The quality of the nozzle, focus lens and focus tracking system are related to the cutting quality
Among several key technologies of laser cutting machines, the quality of the laser cutting head directly affects the quality of the cutting. The common laser cutting machine cutting head consists of a nozzle, a focus lens and a focus tracking system.
(Osendiko A200M-QBH cutting head)
1. The role of laser head nozzle in laser cutting
Laser head nozzles are the most commonly used consumable parts on fiber laser cutting machines. With the development and widespread use of fiber laser cutting technology, the demand for laser head nozzles has increased significantly in recent years. The nozzles are mainly in parallel, convergent and conical forms. The cutting quality is closely related to the form of the nozzle and the size of the nozzle.
The first function is to collect the capacitance signal and transmit it to the signal processor through the ceramic ring. The signal processor sends a signal to the machine tool control center. The machine tool control center makes feedback based on the signal and adjusts the position of the laser head vertically to maintain the distance tracking of the workpiece by the laser head during the cutting process;
The second function is to use its internal shape to guide the gas through the cut workpiece smoothly and form high pressure at the nozzle outlet attachment. The smaller the nozzle outlet aperture, the higher the air pressure formed. If it is oxidation cutting, after passing through the nozzle, part of the working surface provides heat through an oxidation reaction with the cut part to accelerate the cutting; the other part passes through the cutting surface at a high speed, taking away the slag and maintaining appropriate pressure on the cutting surface to ensure smooth cutting.
The third function is to protect the internal lens of the laser head. During laser cutting, especially when drilling holes, slag is often sputtered. The high-pressure gas blown out from the laser head nozzle can block most of the sputtering objects outside and protect the lens from damage.
2. Relationship between focus lens and laser cutting
Focusing lenses have the general characteristics of ordinary optical lenses but also have their own unique features. It can be used to make an ultra-short focal length lens, or form a real image on the end surface, making it easy to obtain a positive real image of the same size as an object.
When cutting with the energy of the laser beam, the original beam emitted by the laser must be focused through the lens to form a high-energy density spot. Transmission lenses are very simple to use. When the laser beam passes through the lens, the lens focuses the laser beam axially onto the workpiece. In common industrial laser systems, nozzles contain the function of gas washing, that is, introduce gas jets at the nozzles to help improve the performance of the interaction between the laser beam and the material. At the same time, high-speed air flow also plays a role in isolating from the optical system. Gas jets prevent material processing contaminants from entering the nozzle and contaminating the lens surface. The reflective focusing system uses an additional beam folder and a rear focus reflector. In this condition, there are two additional optical systems, namely the zinc selenide window and the beam folder, and the window acts to seal the focus system on the nozzle.
Transmission focus heads have two main advantages, namely, the light beam is easy to adjust and allows a small deviation such as eccentricity, that is, allowing the light beam to be shot into the lens at an eccentric or angle deviation. Reflective lenses are suitable for high power levels and are ideal for high-power laser systems. They produce few thermal lens effects and are durable in harsh welding environments. In theory, the parabolic mirror should focus the laser beam to the diffraction limit of the beam. The diffraction limit is the minimum focal spot that can be achieved for a particular laser beam diameter and mode mass. Parabolic mirrors are one of the most difficult mirror systems to adjust, so in high-power laser systems, it is often difficult to reach the diffraction limit focus. Small spots are not always required for welding, so reflectors are suitable for this application.
In recent years, the market demand for high-power lasers has increased, and there is a restrictive relationship between the depth of focus and the focal spot of traditional lenses. Increased focal depth will inevitably lead to the expansion of the size of the focal spot. In many cases, the requirements of laser processing cannot be met. Telefocal depth and high-resolution focusing lenses have become a new market demand.
The focal length and focus position of the focus lens both have an impact on the laser cutting quality. High-speed cutting thin materials are suitable for short-focus long lenses, and thick workpieces are suitable for telephoto long lenses.
3. Focus on the role of tracking system in laser cutting
The focus tracking system of the laser cutting machine is generally composed of a focus cutting head and a tracking sensor system. The cutting head consists of light-guiding focusing, water cooling, air blowing and mechanical adjustment parts; the sensor is composed of a sensing element and an amplification control part. Different sensing elements are different, and tracking systems are also different.
At present, there are mainly two types of tracking systems. The first is a capacitive sensor tracking system, also known as a contactless tracking system; the second is an inductive sensor tracking system, also known as a contact tracking system.
The work flow of the laser head is like this. The laser generates laser light and is transmitted through the external optical path. After the cutting head is focused by a focusing mirror, it acts on the surface of the processed material, gasifies the material or forms a molten pool with the assistance of cutting gas (mainly oxidation). After the cutting auxiliary gas is directed through the cutting head (including nozzle), a strong airflow blows away the generated slag, while preventing the material from gasification and adhering to the surface of the focusing mirror to cause damage, and preventing plasma or a mixture of plasma and gas.
