1) key technologies

There are two types of laser cutting technology:

The first is a pulsed laser applied to metallic materials.

The second is continuous laser for non-metallic materials, the latter is an important application of laser cutting technology.

Several key technologies of laser cutting machine are integrated technology of light, machine and electricity.In laser cutting machine, the parameters of laser beam, the performance and precision of machine and nc system directly affect the efficiency and quality of laser cutting.Especially for parts with higher cutting precision or larger thickness, the following key technologies must be mastered and solved:

Focus position control technology:

One of the advantages of laser cutting is the high energy density of the beam, generally 10W/cm2.Since the energy density is inversely proportional to the area, the focal spot diameter should be as small as possible to produce a narrow slit.At the same time, the focal spot diameter is also proportional to the focal depth of the lens.The smaller the focal depth of the focusing lens, the smaller the focal spot diameter.However, if the lens is too close to the workpiece, the lens will be damaged easily. Therefore, the focal length of 5 "~7.5" (127~190mm) is widely used in the industrial application of high-power CO2 laser cutting machine.The actual focus spot diameter is between 0.1 and 0.4mm.For high quality cutting, the effective depth of focus is also related to the diameter of the lens and the material to be cut.For example, 5 lens is used to cut carbon steel, the focal depth is within the range of +2% of the focal length, that is, about 5mm.Therefore, the control focus is very important relative to the position of the material surface being cut.Concerns about cutting quality, cutting speed and other factors, in principle, 6mm metal material, focus on the surface;6mm carbon steel with focus on the surface;6mm stainless steel with focus below the surface.The specific size is determined by the experiment.

There are three easy ways to determine the focus in industrial production:

(1) printing method: make the cutting head move from top to bottom, and print laser beam on the plastic plate. The point with the smallest printing diameter is the focus.

(2) inclined plate method: the plastic plate placed at an Angle with the vertical axis is used to pull it horizontally to find the smallest place of the laser beam as the focus.

(3) blue spark method: remove the nozzle, blow air, pulse laser on the stainless steel plate, so that the cutting head from top to bottom movement, until the largest blue spark as the focus.

For the cutting machine of flight light path, the beam size before focusing is different due to the divergence Angle of the beam, the length of the near end and the far end of the cutting time.The larger the diameter of the incident beam, the smaller the diameter of the focal spot.In order to reduce the size change of focus spot caused by the change of beam size before focusing, the manufacturers of laser cutting systems at home and abroad provide some special devices for users to choose:

(1) parallel light tube.This is a common method, that is, a parallel optical tube is added to the output end of CO2 laser for beam expansion. After beam expansion, the beam diameter becomes larger and the divergence Angle becomes smaller, so that the beam size is close to the same before the proximal end and the distal end focus within the cutting range.

(2) add an independent lower axis of the moving lens on the cutting head, which is two mutually independent parts with the z-axis controlling the distance between the nozzle and the material surface (stand off).When the machine tool table moves or the optical axis moves, the beam also moves from the proximal end to the distal f-axis at the same time, so that the diameter of the spot after the beam is focused remains consistent throughout the processing area.See figure 2.

(3) control the water pressure of the focusing mirror (generally a metal reflecting focusing system).If the size of the beam before focusing becomes smaller and the diameter of the focal spot becomes larger, the pressure is automatically controlled to change the focusing curvature to make the diameter of the focal spot smaller.

(4) the compensating optical path system in x and y directions is added to the flight optical path cutting machine.That is, when the cutting remote optical path is increased, the compensation optical path is shortened.On the contrary, when the cutting near optical path is reduced, the compensation optical path is increased to keep the optical path length consistent

Cutting quality:

Cutting precision is the first factor to judge the quality of CNC laser cutting machine.Four factors that influence the cutting accuracy of CNC laser cutting machine:

1. The size of laser condensation of the laser generator.If the light spot is very small after aggregation, the cutting precision is very high, if the gap after cutting is also very small.It shows that the precision of laser cutting machine is very high, the quality is very high.But the laser beam is tapered, so the gap is also tapered.Under this condition, the greater the thickness of the workpiece, the lower the accuracy will be, so the larger the slit.

2, the accuracy of the table.If the accuracy of the table is very high, the accuracy of the cutting is also improved.Therefore, the accuracy of the workbench is also a very important factor to measure the accuracy of the laser generator.

3. The laser beam condenses into a cone.When cutting, the laser beam is tapered downward. At this time, if the thickness of the cutting workpiece is very large, the cutting accuracy will be reduced, and the gap will be very large.

4. Different cutting materials will also affect the accuracy of the laser cutting machine.In the same case, the cutting precision of stainless steel and aluminum will be very different, the cutting precision of stainless steel will be higher, and the cut surface will be smoother.

Generally speaking, laser cutting quality can be measured by the following six standards.

1. Cutting surface roughness Rz

2. Slagging size

3. Cut edge perpendicularity and slope u

4. Cut the rounded edge dimension r

5. Stripe backdrag n

6. Flatness F

Cutting and perforating:

Cutting and perforating techniques: any thermal cutting technique, except in a few cases from the edge of the board, usually must be a hole in the board.Previously, a punch was used to punch out a hole in a laser stamping compound, and then a laser was used to cut through the hole.There are two basic methods for piercing a laser cutting machine without a stamping device:

(1) Blast drilling :(Blast drilling) the material is irradiated by a continuous laser to form a pit in the center, and then the molten material is quickly removed by the oxygen flow coaxial to the laser beam to form a hole.Generally, the size of the hole is related to the thickness of the plate. The average diameter of the blasting perforation is half of the thickness of the plate. Therefore, the diameter of the blasting perforation of the relatively thick plate is larger and not round.In addition, because the oxygen pressure used in the perforation is the same as when cutting, the splash is larger.

(2) Pulse perforation :(Pulse drilling) a Pulse laser with peak power is used to melt or vaporize a small amount of material. Air or nitrogen is often used as an auxiliary gas to reduce the expansion of the hole due to exothermic oxidation. The gas pressure is lower than the oxygen pressure when cutting.Each pulse of laser light only produces a small jet of particles that gradually penetrate, so it takes a few seconds for the plate to perforate.Once the perforation is complete, the auxiliary gas is replaced with oxygen for cutting.In this way, the diameter of the perforation is smaller and the quality of the perforation is better than that of the blasting perforation.The laser used for this purpose should not only have higher output power;The time and space characteristics of the beam are more important, so the cross-flow CO2 laser cannot meet the requirement of laser cutting.

In addition, the pulse perforation also requires a more reliable gas-path control system to realize the control of gas species, gas pressure and perforation time.In the case of pulse perforation, the transition technology from pulse perforation at rest to isokinetic continuous cutting of workpiece should be paid more attention to in order to obtain high quality cutting.In theory, it is usually possible to change the cutting conditions of the accelerating segment, such as the focal length, nozzle position, gas pressure, etc., but in practice, it is unlikely to change the above conditions due to the short time.In industrial production, it is practical to change the average power of laser mainly, and there are three specific methods as follows :(the actual results show that the (3) method has the best effect.

(1) change the pulse width

(2) change the pulse frequency

(3) change the pulse width and frequency at the same time

2) components

Laser cutting machine system is generally composed of laser generator, (outside) beam transmission components, work table (machine tool), computer numerical control cabinet, cooler and computer (hardware and software).

(1) machine main part: the machine part of laser cutting machine, the mechanical part that realizes the movement of X, Y and Z axes, including the cutting working platform.It is used to place the workpiece to be cut and move it correctly and accurately according to the control procedure, usually driven by a servo motor.

(2) laser generator: a device for generating laser light source.For the use of laser cutting, except for a few occasions to use YAG solid state laser, most of the use of high electric-optical conversion efficiency and can output higher power of CO2 gas laser.Because laser cutting requires high beam quality, not all lasers can be used for cutting.The gaussian mode is suitable for low-order carbon dioxide lasers with a value of less than 1500W, 100w-3000w and multi-mode lasers with a value of more than 3000W.

(3) external light path: a refracting mirror is used to guide the laser in the desired direction.In order to prevent the beam path from failure, all mirrors shall be protected by a protective cover, and a clean positive pressure protective gas shall be inserted to protect the lens from contamination.A good set of lenses focuses a beam of light that has no divergence into infinitesimal spots.Usually a 5.0-inch focal length lens is used.7.5-inch lens only for >12 mm thick material.

(4) numerical control system: control the machine tool to realize the movement of X, Y and Z axis, and also control the output power of the laser.

(5) stabilized power supply: connected between the laser, the CNC machine tool and the power supply system.It mainly plays a role in preventing interference from external power grid.

(6) cutting head: mainly includes cavity, focusing lens seat, focusing mirror, capacitive sensor, auxiliary gas nozzle and other parts.The cutting head driving device is used to drive the cutting head along the Z axis according to the program, and it is composed of servo motor, screw rod or gear and other driving parts.

(7) operating table: used to control the working process of the whole cutting device.

(8) water chiller: used for cooling laser generator.Laser is the use of electrical energy into light energy devices, such as CO2 gas laser conversion rate is generally 20%, the remaining energy into heat.Cooling water carries excess heat away to keep the laser generator working properly.The chiller also cools the external light path reflector and focusing mirror of the machine tool to ensure the stable beam transmission quality and effectively prevent the lens from being deformed or burst due to high temperature.

(9) gas cylinder: includes working medium gas cylinder and auxiliary gas cylinder of laser cutting machine, which are used to replenish industrial gas of laser vibration and supply auxiliary gas for cutting head.

(10) air compressor and air storage tank: provide and store compressed air.

(11) air cooling dryer and filter: it is used to supply clean dry air to the laser generator and beam path, so as to keep the path and mirror working normally.

(12) exhaust dust removal machine: draw out the smoke and dust generated during processing, and carry out filtration treatment, so that the exhaust gas emissions meet the environmental protection standards.

(13) slagging machine: eliminate the leftover materials and wastes generated during processing.

Laser:

(1) CO2 gas laser

Since laser technology was introduced to cut metal sheets, CO2 lasers have dominated the market.A CO2 laser requires a lot of energy to excite nitrogen molecules to collide with CO2 molecules (the laser gas), causing them to emit photons that eventually form a laser beam that cuts through metal.Molecular activity in the resonator emits heat as well as light, requiring a cooling system to cool the laser gas.This means more energy is used during cooling, further reducing energy efficiency.

(2) fiber laser

The machine using fiber laser occupies a small area, and the laser light source and cooling system are also smaller.There is no laser gas pipeline and no need to adjust the lens.A 2kw or 3kw fiber-optic laser light source only needs 50% of the energy consumption of a 4kw or 6kw CO2 laser light source to achieve the same performance, and it is faster, consumes less energy and has less impact on the environment.

The fiber laser USES solid-state diodes to pump molecules in the double-clad ytterbium-doped fiber. The excited light passes through the fiber core several times, and then the laser is transmitted through the fiber to the focusing head for cutting.Since all the molecular collisions take place inside the fiber, no laser gas is needed, so the energy required is greatly reduced -- about a third of that of a CO2 laser.As less heat is produced, the cooler can be reduced in size.In short, the overall energy consumption of the fiber laser is 70% lower than that of the CO2 laser under the same performance.

The vector describes the path of the laser, which is smoother.Such a laser system cut out the edge of the cover film contour neat and round, smooth without burr, no overflow.The use of mold and other machining methods such as window opening window will be near the burr and overflow after punching, this burr and overflow after bonding bonding pad is very difficult to remove, will directly affect the quality of the subsequent coating.

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