Principle and application of laser cutting Part.two
1) control of gas parameters
In the actual Laser cutting process, there is also the participation of auxiliary gas, which can not only blow away the slag in time, but also play a role in cooling the workpiece and cleaning the lens. The selection of different auxiliary gas can also change the cutting speed and surface quality of the slit, which is of great significance to the
cutting of special metals.
The influence gas parameters include gas type, gas pressure and nozzle diameter.
1 auxiliary gas type
The auxiliary gases include oxygen, air, nitrogen and argon.Air is suitable for cutting aluminum plate, nonmetal and galvanized steel plate. To some extent, it can reduce the oxide film and save the cost.Nitrogen as a protective gas during cutting can prevent the occurrence of oxidation film and combustion (which is easy to happen when the plate is thicker). Argon is used for titanium metal cutting.
2 gas pressure
High pressure and low pressure gas pressure points, according to the technical parameters of Laser machine, high pressure 20 million mpa, maximum low pressure 5 million mpa the basis of selection pressures have maximum thickness of the sheet metal, cutting speed, the viscosity of the molten metal and Laser power. When the material thickness is bigger, fast cutting speed, the viscosity of the liquid metal is high, can choose a few higher pressure;Instead, for thin material, slow cutting metal or liquid viscosity is small, can choose the appropriate low voltage power large appropriately increased (body pressure around the cooling material is good, it is suitable for the special requirement of occasions, no matter choose what kind of pressure, its principles are guaranteed to blow slag as much as possible under the premise of economic effect.
3 nozzle diameter
Selection of nozzle diameter and body pressure selection principle is the same, but it is related to the cutting method for oxygen, as auxiliary gas cutting, due to the burning of the metal, slotted wider, to blow away the slag effectively, quickly to choose large diameter nozzle, for pulse and cutting, cutting small, unfavorable choose too big nozzle nozzle sizes of choice and the choice of pressure sometimes conflict, in the case of can't be satisfactory to both sides, by adjusting the distance between the nozzle and slitting can also play a role.
2)Relationship between material properties and Laser processing
The result of cutting the workpiece may be that the cutting joint is clean, or on the contrary, the slags at the bottom of the cutting joint or the burning marks on the cutting seam, a large part of which is caused by the material and the factors affecting the cutting quality are: alloy composition, material microstructure, surface quality, surface treatment, reflectivity, thermal conductivity, melting point and boiling point.Usually the composition of the alloy affects the strength, weldability, oxidizability and corrosion resistance of the material, so the higher the carbon content, the harder it is to cut.Fine grain cutting joint quality is good: if the material surface has rust or oxidation layer, melting due to the nature of oxidation layer and metal is different, so that the surface of refractory oxide, but also increase the slag, cutting joint will be irregular;The surface roughness reduces the reflectance and improves the thermal efficiency. After shot peening, the cutting quality is much better. Low thermal conductivity leads to heat concentration and high efficiency, so the materials with fine grains, rough surface, no rust and low thermal conductivity are easy to process.Carbon content is high, the surface coating or coating, high reflective rate of difficult to cut materials. High carbon content of the metal belongs to high melting point metal, due to the difficult to melt, increases the cut in time on the one hand, it makes the slot widening, surface heat affected zone expanded, destabilize the cutting quality, on the other hand, high alloy content, increase the viscosity of liquid metal, make the splash and hang slag ratio increase, the processing of the laser power, gas blowing pressure adjustment are put forward higher requirements of coating and paint to strengthen the reflection of light, make the melting because of difficult;At the same time, it also increases the production of slag.
3)Laser cutting should pay attention to the problem
Previously, the main technical parameters of Laser cutting were analyzed, which determined the main aspects of cutting T art. However, it is not necessary to grasp the high quality products as long as you can process them. There are still some problems that need to be paid attention to.
1. The choice of cutting speed and laser cutting speed up to 200-300 - mm/s, the actual processing is often only a third of the maximum speed to 12, because the higher the speed, the less the dynamic precision of the servo mechanism, directly influence the cutting quality. With the experimental results show that when cutting round hole, the higher the cutting speed, the smaller the aperture, machining the hole of roundness is the worse only can be used at the edge of the long straight line cutting biggest rate cut in order to improve efficiency.
2. Cut the wire and the tail line in cutting operations, in order to make the slot connection is good, prevent the beginning and the end burns, often at the start and end a cutting each lead a period of transition line, known as the lead and tail respectively. Lead the workpiece not body and tail line is useless, so want to arrange in the workpiece, at the same time, pay attention to not set the lead at the Angle of not easy heat dissipation. Fuses with the slotted connection as far as possible the use of circular arc transition, make the machine the smooth movement and to avoid corner pause cause burns.
3. Processing of sharp corners
If possible, avoid machining angles without circular arcs. Angles with circular arcs have
the following advantages:
AThe dynamic performance of a axis motion is good.
B small heat affected zone.
C produces less burr. For corners without rounded corners, the maximum radius can be set to be half of the width of the slit. At this time, the cut corners will have no rounded corners.When cutting on thin plate at high speed, it is recommended to use round hole angle-forming method to cut sharp angles. It has the following advantages:
A when cutting the sharp Angle, the axial direction changes uniformly.
B when the Angle is cut, the cutting speed is constant.
C prevents shaft vibration and the generation of burrs.
D the affected area at the sharp Angle is small.
When cutting a thick plate by cutting the sharp Angle on the thick plate with delay method, if the round hole method is also used, the temperature around the sharp Angle will be overheated. The following parameters should be adopted: "Critical Angle dwell tine meter cutting the sharp Angle - the machine moves to the sharp Angle, pauses for a specific time, and then continues the turning movement.