrated circuit mask, repair the integrated circuit memory to improve the yield, but also used for precise dynamic balance adjustment on the gyroscope.
Laser welding featured high strength, small thermal deformation, good sealing, welding size and the nature of disparity, and high melting point (such as ceramics) and easy oxidation of the material.
Laser welded pacemaker featured good sealing, long life, and small size.
Laser heat treatment
With the laser irradiation material, select the appropriate wavelength and control the irradiation time, power density can make the material surface melting and recrystallization and will achieve the purpose of quenching or annealing.
Laser heat treatment has the advantage of being able to control the depth of heat treatment. It can select and control the heat treatment site. The workpiece deformation is small and can handle the shape of complex parts and components, process blind and deep hole of the inner wall.
For example, the cylinder piston can extend the life by laser heat treatment; with laser heat treatment can restore ion bombardment caused by damage to the silicon material.
Strengthen the treatment
Laser surface strengthening technology based on the laser beam of high energy density heating and rapid self-cooling of the workpiece.
In the metal surface laser reinforcement, when the laser beam energy density at the low end, it can be used for metal surface transformation.
When the density of the beam is at the high end, the surface of the workpiece is quite similar to a moving crucible, which can complete a series of metallurgical processes, including surface remelting, surface carbonation, surface alloying and surface cladding.
These functions in the practical application of material substitution technology will bring great economic benefits to the manufacturing industry.
In the tool material modification, the main application is the melting treatment.
Melting treatment is the surface of the metal material melted into a dissolved state under the laser beam irradiation, and quickly solidified to produce a new surface layer.
According to the material surface changes, can be divided into alloying, dissolving, re-melting refinement, glazing and surface composite and so on.
Laser fusing is the use of appropriate parameters of the laser irradiation of the surface of the material, so that the surface in rapid melting, rapid condensation, to obtain more refined homogeneous organization and the required properties of surface modification technology.
It has the following advantages:
- 1Surface melting generally does not add any metal elements, fused layer, and material matrix to form metallurgical bonding.
- In the process of laser melting, impurities and gases can be eliminated, and the magazines obtained by quenching and recrystallization have high hardness, abrasion resistance, and corrosion resistance.
- The melting layer is thin, the thermal effect area is small, the surface roughness and the workpiece size has little effect. Sometimes can no longer follow-up polished and direct use.
- Improve the solubility limit of solute atoms in the matrix, grain and the second phase of the ultra-fine particles to form a metastable phase to obtain a single crystal structure without diffusion or even amorphous, so that the new alloy will obtain the excellent performance which cannot be obtained by the traditional method.
The beam can be guided by the optical path, which can handle parts with special positions and complex shapes.
Integrate the advantages of technology and the shortcomings of widely used technology, the laser technology applied to the surface strengthen treatment of the tool material which will improve the wear resistance of the tool and its life is one of the important ways, especially for ceramics, carbide cutting tools with high hardness, good heat resistance, etc.
It is conducive to improving the processing efficiency and processing accuracy and is able to process materials such as hardened steel under adverse conditions.
Because of their relatively low strength, poor toughness severely limited their application range, so the application of laser surface hardening technology in ceramics, carbide cutting tools have a profound research significance and broad application prospects.
Select the appropriate wavelength of the laser, through a variety of optimization techniques and approximation of the diffraction limit of the focusing system, access to the high-quality light beam, high stability, micro-size focal spot output.
The use of its sharp and sharp “light knife” characteristics, to engrave high-density micro-marks, directly written high-density information;
It can also use its optical trap “force” effect to do holding operation on the tiny transparent ball.
For example, high-precision grating engraving;
Through the CAD / CAM software to simulate and control the pattern (or text), to achieve high-fidelity marking;
The use of optical trap “binding force” to perform the mobile operation of biological cells (biological light tweezers).
Micro fabrication process
(1) The fine machining process
Most of the fine cuts on the convex (outer) surface are made of single crystal diamond tools or cutters.
The tip radius is about 100 μm.
The diamond blade has a 45 ° conical cutting surface when the tool is rotated.
The minimum machinable size of the concave (inner) surface is limited by the size of the tool, such as drilling with a twist drill can be machined as small as the 50μm hole, the smaller hole is no twist drill products, can adopt flat drill.
The key issue in the microfabrication is whether the posture of the tool installation and its coaxially with the axis of the spindle is consistent with the coordinate system.
Otherwise, it is difficult to ensure a small amount of cut.
To this end can be made in the same machine tool for processing, so that the production of tools and microprocessing using the same working conditions, to avoid the error of clamping.
If you use a wire discharge grinding machine on the machine tool, you can use it to wear 50μm wide slot.
(2) fine electric processing technology
Machining of micro shafts and profiled section bars can be done by wire discharge grinding (WEDG).
Its unique discharge circuit allows only 1/100 of the ordinary EDM.
For a smoother surface, you can use WECG after WEDG processing, which removes the thin surface layer with deionized water at low current.
Micro-EDM machines (MEDM) used in the machine, such as Japan’s Matsushita Electric Industrial Co., Ltd. MG-ED71, its positioning control resolution of 0.1μm, the smallest processing aperture of 5μm, the surface roughness of 0.1μm.
When the 9-tooth stainless steel gear with a diameter of 300μm and a thickness of 100μm is machined, the rough contour is first punched with the φ24μm electrode, and the contour is scanned by φ31mm electrode according to the tooth profile.
The precision is ± 3μm.
It can also be used to process the miniature step shaft with a minimum diameter of 30μm and a processed key way section of 10μm x 10μm.
Electrodes for machining small parts should be made on the same machine tool, otherwise, it is difficult to process holes smaller than 100 μm in diameter due to electrode connection and mounting errors. Such as micro-EDM machine tooling electrode or ultrasonic processing tools, can be processed 5 ~ 10μm micro-hole.
Micro-machining and fine machining compared to the material removal rates are low, but the processing size can be smaller, the hole diameter ratio of up to 5 to 10, especially for the fine complex concave cavity processing more superior Sex.
III. Development of laser processing
Laser processing for remanufacturing and its use in other manufacturing industries has its irreplaceable advantages and superior to other processing technologies.
Laser processing for remanufacturing is the development of phase change hardening to laser surface alloying and laser cladding, from the laser alloy coating to the development of composite coating and ceramic coating, making the laser surface processing technology to become a remanufacturing Important means.
It is mainly used 5KW ~ 10KWCO2 high power laser and its system.
Compared with the international laser processing system, China’s laser processing system is very different, accounting for only about 4% of global sales.
Mainly: high-end laser processing system is very few, even don’t have; the main laser is not qualified; fine laser processing equipment gap is large; and for these areas, China’s production and processing enterprises are steadily saving strength and enter into it. The domestic application market has great room for development.
It is expected that China’s laser processing sales will double from RMB3.5 billion in 2008, that is, it will reach 7 billion yuan in output value in the next 2-3 years.
China’s various types of the manufacturing industry have accepted laser processing technology, which can increase the technological content of its products and speed up product upgrading. In order to meet the 21st-century high-tech industrialization, to meet the needs of macro and micro-manufacturing, research and development of high-performance light are imperative.
At present, we are actively developing lasers with characteristics such as ultraviolet, ultrashort pulse, super high power and high beam quality, especially laser light source which can meet the requirements of micro-manufacturing technology, and has become an international competition.